Exploring the potential of soapstock over a glycerol in vitamin K2 production by Bacillus subtilis natto: a comparative analysis

Abstract

Background: Vitamin K2 is an essential nutrient for blood coagulation and cardiovascular health and mainly produced by bacteria strain like B. subtilis. researchers have explored producing strain improvement, cultivation mode, environmental optimization, increased secretion, and using cheaper carbon and nitrogen sources in order to increase vitamin K2 productivity. This study examines the impact of varioius concentration of soapstock, which is a by-product of vegetable oil refining, as an alternative carbon source with lower pirce, in the fermentation medium instead of glycerol on the microbial synthesis of vitamin K2 using B. subtilis natto ATCC 23857.

Results: The results demonstrate that when the glycerol in fermentation medium was substituted with soapstock, by 75% concentartion, the fermentation process produced a yield of 158.16 mg/L of vitamin K2 after 72 h; This was 3.8 times more than the control medium containing glycerol. When the entire culture medium was replaced with wastewater, the vitamin K2 concentration reached 21.18 mg/L, 52% of the control medium's concentration. If the carbon sources in the fermentation medium consisted of 20% soapstock and 47.4 g/L glycerol (maintaining the same final glycerol concentration as the control medium), the vitamin K2 concentration reached 35.7 mg/L or 85.8% of the control medium. The analysis of soapstock fermentation medium characteristics reveals that after fermentation with B. subtilis, the COD of soapstock fermentation medium was dramatically reduced from 259,500 mg/L to 57,830 mg/L.

Conclusions: Using soapstock as an alternative carbon source for fermentation did not negatively impact the bioprocess and increased vitamin K2 production. Therefore, this research introduces an alternative carbon resource for vitamin K2 production and paves the way for the biorefinement of soapstock.

Keywords: Bacillus subtilis natto; Carbon source; Crude glycerol; Soapsotck; Vitamin K2.

Fig. 1

Comparison of kinetics of biomass, glycerol consumption, and vitamin K2 production in control medium and soapstock fermentation medium. a Dry weight, b Residual glycerol concentration, and c Vitamin K2 concentration

Fig. 2

Comparison of the kinetics of biomass, glycerol consumption, and vitamin K2 production in batches 10% + Gly, 20% + Gly, and 30% + Gly. a Dry weight. b Glycerol consumption. c Kinetics of biomass, glycerol concentration and vitamin K2 concentration in batch 20% + Gly

Fig. 3

Kinetics of biomass, glycerol consumption, and vitamin K2 production in different soapstock concentrations. a Kinetics of biomass, glycerol consumption with 10% (v/v) soapstock, b Kinetics of biomass, glycerol consumption and vitamin K2 concentration with (v/v) 20% soapstock, c Kinetics of biomass, glycerol consumption with (v/v) 30% soapstock, d Kinetics of biomass, glycerol consumption and vitamin K2 concentration with (v/v) 50% soapstock, e Kinetics of biomass, glycerol consumption and vitamin K2 concentration with (v/v) 75% soapstock, f Kinetics of biomass, glycerol consumption and vitamin K2 concentration with (v/v) 100% soapstock