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Abstract
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.
Highlights
Okara is a food processing by-product derived from soybeans (Glycine max), being the solid residue that remains after filtering the water-soluble fraction during soymilk or soybean curd production [1]
Two strains, coded Y. lipolytica MIUG D5 and Y. lipolytica American Type Culture Collection (ATCC) 18942 were selected as potential producers of lipases and proteases (Table 1)
The aim of this study was to valorize some agri-food processing by-products such as okara [1] and pork lard [9] by applying an inexpensive and conventional biotechnological method [1], namely solid state fermentation (SSF) using a co-culture of Y. lipolytica and L. paracasei in order to obtain several functional fermented products that have been proposed for use in the food and feed industry [2,6]
Summary
Okara is a food processing by-product derived from soybeans (Glycine max), being the solid residue that remains after filtering the water-soluble fraction during soymilk or soybean curd (tofu) production [1]. About 1.2 kg of okara is obtained from every 1 kg of soybeans that are used in the tofu production [2]. Large amounts of okara are produced annually, especially in Asian countries with high soybean consumption. Even with the large volumes of okara generated by the food industry, most of it is discarded due to the okara’s high moisture content, which makes it very perishable [3,4]. This by-product is a rich source of high-quality proteins, carbohydrates, unsaturated lipids, and dietary fiber, and contains isoflavones, minerals, and oligosaccharides [4]. Its rate of reuse is still low and is intended almost exclusively for animal feed [2,6] or human food, with some limitations due to its oligosaccharide content, which produces flatulence and the disagreeable ‘fishy’ and ‘beany’ flavor, whereas the rest is discarded as industrial garbage [1]
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