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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.

Rice, amongst cereals, has one of the highest potential for the development of functional foods and ingredients. It is commonly consumed in its polished state, but the whole gram or fractions of the grain can be modified by germination and/or fermentation to improve their nutritional and functional value. This study evaluates the use of rice for the production of isomalto-oligosaccharides through germination and solid-state fermentation in combination with enzymatic transglucosylation. In addition, rice fractions obtained by debranning are tested for their prebiotic potential using batch culture fermentations with specific probiotic strains and human faecal microbiota.

A socio-economic study was carried out in northern Ghana to verify the importance of rice parboiling to poverty alleviation. Consumer acceptability and sensory evaluation carried out showed that there was a high correlation between consumer acceptability and sensory attributes developed by a trained panel for both raw and cooked rice. An improved prototype rice parboiling vessel was designed and constructed and this vessel more than doubled the quantity of paddy usually parboiled per batch in northern Ghana. It also reduced fuel and water usage by 50% and 30% respectively. Ghanaian consumers preferred imported rice to locally produced parboiled rice. They also preferred parboiled rice that had a clean, translucent and uniform appearance. Percent starch damage, an important quality indicator increased with parboiling intensity. On intense laboratory parboiling, milling yield increased by 7% over the raw milled sample. Broken grains increased on mild parboiling and only began to decrease when paddy was soaked at 90°C and steamed for at least 8 minutes. The most intensely parboiled sample had a broken level of 5.06%. Water absorption index increased with parboiling intensity. Thiamine content increased linearly with parboiling. Riboflavin however peaked with paddy soaked at 70°C and steamed for 12 minutes and decreased with further intensification of parboiling. X-ray diffraction pattern of the raw milled sample was the A-type. While the severest laboratory parboiled sample had an A-type pattern, the commercially parboiled sample had a typical V-pattern. The characteristic aroma of Ghanaian parboiled rice is influenced mainly by 2-decena, 2-heptenal and acetic acid. Raman and solid-state 13C CP-MAS NMR spectra were used in investigating changes in conformation of the protein and starch components due to parboiling. Artisanal parboiling was just as effective as commercial parboiling in the denaturisation of rice protein.

The Rice Krispies™ process consists essentially of the cooking of short or medium rice grains, followed by a mechanical compression between two rolls (bumping), a tempering step and a toasting operation (puffing) which expands the grains into the finished product. The objectives of this project were to clarify which molecular phenomena take place inside the rice grains during the process and to facilitate the improvement and optimisation of the process parameters. The composition and gelatinisation behaviour of seven different raw rice varieties used either in the United States or the United Kingdom were studied. The glass transition of the cooked rice material was determined by dynamic mechanical thermal analysis (DMTA), which allowed each step of the process to be mapped onto a temperature / moisture content state diagram. The bumping step of the process and its effect on the various molecular entities present in the cooked rice were studied in details. Amylose was found to form complexes with the lipids present in the material during cooking, and these reinforced the cooked rice grain structure. One of the roles of the bumping could be to partially dislocate these amylose-lipid complexes to enable the rice grains expansion at the puffing step of the process. The bumping also reduced the molecular weight of amylopectin, which is thought to weaken the rice grains structure and improve the puffed grains expansion. The mill gap between the bumping rolls was the key factor determining the quality of the puffed product. The temperature at which the rice grains are bumped had a secondary influence on the quality of the puffed rice, within the range 26°C to 57°C. The RVA provided a very effective method to categorise post-bumped samples and could be a useful diagnostic tool in case of production problems. Evidence of physical ageing and moisture content equilibration during the tempering step was found. Physical ageing did not have a detectable effect on the expansion of the rice grains, while it was important that moisture content was equilibrated inside the grains to ensure a proper puffing. Finally, correlations were found between the puffed rice grains expansion and the post-bumped grains height recovery, which made it possible to predict the quality of the expanded grains from the characterisation of the post-bumped rice. Overall, the project is a good example of the application of general starch science concepts to the study of a specific industrial process.