Effect of Gamma-irradiation on the Physicochemical, Functional, and Antioxidant Properties of Unpigmented Brown Whole Rice Flour

Whole grain brown rice, being a rich source of fiber and other bioactive compounds like polyphenols is effective in reducing the risk of chronic diseases including cardiovascular diseases, hypercholesterolemia and Type II diabetes. The study was aimed to evaluate the effect of gamma irradiation on the physicochemical, functional and antioxidant properties of whole grain brown rice flour. The brown rice flour was conditioned to two different moisture contents of 10% and 12% and treated with gamma irradiation doses of 0 kGy (native or control), 2.5 kGy and 5 kGy. Moisture, protein, fat, ash and carbohydrate content of native flour was found as 10 g/100 g, 6.54 g/100 g, 1.54 g/100 g, 1.0 g/100 g, and 81.48 g/100 g, respectively. The hunter color ‘L’, ‘a’, and ‘b’ values of the native brown rice flour sample were found as 81.95, −0.97 and 17.36, respectively and were non-significantly ( p ≥ 0.05) affected by gamma irradiation. Apparent amylose content was observed to decrease significantly ( p ≤ 0.05) from 29.97 to 20.30 g/100 g with the increase in gamma irradiation dose and moisture content. The pasting properties such as peak viscosity, trough viscosity and final viscosity of all the flour samples decreased significantly ( p ≤ 0.05) with the increase in irradiation dose. The functional properties such as water and oil absorption and emulsion capacities were increased while emulsion stability and foaming stability decreased upon irradiation. Irradiation led to an overall increase in the antioxidant activity of rice flours. In general, FTIR spectra revealed a decrease in the absorption intensities of the functional groups. Therefore, it can be concluded that gamma irradiation can be used as a tool to modify the physicochemical properties of rice flours as well as to improve their antioxidant properties.

Characterization and utilization of nixtamalised rice flours in the production of cake

In an attempt to provide an alternate rice processing technique and enhance its nutritional quality, Faro 52 (Upland) and Nerica 8 (Lowland) rice grains were subjected to nixtamalisation involving cooking and soaking in a lime solution. The proximate composition, functional properties and pasting characteristics of the nixtamalised and nonnixtamalised rice flours were evaluated. Cakes produced with the rice flours were also subjected to sensory evaluation. Nixtamalisation significantly increased the protein content of upland (NUPRF) and lowland (NLLRF) rice flours by 28.19% and 27.80%, respectively. Nixtamalisation also enhanced the water absorption capacity of the rice flours, while the oil absorption capacity increased significantly. Pasting viscosities of all the nixtamalised flours were lower than their non-nixtamalised samples, while the pasting temperature increased. Nixtamalised rice cakes were not significantly different in colour, texture, flavour and overall acceptability from non-nixtamalised rice cakes. Nixtamalisation may be beneficial in rice processing for enhanced nutritional content and functionality, and the flour may be useful as a thickener and binder in food systems and the production of acceptable cakes.

Effect of Rice Flour Types on the Properties of Nonwoven Pineapple Leaf Fiber and Thermoplastic Rice Starch Composites

Thermoplastic starches and a nonwoven pineapple leaf sheet (NPALF) were prepared. Two types of flours were used to prepare thermoplastic starches (TPSs) which were Rice flour thermoplastic starch (RTPS) and Glutinous rice flour thermoplastic starch (GTPS). Two layers of thermoplastic starches and NPALF layer were sandwiched and pressed by a hot pressing machine at 150°C with 1500 psi for 15 min. All composites were investigated their densities and tensile properties. The density of all composite types had a lower density than each neat TPSs and types of rice flours did not affect their densities. The tensile property results confirmed NPALF could be used as a reinforcing agent both in GTPS and RTPS composites but their tensile improvement effectiveness in both systems are different. NPALF composite with RTPS did not affect the tensile strength but provided a slight improvement in modulus. Remarkably, NPALF composite using GTPS explored the great improvement performance both in strength and modulus which were increased up to 174% and 308% comparing with neat GTPS. SEM micrograph evidence clearly showed good wetting between GTPS and the reinforcement layer in the composite. This is resulting in the NPALF-GTPS composite showed a strong improvement in tensile properties.

Pasting Properties of Various Waxy Rice Flours: Effect of α-Amylase Activity, Protein, and Amylopectin

Waxy rice is one of the most popular traditional crops served as a staple food in China. In this study, the effect of different factors including α-amylase activity, protein, and amylopectin structure on the pasting properties of four waxy rice varieties were investigated. Rice flours treated with AgNO3 solution, DL-dithiothreitol (DTT) or protease, suggested that both α-amylase activity and protein significantly decrease the pasting viscosity of waxy rice flours. Chain length distribution of amylopectin as measured by high performance ion exchange chromatography (HPAEC-PAD) showed that starch with higher ratio of short chain leading to a higher pasting viscosity. X-Ray diffractograms showed that the crystal type of all the four varieties of rice starches were characteristic A-type. Relative crystallinity of each rice starch was further calculated, and a higher crystallization resulted in a higher viscosity. Our study would provide a fundamental knowledge of the relationship between different factors and waxy starch pasting properties, as well as be a reference for controlling the quality of waxy rice starch-based food.

Chemical, physical, and functional properties of Thai indigenous brown rice flours

Thai indigenous brown rice flours from Nakhon Si Thammarat, Thailand, namely Khai Mod Rin (KMRF) and Noui Khuea (NKRF), were assessed for quality aspects in comparison with brown Jasmine rice flour (JMRF) and commercial rice flour (CMRF) from Chai Nat 1 variety. All the rice flours had different chemical composition, physical characteristic, and techno-functionality. The KMRF, NKRF, and JMRF were classified as a low amylose type (19.56–21.25% dw). All rice flours had low total extractable phenolic content (0.1–0.3 mg GAE/g dw) with some DPPH● scavenging activity (38.87–46.77%). The variations in the bulk density (1.36–1.83 g/cm3), water absorption capacity (0.71–1.17 g/g), solubility (6.93–13.67%), oil absorption capacity (1.39–2.49 g/g), and swelling power (5.71–6.84 g/g) were noticeable. The least gelation concentration ranged from 4.0 to 8.0% where KMRF was easier to form gel than JMRF, and NKRF/CMRF. The foam capacity of the flours was relatively low (1.30–2.60%). The pasting properties differed among rice flours and the lowest pasting temperature was observed in CMRF. Overall, the chemical, physical, functional, and pasting qualities of flours were substantially influenced by rice variety. The findings offered fundamental information on Thai indigenous rice flour that can be used in food preparations for specific uses.