Mechanism Of Water Migration In Air-dried Meat During Hot Air Drying

Dried meat is one of the oldest types of meat products in China.Due to its unique flavor and stability at room temperature,dried meat is popular among consumers.Drying is the most critical production procedure and air drying is the most commonly used drying method.But air drying has the defects of uneven drying,poor product quality,high energy consumption and low degree of automation,which is mainly caused by the ambiguity of mechanism of moisture migration.Therefore,we studied the effect of temperature of air drying on the quality and energy consumption of air-dried meat;revealed the relationship of the crust and moisture migration;analyze the relationship of water-protein interactions and moisture migration;revealed the effect of sarcoplasm protein on the interaction of myofibril and water,in order to understand the mechanism of moisture migration during air during.The effect of different temperature on color,texture,digestibility,acid value and energy consumption of dried meat was studied to confirm the best temperature for air drying.Temperature had a great influence on color and texture?P<0.05?,but didn't have a significantly influence on digestibility and acid value?P>0.05?.The L*value and b*value were significantly higher when the temperature were more than 60?compared with the L*value and b*value when the temperature were less than 55?.Except a*value,all the quality parameters were not significant different between the samples treated by 35?and 15?air drying?P>0.05?.But the drying time of 35?was much shorter than the drying time of 15?air drying.When the temperature was 35?,the red a*value was highest,meanwhile the hardness was lowest,so 35?was suitable for air drying of meat.The relationship of the crust and moisture migration was investigated under the suitable temperature 35?.Thickness of crust significantly increased on the surface of lamb meat?P<0.05?,the moisture content of crust decreased more quickly than interior part of dried meat,shear force of dried meat increased when drying?P<0.05?.Shear force of the dried lamb meat decreased,and the crust disappeared after 48 h storage at 4?,when the moisture migrated from the interior part to the surface,indicating that the formation of crust might be because the moisture of the surface decreased more quickly than the interior part of the meat during drying.Connective tissue and muscle fiber shrunk,the gap between the muscle fibers decreased,the structure of myofibril Z line destroyed,which indicated the water channel in dried meat changed and then influenced the water migration.The relationship of water-protein interactions and moisture migration was investigated during air drying at 35?.The relaxation time of T_2b significantly decreased,but the area of it increased,which indicated water-protein interactions changed during drying.The second derivative spectrum of ATR-FTIR of dried meat showed that the amide?band original spectra contained four peaks,the summit of the first peak significantly decreased indicating the content of?-sheet changed during air drying.There was a significant linear correlation relation between the low-field nuclear magnetic resonance?LF-NMR?relaxation T₂₁?immobilized water?area and the drying rate,and also a significant linear correlation relation between the T₂₁ area and the radios of absorbance of main frequencies of amide?band,this indicated protein-water interaction influenced water migration.Denaturation of myosin,increasement of hydrophobicity of myofibrillar protein,decrement of solubility of myofibrillar protein indicated that interaction between myofibril and water weakened,and then water migrated from myofibril to extra-myofibril space during air drying.In the previous chapter,we found moisture migration was determined by the state of the immobilized water which exists in myofibril.So at last,we studied the effect of sarcoplasm protein on the interaction of myofibril and water.Results show that in vitro models,sarcoplasm protein denatured at 35?,its solubility decreased significantly.At the same time,in situ model,differential scanning calorimetry showed denaturation of sarcoplasm protein,circular dichroism spectrum showed secondary structure of sarcoplasm protein changed.Sarcoplasm was put into 35?environment for different time to obtain several group of sarcoplasm with different denaturation degree.And then the myofibril was incubated with sarcoplasm.The denaturation of sarcoplasm protein induced the decrease of centrifugal losse of the incubation system,indicating water holding capacity of myofibril increased and the state of immobilized water in it changed.