Preparation of low-fat and shape-preserving walnut via combined carbon dioxide osmotic treatment and subcritical fluid defatting

A sequential process, CO2 osmotic treatment combined with subcritical fluid defatting was developed to prepare low-fat walnut kernel preserving shape integrity. The influence of operating parameters involving osmotic pressure and subcritical butane defatting repeats on the defatting effect has been investigated. CO2 osmotic at 25 MPa resulted in defatting rate as 37.12% and minimum perfect kernel rate (81.48%). Increase of defatting repeats from one to three times led to exploding quantities of defatting rate (from 9.98% to 40.61%) but no significant varies of perfect kernel rate (p >0.5). With the increase of defatting rate, the amount of oil bodies in walnut cells decreased, and defatting rate presented negative correlated with hardness and chewiness of products. Hexanal, nonanal and heptaldehyde were the predominant volatile compounds. After defatting, they may be removed as accompanying components and showed a slight downward trend. However, results of electronic nose revealed that there was no significant difference among flavor of walnut with different defatting rate (p >0.5). Slight defatting caused significant variations in the taste of walnuts. As the defatting rate exceeded 18.65%, products expressed similar taste. Overall, coupling CO2 osmotic treatment with subcritical fluid defatting proved to be great potential for application in shape-preserving defatting.