• Energy Research

The sugarcane industry generates several by-products including the harvest residue (straw) and the fibrous fraction following juice extraction (bagasse). The conversion of sugarcane industry by-products into value-added products is of paramount importance from a sustainable circular economy perspective. Also, the increase of second-generation bioethanol production has triggered the development of approaches to convert residues into functional bioproducts thus increasing the overall sustainability of the process. Lignin is the major biopolymer in nature, and one of the three main components of sugarcane bagasse (SCB) and straw (SCS) biomasses. Due to the potential of lignin as natural antioxidant, antimicrobial, and ultraviolet protector, lignin-based research and new product development have significantly increased. Therefore, this review aims at updating the progress on the valorization of SCS and SCB, and emphasizing their main potential bioactivities and applications, thus serving as a valuable reference material for the academy and industry. A brief introduction of the sugarcane and sugar industry in terms of by-products generation and current end-uses is presented. Recent research studies on SCB and SCS delignification techniques, lignin purification/separation and the main physical-chemical differences between SCS and SCB are covered. The most reported biological activities for sugarcane lignin and their potential applications in the cosmetic and materials fields are also detailed in this review. info:eu-repo/semantics/publishedVersion

Lignocellulosic biomass is the most abundant renewable resource on earth and currently most of this biomass is considered a low-value waste. Specifically, lignin is an underrated bioresource that is mostly burned for energy production and few value-added products have been created. Since the agro-food industry produces large amounts of wastes that can be potential sources of high-quality lignin, scientific efforts should be directed to this industry. Thus, this review provides a systematic overview of the trends and evolution of research on agro-food system-derived lignin (from 2010 to 2020), including the extraction of lignin from various agro-food sources and emergent applications of lignin in the agro-food chain. Crops with the highest average production/year (n = 26) were selected as potential lignin sources. The extraction process efficiency (yield) and lignin purity were used as indicators of the raw material potential. Overall, it is notable that research interest on agro-food lignin has increased exponentially over the years, both as source (567%) and application (128%). Wheat, sugarcane, and maize are the most studied sources and are the ones that render the highest lignin yields. As for the extraction methods used, alkaline and organosolv methods are the most employed (∼50%). The main reported applications are related to lignin incorporation in polymers (∼55%) and as antioxidant (∼24%). Studies on agro-food system-derived lignin is of most importance since there are numerous possible sources that are yet to be fully valorized and many promising applications that need to be further developed.

Grape stalks are lignocellulosic residues that can be valorized through the extraction of lignin - an underutilized biopolymer with high potential. Two lignin extraction methods, alkaline and deep eutectic solvents (DES), were studied, and experimental designs were carried out to obtain the best extraction conditions. The defined parameters for alkaline extraction allowed the recovery of ~48 % of lignin with low purity that was further improved with an autohydrolysis pretreatment (~79 % purity; ~32 % yield). Optimum parameters of DES method rendered high purity lignin (~90 %) without the need of a pretreatment and with a better yield (50.2 % (±2.3)) than the alkaline method. Both lignin fractions presented high antioxidant activities, being close to the antioxidant capacity of BHT for DPPH scavenging. Structural analysis proved the presence of lignin in both alkaline and DES samples with similar morphology. Overall, DES method was more efficient in the extraction of lignin from grape stalks besides its greener and sustainable nature. This work uses DES to extract lignin from this biomass while comparing it with a commonly classical method, proving that grape stalks can be used to extract lignin with a sustainable and efficient method rendering a final ingredient with value-added properties.