Isolation and structure investigations of square banana (Musa balbisiana) starch

Starch was isolated from unripe square banana (Musa balbisiana) fruit and characterized physically and chemically. Isolation was done with a 2(3) factorial design using five replicates in the central trial. Evaluated factors were: flour: solvent ratio (1:6 - 1:10, w/v); sodium bisulfite concentration (0.1 - 0.3%); and soaking time (30 - 60 min). Optimum starch isolation in an alkaline medium was obtained with: 1:5 (w/v) flour: solvent ratio; 0.1 % sodium bisulfite concentration; and 60 min soaking time. Starch yield under these conditions was 69.8% with 94.5% purity. Starch granules had an oval-elongate shape, a size range of 24-68 mu m, and average size of 24.6 mu m. Amylose content was 22.2% and amylopectin content 77.8%. Granules had a C-type -ray diffraction pattern and a degree of polymerization (DP) of 3-20 for lengths of branch chains.