Structure characterization and hypoglycemic effects of dual modified resistant starch from indica rice starch

Highlights

• We prepared resistant starch from indica rice starch using a new method that combined physical modification and enzyme modification.

• Indica rice resistant starch has strongly resistant enzymatic properties.

• In vivo experiment indicated our product has hypoglycemic and hypolipidemic effects.

Abstract

Hypoglycemic effects of indica rice resistant starch (IR-RS) were investigated. We prepared IR-RS using a method that combined physical modification and enzyme modification, and the RS content was 47.0%. Differential scanning calorimetry – thermal gravimetric analysis showed that IR-RS have higher enthalpy and less loss of mass than single modified RS, heat-moisture RS and native starch. Scanning electron microscopy revealed that IR-RS displayed more compact spatial structure. IR-RS products displayed a mixture of B-and V-type x-ray diffraction patterns and the cyrstallinity was 51.0%. IR-RS significantly affected body weight, blood glucose, organ indices and serum lipid levels. These results demonstrated that dual modification changed the structure of indica rice starch and affected its digestibility as well as the blood glucose levels of the diabetic mice who consumed it.

Introduction

Type 2 diabetes mellitus (T2DM) is a common endocrine and metabolic disease that is caused by an absolute or relative lack of insulin in the blood, resulting in hyperglycemia and diabetes, which often goes on to cause fat and protein metabolic disorders (Shaw, Sicree, & Zimmet, 2010). The complications of T2DM have been associated with obesity, oxidative damage, dysfunction and eventual organ failure (Huang et al., 2005, Sharma et al., 2008). As the social and economic environment in China has improved, the incidence of diabetes (especially T2DM) has rapidly increased. Although many drugs can treat and control T2DM, including biguanides, sulfonylureas and α-glucosidase inhibitors, the long-term use of anti-diabetic drugs can result in symptoms of hypoglycemia, liver and kidney dysfunction and other adverse reactions (Posuwan et al., 2013). Therefore, the best approach is not to focus on the treatment of diabetes but rather to focus on how to prevent diabetes from occurring.

Resistant starch (RS) functions as a new food ingredient that has a low glycemic index. RS is termed an anti-digested starch, which refers to the fraction of the starch that cannot be digested in the small intestine and is partially fermented in the large intestine to produce short-chain fatty acids and other products (Haralampu, 2000). RS is characterized by a smaller molecular structure with a length of 20–25 glucose residues (linear polysaccharides that are connected by hydrogen bonding). RS has physiologic effects that are similar to those of dietary fiber (Bjorck & Asp, 1994). RS can affect body weight and energy balance (Losel and Claus, 2005) and increase lipid excretion to reduce calorie intake and decrease the serum lipid levels. RS itself contains almost zero calories (Alphons, 1998) and, when used as a low-calorie food additive, can control weight effectively. The ingestion of RS can decrease insulin secretion and control postprandial blood glucose to prevent diabetes (Weickert & Mohlig, 2005). RS can also lower the intestinal pH and promote the absorption of zinc, calcium and magnesium ions (Yonekura & Suzuki, 2005). The food and agriculture organization (FAO) listed RS as a dietary fiber that can be used for the prevention of T2DM (Devries, 2004) in 1990. Therefore, studies examining the preparation and function of RS are becoming increasingly important.

At present, RS can be prepared by physical, chemical and enzymatic modification. Hydrothermal treatments and annealing are physical modifications of starches that involve treating the starches at a moisture content of 30% and temperatures of 100 °C for 30 min, then keeping them at 70 °C for 12 h (Leea, Shinb, Kim, Choi, & Moon, 2011). Acid-alcohol treatment involves the chemical modification of starch with acids that are suspended in alcohol, which has the advantage of high granular recovery and control of molecular degradation coupled with minor changes in granular structure (Robyt, Choe, Hahn, & Fuchs, 1996). Although the chemical method is available for use for industrial purposes, it may be accompanied by safety problems. Previous study (Zhang & Jin, 2011) has reported that the hydrolysis of maize starch with pullulanase can increase the RS content to 44.7%.

Although the three most commonly used raw materials in the starch industry are corn, wheat and potatoes, there has been an increased market demand for rice starch and its derivatives. Most studies on RS have focused on RS derived from potato, wheat, maize and sorghum sources. However, few studies have focused on RS prepared from rice starch. China is the largest rice producer and consumer in the world. Due to its low price and high RS content, indica rice could be the best candidate for high RS production. We prepared RS from indica starch using a new method that combines α-amylase, pullulanase and heat-moisture treatment. In this study, we optimized the reaction parameters in order to increase RS yield, and used in vitro digestion tests, structure detection and animal experiments to study the anti-digestibility, structure and hypoglycemic effects of IR-RS.