Changes in Rice with Variable Temperature Parboiling: Thermal and Spectroscopic Assessment

Abstract

Rapid visco analysis (RVA) and differential scannning calorimetry (DSC) provided overall assessments of the effects of variable temperature soaking at 30, 50, 70, and 90°C and steaming at 4, 8, and 12 min. Calculation of the relative parboiling index (RPI) and percent gelatinization provided good metrics for determining the overall effects of partial parboiling. FT‐Raman and solid‐state 13C CP‐MAS NMR spectroscopies provided insight to conformational changes in protein and starch of paddy rice under various parboiling conditions. RVA showed lower pasting curves and DSC showed lower ΔH with increased temperature and steaming times. A large decrease in viscosity occurred with only the 30‐4 treatment as opposed to raw rice. This observation was consistent with FT‐Raman results that indicated substantial conversion of the protein from α‐helix to other conformations. DSC indicated incomplete gelatinization of starch, even with 90°C soaking and 12 min of steaming. Solid‐state 13C CP‐MAS NMR spectroscopy confirmed this result. However, it indicated the percent of Vh/amorphous plus the remaining crystalline starch in the 90‐12 treatment was equal to the amorphous and partially‐ordered starch in commercially parboiled rice. These results suggest that partial parboiling, 90°C soaking, and more than 8 min of steaming (ideally ≈12 min) of paddy rice is sufficient to induce changes that inactivate enzymes and provide enough starch gelatinization to prevent kernel breakage.

Development of a rice starch-based coating with antioxidant and microbe-barrier properties and study of its effect on tomatoes stored at room temperature

“…2. Retrogradation leads to shifting of the melting peak towards lower temperatures (Himmelsbach, Manful, & Coker, 2008). This shift was higher for the S/G film (T m ¼ 57.4 C) than S/G/L and S/G/L/A films with T m of 62.8 C and 60.1 C respectively, indicating that the incorporation of lipids has caused lowering of the formation of starch retrograded fractions (Silverio, Svensson, Eliasson, & Olofsson, 1996).…”

Soaking Conditions During Brown Rice Parboiling Impact the Level of Breakage‐Susceptible Rice Kernels

“…About 20% of the rice produced worldwide is parboiled (i.e., "partially boiled"). In particular, as the rice grain MC and the severity of heating increase, all starch granules gelatinize (Priestley 1976;Marshall et al 1993;Himmelsbach et al 2008;Manful et al 2008;Patindol et al 2008;Buggenhout et al 2013b). In the first step of rough or brown rice parboiling, rice is soaked in excess water at a temperature below the starch gelatinization temperature to hydrate the starch granules (Bhattacharya 2004;Delcour and Hoseney 2010a;Buggenhout et al 2013a).…”

Parboiling Cereals in Sub-Saharan Africa: Case of Rice

“…Parboiling is a hydrothermal treatment wherein a paddy is soaked in hot water, steamed to complete gelatinization, and dried before milled [11]. This technology adds value to quantitatively and qualitatively milled rice [12,13,14,15].…”

“…It affects the physical properties of rice, nutritional composition, starch characteristics (sticking properties and crystallinity), cooking qualities, etc. [41,6,11,42,43,32]. According to these authors, the purpose of parboiling is to produce physico-chemical and organoleptic modifications that are advantageous from an economic, nutritional and practical point of view.…”

“…Among the technologies developed to reduce nutrient losses during hulling, is parboiling. Rice parboiling consists a hydrothermal treatment of paddy rice followed by steaming and drying before milling [10,11]. It is the most important operation with the potential to improve the efficiency of milling and the economic value of paddy rice as well as the nutritional quality of the finished product.…”