Valorization of tomato waste proteins through production of antioxidant and antibacterial hydrolysates by proteolytic Bacillus subtilis: optimization of fermentation conditions

In this study, protein-rich waste of tomato processing industries was fermented by Bacillus subtilis A14h to produce hydrolysates with antioxidant and antibacterial activities. The effects of different levels of initial pH, incubation temperature, fermentation time, protein concentration and inoculum size on proteolytic activity, release of amino acids and peptides, antioxidant and antibacterial activities of hydrolysates were evaluated and optimized by using response surface methodology (RSM). Results showed that all the evaluated variables significantly influenced the hydrolysis and bioactivities of hydrolysates in polynomial models. Hydrolysates showed remarkable 2, 2'-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity (up to 70 %), ferric ion reducing power, and inhibitory activity against B. cereus (up to 69.8 %) and E. coli (up to 29.8 %). Overall, good correlation between the concentration of amino acids and peptides, and antioxidant as well as antibacterial activities (in particular for B. cereus inhibition activity) was observed. Finally, optimum conditions for fermentative conversion of tomato waste proteins to antioxidant and antibacterial hydrolysates were established. Results of this study showed that tomato waste protein can be valorized to produce antioxidant and antibacterial hydrolysates in a fermentative system using B. subtilis A14h.