การเพิ่มปริมาณสตาร์ชต้านทานการย่อยในแป้งมันเทศสีม่วง

Abstract

The study aims to enhance the amount of resistant starch content in Purple Sweet Potato (PSP) starch. The effects of immersing in organic acid solution (citric acid and stearic acid), at 1 and 2% concentrations (w/v) for overnight in the pre-treatment process and numbers of heating and cooling processes (0-9 cycles) were studied in acid- immersed sample. The acid-treated experiment was designed in a 2 x 2 factorial experiment in CRD with 3 replications. Resistant starch (RS) estimated Glycemic Index (eGI), amylose content, pasting profiles, and scanning electron microscope (SEM) were used to observe the results of the experiment. Thermal properties, crystal structure , crystal morphology and retrogradation kinetics were also studied in heated and cooled sample. The result showed that the highest amount of resistant starch content (11.52 ± 8.9%) was achieved in sample treated with 2% citric acid which was higher than the control (2.59 ± 0.85%) around 344.78 %. But the estimated glycemic index was not significantly different. The amylose content, which is related to the enzymatic digestion ability of the starch, were not significantly different among treatments. Although PSP treated with 2% citric acid gave the highest level of RS but other properties such as estimated Glycemic index, amylose content and pasting profile were significantly lower than 1% stearic acid sample. Therefore, 1% stearic acid was used instead of 2% citric acid in the heating and cooling process study. After getting the condition of appropriate organic acid for immersion, heating and cooling cycles were used to enhance the RS content in PSP. The result showed that 1 cycle of the heating and cooling process gave the highest RS content (18.57 ± 9.47%) which was higher than the control sample of heating and cooling process (9.73 ± 2.62%) around 90.85 %. And SEM showed that the acid-immersed starch granules and the heated-cooled granule were denser packed than control. In thermal properties study, it was found that the gelatinization temperature of heated and cooled sample increased with the number of heating- cooling cycle, but the over heating -cooling process could lose the thermal properties by decreasing gelatinization temperature. The retrogradation kinetic study by Avrami equation found that the Avrami exponent of the samples were less than 1 indicated that the samples had a few changes in the particle structure. The retrogradation rate and Avrami exponent were not significantly different. That could indicate that several heating- cooling cycle did not affect the reaction rate and shape of particle. From this study, it could be suggested that the use of organic acid solution in a suitable concentration for the pre-treatment process and one cycle of the heating and cooling process could enhance the resistant starch content in PSP starch.