Changes in nutritional composition and bioactivity of fermented cereals under Pleurotus ostreatus solid-state fermentation.

INTRODUCTION: The edible and medicinal mushroom Pleurotus ostreatus is increasingly recognized as a functional ingredient, not only as a source of fungal biomass but also as a biological fermenter capable of transforming cereal substrates. This study evaluated time-dependent changes in nutritional composition and bioactivity during P. ostreatus solid-state fermentation of cereals. METHODS: Wheat and rice were fermented with P. ostreatus for 42 days at 25 °C. Antioxidant activity, enzyme activities, total phenolic content (TPC), proximate composition, and amino acid composition were evaluated using standard analytical methods. Antioxidant activity, enzyme activities, and TPC were determined for both substrates. Based on the stepwise evaluation of cereal substrates, proximate composition and amino acid analyses were subsequently performed for wheat. RESULTS: Visual assessment showed that both substrates were fully colonized by day 21. Bioactive compounds and enzyme activities were monitored from days 21 to 42. Enzyme activities showed distinct substrate- and time-dependent patterns: in wheat, esterase and laccase activities peaked on day 35 and peroxidase activity was numerically highest on day 42 but did not differ significantly from day 35, whereas in rice, esterase activity was highest on day 42, and laccase activity on day 28, and peroxidase activity on day 21. Aryl-alcohol oxidase activity remained low in both substrates. TPC and DPPH radical scavenging activity increased during fermentation, with both reaching their highest values on day 28 in wheat. In rice, TPC was highest during the late fermentation stage (days 35-42), whereas DPPH radical scavenging activity peaked on day 35. In wheat, true protein content increased from 6.43 to 18.65 g/100 g DM during the fermentation period, accompanied by an increase in ash content and a gradual decrease in carbohydrate content, while fat content remained relatively stable. The amino acid profile also changed during fermentation, with significant increases in histidine, glutamic acid, and lysine. True protein and total amino acid content continued to increase until day 42, day 28 provided the most balanced essential amino acid profile. CONCLUSION: The optimal fermentation period depends on the desired characteristics of the final product and highlight the importance of monitoring fermentation dynamics to optimize cereal solid-state fermentation.