Effect of fatty acids on the rheological properties of corn and potato starch

Effects of fatty acids (myristic and stearic acid) on the rheological properties of corn and potato starch during heating and cooling were investigated using a Carri-Med CSL2 dynamic rheometer. Potato starch showed a lower gelatinization temperature (TG') as compared to corn starch. Potato starch had a TG' of 61.2degreesC against 71.5degreesC for corn starch. The addition of both the fatty acids inhibited the swelling of the starch granules in both corn and potato starch and consequently, increased the TG'. The storage modulus (G') increased to a maximum and then dropped during heating of both the starches. Potato starch showed a higher peak G' value as compared to corn starch. Addition of stearic acid decreased the peak G' in corn starch and increased the same in potato starch, while the addition of myristic acid resulted in a decrease in peak G' in both the starches. The extent of breakdown in G' during heating was higher for potato starch as compared to corn starch which confirmed the more rigid structure of corn starch granules. During cooling, the G' values increased with decrease in temperature and with the addition of fatty acids. Corn starch showed higher peak loss tangent (tan delta) values than potato starch during heating. Tan delta values decreased during the cooling of corn and potato starch. Retrogradation (synersis) behaviour of both the starches heated in the presence of stearic and myristic acid during storage was also studied. The rate of synersis was more in potato starch than in corn starch. Synersis increased with the increase in storage duration and decreased with the addition of both the fatty acids. (C) 2002 Elsevier Science Ltd. All rights reserved.