Fruit and Vegetable Flavor

Introduction: The quality of fresh produce has traditionally been based on external characteristics of size, color, and absence of surface defects. Fruit and vegetable breeders selected for color, size, disease resistance, yield and other easily quantified horticultural traits. Because flavor and texture characteristics were not a part of the selection process, improvements in these quality attributes have not kept pace with the more easily quantified traits. Public and industry organizations are increasing concerned with the public’s growing dissatisfaction over the flavor and texture of some horticultural produce. Flavor and aroma are perhaps the most elusive and subjective of quality traits. Flavor is taste plus odor and is mainly composed of sweetness, sourness, and aroma, which corresponds to sugars, acids, and volatiles. Other components of flavor include bitterness, eg., related to sesquiterpene lactones in chicory (Peters and Amerongen, 1998), saltiness due to various natural salts, and astringency related to flavonoids, alkaloids (DeRovira, 1997), tannins (Taylor, 1993), and other factors. The perception of sweetness, ie., sugars, one of the most important components of fruit or vegetable flavor, is modified by sourness or acid levels, and aroma compounds. The contribution of aroma to the flavor quality of fresh produce has gained increasing attention. Genetics is the primar determinant of flavor of fresh produce (Baldwin et al., 1991b and 1992; Cunningham et al., 1985), with pre-harvest environment (Romani et al., 1983), cultural practices (Wright and Harris, 1985), harvest maturity (Fellman et al., 1993; Maul et al., 1998; Baldwin et al., 1999a), and postharvest handling (Mattheis et al., 1995; Fellman et al., 1993; Baldwin et al., 1999a and b) having lesser effect. Fruit such as apples and bananas that continue to ripen after harvest are termed climacteric, while those such as citrus and strawberries that do not ripen after harvest are termed non-climacteric. The flavor quality of non-climacteric fruit generally declines after harvest, while climacteric fruit can reach their best flavor after harvested. Climacteric fruit develop better quality if harvested after the start of ripening, while fruit of both will be inferior quality if harvested immature, even if held under optimal postharvest conditions. Human perception of flavor is exceedingly complex. Taste is the detection of nonvolatile compounds (in concentration of parts per hundred) by several types of receptors in the tongue for sugars or polyalcohols, hydronium ions, sodium ions, glucosides and alkaloids, etc. These correspond to the perception of sweet, sour, salty and bitter tastes in food. Aroma compounds can be detected in ppb concentrations and are detected by olfactory nerve endings in the nose (DeRovira, 1997). The brain processes information from these senses to give an integrated flavor experience. This integration makes it difficult to determine the relative importance of each input since the brain can interpret changes in aroma as changes in taste (O’Mahony, 1995) or vice versa. For example, the levels of aroma compounds influenced panelist perception of sweetness and sourness for tomatoes (Lycopersicon esculentum Mill.) (Baldwin et al., 1998). Conversely, levels of taste components influenced panelist perception of aromatic descriptors in mango (Mangifera indica L.) (Malundo et al. 2000a). The perception of certain combinations of chemicals is synergistic, while others combinations mute our perception in a process called masking. In contrast to masking, is anesthetization or blanking in which as olfactory receptors become overloaded. Lighter aroma volatiles, eg., top notes, low molecular weight, polar, hydrophilic compounds, are perceived first and generally have the major impact on perception, while heavier compounds are perceived later, eg., background. notes, high molecular weight, non-polar, hydrophobic compounds (DeRovira, 1997).