Issues of starch in sugarcane processing and prospects of breeding for low starch content in sugarcane

Starch is a sugarcane impurity that adversely affects the quantity and quality of sugar processes and products. The increased production of combine and green harvested sugarcane has increased delivery of starch to sugarcane factories. Starch occurs as granules composed of amylose and amylopectin polysaccharides. Starch can reduce crystallization and centrifugation rates, occlude into the sucrose crystal, increase molasses production, reduce filterability and affination of raw sugars, and impede refinery decolorization processes. The behavior of starch granules on hydration and heating directly influences processing. The enzyme alpha-amylase used to hydrolyze starch in the factory is expensive and not always efficient. Low starch cultivars would be a more preventative, economical, and efficient solution. This paper reviews issues of starch in sugarcane processing, reports on the variations in starch among wild species germplasm, and prospects of breeding for low starch. Significant differences exist in starch levels among Saccharum and allied species and clones within these species. Saccharum species can be grouped into high (S. bengalense, Erianthus and S. spontaneum), medium (S. barberi, S. sinense and S. robustum) and low (S. officinarum and Miscanthus) starch. Cultivated species produce less starch than their wild relatives; thus low starch in sugarcane may be advantageous for sucrose production. Normal distribution in starch for S. spontaneum, a high starch species, suggests that low starch clones can be selected for introgression. When cultivars were crossed to S. spontaneum and the F1s backcrossed to cultivars, the starch content ranked as cultivars <BC1 <F1 clones. Environmental conditions such as freezing temperature tend to decrease starch content in sugarcane. From a breeding standpoint, cultivars developed or selected for low levels of starch are likely to produce relatively low and stable starch content over a wide range of conditions. To avoid increasing selection traits for breeding programs, future research to lower starch in cultivars should focus on selecting parents with low starch in introgression and crossing programs.