Effect of solid-state fermentation with Pleurotus ostreatus on the protein content and other nutritional components of de-seeded carob fruits

Abstract

Carob pulp is a currently underutilized by-product of locust bean gum production from carob pods. It is dense in several valuable nutritional components such as carbohydrates, dietary fiber, minerals and some bioactive substances but low in protein. One of the strategies to facilitate its valorization is suggested as enhancing its protein content. Therefore, solid-state fermentation (SSF) of carob pulp was investigated using the edible fungus species Pleurotus ostreatus. For this purpose, carob pulp was first soaked with water, then treated thermally at 121 °C and subsequently subjected to SSF. During the SSF period of 30 days, samples were drawn every 5 days and analyzed with respect to protein, reducing sugars (glucose and fructose) and dietary fiber contents as well as polyphenol content and antioxidative properties. SSF with Pleurotus ostreatus could be proven to triple the protein content as well as the total fiber content of carob pulp. An increase in protein content is likely connected to the production of fungal biomass. However, a decrease in the reduced sugar content as well as in the antioxidant properties was observed. Results confirmed that SSF using Pleurotus ostreatus could be applied to valorize the carob pulp by boosting its protein content, and thereby a contribution to the circular bioeconomy in food production could be suggested.