Study Of Influence Factors Of Walnut Oil By Aqueous Extraction Procession

Walnut(Juglans regia L.)is a crop with high economic interest in the food industry.The oil content of walnut kernels is over 65%.Compared with other vegetable oils,walnut oil contains a higher content of unsaturated fatty acids,i.e.linoleic acid,oleic acid and linolenic acid.Walnut kernels contain about 15% walnut protein,which is one of the high quality food sources of plant protein.Among walnut oil extraction methods,the aqueous extraction processing(AEP)takes advantages of low cost,simple operation and eco-friendliness.However,oil-in-water(O/W)emulsion is produced in this process and noticeably affects the free oil extraction efficiency.In this study,walnut oil was used as raw material to extract walnut oil by surfactant with salt-aided aqueous extraction(SSAE),aiming to reduce the emulsion produced during the extraction process and increasing the oil yield;To analyze the physical and chemical indicators,fatty acids and oxidative stability of walnut oil obtained by SSAE method;The walnut proteins by alkaline extraction method were obtained and the structural properties of proteins were investigated.Comparison of the microstructure of the residue after different extraction methods by transmission electron microscopy(TEM),and the mechanism of demulsification mechanism was explored.The main conclusions are as follows:(1)The walnut oil was extracted by the AEP,and two different extraction media were selected and aided with different surfactants.The results showed that the highest oil yield of91.2% was obtained when Span 20(1.7 g/100 g)associated with a 1.2 mol/L sodium chloride-aided walnut extraction system at a liquid-to-material ratio of 5:1 at 85 ℃ for 60 min.Compared with the oil yield without the surfactant system(55.3%),it significantly increased the oil yield.(2)Study on the effects of different extraction media on walnut oil and walnut protein.The results showed that compared with the cold pressing method,the physicochemical properties of the walnut oil obtained by the AEP,salt-aided aqueous extraction(SAAE)and SSAE were slightly different but both were conformed the national standards;the fatty acid composition of the walnut oil extracted by the three methods(AEP,SAAE,SSAE)is basic agreement,and the unsaturated fatty acid content is more than 92%,indicating that the addition of surfactant has no significant effect on the fatty acid content of walnut oil;Different extraction methods have great influences on the oxidation stability of walnut oil.The oxidative stability of walnut oil extracted by four methods is: cold pressing method>AEP>SSAE>SAAE;the walnut protein extracted by SSAE method is compared with the original walnut protein.There was no significant change in the secondary structure;the molecular weight of walnut protein was mainly distributed in the range of 35-39 kDa,21-27 kDa,and no significant difference in the walnut protein bands was observed after different extraction methods.(3)The mechanism of extracting walnut oil by SSAE method was investigated.The microstructure of walnut residue was observed by TEM and a series of model emulsions were prepared to simulate the emulsification process and their particle size of the emulsion was determined.The strong demulsification effects by Span 20 may be ascribed to higher surface activity of Span20 than protein.In the competitive adsorption process,the Span 20 displaces protein and ultimately dominates at the O/W interface,thereby causing emulsion instability and easy destruction by centrifugation.