Production of gellan gum from rice and grape wastes and determination of various quality characteristics of gums

In this study, the potential of using agricultural wastes rice bran and grape pomace as a carbon source in the production of gellan gum was investigated. Within the scope of the research, using the standard strain of Sphingomonas paucimobilis (ATCC 31461), gellan gum was produced from rice bran and grape pomace substrates at optimum production parameters. Besides the chemical compositions of the produced gums, their physicochemical, technological and rheological properties were determined. The possibilities of using gums from waste materials in model foods such as mayonnaise, ice cream and marmalade were investigated. Optimum gellan gum yield with rice bran substrate was observed as 11.96 gL-1 at 5% glucose, 10% inoculum and 300 rpm mixing speed, while optimum yield with grape pulp substrate was 12.08 gL-1 at 5% glucose, 4% inoculum and 300 rpm mixing speed. Conversion rates of agricultural wastes to gellan gum were determined as 23.92% and 24.16% for rice bran and grape pulp, respectively. The consistency index of the gums were determined as 43.53Pa.sn, 2.00 Pa.sn and 53.00 Pa.sn, for gum-grape pulp, gum-rice bran and gum-commercial, respectively. It was determined that gum-grape pomace showed better viscosity properties, but it was the gum-rice bran that can best protect its viscosity against temperature. It was determined that the produced gums consist of glucose, rhamnose and glucuronic acid, which are the main monomers for gellan similar to the commercial gum, while there were differences in composition ratios. The acetic acid contents of gellan gums that affect the rheological properties were between 0-2.95% and their molecular weights were between 228kDa-1009kDa. It was determined that acetyl groups are associated with rheological properties, and as the acetic acid content decreases, the rheological properties of the gums were significantly higher. It was determined that the chemical composition, technological and rheological properties of the gums depend on the substrate source. In general, gellan gums were found to give a significant peak at 4.81 ppm in connection with glucose content, which constitutes a significant proportion of scaffolds in 1H-NMR spectra. The conformational structures of the produced gums were revealed by FTIR analysis and it was determined that all gum samples gave similar typical peaks in the 800 cm-1-3400 cm-1 spectral region. It was determined that the produced gellan gums increased the consistency properties in mayonnaise and marmalade model foods and melting stability in ice cream. As a result, the transformation of rice bran and grape pomace agricultural wastes into gellan gum with low cost, high yield and functional features has an industrially strong potential.