Saturday, November 2, 2019

Carbohydrate in fruit and vegetables

Fruits and vegetables are consumed at all times, and due to their convenient size; they are an excellent between-meal snack. They are relatively low in calories and fat (avocado and olives being the exceptions), they have no cholesterol, they are rich in carbohydrates and fiber, they contain vitamin C and carotene, and some are a good source of vitamin B 6.

The empirical composition of carbohydrates may be expressed by the formula CnH2nOn. With regard to their specific chemical properties, carbohydrates may contain a potential aldehyde, -CHO, or ketone, C=O, group. Carbohydrates are part of a healthful diet.

Vegetables are composed chiefly of carbohydrates, mainly simple sugars and complex carbohydrates (starch and dietary fiber). The content ranges from 1-2% in the leaf and stem vegetables to 27% in sweet potato. Root vegetables have the highest carbohydrate content. Dietary fiber content ranges from 0.8% in cucumber to 8.0% in artichoke.

Carbohydrate functions include, among others, the storage of energy reserves and the make-up of much of the structural framework of cells. Simple carbohydrates, which are also the immediate products of photosynthesis, are important components of sensorial quality attributes.

Fruit vary widely in their carbohydrate content (between 1.5% and 26%). Ripe fruit contain no starch; the main sugars are fructose and glucose which are often present in equal proportions. Apple and pear, contain more fructose, while apricot and peach also contain sucrose. Like vegetables, fruit also contain dietary fiber. Various organic acids in unripe fruit produce the typical sour taste. During ripening concentration of these acids falls and that of sugars rises.

Glucose, fructose and sucrose are water-soluble and together they comprise most of the sugars associated with the sweet taste of fruits and vegetables. In many fruits (e.g. apple, pear, strawberry, grape) glucose and fructose are present in greater amounts than sucrose, but in certain vegetables, such as parsnip, beetroot, carrot, onion, sweet corn, pea and sweet potato, and in some ripe fruits such as banana, pineapple, peach and melon, the sucrose content is higher.

Free xylose, in trace amounts, has been reported in onion, strawberries, prunes, apples, pears, grapes, juniper berries, barley malts, brewhouse worts, maple syrup, asparagus, the white and the yolk of eggs, corn, tomatoes, apricots, bamboo shoots, potatoes, beans, alfalfa, beer, and mangoes.

Dietary fiber is composed of non-digestible carbohydrates and lignin intrinsic and intact in plants. Diets rich in dietary fiber have been shown to have a number of beneficial effects, including decreased risk of coronary heart disease and improvement in laxation.

The recommended dietary fiber intake is 14 grams per1,000 calories consumed. The majority of servings from the fruit group should come from whole fruit (fresh, frozen, canned, dried) rather than juice. Increasing the proportion of fruit that is eaten in the form of whole fruit rather than juice is desirable to increase fiber intake.
Carbohydrate in fruit and vegetables
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