3.5 Microstructure analysis
In conclusion, among FLWB, CLA-WB were closer to the quality of commercial walnut butter. Therefore, the walnut butter with CLA addition was selected for further microstructural analysis. Image analysis provided information on the pixel organization of the different regions of the samples (Backes and Bruno, 2013). The walnut butter samples prepared with CLA were further analyzed using optical microscopy Fig. 7 showed the optical microstructure of walnut butter prepared by CLA and commercially available walnut butter. The results indicated that all walnut butter showed a porous matrix structure encasing the oil droplets. Proteins were adsorbed on the surface of the oil droplets while some of them formed aggregates between the oil droplets and the proteins. The aggregation of SS1 and SS2 was higher while the oil droplet size of SS1 was more homogeneous. Emulsion droplets with smaller average particle size may result in a larger total interfacial area of emulsion droplets and more adsorbed proteins (Farshchi et al., 2013), thus preventing aggregation between oil droplets. The formation of high oil content and low interfacial adsorbed proteins may result in unstable oil droplets that tended to form aggregated large oil droplets (Fig. 7F). Due to protein and oil droplet interactions, FLWB had a particle size and emulsion structure, which was similar to that of commercial products (Xu et al., 2020). The results showed that the quality of CLA-WB was closer to that of commercial walnut butter. Further microscopic results showed that the particle size, distribution and aggregation of CLA-6.5 were closer to the microstructure of commercial walnut butter.
Conclusion
In this study, different types and additions of FL (MCT, DG, CLA) were selected to prepare walnut butter. By measuring the physicochemical properties of the three groups of samples, it was obtained that when the addition ratio of CLA and defatted walnut meal was 6.5:3.5, the prepared walnut butter had the similar properties to commercial walnut butter. FLWB with similar processing physical properties and microscopic morphology as commercial walnut butter could be obtained after vibratory ball mill grinding. In addition, FLWB contained 65% CLA had higher bioactive functions. This study provided a new way for the comprehensive development and utilization of defatted walnut meal, which could help the development of functional lipids walnut butter. Vibratory ball milling technology was used to grind walnut butter in a single process to streamline the milling process. which provided a new method for the preparation of functional lipids walnut butter.