Hemicelluloses are an abundant biopolymer resource with interesting properties for applications in coatings and composite materials. The objective of this investigation was to identify variables of industrially relevant extraction processes that increase the purity of hemicelluloses extracted from fruit residues. Our main finding is that extraction with subcritical water, followed by precipitation with alcohol, can be adjusted to yield products with a purity of at least 90%. Purity was determined based on the total concentration of glucose, galactose, xylose, arabinose, and mannose after hydrolysis with sulfuric acid. In the first experimental design (DoE methodology), the effects of extraction temperature (95–155 °C) and time (20–100 min) on yield and purity were studied. A clear trade-off between yield and purity was observed at high temperatures, indicating the selective removal of impurities. In the second experimental design, the influence of extract pH and alcohol concentration on yield and purity was investigated for the raw extract and a concentrate of this extract with 1/6 of the original volume. The concentrate was obtained by ultrafiltration through ceramic hollow-fiber membranes. The highest purity of 96% was achieved with the concentrate after precipitating with 70% alcohol. Key factors for the resource efficiency of the overall process are addressed. It is concluded that extraction with subcritical water and ultrafiltration are promising technologies for producing hemicelluloses from fruit residues for material applications.

The depolymerization of lignocellulosic feedstock with a heterogeneous composition is a major challenge and usually leads to the formation of monosaccharides as main products. Our work aims to convert such...

The depolymerization of lignocellulosic feedstock with a heterogeneous composition is a major challenge and usually leads to the formation of monosaccharides as main products. Our work aims to convert such feedstock into oligomeric glycans as more valuable products compared to sugars, by using mechanocatalysis in a planetary ball mill in a cost-efficient and resource-saving manner. Herein, we utilized raw materials such as wheat straw, beet pulp, cocoa shells and apple pomace as residual natural raw materials from food and feed production. Reaction parameters such as rotational speed, acid content and milling duration were investigated and optimized towards a maximum amount of soluble species and a minimum of monosaccharides. The optimization for cellulose as substrate resulted in a nearly full-soluble fraction containing oligomeric glycans. Based on these results the reaction parameters were transferred and further optimized for lignocellulosic feedstock. For wheat straw a solubility of over 90 % was achieved comprising a mixture of oligomeric glycans as well as partially depolymerized lignin.