Characterization of Aerobic Spore-Forming Bacteria Isolated From Raw Milk, Skim Milk Powder and UHT Milk
Sameh S. Yacoub, Sherif M. Shamsia, Sameh A. Awad, Hamid M. Ziena and Nabil M. Safwat
Thermoduric and thermophilic aerobic spore-forming bacteria are the common causes of spoilage of pasteurized and Ultra-high-temperature (UHT) milk. The presence of high level of aerobic spore-forming bacteria in raw and recombined milk used in making UHT milk increased the spoilage and/or the reduced shelf life in the final product. In this study, 140 samples of (32) raw milk (RM), (8) skim milk powder (SMP) and (100) UHT milk were collected to isolate aerobic spore-forming bacteria. A total of 210 isolates of heat resistant bacteria were classified according to morphological, physiological and biochemical tests. Out of theses isolates, 144 strains from RM (102), SMP (25) and UHT milk (17) were expected to be Bacillus spp. The isolates were evaluated for proteolytic activity and lactose fermentation, 96.55% of the isolates were able to hydrolyze casein, while 42.76 % of the isolates were able to ferment lactose. Thermophilic Bacillus species were the predominant isolates from raw milk and skimmed milk powder. While, mesophilic Bacillus species were the predominant in UHT milk.
Key Words: Raw milk, Skimmed milk, UHT milk, spore-forming bacteria, Bacillus spp.