Enhanced bioconversion of kitchen food waste into aquaculture feed using a mixed culture of Bacillus licheniformis and Yarrowia lipolytica

Abstract

The increasing global population and urbanization have led to a rise in kitchen food waste (KW), posing significant environmental and economic challenges. Converting KW into fish feed offers a sustainable solution for managing KW. This study investigates the conversion of KW to aquatic feed via fermentation, and the innovative use of fermented kitchen waste (FKW) as an alternative protein source in aquaculture feed. Strains L58 and O57, identified as Bacillus licheniformis and Yarrowia lipolytica, were initially screened for high enzymatic activities and salt tolerance. A mixed-strain fermentation approach was employed, with process parameters optimized through central composite designs to maximize soluble protein yield. Fermentation significantly increased the contents of soluble protein, crude protein, and crude fat while reducing total carbohydrates and crude fiber. The total amino acid content increased by 45.5%, with significant gains in 19 amino acids. Feeding trials with juvenile yellow catfish demonstrated that replacing 15-30% of fish meal with FKW significantly improved growth performance, feed utilization, and enhanced the crude protein content in fish flesh. These findings indicate that co-fermenting KW with the two strains efficiently produces high-protein aquaculture feed, offering a sustainable alternative protein source that reduces reliance on fish meal and aids in waste management.

Keywords: Bacillus licheniformis; Yarrowia lipolytica; Fermented feed; Kitchen food waste; Mixed-strain fermentation; Waste management; Yellow catfish (Pelteobagrus fulvidraco).

Fig. 1

Screening of strains producing high enzyme activity: (a) alpha-amylase activity, (b) protease activity, (c) lipase activity. Different lowercase and uppercase letters indicate statistical significance in enzyme activity among bacteria and yeast strains, respectively (p < 0.05).

Fig. 2

Phylogenetic tree, (a) based on rpoB sequences of strain L58, (b) based on 26 S rDNA sequences of strain O57.

Fig. 3

Effect of the fermentation conditions on soluble protein yield. (a) ratio of mixed strains, (b) Inoculation amount, (c) temperature, (d) fermentation time. Data represent mean ± SE (n = 3) and different lowercase letters indicate statistical significance (p < 0.05).

Fig. 4

Contour plots of the interaction effects of; (a) inoculation amount (B) and temperature (C), (b) temperature (C) and fermentation time (D).

Fig. 5

Profile of fermentation process. (a) Soluble protein, (b) viable count. Different lowercase letters indicate statistical significance (p < 0.05).

Fig. 6

Quadratic curve fitting of the weight gain rate as a function of FKW level.