Studies on barley starchy endosperm cell wall degradation by Rhizopus VII

Starchy endosperm cell wall degradation by a fungal starter culture [Noots et al., Journal of Agricultural and Food Chemistry 49 (2001) 975-981] was studied using inoculated non-germinating barley subjected to conditions resembling those of a traditional malting process. The beta-glucanase and xylanase production by Rhizopus VII during processing was investigated and cell wall degradation was assessed by Calcofluor modification, friability, and beta-glucan content determinations. The level of enzymes produced increased progressively during the process step corresponding to germination in a regular malting process. As the majority of the modified, non-germinating barley kernels showed 90-100% modification, the cell wall degradation by the starter culture activity was rapid and largely homogeneous at the kernel level. No distinct pattern of cell wall degradation was identified in kernel longitudinal cross sections. Several lines of experimental evidence suggest that the invasion of the starter culture through the outer layers of the barley kernel is the rate-limiting step for endosperm cell wall degradation. (C) 2003 Published by Elsevier Science Ltd.