Gelation behaviour of gelatin and alginate mixtures

Mixtures of alginate and gelatin were studied by rheology as a function of different parameters, such as temperature, biopolymer concentrations, calcium concentration and ionic strength. In particular conditions, the formation of a mixed gel of alginate and gelatin is obtained. A slow release of calcium ions leads first to an irreversible alginate gel and cooling results in a reversible gelatin gel. Depending on experimental conditions, non-linear behaviours upon gelation of alginate occur and a collapse of alginate gel is directly observable by rheology. These trends are favoured between 35 and 45 °C, by a high total biopolymer concentration or a high calcium concentration and ionic strength. Different mechanisms could be responsible for this collapse, such as a competition between alginate gelation and phase separation in the biopolymer mixture or an over-association of alginate chains at high Ca²⁺ concentration, favoured by the presence of gelatin.     

Isolation,characterization and biological activity of inositol sphingophospholipids fromPhytophthora capsici

Several inositol sphingophospholipids (ISPL) were isolated from mycelia ofPhytophthora capsici, a phytopathogenic fungus of pepper (Capsicum annuum c.v. Yolo Wonder). The sphingophospholipids induce a protective response by cotyledons of young peppers against necrotic lesions caused by the pathogenP. capsici. The ISPL structures were determined by chemical methods, fast atom bombardment mass spectrometry and by fast atom bombardment collision-induced tandem mass spectrometry. All ISPL consisted of ceramides linked to inositol phosphate. The amidelinked fatty acids were found to have 16, 20 and 22 carbon chains. The long chain bases were identified as trimethylsilyl derivatives and shown to be C₁₆-sphingosine and C₁₆-dihydrosphingosine. The protective effect of the ISPL on cotyledons of young peppers against necrotic lesions caused by the pathogenP. capsici was shown not to be dependent on the unsaturation of the C₁₆-sphingosine base and the nature of the acyl chain. We also investigated the effect of growth conditions on the ISPL produced in three different, chemically defined media that are commonly used for fungi cultures. We showed thatP. capsici synthesized one major class of compounds with molecular weights of M_r=833 and 835 containing the 16∶1 base and the 22∶1 or the 22∶0N-acyl group, independent of the growth medium used. The presence of phosphite or fosetyl-A1 did not affect the result. This work is dedicated to Dr. P.M. Molot.     

Filamentous structures of bovine myosin in diluted suspensions and gels

Turbid solutions and fine-stranded gels of myosin from bovine semi-membranous muscle were investigated by transmission and scanning electron microscopy. Evidence is given that the turbidity was caused by filament formation upon dialysis to pH 5.5 and 0.25 M KCl and to pH 4.0 and 0.6 m KCl at 4°C. The filaments formed at pH5.5 and 0.25 m KCl had a backbone with a diameter of c. 25 nm with the myosin heads located close to the filament backbone. The total width of these filaments was c.45nm. The filaments were prepared for electron microscopy by adsorption on various substrates, negative staining, or freeze drying and rotary shadowing. Variations in the preparation technique did not affect the appearance of the filaments. The filaments formed at pH 4.0 and 0.6 m KCl had a more irregular appearance, and the total filament width varied between 20 and 45 nm. Fringes of globular material surrounding the filament backbone were seen but also clusters of myosin molecules protruding further out from the backbone and from the filament ends. Comparison of heat-treated filaments in dilute solutions with strands of the gel network confirmed that the gel strands originated from filaments formed upon dialysis prior to gelation. Typical features of the network structure were junction zones formed by parallel alignments of filaments in pairs and by end-to-side interactions forming so-called Y-junctions. At pH5.5 and 0.25 m KCl these interactions resulted in a rather loose and open network structure. At pH 4.0 and 0.6 M KCl the filaments often interacted approximately at right angles, which resulted in a denser network than that observed atpH5.5 and 0.25 m KCl. The efficient network formation at pH 4.0 gave rise to spontaneous gel formation upon dialysis without any heat treatment. Additional heating did not change the character of the network, and no differences could be observed between unheated and heat-treated gels at low magnifications. At higher magnifications it could be seen that heating resulted in loss of details of the filaments at both pH values and ionic strengths. The shape of the myosin heads was lost, and the heads fused together on the filament backbone.     

Review Article: A new wrinkle on old skin: the role of elastic fibres in skin ageing

Cutaneous ageing is the result of two distinct, biological processes which may occur concurrently: (i) the passage of time, termed intrinsic ageing and (ii) environmental influences, termed extrinsic ageing. Intrinsic ageing of the skin is a slow process which causes changes in tissue structure and impairs function in the absence of additional biological, chemical and physical factors. The clinical features of intrinsically aged skin are not usually evident until old age when, although smooth and unblemished, the skin surface appears pale and is characterized by fine wrinkles with occasional exaggerated expression lines. Functionally, intrinsically aged skin is dry and less elastic than more youthful skin. In contrast, extrinsically aged skin is exemplified by deep, coarse wrinkles, mottled hyperpigmentation and a marked loss of elasticity and recoil. The two major environmental influences which induce extrinsic ageing are: (i) chronic exposure to solar ultraviolet (UV) irradiation (termed photoageing) and (ii) smoking. This review discusses the changes associated with the ageing process in the skin, with particular emphasis on the role played by the elastic fibre network in maintaining dermal function. The review concludes with a discussion of a short‐term assay for independent assessment of the efficacy of anti‐ageing cosmetic products using the elastic fibre component fibrillin‐1 as a biomarker of extracellular matrix repair.     

Thermal pretreatments of carrot pieces using different heating techniques: Effect on quality related aspects

During fruit and vegetable processing, different thermal processes (blanching, pasteurization, sterilization) based on different heating techniques can be used. In this context, it is important to evaluate the impact of blanching on quality related parameters.This paper describes a case study on carrot pieces, studying the effect of thermal pretreatments (high temperature blanching, low temperature blanching and low temperature blanching in combination with Ca²⁺-soaking) on enzyme activity (peroxidase (POD), pectinmethylesterase (PME)), structural properties (degree of methoxylation (DM), texture) and nutritional aspects (β-carotene content). The thermal pretreatments were carried out by conventional heating as well as by microwave heating and ohmic heating, since these new heating methods can become important new technologies in food industry.It has been shown that, depending on the application, selecting the right pretreatment conditions can help to control the enzyme activity. To obtain a firm carrot texture after thermal processing, low temperature blanching seems to be the most appropriate pretreatment condition. This was supported by the micrographs and the analysis of the degree of methoxylation. Furthermore almost no influence of the pretreatments on the β-carotene content of the samples could be noticed. For all quality parameters studied, no unambiguous effect of the heating technique could be detected. Thus, the time/temperature conditions of the thermal pretreatments determine the quality related aspects, independent of the heating technique used.

Industrial relevance

With regard to consumer acceptance, a good quality control of fruit and vegetables is important. Food quality covers a wide range of parameters, including enzyme content, structural properties, nutritional properties, sensorial characteristics etc. This study gives an overview of the effect of blanching, which is a common preprocessing step in food processing, on quality related parameters in carrots. The data deliver integrated information on structural level as well as on nutritional level and on enzyme content. Moreover, novel thermal process technologies (microwave heating, ohmic heating), which gain more and more attention in food industry, are being considered as alternatives for conventional blanching.     

Photochemical patterning of biological molecules inside a glass capillary

A simple way for photochemical patterning of biological molecules onto the inner wall of fused-silica capillary is described. The method is based on a modification of the inner capillary surface with photoactive benzophenone (BP) derivative. The UV irradiation at 365 nm of the capillary filled with a sample solution results in cross-linking of the solutes to the BP moiety via a stable covalent bond. As a proof of concept, oligonucleotides and proteins were arrayed inside the capillary using an inverted microscope as an irradiation device. We demonstrated that the capillary arrays produced in this way are functional and could be used in different bioassays including DNA hybridization, protein interaction studies, and immunoassays. Having a sensitivity comparable to the fluorophore-based assays in a planar format, the capillary array possesses several advantages including submicroliter sample volume and a short assay time. The capillary format should therefore be considered as a possible alternative to a planar format in a number of low-density array applications such as mutation detection and diagnostic immunoassays.