Research on the packaging technology of the hottes

Research on the packaging technology of food anti-corrosion and deterioration II

the existence state of food

intact Sandvik Group is the world's leading advanced product manufacturer. Damaged food is generally not prone to corruption, such as potatoes and apples without crushing and wounds, which can be stored for a long time. If the food tissue breaks down or the cell membrane is broken accurately and reliably, it is easy to be polluted by microorganisms and deteriorate

1.1.2 microorganisms

microorganisms play an important role in the process of food spoilage. If a certain food is thoroughly sterilized or filtered and sterilized, the food will not decay after long-term storage. On the contrary, if a food is contaminated with microorganisms, once the conditions are suitable, it will cause the food to deteriorate. Therefore, microbial pollution is the root cause of food spoilage

there are many kinds of microorganisms that can cause food spoilage, mainly bacteria, yeast and mold. In general, bacteria are often more dominant than yeast. Among these microorganisms, there are pathogenic and non pathogenic bacteria, spores and non spores, thermophilic, thermophilic and psychrophilic bacteria, aerobic or anaerobic bacteria, and bacteria with strong ability to decompose proteins, sugars and fats. The following is a summary of microorganisms that are easy to cause spoilage of different foods:

table some types of food spoilage and microorganisms that cause spoilage

(Microbiology, MJ little perza et al., 1987)

types of food spoilage microorganisms

moldy bread produces Rhizopus nigricans, Penicillium Aspergillus niger Bacillus subtilis

syrup produces mucus and ferments pink moldy Enterobacter aerogenes, Saccharomyces, Zygosaccharomyces, Micrococcus roseus, Aspergillus, Penicillium

fresh fruits and vegetables soft rot gray mold rot Rhizopus Erwinia Botrytis Aspergillus, Pseudomonas (Pseudomonas with rapid release of pseudonh3)

Rhodotorula appears on the surface of pickles and pickles

Alcaligenes, Clostridium, Proteus vulgaris Pseudomonas fluorescens Pseudomonas putrefaciens

moldy Aspergillus, Rhizopus, Penicillium of meat

preserved acid turning green, viscid Pseudomonas, Micrococcus, Lactobacillus, Leuconostoc

fish discoloration Pseudomonas putrefaciens, alkali producing bacteria, Flavobacterium Shewanella putrefaciens

egg green corruption Discoloration, corruption, black corruption, fluorescent Pseudomonas, Pseudomonas, alkali producing bacteria, proteus

poultry viscosity, odorous Pseudomonas, alkali producing bacteria

concentrated orange juice flavor losing lactobacillus, Leuconostoc Acetobacter

⑴ microorganisms that decompose protein food

microorganisms that decompose protein and make food deteriorate, mainly bacteria, molds and yeasts, Most of them are completed by secreting extracellular protease

among bacteria, bacillus, Clostridium, Pseudomonas, Proteus and Streptococcus have strong protein decomposition ability. Even if there is no sugar, they grow well on food with protein as the main component; Clostridium botulinum has a weak ability to decompose protein, but it is anaerobic, which can cause the corruption of cans; Micrococcus, Staphylococcus, Flavobacterium, Alcaligenes and Ehrlichia are weak in protein decomposition

many molds have the ability to decompose proteins, and molds can make better use of natural proteins than bacteria. Common ones are: Penicillium, Mucor, Aspergillus, Trichoderma, Rhizopus, etc. However, most yeasts have very weak ability to decompose protein. For example, Saccharomyces cerevisiae, Pichia pastoris, Hansen's yeast, Candida, Spheroides, etc. can slowly decompose the solidified protein. However, in some foods, yeast cannot compete with bacteria, and bacteria often dominate

⑵ there are few microorganisms that can decompose carbohydrate food

bacteria that can decompose starch with high activity, mainly some species of Bacillus and Clostridium, such as Bacillus subtilis, Bacillus megaterium, Bacillus potato, Bacillus cereus, Clostridium starch, etc., which are the main strains causing rice fermentation and bread viscosity liquefaction; Only some species of Bacillus, Clostridium and sarcococcus can decompose cellulose and hemicellulose; However, most bacteria have the ability to decompose some sugars, especially the ability to use monosaccharides is very common; Some bacteria can utilize organic acids or alcohols; The bacteria that can decompose pectin mainly include some strains of Bacillus, Euclidean Phytophthora and Clostridium, which are involved in the corruption of fruits and vegetables

most molds have the ability to decompose simple carbohydrates; There are not many molds that can decompose cellulose. Several species of Penicillium, Aspergillus, Trichoderma, etc. are common, among which Trichoderma viride, Trichoderma reesei, and Trichoderma kongnii have a particularly strong ability to decompose cellulose. Aspergillus, Mucor, Cladosporium cereus, etc. have strong activity of decomposing pectin; Aspergillus, Mucor and Fusarium also have the ability to use some simple organic acids and alcohols

most yeast cannot hydrolyze starch; A few yeasts, such as endomycetes, can decompose polysaccharides; Very few yeasts, such as fragile wall yeasts, can decompose pectin; Most yeasts have the ability to utilize organic acids

⑶ microorganisms that decompose fatty foods

microorganisms that decompose fat can produce lipases to hydrolyze fat into glycerol and fatty acids. Generally speaking, most aerobic bacteria with strong protein decomposition ability can also decompose fat. Many species of Pseudomonas, Achromobacter, Xanthobacter, Alcaligenes and Bacillus in bacteria have the property of decomposing fat

there are more molds that can decompose fat than bacteria. Aspergillus, Geotrichum candidum, Rhizopus delbrueckii, Penicillium Lou and Cladosporium are common in food

there are few strains of yeast that decompose fat, mainly Candida lipolytica, which does not ferment sugars, but has strong ability to decompose fat and protein. Therefore, whether it is caused by yeast should also be considered when fatty rancidity in meat food, milk and its products

1.1.3 environmental conditions of food

in a sense, environmental factors are also very important to cause food deterioration. Whether contaminated microorganisms in food can grow depends on environmental conditions. For example, meals are easy to deteriorate in hot weather, and moist food is easy to mildew. The environmental factors that affect the deterioration of food are the same as those that affect the growth and reproduction of microorganisms. Some contents have been discussed in the previous relevant chapters, so they will not be repeated. Here, only the most important factors affecting food deterioration, such as temperature, humidity and gas, are discussed

temperature

the effect of temperature changes on microbial growth has been discussed in the previous chapters. According to the adaptability of microorganisms to temperature, microorganisms can be divided into three physiological groups, namely, psychrophilic, thermophilic and thermophilic microorganisms. Each group of microorganisms has the most suitable temperature range for growth, but these three groups of microorganisms can grow and reproduce between 20 ℃ and 30 ℃. When food is in this temperature environment, all kinds of microorganisms can grow and reproduce and cause food deterioration

⑴ effect of low temperature on microbial growth

low temperature is extremely detrimental to microbial growth. However, due to the adaptability of microorganisms, a few microorganisms can grow and reproduce at a temperature of about 5 ℃ or lower (even below -20 ℃), causing food corruption and deterioration. We call this kind of microorganisms low temperature microorganisms. Low temperature microorganisms are the main microorganisms that cause the deterioration of refrigerated and frozen food. The microorganisms that grow in food at low temperature mainly include: Pseudomonas, xanthobacteria, Achromobacter and other gram-negative non bacillus; Gram positive bacteria such as Micrococcus, Lactobacillus, bacillus, bacillus and Clostridium; Candida, Cryptococcus, orbicularia, hyphomyces and other yeasts; Penicillium, Cladosporium, Botrytis and Mucor. See table

for the minimum temperature of different microbial growth in food

the minimum temperature of microbial growth in food (℃) the minimum temperature of microbial growth in food (℃)

pork bacteria-4 Lactobacillus 0 ~ -1

beef mold, yeast, bacteria-1 ~ 1.6 ice cream bacteria-3 ~ -10

mutton mold, yeast Bacteria -1 ~ -5 soybean mold -6.7

ham bacteria 1 ~ 2 peas according to the requirements of gb/t239 (1) 999, soybean mold, yeast -4 ~ 6.7

sausage bacteria 5 Apple mold 0

smoked rib bacteria -5 ~ -10 grape juice yeast 0

fish and shellfish bacteria -4 ~ -7 concentrated orange juice yeast -10

raspberry mold, yeast, bacteria -0.3 ~ -6.5

although these microorganisms can grow at low temperature, However, their metabolic activity is extremely slow, and their growth and reproduction speed is also very slow, so they cause the deterioration of refrigerated food slowly

some microorganisms can grow at very low temperature, and the mechanism is not completely clear. But at least it can be considered that their enzymes can still work at low temperature. In addition, it was also observed that the content of unsaturated fatty acids in the cell membrane of psychrophilic microorganisms was high, which was speculated to be due to the fact that their plasma membrane remained semi fluid at low temperature and could carry out active material transfer. However, other organisms cannot perform their normal functions because of the high content of saturated fatty acids in the cell membrane and become solid at low temperature