Bacterial flora in food and its significance in food hygiene

作者：admin  点击次数：22  发布时间：2025-03-31

As mentioned above, only a small part of the bacteria in nature may exist in food. The composition of the types of bacteria coexisting in food and their relative numbers is called the bacterial phase of food, among which the bacteria with a relatively large number are called dominant bacteria. The degree and characteristics of changes in food under the action of bacteria mainly depend on the bacterial phase, especially the dominant bacteria. The bacterial phase of food can be different due to the influence of factors such as the source of pollution, the physical and chemical properties of the food itself, the environmental conditions, and the symbiotic and antibiotic relationship between bacteria.
The bacterial phase of contaminated food can often be predicted by the physical and chemical properties of food and the environmental conditions in which it is located. For example, meat placed at room temperature is often contaminated by aerobic Bacillus, Micrococcus and Pseudomonas in the early stage: as the spoilage process develops, Enterobacteriaceae will gradually increase; in the middle and late stages, Proteus will occupy a larger proportion. Due to the different bacterial phases and dominant species of food, the changes caused by food spoilage will also have corresponding characteristics. Therefore, the inspection of the bacterial phase of food can also estimate the degree and characteristics of food spoilage. For example, the bacteria that decompose protein mainly include aerobic Bacillus, Pseudomonas, Proteus, and anaerobic Clostridium, the bacteria that decompose fat mainly include Alcaligenes, and the bacteria that decompose starch and cellulose include Bacillus, Clostridium, etc. For another example, some bacteria can produce pigments that make contaminated food have specific colors. Red mainly comes from Serratia marcescens and pink Micrococcus, yellow and yellow-green come from Micrococcus, Flavobacterium, Pseudomonas, etc., and black comes from Clostridium nigrofaciens, Proteus, and Pseudomonas, etc.
(III) Bacterial contamination indicators for evaluating food hygiene quality and their food hygiene significance There are two bacterial contamination indicators that reflect food hygiene quality: one is the total number of colonies, and the other is coliform group. 1. Total colony count in food and its significance in food hygiene
The total colony count refers to the total number of bacterial colonies that can be cultured under strictly specified conditions (culture medium and its pH, incubation temperature and time, counting method, etc.) in the unit mass (g), volume (mL) or surface area (cm') of the sample being tested, expressed in colony forming units (colony forming units, c). The total colony count represents the amount of bacterial contamination in food.
The food hygiene significance of the total colony count is mainly to use it as a sign of the cleanliness of food and to supervise the cleanliness of food. Many food hygiene standards in my country stipulate the total colony count index of food as the allowable limit for controlling food contamination. Secondly, the total colony count can also be used to predict the storage period of food, that is, to use the number of bacteria in food as an indicator to assess the degree of food spoilage (or freshness). The impact of the number of food bacteria on food hygiene quality is more obvious than the bacterial phase. If there are more bacteria in food, it will accelerate its spoilage. Someone has made a comparison. When the total colony count of fish is 10'cf/cm', it can be stored for 6 days at 0℃; when the total colony count is 10'cf/em', it can be stored for 12 days under the same conditions.
2. Coliform group and its food hygiene significance
Coliform group includes Escherichia, Citrobacter, Enterobacter and Klebsiella of the Enterobacteriaceae family. The bacteria in these genera are all from the intestines of humans and warm-blooded animals. They are aerobic and facultative anaerobic, do not form spores, and can ferment lactose to produce acid and gas at 35~37℃. The food hygiene significance of coliform group is mainly as an indicator of food contamination by feces. Because coliform group comes directly from the feces of humans and warm-blooded animals; secondly, it is an indicator of food contamination by intestinal pathogens, because coliform group and intestinal pathogens have the same source, and under normal conditions, the survival time of coliform group in the external environment is consistent with that of major intestinal pathogens.
It is not easy to ensure that there is no coliform bacteria in food. What is important is the degree of contamination. The number of coliform bacteria in food is expressed as the possible number equivalent to 100g or 100m of food, referred to as the maximum probable number of coliform bacteria (MPN). This is a statistical value of the results obtained by testing according to a certain plan. The so-called certain test plan is uniformly adopted in my country. The three-step method of lactose fermentation with three tubes of three dilutions of samples is used, and the corresponding MPN retrieval table is compiled for practical application based on various possible test results.