1. What are the key points for sensory identification of milk and dairy products?
Sensory identification of milk and dairy products mainly refers to observing their color and tissue status, smelling their odor, and tasting their taste. The three should be equally important and indispensable.
For milk, attention should be paid to whether its color is normal, whether the texture is even and delicate, whether the taste is pure, and how creamy it is. At the same time, attention should be paid to impurities, precipitation, odors, and other situations in order to make a comprehensive evaluation.
For dairy products, in addition to paying attention to the above identification content, it is also important to observe and understand the situation such as whether yogurt has whey separation, whether milk powder has clumps, and whether there are water droplets and mold spots on the cheese cut surface in a targeted manner for sensory identification. If necessary, dairy products can be mixed for sensory identification.
2. The impact of hygiene status of raw milk on the quality of milk and dairy products
The quality of raw milk hygiene is directly related to the quality of milk and dairy products. The hygiene and quality problems of raw materials mainly include sick milk (milk from tuberculosis and mastitis cows), high acid milk, fetal milk, colostrum, milk within five days after the application of antibiotics, adulterated milk and deteriorated milk. The milk of cattle suffering from tuberculosis shall not be used as sterilized milk for human consumption, but can only be processed into dairy products. Milk from cows suffering from mastitis, fetal milk 15 days before calving, colostrum 7 days after calving, milk within 5 days of antibiotic application, and spoiled milk shall not be used as disinfected milk or processed into dairy products. High acidity milk shall not be used as raw materials for disinfected milk and high-quality dairy products. The adulterated milk shall be treated according to the situation. The milk added with water, sucrose, salt, soybean milk, starch and other substances shall not be used as sterilized milk for human consumption, but can be used for processing dairy products. Milk mixed with non edible substances shall not be consumed or processed into dairy products.
3. The impact of microbial contamination on the quality of milk and dairy products
Microbial contamination is an important cause of spoilage in milk and dairy products. Microbial contamination may occur in various stages of milk and dairy product processing, such as sterilization, filtration, concentration, fermentation, drying, packaging, etc., due to non-compliance with operating procedures. Therefore, in the processing of milk and dairy products, all containers, equipment, pipelines, tools, packaging materials, etc. that come into contact with milk and dairy products must be thoroughly sterilized to prevent microbial contamination and ensure product quality. In addition, it is necessary to prevent the mixing and contamination of mechanical impurities and volatile substances (such as gasoline) during the processing.
4. What are the effects of storage conditions on the quality of milk and dairy products
(1) Temperature: If the temperature of milk and dairy products is too high during storage, it can accelerate the oxidation and deterioration of some components, as well as the growth and reproduction of microorganisms. Therefore, it is necessary to control the required temperature when storing milk and dairy products. The storage temperature for disinfected milk and hard cheese is 2-10 ℃, the storage temperature for sour milk is 2-8 ℃, the storage temperature for milk powder and condensed milk is below 20 ℃, and the storage temperature for cream is below -15 ℃.
(2) Time: Prolonged storage of milk and dairy products can easily lead to changes in hygiene quality.
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