Functional attributes and bio-assay of modified cereal starches

Abstract

The present project was designed to probe the effect of diversified modification methods on the functional, structural and nutritional attributes of cereal starches. Purposely, starch was extracted from rice and corn grains and modified by Heat Moisture Treatment (HMT), acid hydrolysis, oxidation, cross linking and Octenyl Succinic Anhydride (OSA) modification methods. The compositional analysis of corn and rice revealed 69.84±3.22 % and 79.12±2.86 % starch. The morphological examination depicted regular, polygonal small granules of starch by Scanning Electron Microscopy (SEM). The pasting properties of all the modified corn and rice starches exhibited significant differences. The solubility of modified starches varied from 5.43±0.17 % to 17.27±0.52 % while the light transmittance was highest in oxidized (46.13±2.15 %) trailed by OSA (43.40±2.18 %), acid hydrolysis (26.93±0.95 %), native (23.77±1.16 %), HMT (16.30±0.87 %) and cross link (13.37±0.45 %) in modified rice starches. Similar trend was observed regarding the solubility and light transmittance values of modified corn starches. The modification process reduced syneresis as a function of storage in both rice and corn modified starches with lowest synersis value in OSA modified starches. The structural properties of modified starches were exemplified by SEM and X-ray diffraction (XRD) studies. The photomicrographs revealed that HMT produced slight agglomeration along with granular disruption, acid hydrolysis did not cause any pronounced effect on granule morphology while rough edges and cluster formation occurred in starch granules after cross linking and OSA modification in both the rice and corn starches. The polymorphic forms as examined by XRD depicted that rice starches elucidated A-type crystalline pattern with characteristics peaks at 15.92, 17.24, 17.78 and 22.94º (2θ). All the modified starches exhibited the same pattern and no noticeable changes in rice starch were observed after various modification processes. Likewise, corn starches also illuminated similar A-type crystalline pattern with sharp peaks at 15.92, 17.21, 17.73 and 22.91º (2θ). The diffractrogram explicated that the process of modification occurred in the amorphous zone of starch granules. Furthermore, the modified starches were examined for the nutritionally beneficial component of starch i.e. resistant starch (RS). The resistant starch content of modified rice starches expounded that RS increased from 6.57±0.28 % to 26.75±1.69 %. Likewise, RS content in modified corn starch also boosted from 13.67±0.87 % to 41.76±2.15 %. Furthermore, modified starches were incorporated in wheat flour and their effect on dough and bread quality was assessed. The addition of modified starches significantly affected the rheological properties of wheat flour as determined by farinograph and RVA. Bread prepared by the addition of modified starches especially OSA rice starch revealed significant improvement in texture during storage. The hypocholesterolimic potential of modified starches was demonstrated through bio-assay trial and the provision of modified corn starch supplemented diet caused significant decrease as compared to modified rice starch in serum cholesterol, LDL and triglycerides as 5.07 % , 9.03 % and 6.09 %, correspondingly. Conclusively, modifications of cereal starches noticeably affected their functional properties and enhanced their utilization under rigorous processing conditions. Addition of modified starches in bread showcased their anti staling properties and the bio-assay trial illustrated the prophylactic potential to lower hyperlipidemia.