Ultrasonic and enzymatic pretreatments of Monascus fermentation byproduct for a sustainable production of Bacillus subtilis

Abstract BACKGROUND Monascus fermentation byproduct (MFB) is a biowaste generated after food colorants are extracted. Using MFB to produce probiotics ( Bacillus subtilis ) is a sustainable way for the entire production to be used as food or animal feed additives. However, due to the rigidity of the Monascus mycelium cell wall, B. subtilis cannot sufficiently utilize the nutrients in MFB, leading to low biomass production efficiency. We studied the effects of ultrasonic treatment, papain, β‐glucanase, and chitosanase, and their combinations on improving the levels of soluble components from MFB. The effects of these treatments on mycelium cell walls were visualized using scanning electron microscopy, and their influence on B. subtilis production was analyzed. RESULTS Ultrasonic treatment increased the soluble components by 210 g kg −1 , including 50 g kg −1 protein and 120 g kg −1 carbohydrates. An enzyme mixture increased the soluble components by 160 g kg −1 , including 30 g kg −1 protein and 90 g kg −1 carbohydrates. The combination of the two methods achieved the highest increase of soluble components (up to 400 g kg −1 ) leading to a maximum B. subtilis production of 1 × 10 11 colony‐forming unit mL −1 . This yield was about 20 times greater than that using untreated MFB and about eight times greater than treatments using only ultrasonic or enzymatic methods. CONCLUSION The productivity of B. subtilis production using MFB as the sole medium can be greatly improved by ultrasound or enzymes, which cause the release of intercellular components or cell wall components. © 2020 Society of Chemical Industry