Effects Of Superheated Steam Processing On Pork Meat Quality

Heat processed meat products are very popular among consumers.At present,conventional thermal processing technology has the defects of low production efficiency,high energy consumption,and difficult to control product quality.Superheated steam（SHS）has the advantages of high production efficiency,energy saving and environmental protection,and inhibition of oxidative deterioration.It has been gradually applied to food processing in recent years.However,the heat transfer method is quite different from the conventional technology,and it is necessary to study the variation law of product quality during the processing,in order to provide a theoretical guidance for the process optimization of superheated steam technology.The main results are as follows:（1）Study on the change of moisture content of pork in SHS processing:The change of water content in pork samples under different processing conditions（120,140,160 or 180 ℃）with SHS was studied.The model fitting was used to calculate the relationship between moisture radio of pork loins and time under different processing temperature,fitting equation was obtained,and the corresponding moisture diffusivity was solved for temperature of 120-180 ℃.The results showed that there was an exponential relationship between the moisture ratio and processing time,and the water diffusivity increased with the increase of processing temperature.When the temperature was lower than 160°C,the increase of temperature had a greater influence on the water diffusivity.When the temperature was continuously increased to 180 ℃,the influence was weakened.The moisture diffusivity of pork loins was range from 3.98×10-⁹ to 1.58×10-⁸ under 120-180 ℃.Low field nuclear magnetic resonance（NMR）T₂₁ relaxation determination results show that immobile water seriously lost during the processing.When temperature increased higher than 140 ℃,relaxation time T₂₁ and peak area A₂₁decreased significantly.Therefore,considering the production efficiency and energy saving,the processing temperature should set to 160°C or less.（2）Study on the changes in the eating quality of pork during the superheated steam processing:We evaluated changes in the texture,colour,microstructure and volatile compounds of pork loins after SHS processing at 120,140,160 or 180°C for 5,10,15 and 20 min.The results showed that when the heating temperature was higher than 140°C,the food quality indexes such as texture,color and sensory score of the sample were significantly deteriorated.Scanning electron microscopy micrographs showed that cooked pork with SHS had more complete muscle fiber bundle structure than that of pork in HA.The results of sensory evaluation showed that the samples treated at 140°C for 10 min had the highest comprehensive score.Compared with the hot air group,the pork color and the overall liking score of the superheated steam group were higher,but the flavor score was weaker.Considering those variations,samples cooked at 140°C showed better quality attributes for SHS processing.（3）Effect of superheated steam processing on lipid oxidation and volatile flavor of pork:The difference in fat oxidation degree and flavor of pork samples treated by superheated steam and hot air was studied.The results showed that the degree of fat oxidation in the superheated steam group was significantly lower than that in the hot air group.The results of the electronic nose analysis showed that the flavor difference between the two groups was significant.The alcohol and ketone substances that closely related to fat oxidation in the hot air treatment group were higher.At 20 min,the volatile flavors in the hot air treatment group were seriously lost,while the volatile flavors in the superheated steam samples were better retained.The volatile flavor and free amino acid composition of the two groups were similar.