tailieunhanh - Microbiological Spoilage of Dairy Products

It is said that farms having land to grow crops and forage (PK-3 and PK-10R) were relatively most competitive. The PK-10R farm is said to be most viable farm size, and has the potential of challenging competitors in export markets6. Such farms make effective use of technological advances in breeding practices, ., artificial insemination, to improve their herd quality. Some of them have also installed their own pasteurization or processing equipment. However, there are only 23% of farmers who fall in the PK-10R category, whereas 70% of the farmers have less than four animals. Low animal productivity, lack of balanced. | Microbiological Spoilage of Dairy Products Loralyn H. Ledenbach and Robert T. Marshall Introduction The wide array of available dairy foods challenges the microbiologist engineer and technologist to find the best ways to prevent the entry of microorganisms destroy those that do get in along with their enzymes and prevent the growth and activities of those that escape processing treatments. Troublesome spoilage microorganisms include aerobic psychrotrophic Gram-negative bacteria yeasts molds heterofer-mentative lactobacilli and spore-forming bacteria. Psychrotrophic bacteria can produce large amounts of extracellular hydrolytic enzymes and the extent of recontamination of pasteurized fluid milk products with these bacteria is a major determinant of their shelf life. Fungal spoilage of dairy foods is manifested by the presence of a wide variety of metabolic by-products causing off-odors and flavors in addition to visible changes in color or texture. Coliforms yeasts heterofermentative lactic acid bacteria and spore-forming bacteria can all cause gassing defects in cheeses. The rate of spoilage of many dairy foods is slowed by the application of one or more of the following treatments reducing the pH by fermenting the lactose to lactic acid adding acids or other approved preservatives introducing a desirable microflora that restricts the growth of undesirable microorganisms adding sugar or salt to reduce the water activity aw removing water packaging to limit available oxygen and freezing. The type of spoilage microorganisms differs widely among dairy foods because of the selective effects of practices followed in production formulation processing packaging storage distribution and handling. Types of Dairy Foods The global dairy industry is impressive by large. In 2005 world milk production was estimated at 644 million tons of which 541 million tons was cows milk. The . Ledenbach B Kraft Foods Inc. 801 Waukegan Road Glenview IL 60025 USA e-mail lharris@ .