Valorization of Green Biomass: Alfalfa Pulp as a Potential Platform for Food and Biochemicals

The biorefining industry generates a substantial quantity of lignocellulosic biomass waste, representing a sustainable and renewable bioresource. Innovative approaches are essential for efficiently transforming these materials into valuable products, often requiring pretreatment due to their complex structural nature and the inherent challenges presented by plant cell walls. Diverse pretreatment methods, including physical, chemical, and biological approaches, can effectively modify the arrangement of lignocellulosic structures, facilitating the conversion into mixed sugars and other valuable products. The objective of this study was to conduct a biological treatment of alfalfa pulp using oyster mushrooms for the purpose of producing edible food. Additionally, the potential of utilizing the treated pulp in chemical pretreatment methods for the development of a sugar platform in the fermentation industry was investigated.

A study was conducted to explore the potential of using alfalfa pulp as a substitute substrate for cultivating oyster mushrooms (Pleurotus ostreatus). The study evaluated the major components of different stages of mushroom substrates and monitored changes in lignocellulolytic enzyme activities. The results indicated that alfalfa pulp is highly suitable for oyster mushroom production, with a higher biological efficiency compared to commercially available wheat straw. The lifecycle of oyster mushrooms on alfalfa pulp was reduced to 24 days on the pulp, compared to wheat straw, which could help reduce the risk of contamination during industrial production. The spent mushroom substrate from alfalfa pulp exhibited potential extracellular hydrolytic and oxidative enzyme activity, as well as a significant mycelium content. The cultivation properties also showed promise when the pulp produced from upscaling with a single screw was applied as the substrate. Moreover, the fruiting bodies produced on alfalfa pulp demonstrated acceptable quality and safety, with low levels of trace heavy metals and suitable essential amino acid content. Therefore, cultivating oyster mushrooms using alfalfa pulp offers an alternative method to produce a value-added food product while reducing biomass waste in the green protein biorefining.

Furthermore, aside from its utilization in mushroom cultivation, an examination was conducted to explore the potential applications of byproducts such as side streams pulp and brown juice. Subsequently, a saccharification process was implemented, resulting in the efficient release of monosaccharides as a sugar platform. Additionally, the brown juice was identified as a promising nutritional supplement and, when combined with the saccharified pulp, created a fermentation medium abundant in hexose and pentose, thus exhibiting potential for lactic acid conversion. Additionally, recognizing the efficient utilization of xylose as a crucial requirement is essential for the successful development of a microbial conversion process aimed at producing value-added products from terrestrial lignocellulosic biomass. This thesis also explores the potential application of xylose-metabolism Corynebacterium glutamicum in the utilization of the alfalfa pulp sugar hydrolysate. The slow-growth properties of initially engineered xylose strains were addressed through the utilization of the microbial microdroplet automatic cultivation system for adaptation. The mutant strains exhibited rapid xylose consumption and were subsequently chosen for further investigation. In conclusion, the by-products of alfalfa protein production exhibit significant promise for the development of value-added products, with the potential to enhance the economic and environmental sustainability of the process.