Production and characterization of Pleurotus mycelial biomass as a food ingredient

In recent years, research on alternative food sources has significantly increased to promote sustainable and healthy nutrition. The primary reasons for this include climate change, concerns about the growing human population, and the shift in global consumption habits. Investigating and developing alternative protein sources for a sustainable future is among the primary research topics in this field. Microbial biomass is preferred among alternative protein sources due to its relatively fast and easy production processes, the utilization of agricultural waste as raw material, and the ability to control the final product's characteristics, including nutritional content, at a high level. Fungi are among microbial species that can be used for microbial production. In addition to yeasts and filamentous fungi, macrofungi, which belong to a distinct group, can also be utilized as microbial cultures for biomass production. Oyster mushrooms (Pleurotus spp.) are a type of fungus that can be cultivated as mycelium culture and used for edible biomass production in liquid media. In this study, the production of Pleurotus ostreatus EBK13 strain in liquid culture and its potential as a food ingredient and alternative protein source were investigated. Following shake flask incubation experiments, biomass production was conducted in a bioreactor environment using two different methods. Both methods were laboratory-scale production approaches, with the first being a stirred bioreactor and the second an originally designed bubble column-type bioreactor. The average biomass yield obtained in the bubble column bioreactors (172 g/L) was higher than that obtained in the stirred fermenter (118 g/L). The nutritional content of the produced fungal biomass (FB) was analyzed, revealing an average composition of 15.24% protein, 12.68% fat, 5.19% ash, and 66.89% carbohydrates in dry matter. The produced biomass was stored in a deep freezer and thawed before use, to remove free water. Additionally, this process improved the water content and textural properties of the produced FB. As a result of this process, the obtained biomass was termed freeze-structured or freeze-texturized fungal biomass. To evaluate the applicability of the biomass as a food ingredient, chicken patties were prepared with different substitution ratios (10%, 20%, and 30% of the minced chicken in the recipe). The chemical, physical, and sensory properties of the oven-cooked patties were analyzed. Additionally, the effects of refrigerated storage for two weeks on the microbial and chemical properties of the patties were examined. The substitution of FB in patty formulations resulted in significant changes in the physical, chemical, and sensory properties of the oven-cooked patties. There was no significant difference in cooking yield and diameter reduction between control patties (made with only chicken mince) and patties containing different amounts of FB. In terms of patty thickness, an increase was observed in the control, 10%, and 20% FB-substituted patties, whereas a decrease in thickness was detected in the 30% FB-substituted patties. Substituting chicken meat with up to 20% FB did not cause a significant difference in the crude protein content of the patties; however, a 30% FB substitution significantly reduced the crude protein content. The fat content of the patties tended to increase with FB addition. While the ash content of the patties showed an increase with FB addition, no significant variation was observed based on the proportion of FB substitution. Color analysis showed that L* and b* values increased with FB addition, indicating a lighter and more yellow color. Texture profile analysis demonstrated that increasing the FB substitution rate resulted in decreases in parameters such as hardness, chewiness, and resilience. Sensory analysis results confirmed that the substitution led to a softer texture perception. According to the sensory panel evaluation, the FB-substituted patties were perceived to be different from the control samples only in terms of texture, while no differences were observed in terms of taste, odor, color, aroma, mouthfeel, or appearance. Additionally, FB-substituted patties received higher overall acceptability scores compared to the control samples. During refrigerated storage, pH, oxidation levels, and microbial load were monitored. No significant changes were observed in pH values due to FB substitution. Although not statistically significant, FB addition was found to potentially delay microbial spoilage and significantly reduce oxidation, making it one of the key findings of the study. In conclusion, it was demonstrated that P. ostreatus EBK13 mycelial biomass, produced via liquid culture fermentation, could be incorporated into patty formulations with high nutritional value and high consumer acceptance.