Obtaining Oligo- and Monosaccharides from Agroindustrial and Agricultural Residues Using Hydrothermal Treatments

Abstract

Agricultural and agroindustrial residues are major sources of cellulose, hemicellulose, and starch that can be converted into bioactive compounds, such as oligosaccharides and monosaccharides, using various chemical and biological methods. These bioactive compounds can be used as raw materials by food, cosmetic and pharmaceutical industries, as well as in the production of intermediate products and the development of biomaterials by chemical industries. In Brazil, the major industrial residues, which are corn residues, soybean residues, sugarcane bagasse, palm and coconut fibers, and grape and tomato seeds, among others, are produced at a rate of approximately of 600 million tons per year. Thus, the utilization of these residues using sustainable technology is of great interest. Hydrothermal treatment is a green technology that includes autohydrolysis as well as subcritical and supercritical hydrolysis, in which water is used at high pressures and temperatures to recover polysaccharides from complex vegetal matrices. The hydrolytic mechanisms can be improved by changing the ionic product or the polarity and electrical conductivity of water in subcritical and supercritical states. These properties promote the selective dissolution of the starch, hemicellulose and cellulose in the residues. The conversion of starch and hemicellulose into oligosaccharides and monosaccharides is preferentially performed at temperatures of less than 200°C. In contrast, the conversion of cellulose into oligosaccharides is promoted at temperatures greater than 200°C, with the highest amount oligosaccharide formation occurring at close to the critical point. In this article, the main biomass components, the properties of water under subcritical and supercritical conditions, and the latest studies of polysaccharide conversion in biomasses using hydrothermal treatments are reviewed.

Conversion of Biomass to Organic Acids by Liquefaction Reactions Under Subcritical Conditions

“…After that, this intermediate leads to form various final compounds. One of the final products is levulinic acid and by-product of it is formic acid which is formed at higher reaction temperatures (Zeng et al, 2010;Rosatella et al, 2011;Cardenas-Toro et al, 2014). This obtained data from literature is matching with our findings.…”

“…In order to break these bonds, subcritical water can be used. Hence, usage of subcritical water provides a favorable environment and reaction medium for degradation of cellulose to desired product (levulinic acid) (Cardenas-Toro et al, 2014). After breakdown of glycosic bonds, de-polymerization of cellulose is occurred and hence, oligosaccharides and monosaccharides (glucose) can formed.…”

A study on supercritical water gasification of black liquor conducted in stainless steel and nickel-chromium-molybdenum reactors

“…The formation of gas species starts with the decomposition of monomers generated in hydrolysis. Glucose and fructose are decomposed to aldehydes, erythrose and 5‐HMF (5‐hydroxymethyl‐2‐furfural) which are then decomposed to carboxylic acids with subsequent release of water and carbon dioxide . Xylose and arabinose, hydrolysis products of hemicellulose, are decomposed to glycolaldehyde, glyceraldehyde and furfural .…”

Supercritical water treatment for cello-oligosaccharide production from microcrystalline cellulose

“…An example of the possible applications for oligosaccharides is their use as prebiotics that are added in increasing quantities to foods with the focus on beverages and milk products. [2][3][4] By definition, prebiotics are food ingredients that are not digested by humans and have zero metabolizable energy value. Instead they provide a source of carbon for the intestinal microflora stimulating the beneficial bacteria in the colon.…”