Abstract
Purpose: To evaluate the effect of dry-heating with pectin at different dry heating temperatures, heating times and pH on the gelatinization properties of sweet potato starch.Methods: The gelatinization properties of sweet potato starch - pectin blend were analyzed using a rapid viscosity analyzer (RVA), differential scanning calorimeter (DSC), and gel texture analyzer (TPA).Results: The viscosity of the blends of sweet potato starches and pectin increased initially, and then decreased. Viscosity was highest at 120 °C, with a value of 744 cp. High viscosity values were also obtained after dry-heating for 2 and 7 h (540 cp and 639 cp, respectively). The enthalpy of the blend declined with increasing heat-treatment temperature from 3.973 J/g at 0 °C to 3.021 J/g at 150 °C. The initial (T0), peak (Tp), and terminal (Tc) gelatinization temperatures of the blends were all lower than corresponding values at 0 °C. Gelatinization enthalpy values gradually increased with increase in dryheating time and pH although they were still lower than for the control samples. In addition, as T0, Tp, and Tc values of the blend increased, the gelatinization temperature range became narrower. The hardness and viscosity of the blends increased initially, and then decreased after the dry-heat treatment. The hardness of treated samples was higher than that of control, and peaked at 130 °C, 4 h, and pH 11. The resilience of the blends attained a peak value after 2 h of dry-heat treatment at 120 °C and pH 9.Conclusion: The results show that dry-heating with pectin is an effective way of improving the gelatinization and gel properties of sweet potato starch. This finding is considered significant for the developing of new modified starch from sweet potatoes.Keywords: Sweet potato starch, Pectin, Dry heat, Gelatinization, Viscosity, Hardness, Enthalpy
Highlights
China is the world's largest producer of sweet potatoes, with a total acreage of 42.72 % of total world acreage, and a total annual output of 79.09 million tons, accounting for 80 % of the world's total sweet potato production (FAO) [1]
The present study investigated the effects of factors such as temperature, treatment time, and pH on the viscosity, thermodynamics, and gel properties of the blends of sweet potato starch and pectin subjected to dry-heat treatment
The peak, trough, and final viscosities of the blends formed at 150 °C were only half of those observed at 0 °C. This suggests that the waterinduced swelling of the starch granules and pectin molecules was inhibited at this temperature, thereby making them difficult to break up
Summary
China is the world's largest producer of sweet potatoes, with a total acreage of 42.72 % of total world acreage, and a total annual output of 79.09 million tons, accounting for 80 % of the world's total sweet potato production (FAO) [1]. Sweet potato starch contents can exceed 30%, and its unique properties are widely used in food, pharmaceutical and chemical industries. Pectin is a natural plant colloid widely used in the food industry and can be used as a gelling agent, stabilizer, tissue-forming agent, emulsifier, and thickener. Starch and edible gum are often used together in the health and pharmaceutical industries to improve product quality or to increase product stability [5,6]. Previous studies have shown that blending starches with edible gum and subjecting them to dry-heat conditions can effectively improve the physical properties of the starches and food quality and stability [10,11]
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