80 kinds of fruit processing techniques

Author: Chief Editor: Yu Zhaohai et al
Publisher:
Publishing Date: 1998-10-01
Features: The book introduces the basic principles of fruit processing and provides detailed descriptions of the processing techniques for 80 types of products from various fruits such as citrus, apples, grapes, pears, peaches, hawthorns, jujubes, kiwifruits, plums, apricots, plums, bayberries, cherries, strawberries, and chestnuts. It includes traditional products like canned goods, dried fruits, fruit juices, fruit wines, and fruit jams, as well as modern products. The text is easy to understand and the techniques are reliable, making it suitable for fruit processing enterprises, professionals, and business units to learn and apply. Most of the content is also applicable to ordinary households and general farmers and can serve as a teaching reference for relevant institutions. Excerpt:
(7) Pigment Substances
Pigment substances refer to the total pigments that give fruits their color. They mainly include the following categories:
1. Chlorophyll
The green color of fruits is determined by chlorophyll. Chlorophyll is composed of chlorophyll a and chlorophyll b. Chlorophyll a is blue-green in its pure form, while chlorophyll b is yellow-green. In green plants, their content ratio is approximately 3:1. The higher the chlorophyll content, the more intense the green color of the fruit. Chlorophyll is insoluble in water but soluble in organic solvents such as ethanol and ether. Under acidic conditions, the magnesium ion in the chlorophyll molecule is easily replaced by hydrogen ions, forming de-magnesium chlorophyll, which turns dark black to green-brown. This is why green fruits often turn green-brown or even dark black after processing. In alkaline solutions, chlorophyll can saponify and hydrolyze into chlorophyllates with fresh green color, as well as chlorophyll alcohol and methanol, which serve as the theoretical basis for preserving green color in vegetable processing. Under suitable conditions, the magnesium in chlorophyll can be replaced by copper ions, forming more stable green salts. Among them, sodium copper chlorophyll has the brightest color and is relatively stable to light and heat, making it suitable as a colorant in the food and daily chemical industries.
2. Carotenoids
Carotenoids are lipid-soluble pigments and mainly include α, β, γ-carotenes, lycopene, lutein, capsanthin, and capsorubin, which are widely found in fruits and exhibit yellow, orange, and red colors. Carotenes are present in yellow fruits and vegetables such as carrots, citrus, apricots, and mangoes. They serve as both pigments and nutrients, as they can be converted into vitamin A in animals and humans, hence the name "source of vitamin A." Lycopene is an isomer of carotenes and is the main pigment in ripe tomatoes, also found in the peels of red citrus fruits. Due to its different structure from carotenes, it does not have the vitamin A activity. Lutein is a derivative of carotenes, yellow in color, and widely present in various plants. Carotenoids are relatively stable and generally not easily damaged during processing, but light and oxygen can affect them, especially under the action of oxidants, which can cause discoloration.
3. Anthocyanins
Anthocyanins are the main pigments that give fruits red, purple, and other colors and are water-soluble. In plant tissues, they are often found in the form of glycosides in petal, peel, and cytoplasm of fruit flesh cells, hence the name anthocyanins. Anthocyanins are highly soluble in water, so during processing, to preserve their color, the raw materials must be handled gently during pretreatment operations, avoiding prolonged soaking, washing, or rubbing to prevent significant pigment loss. The color of anthocyanins changes with the pH value of the solution. Generally, they appear red below pH 7, purple around pH 8.5, and blue or blue-purple at pH 11. The different pH values of fruit juices cause anthocyanins to exhibit different colors. During processing, fruits containing anthocyanins should be treated under lower pH conditions to maintain their red color, otherwise, under alkaline conditions, the product may turn purple or blue. Anthocyanins are highly sensitive to light and heat, and foods rich in anthocyanins will quickly turn brown under light or high temperatures. For example, strawberries, cherries, and bayberries will quickly lose their color or darken when boiled in open pots. Anthocyanins can react with metal ions to form salts, appearing purplish-red, blue, or grayish-purple. For instance, they turn grayish-purple when reacting with iron and blue-purple when encountering tin. Therefore, during processing, avoid using iron or tin tools and containers; stainless steel utensils or non-metallic products can be used instead. Anthocyanins form sulfuric acid and lose color in solutions of sulfur dioxide or sulfites. However, once the sulfur is removed, the reaction reverses, and the original color reappears. Thus, fruits preserved with sulfur dioxide or sulfites may temporarily lose color, but they can still show their original red color after heating.