Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Deciphering the aloe vera leaf rind as potent feedstock for bioethanol through enzymatic delignification and its enhanced saccharification Gunasekaran Rajeswari, Samuel Jacob* Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur, 603203, Tamil Nadu, India ARTICLE INFO Keywords: Aloe vera leaf rind Laccase Delignification Saccharification Response surface methodology Reducing sugars ABSTRACT Bio-based pretreatment methods are gaining concern worldwide with substantial efforts are being realistic in effective technology improvement for the utilization of lignocellulosic biomass. However, limited scientific evidence is available for the utilization of aloe vera leaf rind (AVLR) that is spawned as waste during their industrial processing. In the present study, the optimization of laccase mediated delignification of AVLR was performed through response surface methodology (RSM) based on central composite design (CCD) of experi- ments to optimize the influencing parameters such as solid to liquid ratio, reaction temperature and incubation time on delignification of AVLR lignin. The optimum percentage of delignification of about 76.67% was obtained with 3.8% (w/w) residual lignin in the biomass under optimum process conditions such as solid to liquid ratio (1:3.7), 50 °C for 6 h of incubation. The efficiency of laccase mediated pretreatment of AVLR biomass was ex- amined via various analytical techniques (SEM, XRD and FTIR) that advocated the target specific action of biocatalyst (laccase) on AVLR lignin. Enzymatic hydrolysis of raw and delignified AVLR biomass were performed using crude cellulase produced from Aspergillus sp., which resulted in saccharification of about 44.35% ± 1.0 which is approximately 2 fold higher as compared to raw biomass. This shows the viability of laccase mediated pretreatment of AVLR biomass to elevate the reducing sugar yield accessible for the production of bioethanol. 1. Introduction Aloe vera, an xerophyte is deliberated to be innate only to Arabian Peninsula however naturalized elsewhere, occurring abundantly in tropical climate for more than 1000 years for its medical and health benefits (BMC series blog, 2015). Aloe vera also known as wonder plant comprises more than 500 species of succulent short- stemmed plants (Medical news today, 2017). The gel obtained from this plant leaves find its commercial application in cosmetics owing to its "moisturizing emollient effect” as a moisturizer and anti-irritating agent (Drugs.com., 2019). The aloe vera leaf mainly comprised of gel, latex obtained from pericyclic cells and the outer green rind. However, the utilization of aloe vera leaf rind (AVLR) has limited scientific evidence which is presently cured as waste or compost fertilizer. Alternatively, AVLR biomass can be used as potential resource for bioethanol production, which can promote the local agro-economy by dodging its need for over-irrigation. Cellulose from AVLR biomass was first isolated by Cheng et al. (2014) for the preparation of cellulose nano-fibers which is preceded by compositional analysis of rind which constitute 57.72% ± 2.18 (w/w) of α-cellulose. A prerequisite for deployment of efficient pretreatment methods for plant derived lignocellulosic feedstock, since it forms a cross linking between hemicellulose and cellulose which is hindered by the recalcitrant lignin. Bioethanol pro- duction from acid- hydrolyzed AVLR biomass was reported by Hellen Sathya et al. (2017) with certain characterization analysis such as FTIR and mass spectrometry. Besides, a wide variety of toxic intermediates such as hydroxyl methyl furfurals and furan derivatives are formed during acid pretreatment affecting the further saccharification and fermentation process. Additionally, such conventional pretreatment processing requires huge amount of water for neutralizing the acid/ alkali treated biomass which could be circumvented in enzyme based pretreatment (Bak et al., 2009; Boruah et al., 2016). Owing to this, a greener means of pretreatment method was generally preferred by utilizing crude laccase (an oxidoreductase) that can oxidize both phe- nolic and non-phenolic molecules present in lignocellulosic biomass (Avanthi and Banerjee, 2016; Mukhopadhyay et al., 2011; Kunamneni et al., 2007). Laccase, a multi-copper phenol oxidase has a distinctive capability to specifically target and cleave the phenolic moieties present in lignin molecules. However, the phenolic intermediates formed during enzymatic delignification has the ability to act as natural med- iators rather interfering in subsequent hydrolysis by partaking in oxi- dization process of non-phenolic group (Johannes and Majcherczyk, https://doi.org/10.1016/j.indcrop.2019.111876 Received 7 May 2019; Received in revised form 10 July 2019; Accepted 16 October 2019 ⁎ Corresponding author. E-mail address: samueljb@srmist.edu.in (S. Jacob). Industrial Crops & Products xxx (xxxx) xxxx 0926-6690/ © 2019 Elsevier B.V. All rights reserved. Please cite this article as: Gunasekaran Rajeswari and Samuel Jacob, Industrial Crops & Products, https://doi.org/10.1016/j.indcrop.2019.111876