Quality / Components of Quality
Flavor | Texture | Color | Size | Shape | Free from Defects/Disease | Shelf Life
Free from Contaminants | Nutritional and Pytochemical Content
People who grow, market or eat produce all have an interest in its quality. The components of quality are many, and the importance of the various components depends on the type of produce in question as well as who is judging quality. For a consumer, tomato flavor or color might be most important, while for a producer or marketer, size, shelf life, or another component of quality may be the highest priority. This section describes the components of quality; see the Factors section for information about factors that influence quality.
Flavor is a combination of taste, smell and, according to some definitions, the feel of the item in the mouth. We sense five distinct tastes: sweet, sour, salty, bitter and the more recently described umami (meaty). We can detect a much greater number of odors.
The taste and smell of a vegetable or fruit derives from its chemical compounds including sugars, aldehydes, alcohols, ketones, organic acids, esters and sulfur compounds. The specific compounds, their quantity, and combination influence the flavor. Sweetness generally comes from sugars, including sucrose, glucose and fructose. Sourness derives from acids such as malic, citric and oxalic acid. Bitterness is often caused by alkaloids, glycosides, or peptides. Salty and umami tastes are not common in fruits and vegetables. Sulfur compounds produce the odors and strong flavors found in cooked cabbage, onions and related crops.
The basis for flavor development is genetic, but is influenced by growing conditions and postharvest practices. For instance, the sugar content of cantaloupe is higher when there is more sunlight preceding harvest, and the sugar content of potatoes increases when they are stored at low temperatures. Plant stress may result in strong off flavors. For example, in carrots the relative levels of five terpenoids are influenced by plant stress and result in undesirable flavor in stressed plants. Bitterness in cucumber is more prevalent when there is moisture stress and high temperature.
The instrument most commonly used for evaluating flavor at the farm or packinghouse is a refractometer. A refractometer measures the degree to which light is bent as it passes through a solution. The meter is calibrated so that it provides a reading in brix, or percent soluble solids of a solution. Brix readings correspond well to sweetness perceived by people. A refractometer is usually used to measure the sugar content of juice from melons. pH meters can be used to evaluate acidity of fruit or vegetable juice, but this is not commonly done for fresh market produce.
Texture may refer to surface features usually perceived visually, such as the corky ridges of a muskmelon rind, or to attributes of both internal and external tissues perceived when the item is handled or eaten. Measurable components of texture include firmness, resistance to compression, tenderness, cutting firmness, and overall texture as perceived by chewing. Texture is controlled by genetics, growing conditions, stage of growth and postharvest practices.
The definition of desirable texture is sometimes shaped by handling, transportation and marketing methods. For example, firmness is required for today's marketing system for field grown vine-ripe tomatoes. Firmness is also important for peppers, onions, cabbage and apples. Tenderness, closely related to maturity, is important in sweet corn, asparagus, beans, peas and carrots. Specific texture problems can arise in particular commodities: flesh of muskmelon and winter squash may be 'stringy' and tomatoes or apples may be 'mealy'.
Instruments used at farms and packinghouses to measure texture include the penetrometer, used for determining firmness of apples, and the tenderometer, used for measuring the tenderness, and thereby maturity, of peas grown for processing.
Color in fruits and vegetables is due to the presence of pigments in the skin or underlying tissues. The major groups of compounds are chlorophyll (green), carotenoids (orange and yellow), anthocyanins (red to blue), and anthoxanthins (creamy white to colorless). Color development is influenced by genetics, growing conditions, and stage of growth or maturity. Color is measured with a colorimeter, or described in reference to published standards, such as the Munsell Book of Color from the Munsell Color Company.
Color is important for customer appeal and is often a specification in processed products. Color also differentiates between types of sweet corn, cabbage, onion, tomato, mature bell pepper, watermelon and beans. Colors other than „normalš for a commodity may provide a niche or specialty market: purple asparagus, 'Yukon Gold' potatoes and yellow zucchini are examples. The most desirable color for a particular commodity is market dependent and may vary from region to region. Uniformity of color on each item is normally desirable, excepting naturally striped or patterned types. Variable or uneven color development may be considered poor quality.
Size is the most arbitrary aspect of quality, except when small size is due to immaturity. Size is more commonly a specification for a marketing grade rather than an indication of culinary or aesthetic quality. A small tomato usually tastes and looks the same as a large one of the same variety. Thin asparagus is preferred by a minority of consumers, however there is a minimum size for processed product. In some cases small size may be an indication of a poor crop; this is most common in sweet corn, bell peppers, cauliflower, cabbage, carrots and lettuce. The desirable size for a product is usually a dictate of the market. Baby vegetables are the most narrowly defined market based on size. Size is influenced by genetics, growing conditions, and stage of growth.
Shape as a specification of quality is arbitrary in the same sense that size is arbitrary, except that misshapen vegetables are often not pleasing in appearance and provide no uniformity of pack. U.S. grade standards have diagrams of the limits to deformity for each grade. There are numerous reasons for vegetables or fruits to have poor shape. Poor pollination, cold weather during flower or fruit development, and crowding account for most misshapen vegetables and fruit. Uneven water supply can affect potato shape, especially in varieties like 'Russet Burbank'.
Defects and Disease top
Defects can result from insects, poor growing conditions related to weather and moisture supply, physical damage from cultivating or harvesting, or, under some conditions, from pesticide applications. Disease problems can develop on the marketable portion of the commodity in the field or after harvest and packing. Most diseases are progressive and usually result in rejection of loads if found. Diseases of the non-marketable portion of the plant can reduce yields, size, and flavor.
Shelf Life top
Shelf life is the length of time a commodity maintains acceptable quality under a particular set of storage conditions. It varies among commodity and among varieties of the same commodity. Handling, cooling methods, temperature, relative humidity and packaging also influence shelf life. Tomatoes have been developed that ripen more slowly and therefore can remain in the distribution channels longer before they become over mature and unmarketable. They are called extended shelf life (ESL) hybrids and are grown extensively in Mexico and other distant production areas. Continuous cooling from harvest to consumer is required for broccoli and sweet corn when these commodities are moved in the wholesale distribution system. Broccoli that is not cooled has essentially no shelf life. Muskmelon cooled to 40 F may have shelf life from 5 days to 18 days, depending on the variety. Melons with shorter shelf life are more suitable for direct sales, while those with longer shelf life are suitable for shipping.
Contaminants include insects or insect parts, pesticide residues in excess of tolerances, non-agricultural chemicals, microbial pathogens, and other foreign objects. Tolerances for pesticide residues are set by the U.S. Environmental Protection Agency (EPA). Pesticide residues above tolerances should not be a problem when pesticides are used as directed on the label and no produce is harvested until the required time interval (specified on the label) has passed. For more information on pesticides, follow the link under Safety on the main menu.
Microbial pathogens that cause human disease, such as E. coli, Salmonella and others, have been found on cabbage, muskmelons, and other fresh produce items. Minimizing the risk from these pathogens requires good management practices for irrigation and wash water, personal hygiene and manure handling. For more information on microbial pathogens, follow the link under Safety on the main menu.
Nutritional and Phytochemical Content top
The nutritional content of fruits and vegetables varies widely among kinds, types, and varieties. In general, many are good sources of vitamins, minerals, and fiber, while some also have significant amounts of carbohydrate, fat, or protein. Other compounds in fruits and vegetables are not classified as nutrients, yet have a beneficial effect on human health: these are labeled phytochemicals. They include phenolic compounds, terpenoids, pigments, and other types of antioxidants. Increased nutritional or phytochemical content is a goal of some vegetable and fruit breeding programs. Growing conditions and postharvest handling can also influence nutritional and phytochemical content.
At the present time, wholesale buyers and final consumers can not readily evaluate the nutritional or phytochemical content of a particular fruit or vegetable package. As breeding programs develop cultivars that consistently exhibit improved quality in this area, and if the cultivars can be readily identified in the marketplace, this component of quality may come to play a greater role in the market.
Content authors: J. Neibauer and E. Maynard, 2002. Content last modified: March 2011.