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摘要(yào)
Plant-based diets (PBDs) are associated with environmental benefits, human health promotion and animal welfare. There is a worldwide shift towards PBDs, evident from the increased global demand for fresh plant-based products (PBPs). Such shifts in dietary preferences accompanied by evolving food palates, create opportunities to leverage technological advancements and strict quality controls in developing PBPs that can drive consumer acceptance. Flavor, color and texture are important sensory attributes of a food product and, have the largest influence on consumer appeal and acceptance. Among these, flavor is considered the most dominating quality attribute that significantly affects overall eating experience. Current state-of-art technologies rely on physicochemical estimations and sensory-based tests to assess flavor-related attributes in fresh PBPs. However, these methodologies often do not provide any indication about the metabolic features associated with unique flavor profiles and, consequently, can be used in a limited way to define the quality attributes of PBPs. To this end, a systematic understanding of metabolites that contribute to the flavor profiles of PBPs is warranted to complement the existing methodologies. This review will discuss the use of metabolomics for evaluating flavor-associated metabolites in fresh PBPs at post-harvest stage, alongside its applications for quality assessment and grading. We will summarize the current research in this area, discuss technical challenges and considerations pertaining to sampling and analytical techniques, as well as s provide future perspectives and directions for government organizations, industries and other stakeholders associated with the quality assessment of fresh PBPs.
植物(wù)性飲食(PBDs)與環境效益、促進人(rén)類健康和動物(wù)福利有關。從(cóng)全球對新鮮植物(wù)性産品(PBPs)需求的增加可(kě)以看出，全球正在向PBDs轉變。這(zhè)種飲食偏好的轉變伴随着不(bù)斷變化(huà)的食物(wù)口味，爲利用技術進步和嚴格的質量控制(zhì)來(lái)開(kāi)發能夠推動消費(fèi)者接受的pbp創造了機會(huì)。風味、顔色和質地(dì)是(shì)食品重要(yào)的感官屬性，對消費(fèi)者的吸引力和接受程度影響最大(dà)。其中，風味被認爲是(shì)影響整體(tǐ)飲食體(tǐ)驗的最主要(yào)品質屬性。目前最先進的技術依賴于物(wù)理化(huà)學估計和基于感官的測試來(lái)評估新鮮PBPs中的風味相(xiàng)關屬性。然而，這(zhè)些方法通(tōng)常不(bù)能提供與獨特風味特征相(xiàng)關的代謝(xiè)特征的任何指示，因此，隻能以有限的方式用于定義PBPs的質量屬性。爲此，有必要(yào)對影響PBPs風味特征的代謝(xiè)物(wù)進行(xíng)系統的了解，以補充現(xiàn)有的方法。這(zhè)篇綜述将討(tǎo)論在收獲後階段，利用代謝(xiè)組學評估新鮮PBPs中與風味相(xiàng)關的代謝(xiè)物(wù)的方法，以及該方法在質量評估和分(fēn)級中的應用。我們将總結這(zhè)一領域的當前研究，討(tǎo)論與采樣和分(fēn)析技術相(xiàng)關的技術挑戰和注意事項，并爲與政府組織、工(gōng)業(yè)界以及其他與新鮮PBPs質量評估相(xiàng)關的利益相(xiàng)關者提供未來(lái)展望和發展方向。
Keywords: 關鍵詞：
plant-based diets; plant-based products; metabolomics; sensory attributes; flavor
植物(wù)性飲食；植物(wù)性産品；代謝(xiè)組學；感官屬性；風味
1.1. 全球食品口味：邁向可(kě)持續的未來(lái)食品
Increasing urbanization, rising per capita incomes and affordability are shaping the way our food is produced and consumed globally. The associated changes in lifestyle are influencing the composition of food baskets, food consumption patterns and behaviors [1,2,3,4]. With the advent of digitalization and increased access to information, consumers are becoming more cognizant about food and its sources [5]. There is increasing focus on well-being and shifts in consumer preferences toward foods that are grown sustainably. Consequently, plant-based diets (PBDs) are gaining popularity owing to their numerous environmental and human health benefits [6].
日益加劇的城市化(huà)、人(rén)均收入的增加以及消費(fèi)能力的提升正在全球範圍內(nèi)重塑食品的生産和消費(fèi)方式。伴随而來(lái)的生活方式變化(huà)正影響着食品籃子的構成、食品消費(fèi)模式和行(xíng)爲習(xí)慣[1,2,3,4]。随着數字化(huà)時代的到來(lái)和信息獲取的便捷性提高(gāo)，消費(fèi)者對食品及其來(lái)源的認知度也在不(bù)斷增強[5]。人(rén)們越來(lái)越關注健康福祉，消費(fèi)偏好也逐漸轉向可(kě)持續種植的食品。因此，植物(wù)性飲食（PBDs）因其衆多(duō)的環境和人(rén)類健康益處而日益受到歡迎[6]。
1.2. 植物(wù)性飲食：我們了解什麽？
Diet refers to a lifestyle adopted by an individual, and largely relates to an eating plan and regimen for habitual nourishment. With PBD, an individual relies on plant-based products (PBPs) for his/her daily nutritional needs. Typical PBDs maximize the consumption of nutrient-rich plant foods while minimizing processed foods, oils, and animal foods (including dairy products and eggs) [7]. It is pertinent to note that at present, there are varying opinions in the scientific community about idealistic PBDs. However, there is a general cognizance that PBDs are associated with a multitude of human and environmental health benefits. Some epidemiological and interventional human studies have suggested that PBDs exert beneficial health effects against obesity-related metabolic dysfunction, type 2 diabetes mellitus and chronic low-grade inflammation [8,9,10]. Furthermore, the production of PBDs tend to be less resource-intensive and more environmentally friendly for various reasons, including lowered levels of greenhouse gas emissions (GHGEs), in comparison to raising animals for human consumption [11].
飲食是(shì)指個人(rén)所采取的生活方式，主要(yào)與日常飲食計劃和習(xí)慣營養有關。在植物(wù)性飲食（PBD）中，個體(tǐ)依賴植物(wù)性産品（PBPs）來(lái)滿足其日常營養需求。典型的植物(wù)性飲食會(huì)最大(dà)化(huà)營養豐富的植物(wù)性食物(wù)的攝入量，同時盡量減少加工(gōng)食品、油脂和動物(wù)性食物(wù)（包括乳制(zhì)品和雞蛋）的攝入量[7]。值得注意的是(shì)，目前科(kē)學界對于理想化(huà)的植物(wù)性飲食存在不(bù)同意見(jiàn)。然而，普遍認識到的是(shì)，植物(wù)性飲食與人(rén)類和環境的健康益處息息相(xiàng)關。一些流行(xíng)病學和幹預性人(rén)體(tǐ)研究表明，植物(wù)性飲食對與肥胖相(xiàng)關的代謝(xiè)功能障礙、2型糖尿病和慢性低(dī)度炎症具有有益的健康影響[8,9,10]。此外(wài)，與飼養動物(wù)供人(rén)類食用相(xiàng)比，植物(wù)性飲食的生産往往資源消耗較少且更加環保，包括溫室氣體(tǐ)排放量較低(dī)[11]。
As most PBDs rely heavily on plant-based products (PBPs), there will be an increased global demand for PBPs to meet the changing consumer preferences. For the purpose of this review, the scope will be limited to fresh PBPs at the post-harvest stage, where the produce makes its first entry for quality assessments.
由于大(dà)多(duō)數植物(wù)性飲食嚴重依賴植物(wù)性産品（PBPs），因此爲了滿足不(bù)斷變化(huà)的消費(fèi)者偏好，全球對PBPs的需求将會(huì)增加。爲了本綜述的目的，其範圍将僅限于收獲後階段的新鮮PBPs，即這(zhè)些産品在首次進行(xíng)質量評估時所處的階段。
1.3. 植物(wù)性産品：營養和感官特性
PBPs comprise of vegetables, fruits, lentils, grains, legumes, nuts and seeds. They offer a myriad of nutritional and functional benefits for human health promotion. Apart from macronutrients and micronutrients, many of these PBPs provide a range of bioactive compounds to combat inflammation, strengthen antioxidant defenses, and general immune system [12,13,14].
植物(wù)性産品（PBPs）包括蔬菜、水(shuǐ)果、扁豆、谷物(wù)、豆類、堅果和種子。它們爲人(rén)類健康促進提供了衆多(duō)的營養和功能益處。除了宏量營養素和微(wēi)量營養素外(wài)，許多(duō)PBPs還提供了一系列生物(wù)活性化(huà)合物(wù)，以對抗炎症、增強抗氧化(huà)防禦和整體(tǐ)免疫系統[12,13,14]。
A considerable fraction of bioactive compounds/metabolites in PBPs, such as pigments, phytochemicals and other secondary metabolites, contribute to the sensory properties of fresh PBPs. Flavor, color and texture together contribute to the overall eating experience associated with PBPs, and are often a deterministic factor in influencing consumer acceptance. Among these three sensory properties, flavor often has the highest influence on consumer acceptance and behavior. Apart from being a critical quality attribute, flavor also provides valuable information about the nutritional quality of the food [15]. While consumers generally recognize flavor as the most dominant quality attribute for certain PBPs such as fruits and vegetables, it is the interaction of flavor and texture that has a significant effect on consumer acceptance of PBPs [16]. However, for the purpose of this review, we will focus on flavor-related attributes of fresh PBPs.
在植物(wù)性産品（PBPs）中，相(xiàng)當大(dà)一部分(fēn)的生物(wù)活性化(huà)合物(wù)/代謝(xiè)物(wù)，如色素、植物(wù)化(huà)學物(wù)質和其他次級代謝(xiè)物(wù)，對新鮮PBPs的感官特性有所貢獻。風味、顔色和質地(dì)共同構成了與PBPs相(xiàng)關的整體(tǐ)食用體(tǐ)驗，并且通(tōng)常是(shì)影響消費(fèi)者接受度的決定性因素。在這(zhè)三種感官特性中，風味往往對消費(fèi)者的接受度和行(xíng)爲有最大(dà)的影響。除了是(shì)關鍵的質量屬性外(wài)，風味還提供了關于食物(wù)營養質量的有價值信息[15]。雖然消費(fèi)者通(tōng)常認爲風味是(shì)某些PBPs（如水(shuǐ)果和蔬菜）最顯著的質量屬性，但(dàn)風味和質地(dì)的相(xiàng)互作用對消費(fèi)者接受PBPs有顯著影響[16]。然而，爲了本綜述的目的，我們将重點關注新鮮PBPs與風味相(xiàng)關的屬性。
Flavor is perceived primarily by the sense of taste and olfaction (aromatics/aroma) [17]. Aroma and taste receptors, located in the nose and mouth, respectively, are responsible for distinct flavor recognition. It is generally accepted that olfactory stimuli (aroma metabolites) contribute significantly to the flavor experience of most food products. The unique taste sensations and aroma associated with PBPs come from a complex mixture of compounds that belong to different chemical classes. They originate from the primary and secondary metabolism in PBPs and are generally bioactive, with aroma metabolites being volatile in nature while, the taste metabolites often being non-volatile. Both the volatile and non-volatile bioactive fraction in PBPs, such as phenols, flavonoids, isoflavones, terpenes, and glucosinolates, contribute to bitter, acidic, or astringent flavor profiles [18,19]. The presence of these bioactive compounds is an intrinsic property of PBPs, and their synthesis is often influenced by multiple genetic and environmental factors [20,21,22]. Considering the diverse nature of these bioactive compounds and their contribution to the flavor of fresh PBPs, an inclusive approach for their quality assessment at the post-harvest stage is valuable for entire supply chain management. The significance of including a detailed characterization of bioactive compounds for quality assessment has received considerable attention for certain processed food products [23,24,25]. However, quality assessment for fresh PBPs at the post-harvest stage mainly relies on conventional techniques, as discussed in the next section.
風味主要(yào)通(tōng)過味覺和嗅覺（即香氣）來(lái)感知[17]。分(fēn)别位于鼻子和口中的香氣和味覺受體(tǐ)負責不(bù)同的風味識别。通(tōng)常認爲，嗅覺刺激（香氣代謝(xiè)産物(wù)）對大(dà)多(duō)數食品的風味體(tǐ)驗有着顯著的貢獻。與PBPs相(xiàng)關的獨特味覺感受和香氣來(lái)自(zì)于屬于不(bù)同化(huà)學類别的複雜化(huà)合物(wù)混合物(wù)。這(zhè)些化(huà)合物(wù)來(lái)源于PBPs的初級和次級代謝(xiè)，并且通(tōng)常具有生物(wù)活性，其中香氣代謝(xiè)産物(wù)具有揮發性，而味覺代謝(xiè)産物(wù)則通(tōng)常不(bù)具有揮發性。PBPs中的揮發性和非揮發性生物(wù)活性成分(fēn)，如酚類、黃酮類、異黃酮類、萜烯類和硫代葡萄糖苷等，都會(huì)給風味帶來(lái)苦、酸或澀的特征[18,19]。這(zhè)些生物(wù)活性化(huà)合物(wù)的存在是(shì)PBPs的內(nèi)在特性，并且它們的合成往往受到多(duō)種遺傳和環境因素的影響[20,21,22]。考慮到這(zhè)些生物(wù)活性化(huà)合物(wù)的多(duō)樣性和它們對新鮮PBPs風味的貢獻，在收獲後對它們進行(xíng)質量評估的全面方法對于整個供應鏈的管理具有重要(yào)意義。對于某些加工(gōng)食品産品，在質量評估中包括生物(wù)活性化(huà)合物(wù)的詳細表征已受到相(xiàng)當大(dà)的關注[23,24,25]。然而，對于新鮮PBPs在收獲後的質量評估，主要(yào)還是(shì)依賴于傳統技術，這(zhè)将在接下來(lái)的部分(fēn)中討(tǎo)論。
PBPs的質量評估
2.1. 收獲後處理：與風味相(xiàng)關屬性的當前先進技術
At present, the post-harvest quality assessment of fresh PBPs is effectively regulated for attributes related to food safety/human health risk (heavy metals, chemical contamination, microbiological), but loosely regulated for attributes associated with consumer acceptance and eating experience. These regulations are imposed both at international and national levels, as well as within the individual supply chains [26]. Current quality assessment parameters do not effectively inform on the kind of metabolites or chemical compounds that are responsible for the unique flavor profiles of fresh PBPs. However, this could be particularly important for formulating new products in this domain, keeping in mind the changing consumption trends and evolving flavor preferences.
目前，新鮮PBPs的收獲後質量評估在食品安全/人(rén)類健康風險（重金屬、化(huà)學污染、微(wēi)生物(wù)）相(xiàng)關的屬性上得到了有效的監管，但(dàn)在與消費(fèi)者接受度和食用體(tǐ)驗相(xiàng)關的屬性上監管較爲寬松。這(zhè)些監管措施在國(guó)際、國(guó)家(jiā)層面以及各個供應鏈內(nèi)部都得到了實施[26]。然而，當前的質量評估參數并未有效地(dì)提供關于哪種代謝(xiè)物(wù)或化(huà)學化(huà)合物(wù)負責新鮮PBPs獨特風味特征的信息。但(dàn)是(shì)，這(zhè)對于該領域新産品的配方制(zhì)定可(kě)能尤爲重要(yào)，特别是(shì)考慮到不(bù)斷變化(huà)的消費(fèi)趨勢和不(bù)斷演變的風味偏好。
For any PBP, the relative importance of a quality attribute depends on the commodity and its end-use [27]. In general, the post-harvest handling steps for PBPs include identification of the key quality attributes from food safety/human health-related risks (minimum statutory requirements), followed by establishing quality control/quality assurance (QA/QC) procedures to (i) maintain acceptable quality level for the consumer; and (ii) ensure that minimum quality standards are met.
對于任何PBP，一個質量屬性的相(xiàng)對重要(yào)性取決于該商品及其最終用途[27]。一般來(lái)說，PBPs的收獲後處理步驟包括首先識别與食品安全/人(rén)類健康風險相(xiàng)關的關鍵質量屬性（法定最低(dī)要(yào)求），然後建立質量控制(zhì)/質量保證（QA/QC）程序，以（i）保持消費(fèi)者可(kě)接受的質量水(shuǐ)平；（ii）确保達到最低(dī)質量标準。
The quality assessment of fresh PBPs routinely involves sensory and instrumental methods. In general, sensory methods are used for developing new products and determining product standards, while instrumental methods fare better in assessing the quality of the fresh PBPs on a routine basis [28]. Sensory evaluation is usually performed by a trained sensory panel, and it has two components: the analytical component, which is used to detect differences in products, and affective measurements, which determine preference. Instrumental measurements, on the other hand, focus on the chemical and physical characteristics of PBPs, and encompass a wide range of techniques to determine flavor attributes. For example, a hydrometer that can detect total soluble solids is often used to determine sugar levels while, pH meter is used to measure the level of sourness in food products [28].
新鮮PBPs（植物(wù)性産品）的質量評估通(tōng)常涉及感官方法和儀器方法。一般來(lái)說，感官方法用于開(kāi)發新産品和确定産品标準，而儀器方法在日常評估新鮮PBPs的質量方面表現(xiàn)更佳[28]。感官評價通(tōng)常由經過培訓的感官評估小(xiǎo)組進行(xíng)，包括兩個組成部分(fēn)：分(fēn)析性成分(fēn)，用于檢測産品之間(jiān)的差異；以及情感測量，用于确定偏好。另一方面，儀器測量則側重于PBPs的化(huà)學和物(wù)理特性，并采用多(duō)種技術來(lái)确定風味屬性。例如，檢測總可(kě)溶性固體(tǐ)的比重計常用于确定糖分(fēn)水(shuǐ)平，而pH計則用于測量食品産品的酸度水(shuǐ)平[28]。
2.2. Gaps in Current Technologies and Need for Complementary Approaches
2.2 當前技術的不(bù)足與互補方法的需求
Instrumental techniques aimed at evaluating the physical and chemical characteristics of PBPs are advantageous as they: (i) provide high accuracy and great precision; (ii) are often more sensitive to small differences between samples, which assist in determining quality trends; and (iii) they are high-throughput and are often available in semi-automated and automated formats [29]. However, the physicochemical characteristics of PBPs have little relevance to consumer acceptability and thus, the results can be used in a limited way to define the quality attributes of PBPs [30]. For this purpose, sensory evaluation is often recommended to accurately assess the quality attributes of fresh PBPs. Sensory evaluation also has certain disadvantages as it requires a trained sensory panel and it is often time consuming, laborious and challenging.
旨在評估PBPs物(wù)理和化(huà)學特性的儀器技術具有優勢，因爲它們：（i）提供高(gāo)精度和高(gāo)準确性；（ii）通(tōng)常對樣品之間(jiān)的小(xiǎo)差異更敏感，有助于确定質量趨勢；（iii）具有高(gāo)通(tōng)量，并且通(tōng)常以半自(zì)動和自(zì)動格式提供[29]。然而，PBPs的物(wù)理化(huà)學特性與消費(fèi)者接受度之間(jiān)的相(xiàng)關性很(hěn)小(xiǎo)，因此這(zhè)些結果隻能以有限的方式用于定義PBPs的質量屬性[30]。爲此，通(tōng)常建議采用感官評價來(lái)準确評估新鮮PBPs的質量屬性。然而，感官評價也存在一些缺點，如需要(yào)訓練有素的感官評估小(xiǎo)組，且往往耗時、費(fèi)力且具有挑戰性。
To complement and extend the repertoire of the existing methodologies, detailed and quantitative analyses to measure flavor-associated metabolites are warranted. Integrating such technologies in current quality assessment of fresh PBPs will (i) ensure product uniformity; (ii) strengthen consumer acceptability for PBDs and PBPs in general; (iii) complement current assessment platforms for quality and food safety of fresh PBPs; and (iv) aid in determining maturity and degree of ripening of PBPs at the post-harvest stage.
爲了補充和擴展現(xiàn)有方法體(tǐ)系，對與風味相(xiàng)關的代謝(xiè)産物(wù)進行(xíng)詳細和定量的分(fēn)析是(shì)必要(yào)的。将此類技術整合到新鮮PBPs（植物(wù)性産品）的當前質量評估中，将（i）确保産品的一緻性；（ii）增強消費(fèi)者對PBDs（可(kě)能是(shì)指植物(wù)基産品或其他相(xiàng)關術語，但(dàn)在此上下文中可(kě)能指的是(shì)廣義上的植物(wù)性産品）和PBPs的總體(tǐ)接受度；（iii）補充當前對新鮮PBPs質量和食品安全的評估平台；（iv）有助于确定收獲後PBPs的成熟度和成熟程度。
3. Metabolite Fingerprinting for Quality Assessment of PBPs
3. PBPs質量評估的代謝(xiè)物(wù)指紋圖譜
3.1 農食領域的代謝(xiè)組學：當前實踐
Metabolomics allows for studying multiple small molecules or metabolites in a cell, tissue or organism. It is defined as the comprehensive characterization of small molecules present in a biological sample [31,32,33]. Metabolomics routinely utilizes sophisticated and high-throughput analytical platforms such as gas chromatography and liquid chromatography–mass spectrometry (GC–MS and LC–MS) and nuclear magnetic resonance (NMR) spectroscopy [34]. With the advent of chemometrics and advanced analytical platforms, metabolomics has greatly facilitated our understanding of the global metabolome and pathway networks [35]. Metabolomics approaches involve untargeted or targeted analyses, and the selection of the approach is largely dependent on the experimental question and expected outcomes [36]. Untargeted analyses utilize an unbiased profiling or metabolic fingerprinting approach focused on uncovering the global metabolome to evaluate diverse chemical classes of metabolites associated with different pathways. On the other hand, targeted analyses rely on a priori knowledge of the class of metabolites or pathways that are of interest [37]. However, the combination of these analyses is often required to obtain complete information of interest.
代謝(xiè)組學允許研究細胞、組織或生物(wù)體(tǐ)中的多(duō)種小(xiǎo)分(fēn)子或代謝(xiè)産物(wù)。它被定義爲對生物(wù)樣品中存在的小(xiǎo)分(fēn)子進行(xíng)全面表征[31,32,33]。代謝(xiè)組學通(tōng)常使用複雜且高(gāo)通(tōng)量的分(fēn)析平台，如氣相(xiàng)色譜和液相(xiàng)色譜-質譜聯用（GC-MS和LC-MS）以及核磁共振（NMR）光譜[34]。随着化(huà)學計量學和先進分(fēn)析平台的出現(xiàn)，代謝(xiè)組學極大(dà)地(dì)促進了我們對全局代謝(xiè)組和代謝(xiè)途徑網絡的理解[35]。代謝(xiè)組學方法包括非靶向或靶向分(fēn)析，方法的選擇很(hěn)大(dà)程度上取決于實驗問(wèn)題和預期結果[36]。非靶向分(fēn)析采用無偏見(jiàn)的輪廓分(fēn)析或代謝(xiè)指紋圖譜方法，專注于揭示全局代謝(xiè)組，以評估與不(bù)同途徑相(xiàng)關的多(duō)種化(huà)學類别的代謝(xiè)産物(wù)。另一方面，靶向分(fēn)析依賴于對感興趣的代謝(xiè)産物(wù)類别或途徑的先驗知識[37]。然而，爲了獲得完整的感興趣信息，通(tōng)常需要(yào)将這(zhè)兩種分(fēn)析方法結合起來(lái)。
Over the past few decades, metabolomics has been extensively applied to various fields of science owing to new developments in analytical instrumentation and data-analytics platforms [38,39,40,41]. Although still in their infancy, metabolomics-based approaches have gained significant interest in the agri-food sector for a diversity of applications including food processing, quality control, plant breeding for improved crop varieties and product development [42,43]. However, at present, metabolomics-based approaches have not been adopted by the regulatory agencies for food quality assessment, although in some cases they have been found to be efficient, with clear benefits over conventional methods. For instance, metabolomics-based approaches have proved valuable to the food industry for the aroma analysis of fresh and processed PBPs [44,45,46,47]. It is pertinent to note that most of the current research in food metabolomics is focused on evaluating various quality attributes of processed/semi-processed food products. Efforts in the area of fresh produce are mostly restricted to economically important PBPs or PBPs grown for specific end-use [45].
在過去的幾十年裡(lǐ)，由于分(fēn)析儀器和數據分(fēn)析平台的新發展，代謝(xiè)組學已被廣泛應用于科(kē)學的各個領域[38,39,40,41]。盡管仍處于起步階段，但(dàn)基于代謝(xiè)組學的方法在農食行(xíng)業(yè)已經引起了廣泛關注，并應用于多(duō)種領域，包括食品加工(gōng)、質量控制(zhì)、作物(wù)品種改良和産品開(kāi)發[42,43]。然而，目前監管機構尚未将基于代謝(xiè)組學的方法用于食品質量評估，盡管在某些情況下，這(zhè)些方法已被證明是(shì)有效的，并且相(xiàng)對于傳統方法具有明顯優勢。例如，基于代謝(xiè)組學的方法在新鮮和加工(gōng)PBPs的香氣分(fēn)析方面對食品工(gōng)業(yè)具有重要(yào)價值[44,45,46,47]。值得注意的是(shì)，目前食品代謝(xiè)組學的大(dà)部分(fēn)研究都集中在評估加工(gōng)/半加工(gōng)食品産品的各種質量屬性上。而在新鮮農産品領域的研究大(dà)多(duō)局限于經濟上重要(yào)的PBPs或特定最終用途的PBPs[45]。
3.2 基于代謝(xiè)組學評估新鮮PBPs中的風味相(xiàng)關代謝(xiè)産物(wù)
Within the agri-food sector, several diverse areas utilize metabolomics approaches for a variety of applications, as discussed in the previous Section 3.1. One such application involves evaluating the flavor-associated metabolites in fresh PBPs, which are determined by their biochemical composition. As stated in earlier Section 3.1, flavor has the largest influence on consumer behavior and consumption pattern [15], and consequently, most of the research efforts in this domain are catered towards determining the flavor-related metabolites in PBPs. Perception of flavor involves both volatile aroma metabolites as well as non-volatile taste metabolites which belong to different classes.
在農食行(xíng)業(yè)中，如第3.1節所述，代謝(xiè)組學方法被用于多(duō)種應用。其中一項應用就(jiù)是(shì)評估新鮮PBPs中的風味相(xiàng)關代謝(xiè)産物(wù)，這(zhè)些代謝(xiè)産物(wù)由其生化(huà)成分(fēn)決定。正如第3.1節所述，風味對消費(fèi)者行(xíng)爲和消費(fèi)模式有最大(dà)影響[15]，因此該領域的大(dà)部分(fēn)研究都緻力于确定PBPs中的風味相(xiàng)關代謝(xiè)産物(wù)。風味的感知既涉及揮發性香氣代謝(xiè)産物(wù)，也涉及屬于不(bù)同類别的非揮發性味覺代謝(xiè)産物(wù)。
3.2.1 香氣相(xiàng)關代謝(xiè)産物(wù)
In fresh PBPs, a diverse set of volatile chemical compounds contribute to their natural aroma, increasing the complexity of these aroma-associated metabolites. This complexity is further compounded as the volatile compounds interact with each other to create a unique aroma profile for PBPs, which is not merely a sum of the volatile compounds present in them. To date, more than 7000 volatile compounds have been identified in foods, however, a relatively small number (300–400), in specific abundance and ratio, determine the characteristic aroma of the product [48,49].
在新鮮植物(wù)性産品（PBPs）中，一系列複雜的揮發性化(huà)合物(wù)共同構成了其自(zì)然香氣，這(zhè)使得香氣相(xiàng)關代謝(xiè)産物(wù)的分(fēn)析變得尤爲複雜。這(zhè)種複雜性還體(tǐ)現(xiàn)在揮發性化(huà)合物(wù)之間(jiān)的相(xiàng)互作用上，它們共同創造出PBPs獨特的香氣特征，這(zhè)種特征并非僅僅是(shì)這(zhè)些揮發性化(huà)合物(wù)簡單加和的結果。迄今爲止，食品中已鑒定出超過7000種揮發性化(huà)合物(wù)，但(dàn)其中隻有相(xiàng)對較少的一部分(fēn)（300-400種），在特定的豐度和比例下，決定了産品的特征香氣[48,49]。
There are several known classes of volatile aroma metabolites that contribute to the unique flavor of fresh PBPs, such as esters, alcohols, aldehydes, ketones, lactones, terpenoids and apocarotenoids. However, derivatives of amino acids, lipids, phenolic acids and sesquiterpenes are known to be the most important aroma-associated metabolites in PBPs [50]. In certain PBPs, especially fruits and vegetables, sulphurous compounds and derivatives also contribute to their distinct aroma profiles [50].
已知有多(duō)種揮發性香氣代謝(xiè)産物(wù)對新鮮PBPs的獨特風味有貢獻，如酯類、醇類、醛類、酮類、內(nèi)酯類、萜類和脫輔基類胡蘿蔔素等。然而，在PBPs中，氨基酸、脂質、酚酸和倍半萜烯的衍生物(wù)被認爲是(shì)最重要(yào)的香氣相(xiàng)關代謝(xiè)産物(wù)[50]。在某些PBPs中，特别是(shì)水(shuǐ)果和蔬菜，含硫化(huà)合物(wù)及其衍生物(wù)也對其獨特的香氣特征有重要(yào)貢獻[50]。
Volatile aroma metabolites associated with fresh PBPs are generally derived from phytonutrients belonging to fatty acids, amino acids, carotenoids and terpenoid classes [15,51] through a limited number of major biochemical pathways [52]. These pathways are mainly involved in the synthesis of the backbone, while the diversity of these volatiles is achieved via additional chain modification steps and further transformations. Fatty-acid derived volatiles such as alcohols, esters, ketones, acids and lactones form important character-impact aroma compounds that are responsible for flavors of fresh fruits mainly synthesized through α-oxidation, β-oxidation and the lipoxygenase pathway [53].
與新鮮PBPs相(xiàng)關的揮發性香氣代謝(xiè)産物(wù)通(tōng)常來(lái)源于脂肪酸、氨基酸、類胡蘿蔔素和萜類化(huà)合物(wù)等植物(wù)營養素[15,51]，這(zhè)些代謝(xiè)産物(wù)通(tōng)過有限的幾個主要(yào)生化(huà)途徑産生[52]。這(zhè)些途徑主要(yào)涉及香氣化(huà)合物(wù)骨架的合成，而揮發性化(huà)合物(wù)的多(duō)樣性則通(tōng)過額外(wài)的鏈修飾步驟和進一步的轉化(huà)來(lái)實現(xiàn)。脂肪酸衍生的揮發性物(wù)質，如醇類、酯類、酮類、酸類和內(nèi)酯類，是(shì)構成新鮮水(shuǐ)果風味的重要(yào)特征香氣化(huà)合物(wù)，它們主要(yào)通(tōng)過α-氧化(huà)、β-氧化(huà)和脂氧合酶途徑合成[53]。
Similarly, amino acid-derived volatile compounds are produced either through amino-acid precursors (direct) or through acyl-coAs (indirect) and they mainly belong to alcohols, esters, and vegetables. Amino acid-derived volatiles represent dominant classes in PBPs, specifically fruits, vegetables, and grains [15,19,54,55]. For instance, the amino acid proline is the nitrogen precursor for 2-acetyl-1-pyrroline, a volatile compound that is associated with the aroma of certain rice varieties. Similarly, methionine and tryptophan are involved in side-chain modifications of sulphur containing glucosinolates, which result in volatile degradation products, namely isothiocyanates, that contribute to the characteristic aroma associated with Brassica genus [56]. Terpenoids make up the largest class of plant secondary metabolites, many of them being volatile in nature, that contribute to the aroma of fresh PBPs. Hemiterpenes (C5), monoterpenes (C10), sesquiterpenes (C15), homoterpenes (C11 and C16), and some diterpenes (C20) have higher vapor pressure, allowing their release into the surrounding atmosphere and volatilize. All the terpenoids are derived from the universal C5 precursor isopentenyl diphosphate (IPP) and its allylic isomer dimethylallyl diphosphate (DMAPP) [57]. Many terpene volatiles are direct products of terpene biosynthesis enzymes, while some are derived through modifications and additional transformations of primary terpene skeletons, mainly via hydroxylation, dehydrogenation, acylation. For instance, hydroxylation of limonene results in the formation of trans-isopiperitenol and trans-carveol through different catalyzing enzymes and these hydroxylated terpenes are associated with characteristic flavor of certain PBPs [58,59]. Similarly, acetylation of certain terpenes like geraniol results in the formation of geranyl acetate, which has a pleasant fruity aroma and is found in many PBPs. Apart from fatty acid, amino acid and terpenoid pathways, carotenoid pathways represent another major class of volatiles in PBPs. Carotenoid derivatives mainly derived via the oxidation cleavage of carotenoids result in the formation of volatile apocarotenoid derivatives [60]. These volatiles contribute to the aroma of several vegetables and fruits [61].
萜類化(huà)合物(wù)是(shì)植物(wù)次生代謝(xiè)産物(wù)中最大(dà)的一類，其中許多(duō)具有揮發性，對新鮮植物(wù)源性副産物(wù)的香氣有重要(yào)貢獻。半萜類（C5）、單萜類（C10）、倍半萜類（C15）、同萜類（C11和C16）以及某些二萜類（C20）具有較高(gāo)的蒸氣壓，能夠釋放到周圍大(dà)氣中并揮發。所有萜類化(huà)合物(wù)都來(lái)源于通(tōng)用的C5前體(tǐ)異戊烯基焦磷酸（Isopentenyl Diphosphate, IPP）及其烯丙基異構體(tǐ)二甲基烯丙基焦磷酸（Dimethylallyl Diphosphate, DMAPP）[57]。許多(duō)萜類揮發性物(wù)質是(shì)萜類生物(wù)合成酶的直接産物(wù)，而另一些則是(shì)通(tōng)過初級萜類骨架的修飾和額外(wài)轉化(huà)産生的，主要(yào)通(tōng)過羟基化(huà)、脫氫、酰化(huà)等方式。例如，檸檬烯的羟基化(huà)通(tōng)過不(bù)同的催化(huà)酶作用産生反式異胡椒醇和反式香芹醇，這(zhè)些羟基化(huà)的萜類與某些植物(wù)源性副産物(wù)的特征風味有關[58,59]。同樣地(dì)，某些萜類化(huà)合物(wù)如香葉醇的乙酰化(huà)會(huì)形成香葉基乙酸酯，它具有令人(rén)愉悅的果香，并存在于許多(duō)植物(wù)源性副産物(wù)（PBPs）中。除了脂肪酸、氨基酸和萜類途徑外(wài)，類胡蘿蔔素途徑也是(shì)PBPs中揮發性化(huà)合物(wù)的主要(yào)類别之一。類胡蘿蔔素衍生物(wù)主要(yào)通(tōng)過類胡蘿蔔素的氧化(huà)裂解形成，進而産生揮發性的脫輔基類胡蘿蔔素衍生物(wù)[60]。這(zhè)些揮發性化(huà)合物(wù)對多(duō)種蔬菜和水(shuǐ)果的香氣有重要(yào)貢獻[61]。
In the past few years, several research studies have exploited metabolomics approaches to evaluate these diverse classes of aroma metabolites in a variety of fresh PBPs. We provide a representative summary for some of these aroma metabolites in selected fresh PBPs (Table 1). Studies have utilized different kinds of analytical platforms and extraction approaches to analyze chemical classes that contribute to the unique aroma and flavor of fresh PBPs, as summarized in Table 1.
Table 1. Aroma-related metabolites determined using different analytical platforms in fresh plant-based products (PBPs). A representative summary of recent research studies in this area.
| S.no | Metabolites Classes | PBP Type | Analytical Platform | References |
|---|---|---|---|---|
| 1 | Esters, alcohols, aldehydes, ketones, lactones, terpenoids, sulphur compounds | Melons (Cucumis melo L.) | GC-MS GC-O | [62] |
| 2 | Alcohols, acids, and carbonyl compounds, terpenoids and norisoprenoids, furan, phenols and phenylpropanoids, benzonoids, furans | Kiwifruit (Actinidia deliciosa) | GC-O | [52] |
| 3 | Monoterpene hydrocarbons and oxides, sesquiterpenes, aldehydes, alcohols, esters | Japanese citrus fruit (Citrus nagato-yuzukichi Tanaka) | GC-MS | [63] |
| 4 | Esters, alcohol, fatty acid esters, carboxylic acid esters | Pear fruit (Pyrus communis) | HRGC-C/P-IRMS | [64] |
| 5 | Esters, aldehydes, alcohol, benzenic derivatives, ethers | Ambul Banana (Musa acuminata, AAB) | GC-MS | [65] |
| 6 | Aldehydes and alcohols | Potato (Solanum tuberosum) | GC-FID | [66] |
| 7 | Aliphatic acids, aldehydes, alcohols, Oxygenated and nonoxygenated monoterpenes, phenolic derivatives, nor-isoprenes | Tomato (Solanum lycopersicum) | GC | [67] |
| 8 | C8-C9 unsaturated aldehydes and ketones | Oat (Avena sativa) | GC-MS, GC-O | [68] |
| 9 | Ketones, alcohols, esters, and heterocycle compounds | Intermediate wheatgrass (Thinopyrum intermedium) | GC-MS-O | [69] |
| 10 | Unsaturated hydrocarbons, carboxylic acid esters, phenol ethers | Rice (Oryza sativa) | GCGC-TOFMS | [70] |
| 11 | Alcohols, aldehydes, ketones, nitrogen-compounds, Straight- and branched-chain hydrocarbons | Jasmine brown rice (Oryza sativa) | GC-MS | [71] |
| 12 | Ketones, aldehydes, pyrazines, alcohols, aromatic hydrocarbons, furans, pyrroles, terpenes, and acids | Turkish Tombul Hazelnut (Corylus avellana L.) | GC-MS | [72] |
| 13 | Alcohols, aldehydes, esters, benzene derivates, linear hydrocarbons, ketones furans | Dark Black Walnut (Juglans nigra) | GCMS | [73] |
| 14 | Monoterpenes | Pistachio nuts (Pistacia vera L.) | GC-MS | [74] |
| 15 | Pyrazines, aldehydes, alcohols, ketones, esters, carbonic acids, furan derivatives, pyrroles, pyridines, pyran derivatives, hydrocarbons, phenols, sulphur compounds, lactones | Wheat flour bread (Triticum aestivum) | GC-MS | [75] |
| 16 | Aliphatic hydrocarbons, monoterpenes and such | Walnuts (Juglans regia L.) | GC–MS | [76] |
| S.no | 代謝(xiè)物(wù)類别 | PBP類型 | 分(fēn)析平台 | 參考文獻 |
|---|---|---|---|---|
| 1 | 酯類、醇類、醛類、酮類、內(nèi)酯類、萜類、含硫化(huà)合物(wù) | 甜瓜（Cucumis melo L.） | GC-MS, GC-O | [62] |
| 2 | 醇類、酸類、羰基化(huà)合物(wù)、萜類和降異戊二烯類、呋喃類、酚類和苯丙素類、苯并類、呋喃類 | 猕猴桃（Actinidia deliciosa） | GC-O | [52] |
| 3 | 單萜烴和氧化(huà)物(wù)、倍半萜類、醛類、醇類、酯類 | 日本柑橘（Citrus nagato-yuzukichi Tanaka） | GC-MS | [63] |
| 4 | 酯類、醇類、脂肪酸酯類、羧酸酯類 | 梨果（Pyrus communis） | HRGC-C/P-IRMS | [64] |
| 5 | 酯類、醛類、醇類、苯衍生物(wù)、醚類 | 大(dà)蕉（Musa acuminata, AAB） | GC-MS | [65] |
| 6 | 醛類和醇類 | 馬鈴薯（Solanum tuberosum） | GC-FID | [66] |
| 7 | 脂肪酸、醛類、醇類、含氧和不(bù)含氧的單萜類、酚類衍生物(wù)、降異戊二烯類 | 番茄（Solanum lycopersicum） | GC | [67] |
| 8 | C8-C9不(bù)飽和醛類和酮類 | 燕麥（Avena sativa） | GC-MS, GC-O | [68] |
| 9 | 酮類、醇類、酯類和雜環化(huà)合物(wù) | 中間(jiān)型小(xiǎo)麥草（Thinopyrum intermedium） | GC-MS-O | [69] |
| 10 | 不(bù)飽和烴類、羧酸酯類、酚醚類 | 水(shuǐ)稻（Oryza sativa） | GCGC-TOFMS | [70] |
| 11 | 醇類、醛類、酮類、含氮化(huà)合物(wù)、直鏈和支鏈烴類 | 茉莉香米（Oryza sativa） | GC-MS | [71] |
| 12 | 酮類、醛類、吡嗪類、醇類、芳香烴類、呋喃類、吡咯類、萜類、酸類 | 土(tǔ)耳其Tombul榛子（Corylus avellana L.） | GC-MS | [72] |
| 13 | 醇類、醛類、酯類、苯衍生物(wù)、線性烴類、酮類、呋喃類 | 黑核桃（Juglans nigra） | GCMS | [73] |
| 14 | 單萜類 | 開(kāi)心果（Pistacia vera L.） | GC-MS | [74] |
| 15 | 吡嗪類、醛類、醇類、酮類、酯類、碳酸類、呋喃衍生物(wù)、吡咯類、吡啶類、吡喃衍生物(wù)、烴類、酚類、含硫化(huà)合物(wù)、內(nèi)酯類 | 小(xiǎo)麥面粉面包（Triticum aestivum） | GC-MS | [75] |
| 16 | 脂肪烴類、單萜類 | 核桃Walnuts (Juglans regia L.) | GC-MS | [76] |
3.2.2. 味覺相(xiàng)關代謝(xiè)物(wù)
Taste metabolites are quite closely linked with aroma metabolites. These metabolites are generally non-volatile in nature, and they contribute to the flavor profiles by enhancing the gustatory experience via accentuation of the volatile aroma metabolites. There are five kinds of taste perceptions, namely, sweet, salty, bitter, sour and umami. Different chemical classes of metabolites contribute to the taste sensation in PBPs. Sweetness generally comes from sugars, including sucrose, glucose, and fructose. The levels of these sugars are often influenced by genetic and environmental factors and are highly associated with the degree of ripening. A wide variety of PBPs, including fruits and vegetables, have varying levels of these sugars and their biosynthesis is genetically controlled and regulated. Sourness is derived from acids such as malic, citric, and oxalic acid. Bitterness is often associated with presence of polyphenols, alkaloids, tannins, certain glycosides, or peptides. For example, tannins provide the bitter notes and complements the flavor of several PBPs including tea and immature berries [77,78]. Among polyphenols, the taste of bitterness and tactile sensation are often associated with flavonoid phenols, including flavanols and flavonols. Some of the metabolites from these families such as proanthocyanidins or condensed tannins are abundant in wine and tea [79]. Salty and umami tastes are not common in PBPs. Among the taste sensations in PBPs, bitterness is the most complex, as structurally diverse chemical compounds/metabolites can elicit a single bitter taste, which suggests that multiple mechanisms are responsible for the perception and transduction of bitterness. It is also pertinent to note that small changes in chemical structure can transform bitter compounds to sweet or vice versa. Scientific evidence also suggests that bitter and sweet tastes, when present together, can enhance, or suppress each other [80]. In recent years, research initiatives have been directed towards evaluating metabolites that contribute to different taste sensations in a variety of fresh PBPs including fruits and vegetables. Among the taste-associated metabolites, polyphenols are studied extensively among a wide range of PBPs. Polyphenols are a ubiquitous class of non-volatile plant secondary metabolites and apart their sensory attributes, they are also known for their anti-inflammatory and other metabolic effects [81,82,83,84]. Polyphenols are biosynthesized by plants for chemical defense against predators and among them, class of flavonoids are associated with taste sensations in PBPs. Most of them contribute to a bitter taste in PBPs [77,78], but owing to their health benefits, several efforts are directed towards debittering the food products to increase its consumer acceptance [81]. This interest could also be partly responsible in the research impetus on understanding composition of polyphenols and their sensory attributes in PBPs. Representative research studies reporting diverse classes of polyphenols in various PBPs using various analytical platforms are summarized in Table 2.
味覺代謝(xiè)物(wù)與香氣代謝(xiè)物(wù)聯系十分(fēn)密切。這(zhè)些代謝(xiè)物(wù)在本質上通(tōng)常是(shì)不(bù)揮發的，它們通(tōng)過增強揮發性香氣代謝(xiè)物(wù)來(lái)增強味覺體(tǐ)驗，從(cóng)而貢獻風味譜。有五種味覺，即甜、鹹、苦、酸和鮮味。不(bù)同化(huà)學類型的代謝(xiè)物(wù)有助于PBPs的味覺。甜味通(tōng)常來(lái)自(zì)糖，包括蔗糖、葡萄糖和果糖。這(zhè)些糖的水(shuǐ)平往往受到遺傳和環境因素的影響，并與成熟程度高(gāo)度相(xiàng)關。包括水(shuǐ)果和蔬菜在內(nèi)的多(duō)種PBPs含有不(bù)同水(shuǐ)平的這(zhè)些糖，其生物(wù)合成受遺傳控制(zhì)和調節。酸是(shì)由蘋果酸、檸檬酸和草酸等酸産生的。苦味通(tōng)常與多(duō)酚、生物(wù)堿、單甯、某些糖苷或肽有關。例如，單甯提供了苦味，并補充了包括茶和未成熟漿果在內(nèi)的幾種PBPs的風味[77,78]。在多(duō)酚中，苦味和觸覺的味道(dào)往往與黃酮酚有關，包括黃烷醇和黃酮醇。這(zhè)些家(jiā)族的一些代謝(xiè)物(wù)如原花青素或濃縮單甯在葡萄酒和茶中含量豐富[79]。鹹味和鮮味在PBPs中并不(bù)常見(jiàn)。在PBPs的味覺感受中，苦味是(shì)最複雜的，因爲不(bù)同結構的化(huà)合物(wù)/代謝(xiè)物(wù)可(kě)以引起單一的苦味，這(zhè)表明苦味的感知和轉導有多(duō)種機制(zhì)。同樣值得注意的是(shì)，化(huà)學結構的微(wēi)小(xiǎo)變化(huà)可(kě)以将苦的化(huà)合物(wù)轉變爲甜的化(huà)合物(wù)，反之亦然。科(kē)學證據還表明，苦和甜的味道(dào)如果同時存在，會(huì)相(xiàng)互增強或抑制(zhì)[80]。近年來(lái)，研究的主要(yào)方向是(shì)評估在包括水(shuǐ)果和蔬菜在內(nèi)的各種新鮮PBPs中有助于不(bù)同味覺感覺的代謝(xiè)物(wù)。在與味覺相(xiàng)關的代謝(xiè)物(wù)中，多(duō)酚在廣泛的PBPs中被廣泛研究。多(duō)酚是(shì)一種普遍存在的非揮發性植物(wù)次生代謝(xiè)物(wù)，除了其感官特性外(wài)，它們還具有抗炎和其他代謝(xiè)作用[81,82,83,84]。多(duō)酚是(shì)由植物(wù)生物(wù)合成的，用于抵禦捕食者的化(huà)學防禦，其中類黃酮與PBPs的味覺有關。它們中的大(dà)多(duō)數導緻PBPs中有苦味[77,78]，但(dàn)由于它們對健康有益，因此有幾項努力旨在通(tōng)過扣除食品來(lái)提高(gāo)消費(fèi)者的接受度[81]。這(zhè)種興趣也在一定程度上推動了對PBPs中多(duō)酚的組成及其感官特性的研究。表2總結了使用不(bù)同分(fēn)析平台的不(bù)同PBPs中不(bù)同類别的多(duō)酚的代表性研究。
Table 2. Taste-related metabolites determined using different analytical platforms in fresh PBPs. A representative summary of recent research studies in this area.
表2。使用不(bù)同的分(fēn)析平台測定新鮮PBPs中的味道(dào)相(xiàng)關代謝(xiè)物(wù)。該領域的代表性研究綜述。
| S.no | Metabolites Classes | PBP Type | Analytical Platform | References |
|---|---|---|---|---|
| 1 | Hydroxycinnamic acid glycosides, quercetin glycoside derivatives | Mountain papaya (Vas concellea pubescens) | LC-DAD-MS | [82] |
| 2 | Phenolics, myricetin hexoside, myricetin deoxyhexoside derivatives, quercetin hexoside, quercetin deoxyhexoside derivatives | Bayberries (Myrica rubra Sieb. et Zucc) | HPLC-DAD-ESI-MS | [83] |
| 3 | Simple phenolic and hydroxycinnamoylquinic acids and flavons, flavonols, flavanone and dihydrochalcone derivatives | Tomato (Solanum lycopersicum) | HPLC–ESI-QTOF | [84] |
| 4 | Anthocyanidins, aliphatic or aromatic acylated groups, sugar moieties | Eggplant (Solanum melongena); red leaf lettuce (Lactuca sativa); Pistachio (Pistacia vera) and others | HPLC-DAD-ESI-MS-MS | [85] |
| 5 | Proanthocyanidins, phenolic acids | Barley (Hordeum vulgare) | HPLC-DAD-MS | [86] |
| S.no | 代謝(xiè)産物(wù)類别 | 植物(wù)基産品(PBP)類型 | 分(fēn)析平台 | 參考文獻 |
|---|---|---|---|---|
| 1 | 羟基肉桂酸糖苷、槲皮素糖苷衍生物(wù) | 山(shān)木(mù)瓜（Vasconcellea pubescens） | 液相(xiàng)色譜-二極管陣列檢測-質譜（LC-DAD-MS） | [82] |
| 2 | 酚類、楊梅素己糖苷、楊梅素脫氧己糖苷衍生物(wù)、槲皮素己糖苷、槲皮素脫氧己糖苷衍生物(wù) | 楊梅（Myrica rubra Sieb. et Zucc） | 高(gāo)效液相(xiàng)色譜-二極管陣列檢測-電(diàn)噴霧電(diàn)離(lí)質譜（HPLC-DAD-ESI-MS） | [83] |
| 3 | 簡單酚類、羟基肉桂酰奎尼酸及黃酮類、黃酮醇類、黃烷酮類和二氫查爾酮類衍生物(wù) | 番茄（Solanum lycopersicum） | 高(gāo)效液相(xiàng)色譜-電(diàn)噴霧電(diàn)離(lí)四極杆飛行(xíng)時間(jiān)質譜（HPLC–ESI-QTOF） | [84] |
| 4 | 花青素、脂族或芳香族酰化(huà)基團、糖基 | 茄子（Solanum melongena）、紅葉莴苣（Lactuca sativa）、開(kāi)心果（Pistacia vera）等 | 高(gāo)效液相(xiàng)色譜-二極管陣列檢測-電(diàn)噴霧電(diàn)離(lí)串聯質譜（HPLC-DAD-ESI-MS-MS） | [85] |
| 5 | 原花青素、酚酸 | 大(dà)麥（Hordeum vulgare） | 高(gāo)效液相(xiàng)色譜-二極管陣列檢測-質譜（HPLC-DAD-MS） | [86] |
Currently, for flavor-associated metabolite profiling, several extraction techniques and analytical platforms are employed to capture the analytes of interest, which are discussed in the next section. The number of studies reported in this area are progressively increasing with the advent of rapidly evolving analytical platforms, curated databases, automated sample, and liquid handling systems. There is a scientific cognizance about the potential of metabolomics for this growing field, although it has not been widely adopted for routine quality assessment due to a variety of factors including sampling considerations and technical challenges.
目前，在風味相(xiàng)關代謝(xiè)物(wù)分(fēn)析方面，采用了多(duō)種提取技術和分(fēn)析平台來(lái)捕獲感興趣的分(fēn)析物(wù)，這(zhè)将在下一節中詳細討(tǎo)論。随着快(kuài)速發展的分(fēn)析平台、經過整理的數據庫、自(zì)動化(huà)樣品處理和液體(tǐ)處理系統的出現(xiàn)，該領域的研究報告數量正在逐漸增加。盡管科(kē)學界認識到代謝(xiè)組學在這(zhè)一新興領域的潛力，但(dàn)由于采樣考慮和技術挑戰等多(duō)種因素，它尚未被農業(yè)食品部門和監管機構廣泛采用于常規質量評估。
3.3 代謝(xiè)組學的采樣和其他考慮因素
As detailed in the earlier Section 3.2, the use of metabolomics in evaluating flavor attributes of fresh PBPs is gaining considerable interest in the scientific community. However, its widespread adoption by agri-food related sectors and regulatory agencies would require streamlining (i) sampling protocols; (ii) pre-concentration and extraction procedures; and (iii) analytical platforms and approaches. We describe below these three important points for consideration in order to successfully employ metabolomics for evaluating flavor-associated metabolites in fresh PBPs.
如之前第3.2節所述，代謝(xiè)組學在評估新鮮植物(wù)基産品（PBPs）的風味特性方面正受到科(kē)學界的廣泛關注。然而，要(yào)使其在農業(yè)食品部門和監管機構中得到廣泛應用，需要(yào)優化(huà)以下三個方面：（i）采樣協議；（ii）預濃縮和提取程序；（iii）分(fēn)析平台與方法。在成功應用代謝(xiè)組學來(lái)評估新鮮植物(wù)基産品（PBPs）中的風味相(xiàng)關代謝(xiè)物(wù)時，分(fēn)析平台與方法是(shì)另一個至關重要(yào)的考慮因素。
(i)Sampling protocols: As the biosynthesis of flavor-associated metabolites in fresh PBPs is often influenced by several genetic and environmental factors [87], sampling protocols are a critical step in determining true readouts. Environmental factors including farm/management practices, degree of maturity and post-harvest handling will affect the abundance of these bioactive metabolites in the fresh PBPs [88]. Apart from the environmental factors, the nature of these metabolites and their chemistries will also influence the sampling protocols and operational procedures as some metabolites are found in bound form, while others are released only upon tissue disruption.
(i) 采樣協議：由于新鮮植物(wù)基産品（PBPs）中風味相(xiàng)關代謝(xiè)物(wù)的生物(wù)合成往往受到多(duō)種遺傳和環境因素的影響[87]，因此采樣協議是(shì)确定真實結果的關鍵步驟。環境因素，包括農場(chǎng)/管理實踐、成熟度和采後處理，都會(huì)影響這(zhè)些生物(wù)活性代謝(xiè)物(wù)在新鮮PBPs中的含量[88]。除了環境因素外(wài)，這(zhè)些代謝(xiè)物(wù)的性質和化(huà)學結構也會(huì)影響采樣協議和操作程序，因爲一些代謝(xiè)物(wù)以結合形式存在，而其他代謝(xiè)物(wù)則僅在組織破壞時釋放。
For instance, certain aroma metabolites are only released upon cell disruption when enzymes and their corresponding substrates interact [89]. However, some aroma compounds are bound to sugars as glycosides or glucosinolates [90] and odorous aglycones could be released from the sugar moiety during post-harvest stages. Hence, it is pertinent to adopt sampling protocols that can capture the metabolites of interest in a PBP.
例如，某些香氣代謝(xiè)物(wù)僅在細胞破壞時酶與其相(xiàng)應底物(wù)相(xiàng)互作用時釋放[89]。然而，一些香氣化(huà)合物(wù)以糖苷或硫代葡萄糖苷的形式與糖結合[90]，在采後階段糖基部分(fēn)可(kě)能釋放出有氣味的配基。因此，采用能夠捕獲PBP中感興趣代謝(xiè)物(wù)的采樣協議至關重要(yào)。
To simplify, protocols can be standardized for certain families of PBPs, which are known to have similar metabolite classes. For instance, members of Brassica genus (such as broccoli, cabbage, kale) are known to contain glucosinolates (GSLs, sulphur rich secondary metabolites) contributing to their bitter taste and unique aroma [91], and sampling protocols can be standardized across members of this genus for efficient capture of GSLs. Alternatively, protocols can be standardized across different PBPs for the same families of metabolites, such as benzenoids, alcohols and esters.
爲了簡化(huà)操作，可(kě)以對具有相(xiàng)似代謝(xiè)物(wù)類别的某些PBP家(jiā)族制(zhì)定标準化(huà)的采樣協議。例如，十字花科(kē)屬（如西蘭花、卷心菜、羽衣甘藍）的植物(wù)以含有硫代葡萄糖苷（GSLs，富含硫的次級代謝(xiè)物(wù)）而聞名，這(zhè)些物(wù)質爲其提供了苦味和獨特香氣[91]，因此可(kě)以對該屬內(nèi)的成員(yuán)制(zhì)定标準化(huà)的采樣協議，以有效捕獲GSLs。另外(wài)，也可(kě)以針對不(bù)同PBPs中相(xiàng)同類别的代謝(xiè)物(wù)（如苯環化(huà)合物(wù)、醇類和酯類）制(zhì)定标準化(huà)的采樣協議。
Sampling time-points are equally important, as it is known that PBPs have varying levels and kinds of metabolites at different growth and maturity stages. For instance, it is known that the growth stage has an influence on specific GSLs composition and content among members from Brassica genus [92]. Similarly, anthocyanins are also regulated differently at different developmental and ripening stages [93].
采樣時間(jiān)點同樣重要(yào)，因爲已知PBPs在不(bù)同生長和成熟階段具有不(bù)同水(shuǐ)平和種類的代謝(xiè)物(wù)。例如，已知生長階段會(huì)影響十字花科(kē)屬成員(yuán)中特定GSLs的組成和含量[92]。因此，在選擇采樣時間(jiān)點時，應充分(fēn)考慮PBPs的生長和成熟周期，以确保捕獲到最具代表性的風味相(xiàng)關代謝(xiè)物(wù)。同樣地(dì)，花青素（Anthocyanins）在不(bù)同發育和成熟階段也受到不(bù)同的調控[93]。
(ii)Pre-processing and extraction procedures: Apart from sampling protocols, the choice and selection of pre-processing and extraction procedures are equally important due to the thermolabile nature and trace concentrations of these metabolites in fresh PBPs. Extraction procedures largely depend on (i) the nature and chemistry of metabolites (polar/non-polar; volatile/non-volatile); (ii) the thermal stability and sensitivity; and (iii) their occurrence and subsequent release. A variety of methods are prescribed for the extraction and characterization of metabolites linked to the flavor properties of fresh PBPs.
(ii) 預處理和提取程序：除了采樣協議外(wài)，選擇和确定預處理和提取程序對于新鮮PBPs中這(zhè)些代謝(xiè)物(wù)的分(fēn)析同樣至關重要(yào)，因爲這(zhè)些代謝(xiè)物(wù)在新鮮PBPs中具有熱(rè)不(bù)穩定性和痕量濃度的特點。提取程序主要(yào)依賴于（i）代謝(xiè)物(wù)的性質和化(huà)學結構（極性/非極性；揮發性/非揮發性）；（ii）熱(rè)穩定性和敏感性；以及（iii）它們的存在和随後的釋放。針對與新鮮PBPs風味特性相(xiàng)關的代謝(xiè)物(wù)的提取和表征，已經規定了多(duō)種方法。
Due to the volatile nature of a variety of aroma-metabolites, headspace analyses involving the gas phase in equilibrium with PBPs are commonly utilized for flavor analyses. The headspace-solid phase microextraction (HS-SPME) is notable for being sensitive, solvent-free and has been successfully employed for flavor extraction of fresh PBPs [94,95]. SPME fiber coatings with different polarities are often required for effective capture of aroma-metabolites with varying chemistries and affinities [96]. However, the limitations of SPME have been pointed out for the quantitation of certain volatile classes of aroma-metabolites [97].
由于多(duō)種香氣代謝(xiè)物(wù)具有揮發性，因此常與PBPs處于平衡狀态的氣相(xiàng)進行(xíng)頂空分(fēn)析，以進行(xíng)風味分(fēn)析。頂空固相(xiàng)微(wēi)萃取（HS-SPME）因其靈敏度高(gāo)、無需溶劑的特點而被廣泛應用于新鮮PBPs的風味提取[94,95]。爲了有效捕獲具有不(bù)同化(huà)學性質和親和力的香氣代謝(xiè)物(wù)，通(tōng)常需要(yào)具有不(bù)同極性的SPME纖維塗層[96]。然而，SPME在定量某些揮發性香氣代謝(xiè)物(wù)方面存在局限性[97]。
Other techniques used for capturing volatile and semi-volatile metabolites from PBPs are solvent-less enrichment techniques, such as stir bar sorptive extraction (SBSE) [98] and headspace sorptive extraction, (HSSE) wherein stir bar (covered in polysiloxane) is exposed to the sample (either in gaseous or liquid sample media). After extraction, compounds are thermally desorbed before analyses. Extraction techniques assisted by solvents and thermal distillation have been utilized for certain classes of organosulphur metabolites. Steam distillation (SD), simultaneous distillation and solvent extraction (SDE), and solid-phase trapping solvent extraction (SPTE) are used to characterize sulphur-rich aroma-metabolites in certain fresh PBPs such as garlic and onion [98]. Similarly, liquid–liquid extraction (LLE) and solvent-assisted flavor evaporation (SAFE) are used as preferred extraction techniques for furan derivatives that contribute to flavor profiles of certain PBPs [99]. It is pertinent to note here that several extraction techniques have been evaluated based on trapping, capture and dissolution of metabolites to enhance metabolite coverage from plant matrices.
除了溶劑提取方法外(wài)，從(cóng)植物(wù)源揮發性和半揮發性代謝(xiè)物(wù)（PBPs）中捕獲這(zhè)些物(wù)質還采用了無溶劑富集技術，如攪拌棒吸附萃取（Stir Bar Sorptive Extraction, SBSE）[98]和頂空吸附萃取（Headspace Sorptive Extraction, HSSE）。在SBSE中，覆蓋有聚矽氧烷的攪拌棒被暴露于樣品中（樣品可(kě)以是(shì)氣态或液态介質）。提取後，化(huà)合物(wù)在進行(xíng)分(fēn)析前會(huì)經過熱(rè)解析。對于某些類别的有機硫代謝(xiè)物(wù)，則采用了溶劑輔助和熱(rè)蒸餾的提取技術。蒸汽蒸餾（Steam Distillation, SD）、同時蒸餾萃取（Simultaneous Distillation and Solvent Extraction, SDE）和固相(xiàng)捕集溶劑萃取（Solid-Phase Trapping Solvent Extraction, SPTE）等技術被用于表征大(dà)蒜、洋蔥等某些新鮮PBPs中富含硫的芳香代謝(xiè)物(wù)[98]。類似地(dì)，液液萃取（Liquid-Liquid Extraction, LLE）和溶劑輔助風味蒸發（Solvent-Assisted Flavor Evaporation, SAFE）被用作提取某些PBPs中貢獻風味輪廓的呋喃衍生物(wù)的首選技術[99]。這(zhè)裡(lǐ)需要(yào)特别指出的是(shì)，已經根據代謝(xiè)物(wù)的捕獲、收集和溶解來(lái)評估了幾種提取技術，以從(cóng)植物(wù)基質中增強代謝(xiè)物(wù)的覆蓋範圍。
(iii)Analytical platforms and approaches: As seen in the previous section, analytical approaches and platforms are also dependent on the metabolites of interest. GC-O or GC-MS (gas-chromatography-olfactory/gas-chromatography mass-spectrometry) are routinely employed for the detection of aroma- and odor-producing metabolites [63,65,69]. In olfactometric techniques, the nose is used as a GC detector. The GC system can be set up with the column split, and a portion of the effluent goes to the sniffing port and the remainder is fed to the GC detector (FID or an MS detector). GC-O produces an aromagram, which lists the odor character of each peak in a GC run. This method is dependent on the analyst and his sensory perception and, hence, this is a powerful technique which can bridge the conventional sensory evaluation and panel tests with more quantitative information. GC-O can be employed to distinguish between characteristic and off-odors in fresh PBPs, which will assist in quality assessment in terms of food safety and consumer acceptability. While GC-O is more to detect odor and aroma-metabolites, when it is paired with MS detector, it can be used as an identification tool to characterize and quantitate certain metabolites of interest [100]. Other instrumental methods used include NMR and LC-MS. LC-MS platforms are mainly restricted for non-volatile classes of metabolites [82,83,84] such as organic acids, sugars and certain polyphenols which contribute to characteristic taste notes in fresh PBPs.
（iii）分(fēn)析平台和方法：正如前一節所看到的，分(fēn)析方法和平台也取決于感興趣的代謝(xiè)物(wù)。氣相(xiàng)色譜-嗅覺分(fēn)析（GC-O）或氣相(xiàng)色譜-質譜聯用（GC-MS）常用于檢測産生香氣和異味的代謝(xiè)物(wù)[63,65,69]。在嗅覺測定技術中，鼻子被用作氣相(xiàng)色譜的檢測器。氣相(xiàng)色譜系統可(kě)以設置成分(fēn)流柱，一部分(fēn)流出物(wù)進入嗅探口，其餘部分(fēn)送入氣相(xiàng)色譜檢測器（FID或MS檢測器）。GC-O會(huì)産生一個氣味圖，列出氣相(xiàng)色譜運行(xíng)中每個峰的氣味特征。這(zhè)種方法依賴于分(fēn)析人(rén)員(yuán)及其感官感知，因此，這(zhè)是(shì)一種強大(dà)的技術，可(kě)以将傳統的感官評估和小(xiǎo)組測試與更多(duō)定量信息相(xiàng)結合。GC-O可(kě)用于區分(fēn)新鮮PBPs中的特征氣味和異味，這(zhè)将有助于食品安全和消費(fèi)者接受度方面的質量評估。雖然GC-O主要(yào)用于檢測氣味和香氣代謝(xiè)物(wù)，但(dàn)當它與MS檢測器結合時，可(kě)用作表征和定量某些感興趣代謝(xiè)物(wù)的鑒定工(gōng)具[100]。其他使用的儀器方法包括核磁共振（NMR）和液相(xiàng)色譜-質譜聯用（LC-MS）。LC-MS平台主要(yào)局限于非揮發性代謝(xiè)物(wù)類别[82,83,84]，如有機酸、糖類和某些多(duō)酚，這(zhè)些物(wù)質對新鮮PBPs的特征風味有貢獻。
Lately, biosensors (such as electronic noses and electronic tongues) based on pattern recognition of flavor and aroma metabolites have been developed that can crudely mimic the human taste and olfactory receptors and their communication with the human brain [101,102]. These electronic noses (e-noses) and electronic tongues (e-tongues) do not generate information on sample composition but provide a digital fingerprint through pattern recognition. These devices are capable of mimicking human smell and taste sensors based on previous exposure leading to pattern recognition through neural networks. This is useful for routine post-harvest quality assessment of fresh PBPs to evaluate produce for optimum flavor attributes. For instance, it can be used to evaluate effects on storage conditions on quality of fresh PBPs [103]. Recently, e-noses have been utilized for diverse PBPs (especially fruits and vegetables) to evaluate volatile metabolites that are associated with flavor and/or post-harvest quality of PBPs [104,105,106]. Most often, these sensors have been used in combination with GC-O/ GC-MS techniques with or without sensory analyses, as summarized in Table 3.
近年來(lái)，基于風味和香氣代謝(xiè)物(wù)模式識别的生物(wù)傳感器（如電(diàn)子鼻和電(diàn)子舌）得到了發展，這(zhè)些傳感器能夠粗略地(dì)模拟人(rén)類味覺和嗅覺受體(tǐ)及其與大(dà)腦的通(tōng)訊[101,102]。這(zhè)些電(diàn)子鼻（e-noses）和電(diàn)子舌（e-tongues）不(bù)産生關于樣品組成的信息，但(dàn)通(tōng)過模式識别提供數字指紋。這(zhè)些設備能夠基于先前的暴露來(lái)模拟人(rén)類的嗅覺和味覺傳感器，并通(tōng)過神經網絡進行(xíng)模式識别。這(zhè)對于新鮮PBPs的日常收獲後質量評估非常有用，可(kě)以評估産品的最佳風味特性。例如，它可(kě)以用于評估儲存條件(jiàn)對新鮮PBPs質量的影響[103]。最近，電(diàn)子鼻已被用于各種PBPs（尤其是(shì)水(shuǐ)果和蔬菜）中，以評估與風味和/或收獲後質量相(xiàng)關的揮發性代謝(xiè)物(wù)[104,105,106]。這(zhè)些傳感器通(tōng)常與GC-O/GC-MS技術結合使用，無論是(shì)否進行(xíng)感官分(fēn)析，如表3所示。
Table 3. Representative summary of recent studies reporting application of e-nose with or without other analytical platforms to evaluate flavor-associated metabolites in fresh PBPs.
表3. 近期研究報告中将電(diàn)子鼻與其他分(fēn)析平台結合使用或單獨使用以評估新鮮PBPs中風味相(xiàng)關代謝(xiè)物(wù)的代表性總結。
| Metabolites Class | PBP Used | Analytical Platform | Reference |
|---|---|---|---|
| Aldehydes, Alcohols and ketones | Apricots (Prunus armeniaca) | GC; e-nose; sensory analysis | [104] |
| Alcohols, terpene, aromatic hydrocarbons, aliphatic hydrocarbons | Mango (Mangifera indica) | GC; e-nose | [105] |
| Aromatic and aliphatic hydrocarbons | Blueberry (Vaccinium corymbosum) | e-nose | [106] |
| Alcohol, ester, aldehyde, terpenes | Grapes (Vitis vinifera) | GC; e-nose | [107] |
| Aldehydes, Alcohol, ketones | Tomato (Lycopersicon esculentum) | e-nose | [108] |
| Aldehydes, ketones, sulphur compounds, alkanes, terpenes, alcohols | Pineapple (Ananus Comosus) | e-nose | [109] |
| Acids, esters, Aldehydes, ketones, aliphatic and aromatic hydrocarbons | Citrus | GC-MS; e-nose | [110] |
| Ester, carboxylic acids, alcohols, Aldehydes, monterpenes | White and red fleshed peach (Prunus persica) | GC-MS; e-nose | [111] |
| Carboxylic acid, ester, alcohol, | Snake fruit (Salacca zalacca) | GC-MS; e-nose | [112] |
| Pyruvic acid | Onion (Allium cepa) | HPLC; e-nose | [113] |
| 物(wù)性生物(wù)産品（PBP） | 分(fēn)析平台 | 參考文獻 | |
|---|---|---|---|
| 醛類、醇類和酮類 | 杏（Prunus armeniaca） | 氣相(xiàng)色譜（GC）；電(diàn)子鼻（e-nose）；感官分(fēn)析 | [104] |
| 醇類、萜烯、芳香烴、脂肪烴 | 芒果（Mangifera indica） | 氣相(xiàng)色譜（GC）；電(diàn)子鼻（e-nose） | [105] |
| 芳香烴和脂肪烴 | 藍莓（Vaccinium corymbosum） | 電(diàn)子鼻（e-nose） | [106] |
| 醇類、酯類、醛類、萜烯 | 葡萄（Vitis vinifera） | 氣相(xiàng)色譜（GC）；電(diàn)子鼻（e-nose） | [107] |
| 醛類、醇類、酮類 | 番茄（Lycopersicon esculentum） | 電(diàn)子鼻（e-nose） | [108] |
| 醛類、酮類、硫化(huà)物(wù)、烷烴、萜烯、醇類 | 菠蘿（Ananas comosus） | 電(diàn)子鼻（e-nose） | [109] |
| 酸類、酯類、醛類、酮類、脂肪烴和芳香烴 | 柑橘類 | 氣相(xiàng)色譜-質譜聯用（GC-MS）；電(diàn)子鼻（e-nose） | [110] |
| 酯類、羧酸類、醇類、醛類、單萜烯 | 白(bái)肉和紅肉桃（Prunus persica） | 氣相(xiàng)色譜-質譜聯用（GC-MS）；電(diàn)子鼻（e-nose） | [111] |
| 羧酸類、酯類、醇類 | 蛇皮果（Salacca zalacca） | 氣相(xiàng)色譜-質譜聯用（GC-MS）；電(diàn)子鼻（e-nose） | [112] |
| 丙酮酸 | 洋蔥（Allium cepa） | 高(gāo)效液相(xiàng)色譜（HPLC）；電(diàn)子鼻（e-nose） | [113] |
To summarize, reliable and credible estimations of metabolites corresponding to flavor-related sensory attributes in PBPs require careful sampling strategies, thorough pre-processing and extraction procedures followed by robust analytical platforms.
總結來(lái)說，爲了對植物(wù)性生物(wù)産品（PBPs）中與風味相(xiàng)關的感官屬性進行(xíng)可(kě)靠且可(kě)信的代謝(xiè)物(wù)估算，需要(yào)精心的采樣策略、徹底的預處理和提取程序，以及強大(dà)的分(fēn)析平台。
3.4 植物(wù)性生物(wù)産品的代謝(xiè)組學與質量評估
The quality of the fresh PBPs in terms of their nutritive value and flavor profiles is essentially driven by their biochemical composition. Biochemical composition is also a key factor in determining other important properties of fresh PBPs such as shelf life, nutritional stability, and economic value. New tools are required to define “quality” to include more quantitative information about the biochemical composition of food, as consumers’ expectations continue to grow with respect to food quality and safety [114]. Meanwhile, current quality assessment relies heavily on classical methodologies which can largely inform general consumer acceptability, but they lack the ability to provide detailed information on biochemical composition or metabolites that correspond to unique flavors of fresh PBPs.
新鮮PBPs的營養價值和風味特征主要(yào)由其生化(huà)組成決定。生化(huà)組成也是(shì)決定新鮮PBPs其他重要(yào)屬性（如保質期、營養穩定性和經濟價值）的關鍵因素。随着消費(fèi)者對食品質量和安全性的期望不(bù)斷提高(gāo)，需要(yào)新的工(gōng)具來(lái)定義“質量”，以包含更多(duō)關于食品生化(huà)組成的定量信息[114]。然而，目前的質量評估主要(yào)依賴于傳統方法，這(zhè)些方法雖然能在很(hěn)大(dà)程度上反映一般消費(fèi)者的接受度，但(dàn)缺乏提供關于新鮮PBPs獨特風味對應生化(huà)組成或代謝(xiè)物(wù)的詳細信息的能力。
To this end, metabolomics can pave the way for decoding the composition and nature of flavor-associated metabolites in fresh PBPs, which can open avenues for further improvements of PBPs [115,116]. As such, the scope of metabolomics in this domain extends beyond just quality assessment for flavor-associated metabolites; it can be further utilized for (i) biomarker-detection related to food safety; (ii) development of new crops with better genetic traits; (iii) determination of food contaminants/adulterants; and (iv) new investigations on food bioactivities [117,118,119].
爲此，代謝(xiè)組學可(kě)以爲解碼新鮮PBPs中風味相(xiàng)關代謝(xiè)物(wù)的組成和性質鋪平道(dào)路(lù)，從(cóng)而爲PBPs的進一步改進開(kāi)辟途徑[115,116]。因此，代謝(xiè)組學在這(zhè)一領域的範圍不(bù)僅限于風味相(xiàng)關代謝(xiè)物(wù)的質量評估；它還可(kě)以進一步用于（i）食品安全相(xiàng)關的生物(wù)标志(zhì)物(wù)檢測；（ii）開(kāi)發具有更好遺傳性狀的新作物(wù)；（iii）确定食品污染物(wù)/摻假物(wù)；以及（iv）對食品生物(wù)活性的新研究[117,118,119]。這(zhè)些應用展示了代謝(xiè)組學在提升PBPs質量、安全性和市場(chǎng)價值方面的巨大(dà)潛力。
Although a distinct research area on food metabolomics has been established in the scientific community in relation to the application of metabolomics in food system processes [119,120] from farm to consumers, its widespread adoption comes with certain unparalleled challenges (as discussed in Section 3.3). These challenges are often compounded by the nature of the food metabolome, which is complex and variable in nature as thousands of metabolites are present in fresh PBPs with varying polarities and chemistries [121]. Measuring and quantifying the metabolome that best represents the flavor profiles of fresh PBPs can pose analytical challenges as it may not be possible to detect all of them in a single analysis. To this end, utilizing multiple analytical techniques and approaches is often recommended in food metabolomics which can complement each other and provide a wider coverage [122,123].
盡管在科(kē)學界中已經建立了與食品系統中從(cóng)農場(chǎng)到消費(fèi)者過程中代謝(xiè)組學應用相(xiàng)關的食品代謝(xiè)組學這(zhè)一獨特研究領域[119,120]，但(dàn)其廣泛應用仍面臨一些無與倫比的挑戰（如第3.3節所述）。這(zhè)些挑戰往往因食品代謝(xiè)組的複雜性和可(kě)變性而加劇，因爲新鮮PBPs中存在數以千計的代謝(xiè)産物(wù)，它們具有不(bù)同的極性和化(huà)學性質[121]。測量和量化(huà)最能代表新鮮PBPs風味特征的代謝(xiè)組可(kě)能會(huì)帶來(lái)分(fēn)析挑戰，因爲可(kě)能無法在一次分(fēn)析中檢測到所有代謝(xiè)物(wù)。爲此，在食品代謝(xiè)組學中通(tōng)常推薦使用多(duō)種分(fēn)析技術和方法，它們可(kě)以相(xiàng)互補充，提供更廣泛的覆蓋範圍[122,123]。
In addition to this, the food matrix of PBPs will also affect the detection and quantification of compounds that are present at very low concentrations in fresh PBPs or are present in bound forms and unstable forms (as discussed in Section 3.3). Apart from these analytical and sampling-related hurdles, there are certain challenges at downstream data processing and integration with current quality assessment methodologies, and these will be discussed in the next section.
除了這(zhè)一點外(wài)，PBPs的食品基質也會(huì)影響在新鮮PBPs中以極低(dī)濃度存在或以結合形式和不(bù)穩定形式存在的化(huà)合物(wù)的檢測和量化(huà)（如第3.3節所述）。除了這(zhè)些分(fēn)析和采樣相(xiàng)關的障礙外(wài)，在下遊數據處理和與當前質量評估方法的集成方面也存在某些挑戰，這(zhè)些将在下一節中討(tǎo)論。
4. 新鮮PBPs的風味評估：未來(lái)方向
As discussed in Section 3.3 and Section 3.4, there is an immediate need to extend and complement the current repertoire of sensory-based and coarse instrumental estimations to evaluate the flavor- associated metabolites in fresh PBPs. This need is fueled by several socio-economic and psychological factors that have been discussed in the earlier section (Section 1.1 and Section 1.2). Against this background, the current quality assessment methodologies for fresh PBPs will need to be more inclusive of systematic metabolic estimations for flavor attributes in fresh PBPs. Metabolomics can prove to be a valuable tool in this regard, however, utilizing this technique with other routine quality assessment methodologies will require careful considerations at multiple levels. Additionally, it is pertinent to note here that although metabolomics can provide useful biochemical insights about flavor-associated metabolites in PBPs, it cannot provide any information on the human perception of food flavors, which is often influenced by physiological, psychological, genetics and other associated socio-cultural factors [124,125,126]. These factors contribute to the inter-individual variation and cause stark differences in perception of these metabolites by various population groups. To account for these differences, sensory-based tests will remain critical to obtain holistic understanding on consumer acceptance and behavior.
正如第3.3節和第3.4節所討(tǎo)論的，目前迫切需要(yào)擴展和補充基于感官和粗略儀器評估的現(xiàn)有方法，以評估新鮮PBPs中與風味相(xiàng)關的代謝(xiè)物(wù)。這(zhè)一需求受到前幾節（第1.1節和第1.2節）中討(tǎo)論的多(duō)個社會(huì)經濟和心理因素的推動。在此背景下，當前對新鮮PBPs的質量評估方法需要(yào)更加全面地(dì)納入對風味特性的系統性代謝(xiè)評估。代謝(xiè)組學在這(zhè)方面可(kě)以證明是(shì)一個有價值的工(gōng)具，然而，将這(zhè)一技術與其他常規質量評估方法結合使用時，需要(yào)在多(duō)個層面上進行(xíng)仔細考慮。此外(wài)，值得注意的是(shì)，盡管代謝(xiè)組學可(kě)以提供關于PBPs中與風味相(xiàng)關的代謝(xiè)物(wù)的有用生化(huà)見(jiàn)解，但(dàn)它無法提供關于人(rén)類對食物(wù)風味感知的任何信息，這(zhè)種感知往往受到生理、心理、遺傳和其他相(xiàng)關社會(huì)文化(huà)因素的影響[124,125,126]。這(zhè)些因素導緻了個體(tǐ)差異，并導緻不(bù)同人(rén)群對這(zhè)些代謝(xiè)物(wù)的感知存在顯著差異。爲了解釋這(zhè)些差異，基于感官的測試對于全面了解消費(fèi)者的接受度和行(xíng)爲仍然至關重要(yào)。
To harness the potential of metabolomics for evaluating flavor-associated metabolites in PBPs, it is important to keep in mind that both pre and post-harvest procedures including the extraction and analysis of metabolites will have great bearing on the observed results (Figure 1). In order to complement the existing sensory-based and instrumental measurements, a clear interface and seamless integration has to be established between the pre and post-harvest procedure in order to s to ensure aa smooth workflow for rapid quality assessment of fresh PBPs (Figure 2).
爲了利用代謝(xiè)組學評估PBPs中與風味相(xiàng)關的代謝(xiè)物(wù)的潛力，重要(yào)的是(shì)要(yào)記住，包括代謝(xiè)物(wù)提取和分(fēn)析在內(nèi)的采收前和采收後程序都将對觀察到的結果産生重大(dà)影響（見(jiàn)圖1）。爲了補充現(xiàn)有的基于感官和儀器的測量方法，必須在采收前和采收後程序之間(jiān)建立一個清晰的界面和無縫集成，以确保爲新鮮PBPs的快(kuài)速質量評估提供順暢的工(gōng)作流程（見(jiàn)圖2）。
Figure 1. Considerations for utilizing metabolomics for evaluating flavor-associated metabolites in fresh PBPs. Here, we describe the various factors that will have an effect on metabolite estimations in fresh PBPs.
圖1. 利用代謝(xiè)組學評估新鮮PBPs中與風味相(xiàng)關的代謝(xiè)物(wù)的考慮因素。 在此，我們描述了各種将影響新鮮PBPs中代謝(xiè)物(wù)估計的因素。
Figure 2. Framework for integrating metabolomics with current state-of-the-art technologies for the organoleptic evaluation of fresh PBPs. While physicochemical measurements are coarse-scale estimations, metabolomics and sensory-based tests serve as fine-scale estimations to achieve a holistic flavor profiling of fresh PBPs. Data integration platforms would play a crucial role to achieve seamless data stitching for meaningful insights.
圖2。将代謝(xiè)組學與當前最先進的技術相(xiàng)結合的框架，用于新鮮PBPs的感官評估。雖然物(wù)理化(huà)學測量是(shì)粗略的估計，但(dàn)代謝(xiè)組學和基于感官的測試可(kě)以作爲精細的估計，以實現(xiàn)新鮮PBPs的整體(tǐ)風味分(fēn)析。數據集成平台将在實現(xiàn)無縫數據拼接以獲得有意義的見(jiàn)解方面發揮關鍵作用。
Integrating metabolomics with the current state-of-the-art technologies for quality assessment will require synchronized efforts at several points—all the way from data collection to data analyses. To maximize the potential of metabolomics approaches, data collation from various platforms along with careful data interpretation will undoubtedly play a key role. This can lead to several other technical challenges, depending upon the category of PBPs in question, and the nature of information required. Some of the technical challenges could be related to the availability of (i) the right instrumental platform or extraction protocols for metabolites of interest; (ii) reference databases and spectral libraries for matching interesting metabolic features in PBPs; and (iii) the complete metabolome or databank for the plant source in question.
将代謝(xiè)組學與當前最先進的質量評估技術相(xiàng)結合，需要(yào)在從(cóng)數據收集到數據分(fēn)析的各個方面同步努力。爲了最大(dà)限度地(dì)發揮代謝(xiè)組學方法的潛力，來(lái)自(zì)各個平台的數據整理以及仔細的數據解釋無疑将發揮關鍵作用。這(zhè)可(kě)能會(huì)導緻其他一些技術挑戰，這(zhè)取決于所討(tǎo)論的pbp的類别和所需信息的性質。一些技術挑戰可(kě)能與(i)合适的儀器平台或感興趣的代謝(xiè)物(wù)提取方案的可(kě)用性有關;(ii)參考數據庫和譜庫，用于匹配PBPs中有趣的代謝(xiè)特征;(iii)有關植物(wù)來(lái)源的完整代謝(xiè)組或數據庫。
Owing to the rapid developments in extraction and analytical methodologies, several options are available to analyze metabolites with varying chemistries, thereby increasing the global metabolite coverage. With these developments, the first technical hurdle can be conquered with few rounds of trials and optimization. However, the second and third technical challenges pose the greatest difficulty, not just for the agri-food domain, but also for other scientific domains, as a lack of reference databases and metabolome information makes it difficult to interpret the data and obtain meaningful insights. Lately, several curated databases have been made available in the plant domain specifically for diverse phytochemicals and bioactive metabolites to help the research community [127,128]. As the plant metabolome is highly diverse, with thousands of metabolites, it presents a laborious and technically challenging task to annotate every single metabolite. To overcome this challenge, efforts can be strategized towards the identification of candidate/marker metabolic members from different classes that can best represent the specific PBPs. This would eliminate the need to identify each metabolite and, at the same time, will serve as reference for rapid screening of PBPs based on presence of certain key metabolite classes. The choice and selection of such metabolite classes would depend upon the type of PBPs and their ultimate end-use. Monitoring glucosinolates (sulphur containing metabolites) in members from Brassica genus can be a classical example for this, as these metabolites are (i) unique to Brassica family members; (ii) associated with the flavor attributes of these plant types; and (iii) known for their human health benefits. Similarly, eucalyptols (cyclic ether, monoterpenoids) are unique to members of the Myrtaceae family and they are known for imparting a mint-like aroma and spicy taste notes. Other examples include PBPs from Amaryllidaceae that contain S-alk(en)yl-l-cysteine sulfoxides. Another way to approach this challenge will be to generate reference metabolic fingerprints of PBPs and utilize machine learning-based algorithms for pattern recognitions and high-throughput screening. This approach relies on the premise that if sampling, extraction and analytical conditions are kept the same, metabolic fingerprint from two PBPs samples of same type would be identical or similar to a large extent. However, this approach should be utilized as a fast screen and for more quantitative information, in-depth analyses are recommended. Apart from these technical challenges, a systematic method to integrate and collate the data from various platforms is warranted to maximize the potential of multi-platforms in the sensory evaluation of fresh PBPs.
由于提取和分(fēn)析方法的迅速發展，有幾種選擇可(kě)用于分(fēn)析具有不(bù)同化(huà)學性質的代謝(xiè)物(wù)，從(cóng)而增加了全球代謝(xiè)物(wù)的覆蓋率。有了這(zhè)些發展，第一個技術障礙可(kě)以通(tōng)過幾輪試驗和優化(huà)來(lái)克服。然而，第二和第三個技術挑戰帶來(lái)了最大(dà)的困難，不(bù)僅對農業(yè)食品領域，而且對其他科(kē)學領域也是(shì)如此，因爲缺乏參考數據庫和代謝(xiè)組信息使得難以解釋數據并獲得有意義的見(jiàn)解。最近，在植物(wù)領域專門爲各種植物(wù)化(huà)學物(wù)質和生物(wù)活性代謝(xiè)物(wù)建立了幾個數據庫，以幫助研究界[127,128]。由于植物(wù)代謝(xiè)組具有高(gāo)度多(duō)樣性，有數千種代謝(xiè)物(wù)，因此對每一種代謝(xiè)物(wù)進行(xíng)注釋是(shì)一項艱苦且具有技術挑戰性的任務。爲了克服這(zhè)一挑戰，可(kě)以從(cóng)不(bù)同的類别中确定最能代表特定PBPs的候選/标記代謝(xiè)成員(yuán)。這(zhè)将消除識别每種代謝(xiè)物(wù)的需要(yào)，同時，将作爲基于某些關鍵代謝(xiè)物(wù)類别的PBPs快(kuài)速篩選的參考。這(zhè)些代謝(xiè)物(wù)類别的選擇将取決于PBPs的類型及其最終用途。監測來(lái)自(zì)芸苔屬成員(yuán)的硫代葡萄糖苷(含硫代謝(xiè)物(wù))可(kě)能是(shì)一個典型的例子，因爲這(zhè)些代謝(xiè)物(wù)是(shì)(i)芸苔屬成員(yuán)所特有的;(ii)與這(zhè)些植物(wù)類型的風味屬性有關;(三)以對人(rén)體(tǐ)健康有益而聞名。類似地(dì)，桉樹精油(環醚，單萜類)是(shì)桃金娘科(kē)成員(yuán)所特有的，它們以賦予薄荷般的香氣和辛辣的味道(dào)而聞名。其他的例子包括來(lái)自(zì)Amaryllidaceae的PBPs，它含有S-alk(en)yl-l-半胱氨酸亞砜。解決這(zhè)一挑戰的另一種方法是(shì)生成PBPs的參考代謝(xiè)指紋，并利用基于機器學習(xí)的算法進行(xíng)模式識别和高(gāo)通(tōng)量篩選。該方法的前提是(shì)，在取樣、提取和分(fēn)析條件(jiàn)相(xiàng)同的情況下，同一類型的兩個PBPs樣品的代謝(xiè)指紋在很(hěn)大(dà)程度上是(shì)相(xiàng)同或相(xiàng)似的。但(dàn)是(shì)，這(zhè)種方法應該用作快(kuài)速篩選，并建議進行(xíng)深入分(fēn)析以獲得更多(duō)定量信息。除了這(zhè)些技術挑戰之外(wài)，需要(yào)一種系統的方法來(lái)整合和整理來(lái)自(zì)不(bù)同平台的數據，以最大(dà)限度地(dì)發揮多(duō)平台在新鮮PBPs感官評估中的潛力。
A significant improvement has been achieved in recent years in data integration and chemometrics pipelines, making it easier to obtain integrated biological outputs from different platforms. In recent years, numerous tools have been developed, written in most used programming languages such as Python, R, and Matlab® to aid in metabolomics data curation and management [127]. Additionally, several platforms are being made available for sharing scripts and workflows through open-access repositories (Github, StackOverflow). Interactive and intuitive data integration workflows are being developed that have adopted artificial intelligence (AI) and machine learning (ML) approaches [129,130]. Data integration platforms that combine e-noses and e-tongues with high resolution MS and analytical instrumentation could be a way to logically bridge current gaps between human-based sensory tests and metabolic estimations. Although these artificial sensory techniques cannot integrate taste and smell as can be done by the human sensory system, they can generate reliably consistent data in a high-throughput format. With the availability of the requisite computational power, it is possible to integrate such modular information from these artificial sensors to obtain meaningful insights [131,132].
近年來(lái)，在數據集成和化(huà)學計量學管道(dào)方面取得了重大(dà)進展，使得從(cóng)不(bù)同平台獲得綜合生物(wù)輸出變得更加容易。近年來(lái)，已經開(kāi)發了許多(duō)工(gōng)具，用最常用的編程語言(如Python、R和Matlab®)編寫，以幫助代謝(xiè)組學數據的管理和管理[127]。此外(wài)，有幾個平台可(kě)以通(tōng)過開(kāi)放訪問(wèn)存儲庫(Github, StackOverflow)共享腳本和工(gōng)作流。采用人(rén)工(gōng)智能(AI)和機器學習(xí)(ML)方法的交互式和直觀的數據集成工(gōng)作流程正在開(kāi)發[129,130]。将電(diàn)子鼻和電(diàn)子舌與高(gāo)分(fēn)辨率質譜和分(fēn)析儀器相(xiàng)結合的數據集成平台可(kě)能是(shì)一種從(cóng)邏輯上彌合目前基于人(rén)類的感官測試和代謝(xiè)估計之間(jiān)差距的方法。雖然這(zhè)些人(rén)工(gōng)感官技術不(bù)能像人(rén)類感官系統那樣整合味覺和嗅覺，但(dàn)它們可(kě)以以高(gāo)通(tōng)量格式生成可(kě)靠一緻的數據。有了必要(yào)的計算能力，就(jiù)有可(kě)能整合這(zhè)些人(rén)工(gōng)傳感器的模塊化(huà)信息，以獲得有意義的見(jiàn)解[131,132]。
This will be particularly resourceful for innovations and new product developments in this domain as we continue to witness intense reformation and diversification of food palates globally. In addition, integrating these platforms with trained artificial intelligence can further uplift them to smart sensing platforms that can, to an extent, also predict emerging food safety threats in terms of adulterants and/or pathogens. To make this a real scenario, coordinated efforts and synchronized response will be required from several stakeholders working in this evolving domain.
随着我們繼續見(jiàn)證全球食品口味的激烈改革和多(duō)樣化(huà)，這(zhè)将爲該領域的創新和新産品開(kāi)發提供特别豐富的資源。此外(wài)，将這(zhè)些平台與訓練有素的人(rén)工(gōng)智能相(xiàng)結合，可(kě)以進一步将其提升爲智能傳感平台，在某種程度上，還可(kě)以預測摻假和/或病原體(tǐ)方面出現(xiàn)的食品安全威脅。爲了使這(zhè)成爲一個真實的場(chǎng)景，将需要(yào)在這(zhè)個不(bù)斷發展的領域中工(gōng)作的幾個利益相(xiàng)關者協調努力和同步響應。
5. 結論
To conclude, utilizing metabolomics for evaluating flavor-associated metabolites in PBPs would likely become a necessity in coming years and it will see multiple applications from product authenticity, quality assessment, new product development and enhanced food safety.
利用代謝(xiè)組學來(lái)評估植物(wù)基産品（PBPs）中與風味相(xiàng)關的代謝(xiè)物(wù)，在未來(lái)幾年內(nèi)很(hěn)可(kě)能會(huì)成爲一種必然需求，并且将在産品真實性驗證、質量評估、新産品開(kāi)發和增強的食品安全等多(duō)個方面展現(xiàn)出廣泛的應用。
原文鏈接：
Pavagadhi S, Swarup S. Metabolomics for Evaluating Flavor-Associated Metabolites in Plant-Based Products. Metabolites. 2020; 10(5):197. https://doi.org/10.3390/metabo10050197
