Grape pomace as a promising source for gellan gum production

Abstract

The aim of the present study was to determine the potential use of grape pomace, local agricultural waste, as a sole carbon source in the production of gellan gum. For this purpose, optimization of fermentation conditions of Sphingomonas paucimobilis (ATCC 31461) to produce gellan gum with the maximum yield was studied. This study clearly confirmed that gellan yield depended on carbon source concentration, bacterial inoculum volume and mixing rate. Maximum yield was found as 12.08 g/L at 5% carbon ratio, 4% inoculum volume and mixing rate at 300 rpm. The conversion ratio of waste product into gellan gum was identified as 0.24 gellan gum/grape pomace (g/g). Commercial gellan gum samples had glucose:rhamnose:glucuronic acid ratio as around 2.6:1.15:1, while biosynthesized gellan gum had 2.6:0.5:1 which indicated the effect of carbon source on chemical composition of gelllan gum. The molecular weights of biosynthesized and commercial gellan were determined as 6.88 × 105, 1 × 106, respectively. FTIR and 1H NMR spectral analysis were applied for the purpose of clarifying structures of polymers. Regarding the rheological properties, Herschel–Bulkley model better described the flow behavior of the gum solutions. The commercial gellan gum showed higher viscosity than the biosynthesized gellan. Rheological properties of polymer were affected by changes in the acyl substitution. The biosynthesized gellan from grape pomace showed better stability against temperature changes than commercial gellan gum.