Introduction
Spontaneous fermentation of different food industry by-products has been proved to yield a product with enhanced nutritional value. What is more, this process is known to increase some substrate’s protein and enrich their amino acids profile. Furthermore, it has also been confirmed that fermentation of cereals and legumes bioconverts their carbohydrates, making them more digestible (Adebo et al., 2022). Therefore, due to the current pursuit of a truly sustainable substitute for fishmeal in aquaculture emphasizes the need to find potential raw materials with high-nutritional value for aquafeed production.
Materials and methods
Different by-products from animal and vegetal origin were prepared for spontaneous fermentation and kept at 22ºC for 7 days. Samples of each fermented material were taken after 1 and 7 days of fermentation in 5 ml aliquots and preserved frozen for further chemical analysis. Then, a proximal nutritional composition analysis was performed on every sample to determine their crude protein level. On the other hand, a metagenomic analysis was performed by extracting bacterial DNA from the fermented samples. Last, a high-throughput sequencing of the 16S rRNA gene was conducted with an Ilumina MiSeq platform in order to analyze the bacterial diversity by using Claudio Braulio shini program.
Results and discussion
Most vegetal materials and yeasts increased their CP level after the spontaneous fermentation, whereas biofloc, all animal by-products and some cereals weren’t enhanced by the process (Table 1). Alpha diversity metrics showed a gradual decline of the microbial biodiversity during the 7 days of the fermentation. Furthermore, shifts in diversity were observed between the fermented and unfermented bacterial communities, underscoring the impact of fermentation. Beta diversity metrics also showed significant differences in the fermented microbial communities and confirmed a restructuring of the microbial profile from the fermented and unfermented samples over time (Figure 1). The taxonomic composition analysis, dynamic changes at phylum and genera level were observed throughout the fermentation process.
Although fermentation of vegetal materials has been previously proved to enhance their nutritional value by making them more protein-rich, some of the tested cereals (rice, wheat gluten, corn and pea meal) experienced a decrease in their CP levels probably due to bacterial difficulties when digesting complex carbohydrate molecules. As for animal by-products, all tested substances rotted and suffered a decrease on their CP after just 24 hours of fermentation, maybe because bacteria cannot feed on matrixes with scarce carbohydrates. On the other hand, fermentation did cause an exponential rise of most plants and yeasts protein content. However, some vegetal materials performed better than others by reaching higher protein levels after 7 days of fermentation (soybean meal,flax), while the increase of bacterial protein in other substances stabilized or stopped after 24 hours of fermentation (cameline, beetroot). For this reason, further research needs to be done to optimize spontaneous fermentation, as many authors claim that the addition of exogenous bacteria may boost the process and enrich the resultant products with probiotics (Rajesh et al., 2010). As for the intestinal microflora population shifts, it is possible that the blooming of some taxons can also trigger the decline of others due to unsustainable competence for the same resources. Consequently, additional inquiry is required to determine how different microbial species may affect each other.
Conclusion
Vegetal materials are more efficient at fermenting than other animal and biofloc by-products, yielding a product with enhanced protein content that can be used as a potential ingredient for aquafeeds. Nevertheless, further research needs to be done to optimize the fermentation process and test its potential to enhance alternative aquafeed ingredients.
Acknowledgments
This work was supported by I+D+i Research Project: “Pursuing the zero waste in Biofloc Technology to produce a sustainable and biosafe aquaculture product (ZeroFloc)” (PID2023-149570OB-I00). R. Olivares-Perona and I. Megder have a technician contract from ThinkInAzul programme funded by the Spanish Ministry of Science and Innovation with European Union NextGenerationEU funds (GVA-THINKINAZUL/2021/006).
References
Adebo, J. A., Njobeh, P. B., Gbashi, S., Oyedeji, A. B., Ogundele, O. M., Oyeyinka, S. A., & Adebo, O. A. (2022). Fermentation of Cereals and Legumes: Impact on Nutritional Constituents and Nutrient Bioavailability. In Fermentation (Vol. 8, Issue 2). MDPI. https://doi.org/10.3390/fermentation8020063
Rajesh, N., Imelda-Joseph, & Paul Raj, R. (2010). Value addition of vegetable wastes by solid-state fermentation using Aspergillus niger for use in aquafeed industry. Waste Management, 30(11), 2223–2227. https://doi.org/10.1016/J.WASMAN.2009.12.017