Effect of waste grape pomace on citric acid bioproduction by submerged fermentation

Abstract

Citric acid is of great economic importance due to its wide range of applications. Citric acid, which is a versatile and widely used organic acid, constitutes 60% of organic acids used in the food industry and 10% of those in the pharmaceutical industry. Citric acid is produced using various agricultural wastes as a substrate through solid state or submerged fermentation. In this study waste grape pomace was proposed as a valuable substrate alternative for citric acid production using submerged fermentation. Initially screening of citric acid production capacity was conducted using 6 different Aspergillus niger strains (3 wildtype strains isolated from dried figs and 3 commercial ATCC strains) on synthetic medium. The wild type AN2 was determined as the highest producing strain with 14.32 mg/mL citric acid following 192 h fermentation. Then the waste grape pomace concentration effect on citric acid production was studied by five different concentrations in the range of 100-300 g of pomace in 1 L medium for 192 h fermentation. Using the wild type AN2 strain the highest production of citric acid and yield was achieved with 250 g/L grape pomace concentration as 28.26 mg/mL and 87%, respectively. Moreover, biomass production of the strains in grape pomace medium showed similar pattern with the citric acid production except biomass formation was increased with the grape pomace concentration increases. This study presented that comparing with synthetic medium waste grape pomace can be valuable substrate alternative for citric acid production using submerged fermentation. The study also contributed to the literature as waste grape pomace could be valuable substrate for future research studies.