Abstract
This study aimed to improve the nutritional value of soybean meal (SBM) by solid-state fermentation (SSF) using Bacillus subtilis natto (B. s. natto) to overcome the limitations of SBM usage in aquafeed. The response surface methodology (RSM) was employed to explore the relationships of fermentation conditions, such as temperature, time, water-substrate ratio, and layer thickness, on the degree of protein hydrolysis (DH) and the crude protein (CP) content. The optimum conditions for achieving the higher DH (15.96%) and CP (55.76%) were 43.82 °C, 62.32 h, 1.08 of water-substrate ratio, and a layer thickness of 2.02 cm. CP and DH in the fermented soybean meal (FSM) increased by 9.8% and 177.1%, respectively, and crude fiber decreased by 14.1% compared to SBM. The protein dispersibility index (PDI) decreased by 29.8%, while KOH protein solubility (KPS) was significantly increased by 17.4%. Flavonoids and total phenolic acid content in FSM were increased by 231.0% and 309.4%, respectively. Neutral protease activity (NPA) also reached a high level (1723.6 U g−1). Total essential amino acids (EAA) in FSM increased by 12.2%, higher than the 10.8% increase of total non-essential amino acids (NEAA), while the total free amino acids content was 12.76 times higher than that of SBM. Major anti-nutritional factors in SBM were significantly reduced during the process, and almost all SBM protein macromolecules were decomposed. Together with the cost-effectiveness of SSF, B. s. natto-fermented SBM products have great potential to improve the plant composition and replace high-cost ingredients in aquafeed, contributing to food security and environmental sustainability.
Highlights
For over 60 years, the growth rate of the global apparent food fish consumption has exceeded that of the world population, and it is estimated that about 59% of fish available for human consumption will come from aquaculture production by 2030, up from52% in 2018 [1]
Considering the single factor in the fermentation process, the following optimum conditions were achieved for the establishment of the interactive effects, which could be useful when the target is only a single factor to maximize degree of protein hydrolysis (DH) (%) and could be used to pilot optimum fermentation conditions using other related microbial species
In this work, 1010 colony forming units (CFU)/kg B. s. natto was selected as the initial optimal amount of inoculum for the following response surface methodology (RSM) experiments
Summary
For over 60 years, the growth rate of the global apparent food fish consumption has exceeded that of the world population, and it is estimated that about 59% of fish available for human consumption will come from aquaculture production by 2030, up from52% in 2018 [1]. Fermentation 2021, 7, 306 especially for species with high nutritional needs (carnivores), due to the high quality and digestibility of its proteins, its balanced amino acid composition, and the quasi-inexistence of anti-nutritional factors (ANFs) [2,3,4]. The replacement of fishmeal in aquaculture is a major issue related to economic and environmental sustainability [9,10,11]. Used as one of the best alternatives to fishmeal, soybean meal (SBM) has partially or completely replaced fishmeal in animal feed [12,13] but shows imbalanced amino acid composition, high level of carbohydrate content, and potential ANFs, which may lead to adverse effects on digestion, nutrient utilization, and intestinal health [14,15,16,17]
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