Influence of formaldehyde and hydrogen peroxide as preservatives on the properties of buffalo's milk proteins

This work was planned to study the effect of formaldehyde (FA) and hydrogen peroxide (H2O2) on the coagulation, chemical and biological properties of milk proteins. Thus, raw buffalo's skim milk samples (100 ml each) were spiked using FA (40%) or H2O2 at the level of nil (control), 0.025, 0.050, 0.100, 0.200, 0.300, 0.400 and 0.500%. The obtained results indicated that the rennetability, curd firmness and curd synersis of milk were significantly weakened by FA more than occurred by H2O2. There was a negative relationship between the synersis rate and the preservative level. While, sephadex G100 chromatograms of liquid milk, acid and rennet curds indicated that opposite to the effect of H2O2 the presence of FA led to an increase in the absorbency measured for the casein peak positively associated according to its level. That was at the expense of other two peak of whey proteins. However, the milk protein fractionation by sodium dodecyl sul fate polyacrylamide gel electrophoresis (SDS-PAGE) of the two curds confirmed that, although the level of alpha s2-casein (Cn) was not affected, the levels of alpha s1-Cn and beta-Cn raised in the presence of FA and decreased due to H2O2 opposite to that behaved by gamma-Cns. The SDS-PAGE electrogram of whey proteins residues remained in the curd exhibited no response whether to the kind or the level of preservative spiked. Compositionally, the presence of 0.3% preservatives regardless their kinds, decreased significantly the levels of the total amino acids (T.A.A.) whether essential or non essential A.A. Nutritionally, this decline in A.A. levels contributed to preservative adding resulted in significant reduction in the calculated percentages of protein efficiency ratio (PER), biological value (B.V.) and net protein utilization (NPU). All nutritional aspects were higher in the protein of liquid milk followed by rennet curd while, the acid curd came in last order.