Study On The Foaming Properties And Its Mechanism Of Jackfruit Seed Protein Isolate Induced By Preheating And Ultrasound Treatments

Jackfruit has a high annual output(30 t/hm²),but its seeds are often discarded as the main by-product.Protein is account for about 20%of jackfruit seeds,the study reported,the ratio of essential amino acids to total amino acids of jackfruit seed isolate(JSPI)was 48.39%,higher than soybean protein(37.79%),which could be a good source of protein.Foam property is one of the important functional properties of protein,the previous research showed,JSPI had a good foaming ability,which could be a good foaming agent,however,the foaming property of JSPI still have a certain gap compared with animal protein.At present,there are relatively few studies on JSPI,even fewer studies on its modification.Therefore,the modification of foaming property of JSPI has important scientific research significance and economic significance for expanding the application field of jackfruit in the food industry.The JSPI was modified by preheating and ultrasound treatments.The preparation technology for the best foaming properties:preheating temperature,ultrasonic power and ultrasonic time.On the basis of optimal conditions,the JSPI were treated by temperature and ultrasound,the relationship between the foaming property and structure of JSPI under synergistic treatment was explored,as well as the influence on other functional and physicochemical properties.The main research contents and experimental results of this study were showed:1.Optimization of foaming conditions and correlation properties of JSPI.The purity of JSPI extracted in this paper was 81.35%.The optimal conditions for the preparation of foaming properties were obtained by condition optimization:preheating temperature was 60?,ultrasonic power was 600 W,and ultrasonic time was 20 min.Correlation performance analysis showed:(1)The foam viscosity was higher than that of JSPI after 600 W ultrasonic treated,lower than JSPI after 60?,60?+600 W treated,a high viscosity was beneficial to maintain the stability of foam.(2)A lot of small bubbles were appeared after heating and ultrasonic treated,and the foam density increased,the foam size distribution was uneven.(3)600 W ultrasound had no significant effect on the T₀,T_p,T_eof JSPI(p>0.05),the T₀ and T_pof 60?,60?+600 W treated were higher than JSPI,the enthalpy was reduced significantly after 600 W,60?,60?+600 W treated.(4)The JSPI had high nutritional value and could be used as a good source of amino acids.600 W,60?,60?+600 W treated had little effect on the essential amino acid content of JSPI,there was no loss of nutrient composition of JSPI.2.The effect of preheating ultrasound on foaming properties and other functional properties of JSPI.The results were as follows:Compared with JSPI,the foaming ability after 60?+600 W treated increased to 58.44%,which was higher than that treated by 600 W(45.25%)and 60?(29.64%),indicating that 60?and600 W had synergistic effect on the foaming ability of the JSPI,the foam stability did not improve.There was no significant difference in foaming ability and foam stability between 60?+600 W and soybean protein(p>0.05).Other functional properties results showed:(1)At p H 3.0,the solubility of 600 W ultrasonic treated was similar to JSPI,with the increase of p H value,it was higher than JSPI.The solubility was lower than protein isolate at any p H after 60?and 60?+600 W treated.(2)Compared with JSPI,the emulsifying capacity(EC)the emulsifying stability(ES)increased after 600 W treated.The EC decreased,but the ES increased after 60?and 60?+600 W treated.(3)The best gelation was obtained after 600 W ultrasonic treated,the minimum gel strength was 8%,the worst gelation after60?+600 W treated,was 13%.(4)The Oil-holding capacity(OHC)increased from1.49 g/g to 1.62 g/g after 600 W treated,the Water-holding capacity(WHC)of JSPI increased from 1.75 g/g to 2.44 g/g after 60?treated,the WHC of JSPI increased after 60?+600 W treated,and there was no significant difference in OHC(1.59 g/g)with 600 W treated.3.The correlation analysis of structure and foaming ability of JSPI treated with preheat ultrasound.The SDS-PAGE gel electrophoresis,circular dichroism,endogenous fluorescence,surface hydrophobicity(H₀)and surface sulfhydryl(SH)groups were used to study the effect of preheating ultrasound treated on protein structure,the results showed:(1)600 W ultrasound did not change the molecular weight of JSPI,a new band appeared after 60??60?+600 W,and a molecular weight band disappeared after 60?+600 W treated.(2)The contents of?-helix and?-turn decreased of JSPI after 600 W,60?,60?+600 W treated,while the contents of?-sheet and irregular coil increased.The increasing?-sheet and irregular coil content could increase the flexibility of protein molecules,thereby generating a conformation that is more suitable for interface adsorption,which could improve foaming.(3)Compared with JSPI,the fluorescence intensity was increased after 600W,60?and 60?+600 W treated,and had different degrees of red-shift.(4)Compared with JSPI,the H₀ increased significantly after 600 W,60?and60?+600 W treated,and the highest H₀ value appeared after 60?+600 W treated.The increase of surface hydrophobicity could reduce the protein's adsorption barriers to the water-air interface,and expose more hydrophobic groups,which could enhance the adsorption to the interface and improve foaming.(5)Compared with JSPI,the size was reduced after 600 W treated,and increased by 60?,60?+600 W treated.(6)Compared with JSPI,the negative potential enhanced after 600 W ultrasound treated,and decreased after 60?and 60?+600 W treated.The value of electric potential was related to the stability of the solution system.The decreasing of surface charge would reduce the electrostatic barrier and enhance the adsorption of protein on the interface,which was helpful to improve the foaming property,but it could lead to instability of the protein solution system and affect the stability of protein foam.(7)The SH contents after 600 W,60?,60?+600W treated increased(p<0.05).On this basis,correlation analysis was used to explore the relationship between structural changes and the foam ability of JSPI,the foaming property was positively correlated with H₀,SH content,?-folding and irregular crimp content,and negatively correlated with potential absolute value and particle size.Among them,it was closely related to surface hydrophobicity(H₀)and structure looseness.