Quality is the composite of attributes that differentiate among units of a product and have significance in determining among units of a product and have significance in determining the degree of acceptability of the unit by the buyer. The emphasis on the cosmetic value of a vegetable does not always equate with the body’s need for a high nutritive value. In India, plant breeders always focus on higher yield, disease resistance, herbicide resistance, drought and salinity tolerance and to some extent quality. Only the physical aspect of quality i.e. shape, size, texture, color and tenderness are given due consideration in the breeding programmes. However, there is little or no emphasis on biochemical quality which includes protein, vitamin, sugars, dry matter, alkaloids etc. the increasing quality consciousness in developed countries will demand more emphasis on quality in future breeding programmes. This is the need of the hour especially in our country with future plant of globalization of agricultural produce. It would be impossible to penetrate in the foreign market with inferior quality produce.
Vegetables not only provide flavor, diversity to diet but are also beneficial for our health. Vegetables have emerged as most important food source because of high nutritive value as well as protecting ability from many diseases.
Source of nutrition
Carbohydrates contain carbon, hydrogen and oxygen in the proportion of C(H2O)x where x is ≥3 in plant the main carbohydrates of nutritional value are glucose, fructose, sucrose and polysaccharide starch. The carbohydrate content is generally low in most vegetables except certain starchy vegetables i.e Cassava, Sweet corn and potato. As the carbohydrates are low in vegetables they are unable to provide sufficient amount of energy. The contribution to daily caloric demand is about 110 K cal which is only 4-5 per cent of the total. However, in vegetables, carbohydrates are responsible for sweetness and flavor. Total soluble solids directly associated with the amount of sugars. In tomato, 50 percent of TSS is due to presence of glucose, fructose and sucrose; in peas, 14 per cent of TSS is due to presence of glucose and fructose (Kallu,1994). Improvement in sugar leads to improvement in taste and flavor. TSS is directly correlated to yield. The plants with heavy foliage and large leaf area should be selected to enhance photosynthetic efficiency. Most of legumes contain starchyose and raffinose which are not digested by humans and in large intestine they fermented by anaerobic bacteria causing intestinal disturbance (Adjei-Twun et al., 1976).
All living matter contains proteins. They serve as the building blocks of living cells. The common components of proteins are the 20 amino acids. Among these twenty amino acids, nine amino acids cannot be produced by the human body and are called ‘essential amino acids’. Humans must obtain essential amino acids from animal or vegetable proteins. The essential amino acids include methionine, arginine, tryptophan, tyrosine, valine, isoleucine, leucine, phenylalanine and lysine. The quality of protein as a nutrient is based on the proportion of its essential amino acids of that ideally required by the body. The quality index of the protein is worked out from the protein efficiency ratio (PER). It is defined as the gain in animal body weight per gram protein intake. The average protein content in vegetables is lower (2.5 gm/100gm) whereas legumes contain higher content of protein i.e 25gm/100gm), however the quality index of protein is rated high among the common plant foods. Kallu (1994) reported large variation for amino acids in the seeds of Phaseolous sp., and Vigna sp. Pisum sativum and certain wild species have shown high amount of essential amino acid which should be involved in hybridization programme.
FatFat provide convenient, concentrated source of calories. They are the integrated part of biological membrane. Fats are made up of glycerol and fatty acid. Triglycerol class of lipid is the storage fats. It is the concentrated source of energy i.e. 94 K cal of energy is released upon combustion of one gram of fats. Vegetables as compared to other fat rich source contain negligible (0.3%) amount and in legumes 1.5 per cent which are unsaturated fats. The inclusion of high fats in diet tends to increase the blood cholesterol level that is strongly linked with coronary heart disease. Animal products which are the source of high quality protein contained large amount cholesterol. From this perspective fruits and vegetables with very low fat content assume greater importance in the diet.
Vitamins are required for normal body functions and some may be provided in a precursor form. Fat soluble vitamins are stored in the body (Vit A,D, E and K) but water soluble vitamins are not and must be supplied daily. Vegetables provide major amount of fat-soluble vitamin A and water soluble Vitamin C, thiamine, riboflavin and niacin. Carotene, a vitamin A precursor, is orange in color and is found in carrots, sweet potatoes, tomatoes and leafy vegetables. Carotene is very during the handling and storage of most vegetables. Vitamin A is essential for the maintenance of cells and for vision. About 4000IU are recommended daily by humans; leafy vegetables, sweet potatoes, capsicum and tomatoes are good sources of vitamin C. Vitamin C is essential for good health and bone formation and the healing of wounds. Thiamine (B1), riboflavin (B2) and niacin (B3) are recommended 1-2 mg per day. Many vegetables are good source of these vitamin but leafy vegetables, beans are good sources.
Many minerals are important in body functions and sodium chloride and iodine may be supplied by table salt. The most important minerals found in vegetables are calcium, potassium, phosphorus, sulphur, iron, and magnesium. About 750mg of macronutrient are recommended per day. Vegetables and fruits supply about 25 per cent of the required magnesium and about 20% of the iron requirement. Vegetables as compared to other food are excellent source of macronutrients especially asparagus, broccoli, capsicum, kale, cauliflower, colocasia are rich source of minerals. Sol fertilizers do influence the mineral composition of plants.
Factors Affecting Nutritional Quality
- Cultivar or genetic makeup of plant
- Environment in which crop is grown
- Holding and storage prior to processing
Protective Role of Vegetables
A balanced diet alone may not be able to protect from diseases due to polluted environment or other factors. Under such inevitable situation the essential nutrients so not appear to be enough but in addition they require the protective elements. The food enriched with protective elements will certain well over medicine. The evidences are accumulating that people who habitually consume diet high in plant foods have lower risks of coronary heart disease, non insulin dependent diabetesand cancer of colon, ling, stomach etc.(Block et al., 1997).
Crude fibre in some vegetables consists of mixture of cellulose, hemicelluloses, pentosans and lignins which cannot be hydrolysed by dilute alkalies and acid. Vegetables although caontain less content of fiber but are of better quality than the fibre of bread etc. and responsible for bringing down the incidence of colon cancer with multiple mode of action (Quebedeaux and bliss, 1988). The national institutes of science recommended 30-40 gm of fibre per day. Recent studies show that flavonoids play important role in cancer chemoprevention (Yoshida et al., 1990 and Huang et al., 1994). Flavonoids reported to inhibit enzymes such as prostaglandin synthase, lipoxygenase and cyclooxygenase closely related to tumorigenesis (Laughton et al., 1991 and Smith and Yang, 1994). The common flavonoids present in vegetables are quercetin, duteolin, kaempferol and myricetin. Capsicum contains highest amount of total flavonoids (10-850mg/Kg) and quercetin (10-780 mg/Kg) the other vegetables like onion (280-490mg/Kg), kale (110mg/Kg), broccoli (30mg/Kg) and French bean (30-45mg/Kg) and good flavonoid contents. Kale have good amount of kaempferol. It may also prevent activation of carcinogens. The preventing activity of flavonoids is due their antioxidant activity. Carotenoids and vitamin C also reported to prevent cancer of lungs and other organs. The protective role of vitamin C may in part lies in its scavenging action of free radicals. In a recent study, it was indicated that yellow orange vegetables and dark green vegetables are more protective than β-carotene (Ziegler et al., 1996). They also found the protective effect of lycopene (a carotenoid) against prostate cancer. The cruciferous vegetables contain high amount of glucosinolates that lower the incidence of cancer by detoxifying carcinogens.
Vegetables contain low amount of fat, high potassium ion concentration (lower blood pressure) and soluble dietary fibre. These factors have been attributed for their preventive role in cardiac disorders. These protective elements which are present in high contents in different vegetables also be considered as quality parameters.
In addition to the beneficial role of vegetables on human health certain anti nutritional factors like enzyme inhibitors (legumes, beans, potato), oxalates (spinach, beet, chard, rubarb leaves), NO3 and NO2- anions and alkaloids like solanine (potato) and tomatine in tomato. All are responsible for various serious complications. Efforts should be made to select the cultivar having high nutrient content, protective elements and low concentration of anti nutritional factor for good health.
Further Reading: Gopalan C, Sastri BVR, Balasubramanian SC, Rao BSN, Deosthale, YG and Plant KC. 1980. Nutritive value of Indian foods. National Institute of nutrition ICMR, Hyderabad, India. Huang MT, Ferrano T and HO CT. 1994. Cancer chemo preservation by phytochemicals in fruits and vegetables In: “ Food phytochemicals for cancer preservation I” American chemical society, Washington DC. Smith IJ and Yang CS. 1994. Effect of food phytochemicals on xenobiotic metabolism and tumerogenesis. In: Food phytochemicals for cancer preservation. American Chemical Society, Washington DC. Wyatt CJ, Consueto VA, Grijalva I and Valencis ME. 1995. Dietary intake of sodium, potassium and blood pressure in lacto ovo vegetarian Nutr. Res. 15. 819.