Microstructure observation of multilayers separated from wheat bran

Abstract

In order to understand more clearly the morphology of the structural layers of the soft and hard wheat bran to understand the effect of mechanical force on the wheat grain, we observed the microstructure of each layer of the wheat bran from soft and hard mature wheat. Based on the differences in mechanical properties and water permeability of each wheat bran layer, the mature wheat grains were alternately treated under cold and heat conditions and separated by manual dissection. The microstructure of each layer of wheat bran from soft and hard mature wheat was determined by optical and fluorescence microscopy. Seven different structure layers were observed by optical microscopy, named them as epidermis, epicarp, cross cells, tube cells, testa, nucellar layer, and aleurone layer. All the layers of the outer bran of wheat grains were separated, except for the tube cells layer. The autofluorescence imagings of five layers were obtained. It was found that the morphology of the structural layers of the soft and hard wheat bran did not differ much, except for the aleurone layer. The aleurone layer of soft wheat bran was significantly different from that of the hard wheat bran, which is fuller and denser compared to soft wheat. In this study, more aleurone grains were lost in the aleurone layer obtained by the outside-in peeling method. The mastery of the morphology of each structural layer of the bran helps us to quickly quantify the degree of peeling of wheat milling, and to make immediate adjustments to the process. At the same time, we understand that the contents of the aleurone cells have different binding strengths with the nucellar layer and the starchy endosperm. The paper is instructive to deep investigation of wheat milling mechanism and product process refinement.