**1. Introduction**

Lignocellulosic biomass is widely considered one of the most promising low-cost feedstocks for the production of renewable energy and value-added chemicals. It is primarily composed of three major components, namely: cellulose (40–60%), hemicellulose (20–40%), and lignin (10–25%) [1]. Waste agricultural residues generated during crop harvesting and processing (e.g., rice straw, wheat straw, corn stover, corn cobs, sugarcane bagasse, sorghum bagasse, etc.) are renewable biomass resources that are readily available and inexpensive [2]. A significant amount of research has focused on developing environmentally friendly methods of utilising lignocellulosic biomass. In this regard, enzymatic conversion has emerged as a major technological platform that offers several advantages

such as environmental benefits and lower energy costs, with no formation of undesirable by-products. Due to the complexity and heterogeneity in the structure of biomass, its enzymatic conversion requires the synergistic cooperation of several enzymes [3]. A detailed understanding of this synergistic cooperation is key in the development of enzyme cocktails for the optimal production of value-added chemicals from lignocellulosic biomass.

Feruloyl esterases (FAEs, EC 3.1.1.73) and endo-xylanases (EC 3.2.1.8) are essential enzymes for the degradation of xylan, the most abundant hemicellulose in biomass. FAEs catalyze the cleavage of covalent ester linkages between hydroxycinnamic acids and polysaccharides, releasing ferulic acid (FA) and *p*-coumaric acid (*p*-CA) from lignocellulosic biomass [4,5]. FA, the most abundant hydroxycinnamic acid, is usually esterified at the C-5 hydroxy group of the arabinofuranosyl units of arabinoxylan of commelinid plants [6]. Hydroxycinnamic acids are used in the food industry as precursors for vanillin, *p*-hydroxybenzoic acid and 4-vinylphenol production, and as food preservatives because of their antimicrobial properties [7], while in the pharmaceutical industry, they can be used for their antioxidant and anti-inflammatory properties [8–11]. Application of FAEs not only releases hydroxycinnamic acid, but also decreases biomass recalcitrance, making it more accessible for further hydrolysis by carbohydrate-active enzymes [11]. Endo-xylanases are essential in degrading xylan as they catalyze the random cleavage of β-1,4-D-xylosidic linkages, generating xylo-oligosaccharides (XOS) [12]. The enzymes have been classified into glycoside hydrolase (GH) families 5, 8, 10, 11, 30, 43, 62 and 98, with GH10 and 11 being the two families that have been extensively characterized (www.cazy.org). Endo-xylanase generated XOS from agricultural residues are used in food, feed, and pharmaceutical industries due to their prebiotic and antioxidant activity [13,14].

FAEs exhibit a synergistic interaction with xylanases during the hydrolysis of a range of lignocellulosic substrates, which is demonstrated by improved yields in the production of XOS and FA. Xylanases generate ferulated XOS, which become preferred substrates for FAEs to cleave ester bonds from, liberating FA as a product [15]. The removal of FA then increases the accessibility of xylanases to XOS for further hydrolysis into shorter XOS and/or xylose. Studies have reported significant increases in the amount of FA released from arabinoxylan after the enzymatic hydrolysis by FAEs in the presence of xylanases [16–18]. Although FAEs from different microorganisms have been used for the co-production of FA and XOS, some of these FAEs show limited hydrolysis efficiencies. Therefore, novel FAEs with exceptional catalytic properties are still required for the formulation of more efficient enzyme cocktails.

Rashamuse and co-workers [19] functionally screened novel FAEs from the hindgut prokaryotic symbionts of *Trinervitermes trinervoides* termite species, but the application of these enzymes in degrading agricultural residues has not yet been explored. In this study, the synergistic action of two new termite metagenome derived FAEs (FAE5 and FAE6) and a GH11 xylanase from *Thermomyces lanuginosus* was optimized on insoluble wheat arabinoxylan (model substrate) and then applied to corn cobs (a natural substrate) for the production of XOS and hydroxycinnamic acids. The study presented demonstrated that high quantities of XOS, *p*-CA and FA were generated from corn cobs as a result of synergistic interactions between Xyn11 and FAE5 or FAE6.
