AbstractThe lactic acid fermentation of cheese whey permeate by Lactobacillus helveticus was studied. Precipitate formation during autoclaving of whey permeate was examined. Precipitation was found to be pH and temperature dependent. Qualitative analysis suggested that the precipitate was a calcium-phosphate complex. Solubilisation was achieved both by acidification and use of the sequestering agent EDTA. Optimisation of L. helveticus growth in whey permeate was carried out using factorial design, as opposed to a traditional univariate approach. Using this technique, the variation of specific growth rate with pH, temperature and stiirer speed was assessed.
Cell growth and lactic acid formation in whey permeate containing various supplements, were investigated. Yeast extract was the most effective nitrogen/growth factor supplement. Maximum lactic acid production was achieved in permeate containing yeast extract (0.75% w/v), Tween 80 (0.1% v/v) and sodium acetate (0.05% w/v). Optimisation of lactic acid production in supplemented whey permeate was performed using factorial design. Optimum conditions for both acid formation and cell growth were pH 5.9, temperature 42°C and stirrer speed 200 rpm.
Fourier transform infrared spectroscopy was applied to the on line and off line quantitative analysis of lactose and lactic acid during the fermentation process. This technique enabled substrate and product levels to be assessed quickly and simply, with no sample pre-treatment. Continuous culture of L. helveticus in MRS medium and supplemented whey permeate was carried out. Substrate conversion and lactic acid productivity decreased with increasing dilution rate. Maximum productivity corresponded to a dilution rate of 0.3 h" 1, whereas minimum residual substrate occured at a dilution rate of 0.1 h' 1 . Translation of the fermentation process from bench scale (11) to pilot scale (161) appeared to be successful. Completion times, productivity and lactose utilisation compared favourably with bench scale results.
|Date of Award
|Bill George (Supervisor)