Effect of cross linking on the physicochemical properties of cola starch

Cola starch from Cola nitida (rubra) was isolated using 1% (w/v) sodium metabisulphite solution and was chemically modified with sodium tripolyphosphate (STPP) and acetic anhydride (ACOH) as cross-linking agents. The physicochemical and functional properties of the cross linked (modified starch) were compared with the native (unmodified) cola starch. The results presented important changes in the pasting, thermal transition and morphology of the native starch. The morphology of cross linked cola starch appears different from that of the native starch. The shape of the granules appears distorted and the general smoothness of the wall was replaced with some edges. Presence of slight aggregation of the starch granules was also observed. The physicochemical properties of the cross linked starch were obtained as follows: swelling 7.35 to 7.86% for ACOH, 6.00 t 6.20% for STPP, solubility 6.38 to 6.52% for ACOH and 6.23 to 6.48% for STPP, amylose (%): 23.88 for STPP and 24.58 for ACOH while the corresponding values for the native starch were, swelling: 8.85%. solubility: 7.48% and amylose: 24.76%. The results showed a decrease in percent swelling and solubility of cross linked starch compared to the native starch. Comparable values were obtained for both cross linking agents. The Rapid Visco Analyser (RVA) showed that both cross linking agents affected the peak, breakdown, set back and final viscosities of the native cola starch. The peak, breakdown, and set back viscosities of the cross-linked cola starch were lower than that of the native starch, while the final viscosity of the cola starch is lower than that of the cross linked starch. The extent of change is a function of temperature and heating times. The observed trends are consistent with other modified starches that have found useful applications in food and confectionery industries. Key words: Cross-linked (modified) starch, native starch, isolation, starch modification, physicochemical characteristics.