Hygiene and management of fruit and vegetable foods
作者：admin 点击次数：120 发布时间：2025-05-29
Fruits and vegetables are important foods for human beings, in addition to providing people with important vitamins and inorganic salts and other nutrients, the cellulose and pectin and other substances contained in them have important physiological functions for the human body, cellulose promotes intestinal peristalsis, is conducive to defecation, and the same is true for pectin. In recent years, scholars in Europe, the United States and Japan have studied that cellulose and pectin can reduce the damaging effect of toxic substances on the body in addition to the above-mentioned physiological functions. For example, ingestion of pectin can increase the excretion of lead in the body and promote the metabolic process of toxic substances. In addition, dietary fiber has been found to enhance the activity of cholesterol 7a-hydroxylase in the liver, which is involved in cholesterol metabolism. Therefore, eating more fresh fruits and vegetables can prevent atherosclerosis.
1. Fruit and vegetable and microbial pollution
Generally, the normal internal tissues of fruits and vegetables should be sterile, but sometimes microorganisms can exist in the internal tissues of fruits and vegetables. For example, yeast can be isolated from some apples, and some yeast and paper fungi of the genus Pseudomonas can also be isolated from tomatoes. These microorganisms invade and live in plants long before flowering and fruiting. In addition, fruits and vegetables are attacked by plant pathogenic organisms and cause lesions, and these plant pathogenic microorganisms enter the plant from roots, stems, leaves, flowers and fruits during the growth period of fruits and vegetables or before harvest. Another way is to invade people in post-harvest packaging, transportation and storage, which will contaminate a large number of saprophytic microorganisms.
When the epidermis of fruits and vegetables is damaged, the waxy covering is destroyed and it is more susceptible to microbial infection, and the only organisms that begin to cause the deterioration of fruits and vegetables are yeast and mold. After the mold invades the fruit and vegetable tissue, the cellulose in the cell wall is first destroyed, and then the pectin, protein, starch, organic acids, and sugars in the fruit and vegetable cells are broken down, and the bacteria begin to multiply.
(1) Microorganisms cause deterioration of fruits and vegetablesWhen the epidermal tissue of fruits and vegetables is stabbed by insects or other mechanical damage, microorganisms will invade and multiply, thereby promoting the decay and deterioration of fruits and vegetables, especially fruits and vegetables with high maturity, which are more easily damaged, even if we are not perceptible to the naked eye
microorganisms can also invade people with very small damage. The material composition of fruits and vegetables is characterized by carbohydrates and water, and high water content, which is an important factor for fruits and vegetables to easily cause microbial deterioration; Secondly, the pH of fruits < 4.5, and the pH of vegetables is between 5~7, which determines the water
Microbial groups that can grow and reproduce in fruits and vegetables. The microorganisms that cause fruit spoilage can only be yeasts and molds at first. The microorganisms that cause vegetables to spoil are molds, yeasts, and a few bacteria. Therefore, the most common phenomenon is that molds multiply in the lesions of the epidermis of fruits and vegetables or in the places where pollutants adhere to the surface of fruits and vegetables, and after invading the tissues of fruits and vegetables, the cellulose of the tissue cell wall is first destroyed, and then decomposes pectin proteins, starches, organic acids, sugars and other substances, and then bacteria begin to multiply. Of course, there are bacteria and mother bacteria that are caused by the beginning, but the first to multiply on fruits can only be yeasts and molds. Due to the reproduction of microorganisms, dark spots appear on the appearance of fruits and vegetables, and the tissues become soft, fluffy, dimple, and changeable
shape, and gradually become slurry or even watery, and produce a variety of different flavors, such as sour, aromatic, wine, etc. It is important to note that fresh fruits and vegetables are live foods that remain alive during storage. The reason is that the enzymes in its tissues are still active, so the nutrients stored in the tissues before harvest can be used to maintain their life activities, and continue to change in the direction of maturity, but this change is to promote decomposition, and there is no longer synthesis, until the nutrients are completely consumed, so that the fruit and vegetable tissues are all disintegrated and deteriorated, which has a certain synergistic effect with the deterioration caused by microorganisms. (2) Microorganisms in the refrigeration of fruits and vegetables
Because low temperature can inhibit the activity of microorganisms and various enzymes, low temperature can extend the shelf life of fruits and vegetables. However, if the temperature is too low, it will freeze fruits and vegetables, thereby causing changes in the physical properties of fruit and vegetable tissues, so under normal circumstances, refrigeration is used to preserve fruits and vegetables, because the growth of most microorganisms has been inhibited under refrigeration, and the growth rate has been reduced to a very slow degree. Refrigeration is very effective in preventing the spoilage of fruits and vegetables for a certain period of time. However, some microorganisms such as Pseudomonas in bacteria can still grow, so the length of the shelf life also depends on a variety of factors, such as the type and number of microorganisms in the vegetables, the damage to the skin of fruits and vegetables, the pH of fruits and vegetables, the maturity of fruits and vegetables, and the temperature and hygiene of the refrigerated environment.
(3) Microorganisms cause the deterioration of fruit juice
Fruit raw materials carry a certain number of microorganisms, and in the process of juice making, it is inevitable to be polluted by microorganisms, and whether microorganisms can grow and reproduce after entering human juice mainly depends on the pH of the juice and the sugar content in the juice.
Due to the low acidity of the juice, the pH is between 2.4~4.2, and the sugar content is high, so the microorganisms growing in the juice are mainly yeasts, molds and a very small number of bacteria.
1. Bacteria in fruit juices
The bacteria grown in fruit juice are mainly lactic acid bacteria, which can grow in fruit juice with a pH of > 3.5 or above, such as phytobacterium, leuconostoc and Streptococcus gelidum, which can use sugar and organic acids in fruit juice to grow and reproduce and produce lactic acid, CO, etc., as well as a small amount of diaceone, 3-hydroxy-2-butanone and other flavor substances; Leuconostoc produces thickening substances such as mucopolysaccharides, which spoils the juice.
Other bacteria do not multiply when they survive in low-pH juices. When pH > 4.0, butyric acid bacteria (Clostridium weisseri) are susceptible to growth for butyric acid fermentation.
2. Yeast in fruit juice Yeast is a class of microorganisms with the largest number and variety of microorganisms contained in fruit juice, which are brought from fresh fruits or polluted by the environment during the pressing process, of course, fermented juice may also be contaminated during fermentation. The yeasts in fruit juice are mainly Candida spp., Cycloyeast Yeast, Cryptococcus spp., and Red Yeast Yeast, and apple juice is often seen growing when it is stored in a low C0, gas (this bacterium can produce fruit-flavored esters).
Yeasts of the genus Vietnam, Saccharomyces cerevisiae, Saccharomyces cerevisiae, and yeast are often found in citrus juice, which are contaminated during processing.
Due to the high sugar content and high acidity of fruit juice concentrate, the growth of bacteria is inhibited, and some osmotic yeasts and molds are grown in it, such as Luceria pastori, honey yeast, etc.
3. Mold in juice
Mold causes unpleasant odors when juices spoil.
Penicillium is the most common mold present in fruit juice, such as Penicillium dilatorium, Penicillium cchito, etc. The second is Aspergillus bacteria, such as Aspergillus niduno, Aspergillus fumigatus, etc., because the spores of Aspergillus have strong resistance and can survive for a long time. However, molds are generally susceptible to the inhibition of CO, so the juice filled with C0 can prevent bacteria.
In addition, some molds from Alternaria spp., Mycomycephala, P. mealosporum and Fusarium spp. are also present in freshly squeezed juices, but they are not easy to find in stored juices.
4. Defects caused by microorganisms in the deterioration of fruit juice
(1) In addition to chemical factors that can cause fruit juice deterioration, most of the causes of fruit juice intercoloration are caused by yeast production of alcohol, of course, sometimes it can also be caused by mold.
Yeasts that usually cause cloudiness are some species in the genus Saccharomyces circula. And the molds that cause turbidity are some heat-resistant frosty fungi, such as Snow-white silk cleatella. However, when the mold grows in small amounts in the juice, it does not become turbid, but only spoils the flavor of the juice, resulting in musty and foul smells.
(2) Alcohol production The microorganisms that cause fruit juice to produce ethanol and deteriorate are mainly yeasts. Yeast can tolerate CO, when the juice contains a higher concentration of C0, although the yeast can not grow obviously, but can still maintain vitality, once CO, the concentration is reduced, can restore the ability to grow and reproduce the surface caused by the storage of juice to produce ethanol.
In addition, a small number of molds and bacteria can also cause alcohol spoilage in fruit juices, such as some species in Glycol Bacillus, Leuconostoc, Aspergillus trichotomy, and Fusarium.
(3) Changes in organic acidsJuice contains a variety of organic acids such as tartaric acid, citric acid, malic acid, which form the unique flavor of fruit juice at a certain content, and when microorganisms grow and multiply, they decompose some organic acids, thereby changing their content ratio, thus making the juice deteriorate, which is manifested as the original flavor being destroyed, and sometimes even producing some unpleasant odors. The microorganisms that cause changes in organic acids are mainly bacteria and molds, and yeast has a weak effect on organic acids.