Effects Of Supercritical CO₂ Degrease And Ultrasonic Treatment On Functional Properties Of Tussah Pupa Protein

Tussah silkworm had a long history and originated in China,and its output is huge in recent years.The protein in tussah silkworm pupa has reasonable amino acid ratio,rich nutrition and excellent functional properties,which has been gradually accepted by the public as a substitute for traditional animal derived food protein.However,due to the lack of deep processing technology of tussah pupal protein,its further application in food industry is limited,resulting in a waste of resources.So how to improve the utilization value of Tussah silkworm pupa protein will play an important role on our country Tussah silkworm pupa development.The supercritical CO₂ degreased process of tussah silkworm was optimized in this study.After that,ultrasonic assisted technology was used to extract tussah pupal protein,and the effects of supercritical CO₂ degrease and ultrasonic treatment on physicochemical properties and nutritional value of tussah pupal protein were studied.Specific experimental results are as follows:1.In this study,SC-CO₂ degreased was used to degrease Tussah silkworm pupa.Using degreasing rate as index,single factor experiments of degreased time,temperature,pressure and CO₂ flow rate were carried out.Response surface analysis（RSM）and BP-GA were used to optimize the conditions of SC-CO₂ degreased in Tussah silkworm pupa.It is found that the optimization effect of BP-GA is better than that of RSM.The optimum conditions for degreased were as follows:temperature44.5^oC,pressure 26.8 Mpa,CO₂ flow rate 33.7 L/h,degreasing rate 97.18%.Soxhlet ethanol solvent extraction and SC-CO₂ defat powder were compared.It was found that the degreased powder whiteness of SC-CO₂ was higher（65.69±0.06）.The residual oil ratio（3.19±0.82）was lower;No odor.2.In this study,the protein of tussah pupa was extracted by ultrasonic-assisted alkali dissolution and acid precipitation.It was found that the highest extraction rate of protein by supercritical degreased-ultrasonic treatment was 45.63±0.32%.The solubility is the largest,reaching 64.39 mg/ml;At the same time,the water holding capacity,foaming and emulsifying properties have been improved.With the increase of p H,the viscosity of protein in different treatments increased,reaching the maximum at p H12.No matter in acidic,neutral or alkaline environment,the viscosity of supercritical-ultrasonic group is the largest,which is 21.02,23.53 and 24.09 m Pa.s respectively.The largest particle size is soxhlet degreased-alkali extraction protein,reaching 609.79±54.65 nm,and the smallest is supercritical degreased-ultrasonic treatment protein,reaching 151.70±0.8 nm.After supercritical degreased and ultrasonic treatment,the hydrophobicity of protein surface increased,and H₀ was 264.68.Ultraviolet,fluorescence and FTIR spectra show that the secondary and tertiary structures of tussah pupa protein have changed.These observations indicate that the change of silkworm chrysalis protein structure is a direct factor affecting functional characteristics.3.Supercritical degreased and ultrasonic treatment significantly improved the antioxidant capacity of silkworm chrysalis protein.When the concentration of tussah pupa protein was 5 mg/m L,the DPPH scavenging ability,hydroxyl radical scavenging ability and superoxide anion scavenging ability of the protein after supercritical degreasing-ultrasonic treatment reached 85.57%,39.39%and 40.91%respectively.When the protein concentration of tussah pupa was 10 mg/m L,the total reducing force is 0.58（700 nm）.In addition,the amino acid composition of treated silkworm chrysalis protein tends to be more reasonable,the content of essential amino acids increases by21.09%,the amino acid score（AAS）and chemical score（CS）are improved,and its essential amino acid index（EAAI）reaches the maximum,which is 79.22.The results showed that SC-CO₂ degreased and ultrasonic treatment improved the nutritional value of tussah pupa protein.In summary,SC-CO₂ degreased and ultrasonic-assisted treatment were used in this study to improve the physical and chemical properties,functional activity and nutritional value of tussah pupa protein.The prepared functional tussah pupa protein can be used in various fields such as food,and valuable products can be created by using them as raw materials,which will help to recycle and reuse tussah pupa and contribute to the long-term development of food industry.