Herminia Domínguez

Natural antioxidants from residual sources

The growing interest in the substitution of synthetic food antioxidants by natural ones has fostered research on vegetable sources and the screening of raw materials for identifying new antioxidants. Oxidation reactions are not an exclusive concern for the food industry, and antioxidants are widely needed to prevent deterioration of other oxidisable goods, such as cosmetics, pharmaceuticals and plastics. Polyphenols are the major plant compounds with antioxidant activity, although they are not the only ones. In addition, other biological properties such as anticarcinogenicity, antimutagenicity, antiallergenicity and antiaging activity have been reported for natural and synthetic antioxidants. Special attention is focussed on their extraction from inexpensive or residual sources from agricultural industries. The aim of this review, after presenting general aspects about natural antioxidants, is to focus on the extraction of antioxidant compounds (mainly polyphenols) from agricultural and industrial wastes, as well as to summarize available data on the factors affecting their antioxidant activity and stability, and, in some cases, the reported major active compounds identified.

Xylooligosaccharides: manufacture and applications

Xylooligosaccharides (sugar oligomers made up of xylose units) are useful for a variety of purposes. This article reviews the production of xylooligosaccharides from lignocellulosic materials (by chemical or enzymatic methods) and the purification of the end products, as well as their application as food ingredients, with special attention to the beneficial effects caused on health by these types of compounds.

Mild autohydrolysis: an environmentally friendly technology for xylooligosaccharide production from wood

Eucalyptus globulus wood samples were subjected to hydrothermal treatments under mild operational conditions (145–190 ° C, liquor to solid ratio 6–10 g g−1, reaction times up to 7.5 h). Residual xylan, xylooligosaccharides, other sugars, furfural, glucan and lignin contents were determined. Negligible effects were caused by hydrothermal treatments on both cellulose and lignin. Kinetic models were developed which describe the hydrolysis of hemicelluloses. Xylan degradation, xylooligosaccharide and xylose generation, and xylose dehydration to furfural were accurately described by models based on pseudohomogeneous, first-order kinetics with Arrhenius-type temperature dependence. These models are useful for a technical evaluation of this environmentally friendly technology. © 1999 Society of Chemical Industry

Biotechnological production of xylitol. Part 3: Operation in culture media made from lignocellulose hydrolysates

The acid hydrolysis of lignocellulosic materials for obtaining xylose solutions and the utilization of hydrolysates for making culture media for xylitol production are reviewed. Strategies for enhancing bioconversion of hydrolysates, including microorganism adaptation and physico-chemical processing of hydrolysates, are discussed. The effects caused by other influential factors (such as type and concentration of inhibitors, degree of hydrolysate concentration, cell concentration, pH, available oxygen and media supplementation) are also considered.

Autohydrolysis of corncob: study of non-isothermal operation for xylooligosaccharide production

Abstract Corncob samples were treated with water (autohydrolysis reaction) under non-isothermal conditions (reaction temperature up to 216°C) using a liquid to solid ratio of 8:1 kg/kg. The experimental variables considered were solid residue yield, solid residue composition (defined by the contents of cellulose, xylan, araban, acetyl groups and lignin in the solid residues) and composition of liquors (characterised by the concentrations of xylooligomers, xylose, glucose, arabinose, acetic acid and furfural). Most of the cellulose was retained in the solid phase, whereas partial delignification (up to 26% lignin removal) was achieved. Up to 94% of xylan was removed, producing xylooligomers (useful as food additives) and other reaction byproducts (including xylose and furfural). The decomposition of xylan into xylooligomers, with further generation of xylose, furfural and degradation products, was modelled by a series of parallel and consecutive reactions, which were assumed to be first order with coefficients showing an Arrhenius-type dependence on temperature.

Biotechnological production of xylitol. Part 1: Interest of xylitol and fundamentals of its biosynthesis

Xylitol, a polyol with growing market as a sweetener, can be produced by either chemical or biotechnological methods. The chemical properties of xylitol relevant to its food applications are summarized. The applicable production technologies (extraction from vegetables and fruits, chemical synthesis and biotechnological processes based on the utilization of bacteria, fungi or yeast) are described. Special attention is paid to the fundamentals of xylose metabolism by yeast, since this is a key factor affecting the feasibility of the most promising biotechnological methods for xylitol production. Other related technologies, involving the utilization of enzymes, combinations of enzymes and microorganisms or mixed cultures of microorganisms, are also described.

Kinetic modelling of corncob autohydrolysis

Abstract Corncobs were reacted with water and treated at temperatures in the range 145–190°C during 0–12.3 h at a liquor to solid ratio of 8 or 10 kg/kg (autohydrolysis treatments), to hydrolyse the hemicellulose fraction to xylooligomers (useful as food ingredients) and xylose (a carbon source for further fermentation stages). The time-courses of xylan and xylan-degradation products (including xylooligomers, xylose, furfural and other degradation products) were established. The kinetics of xylan degradation was modelled by means of a mechanism involving sequential, first order, pseudohomogeneous kinetics. The values of the kinetic coefficients were calculated, and their dependence on temperature was established using Arrhenius-type equations. The proposed model provides a satisfactory interpretation of the experimental data, allowing the selection of optimized operational conditions.

In vitro antioxidant properties of crude extracts and compounds from brown algae

Research on the bioactives from seaweeds has increased in recent years. Antioxidant activity is one of the most studied, due to the interest of these compounds both as preservatives and protectors against oxidation in food and cosmetics and also due to their health implications, mainly in relation to their potential as functional ingredients. Brown algae present higher antioxidant potential in comparison with red and green families and contain compounds not found in terrestrial sources. In vitro antioxidant chemical methods, used as a first approach to evaluate potential agents to protect from lipid oxidation in foods, confirmed that the brown algae crude extracts, fractions and pure components are comparatively similar or superior to synthetic antioxidants. Particular emphasis on the fucoidan and phlorotannin polymeric fractions is given, considering variations associated with the species, collection area, season, and extraction and purification technologies.

Improved xylitol production with Debaryomyces hansenii Y-7426 from raw or detoxified wood hydrolysates

Abstract Xylose solutions obtained by acid prehydrolysis of raw or NaOH-treated Eucalyptus globulus wood samples were used for making fermentation media useful for xylitol production with Debaryomyces hansenii NRRL Y-7426. Several physicochemical treatments for detoxification of hydrolysates were tested including overliming, sulfite addition, adsorption in charcoal, and concentration by evaporation. Despite the relatively low xylose concentration of hydrolysates, high xylitol yields (up to 0.84 g xylitol g −1 consumed xylose) were obtained at good productivities (up to 0.53 g xylitol l −1 h −1 ). The improvements obtained with the several strategies assayed are discussed in terms of overall productivities and product yield.