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Hammam Sousse, Tunisia

Hachana Y.,Superior Institute of Agriculture | Kraiem K.,Superior Institute of Agriculture | Paape M.J.,U.S. Department of Agriculture
Milchwissenschaft | Year: 2010

The effect of somatic cell count (SCC) and total bacterial count (TBC) in raw milk on casein fractions in UHT processed milk by indirect heating was investigated. Before UHT treatment, bulk tank raw milk was categorized into groups according to SCC and TBC To study the effect of SCC, four groups of raw milk were selected: Group A (<100,000 cells mL-1), Group B (100,000-400,000 cells mL-1), Group C (400,000-800,000 cells mL -1) and Group D (800,000-1,200,000 cells mL-1). All groups had a low TBC (<100,000 cfu mL-1). To study the effect of TBC, two groups of raw milk were selected: Low TBC (<100,000 cfu mL-1) and high TBC (1 -2 million cfu mL-1). The SCC of both groups was less than 100,000 cells mL-1. UHT-processed milk prepared from each group was analyzed for casein fractions through Reversed-Phase HPLC Somatic cell count and TBC in raw milk increased the proteolysis of UHT processed milk. High SCC caused a decrease (P<0.05) in the concentrations of the αs- and β-casein, while high TBC caused a decrease (P<0.05) in K-, β- and αs-casein. An increase (P<0.05) in the γ-casein concentration was observed for milk with either a high SCC or a high TBC.

Hachana Y.,Superior Institute of Agriculture | Paape M.J.,U.S. Department of Agriculture
International Journal of Food Sciences and Nutrition | Year: 2012

For yoghurts were made from milk with different levels of somatic cell count (SCC) (low 95,000 cells ml -1, intermediate 398,000 cells ml -1 and high 1,150,000 cells ml -1). Yoghurt samples were analysed for the degree of proteolysis, lipolysis (free fatty acid (FFA) content), acidity, pH and apparent viscosity on days 1, 14 and 28. The SCC had no significant effect (p>0.05) on either the acidity or the pH of the yoghurt after 1 day of cold storage. However, significant effects (p < 0.05) of SCC were observed after 14 and 28 days of storage. Yoghurt samples made from intermediate and high SCC milk showed higher viscosity (p < 0.05) and lower (p < 0.05) casein content on days 14 and 28 of cold storage than yoghurt made from low SCC milk. High FFA concentrations (p < 0.05) were observed only in yoghurt made from high SCC milk. High SCC in milk increased both proteolysis and lipolysis in yoghurt during storage. © 2011 Informa UK, Ltd.

Hachana Y.,Superior Institute of Agriculture | Kraiem K.,Superior Institute of Agriculture | Paape M.J.,U.S. Department of Agriculture
Food Science and Technology Research | Year: 2010

The present study examined the enzymes responsible for proteolysis of casein in milk. Reversed-phase HPLC was used to differentiate the peptide products, of each proteinase, soluble in 12% trichloroacetic acid and in pH 4.6 milk filtrates. Peptides produced by bacterial proteinase were less hydrophobic and eluted early in the RP-HPLC chromatogram, while peptides produced by plasmin and somatic cell proteinase were more hydrophobic and eluted later. β-caseins were preferential substrates for plasmin, whereas α s-and κ-caseins were hydrolysed to a lesser extent. Proteases from bacterial origin predominantly affected κ-casein, while ß-casein and α s-casein were less susceptible. Somatic cell proteinase degraded mainly β-casein, followed by α s-casein and κ-casein. When milk was contaminated by bacterial proteinases, chromatograms of the TCA 12% filtrate showed early peaks, while the pH 4.6 filtrate showed early and late peaks when proteolysis was caused by either plasmin, somatic cell proteinase or bacterial proteinase.

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