Pectic substances,pectic enzymes and haze formation in fruit juices

The pectic substances, located primarily in the middle lamella between cells in higher plant tissues, are complex polysaccharides. They include the negatively charged rhamnogalacturonans, and the neutral arabinogalactans I and II and l-arabinans. These polysaccharides add viscosity to juices but may also form hazes and precipitates and retard maximum recovery of juices from the fruit. The rhamnogalacturonans are degraded by the enzymes pectin methylesterase and polygalacturonase normally present in plant tissues and by these enzymes and pectate lyase in microbially derived commercial pectic enzymes added during processing. The presence of a?abinofuranosidase, which degrades l-arabinans, in commercial pectic enzyme preparations, can cause haze formation in juices such as apple and pear.     

Considering human toxicity as an impact category in life cycle assessment

Characterization of toxic chemicals with relevance to human exposure does normally not belong to Life Cycle Assessments (LCA) and is still a topic of research. The concept of hazard potential classes proposed in this paper is primarily based on threshold limit values that are considered to be a measure of the severity of potential effects. In the absence of threshold limit values the R-phrases of the ordinance of dangerous substances are used. Substances are assigned to five hazard potential classes (A to E). Potentially dangerous chemicals are identified and substances of low toxicological relevance are excluded from further evaluation. The location where a probable exposure might occur (indoor versus outdoor) and inter-media transport of substances is considered. The product comparison is based both on the results of the proposed “semi-quantitative screening method” and on toxicological expert knowledge.     

Kinetic and electrophoretic characterization of NADP dependent dehydrogenases from root tissues of Norway spruce [Picea abies (L.) Karst.] employing a rapid one-step extraction procedure

Summary The NADPH generating enzymes glucose-6-phosphate dehydrogenase (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (EC 1.1.1.44), and isocitrate-dehydrogenase (NADP dependent; EC 1.1.1.42) have been characterized in spruce [Picea abies (L.) Karst.] roots. Interference from inherent phenolic compounds was minimized by complexation with borate and insoluble polyvinylpyrrolidone in the presence of 2-mercaptoethanol and NADP. A further addition of protective substances had no (bovine serum albumin) or even an inhibitory effect (ascorbate) on the enzyme activities. The enzymes were shown to be strictly NADP specific. The optimal pH values and the apparent Michaelis constants from spruce roots are in good agreement with data from different photosynthetic organisms and gametophytic tissues of conifers. Native electrophoresis and subsequent activity staining showed the same banding patterns for enzymes both from root and needle tissues. In addition, the applicability of a highly sensitive dot-blot assay for the accurate quantification of the extracted protein is shown.     

Interaction between humic substances and carbohydrates in a Pampasic pond (Argentina)

Interaction between humic substances from a Pampasic pond and carbohydrates was studied. Determinations were performed by gel chromatography using radiolabeled glucose. The results showed that upon lowering the pH the interaction decreases in relation to the steric arrangement that causes the diminution of the accessibility of the available sites. Results of displacement experiments carried out by addition of unlabeled glucose, galactose, saccharose and starch, confirmed that the interaction occurs mainly through labile non specific bonds and is, to a certain degree, independent of the carbohydrate molecular weight involved. This revised version was published online in July 2006 with corrections to the Cover Date.