Harnessing Waste Reuse: Lipase Immobilization on Lignocellulosic Wastes for Sustainable Biocatalysis and Circular Economy Enhancement

Enzymes are biocatalysts that can catalyze a wide range of reactions under mild conditions with high specificity and efficiency [1]. For this reason, in recent years, they have been extensively studied to be made suitable for industrial applications to reduce production costs thanks to their characteristics. Lipases (triacylglycerol hydrolases E.C. 3.1.1.3) are among the most used enzymes in the industrial field (food, pharmaceuticals, and cosmetics) since they can catalyze different types of reactions (hydrolysis, esterification, transesterification, etc. [2]) due to their high substrate specificity and stereoselectivity [2]. However, enzymatic immobilization is a delicate and intricate process that is affected by various factors such as the characteristics of enzymes, environmental dynamics, etc. but one of the crucial points is the choice of the support materials [3]. They must have several properties such as high surface area and permeability, mechanical strength, chemical and thermal stability, biocompatibility, insolubility in water, cost-effectiveness, and presence of suitable functional groups [4]. Furthermore, with a view to a circular economy and environmental sustainability, lately, there has also been an attempt to use supports with a low ecological impact [5]. Lignocellulosic materials produced as residues from agriculture and agroforestry sectors containing a complex mixture of biomass composed of cellulose, hemicellulose, and lignin are some of the most innovative examples [6]. This study investigates the immobilization of lipase from Candida Rugosa (CRL) on lignocellulosic wastes derived from rice husk (RH), brewer’s spent grain (BSG), hemp tea waste (HTW), green tea waste (GTW), vine bark (VB), and spent coffee grounds (SCG), focusing on the characterization of these materials and their impact on the lipase-support interaction. The wastes were subjected to a meticulous characterization by ATR-FTIR, BET, and SEM analysis, lignin content, and surface hydrophobicity determination. Investigation of parameters influencing immobilization performance revealed the importance of hydrophobic interactions. The study of enzymatic desorption caused by ionic strength and detergent treatments indicated mixed hydrophobic and electrostatic interactions in most supports, except for HTW and GTW, where hydrophobic interactions dominated. Notably, hemp tea waste (HTW) and spent coffee grounds (SCG) emerged as superior supports, exhibiting better immobilization performance having the highest activity recovery %, immobilization yield %, immobilization efficiency and immobilized activity (U/g). In conclusion, lipases immobilization on lignocellulosic wastes appeared to be a technological and economic improvement of biocatalytic production, indicating the possibility of achieving sustainable production based on the circular economy and approaching the “zero waste” model.