This study reports the biovalorization of the two agri-food by-products (pork lard and freeze-dried okara) through solid-state fermentation using a monoculture of Yarrowia lipolytica or a co-culture of Y. lipolytica and Lactobacillus paracasei, for developing a valuable fermented product with antioxidant and antimicrobial activity. First, some yeast strains were selected based on their properties to produce enzymes (protease and lipase) by cultivation on 5% (w/v) pork lard or 2% (w/v) freeze-dried okara. Two selected strains, Y. lipolytica MIUG D5 and Y. lipolytica ATCC 18942, were further used for the fermentation alone or in a co-culture with L. paracasei MIUG BL2. The Plackett–Burman experimental design was used to establish the effects of the fermentation parameters in order to obtain a fermented product with improved antioxidant and antimicrobial activities. As the Plackett–Burman experimental design are independent variables, the concentrations of the freeze-dried okara, pork lard, glycerol, inoculums type, inoculum concentration, and the fermentation time were analyzed. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging potential and the antimicrobial activity against aerobic spore-forming microorganisms were assessed as responses. For the fermented products, an antioxidant potential between 6.77–17.78 mM TE/g was obtained while the antimicrobial activity against Aspergillus niger ranged from 24 to 64%. Based on the statistical analysis, the time of the yeast fermentation and the concentration of pork lard were selected as variables with the influence on the SSF fermentation process and the functional properties of the fermented product. In the general context of a circular economy, the results demonstrate the possibility of bio-transforming the freeze-dried okara and the pork lard using Y. lipolytica as a valuable workhorse for the lactic acid bacteria (LAB) metabolism and postbiotics production into a fermented product, which is recommended for use as a food and feed ingredient with biotic properties.
Experimental design and solid state fermentation: A holistic approach to improve cultural medium for the production of fungal secondary metabolites
