Diverse Exopolysaccharide Producing Bacteria Isolated from Milled Sugarcane: Implications for Cane Spoilage and Sucrose Yield

Abstract

Bacterial deterioration of sugarcane during harvesting and processing is correlated with significant loss of sucrose yield and the accumulation of bacterial polysaccharides. Dextran, a homoglucan produced by Leuconostoc mesenteroides, has been cited as the primary polysaccharide associated with sugarcane deterioration. A culture-based approach was used to isolate extracellular polysaccharide (EPS) producing bacterial strains from milled sugarcane stalks. Ribosomal RNA sequencing analysis grouped 25 isolates into 4 genera. This study identified 2 bacterial genera not previously associated with EPS production or sucrose degradation. All isolates produced polysaccharide when grown in the presence of sucrose. Monosaccharide analysis of purified polymers by Gas Chromatography revealed 17 EPSs consisting solely of glucose (homoglucans), while the remainder contained traces of mannose or fructose. Dextranase treatment of polysaccharides yielded full digestion profiles for only 11 extracts. Incomplete hydrolysis profiles of the remaining polysaccharides suggest the release of longer oligosaccharides which may interfere with sucrose crystal formation.

Fungal Deterioration of the Bagasse Storage from the Harvested Sugarcane

“…Microbial communities thriving the harvested sugarcane play a crucial role in this deterioration. Moreover, other factors, such as storage time, temperature, and environmental conditions, are also important (Solomon, 2009;Solomon et al, 2011;Hector et al, 2015). As per our knowledge, the sucrose-related dynamics of fungi in stored sugarcane remain unexplored.…”

“…Sugarcane is one of the most important crops for sugar and bioethanol production (Goldemberg et al, 2008). The estimated annual gross output of sugar from sugarcane is valued as high as $76 billion (Hector et al, 2015). Sugarcane is a perishable commodity and must be processed into sugar quickly after harvesting.…”

“…Sugarcane is a perishable commodity and must be processed into sugar quickly after harvesting. The postharvest deterioration of sugarcane is a severe problem for the sugar industry, causing 20-30 percent sucrose losses in cane-producing countries (Eggleston, 2002;Solomon, 2009;Saxena, 2010;Hector et al, 2015). Many factors are associated with the deterioration of the harvested cane, including cane cultivar and its maturity, mechanical or manual harvesting, exposure to microbes, cut-to-crush delay, and storage (Solomon, 2009;Solomon et al, 2011;Hector et al, 2015).…”

“…In many countries, the harvested cane is kept in the eld for 3-5 days due to the awed eld transport system and 1-3 days in the factory storage under undesirable conditions (Solomon, 2009;Hector et al, 2015). Sucrose inversions in the deterioration of harvested cane result from the chemical (acid) and enzymic inversion and microbial activity.…”

“…Over 400 species of actinomycetes, bacteria, and fungi are associated with sugarcane and its products (Stevenson and Rands, 1938). After milling, Penicillium, Lactobacillus, Leuconostoc, and yeast invade the stored sugarcane (Hector et al, 2015;Misra et al, 2017;Misra et al, 2019). These acid-producing microorganisms are the principal cause of deterioration, which lowers the sucrose content, juice purity, and pH, especially under anaerobic conditions such as mud-coated canes and the cane stored in large piles with poor ventilation (Solomon, 2009;Misra et al, 2017).…”