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

Authors: YEGIN, SIRMA - Ege University; Saha, Badal; Kennedy, Gregory - Greg; LEATHERS, TIMOTHY - Former ARS Employee

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2018
Publication Date: 1/2/2019
Citation: Yegin, S., Saha, B.C., Kennedy, G.J., Leathers, T. 2019. 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. Bioresource Technology. 278: 130-137. https://doi.org/10.1016/j.biortech.2018.12.119.
DOI: https://doi.org/10.1016/j.biortech.2018.12.119

Interpretive Summary: Polymalic acid is a natural biopolyester having a wide range of applications in the food, agriculture, chemical and pharmaceutical industries. It can be produced from glucose by fermentation with a fungus. However, lignocellulosic biomass has the potential to serve as a low-cost source of sugars for its production. Barley straw hydrolysate was previously shown to be inhibitory to the production of polymalic acid, negating its use as a source of inexpensive sugars. In this research, it was demonstrated for the first time that by using waste egg shell powder as a component of the cell growth medium, polymalic acid could be produced from barley straw hydrolysate without adding an extra process step to remove inhibitors. The results will be very useful in developing a bioprocess technology for its production from biomass by the fungus.

Technical Abstract: 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 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 biomaterials.