| Abstract | Recently, resistant starch has gained interest with regard to functional properties and in general potent health benefits. Phathumthani 80 (RD 31) and Berry rice are of great interest for the development of high resistant starch due to the high amylose content and high antioxidant capacity, respectively. Resistant starch represents that fraction of the starch which resists digestion by the hydrolytic enzymes in the upper gastrointestinal tract. Upon reaching the colon, resistant starch is fermented by probiotics producing short-chain fatty acids. Resistant starch, therefore, has positive influence on the digestive tract function, colon microflora, the blood cholesterol level, the glycemic index, obesity, type 2 diabetes as well as celiac disease. Resistant starch has been categorized as dietary fibers due to similar physiological benefits as other dietary fibers. Among different types of resistant starches, ranging from type 1 to type 5, retrograded resistant starch (type 3) has great commercial interests. The nature of the native starch along with process involved in production of resistant starch greatly influence the degree of resistant starch formation.
The lintnerization or acid hydrolysis technique to produce RS 3 involves hydrolysis of α-1,4 and α-1,6 glycosidic linkages from amylose and amylopectin. The gelatinization and retrogradation technique to produce RS 3 involves leaching of amylose during heating process and reassociation of the amylose as double helices during the cooling step. The freeze-thaw technique involves formation of ice crystals in starch gel during freezing step and starch retrogradation during the thawing process. In this research, effects of different treatments including lintnerization at different concentration of acid (1, 1.5 and 2N of HCl); autoclaving (135 °C for 30 min); lintnerization followed by autoclaving; and freeze thawing treatments (-20 °C for 24 h and 30 °C for 90 min) on the formation of resistant starch, glycemic index, and functional properties of the Pathumthani 80 (RD 31) rice and Berry rice were evaluated. The treated rice starch with the highest resistant starch content was selected for the development of the high resistant starch and low glycemic gluten free noodle. Further, the effect of addition of xanthan gum, inulin and rice bran in the physiochemical properties of the gluten free noodle formulation was evaluated and the shelf life of the fresh noodle was evaluated over a period of 5 days.
The Pathumthani 80 (RD 31) rice starch on lintnerization treatment showed significant (p 0.05) increase in the resistant starch content (13.73 – 64.0%) compared to rice flour (3.84%), and native rice starch (8.44%). Meanwhile, the autoclaved rice starch showed the highest resistant starch content (64.95%) and the lowest glycemic index (46.12%). However, the antioxidant properties and pasting properties were observed to decrease with the increase in the treatment of the native starch. The lintnerization followed by autoclaving treatment significantly increased the solubility and water holding capacity, reduced the swelling power, and disrupted the crystalline structure of the starch granules. The Fourier transform infrared analysis of RD 31 native and treated starches showed the modified structures and bonding of the starch granules with different treatment. Further, with acid hydrolysis and heat treatment, the color attributes of the starch were appeared to be darker in color.
Berry rice is a pigmented rice that has been reported to possess health promoting properties. The modification treatment significantly (p 0.05) decreased the amylose content. The lintnerization treatment, autoclaving treatment and lintnerization followed by autoclaving treatment increased resistant starch content, while the resistant starch increased gradually with the freeze thaw treatment. The glycemic index had a negative correlation with resistant starch and was observed to decrease significantly (p 0.05) with the treatment. Further, the
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effect of lintnerization and autoclaving treatment on functional properties (solubility capacity, swelling power, water holding capacity) and pasting properties were evaluated. A significant difference was noticed in functional properties between the starches. The solubility capacity of the modified starch, particularly the autoclaved starch, was higher than the native starch. The pasting properties of the treated starch samples were lower than the native rice starch. Scanning electron microscopy (SEM) images revealed differences in the starch granule surface morphology with the various treatments. The FTIR spectra showed peaks of C-O-C bonding showing a glycosidic linkage between the lintnerized starch and CH stretching region at approximately 2800-3000 cm-1. The color of the acid and heat treatment of starch resulted in changes to some attributes such as the darker color.
Finally, this research project aimed to develop gluten-free noodles with higher nutritional and functional properties. The effects of replacement of wheat flour with the Pathumthani 80 (RD 31) native autoclaved resistant starch (NARS) followed by addition of xanthan gum (XG), inulin and defatted rice bran was evaluated. Initially, replacement of wheat flour with RD 31-NARS at different proportion (20, 40, 60, 80, 100% of wheat flour) showed the significant (p ˂ 0.05) increase in resistant starch content and decrease in glycemic index. Higher the ratio of resistant starch, higher the noodles viscosity, solubility capacity and swelling capacity but lower the water holding capacity and lose of firm texture (p < 0.05). Secondly, the addition of XG at different proportion (0.625, 1.25, 2.5 and 5%) on the RD 31- NARS (100%) noodles showed significant (p ˂ 0.05) decrease in resistant starch content and increase in glycemic index with the increase in ratio of XG. However, the addition of XG increased the firmness of noodles, cooking time, water absorption and decreased the cooking loss. Gluten-free noodle with 2.5% XG received higher sensory score and was selected for further addition of inulin and defatted rice bran at different concentration (2.5% and 5%). Addition of inulin and defatted rice bran significantly (p ˂ 0.05) increased crude fiber content, reduced resistant starch content and glycemic index value and increased the water absorption and texture of noodle. The storage stability of the noodles was studied in terms of changes in textural properties, sensory quality and microbial growth. |