Microbiological Studies on Market Milk 1. Features of Deterioration and Psychrophilic Bacterial Flora in Market Milk, Stored at Low and Moderate Temperatures

• Published in: Food Hygiene and Safety Science (Shokuhin Eiseigaku Zasshi) Vol. 7; no. 1; pp. 14 - 19
• Main Authors: HAMAMOTO, Michio, HIROTA, Tetsuji, KANAUCHI, Toshiro
• Format: Journal Article
• Language: English
• Published: Japanese Society for Food Hygiene and Safety 05.02.1966
• DOI: 10.3358/shokueishi.7.14
• ISSN: 0015-6426

Composite samples of commercially bottled market milk were stored at 4, 8 and 21°C, and bacterial growth, declination of protein stability and development of undesirable fiavor were examined during storage, and psychrophilic bacterial flora of each sample was analysed. Each sample gave a positive reaction in dye reduction test when bacterial count reached 107/ml, and thereafter, protein stability began to decline when the highest bacterial count (108-109/ml) was obtained, then acids and undesirable flavors simmultaneously developed. The effects of lower temperature on the deterioration of milk were characterized by the delay of bacterial growth and the slower rate of enzymatic deterioration of milk components. Psychrophilic strains isolated from stored milk samples were classified into 9 types, Pseudomonas fluorescens, Alcaligenes viscolactis, 1 type of Pseudomonas sp., Flavobacterium solare, 2 types of Achromobacter sp., Brevibacterium ammoniagenes, Aerobacter aerogems and Bacillus circulans. The distribution of micro-organism, such as Ps. fluorescens, 1 type of Achromobacter sp. and Br. ammoniagenes, which grew well at 0°C were 98% in milk stored at 4°C, 44.9% at 8°C and 0% at 21°C. Dye reduction test and the test that 2ml of 70% ethanol is added to 1ml of milk, are considered to be available for routine measurement of deterioration of the stored product.