Optimization of Ultrasound Assisted Extraction of Bioactive Compounds from Apple Pomace.

In the present work, the optimization of the extraction of antioxidant compounds from apple pomace using ultrasound technology as an environmentally friendly and intensification process was developed. Different sonication powers, extraction temperatures and extraction times were studied and their influence on extraction yield and characteristics of the extracted samples (total phenolic compounds, flavonoid content and antioxidant capacity) are presented. The elaborated experimental design and the analysis of Pareto and response surface diagrams allowed us to determine the optimal extraction conditions. The conditions that allow the maximum extraction of phenolic compounds were found at 20 min, 90 °C and 50% ultrasound amplitude. Nevertheless, at these conditions, the antioxidant capacity measured by DPPH decreased in the extracted samples.

Xylan-cellulose films: improvement of hydrophobicity, thermal and mechanical properties.

Xylan-rich hemicellulose from corn cob has been used for new material elaboration. Commercial cellulose was used as reinforcement in different percentages to improve properties of the films. Two types of composites were elaborated by solvent casting. Hydrophilic films, composed by bleached hemicellulose (BH), unmodified cellulose and glycerol as plasticizer, and hydrophobic films formed by acetylated bleached hemicellulose (BAH) and acetylated cellulose. The degree of substitution of BAH was 1.8 and acetylated cellulose presented a degree of substitution of 0.54. Thermal and mechanical properties of films were analyzed. A significant improvement was observed in the thermal behavior of hydrophobic films (Tmax ∼ 368 °C) respect to hydrophilic films (Tmax ∼ 300 °C). Although the addition of cellulose clearly increase the properties of both type of films, hydrophobic films (Young's modulus ∼ 2300 MPa, strength ∼ 44.1MPa, strain at break ∼ 5.7%) showed better mechanical properties than hydrophilic films (Young's modulus ∼ 3 MPa, strength ∼ 3.3 MPa, strain at break ∼ 5.3%).

Corncob arabinoxylan for new materials.

Corncob agricultural waste was used as a source of arabinoxylan for preparation of films. Three arabinoxylan samples were prepared: crude extract (CCAX), purified by a washing step, and purified by bleaching CCAX. Films prepared with untreated CCAX were water soluble, yellowish in color and had poor mechanical properties. After the purification processes the Young's modulus increased from ∼ 293 MPa to ∼ 1400-1600 MPa, and strength was improved from ∼ 9 MPa to around 53 MPa, while the strain at break was kept at ∼ 8% both in untreated and purified CCAX. The contact angle was increased from ∼ 21.3° to 67-74° after washing or bleaching CCAX. Acetylation of bleached CCAX showed the highest thermal resistance (325 °C), had low Tg (125°C) and a high contact angle (80°), and its films were stronger (strength ∼ 67 MPa; Young's modulus ∼ 2241 MPa) and more flexible (∼ 13%). These characteristics make purified CCAX a suitable material to be used as a matrix for film applications.

Effect of alkaline and autohydrolysis processes on the purity of obtained hemicelluloses from corn stalks.

A study of the potential of autohydrolysis and alkaline extraction processes from corn stalks was performed for high purity hemicellulose extraction. The influence of process parameters on the purity of obtained hemicelluloses was analyzed. An experimental design was developed for the autohydrolysis treatments to determine the optimal conditions to solubilize the hemicelluloses with lowest content in contaminants. On the other hand, alkaline extraction, including raw material pretreatment (dewaxing and delignification step) was carried out analyzing the effectiveness of this processes for maximum pure hemicellulose recovery. The maximum yield (54% of the raw material hemicelluloses) and the best physicochemical properties (highest hemicellulose content free of lignin) were obtained with these pretreatments in alkaline extraction. Moreover, the effect of lignin removal by sulfuric acid from the autohydrolysis liquors before hemicellulose precipitation was studied. This purification step has allowed to obtain lignin-free autohydrolysis hemicellulose but with the presence of sulfur as predominant contaminant.