High Pressure Processing in Infusion and Gelatinization: An application on Rice.

Abstract

Rice, one of the most widely consumed foods across the world is a cereal grain, which forms the staple diet of many people. The process of obtaining white rice involves the husking of paddy/rough rice followed by polishing to remove the bran layer. When brown rice is polished rice loses many vitamins and minerals through the bran. An important nutrient of these is thiamine (Vitamin B1), an essential vitamin, deficiency of which is known to cause a disease called beriberi. Brown rice does not have a long shelf-life because it is prone to oxidation due to the presence of unsaturated fatty acids in the bran layers. It also possesses a nutty flavour, which is not very palatable. The rice endosperm is very tough and non-porous. Gelatinization of rice can be a useful tool to impregnate nutrients in it. High Pressure Processing (HPP) is a novel technology that involves subjecting foods to high hydrostatic pressures of the order of 100-600 MPa. This technology has been proven successful for inactivation of numerous microorganisms, spores and enzymes in foods, leading to increased shelf life. HPP is not limited to cold pasteurization but has many other applications. In this thesis, the other applications of HPP, such as gelatinization, forced water absorption and infusion of nutrients have been extensively reviewed. The use of high pressure in producing cold gelatinizing effects, imparting unique properties to food and improving food quality has been discussed, highlighting the latest published studies and the innovative methods adopted. The research work conducted outlines the treatment of paddy rice with HPP and thereby obtaining rice that possesses higher amounts of natural thiamine. The mechanisms involved in the transfer of thiamine included the concepts of high pressure gelatinization and high pressure infusion. Differential Scanning Calorimetry and X-Ray Diffraction were conducted to find the degree of gelatinization and crystallinity, respectively, of samples subjected to different treatment temperatures (50 °C and 70 °C), pressures (450 MPa and 600 MPa) and times (15 min and 30 min) during HPP. The rice samples were checked for thiamine using the fluorometric method. It was observed that HPP produced 56-68% gelatinization in rice and significantly increased thiamine content of it with higher temperature and pressure. This method of treatment was found to be shorter and showed good potential in thiamine enhancement of white rice with higher organoleptic attributes.