Effect Of High Pressure Treatment On The Physical Quality Of Brown Rice

Brown rice is covered with bran layer, aleurone layer and embryo, has rich nutritional contents, such as vitamin B, minerals and dietary fiber. However, the sensory property and cooking property of brown rice is bad. High pressure technology is a new non-thermal food processing method, it can induce damage to the cell wall. We can use HPP to destroy or change the morphological character of brown rice surface and starch granules, so that the sensory property and cooking property can be improved. The improvement of physical property of brown rice by using high pressure processing(HPP) is studied. The following aspects were studied.1. The water absorption ratio of brown rice increased with soaking temperature and soaking time, reaching the top27.5%. Much less water was absorbed into the grain after HPP, it is more energy-saving for the drying process. Comparison was made between HPP and soaking process, the hardness and cooking time of brown rice after treatment were investigated. Results showed that HPP reduced the hardness of brown rice for48%, and for soaking was only28%. The cooking time of brown rice decreased for60%after HPP, and44%for soaking process. This can be explained that HPP changed or destroyed the micro-structure of brown rice, which resulting in better hydroscopicity and gelatinization property.2. The effects of high pressure on other physical properties were evaluated, including gumminess, springiness and chewiness, gel consistency, viscosity, gelatinization property. Result shows that treatment of200-400MPa has little effect on gumminess, springiness and chewiness, which decreased significantly after treated at higher than500MPa. The biggest reduction of gumminess, springiness and chewiness are62%,35.2%,72%, respectively. It indicated that HPP makes brown rice easier to be chewed. After HPP treatment, the gel consistency, peak viscosity and break down were improved by14.7%,36.7%and47.3%. This means that brown rice become softer and has better viscosity property. Gelatinization enthalpy of brown rice reduced after HPP treatment, which implied a shorter cooking time.3. The contents vitamin B1, Ca and Fe were detected after treated at different pressures. Results showed that the toss of vitamin B1was mainly induced by soaking, rather than HPP. Comparing with the white rice, the tosses of Ca and Fe were much smaller after HPP treatment. Although HPP induced a degree of loss in nutriment in brown rice, however, referring to the Ca and Fe, it has big advantage over the white rice.4. Scanning Electron Microscope (SEM) was used to investigate the effect of high pressure on the morphological character of the rice surface and starch granules. Separations among the bran layer, pericarp and albuminous cells were discovered after HPP. The structure of starch granules was turned from polyhedron to spheroidicity. After treated at500MPa, small pores appeared among albuminous cells and starch granules were damaged in some extent.5. A new zongzi product was developed by using HPP. Results showed that HPP reduced the amylose content in the rice, improved the gel consistency and sensory score. Aiming at the amylose, gel consistency and sensory evaluation, after treated at300MPa for15min, the late japonica rice from northeast of China could match the products that made from sticky rice.