Processing and quality of glutinous rice

Abstract

The loss of stickiness of aged glutinous rice is one of the quality issues. This thesis examined the various factors that could affect the loss of stickiness of glutinous rice and potential pre-treatments and storage conditions that could be helpful to maintain the stickiness during storage. In this work, the effect of modified atmospheric packaging and various pre-processing treatments such as alkali washing, starch modification, and parboiling were assessed.Initially, the effect of different rehydration temperatures (30 to 50ºC) and cooking times (2.7 to10.7 min) at 95ºC on the pasting properties of flour of three glutinous varieties (TDK11, TDK8, and Hom Mali Niaw) was investigated using the RVA. Increased soaking temperature and time resulted in reduced pasting temperature for all varieties. Extended holding at a cooking temperature (95ºC) had a more significant (P<0.05) effect on final gel viscosity.Rice is usually consumed in the form of whole grains. Therefore, it is important to study the cooking kinetics of whole rice grain. To study the water uptake rate and cooking kinetics of TDK8 (fresh and aged) and TDK11, a novel in situ method using Thermal Mechanical Compression Test (TMCT) attached to a texture analyzer was developed. The TMCT cooking method was found valid for in situ analysis of rice cooking by using sample sizes as small as 0.50 g.A new method (X-ray photoelectron spectroscopy) employed to quantify the surface composition of raw and cooked rice grains showed that the surface of uncooked grains of glutinous (TDK11) rice had a higher content of protein and lipids (49.7 and 36.2 %, respectively) to starch (13.4 %) compared the bulk composition (protein ~ 6.6 %, lipids ~ 0.8 %, and starch ~ 92.6 %). Protein was hypothesized to contribute to the loss of stickiness. An alkali washing with different concentrations of NaOH (0 to 0.2 %) of milled grains of TDK8 and Doongara resulted in a significant (P<0.05) increase in the stickiness and hardness of cooked rice grains, and final viscosity of rice flour, and a decrease in the amount of retrograded starch. In another study, the acetylation of starch in the whole grain of TDK8 and Doongara was achieved using various acetic anhydride concentrations (1-7 g per 100 g of milled grains in 225 mL of water). Results showed that acetylation reduced the crystallinity of starch with a significant (P<0.05) reduction in peak and final viscosities, and reduced thermal transition temperatures and enthalpy. Furthermore, the texture of cooked grains was softer and more adhesive. A significant reduction in the glycemic index (GI) of acetylated samples was also observed using the in vitro digestion method.iii Parboiling of TDK8 and TDK11 was undertaken using various soaking mediums water (control), 3 % NaCl solution and 0.2 % acetic acid solution. These saline and acetic acid soakings improved the milling efficiency (39 to 41 % HRY for TDK8 and 48 to 53 % HRY for TDK11) when compared to the control (26 % HRY for TDK8 and 29 % HRY TDK11). Saline and acetic acid soaking re...

Rice for Food Security: Revisiting Its Production, Diversity, Rice Milling Process and Nutrient Content

“…Owing to the unique starch composition of glutinous rice, the rice exhibits unique processing properties. The productivity of rice milling and grain quality can be enhanced through various pretreatments such as tempering during the post-harvest tempering process and parboiling, which reduces internal slits and increases head rice output [29,30].…”

“…The husk, also known as the hull, is the most visible element of a rough rice grain. The hull is the outer layer that surrounds the caryopsis and, while it is inedible, it accounts for approximately 20% to 25% of the total grain weight [29]. The hull acts as a barrier against invasion and environmental changes.…”

“…Rice amylopectin has an iodine affinity of 0.4% to 0.90% in low-and intermediate-amylose rice, but only 2% to 3% in high-amylose rice. Isoamylasedebranched amylopectin has longer chain fractions (DPn > 100) (9-14%) in high-amylose samples and a higher iodine affinity than low-and intermediate-amylose samples (2-5%) and waxy rice amylopectin (0%) [29,45]. Milled rice is classified as waxy (1-2%), very low amylose (2-12%), low amylose (12-20%), intermediate (20-25%), or high (25-33%) based on colourimetric starch-iodine colour absorption standards at 590-620 nm [46,47].…”

“…The proportion of protein and fat in food reduces proportionally as the degree of polish increases. This component is primarily found in the outer layers of the kernel [29].…”

“…Benzene formaldehyde, decyl aldehyde, hexanal, pentanal, non-anal, and heptanal were detected at relatively high concentrations. Some twenty-three different volatile ketones were identified, with 19 being found in indica rice and 13 in japonica rice [29]. The ketones were significantly less abundant than the aldehydes [103].…”