Reactive oxygen species turnover, phenolics metabolism, and some key gene expressions modulate postharvest physiological deterioration in cassava tubers.

Rapid postharvest physiological deterioration (PPD) in cassava (Manihot esculenta Crantz) tuber is a significant concern during storage. The freshly harvested tubers start spoiling within 24 to 72 h. Accumulation of H2O2 is one of the earliest biochemical events that occurred during PPD, which was detected using the 3,3 diaminobenzidine (DAB) in two contrast cassava genotypes, MNP Local A (29-57 µg g-1) and Sree Prakash (64-141 µg g-1). Accumulating the fluorescence hydroxycoumarin compounds emitted by the cassava tubers observed under an ultraviolet (UV) lamp showed significant variations at 0, 3, 6, 9, 12, and 15 days of storage. The total phenolics and carotenoids significantly and negatively correlated with PPD progression; however, the anthocyanin and flavonoids positively correlated with the PPD-anchored ROS accumulation. The primary compound, Phthalic acid, di(2-propylpentyl) ester, was identified in both the cassava tubers, Sree Prakash (57.21 and 35.21%), and MNP Local A (75.58 and 60.21%) at 0, and 72 h of PPD, respectively. The expression of PPD-associated genes APX-2, APX-3, PAL, and AP was higher at 6-12 days of PPD, which signified the synthesis of ROS turnover and phenylpropanoid biosynthesis. A significant, strong, and positive correlation was established between the secondary metabolites and PPD signaling gene expression, which was inversely correlated with hydroxycoumarin and H2O2 accumulation. MNP Local A tubers exhibited longer storage life of 15 days with a low PPD score, higher metabolites synthesis, and gene expression. The PPD-resistant lines may be used to augment cassava breeding strategies for large-scale commercial and industrial use.

Drying characteristics of ready-to-eat komal chawal rice: processing and modeling.

A traditional ready-to-eat rice from Assam, India, known as komal chawal is produced by steaming of steeped chokuwa paddy, which is a low-amylose variety, and by drying the steamed paddy under shade as a measure of controlling the drying rate for sustenance of a quick rehydration quality. As an improvement over this traditional method in terms of production time, komal chawal is produced by parboiling the chokuwa brown rice with model predicted soaking and steaming conditions. Thin-layer drying behavior of the steamed brown rice was studied at drying temperatures of 40-60 °C, at an air velocity of 1 m/s. Among different thin-layer drying models, Page equation fitted best to the drying data, with the coefficient of determination (R2) and root mean square error as the measures for selection of the best fitted model. While the moisture diffusivity values were in the range of 2.08 × 10-10-3.34 × 10-10 m2/s, the effects of drying air temperature on the drying rate was modeled with an activation energy of 20.44 kJ/mol for an the Arrhenius kind of temperature dependence of diffusivity. Based on the effects of drying temperature on rehydration, textural, and pasting properties of the product a lower drying temperature is recommended.

Effect of iron and folic acid fortification on in vitro bioavailability and starch hydrolysis in ready-to-eat parboiled rice.

Iron (Fe) and folic acid (FA) fortified parboiled rice was produced by applying 'brown rice parboiling' method. The effect of milling and the effectiveness of fortification were tested in relation to the amount of bioaccessible and bioavailable form of Fe and FA. An in vitro starch hydrolysis assay was employed to assess the effect on simulated glycaemic index (GI). The % bioaccessiblity of Fe and FA in the unmilled fortified rice were in the range of 57.6-65.8%, and 55.1-91.9%, respectively. The % bioavailability in the unfortified parboiled rice was negligible as compared to Fe (14.7-32.1%) and FA (13.5-27.5%) fortified rice. The GI of unfortified and fortified parboiled rice samples was in the range of 56-69, which was lower than the raw rice. The results demonstrated that this approach can be a novel and rapid method to produce micronutrient enhanced ready-to-eat rice.

Quality of ready-to-eat komal chawal produced by brown rice parboiling method.

Komal chawal, meaning soft rice, produced by brown rice parboiling of a low amylose rice variety chokuwa, was studied for its physical, physico-chemical, morphological and structural characteristics. The product was produced by soaking the brown rice at 60 °C for 90 min, followed by steaming and air drying to 12.0% (wb). The two steaming conditions used were: (1) open-steaming at atmospheric pressure for 20 min and (2) pressure-steaming at 1 atm (gauge) for 10 min. The three different drying temperatures used were 40, 50 and 60 °C. When soaked in water at 60 °C for 20 min the product attained a hardness value of cooked rice. The extent of changes in the kernel and flour properties as compared to the raw form were affected by the severity of the steaming condition and drying air temperature. The pressure steamed samples exhibited virtually persistent growth in paste viscosity in the profiles obtained from the rapid viscosity analyzer. X-ray diffraction analysis of flours revealed a loss of A-type pattern and formation of feeble peaks of A + V-type mixed patterns in steam-treated samples. Scanning electron photomicrographs showed the loss of the polygonal shape by starch granules during processing. The values of rehydration ratio, equilibrium moisture content for rehydration, sediment volume, extent of color change as denoted by total color difference, and the percent head rice yield were higher in pressure steamed komal chawal samples.