This research aimed to evaluate in vitro organic matter digestibility, fermentation characteristics and methane production of fruit and vegetable discards processed by solid state fermentation (SSF) by Rhizopus sp. Mixtures were composed of approximately 28% citric fruits, 35% other fruits and 37% vegetables. Fruit and vegetables were processed and fermented to obtain a stabilized product. Nutritional characterization and in vitro ruminal fermentation tests were performed to determine the effect of fungal bioconversion on digestibility, end products and gas production kinetics. Results indicate that SSF reduced organic matter and reducing sugars, while it increased crude protein and neutral detergent fiber, acid detergent fiber and neutral detergent insoluble protein. The in vitro gas production showed that SSF led to a reduction of the organic matter digestibility (p < 0.001), short chain fatty acids (SCFA; p = 0.003) and CH₄ (p = 0.002). SSF reduced the gas production from the insoluble fraction (p = 0.001), without modifying the production rate (p = 0.676) or the lag time (p = 0.574). Regarding SCFA profile, SSF increased acetic (p = 0.020) and decreased propionic (p = 0.004) and butyric (p = 0.006) acids proportions, increasing acetic to propionic (p = 0.008) and acetic plus butyric to propionic (p = 0.011) ratios. SSF succeeded in obtaining a stabilized material enriched in protein, but at the expense of a reduction of protein availability and organic matter digestibility. These changes should be considered before including them in a ruminant’s rations.

Non-alcoholic fatty liver disease (NAFLD) is considered the most common chronic liver alteration whose prevalence is increasing in Western countries. Microalgae and macroalgae have attracted great interest due to the high content in bioactive compounds with beneficial effects on health. The aim of the present study is to assess the potential interest of extracts rich in proteins obtained from the microalgae Chlorella vulgaris and Nannochloropsis gaditana and the macroalga Gracilaria vermiculophylla in the prevention of lipid accumulation in AML-12 hepatocytes. Toxicity was not observed at any of the tested doses. Both microalgae and the macroalga were effective in preventing triglyceride accumulation, with Nannochloropsis gaditana being the most effective one. Although the three algae extracts were able to increase different catabolic pathways involved in triglyceride metabolism, the mechanisms underlying the anti-steatotic effect were different in each algae extract. In conclusion, the present study demonstrates that Chlorella vulgaris, Nannochloropsis gaditana and Gracilaria vermiculophylla extracts are able to partially prevent the accumulation of triglycerides induced by palmitic acid in cultured hepatocytes, a model used to mimic the steatosis induced in liver by dietary patterns rich in saturated fat.

Microalgae are among the most suitable sources of new protein ingredients and bioactive compounds, although their cost-effective production still remains a developmental bottleneck. Heterotrophic growth has advantages, such as higher productivity and non-dependence on light and CO₂, but it has not yet been fully implemented. The aim of this study was to increase the biomass and protein of Chlorella protothecoides in heterotrophic conditions using expired fruit and vegetable juices (FVJ) and to compare the results to those obtained using a modified Bristol (MB) medium. The initial amounts of sugars (15 g L⁻¹) and yeast extract (8 g L⁻¹) led to the highest protein production (43%) and protein yield (5.2 g L⁻¹) in trials using 1 L bottles. Bioreactor trials using FVJ resulted in a similar biomass productivity (2.94 g L⁻¹ d⁻¹) compared to MB (3.04 g L⁻¹ d⁻¹) and in enhanced polyunsaturated fatty acid content; nonetheless, a lower amount of essential amino acids (EAA) was obtained. Biomass was further processed by ultra-high-pressure homogenisation for protein concentration and residual pellet production. The protein extracts showed significant increases in EAA (11.8% and 26% increase in MB and FVJ, respectively). Residual biomass showed potential as a source of lutein and antimicrobial compounds. The results indicate that FVJ is a promising source of nutrients for the heterotrophic production of C. protothecoides, and that the extracts obtained present nutritional profiles and bioactivities of potential interest.