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Rice agglomeration : influence of the grain, starch retrogration and additives

  • Simapaisan, Piyawan
Publication Date
Jan 01, 2013
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A feature of cooked rice is that it may agglomerate and lose its free flowing properties. Quantification of the level of agglomeration is necessary if the phenomenon is to be understood. In this work texture measurement were made that related the forces required to break apart the rice grains and these values seemed reproducible and reflected the observations on the amount of rice agglomeration. A model system was developed and validated where washed rice grains were mixed with a range of starches to represent the material occurring external to the grains. Starches of different botanical source had different properties in regard to their agglomeration properties with potato starch causing the highest levels of agglomeration and tapioca the least, rice and maize being of an intermediate level. The addition of lipid to tapioca starch did not alter its behaviour in regard to agglomeration. Reduction in the average molecular weight of the external starch (by enzymatic breakdown, addition of maltodextrins) did seem to reduce the forces to break the rice agglomerates. It was assumed that retrogradation of the starch in the rice grains and in the external starch would increase the forces required to break down rice agglomerates. This was the case of forces increased on storage. The enthalpies within the rice grains (4.4 Jig starch) were higher than in the external starch (2.7 Jig starch). It could be expected that there was more amylose in the external starch. Manipulation of the amount of recrysta1lisation and the rates at which it occurred was difficult to achieve by storage at different temperatures (4°C and 40°C). This may have been due to water diffusion between the grain and the external phase. There was evidence of moisture migration in the system from the NMR data (change in T2 mobility values) and in that the amount of starch in the external phase was very relevant to rice agglomeration, but the concentration of the starch was not statistically important. The addition of flavouring materials, i.e. sodium chloride, sucrose, citric acid and particles (black peppers and tomato puree), affected the rice agglomeration. The NaCI and sucrose reduced the force required to separate the rice samples, whereas the citric acid and the particles increased aggregation. For the hard particle (black pepper), small particle sizes were more effective in reinforcing grain aggregation. / EThOS - Electronic Theses Online Service / GB / United Kingdom

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