what is rancidity and Slime formation in Milk products?
Answers
Answer:
Rancidification is the process of complete or incomplete oxidation or hydrolysis of fats and oils when exposed to air, light, or moisture or by bacterial action, resulting in unpleasant taste and odor. ... When these processes occur in food, undesirable odors and flavors can result.
Explanation:
Summary
Dairy processing involves pasteurization, commercial sterilization, fermentation, dehydration, refrigeration, and freezing. In this chapter, contamination and spoilage of milk and milk products and interaction of microorganisms with dairy foods are overviewed. Spoilage of milk and milk products results from growth of fermentative bacteria when storage temperatures are sufficiently high for psychrotrophs. Heat‐resistant proteinases of psychrotrophic bacteria cause spoilage in processed milk because of enzyme‐retaining activity after the heat treatment. The most common fermentative spoilage of fluid milk products is souring caused by thermoduric lactic acid bacteria (LAB). Concentrated milk products can be divided into three groups: evaporated milk, sweetened or unsweetened condensed milk, and concentrated milk. Psychrotrophic bacteria have primary importance in cheese spoilage since these bacteria produce very active proteolytic and lipolytic enzymes. Centrifugation, clarification, or separation will remove some microorganisms from milk.
Answer:
The numbered list below identifies seven types of bacteria according to how they change the properties of milk. Often these changes are negative (spoilage) but as we will see in later sections, many of these bacteria are important to the development of cheese flavour. Before proceeding to the list, please note the following definitions:
- Psychrotrophic refers to microorganisms which are able to grow at temperatures less than 7C. Cold milk storage and transport selects for psychrotrophic bacteria which are often proteolytic and lipolytic. Common psychrotrophic bacteria in milk are species of Micrococci, Bacilli, Staphyloccoci, Lactobacilli, Pseudomonas, and coliforms. Pseudomonas species are the most common and typically have the most impact on quality. At temperatures of 2 - 4C, bacterial growth in milk is mainly due to strains of Pseudomonas flourescens. Little growth occurs at temperature less than 2C.
- Spore forming bacteria are able to exist in a highly stable form called 'spores'. In the spore state, these bacteria are able to withstand greater extremes of acidity, temperature and desiccation.
- Enzymes are biological catalysts that accelerate the rates of biochemical reactions. Bacterial enzymes are most significant to milk spoilage and cheese ripening but it is important to distinguish between the enzyme and the bacterial source. For example, many psychrotrophic bacteria produce heat stable enzymes which remain active in milk and cheese even after the bacteria are killed by pasteurization.