The structure and function of β-glucan in barley have been reported to change significantly after fermentation with Lactobacillus plantarum dy-1, but little information is available to explain this phenomenon. The Carbohydrate-Active enZYmes database revealed that L. plantarum dy-1 encodes 158 types of glycosidic hydrolases, among which we have identified an endoglucanase. Therefore, we conducted a heterologous expression of this endoglucanase gene, namely Lpeg14265. The pH of 6.0 and the temperature of 60 °C were optimal for LPEG14265. The physiological activities of β-glucan, such as the capacity to adsorb cholesterol or to block α-amylase and α-glucosidase, increased as a result of enzymatic hydrolysis of LPEG14265, which also caused a significant change in the microstructure of barley bran. Based on these findings, it was concluded that barley bran, a by-product of agriculture, may be processed with LPEG14265 to reveal its potential value, which could have applications in the brewing and feed industries, among others.