Microbial Succession and Identification of Effective Indigenous Pectinolytic Yeasts From Orange Juice Processing Wastewater

Abstract

Although the management of citrus residues is of concern, their valorization is a challenging alternative. In this work, raw orange juice processing wastewater was spontaneously fermented to determine the succession in microbial communities and identify new indigenous microbial strains of high pectinolytic activity. Pectinolytic strains were isolated using citrus pectin as growth substrate. A shift in fungal population observed during spontaneous fermentation, where the abundances of Hanseniaspora, Cystofilobasidium and Meyerozyma were significantly increased, whereas Pichia fermentans followed by Saccharomyces spp. became the predominant taxa in the fermented wastewater. A significant reduction in the relative abundance of homofermentative aerococci and an increase in the relative abundance of heterofermentative leuconostocs and lactobacilli occurred during fermentation, while enterococci were predominant throughout the fermentation process. Regarding ecological indices, opposite changes took place in the bacterial compared to fungal community structure, but in a less pronounced degree. Examination of beta-diversity revealed the key role of Pichia species in driving fungal community structure during fermentation. P. fermentans, the predominant taxon in the fermented wastewater, was found to be the most effective pectinolytic microorganism. Pectin hydrolysis, carbohydrate fermentation to ethanol, lactic acid and acetate, and citric acid fermentation were the most important factors, influencing microbial community structure.