Advisor(s)
Abstract(s)
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 pressur
Description
Keywords
Biotecnologia Leite desnatado Caseína Formores de esporos termofílicos