Bioactive compounds, sensory attributes, and flavor perceptions involved in taste-active molecules in fruits and vegetables

Abstract

Fruit and vegetables as kind of foods, are characterized by the presence of health beneficial components like dietary fibers, antioxidants, vitamins, minerals, and bioactive compounds, which could be obtained from fruit (22%) and vegetables (27%) sources and their waste (1). Bioactive compounds in fruit and vegetables are related to sensory attributes and flavor perceptions linked to taste-active molecules when are consumed as part of human diet (2,3). Sensory attributes in fruit and vegetables including the food stuffs and beverages derived from their processing and waste, which are related to taste-active molecules which emphasize the principal flavor perceptions perceived during handling, processing and consumption of fruit and vegetables (4)(5)(6). In addition, the perceived flavor in fruit and vegetables is formed by the complex interaction between taste and odor, volatile and non-volatile compounds which act as taste-active molecules in fruit and vegetables being responsible for flavor, and sensory attributes identified in gustatory system (7)(8)(9). The pathways that identify the taste-active molecules signals are related to the G protein-coupled receptors, Gαi2, PLC-β2, IP3R3, PLA2IIa, TRPM5, KCNQ1, gustative neurons, in taste bud cells, intracellular signaling, and central nervous system (9,10). The aim of this article is present an analysis about principal bioactive compounds identified in several fruit and vegetables, to recognize sensory attributes and flavor perceptions involved in taste-active molecules present in fruit and vegetables.Principal bioactive compounds present in fruit and vegetables are related to taste-active molecules, being responsible for odor, flavor, aroma during growth, maturation, ripening, transformation process before consumption and heating process, throughout anabolic and catabolic pathways, also autoxidation and enzymatic reactions (7). In Table 1, are presented the principal bioactive compounds related to taste-active molecules in fruit and vegetables:Taste-active molecules of flavor References Flavonoids Rutin, chrysin, apigenin, luteolin (3,8,11).Quercetin, kaempferol, myricetin, fisetin (3,8,11).Proanthocyanidins, catechin, epicatechin, epigallocatechin (3,8,11).Flavanone, hesperidin, naringin, naringenin (3,8,11).Isoflavonoids Genistein, daidzein(3,8,11). Anthocyanidins Apigenin, malvidin, cyaniding, delphinidin, tannins (3,8,11).Terpenes Linalool, α-terpineol, terpineol-4-ol, steviosides, rebaudiosides, cucurbitacins (8,12,13).Eugenol, vanillin, apigenin, flavonoids, coumarins (8,14).Carotenoids β-cryptoxanthin, α-carotene, β-carotene (8,15).Capsaicin, dihydrocapsaicin, nordihydrocapsaicinAmino acids Histidine, arginine, methionine, valine, leucine, isoleucine, phenylalanine, tryptophan (13,17,18).Fatty acids α-linoleic acid, oleic acid (Antioxidants Ascorbic acid, dehydroascorbic acid, β-carotene (20)Flavor is determined by taste-active molecules throughout specialized taste receptor cells in the tongue that perceive different kind of taste, beside of the interaction of volatile constituents with the olfactory and gustative receptors (9,19,28). Tastings are sensed and transduced to gustatory neurons, being finally identified in the brain as basic tastes: sweetness, sourness, saltiness, bitterness flavors (9,10).The pathways that identify the taste-active molecules signals are related to the G protein-coupled receptors, Gαi2, PLC-β2, IP3R3, PLA2IIa, TRPM5, KCNQ1, gustative neurons, in taste bud cells, intracellular signaling, and central nervous system. GPCR receptors are implicated in biological processes, like neurotransmission, chemoattraction, operational of sense organs (taste, smell, and vision), and the regulation of appetite, blood pressure, digestion, etc. GPCR proteins, T1R and T2R as taste receptors are ubicated on the surfaces of sensory cells in each taste bud being recognized (9,10).Therefore, the signals generated upon reception of taste activate the coupling G proteins and effectors, creating the stimulus in taste cells and transmitting the signals to gustatory neurons synapsed with the taste cells by means of signal transduction-transmission process (10). On the other hand, T1R2-T1R3 receptors identify sweetness, T1R1-T1R3 perceive amino acid flavors, and T2R distinguish bitterness (9,10,19).Bitter flavor is a basic taste considered disagreeable, related to phenolic compounds. In citrus fruits and juices, flavonones and neohesperidin flavonoids imparting a bitter taste. Cucurbitacins are triterpenoids provide bitter flavor. Amino acids with hydrophobic side chains produce bitter taste related to histidine, arginine, methionine, valine, leucine, isoleucine, phenylalanine, and tryptophan compounds. Alkaloids such as spermine is the substance responsible for the bitter taste in the berry fruit goji berry (13,17,18,28,29). Astringent flavor sensation is identified as the complex of sensations between the oral epithelial cells and tannins, which arises when the oral cavities are exposed to the sensation-instigating molecules that cause a minimum of three distinct sensations inside the mouth: picked in the cheeks and face muscles, dryness in the mouth and roughness in the oral tissues by means of physiological and psychological mechanisms on non-gustatory mucosal surfaces, including mouth friction and salivary flux (4,(30)(31)(32).Volatile flavors involve amino acids, glucosinolates, terpenes, phenols, which provide: flowery, sweet, light, fruity, and fatty flavors in fruit varieties (19). In vegetables are related to aldehydes, alcohols, ketones, esters, terpenes, and sulfur-containing compounds during fermentation process (8,33,34). Nonvolatile flavors include soluble sugars (sucrose, fructose, and glucose), and organic acids (malic acid and citric acid), considered as important indices for evaluating the flavors of fruits. These compounds are responsible for the sour, sweet, and delicious tastes of fruit (7,8). Aldehydes and alcohols are responsible of flavors in fruits, vegetables, and green leaves, related to saturated and unsaturated fatty acids, that provide fresh, green, and fruity aromas of fruits. Esters, alcohols, acids, and fatty acid carboxyl groups are produced by the oxidative degradation of linoleic acid and linolenic acid in fruit through: α, β-oxidation pathway; oxidation via lipoxygenase pathway; and self-oxidation pathway (8,33). Low-carbon alcohols, aldehydes, acids, and esters in fruit and vegetables, mostly are produced from amino acids through dehydrogenase, deaminase, decarboxylase, and ester synthase pathways to produce 2-methyl-1-butanol and 3-methyl-1-butanol formed during amino acid catabolism (8,12).Fresh flavor is associated with ripening of fruit and vegetables, which gives a fruity flavor (sweet and intense aromatic flavors) when are consumed in fresh-cut form or minimally-processed, being preferred by consumers for their appealing taste, nutritional value and healthy perception (35)(36)(37).Sour flavor is related to organic acids (malic, citric acids), which also determine the pH levels and ripening stages of fruit and vegetables and flavor properties of their processed products (8,(38)(39)(40)(41).Sweetness is considered the main factor of fruit consumer preferences attributed to the soluble sugars (glucose, fructose, and sucrose), which are key to determining their quality. Are produced by means of glucose metabolism pathway, sucrose is converted into glucose by hexokinase, and fructokinase enzymes, that are involved in the phosphorylation of fructose and glucose to produce fructose-6phosphate and glucose-6-phosphate as characteristic sweet flavor compounds (8,25).Pungent flavor is associated to the degree of spiciness or heat experienced when the pepper is eaten as natural or processed product. Pungency is provided by capsaicinoids like capsaicin, dihydrocapsaicin, and nordihydrocapsaicin, by means of phenylpropanoid and branched-chain fatty acid pathways, being responsible for principal pungent flavor in peppers, which are used as appetite stimulants, flavoring agents. Peppers are classified as pungent (hot peppers) and non-pungent (sweet peppers) according to Scoville Heat Units (SHU), considering capsicum species, variety, genotype, and environmental growth conditions [ (16,(42)(43)(44)(45).Sensory attributes and flavor perceptions in fruit and vegetables are related to a variety of taste-active molecules that are linked to bioactive compounds like sugars, acids, alkaloids, tannins, aldehydes, esters, ketones, alcohols, trienes, sulfur-containing compounds, among other compounds that provide the sour, sweet, bitter, and pungent flavors perceived in gustatory system, being a key factor to sensory food choice by consumers.

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