While olive oil is an important food product in the Mediterranean Sea Basin, olive oil mill wastewater (OOMW) and olive pomace, which are by-products of olive oil, are released in excessive quantities. OMWW is an important source of environmental pollutants due to its slightly acidic pH, high contents of phenol and chemical oxygen demand (COD). To overcome this problem, it was aimed to investigate the potential use of OOMW as an alternative substrate for biomass production by filamentous fungi in this study. For the cultivation, three edible fungi (Aspergillus oryzae CBS 819.72, Neurospora intermedia CBS 131.92, and Rhizopus delemar CBS 145940) were tested. Among them, A. oryzae was found to be a promising fungus in biomass production containing 14.9% protein. The protein content of the biomass was improved to 44.9% (w/w) by adding a nitrogen source (sodium nitrate) and removing the suspended solids. Concomitantly, 35-44% of COD reduction was also obtained after the fungal cultivation. Thus, the potential use of olive oil mill wastewater for the cultivation of fungal biomass was determined and at the same time, its pre-treatment was provided. However, the content of the obtained fungal biomass should be determined and its usability as feed should be investigated.

Thin stillage holds promise as a substrate for cultivating filamentous fungi. The suspended solids content of thin stillage directly influences biomass production. However, little attention has been given to its effects on fungal cultivation and composition, which is the focus of the current study. Various thin stillage dilutions were used to cultivate Zygomycete and Ascomycetes. Biomass and nutrient uptake were monitored during the cultivation. The harvested biomass was analyzed to assess nutrient composition in relation to fish dietary requirements. Thin stillage diluted to 75 % significantly enhanced fungal biomass production, with increases of 160 %, 213 %, and 235 % for A. oryzae, R. delemar, and N. intermedia, respectively. The harvested fungal biomass boasted approximately 50 % protein content, constituting 45 % essential amino acids. These findings underscore the potential of cultivating fungi in diluted thin stillage to boost biomass production and its high-quality nutritional composition positions it as a valuable candidate for fish feed formulations.

A fungal biorefinery is presented to valorize food waste to fungal monofilaments with tunable properties for different textile applications. Rhizopus delemar is successfully grown on bread waste and the fibrous cell wall is isolated. A spinnable hydrogel is produced from cell wall by protonation of amino groups of chitosan followed by homogenization and concentration. Fungal hydrogel is wet spun to form fungal monofilaments which underwent post-treatments to tune the properties. The highest tensile strength of untreated monofilaments is 65 MPa (and 4% elongation at break). The overall highest tensile strength of 140.9 MPa, is achieved by water post-treatment. Moreover, post-treatment with 3% glycerol resulted in the highest elongation % at break, i.e., 14%. The uniformity of the monofilaments also increased after the post-treatments. The obtained monofilaments are compared with commercial fibers using Ashby's plots and potential applications are discussed. The wet spun monofilaments are located in the category of natural fibers in Ashby's plots. After water and glycerol treatments, the properties shifted toward metals and elastomers, respectively. The compatibility of the monofilaments with human skin cells is supported by a biocompatibility assay. These findings demonstrate fungal monofilaments with tunable properties fitting a wide range of sustainable textiles applications. 

The fungus Rhizopus delemar was grown on bread waste in a submerged cultivation process and wet-laid into films. Alkali or enzyme treatments were used to isolate the fungal cell wall. A heat treatment was also applied to deactivate biological activity of the fungus. Homogenization of fungal biomass was done by an iterative ultrafine grinding process. Finally, the biomass was cast into films by a wet-laid process. Ultrafine grinding resulted in densification of the films. Fungal films showed tensile strengths of up to 18.1 MPa, a Young's modulus of 2.3 GPa and a strain at break of 1.4%. Highest tensile strength was achieved using alkali treatment, with SEM analysis showing a dense and highly organized structure. In contrast, less organized structures were obtained using enzymatic or heat treatments. A cell viability assay and fluorescent staining confirmed the biocompatibility of the films. A promising route for food waste valorization to sustainable fungal wet-laid films was established. © 2022 The Authors

In this study, ethanol organosolv treatment of oat husk and the potential effects of phosphoric acid and oxalic acid as alternatives to sulfuric acid were investigated. These acids were determined as effective as sulfuric acid to obtain high quality lignin and glucan and they can be used instead of sulfuric acid in solvent acidification. To determine the purity and recovery of both lignin and glucan, the effects of initial substrate amount, solid-to-liquid ratio, and amount of washing solutions were also examined using a one-factor-at-a-time strategy. Reducing the amount of washing solutions (water, solvent, or both) negatively affected lignin recovery, but it did not affect glucan recovery. The optimum conditions for pretreatment of the oat husk at higher glucan recovery were obtained with 50% aqueous ethanol acidified with oxalic acid at 210 degrees C for 90 min and solid-to-liquid ratio of 1:2. In the mixture of evaporated glucan-rich and hemicellulose-rich fractions obtained through the optimized condition, 4.62 g/L biomass containing 10.27% protein was produced by the cultivation of Aspergillus oryzae. The fractions obtained from organosolv treatment can be used to obtain value-added products such as biomass production, and thus contributing to a sustainable economy by integrating lignocellulosic substrate residues into the biorefinery.

The existing recycling methods of PHA-based material are ineffective in terms of increasing resource efficiency and the production of high value end-of-life products. Therefore, in this study, a novel approach of acidogenic fermentation was proposed to recycle PHB-based composites reinforced with natural fibers such as cellulose, chitin, chitosan, orange waste, sawdust, soy protein, and starch. The inclusion of cellulose, chitosan, and sawdust improved the impact properties of the composites while other fillers had various effects on the mechanical properties. These three composites and neat PHB were subsequently subjected to biological degradation via acidogenic digestion to determine the possibility of converting PHB-based composites into volatile fatty acids (VFAs). Two different pH levels of 6 and 10 were applied to assess the effect of pH on the bioconversion and inhibition of the methanogenesis. The results showed promising PHB degradation, contributing to considerable VFA production of 2.5 g/L at pH 6 after 47 days. At pH 6, the presence of the natural fibers in the biocomposites promoted the degradation rate. On the contrary, pH 10 proved to be more suitable for the degradation of the fibers. The VFA which is produced can be recirculated into PHB production, fitting with the concept of a circulating bioeconomy.

BACKGROUND

Vegetable oil is more difficult for microorganisms to degrade compared with carbohydrates and protein. Oil-rich waste creates serious environmental and health concerns if it remains untreated. The aim of the work reported here was to evaluate the effects on the nutritional composition of filamentous fungal biomass by growing it in pure olive oil as a carbon source.

RESULTS

The growth of different filamentous fungal strains (Aspergillus oryzae, Neurospora intermedia and Rhizopus oryzae) was investigated in pure olive oil. A pre-germination stage of either glucose or yeast extract was necessary for successful fungal growth in olive oil. A. oryzae showed superior performance in comparison with N. intermedia and R. oryzae in terms of biomass growth. The obtained biomass from A. oryzae and N. intermedia was analyzed for protein, fat, ash and alkali-insoluble material, where the presence of olive oil had a steering effect on biomass growth (16 g L−1 with oil versus 4 g L−1 without oil). Nutritional composition of the fungal biomass of A. oryzae contained 0.33% fat and 48% protein when cultivated in medium without olive oil supplementation, while 31% fat and 14% protein contents were observed in the presence of olive oil-containing medium. Similar trends for fat and protein contents were observed for the biomass of N. intermedia. Moreover, microscopy confirmed the presence of oil globules inside the fungal cells.

CONCLUSIONS

Fat composition of fungal biomass can be steered through addition of olive oil, which increases the versatility of the produced biomass for various applications, namely in feed, food and biofuel production.

Here, cell wall of a zygomycete fungus, Rhizopus delemar, grown on bread waste was wet spun into monofilaments. Using the whole cell wall material omits the common chitosan isolation and purification steps and leads to higher material utilization. The fungal cell wall contained 36.9% and 19.7% chitosan and chitin, respectively. Solid state NMR of the fungal cell wall material confirmed the presence of chitosan, chitin, and other carbohydrates. Hydrogels were prepared by ultrafine grinding of the cell wall, followed by addition of lactic acid to protonate the amino groups of chitosan, and subsequently wet spun into monofilaments. The monofilament inhibited the growth of Bacillus megaterium (Gram+ bacterium) and Escherichia coli (Gram- bacterium) significantly (92.2% and 99.7% respectively). Cytotoxicity was evaluated using an in vitro assay with human dermal fibroblasts, indicating no toxic inducement from exposure of the monofilaments. The antimicrobial and biocompatible fungal monofilaments, open new avenues for sustainable biomedical textiles from abundant food waste. © 2022 The Authors

Apple is among the most consumed fruits in the world and the expansion of their processing is increasing the generation of waste such as apple pomace. It finds some applications in food and feed systems, anaerobic digestion, and composting; however it most ends in landfills or in informal disposal. Therefore, waste management strategies that address this waste accumulation need to be explored. This review provides a state-of-art of valorization strategies adopted for recovery of value added products from apple processing-derived waste and discusses on their development stage. The research community has laid most of its efforts on incorporation of apple pomace into feed and food systems and in the development of pectin- and phenolics-extraction methods. Incorporation of apple pomace in feed and food systems is still negligible due to its low protein and high fiber contents. Therefore, coupling apple pomace with microbial conversion for nutritional upgrade could change this scenario. Some environmentally-friendly techniques have been developed for extraction of pectin and phenolics, but major developments are needed on their integration to attain tailored extraction of several compounds. Recovery of value added routes of apple pomace towards production of bio-chemicals are characterized by lack of deep research studies and of a holistic approach. Integrated approach with techno-economic analysis, life-cycle assessment, and inter-sectorial initiatives will possibly reveal the most promising valorization routes. 

Brewer’s spent grain (BSG) is the main solid by-product of the brewing sector. High moisture and nutrient-rich content render BSG easily perishable, leading to waste generation and environmental impacts. BSG has narrow applications in both feed and food sectors due to its composition including high fiber and low protein. Therefore, a processing strategy leading to the nutritional valorization of BSG could widen its applications. In this study, submerged cultivation of edible filamentous fungi (Aspergillus oryzae, Neurospora intermedia, and Rhizopus delemar) was introduced as a strategy to enhance the protein content of BSG. The growth of all strains in BSG increased the protein content of the fermented BSG. The highest increase of protein content (from 22.6% to 34.6%), was obtained by cultivation using A. oryzae and medium supplementation. The protein content increase was followed by a decrease in the content of polysaccharides (up to ca. 50%), namely starch, glucan, xylan, and arabinan. The addition of cellulase resulted in enhanced ethanol production from BSG but led to lower concentration of recovered solids. In conclusion, simple processing of BSG using edible filamentous fungi can lead to quality improvement of BSG, providing potential economic and environmental benefits to the brewing sector.