Browsing by Author "Ryoba, Ruth Nnala Z."

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Studies on preparation and use of bovine pepsin from adult cattle Abomasa as rennet substitute for small scale cheese processing
(Sokoine University of Agriculture, 1999) Ryoba, Ruth Nnala Z.
World-wide shortage of rennet has stimulated interest in the search for rennet substitutes. In order to overcome the scarcity and high price for rennet in Tanzania, studies on preparation of a rennet substitute from cattle abomasa were undertaken in three experiments Experiment one dealt with investigations into the optimisation of pepsin extraction conditions i.e. on regions of abomasa, extraction of dry versus fresh material, drying methods, ionic strength, extraction pH, temperature, time, activation pH and clarification methods. Results showed that the fundic region, sundrying, 10% salt, extraction with HCL at pH 3 fbr 3 days, at 37° C, activation pH 2 fbr 30 min and clarification using NazHPC^.H?。produce an extract with maximum milk clotting activity (MCA). Optimum conditions were applied to extract pepsin with dilute HCL, vinegar and lemon juice. Vinegar (VP) and HCL (HP) gave better yield, shelf-life, proteolytic activity, chymosin:pepsin ratio, microbial quality and formagraph characteristics than lemon juice. Concentrating VP extract lead to greater loss in MCA than for HP extract. In experiment two, HP extract was purified by DEAE cellulose chromatography, gel filtration, mono Q and phenyl sepharose chromatography. Studies on the purified enzyme with regard to formagraph characteristics, molecular mass, sodium dodecylsulphate gel electrophoresis (SDS-PAGE) and N-terminal amino acid sequence showed that pepsin was homogenous with fold purification of 366, recovery rate of 32.7%,Ill Specific activity 3920 MCA (units/mg), molecular mass 34,500 Da. The N-terminus of purified pepsin contained no lysine and the MCA decreased with enzyme purity. In experiment 3, HP and VP extracts were mixed with rennet at 0, 25, 50, 75, 100% and used for making three types of cheese. Renneting time (RT) for cheese milk, butterfat (%BF) and total nitrogen (%TN) in whey, chemical composition and microbial quality of cheese samples obtained at different storage time intervals, sensory evaluation at maturity and overall quality assessment were determined. RT and TN losses increased with level of pepsin; chemical composition of all cheese types were significantly different (Pv.001). The pH in SUA Pastafilata and SUA Alpine and TN in Tilsiter cheese were not significantly different (P>0.05). Sensory evaluation was not significantly different (P>0.05) in smell, taste, appearance and bitterness, however, bitterness in SUA Pastafilata and appearance in SUA Alpine were significantly different (P<0.05); appearance in SUA Pastafilata and village Alpine were significant different (P<0.01). Bitterness, taste in SUA Alpine and bitterness in Tilsiter cheeses were highly significant different (P<.001). Overall quality assessment of cheese did not show significant differences (P>0.05). Therefore all enzyme combinations were suitable for all types of cheese implying that pepsin was an appropriate rennet substitute.