Effect of some physico‐chemical treatments on the kinetics of autolysed‐yeast extract production from whey

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Abstract
In this work, the effects of salt and mechanical cell breaking on the overall activity of the endogenous enzymes of Kluyveromyces fragilis grown on whey‐based media were studied at the optimal values of temperature (54°C) and initial concentration of yeast and whey protein (100 g dm−3) previously selected. An unstructured kinetic model of first order was found to be capable of simulating quite satisfactorily the time course of residual suspended solids (Y) in the slurry, as well as Kjeldahl (KP) and Lowry (LP) protein and total carbohydrates (G) accumulation in the clear extract. The autolysis kinetic rate constant (ka), and yield factors for Kjeldahl and Lowry protein and reducing sugars on total solids hydrolysed were found to be insensitive to the salt level and preliminary mechanical disruption of cells. Nevertheless, maximum production of yeast‐whey protein extracts was achieved when the endogenous enzymes of ground cells are induced by 5% w/v salt addition. Except for their respective salt contents, both autolysates exhibited no apparent difference in chemical composition.