Impurity and cost considerations for nutrient supplementation of whey permeate fermentations to produce lactic acid for biodegradable plastics

摘要

A potential application for whey permeate is to ferment it to lactic acid for use in the manufacture of biodegradable plastics. High purity lactic acid is required, thus the separation of impurities after fermentation is a major process cost. For batch fermentations, whey permeate requires nutrient supplementation, which can add to impurity levels at the end of fermentation. This work presents the results of whey permeate fermentations using L. casei, supplemented with yeast extract, whey protein hydrolysate, and malt combing nuts (MCN). There is an emphasis on investigating how little supplement needs to be added while still achieving high lactose conversion and lactic acid yield in a reasonable fermentation time. This was around 0.4% w/w for yeast extract, 5% for the hydrolysate (10% whey protein solution) and 5% for MCN. At these levels of supplement addition, the majority of the supplement is actually not utilised and just contributes to a major increase in the concentration of impurities at the end of the fermentation with a corresponding increase in separation cost, in addition to raw material cost.