# Production of Sustainable Postbiotics from Sugarcane Straw for Potential Food Applications
## 1 Introduction  
The development of food products and ingredients with the potential to modulate gut microbiota has been growing in recent years, owing to the overall impact on health. These products can be prebiotics, probiotics, symbiotics, and more recently, postbiotics [1, 2]. Definitions of these concepts have been published by the International Scientific Association of Probiotics and Prebiotics (ISAPP). Prebiotics are compounds that are specifically exploited by microorganisms giving a health advantage, while probiotics are living bacteria that, when consumed in the right amounts, help the host's health. A mixture of live microorganisms and substrate(s) that host microorganisms use in a specific way to promote the host's health is referred to as a symbiotic connection. Postbiotic extract is a \"preparation of inanimate microorganisms and/or their components that confers a health benefit on the host\" [3, 4]. Postbiotics involves not only dead microorganisms, fractions, and lysates that may include cell wall fractions and exopolysaccharide, but it also involves metabolites suchas enzymes, short-chain fatty acids (SCFA), peptides, peptidoglycan, teichoic acids, cell surface proteins, polysaccharides, and organic acids that are produced by living microorganisms that can be excreted and released after cellular lysis [5]. Due to the high heterogeneity of substances classified as postbiotics, they might have a high diversity of mechanisms of action. Because of their dose safety, long shelf-life, and their action as signaling molecules, they exert pharmacological properties such as anti-inflammatory, immunomodulatory, anti-obeseogenic, antihypertensive, hypocholesterolemomic, anti-proliferative, and antioxidant activities [6]. The production of postbiotics has been facilitated by the use of culture media containing synthetic compounds and saccharose, and the most widely used microorganisms are derived from lactic acid bacteria, specifically from the _Lactobacillus_ genera and/or yeasts, particularly _Saccharomyces cerevisiae_[7]. Finding alternative substrate sources that are plentiful, affordable, and renewable is necessary, though, e.g., the agricultural and industrial by-products, which represent a significant opportunity to produce postbiotics rich in other compounds with enhanced bioactivities at reduced costs [7]. Some works have already reported using by-products as substrates for postbiotic production, such as cheese whey, milk permeate, and lignocellulosic biomass [8; 9]. Recently, it was demonstrated that the juice from _Parmentiera aculeta_, a plant that is available in Mexico, increased synthesis of postbiotics like succinic acid, formic, acetic, propionic, and lactic acids as well as development of _Lactobacillus plantarum_[10]. Lignocellulosic biomass has grown in importance within the context of biorefinery, which aims to effectively use biomass to produce bioproducts with high-added value with sustainability. The most affordable and copious renewable carbon source currently accessible is lignocellulosic biomass [11]. Despite the potential that postbiotics have in the food industry, they may present some issues related to their production costs, hence, they are less competitive than their counterparts made from plants or chemical compounds. Using agro-industrial residues, such as sugarcane straw, presents an alternative to achieve an economical and sustainable process. Sugarcane (_Saccharum officinarum_ L.) is a crop that produces a higher quantity of by-products discarded after harvesting, including straw residues [12]. According to estimates, 140 kg of dry straw are produced for every ton of sugarcane processed [13]. Straw may have two final destinations: it can be used for land cover or burned to supply energy to industries. The primary constituents of sugarcane straw are cellulose (34-43%), hemicelluloses (23-38%, primarily xylans), and lignin (11-25%), with extractives such polyphenols and inorganic compounds making up the remainder [14].