Plant-based food in the freezer (4)
(3) Pectin Pectin is a linear polysaccharide linked by galacturonic acid. It is the main component of the cell wall of fruits and vegetables and an important factor affecting the texture of the fruit. The hardness and brittleness of the fruit are closely related to the content and form of pectin in the raw materials, and the pectin solution has a higher viscosity. It shows the pectin content of some fruits and vegetables. Pectin has three states in fruits and vegetables:
① Proto-pectin: It is a non-water-soluble substance that exists in plants and immature fruits and combines with cellulose and hemicellulose. It is also called pectin fiber, which makes the fruit appear firm, brittle, and insoluble in water. When the fruit is mature, it is prone to hydrolysis under the action of acid, alkali or enzyme to produce pectin.
② Pectin: It exists in the cell fluid, is soluble in water, and has no binding effect, thus forming a loose tissue. The degradation of pectin is affected by both fruit maturity and storage conditions. When the fruit further matures and ages, pectin continues to be decomposed into pectic acid and methanol by the action of pectinase.
③Pectic acid: It has no binding ability, and is slightly soluble in water. When it meets calcium, it becomes calcium pectate and precipitates. The change of fruit hardness is closely related to the change of pectin substance. A fruit hardness meter can be used to determine the fruit hardness of apples, pears, etc., to determine the degree of maturity, and as an indicator of the fruit storage effect.
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(4) Cellulose and hemicellulose. Cellulose and hemicellulose are widely distributed in the plant kingdom and the quantity is very large. Cellulose is more common in fruits and vegetables. It is a complex polysaccharide compound formed by the condensation of countless glucose molecules. It is the main component of plant cell walls. It supports the shape of fruits and vegetables and cannot be digested by the human body, but it can promote Peristalsis of the intestines. There are many kinds of organic acids in fruits and vegetables, including citric acid, malic acid and tartaric acid. Since they are the most abundant in fruits, they are often collectively referred to as fruit acids. Some fruits and berries also contain trace amounts of succinic acid, oxalic acid, benzoic acid and formic acid. Organic acids are mainly used in fruit and vegetable raw materials and fruit and vegetable processing, of which tartaric acid has the strongest acidity. The generation of acid sensation is related to the type and concentration of acid, as well as the temperature of the system, the buffering effect and the content of other substances. The buffering effect of the system increases, which can increase the softness of the acid. Generally, the content of organic acids is the highest after fruit development is completed. With maturity and aging, organic acids participate in the respiration of fruits and vegetables and are consumed as the matrix of respiration, and their content shows a downward trend. During storage, the organic acid of the fruit decreases faster than sugar, and the higher the temperature, the more organic acid is consumed, resulting in a gradual increase in the sugar-acid ratio. The content of organic acids in fruits and vegetables and the change rate of organic acids during storage are usually used as an indicator to judge whether the fruits and vegetables are mature and the storage environment is suitable.
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