Analysis of growth behaviour of thermophile spore formers in different milk based media

Abstract To reduce the thermophilic spore formers in milk powder, it is essential to study the physical and chemical factors of milk that attribute to the growth of thermophilic spore formers for further research. Anoxybacillus flavithermus and Geobacillus stearothermophillus species being important contaminants of dairy industry, four strains from these species were selected and cultured on three milk based media, so that, the influence of the dry matter concentration, osmotic pressure and protein source of those three media on the growth of the test organisms can be determined. The first media is skimmed milk concentrate with 20, 22, 24 and 26% of dry matter respectively, followed by the second media which is casein concentrate with 5% dry matter and lastly the third media, whey concentrate was prepared and heat treated with UHT experimental set up. Then the day culture of the four strains was prepared at 55 °C and 110 rpm. Then enumeration of cell count and spore count after the time interval of 2 h, 6 h and 24 h was performed by plate count method. Freezing point measurement and density measurement of three milk based media was taken for the determination of osmotic pressure. The four test organisms showed growth and spore formation in all the four skimmed milk concentrates with different dry matter concentration and osmotic pressure. They also showed good growth in the other two media, casein and whey concentrate. The results obtained suggest that the dry matter concentration, osmotic pressure of skimmed milk was not enough to prevent the growth of thermophilic spore formers and it could be that, dry milk concentration above 26% would prevent the growth of thermophilic spore formers. In addition to that, results obtained suggest that the protein sources casein and whey of the milk influences the growth of thermophilic spore formers. This thesis work would be useful for the upcoming research to determine the border dry matter concentration for the survival of thermophilic bacteria. So that border dry matter concentration can be maintained during the milk powder production to prevent the thermophilic spore formers growth. Keywords: Thermophilic spore formers, skimmed milk, casein, whey, dry matter, osmotic pressu