Parboiled rice flour swelled and dissolved more than raw rice flour in water at temperatures below 70"C, but less than raw rice at higher temperatures. This difference between raw and parboiled rice increased with an increasing degree of parboiling. A sample of parboiled rice produced by dry-heating soaked paddy in hot sand behaved differently; but when it was wetted and tempered to favour reassociation of starch, its properties fell in line with normal steamparboiled rice. The above behaviours of raw and parboiled rice flour were similar to those of corresponding whole-grain rice. They also reinforce the earlier suggestion of starch reassociation in conventional parboiled rice.
Viscosities of dispersions of raw and various processed rice flours in water were emmined with a coaxial cylinder viaccrmeter. The measured viscosity increwd with increasing degree of processing and with a reduced level of apparent starch reassociutiort in the processed rice. Measurement of the apparent wiSCo&ty of cold slurries could thus be a simple practical test of processed, including parboiled, rice and of the degree of processing. The system showed timedependent thinning and a typical locrp in the shear rate-viscosity curve, showing that it w a s t h k t m p i c in nature. The viscosities were prqlmrtimuzl to the hydration power and slumy-sedimentation behaviour of the samples. J m d o Teztum Studies 14 (1988) 21-30.AU Rightd Reserved ScopyriS i t 198s bg Food & N u t n t h Press, Zne., Westport, Gm?iectbt 21
Parboiling of paddy by mere hot water soaking, without steaming, has the advantage of not requiring a boiler. Soaking at a temperature 10-15°C above the gelatinization temperature (i.e. generally at about 80-85°C) is necessary to achieve fair to moderate gelatinization (i.e. parboiling). However, soaking at such temperatures for a time sufficient for the water to penetrate and gelatinize the grain core invariably leads to over-imbibition of moisture, husk splitting and leaching; soaking for less time, on the other hand, leaves many grains with 'white belly'. The best method therefore is to soak the grain for such time as to imbibe about 30% moisture (wet basis) (i.e. for about 1Y2-2 hr), drain out the water, and temper the hot paddy for another 1-2 hr. This process yields optimally parboiled paddy without 'white belly' or grain splitting and with reasonably good milling quality and colour.
Two popular rice products, namely expanded rice and flaked rice, are prepared from parboiled rice. As about 90% dry weight of milled rice is starch, the behaviour of rice and its products reflects largely the behaviour of its starch. The above precooked rice products which undergo a high degree of thermal and/or mechanical treatment during processing have a high degree of gelatinization and display therefore properties like those of pregelatinized starch. Both expanded rice and flaked rice have high water binding capacity and coldswelling properties. Under suitable moisture conditions they undergo retrogradation and show reduced hydration and viscosity. Normal steam-parboild rice shows much lower viscosity because of a comparatively low degree of starch gelatinization during processing and its subsequent retrogradation. Rheologically the cold slurry of these products indicates a thixotropic system demonstrating time dependent thinning. Further, a dependence on slurry concentration and degree of processing and a yield value behind a certain concentration were also apparent. The cold swelling properties of flaked rice and expanded rice show potential use of their flour as a possible subsitute for pregelatinized starch in food and other industries. Rheologische Eigenschaften bestimmterReisverarbeitungsprodukte. Zwei volkstumliche Reisprodukte -Puffreis und Reisflocken werden aus Parboiled-Reis hergestellt. Da Starke rund 90% der Trockensubstanz von gemahlenem Reis ausmacht, stellt das Verhalten von Reis und seinen Produkten im wesentlichen das Verhalten der Starke selbst dar. Die oben erwahnten vorgekochten Reisprodukte, die wahrend ihrer Herstellung in erheblichem Umfang eine thermische und/oder mechanische Behandlung erfahren, weisen einen hohen Verkleisterungsgrad auf und besitzen demzufolge Eigenschaften, die denen von Quellstarke entsprechen. Sowohl Puffreis als auch Reisflocken haben ein hohes Wasserbindungsvermogen und gleichermaflen stark ausgepragte Kaltwasser-Quelleigenschaften. Unter entsprechenden Feuchtigkeitsbedingungen erleiden sie Retrogradation und zeigen verringerte Hydratation und Viskositat. Normaler Dampf-Parboiled-Reis besitzt eine wesentlich geringere Viskositat aufgrund eines vergleichsweise niedrigen Verkleisterungsgrades als Folge der Verarbeitung und der daraus resultierenden Retrogradation. Rheologisch zeigt ein kalter waljriger Ansatz dieser Produkte ein thixotropes System an, das aufeine zeitabhangige Verdunnung hinweist. Daruber hinaus sind eine Abhangigkeit von der Slurry-Konzentration und dem Ausmalj der Verarbeitung sowie der EinflulJ einer bestimmten Konzentration auf die Ausbeute offensichtlich. Die Quelleigenschaften von Reisflocken und Puffreis in kaltem Wasser eroffnen einen potentiellen Einsatz ihrer Mehle in Lebensmitteln und anderen Anwendungsbereichen als moglicher Ersatz fur Quellstarke.
In this study, element-free Galerkin method (EFGM), a meshless method, is proposed for wrinkling analysis of pre-stressed rectangular membranes. The mathematical model for studying wrinkling of pre-stressed membranes is derived by considering the bending stiffness, though it is negligible. Moving least-square approximation for deflection is constructed by considering three degrees of freedom per node. Essential boundary conditions are imposed using scaled transformation matrix method. Initially, compression-induced buckling of a homogeneous thin plate without pre-stress is solved to validate the method and then a pre-stressed homogeneous membrane is analyzed for both compression-induced and shear-induced wrinkling. Capabilities of the proposed method for membrane analysis are compared with that of the finite element method (FEM). Comparative study on wrinkling analysis using EFGM and different FEM element types in a commercial FEM package shows that in lower modes both methods show satisfying consistency in eigenvalues with respect to the total of number of nodes, while at higher modes EFGM shows better consistency than FEM. Further, the study is extended to wrinkling of nonhomogeneous membranes subjected to linearly-varying in-plane load. The results obtained from EFGM analysis is compared and found to be matching well with those available in the literature.
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