Abstract
This study had investigated the effect of freezing on the bacterial counts in raw milk. In specific, we estimated the total bacterial counts and the counts of total coliform, Salt tolerant bacteria, Staphylococcus spp., Thermopilic Lactobacilli, Mesophilic Lactobacilli, Leuconostoc spp., Lactococci and Streptococci. Thirty samples of raw cow milk were frozen at -18-20°C for eight weeks and tested on a weekly basis. The results showed that the bacterial counts had significantly decreased as the freezing period increased. Thus, the total count had significantly decreased from (6.5*105 cfu/ml) in fresh milk to (5.0*103 cfu/ml) in frozen milk after eight weeks (P1%). The decrease in the bacterial counts was different between the different bacterial groups. The highest decrease was for Salt tolerant bacteria from (9.8*105 cfu/ml) to (7.6*103 cfu/ml), while the lowest decrease was for Staphylococcus spp from (3.6*103cfu/ml) to (8.2*101cfu/ml). The study recommends freezing as an important storage method for raw milk.
Highlights
Milk is considered as a suitable media for microbial growth for several reasons, it is a rich source of nutrients, the pH of the milk is approximately neutral and its water content is high
The results showed that the bacterial counts had significantly decreased as the freezing period increased
The highest decrease was for Salt tolerant bacteria from (9.8*105 cfu/ml) to (7.6*103 cfu/ml), while the lowest decrease was for Staphylococcus spp from (3.6*103cfu/ml) to (8.2*101cfu/ml)
Summary
Milk is considered as a suitable media for microbial growth for several reasons, it is a rich source of nutrients, the pH of the milk is approximately neutral and its water content is high. Sanchez et al (2003) studied the effect of freezing on goat milk Unlike cow milk, they did not find significant decrease in E. coli count in goat milk samples after freezing at -20 °C, and even after 730 days of storage at -80 °C. They did not find significant decrease in E. coli count in goat milk samples after freezing at -20 °C, and even after 730 days of storage at -80 °C These results were explained by the differences in milk composition. Hubackova and Rysanek (2007) examined the effects of freezing and subsequent storage on quantitative results of bacteriologic culturing of selected alimentary pathogens and indicator microorganisms in milk They documented that freezing had a considerable adverse effect on the recovery of E. coli after 7 days of storage. Freezing caused a slight increase in Staphylococcus aureus counts in milk samples after 72 hours and 7 days of storage. Pazzola et al (2013) investigated the effect of long-term www.ccsenet.org/ijb
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
