Lignocellulosic biomass: a sustainable platform for the production of bio-based chemicals and polymers

Extraction and analysis of phenolics in food

Water, the most abundant constituent of natural foods, is a ubiquitous plasticizer of most natural and fabricated food ingredients and products. Many of the new concepts and developments in modern food science and technology revolve around the role of water, and its manipulation, in food manufacturing, processing, and preservation. This article reviews the effects of water, as a near-universal solvent and plasticizer, on the behavior of polymeric (as well as oligomeric and monomeric) food materials and systems, with emphasis on the impact of water content (in terms of increasing system mobility and eventual water "availability") on food quality, safety, stability, and technological performance. This review describes a new perspective on moisture management, an old and established discipline now evolving to a theoretical basis of fundamental structure-property principles from the field of synthetic polymer science, including the innovative concepts of "water dynamics" and "glass dynamics". These integrated concepts focus on the non-equilibrium nature of all "real world" food products and processes, and stress the importance to successful moisture management of the maintenance of food systems in kinetically metastable, dynamically constrained glassy states rather than equilibrium thermodynamic phases. The understanding derived from this "food polymer science" approach to water relationships in foods has led to new insights and advances beyond the limited applicability of traditional concepts involving water activity. This article is neither a conventional nor comprehensive review of water activity, but rather a critical overview that presents and discusses current, usable information on moisture management theory, research, and practice applicable to food systems covering the broadest ranges of moisture content and processing/storage temperature conditions.

Beyond water activity: recent advances based on an alternative approach to the assessment of food quality and safety

Phenolics in cereals, fruits and vegetables: Occurrence, extraction and analysis

There is a rapidly growing body of literature covering the role of plant secondary metabolites in food and their potential effects on human health. Furthermore, consumers are increasingly aware of diet related health problems, therefore demanding natural ingredients which are expected to be safe and health-promoting. By-products of plant food processing represent a major disposal problem for the industry concerned, but they are also promising sources of compounds which may be used because of their favourable technological or nutritional properties. The purpose of this review is to highlight the potential of selected by-products as a source of functional compounds.

By-products of plant food processing as a source of functional compounds — recent developments

Mechanical properties with respect to water content of gelatin films in glassy state

Texture is a major quality attribute of plant-based foods The plant cell wall is a key determinant of texture in fruit and vegetables; its properties influence the way in which plant tissues undergo mechanical deformation and failure during mastication Processes such as cooking, and physiological events such as ripening can reduce the strength of cell adhesion in many vegetables and fruit through depolymerization of pectic polysaccharides There is considerable interest in reducing such cell separation to prevent over-softening, loss of juiciness and development of mealiness Recent research on Chinese water chestnut has implicated diferulic acid cell-wall crosslinks in the thermal stability of cell adhesion and, therefore, maintenance of crispness after cooking In this review, we discuss the potential for exploiting this finding in other edible plant organs, and assess the likely effects that enhanced crosslinking might have on other quality attributes

New approaches to understanding and controlling cell separation in relation to fruit and vegetable texture

The mechanical properties of plant organs depend upon anatomical structure, cell-cell adhesion, cell turgidity, and the mechanical properties of their cell walls. By testing the mechanical responses of Arabidopsis mutants, it is possible to deduce the contribution that polymers of the cell wall make to organ strength. We developed a method to measure the tensile parameters of the expanded regions of turgid or plasmolyzed dark-grown Arabidopsis hypocotyls and applied it to the fucose biosynthesis mutant mur1 , the xyloglucan glycosyltransferase mutants mur2 and mur3 , and the katanin mutant bot1 . Hypocotyls from plants grown in the presence of increasing concentrations of dichlorobenzonitrile, an inhibitor of cellulose synthesis, were considerably weakened, indicating the validity of our approach. In order of decreasing strength, the hypocotyls of mur2 > bot1 and mur1 > mur3 were each found to have reduced strength and a proportionate reduction in modulus compared with wild type. The tensile properties of the hypocotyls and of the inflorescence stems of mur1 were rescued by growth in the presence of high concentrations of borate, which is known to cross-link the pectic component rhamnogalacturonan II. From comparison of the mechanical responses of mur2 and mur3 , we deduce that galactose-containing side chains of xyloglucan make a major contribution to overall wall strength, whereas xyloglucan fucosylation plays a comparatively minor role. We conclude that borate-complexed rhamnogalacturonan II and galactosylated xyloglucan contribute to the tensile strength of cell walls.

Tensile properties of Arabidopsis cell walls depend on both a xyloglucan cross-linked microfibrillar network and rhamnogalacturonan II-borate complexes.

Effect of water as a diluent on the glass transition behaviour of malto-oligosaccharides, amylose and amylopectin.

Polarized one- and two-dimensional infrared spectra were obtained from the epidermis of onion (Allium cepa) under hydrated and mechanically stressed conditions. By Fourier-transform infrared microspectroscopy, the orientation of macromolecules in single cell walls was determined. Cellulose and pectin exhibited little orientation in native epidermal cell walls, but when a mechanical stress was placed on the tissue these molecules showed distinct reorientation as the cells were elongated. When the stress was removed the tissue recovered slightly, but a relatively large plastic deformation remained. The plastic deformation was confirmed in microscopic images by retention of some elongation of cells within the tissue and by residual molecular orientation in the infrared spectra of the cell wall. Two-dimensional infrared spectroscopy was used to determine the nature of the interaction between the polysaccharide networks during deformation. The results provide evidence that cellulose and xyloglucan associate while pectin creates an independent network that exhibits different reorientation rates in the wet onion cell walls. The pectin chains respond faster to oscillation than the more rigid cellulose.

Andrew C. Smith

Papers

Mechanical properties with respect to water content of gelatin films in glassy state

New approaches to understanding and controlling cell separation in relation to fruit and vegetable texture

Tensile properties of Arabidopsis cell walls depend on both a xyloglucan cross-linked microfibrillar network and rhamnogalacturonan II-borate complexes.

Effect of water as a diluent on the glass transition behaviour of malto-oligosaccharides, amylose and amylopectin.

The mechanical properties and molecular dynamics of plant cell wall polysaccharides studied by Fourier-transform infrared spectroscopy.