Processing And Eating Quality Evaluation Of Rice Tea

Rice tea is the traditional characteristical food in Hubei, Hunan and other regions, which we eat or drink, we won’t feel hungry or thirst. Processing methods and product characteristics in different regions also vary, raw materials selection, process, nutritional quality and processing mechanism of rice tea is lack of systematic research. In this paper, take indica rice, glutinous rice, and rice as raw material, we make a research on effects of water addition, rice-wetting time, roasting temperature and time on the quality of rice tea, and determine the optimum processing parameters, while exploring the change of pasting properties, crystal properties, rheological properties, thermal degradation and protein, and make an evalution on eating quality including flavoring substances, starch and protein digestibility and food safety. The main results are as follows:1. Effects of water addition, rice-wetting time, roasting temperature and time on the qualtity of rice tea are studied. The optimum process parameters of rice tea are determined, water addition(10%), rice-wetting time(10 minutes), roasting (35 minutes at 200℃) are the optimal parameters of rice tea processing.2. Effects of roasting conditions on the physicochemical properties of rice tea are studied. Peak viscosity and hot viscosity in brabender viscosity curve decline sharply, falling number of 0, good cold stability, smaller regenerative value and setback than rice. Edges of rice tea disappear, particle surface becomes rough, and the specific surface area increases, showing honeycomb. Diffraction intensity of roasted rice decreases, crystallinity first decreases and then increases, diffraction peak intensity of 20° increases. Crystallinity of roasted indica rice falls less than roasted rice, diffraction peak of 20° disappear. Pasting peak of rice roasted 45 minutes first appeared. G’of rice roasted 20 minutes is the maxest. Ss roasting time continues, G " ascendes first and decends then. The higher the temperature of roasting, the smaller G’ of the starch, the greater G" of the starch. At frequency sweep, G’ and G " of the sample increase, with the extension of roasteing time, G’ first decreases and then increases, G" gradually increases; the higher the temperature, the greater change of G’, G ", and loss angle; loss angle of rice tea first increases and then decreases. Thermal weight loss of roasting processing of rice tea is divided into three stages, followed as the loss of water vapor, starch or protein degradation and carbon dioxide gas to escape; moisture starch content has no effect on the temperature of pyrolysis, heating rate is higher, the higher the pyrolysis temperature of starch, cracker temperature of glutinous rice is highest. TGA kinetic equation is y =-5.6841x+23.473 (R2=0.9902); roasting makes essential amino acid content decreases and then increase, lysine and arginine content decrease, hydrophobic amino acids increases, methionine and cystine content decreases; lysine score decreases, the second limiting amino acid threonine score increases.3. Volatile flavor compounds of rice tea are studied. Electronic nose can well distinguish between rice tea roasted at different time and temperature, and can not distinguish between rice tea of different varieties; the volatile flavor compounds of rice tea are mainly furans, pyrazines and pyridines substances.4. The digestibility of rice tea is studied. Ready digestible starch increases and then decreases, slowly digestible starch and resistant starch decreases and then increases during the processing of roasting. Compared with rice, after adding oil and fat to roasted rice, the digestion of starch reduces, and the amplitude of reduction is greater than rice, glycemic index of roasted rice is less than rice. While rice and roasted rice are placed one day, starch digestion of rice decreases larger than roasted rice. Roasting can reduce protein digestion.5. Safety evaluation of rice tea processing is studied. The increase of water addition and infiltration time contributes to reduce levels of acrylamide, acrylamide content increases along with temperature and then decreases, the extension of roasting time promotes accumulation of the amount of acrylamide. Advanced glycation endproducts content increases with water addition and then decreases, higher roasting temperature and greater time make higher advanced glycation endproducts content in rice tea. Acrylamide and advanced glycation endproducts content of rice tea at different processing conditions are 130～187μg/kg and 104～480AU/g.