Potential of lactic acid bacteria fermentation as a strategy for valorisation and biotransformation of mushrooms

Abstract

Consumers increasingly recognise the importance of healthy eating and the potential benefits of incorporating mushrooms into their diets. Known for their rich nutritional profile, mushrooms provide essential vitamins, minerals, fibre, and antioxidants, making them valuable plant-based food sources. They are also rich in bioactive compounds with anti-inflammatory, antioxidant, antitumor, antiviral, and antimicrobial properties, promoting health and reducing disease risks in humans. Among various bioactive components in mushrooms, phenolic compounds are particularly noteworthy. These compounds are considered significant secondary metabolites in mushrooms and are found in free and bound forms within food matrices. However, the bioaccessibility and bioavailability of bound phenolic compounds are lower than that of free phenolic compounds due to their covalent bonds to cell wall matrices, which prevent absorption in the small intestine. Additionally, mushroom production generates various by-products, which pose environmental and financial challenges due to their disposal. Innovative processing techniques are required to enhance the bioavailability of phenolic compounds and add value to mushroom by-products. Fermentation with lactic acid bacteria (LAB) is effective in this context. LAB fermentation not only extends the shelf life and improves sensory properties but also breaks down macronutrients such as carbohydrates and proteins. This alters the nutritional composition of the food and facilitates the transformation of bound phenolic compounds into more bioavailable forms, similar to free phenolic compounds. Through LAB fermentation, macronutrients are transformed, antioxidative peptides are released, and phenolic compounds are modified. This process enhances the health benefits of mushrooms by increasing the bioavailability of mushroom phenolics, making them more accessible for absorption and use by the body. Therefore, fermentation techniques can significantly improve mushrooms' use, health benefits, and by-products. Given this information, a research framework for this doctoral thesis explores modifying industrial mushroom wastes and specific extracted components, as well as mushrooms like L. edodes and La. deliciosus, which may become waste due to their short shelf life. The research plan is based on processing mushroom waste and mushrooms through LAB fermentation. The objectives of this doctoral thesis are: (i) to valorise the mushroom waste generated from bioactive substance extraction, modifying its structure and nutritional composition through fermentation with lactic acid bacteria; (ii) to ferment the mushrooms with lactic acid bacteria to facilitate the transition of phenolic compounds from bound to free form, altering the structure of L. edodes and La. deliciosus; (iii) to determine biotransformation of these phenolic compounds use analytical identification; (iv) to investigate the effects of LAB fermentation on the bioaccessibility and intestinal transport of mushroom phenolics using an in vitro gastrointestinal digestion model. To achieve these objectives, three different experimental studies (Chapters 3-5) were conducted within the scope of this thesis. The first study focused on the fermentation of L. edodes mushroom waste, L. edodes residue (LER), with lactic acid bacteria compared to L. edodes itself (LE), examining changes in its structure and nutritional composition for functional properties (Chapter 3). The second study was based on the changes in phenolic components, interactions with other metabolites, and the profiling of phenolic substances in fermented L. edodes and La. deliciosus (Chapter 4). Based on the previous chapter's findings, the third study examined phenolic components' bioaccessibility and antioxidant activity trends in an in vitro gastrointestinal digestion model.