Biosynthesis of succinoglycan by Agrobacterium radiobacter NBRC 12665 immobilized on loofa sponge and cultivated in sugar cane molasses. Structural and rheological characterization of biopolymer

Abstract

Succinoglycans are heteropolysaccharides synthesized by bacteria. It possesses thickening and texturizing properties, making it useful in a number of applications in food, pharmaceutical and chemical industries. Agrobacterium radiobacter NBRC 12665 cells were immobilized in the loofa sponge matrix and used to produce succinoglycan. Production of the biopolymer using the substrates sugar cane molasses, sucrose, glucose and lactose at concentrations of 2.5%, 5.0% and 7.5% for eight days was analyzed. The best results were obtained using sugar cane molasses (14.0g/L) and lactose (12g/L) at 7.5% with immobilized cells. Under optimum conditions, it was possible to re-use the matrix to produce succinoglycan in five consecutive eight day operating cycles. Scanning electron microscopy and Fourier Transform Infrared Spectroscopy (FTIR) confirmed the immobilization of the microorganism in the loofa sponge. FTIR of the biopolymer revealed the presence of residues of carbohydrate and carboxylic groups. The use of mixed ions exchange resin for removal of the succinoglycan pigments from molasses resulted in a depigmentation of 74% in the color of the biopolymer and 65% in its turbidity. Succinoglycans obtained from lactose and sugar cane molasses exhibited molecular weights of 2.734ÿ106g/mol and 2.326ÿ106g/mol, respectively. Rheological analysis of the succinoglycans in terms of concentration (0.5⿿2.0%), temperature (5⿿75°C) and pH (2.5⿿10.0) revealed non-Newtonian and shear thinning behavior of the biopolymer. The technique of immobilization in loofa sponge and use of sugar cane molasses as a low cost carbon source produced significant and effective results for the industrial production of succinoglycan.