Orange peel waste upstream integrated processing to terpenes, phenolics, pectin and monosaccharides: Optimization approaches

Abstract

Complete processing of biomass feedstock is critical to the success of integrated biorefineries. In this work, a first optimization study regarding orange peel waste (OPW) acetone extraction, and acid and enzymatic hydrolysis was developed via Taguchi design of experiments, leading to high yields in essential oils, phenolic compounds, highly-methylated pectin and free sugars and monomers, and leaving a low amount of solid residue. Acetone, a class 3 GRAS solvent, was chosen due to its high efficiency as extractant and dehydrating agent. After essential oil and phenolics extraction (22.5 g⋅ kg−1 dry solid –DS- and 15.7 g gallic acid equivalents⋅ kg−1 DS, respectively), either acid hydrolysis was optimized to yield a high amount of pectin (19.62% yield referred to dry solid; >70% methylation grade) or the best conditions for enzymatic hydrolysis/water extraction were found, which rendered galacturonic acid (250 g⋅ kg−1 DS) and monosaccharides (296 g⋅ kg−1 DS of glucose and 168 g⋅ kg−1 DS of a fructose and galactose mixture). For extraction with acetone, particle diameter, pH, stirring rate and liquid to solid ratio (L/S) were optimized. To extract pectin by acid hydrolysis, these variables were also studied with the exception that reaction time was optimized instead of L/S ratio. In enzymatic hydrolysis, L/S ratio and additional quantities of enzymatic cocktails were selected for optimization. The predictions of the best results were later validated through confirmation runs, showing good accordance to results found in literature, including those from intensified extractions by physical or acid methods (microwaves, ultrasounds, electric pulses or depressurization).