Study On Quality And Nutritive Characteristics Of Low - Pressure Boiled Grass Meat

This article studies on Grass Carp back muscles as raw material, using low temperature and low pressure boiling heating technology, through the study of grass carp (8cm * 8cm * 2.5cm) in different low pressure (0.8bar,0.6bar,0.4bar) and ordinary pressure(1bar) changes of heat transfer rate, sensory quality, physical and chemical properties and nutritional quality indexes under the conditions of cooking, the new method--the application of molecular techniques in the low temperature processing of aquatic products to provide a useful reference. The main conclusions are as follows:(1) The comparison among heat transfer rate, sensory evaluation and flavor material of boiled grass carp meat.Under ordinary pressure(1 bar) and different pressures(0.8bar、0.6bar、0.4bar, core temperature 70℃). The results indicate:with the decrease of pressure, the core temperature heating rate slows down and the heating time extends even longer. For example, under 1bar, grass carp meat needs 420s reaching 70℃ of core temperature;under 0.6bar,570s; under 0.4bar, 630s.When the pressure reduces below 0.6bar,the variation of pressure has no effects on sensory evaluation(p>0.05). Analyzing the flavor material of boiled grass carp meat under different low pressures through electronic tongue, the result shows there exists distinct changes among the flavor material; Analyzing the thermal change of grass carp meat protein by DSC, three enthalpy changes points are detected out:45.7℃、53.6℃、76.6℃,the first two belongs to myosin and the third one goes to muscle actin.(2) The effects caused by the cooking method boiling on grass carp meat quality under different low pressures.This chapter studies the effects caused by boiling under ordinary pressure(1 bar) and different pressures(0.8bar,0.6bar,0.4bar,core temperature 70℃) from following aspects:cooking ratio (WCL), water-holding ratio (WHL), colour and lustre, pH, volatile compounds and the whole texture (TPA).The result proves that there are significant differences of grass carp meat quality between boiling under low pressure and ordinary pressure(1 bar).Under the low pressure0.4bar,the minimum weight loss ratio on heating is 9.88%,notably distinct from under other pressures (p<0.05).When heating pressure decreased to 0.6bar or below, the condition has no effects on water-holding ratio and colour and lustre of grass carp meat (p>0.05);When grass carp under low pressure, the decrease of heating pressure has no effects on pH of grass carp meat. The species of volatile compounds under low pressure are more than that under ordinary pressure (1 bar), e. g. volatile compounds species in grass carp meat respectively includes 28、 22、31、29、27 under 1bar、0.8bar、0.6bar、0.4bar, which shows that heating under low pressure is beneficial to retention of volatile compounds in grass carp meat. The TPA texture properties of grass carp meat boiled under low pressure are rarely different from that under ordinary pressure (1 bar).(3) The effects caused by the cooking method boiling on nutritive peculiarity of grass carp meat under different low pressures.This chapter studies the effects caused by boiling under ordinary pressure(1 bar) and different pressures(0.8bar,0.6bar,0.4bar,core temperature 70℃) on following contents:water content, ash content, crude fat, crude protein,totaxin,potassium(K),fatty acid, amino acid and purine. The results show that there exists significant differences about nutritive peculiarity of grass carp meat between boiled under low pressures and under ordinary pressure(1 bar),turning out that nutritive peculiarity of grass carp meat boiled under 0.6bar has the best evaluation, accounting for the maximum of72.81% water content,0.98%ash content,1.31%crude fat, 30.60mg/kg potassium(K).When heating pressure reduces to 0.6bar or below, the decrease of heating pressure causes no significant effect on contents of water, ash and crude fat. When under 0.6bar, the crude protein content in boiled grass carp meat reaches the highest point of 17.94%,whereas there shows no changes of protein content under other three low pressure conditions (p>0.05); When under 0.4bar, the a-totaxin content in boiled grass carp meat grease reaches the highest point of 163.63mg/kg, whereas there shows no changes of a-totaxin content when reducing the heating pressure. There are 18 fatty acids detected out from raw grass carp meat grease, while 15 fatty acids detected out from grass carp meat grease boiled under different low pressures. Under 0.4bar, the highest content of MUFA is 40.25%; Under 0.6bar, the highest content of FUFA is 38.59%.Through acid hydrolysis of grass carp meat, there are 17amino acids detected out, including 4flavor amino acids,3 half essential amino acids,7 essential amino acids and 3 nonessential amino acids. When the grass carp meat boiled under different pressures, TAA and TEAA decrease apparently; When under ordinary pressure (1bar),the least amounts of TAA and TEAA are 15.161g/100g and 6.408g/100g; When under 0.6bar, the TAA and TEAA amounts reach the highest of 17.441 g/100gand 7.732g/100g respectively, which indicates that the ratio of TDAA/TAA and TEAA/TAA is more than that under any other conditions,35.92% and 44.33% accordingly; Hypoxanthine is the major component of purine compounds in the grass carp meat. Under 0.4bar, the lowest amount of purine content is 0.62mg/g and under 0.6bar, the nutritive peculiarity of boiled grass carp gets the highest evaluation.