The Study Of Preparation Of Walnut Butter And Its Hydro Mechanical Characteristics

Xinjiang is one of the largest walnut producing provinces in China with abundant resources. However, the currently available limited proceeding technologies caused huge waste of resources and lack of walnut by-products. Based on the nutrition, medical usage, and present proceeding situation of walnut products in Xinjiang, this study took the walnut as raw materials, investigated the peeling process, preparing butter, nutrition contents, and stability of processes of walnut products in order to make full use and increase the added value of walnut product processing in Xinjiang. The results of the study are as follows:(1) Based on the comparative analysis of alkali peeling, soak-baked peeling, boiled peeling and liquid nitrogen peeling processes, the soak-baked peeling was selected as the optimal method for skin peeling of walnut meat. According to the response surface design, the best parameters of walnut meat skin peeling process were confirmed as the followings: soaking time is 11 min, baking temperature is 60?, baking time is 26 min. The peeling rate reached to 92.99% under these optimum process parameters.(2) Based on single factor effect experiment results of the water proportion, pure walnut sauce and sucrose fatty acid ester and xanthan gum on the walnut butter's stability, slurry mixing speed of 500 r/min and 4 minutes mixing time during the adding water, slurry mixing speed of 400 r/min and 4 minutes mixing time during the adding sucrose fatty acid ester and xanthan gum were selected. According to the response surface design, the best parameters of preparing stable walnut butter process were confirmed as the followings: the proportion of pure walnut sauce and water is 1:0.8, amount of sucrose fatty acid ester is 0.20%, amount of xanthan gum is 0.20%. The centrifugal sedimentation rate of 2.93% and stability factor of 98.25% walnut butter have reached under this optimum condition.(3) Based on the study of walnut butter's fluid type, it was confirmed that the walnut butter is pseudoplastic fluid and it appeared as pseudoplastic flow and thixotropy. By comparing the hydrodynamical characteristics of walnut butter, peanut butter and sesame butter, it was found out that in a fixed shear rate, the viscosity of all butters decrease with increase of temperature, and the viscosity of walnut butter is the lowest; in a fixed temperature, the shear stress of all butters increase with the increase of shear rate and their viscosity gradually decreased with the increase of shear rate. Based on the analysis of hydrodynamical characteristics, it was concluded that the order of the stability of these three kinds of butters, from best to worst is: walnut butter>sesame butter>peanut butter.(4) Based on the result of physico-chemical properties analysis on walnut butter, peanut butter and sesame butter, it was found out that the contents of protein, fat and 17 kinds of amino acid in walnut butter is higher than that of peanut butter and sesame butter. The microbial index and heavy metals index of walnut butter reached the industrial standards and much lower than the safety limit. Applying fuzzy mathematical method of sensory evaluation, the overall quality of these three kinds of butters, from best to worst, is confirmed as: walnut butter>peanut butter>sesame butter.The results of stability, hydromechanical properties and quality analysis of walnut butter show that the walnut butter has as good as product quality comparing to similar products on the market.