Combined Extraction/Purification-Catalytic Microwave-Assisted Conversion of Laurus nobilis L. Pruning Waste Polysaccharides into Methyl Levulinate

In the present work, the extraction and characterization of polysaccharides derived from bay tree pruning waste and their upgrading into methyl levulinate (MLA) are reported. The extraction was carried out by autohydrolysis under different conditions. The obtained fractions were characterized in terms of carbohydrates, phenolic acids, and proteins as well as in terms of molecular weight distribution. Optimum extraction conditions were found to be 160 °C for 45 min, and the polysaccharide fraction was found to be mainly composed of glucose (181.30 mg/g), xylose (172.41 mg/g), and galactose (45.44 mg/g). These carbohydrates presented a number-average molar mass (Mn) of 6.04 KDa and a weight-average molar mass (Mw) of 183.4 KDa. In addition, their phenolic acids were mostly p-coumaric and ferulic acids (0.60 and 0.12 mg/g, respectively). The catalytic conversion of bay tree polysaccharides into MLA using a simple catalyst such as Al₂(SO₄)₃ was subsequently conducted under microwave irradiation. Optimum reaction conditions produced up to 40 wt % of MLA.