Preparation,Characterization Of ?-PGA Hydrogel And Its Application To Preservation Of Mushrooms

?-PGA is a polyamino acid-containing material obtained by fermentation of Bacillus subtilis.The ?-PGA hydrogel obtained after cross-linking not only has biodegradability,water retention and biocompatibility,but also has more Strong water absorption,pH sensitivity and chemical readability.In recent years,?-PGA hydrogels have broad prospects in many fields due to their better properties,such as food,agriculture,medicine,cosmetics,tissue engineering and environmental treatment.At present,?-PGA is mainly produced by microbial fermentation,but the pigment in the fermentation broth will affect the separation and purification and the appearance quality of the product,so the decolorization of the fermentation broth is very important.At the same time,the preparation of ?-PGA hydrogel by chemical crosslinking method has the advantages of simplicity and easy operation.This thesis mainly studies the decolorization and refinement of ?-PGA,the preparation,properties and structure of hydrogel,and the application performance of ?-PGA hydrogel in the preservation of shiitake mushrooms.(1)Decolorization of ?-PGA fermentation broth: The decolorization of ?-PGA fermentation broth was carried out with activated carbon,and the decolorization effect of activated carbon with different particle size and morphology was compared.The results showed that the mixture of granules and powdered activated carbon had a good adsorption effect on the pigment in the fermentation broth.The optimal conditions were The ratio of activated carbon granules to powder is 1:4,3 % activated carbon,and the decolorization effect of ?-PGA fermentation broth is best after decolorization at 30 °C for 120 min.Under this condition,the decolorization rate of the fermentation broth was 99.41 %,and the light transmittance was 99.8 %.(2)Structural characterization of ?-PGA hydrogel: The ?-PGA hydrogel was prepared by using polyethylene glycol diglycidyl ether as cross-linking agent.The?-PGA hydrogel was characterized by FT-IR and XRD.The results showed that the hydrogel was composed of ?-PGA.The carbonyl bond of the carbonyl group and the carboxyl group is bonded.SEM revealed that the cross-sectional area of the ?-PGAhydrogel was highly porous and the spatial structure was a network structure.(3)Determination of properties of ?-PGA hydrogel: The effects of ?-PGA concentration,crosslinking agent dosage,crosslinking time and temperature on the properties of ?-PGA hydrogels were studied by water absorption,water retention and compression modulus.The optimum conditions for PGA hydrogel were 9 % ?-PGA and 0.5 mL/L crosslinker dosage,crosslinking temperature 60 ° C,and crosslinking time 10 h.The ?-PGA hydrogel prepared under this condition had a water absorption rate of 1339.17,the water retention rate of 81.58 %,and the compression modulus of6.92 MPa.(4)Application of ?-PGA hydrogel to fresh-keeping of shiitake mushrooms: The shiitake mushroom was coated with different concentrations of ?-PGA hydrogel,stored at 4 °C,and the trend of quality index was detected by time-lapse.It indicated that 0.5-1.5% ?-PGA hydrogel had good preservation effect on shiitake mushrooms,and 1% ?-PGA hydrogel treated mushrooms had the best fresh-keeping effect,which could significantly prolong the storage and preservation period of shiitake mushrooms.After 30 days of storage,the water content was 15.3% higher than the control,and the Vc content was 2.5 times that of the control,while the PPO activity and browning degree were significantly lower than the control.