Production and characterization of resistant starch from high amylose rice and barnyard millet and their application in the development of low glycemic index idl

Abstract

Increasing rapidity of chronic diseases and their associated metabolic disorders is due to two factors namely: the increasing prevalence of overconsumption and inactivity associated with the lifestyle of economically developed countries. Diabetes mellitus is one such Non-Communicable Chronic Disease (NCCD). Diabetes mellitus is a group of metabolic disorders identified by high blood glucose levels. The amount and type of carbohydrate intake has a significant connection to the high Glycemic Index (GI) of foods and high Glycemic Load (GL) of diets and risk of chronic disease. There is an increased demand and expectation for diets characterized by low GI foods, and potential to lower the risk of Type II diabetes. A major disadvantage in this connection is shortage of low GI foods, where most of the staple foods are starchy in nature and are digested almost immediately causing blood sugar to spike rapidly in the individual consumers. The South Indian diet primarily comprises of rice and its products, which generally consist of almost 70% starch, with relatively high GI. The digestibility of the rice ranges between 64±9 to 93±11 % and thus almost all varieties of rice (white, brown or parboiled) except for high amylose variety can be classified as high GI foods and cannot be potentially used in low GI diet. Barnyard millet (Echinochloa frumentacaea) is one of the hardiest millets, known for its high digestibility and rich source of dietary fiber. The carbohydrate content is low and slowly digestible, which makes barnyard millet suitable for formulating low GI foods. In this context, modification of starches to change its properties such that it can withstand extreme heat, acidity, shear, time, temperature; have enhanced viscostability; desirable or optimal gelatinization time etc.by physical, enzymatic, and/or chemical could be an alternative means for lowering the GI of food. Therefore, formulation of low GI food products that meet consumers demand for a healthy life style with suitable processing technologies is imperative. The focus of the present work has been to study the effect of different dry heat processing in the development of resistant starch (RS) in rice and barnyard millet. Using these materials with modified starch, a traditional fermented food idli was reformulated to develop a functional food product with low GI.The work includes identification of appropriate dry heat method for rice and millet processing which gives high RS and optimization of the combinations of treated ADT-46 rice and barnyard millet for low GI by assessing their in vitro carbohydrate digestibility (RDS and SDS). In-vitro digestibility RDS, SDS, GI and RS content of the idli samples were determined. For the preliminary study, ADT-46 raw or parboiled rice was heattreated by four different dry heat treatment methods (Pan roasting, Fluidized bed drying, tray drying, Convective Microwave heating) with the timetemperature combination of 110°C and 120°C for 10 min. In all the four methods of dry heat treatment used, the parboiled rice resulted in higher RS content. The most effective treatment was by convective microwave oven at 120°C, 20 min. For the subsequent study, ADT-46 parboiled rice (30 g) and barnyard millet (30 g) were heat treated by the four different dry heat techniques at different temperatures between 110°C and 250 ± 2°C and for time periods ranging between 10 and 30 min with 10-unit increments in both temperature and time. The time-temperature was optimized by determining the RS yield. Convective microwave heat-treated samples gave the maximum RS in both rice (26.25 ± 0.14 g per100 g at 180°C, 10 min) and barnyard millet (15.08 ± 0.20 g per100 g at 170°C, 20 min).Idli batter and idli were prepared based on the results obtained from survey on consumer preference and practices. The control idli batter was prepared out of idli rice and legume (black gram / urad dhal) in ratio of 3:1. Idli with heat-treated rice and barnyard millet was prepared in the following combinations newline