Insights into the structural characteristics and in vitro starch digestibility on parboiled rice as affected by ultrasound treatment in soaking process

This study investigated ultrasound treatment as a protective parboiling technology for producing low GI rice. Indica and Japonica rice with different amylose contents were subjected to different ultrasound times (15 min, 30 min, and 60 min) and amplitudes (30, 60, and 100%) under soaking conditions for parboiling applications. Starch granules merged and lost their shape when ultrasound treatment time and amplitudes were increased up to 15 min and 30%, respectively. It increased the crystallinity, gelatinization temperatures and decreased pasting viscosity, promoting more resistant starch. The predicted glycemic index (GI) was reduced from 62.9 and 57.6 to 51.3 and 47.1 for Japonica and Indica, respectively. These results suggested that ultrasound soaking is a promising physical method to produce parboiled rice with a lower GI by promoting the formation of amylose chains and decreasing enzyme penetration efficiency.

Microstructural, physicochemical properties and starch digestibility of brown rice flour treated with extrusion and heat moisture

Effects of heat moisture treatment (HMT), extrusion treatment (ET), and the combination treatment (HMT-ET) on microstructural, physicochemical properties, and starch digestibility of brown rice flour (BRF) were investigated. With a rise in resistant starch (RS), melting temperature, and a decrease in swelling capacity (SC), peak viscosity, and apparent amylose content (AAC), the HMT-ET BRF showed a significant lower expected glycemic index (eGI) than HMT and ET. XRD and FTIR results showed ET, HMT-ET caused the transition of starch crystals from amorphous to crystalline region, suggesting the formation of the starch-lipid complex. The analysis of DSC and RVA proved HMT-ET flours induced starch gelatinization and inhibited the starch retrogradation of BRF compared with the other three flours. Correlation analysis suggested that the combined effect of HMT and ET was response for the changes in physicochemical properties and reduction of in vitro starch digestibility. Overall, the BRF after HMT-ET with improved physicochemical properties and starch digestibility could be better utilized as a good substitute for carbohydrate sources.

Reactive Extrusion-Assisted Process to Obtain Starch Hydrogels through Reaction with Organic Acids

A totally green process based on reactive extrusion was used for the production of cassava starch hydrogels through reaction with two organic crosslinking agents, citric (CA) and tartaric (TA) acids. CA and TA were used at different concentrations (0, 2.5, 5.0, 10.0, 15.0, and 20.0%). Degree of substitution (DS) of hydrogels ranged from 0.023 to 0.365. Fourier transform infrared spectroscopy results showed a new band appearing at 1730 cm−1 associated with ester carbonyl groups. X-ray diffraction indicated that reactive extrusion resulted in the disappearance of diffraction peaks of native starch and samples with lower crystallinity indices ranging from 37% (native starch) to 8–11% in starch hydrogels. Morphology analysis showed that the original granular structure of starch was lost and replaced by a rougher and irregular structure. Water holding capacity values of starch hydrogels obtained by reactive extrusion were superior to those of native starch and the control sample (extruded without the crosslinking agents). Hydrogels obtained with the highest CA or TA concentration (20.0%) resulted in the higher DS and swelling capacities, resulting in samples with 870 and 810% of water retention, respectively. Reactive extrusion was effective in obtaining starch hydrogels by reaction with organic acids.

Enhancing the functional properties of rice starch through biopolymer blending for industrial applications: A review

Rice starch has been used in various agri-food products due to its hypoallergenic properties. However, rice starch has poor solubility, lower resistant starch content with reduced retrogradation and poor functional properties. Hence, its industrial applications are rather limited. The lack of comprehensive information and a holistic understanding of the interaction between rice starch and endo/exogenous constituents to improve physico-chemical properties is a prerequisite in designing industrial products with enhanced functional attributes. In this comprehensive review, we highlight the potentials of physically mixing of biopolymers in upgrading the functional characteristics of rice starch as a raw material for industrial applications. Specifically, this review tackles rice starch modifications by adding natural/synthetic polymers and plasticizers, leading to functional blends or composites in developing sustainable packaging materials, pharma- and nutraceutical products. Moreover, a brief discussion on rice starch chemical and genetic modifications to alter starch quality for the deployment of rice starch industrial application is also highlighted.

Resistant structure of extruded starch: Effects of fatty acids with different chain lengths and degree of unsaturation

This study investigated the formation mechanism of enzyme-resistant structures in extruded starch, specifically, fatty acid-starch complexes (FASCs). The effects of fatty acids (FAs) with different carbon-chain lengths (C12-C18) and degrees of unsaturation (C18:0-C18:2) on complex formation were evaluated, with fluorescence microscopy verifying complex formation. The complexed-lipid content and degree of relative crystallinity increased with the carbon-chain length and degree of FA unsaturation. FAs with fewer carbons were more likely to generate stable complexes (e.g., form II, melted at 100-120 °C), while FAs with more carbons tended to produce relatively unstable complexes (e.g., form I, melted at 80-100 °C). After reheating and cooling, a new amylose-lipid complex and an amylose-amylopectin network was formed in the unsaturated FASC samples, which restricted the penetration of enzymes into starch granules. A starch-linoleic acid complex exhibited the highest resistant starch content (15.7%) and lowest predicted glycaemic index (88.4).

Characterization of complexes formed between debranched starch and fatty acids having different carbon chain lengths

Recently, amylose-lipid complexes have attracted widespread attention because of their various applications. However, DBS complexed with fatty acids of different carbon chain length are rarely studied. This study aimed to probe the complexation of DBS with saturated fatty acids having different carbon chain lengths (C6-C18). The results revealed that DBS was able to form V-type complexes with all the fatty acids considered. Compared to DBS, the relative crystallinity of the complexes increased 2-3 times. DBS with lauric acid and myristic acid formed three types V-type complexes (type I, type IIa, and type IIb). The complexing index followed the order of hexanoic acid > octanoic acid > capric acid > lauric acid > myristic acid > palmitic acid > stearic acid. Furthermore, lauric acid and myristic acid formed complexes with DBS more easily compared with other fatty acids.