Effects Of Physical Modification On The Functional And Enzymatic Hydrolysis Properties Of Silkworm Pupa Protein

China is the largest producer of silk in the word,with a long history of sericulture.Nowadays,more than five hundred thousand tons of fresh silkworm pupa were produced per year.The protein contain is about 50-60% of dried pupa with 18 amino acids.The ratio of amino acids in silkworm pupa is similar to the recommendation of FAO/WHO.So,silkworm pupa is a quality protein resources for high-value utilization.But,because of the special odor and special processing technology,the properly utilization of silkworm pupa protein is limited,and leads to the protein waste.In order to improve the utilization of silkworm pupa protein,different methods of micronization and ultrasonic on the protein properties were studied in this thesis.Following the changes of amino acids composition,physical and chemical properties,functional properties,and enzymatic hydrolysis properties,and biological activities are also carried out.The main results as followings.Process optimization of modified protein in silkworm pupa by grinding ball superfine comminution.Single factors such as ratio of material to liquid,time,temperature,and pH have been selected to study effects on the solubility of silkworm pupa protein.Then,response surface analysis was conducted to optimize the modification conditions for silkworm pupa protein.Results indicated that the optimum conditions are as follows: protein concentration of 8.29 %,pH 8.7,treated time of 61 s.Under the optimum condition,the solubility,emulsibility,emulsifying stability,foaming ability and foaming stability of the treated silkworm pupa protein were increased by 259.6%,50.0%,141.7%,61.0% and 33.8%,respectively,while its water-holding capacity and oil-holding capacity were decreased by 25.3% and 27.2%,respectively.In order to predict and control the degree of hydrolysis(DH)of silkworm pupa protein,the enzymatic hydrolysis kinetics of untreated and micronization-treated silkworm pupa proteins were studied using combining mathematical derivation and experimental research.The results showed that the DH values of untreated and micronization-treated silkworm pupa proteins increased with the increase of alcalase concentration,while decreased with the increase of initial substrate concentration.The kinetic model of alcalase hydrolysis for untreated silkworm pupa protein was DH=3.86 ln [1 +(7.0199 E0/S0-0.0064)t].The kinetic model of alcalase hydrolysisfor ultrasonic-treated silkworm pupa protein was DH=5.38 ln [1 +(5.1482 E0/S0-0.0019)t].The untreated and micronization treated silkworm pupa proteins had the maximum critical initial substrate concentration when they were hydrolyzed using alcalase.Results showed that the kinetic models were basically consistent with the real hydrolysis,and could were used to predict the hydrolysis process of untreated and micronization-treated silkworm pupa proteins.Thus the kinetic models have significant application value.Process optimization of modified protein in silkworm pupa by ultrasonic treatment.Based on the effects of the protein concentration,ultrasonic power,temperature and treated time on the solubility of silkworm pupa protein,the processing conditions of modified protein in silkworm pupa were optimized by response surface analysis.The optimum conditions were obtained with ultrasonic power of 81.6%,protein concentration of 10.84%,temperature of 37.4?,and treated time of 96.4min.Under this condition,the properties of solubility were up to 15.63g/L.The solubility,emulsibility,foaming ability of the treated silkworm pupa protein were increased by 303.8%,87.5%,39.5%,respectively.In order to predict and control the degree of hydrolysis(DH)of silkworm pupa protein,the enzymatic hydrolysis kinetics of untreated and ultrasonic-treated silkworm pupa proteins were studied using combining mathematical derivation and experimental research.The results showed that the DH values of untreated and ultrasonic-treated silkworm pupa proteins increased with the increase of alcalase concentration,while decreased with the increase of initial substrate concentration.The kinetic model of alcalase hydrolysis for untreated silkworm pupa protein was DH=3.86 ln [1 +(7.0199 E0/S0-0.0064)t].The kinetic model of alcalase hydrolysis for ultrasonic-treated silkworm pupa protein was DH=5.30 ln [1 +(5.85 E0/S0-0.002)t].The untreated and ultrasonic-treated silkworm pupa proteins had the maximum critical initial substrate concentration when they were hydrolyzed using alcalase.Results showed that the kinetic models were basically consistent with the real hydrolysis,and could were used to predict the hydrolysis process of untreated and ultrasonic-treated silkworm pupa proteins.Thus the kinetic models have significant application value.To improve the properties of silkworm pupa protein,the effects of different modification techniques included enzymolysis,ultrasound,and micronization on the molecular structure and bioactivity of silkworm pupa protein has been evaluated inthis study.The results showed that enzymolysis modification led to the most substantial change in the area and shape of the infrared(IR)absorption peaks,decreased in size with an increased number of cracks of modified protein by scanning electron microscopy images,followed by ultrasound and micronization modification.After modification by enzymolysis,ultrasound,and micronization,the sulfhydryl concentrations of silkworm pupa protein were increased by 48.56%,34.82%,and12.46%,respectively;disulfide bond concentrations were reduced by 40.47%,10.79%,and 11.72%,respectively.Furthermore,the ratios of essential amino acids among total amino acids increased by13.85%,2.22%,and 6.93%,respectively.Antioxidant activity and ACE-inhibitory activity of silkworm pupa protein also increased notably after modifications.