Application of a digital image procedure to evaluate microstructure of caseinate and soy protein acid gels

Acid gelation of proteins is commonly used in the food industry and it can be induced by the addition of glucono-δ-lactone (GDL). The aim of this work was to use textural analysis of images in order to assess possible changes in the microstructure of bovine sodium caseinate (NaCAS) and soy protein isolate (SPI) acid gels. The gelation rate of NaCAS related to the amount of GDL was evaluated. Also, the effect of the presence of NaCAS hydrolysates obtained at different hydrolysis times by the enzyme of Bacillus sp. P7 was studied. Finally, SPI acid gels were evaluated in the presence of whey soy protein isolate (WSP) in different ratios. The gel images were obtained by conventional optical microscopy and texture parameters were obtained by using specific programs which were developed in Python language. Shannon entropy, smoothness, mean normalized grey-level variance and uniformity were analyzed as estimators of the texture of the images obtained. Results obtained in the evaluated systems showed that these parameters were able to represent the structural changes in the gel network, as changes in size of pores or in degree of compactness. Also, these results were contrasted with rheological properties of the systems evaluated.

► We evaluate gel microstructure changes with an economical and sensitive technique. ► Pore diameters and the elasticity of gels depend on the rate of gelling process. ► Hydrolysate addition not significantly alter sodium caseinate gel microstructure. ► Whey soy protein addition results in soy protein isolate weaker gels.