Valorization of shalgam juice plant waste for the production of carotenoids by Rhodotorula glutinis

Abstract

Food waste is an emerging global problem that should not be underestimated. One of the most abundant wastes in Türkiye and neighbour countries is the waste of shalgam juice plants (WSJP). In this study, WSJP was used as a growth medium for Rhodotorula glutinis. The effects of initial medium pH (3.4-5.4), carbon (0-60 g/L glycerol) and nitrogen sources (0-1 g/L urea) were investigated on biomass, medium pH, reducing sugar concentration, total lipid and carotenoid contents, as well as carotenoid composition (torulene, torularhodin, β-carotene). When crude waste extract (no additional nutrient) was used as growth medium (initial medium pH 3.4, 6.14 g/L sugar), biomass was relatively low (1.47±0.055 g/L), due to acidic pH and insufficient nutrients. However, these stress conditions increased the production of total lipid and carotenoid contents by R. glutinis. The highest lipid and carotenoid contents were obtained as 0.14±0.0004 g/g dry cell weight (dcw) and 1221.57±0.59 µg/g dcw, respectively, under these circumstances. As additional stress factor fermentation medium -crude WSJP extract- was illuminated for 72 h. This increased lipid content by 1.7-fold, while showing low impact on carotenoid content. Interestingly, illumination changed the carotenoid composition by decreasing torulene and β-carotene percentages, but increasing torularhodin percentage. On the other hand, tuning the initial pH to an ambient value (5.4) and the addition of carbon and nitrogen sources stimulated cell growth (4.67±0.07 g/L). This study presents the first time use of WSJP extract as a growth medium, without any additional nutrition, moreover, the simultaneous production of high-value added carotenoids.