Improving the Nutritional Profile of Intermediate Wheatgrass by Solid-State Fermentation with Aspergillus oryzae Strains

Aspergillus oryzae has been used to ferment various cereal grains throughout history, as seen in the examples of sake, soy sauce, and miso. It is known that this fermentation enhances the nutritional quality of the raw materials by breaking down complex molecules into simpler, more digestible forms and increasing the bioactive compounds. In this study, intermediate wheatgrass (IWG) was fermented with three different strains of A. oryzae suitable for making sake, soy sauce, and miso. Whole IWG flour was mixed with water (1:2 w/w), autoclaved at 121 °C for 20 min, cooled, mixed with A. oryzae spores, and fermented for seven days at 30 °C. Sugars, protein, amino acids, kojic acid, total phenolic content, total flavonoid content, and DPPH radical scavenging activity were measured. The protein content increased significantly (p < 0.05) from 18.0 g/100 g to over 30 g/100 g after seven days. Lysine showed a positive correlation with protein content across all three strains, with its ratio increasing as the protein content increased, while all other essential amino acids displayed a negative correlation and a decreasing ratio with the protein content. Autoclaving increased the verbascose content of IWG, and further increases were observed during the first two days of fermentation across all three strains, followed by a subsequent decline. Peak glucose content was observed on days 3~4 but also decreased in the subsequent days. Total phenolic content, total flavonoid content, kojic acid, and DPPH scavenging activity peaked around day 4~5 for all three strains, followed by a slight decrease in the subsequent days. The findings of this study highlight the potential of solid-state fermentation to improve the nutritional profile of IWG, emphasizing that the selection of A. oryzae strains and the fermentation duration can affect the fermentation outcome and nutritional enhancements.