Valorization of egg shell as a detoxifying and buffering agent for efficient polymalic acid production by Aureobasidium pullulans NRRL Y-2311-1 from barley straw hydrolysate

Stepwise formulation of a versatile and cost-effective medium based on barley straw hydrolysate and egg shell for efficient polymalic acid production by A. pullulans NRRL Y-2311-1 was carried out for the first time. The strain did not grow and produce polymalic acid when dilute acid pretreated barley straw hydrolysate (total fermentable sugars: 94.60 g/L; furfural: 1.01 g/L; hydroxymethylfurfural: 0.55 g/L; acetic acid: 5.06 g/L) was directly used in medium formulation without detoxification (e.g. charcoal pretreatment). When CaCO3 in the medium formulation was substituted with egg shell powder, efficient production of polymalic acid was achieved without a detoxification step. Utilization of 40 g/L of egg shell powder led to 43.54 g polymalic acid production per L with the productivity of 0.30 g/L/h and yield of 0.48 g/g. The bioprocess strategy used in this study can also be utilized for mass production of several other industrially important microbial organic acids and bio-materials.