Introduction and methods
Nowadays, the aquaculture sector faces the challenge of finding sustainable alternatives ingredients in order to replace fishmeal as the main protein source in aquafeeds. In this context, previous studies have demonstrated that both spontaneous and bacterial-assisted fermentation of diverse raw materials can enhance their nutritional value. Notably, fermentation processes have been shown to increase crude protein content and improve amino acid profiles. Additionally, the fermentation of cereals and legumes promotes the bioconversion of complex carbohydrates, thereby increasing their digestibility . Consequently, the development of sustainable fishmeal substitutes necessitates a through evaluation of the effects of novel protein-rich ingredients on Penaeus vannamei growth performance and nutrient digestibility.
To address this, various animal- and plant-derived by-products were subjected to spontaneous fermentation at 22 °C for 7 days. Crude protein content was subsequently analyzed to identify substrates exhibiting the greatest increases. Selected by-products were then further processed through three independent assisted-fermentation trials: using Bacillus spp., Streptococcus spp., and a mixed culture of both genera. Finally, the complete amino acid profile of each by-product subjected to the three independent bacterial-assisted fermentation treatments was determined. Those materials exhibiting increased levels of lysine, methionine, and arginine were identified as promising ingredients for feed formulation.
Results and discussion
The crude protein content of all tested substrates increased after fermentation, regardless of the treatment applied, confirming the general effectiveness of microbial processes in enhancing protein concentration (Table 1). Nevertheless, bacterial-assisted fermentation proved more effective than the spontaneous process across all substrates, showing consistent results with previous works .
Bacillus spp. generally yielded the highest CP increases in soybean meal, degreased canola, flax sunflower seeds and brewer's spent grain, likely due to its ability to release proteases and peptide enzymes that allow a better degradation of the substrate . On the other hand, Streptococcus spp. showed substrate-specific advantages, particularly in degreased cameline . Last, the combined inoculum demonstrated a clear synergistic effect only in Ulva laciniulata, suggesting that microbial interactions depend strongly on substrate composition and biochemical accessibility .
Table 1.Crude protein expressed as dry matter percentage (CP (dm%)) of the different tested materials before and after the fermentation processes.
CP (%) Before fermentation
CP (%) After Fermentation
Spontaneous
Bacillus spp
Streptococcus spp
Mix B+S
Ulva lacinulata
20.59±0,001
21.70±0.320
29.93±0.970
30.18 ±0.480
36.41±0.630
Soybean meal
50.37±0.001
53.81±0.620
56.67±1.550
56.64 ±0.860
56.09±1.810
Degreased cameline
38.20±0.001
40.54 ±0.230
40.90 ±1.660
41.90 ±0.860
40.90 ±1.810
Degreased canola
39.95±0.001
42.80 ±0.140
47.40 ±0.520
46.40 ±0.700
46.77 ±0.830
Flax
21.51±0.001
24.09 ±0.260
25.34 ±0.090
24.13 ±0.001
23.11 ±0.220
Sunflower seeds
20.63±0,001
21.26 ±0.630
21.71 ±1.030
19.52 ±0.550
18.46 ±1.630
Brewer's spent grain
27.94 ±0.001
29.01 ±0,210
40.38 ±1.820
40.22 ±3,060
35.64 ±9.370
Overall, these findings reinforce the importance of selecting appropriate microbial strains tailored to each substrate to optimize protein enrichment. Furthermore, additional research is required to assess the digestibility of the selected by-products, with the aim of formulating alternative diets and subsequently conducting in vivo growth trials using Penaeus vannamei specimens.
Acknowledgment
This abstract is part of the "ZeroFloc" R&D&I project (PID2023-149570OB-I00), funded by MICIU/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. M. Querol-Edo holds a predoctoral FPU contract (FPU24/00525) funded by the Ministry Science, Innovation and Universities.
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