EFFECT OF FROZEN STORAGE ON THE MICROBIOLOGICAL AND TECHNOLOGICAL PROPERTIES OF BUFFALO’S MILK | ||
| Journal of Food and Dairy Sciences | ||
| Article 3, Volume 1, Issue 12, December 2010, Pages 765-779 PDF (588.9 K) | ||
| Document Type: Original Article | ||
| DOI: 10.21608/jfds.2010.82516 | ||
| Authors | ||
| Z. M. R. Hassan; L. F. Hamzawi; M. Y. Abo el Naga | ||
| Food Sci. Dept., Fac. Agric., Ain Shams Univ., Shoubra El- Khaima, Cairo, Egypt. | ||
| Abstract | ||
| Properties of whole, skimmed, raw, pasteurized, and UF concentrated buffalo milk samples during prolonged frozen storage up to 12 weeks at temperature (-22±2°C) were studied. In order to define the microbiological quality of frozen milk, total viable count, yeasts & moulds and psychrophilic bacterial counts were determined. The numbers of total bacterial count in control raw buffalo, pasteurized whole milk; raw skimmed, pasteurized skim milk decreased during frozen storage of 12 weeks at -22 ºC ±2. Freezing-storage reduced also yeast and mold counts. On the other hand, the number of total bacteria in concentrated buffalo milk also decreased during the freezing storage. Yeasts and molds counts were absent in frozen concentrated milk after-storage. However, results of technological properties, i.e. curd firmness (indicated by curd penetration), coagulation time, syneresis and colour of the resultant curd showed that frozen storage had different influence on these properties depending on the presence of fat (raw and skimmed milk), heat treatment, and concentration of milk. During freezing storage, curd penetration values, were increased. Rennet coagulation time (RCT) of milk samples and its UF retentates increased compared with control milk samples. The change in the RCT was more pronounced in buffalo’s milk during the12 weeks frozen period. The syneresis of renneted milk gels is influenced in the present experimental treatments. Curd syneresis decreased by increasing storage period in all treatments, being the lowest after 12 weeks of storage .It could be concluded that suitable frozen conditions for buffalo milk could be successfully obtained at -22 ± 2 ْ°C for 12 weeks. In raw whole milk the lightness (L-values) decreased, while redness (a-values) and yellowness (b-values) increased during storage period of buffalo milk. Hue and chroma values of raw skim milk were reduced during frozen storage. In pasteurized skim milk, the b-values increased towards the negative side, resulting in an increase in both Hue and chroma of frozen pasteurized skim milk. Hue values of concentrated milk were lower than those of raw milk, while colour intensity (chroma) was remarkably higher than those of raw milk. The increase in chroma is best to be applied as an intensity indicator of Millard's reaction, which is the case in heat concentrated milk. | ||
| Keywords | ||
| Frozen milk; Microbiological analysis; Technological analysis; concentrated milk; Pasteurized milk; curd firmness; coagulation time; syneresis; Colour parameters | ||
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