Fruit and vegetable processing wastes are global challenges but also suitable sources with a variety of nutrients for different fermentative products using bacteria, yeast or fungi. The interaction of microorganisms with bioactive compounds in fruit waste can have inhibitory or enhancing effect on microbial growth. In this study, the antimicrobial effect of 10 bioactive compounds, including octanol, ellagic acid, (−)-epicatechin, quercetin, betanin, ascorbic acid, limonene, hexanal, car-3-ene, and myrcene in the range of 0–240 mg/L on filamentous fungi Aspergillus oryzae and Aspergillus niger were investigated. These fungi were both found to be resistant to all compounds except octanol, which can be used as a natural antifungal agent, specifically against A. oryzae and A. niger contamination. On the contrary, polyphenols (quercetin and ellagic acid), ascorbic acid, and hexanal enhanced A. niger biomass yield 28%, 7.8%, 16%, and 6%, respectively. Furthermore, 240 mg/L car-3-ene was found to increase A. oryzae biomass yield 8%, while a 9% decrease was observed at lower concentration, 24 mg/L. Similarly, up to 17% decrease of biomass yield was observed from betanin and myrcene. The resistant nature of the fungi against FPW bioactive compounds shows the potential of these fungi for further application in waste valorization. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Sustainable development of society and industry is necessary for a safer future that is being challenged by environmental pollution, climate change, and scarcity of food and nutrition. Materials considered as waste can be converted into value-added products and energy, hence regained to the economy. Filamentous fungi are saprophytic microorganisms that show great potential for bioconversion of organic waste materials into a wide range of products, including ethanol, enzymes, fungal biomass, and organic acids. In this study, industrial residuals from bioethanol plants (thin stillage), agro-industrial residuals (oat husks), and fruit-processing residuals were considered as potential substrates for filamentous fungi. Different filamentous fungi species were investigated due to their edibility and ability to produce ethanol. The aim of this study was to investigate 1) the feasibility of a biorefinery concept and contribution of fungal products to the process economy, 2) the valorization of oat husks in the fungal biorefinery and its contribution to the process economy, and 3) the effect of bioactive compounds existing in fruit residuals on filamentous fungi in a synthetic medium.

Bioconversion of thin stillage into value-added products, e.g., additional ethanol produced by filamentous fungi and edible fungal biomass for various feed/food markets, improved the process economy of a conventional bioethanol plant. Techno-economic analysis was carried out with Aspen Plus® and Aspen Process Economic Analyzer®. The economy of the conventional bioethanol plant was improved to 76% and 5.6-fold higher net present value when the fungal product was sold as fish feed and human food, respectively. When the fungal product was sold as human food, Aspergillus oryzae was more advantageous than Neurospora intermedia. It is possible to integrate lignocellulosic material into the fungi-based biorefinery and produce additional products, e.g., lignin and fungal biomass as feed/food products. Several scenarios for integrating organosolv pretreatment into the biorefinery were investigated. When protein-rich biomass was sold as feed and food, 71% and 7.9-fold higher net present value was obtained, respectively, compared to the conventional ethanol plant. Similarly, other materials, e.g., fruit residuals, can be valorized through the fungal biorefinery. However, bioactive compounds in fruit residuals have antimicrobial effects; therefore, it is essential to assess the sensitivity of fungi toward them for efficient processes. In addition to the fungi species utilized in thin stillage and oat husk valorization, two other industrially important fungi, Rhizopus oligosporus and A. niger, were tested against 10 bioactive compounds with antimicrobial properties (octanol, ellagic acid, (-)-epicatechin, quercetin, betanin, ascorbic acid, limonene, hexanal, car-3-ene, and myrcene). The bioactive compounds were added to a synthetic medium to reach final concentrations of 2.4, 24 and 240 mg/L, within their natural concentration in fruit/fruit residuals. A. oryzae, A. niger and N. intermedia were inhibited by octanol, while the latter fungus was also inhibited by D-Limonene at 240 mg/L. On the other hand, R. oligosporus was resistant to inhibitory compounds and increased the biomass yield. The highest change in biomass yield was in the presence of ellagic acid with up to a 4-fold increase. Ethanol and lactic acid yields were increased 38% and 30% in the presence of ellagic acid and betanin, respectively. Similarly, the existence of quercetin and ellagic acid, ascorbic acid, and hexanal increased the biomass yield of A. niger up to 28%.

These studies can contribute to developing efficient and feasible biorefineries, in which filamentous fungi convert the industrial residuals into value-added products.

The fermentation of fruit processing residuals (FPRs) with filamentous fungi can provide protein-rich food products. However, FPRs that contain bioactive compounds with antimicrobial properties present a major challenge. In this work, the resistance of two edible filamentous fungi, Rhizopus oligosporus and Neurospora intermedia, to 10 typically inhibiting bioactive compounds available in FPRs (epicatechin, quercetin, ellagic acid, betanin, octanol, hexanal, D-limonene, myrcene, car-3-ene, and ascorbic acid) was examined. These compounds’ inhibitory and stimulatory effects on fungal growth were examined individually. Three different concentrations (2.4, 24, and 240 mg/L) within the natural concentration range of these compounds in FPRs were tested. These bioactive compounds stimulated the growth yield and glucose consumption rate of R. oligosporus, while there was no increase in the biomass yield of N. intermedia. Ellagic acid caused an up to four-fold increase in the biomass yield of R. oligosporus. In addition, octanol and D-limonene showed antifungal effects against N. intermedia. These results may be helpful in the development of fungus-based novel fermented foods. View Full-Text

The dairy industry generates excessive amounts of waste and by-products while it gives a wide range of dairy products. Alternative biotechnological uses of these wastes need to be determined to aerobic and anaerobic treatment systems due to their high chemical oxygen demand (COD) levels and rich nutrient (lactose, protein and fat) contents. This work presents a critical review on the fermentation-engineering aspects based on defining the effective use of dairy effluents in the production of various microbial products such as biofuel, enzyme, organic acid, polymer, biomass production, etc. In addition to microbial processes, techno-economic analyses to the integration of some microbial products into the biorefinery and feasibility of the related processes have been presented. Overall, the inclusion of dairy wastes into the designed microbial processes seems also promising for commercial approaches. Especially the digestion of dairy wastes with cow manure and/or different substrates will provide a positive net present value (NPV) and a payback period (PBP) less than 10 years to the plant in terms of biogas production.

This study was dedicated to techno-economic analysis of an integrated 1st and 2nd generation biorefinery, where the organosolv pretreated oat husk and thin stillage is valorized through filamentous fungi and baker yeast. By this strategy, process economy can benefit from multiple value-added products including lignin (80% purity), and protein-rich biomass as feed/food ingredients. Ethanol recovery of organosolv pretreatment benefits the already existing equipment in 1st generation ethanol plant. The best results shows that the integration of 10 tons/h oat husk into a process using 18.8 tons/h grains results in increasing ethanol production from 5.2 to 7.5 tons/h, in addition to 1.6 tons/h lignin (80% purity) and 7.6 tons/h fungal biomass. Integrated process is beneficial not only for 2nd but also for 1st generation ethanol production. Selling the fungal biomass as feed and food increased the net present value (NPV) in comparison to conventional ethanol plant by 71% and 7.9-fold, respectively. © 2021 The Authors

The feasibility of dry-grind bioethanol plants is extremely dependent on selling prices of ethanol and by-products, known as Dried distillers grains with solubles (DDGS), and sold as animal feed. Increasing the amount and quality of the by-products can widen potential feed and food markets and improve the process economy and robustness to price fluctuations of ethanol and grain. In this study, the techno-economic analysis of a bioethanol plant was investigated. Integration of edible filamentous fungi into the process leading to the conversion of sidestreams into ethanol and protein-rich fungal biomass for food and feed applications was considered, and its impact was investigated. Sensitivity analysis considered variations on process capacity, on the price of grain and ethanol, and on the price of fungal biomass considering its use for various animal feed (e.g., pig and fish) and human food markets. Selling the fungal biomass in the human food market resulted in 5.56 times higher NPV (net present value) than the base case bioethanol plant after 20 years. Integration of a low-performing strain towards ethanol, followed by the usage of the fungal biomass in the food sector, was found to be the most resistant scenario to the low ethanol selling price and increasing grain price. This study showed that the competitiveness of ethanol plants in the fuel market could be reinforced while meeting the increasing demand for protein sources.

A major issue hindering efficient industrial ethanol fermentation from sugar-based feedstock is excessive unwanted bacterial contamination. In industrial scale fermentation, reaching complete sterility is costly, laborious, and difficult to sustain in long-term operation. A physical selective separation of a co-culture of Saccharomyces cerevisiae and an Enterobacter cloacae complex from a buffer solution and fermentation media at dilution rates of 0.1–1 1/h were examined using an immersed membrane bioreactor (iMBR). The effect of the presence of yeast, inoculum size, membrane pore size, and surface area, backwashing and dilution rate on bacteria removal were assessed by evaluating changes in the filtration conditions, medium turbidity, and concentration of compounds and cell biomass. The results showed that using the iMBR with dilution rate of 0.5 1/h results in successful removal of 93% of contaminating bacteria in the single culture and nearly complete bacteria decontamination in yeast-bacteria co-culture. During continuous fermentation, application of lower permeate fluxes provided a stable filtration of the mixed culture with enhanced bacteria washout. This physical selective separation of bacteria from yeast can enhance final ethanol quality and yields, process profitability, yeast metabolic activity, and decrease downstream processing costs.