The development and evaluation of improved rice parboiling technology in Ghana
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.