Perception of Quality: Flavor

Perception of Quality: Flavor
The perception
Flavor like appearance and texture, is a function of chemical composition. Sweet, sour, bitter and astringent are the taste attributes of plant products. Sweetness is a property of organic acids. Glucose, fructose and sucrose predominate on fruits, with a wide variation. Citric acid is the primary acid presenting citrus fruits, while malic and tartaric acids predominate in apples and grapes, respectively. The perception of sweetness or sourness however, is primarily related to the ratio of sugar to acid present, particularly in sweet fruits and their products.

Sugar and acid ratio
Ripening of fruits usually involved the increase of sugars and the decrease of acids. In other crops such as sweet corn, sugars are converted into starch, which is undesirable. Sweetness is not desirable in all fruits and vegetables, however. The total sugar and acid content contributes to the flavor of tomatoes, and the presence of sugars in potatoes leads to objectionable browning in fried products such as chips and French fries. Other chemical compounds in citrus fruits are bitter, while tannins impart astringency.

Flavor Chemistry
Flavor is a combination of taste and aroma. Flavor impart compounds such as nootkatone in grapefruit and benzaldehyde in cherries are complemented by numerous other chemicals to give the distinctive aroma that we associate with a particular fruit and is so difficult to reproduce synthetically. Vegetables tend to have more delicate aromas, some of which are attributed to specific compounds, such as phthalides in celery. And others are metabolites of lipoxygenase. A conversion of compound present in the fresh flavor, e.g., the formation of alkyloxazoles to give the characteristic aroma of French fries potatoes.
Perception of Quality: Flavor

Perception of Quality: Color and Texture

Perception of Quality: Color and Texture
Color, a primary indicator of maturity of ripeness, is derived from the pigments found in the product. Loss of the green pigment chlorophyll to unmask yellow carotenoids is a desirable part of the ripening process in many fruits, such as peaches and yellow cultivars of apples. A similar yellowing of green vegetables such as broccoli is considered undesirable. Other pigments of important in fruits and vegetables include lycopene, the red pigment in tomatoes and watermelon: the betacyanins, the red and yellow pigments in beets; and the anthocyanins, the reds, blues, and purples of many fruits and vegetables, including apples, blueberries, and red cabbage. Browning on these products is primarily due to an enzymatic reaction that occurs in response to rupture of the cell membranes.

Texture, like appearance, is evaluated in the context of specific expectations. Crispness and crunchiness are expected in fresh apples, carrots, and celery, but softness or tenderness is desired is asparagus, peas, and plums. The texture of plant products is a consequence of cell wall structure and internal pressure within the cells. Products that maintain structure and turgor during handling and storage remain crisp and may contain an abundance of cell-wall biopolymers. Soft fruits undergo an enzymatic degradation of the cell-wall polysaccharides during ripening. In many fruits, such as peaches and tomatoes, the softening is attributed to pectinolytic enzymes, but cellulose may be important in the ripening of avocadoes. Lignin, a complex biopolymer containing phenolics, can accumulate in cell walls and lead to an objectionable woody texture in products such as asparagus. The mushy texture associated with bruises results from the release, upon rupture of cells, of enzymes that degrade cell-wall polysaccharides, primarily pectin.
Perception of Quality: Color and Texture