Anti/pro-oxidative properties of selected standard chemicals and tea extracts investigated by DNA-based electrochemical biosensor

A DNA-modified screen-printed carbon electrode and the [Co(phen)₃]³⁺ complex as an electrochemical DNA marker were used for the evaluation of anti/pro-oxidative properties of -tocopherol, -carotene, quercetin, kaempferol and myricetin, as well as various tea extracts. Reactive oxygen species were generated using a model cleavage mixture composed of 5×10^–7 M [Cu(phen)₂]²⁺ as the catalyst, 1×10^–3 M ascorbic acid as the chemical reductant and air oxygen as the natural oxidant. The antioxidative activity of standard chemicals increases with their concentration, reaching a maximum where prooxidative behaviour becomes of importance. Antioxidative effects of tea exctracts varied with the temperature of their preparation. Similar results were obtained by the 2, 2-diphenyl-1-picrylhydrazyl free radical method.     

Provitamin A carotenoids in table olives according to processing styles, cultivars, and commercial presentations

The concentration of provitamin A carotenoids in table olives was determined. Only -carotene was found in all commercial presentations. -carotene was also present in final products containing carrots. Concentrations of -carotene, referring to 100 g edible portion, ranged from an average of 197 to 1,387 g in green olives, from 37 to 726 g in directly brined olives and from 39 to 333 in ripe (darkened by oxidation) olives. Thus, some commercial presentations of table olives can be considered reasonable sources of provitamin A. Several groups were formed within elaboration styles and cultivars, according to commercial presentations. Their averages and other statistical estimations are also given. These results may be used by the industry as a source of information for nutritional labelling or by nutritionists to estimate provitamin A intakes in diets that include table olives.     

Evolution of soluble carbohydrates during the development of pea, faba bean and lupin seeds

Seeds of pea (Pisum sativum L. cv. Ergo), faba bean (Vicia faba ssp. minor Harz., cv. Tibo) and yellow pea lupin (Lupinus luteus L. cv. Juno) were sampled at different days after flowering (DAF) and their content of soluble carbohydrates was determined: Analysis of samples showed thatmyo-inositol, fructose, glucose, galactose and sucrose were found in high abundance early in development and their content decreased gradually during maturation. -Galactosides, which includes the content of raffinose, stachyose and verbascose, started to appear later in seed development, at 37 DAF in peas, 40 DAF in faba beans and 45 DAF in lupins. Their accumulation increased considerably during seed growth, and the maximum content was obtained in mature seeds; 3.8% in peas, 4.5% in faba beans and 10.4% in lupins. Results obtained for these sugars during seed development were fitted to modelling curves in order to predict sugar content at different development stages.     

Effect of α- and δ-tocopherol on the oxidative stability of a mixed hydrogenated fat under frying conditions

Information on the antioxidative potential of -tocopherol is scanty, in particular for frying conditions. This study was aimed at assessing the antioxidative effects and degradation of - and -tocopherol between 0.01 and 0.1% on the oxidation of a commercial frying fat at 160 °C. Oxidation experiments were performed by assessing every 15 or 30 min the peroxide value and conjugated dienes as primary oxidation products, p-anisidine reactive products and hexanal as secondary oxidation products, as well as the stability of tocopherols. The fatty acid composition was determined after 6 h. The fat samples enriched with -tocopherol were considerably less resistant to oxidation compared to those with -tocopherol. Both primary and secondary oxidation parameters increased their speed of formation with -tocopherol but not with -tocopherol. The latter observation is confirmed for the total amount of oxidation and also for the first stage, showing a lag phase only for -tocopherol. These antioxidative effects can be due to the higher stability of -tocopherol compared to -tocopherol, which is oxidized faster into tocopheryl radicals, which can participate in side reactions that result in an acceleration of the oxidation speed. Neither -tocopherol nor -tocopherol influenced the fatty acid pattern. The investigation showed that during mild frying conditions the tocopherol homologues displayed various antioxidant activities. The less effective homologue, -tocopherol, underwent disintegration more quickly than -tocopherol.     

Modelling of drying and rehydration of carrots using Peleg’s model

The drying and rehydration process of conventionally and organically cultivated carrots was studied and the resulting data were fitted to the Pelegs model. Carrots were fluid-bed and halogen dried and after that soaked in water at room temperature. The Pelegs model gave a good prediction of water removal and water uptake in all experiments (R>0,994). During the drying process the Pelegs rate constant (K₁) was affected by temperature. K₁ values decreased with the increase of the drying temperature. This relation was linear for fluid-bed drying and exponential for halogen drying, which implied a higher impact of the drying temperature on the dehydration kinetics during halogen drying. The lower K₁ values for fluid-bed drying suggested higher initial drying rates in comparison with halogen drying at all drying temperatures. The temperature dependence of 1/K₁ followed an Arrhenius-type relationship. Both Pelegs rehydration constants (K₁ and K₂) increased with the increase of the drying temperature. This implied regular decrease of initial rehydration rate and water uptake with the increase of the drying temperature.     

Effects of high O2 levels on post-harvest quality and shelf life of table grapes during long-term storage

Freshly harvested Kyoho table grapes (Vitis vinifera × V. labrusca) were stored in controlled atmospheric chambers, either in air, 80% O₂, or 40% O₂ + 30% CO_2, for up to 60 days at 0 °C in 95% relative humidity followed by 5 days in air at 20 °C. Physical and chemical properties were recorded initially and at 15-day intervals during storage. Storage in 80% O₂ or 40% O₂ + 30% CO₂ improved berry hardness, springiness, chewiness, flavors and membrane integrity over control stored in air. In addition, these high O₂ storage conditions significantly reduced fruit decay, berry drop, rachis browning and weight loss, delayed the decrease of soluble solids, titratable acidity and ascorbic acid of table grapes, compared with storage in air. Treatment in 80% O₂ resulted in a significantly firmer berry, better texture, berry adherence strength, and sensory scores than those treated with 40% O₂ + 30% CO₂, but did not significantly affect cohesiveness, springiness, aroma and membrane integrity. Data obtained in this study suggest that high oxygen treatment improve the quality of table grapes and extend its shelf life.     

Effect of substitution of aspartame for sucrose on instrumental texture profile of hydrocolloids gelled systems

The effect of substituting aspartame (0.04–0.16% w/w) for sucrose (5–25% w/w) on the instrumental texture profile of three hydrocolloid gelled systems: -carrageenan, gellan gum and -carrageenan/locust bean gum at three different concentrations (0.3, 0.75 and 1.2% w/w) was studied. In gellan gels hardness and chewiness increased with sucrose concentration but not so in either -carrageenan or -carrageenan/LBG gels where no changes in these parameters were detected. Addition of sucrose also produced a small but significant increase in cohesiveness in gellan gels. The effect of sucrose concentration on all texture parameters of gellan gels was higher as gellan concentration increased. Aspartame addition did not affect TPA parameters. TPA results obtained for aspartame gels did not differ from those corresponding to the unsweetened gels considered here. Summarising the above information it can be said that substituting aspartame for sucrose in this type of sweetened gel changed the textural properties and that the changes produced depended on the hydrocolloid type and concentration and on the sucrose concentration replaced.     

The antigenic response of<Emphasis Type="Italic"> β</Emphasis>-lactoglobulin is modulated by thermally induced aggregation

The antigenic response of thermally denatured and aggregated -lactoglobulin was determined by an indirect competitive enzyme-linked immunosorbent assay using polyclonal antibodies from the egg yolk of chicken immunized with heat-denatured -lactoglobulin as a measure for the potential antigenicity/allergenicity. The heat denaturation and the aggregation of heated whey protein isolate solutions were followed by reversed-phase high-performance liquid chromatography and photon correlation spectroscopy. Thermally modified whey proteins showed a remarkable increase of antigenicity when heated to 90 °C, possibly as a consequence of the exposure or formerly hidden epitopes. Above 90 °C, the antigenic response decreased owing to the loss of conformational epitopes and masking of sequential epitopes in the course of aggregation to particles. When large and compact particles were formed, the antigenicity was reduced remarkably. Depending the heating conditions applied, the structure and the size of whey protein particles and thus the potential allergenicity may be modulated in a wide range.     

Optimised quantification method for yeast-derived 1,3-β-<Emphasis Type="SmallCaps">d</Emphasis>-glucan and α-<Emphasis Type="SmallCaps">d</Emphasis>-mannan

The polysaccharides 1,3--d-glucan and -d-mannan show numerous beneficial effects for the health of humans and animals. For several years, an increasing number of glucan- and mannan-containing products intended for food and feed applications are commercially available. For the determination of glucan and mannan contents, however, widely accepted methods have not yet been established. We have developed a practicable and reliable quantification method characterised by acidic hydrolysis with trifluoroacetic acid and subsequent determination of released d-glucose and d-mannose. The unavoidable loss of the monosaccharides due to the acidic conditions was minimised by optimisation of the hydrolysis parameters. The best conditions found were compared with literature methods in order to demonstrate the suitability. Finally, glucan and mannan contents of various commercial products were determined and compared to the specifications given by the manufacturers.     

Antioxidative activity of<Emphasis Type="Italic"> Geranium macrorrhizum</Emphasis>

The composition of radical-scavenging compounds from Geranium macrorrhizum leaves was analyzed and the antioxidative activities of various extracts was determined. Seven compounds, namely gallic acid, ellagic acid, 4-galloyl quinic acid, the flavonoid quercetin and three of its glycosides, quercetin-3--glucopyranoside, quercetin-3--galactopyranoside and quercetin-4--glucopyranoside were isolated and identified in the various fractions. The radical-scavenging activity of the isolated compounds was measured using DPPH^· and ABTS^·+ scavenging assays and compared with the activity of rosmarinic acid. Quercetin-3-glucopyranoside and quercetin-3-galactopyranoside showed the highest antioxidative capacities. Antioxidative activities of all plant fractions were assessed by model system tests (superoxide anion and hydrogen peroxide scavenging) and by oxidation tests (-carotene bleaching, peroxide value, UV absorbance and headspace-gas chromatography hexanal determination). The ethanol-butanol fraction of the plant possessed the highest activity in most of the tests.     

Potential DNA–protein cross-link products formed by sugar degradation products: identification of N 6-[2-(N 2-2′-deoxyguanosyl)propionyl]lysine

Sugar degradation products are formed during heat treatment of food as well as endogenously in vivo. As reactive carbonyl compounds, they react readily with proteins or DNA to form protein- or DNA-bound advanced glycation end products (glycation reaction or Maillard reaction). In this study, we investigated the formation of potential DNA–protein cross-link products from sugar degradation products. 2-Deoxyguanosine, l-lysine and different carbohydrates were incubated at 37 °C. The sugar degradation products dihydroxyacetone and d,l-glyceraldehyde lead to the formation of two new cross-link products. The new compounds were isolated by preparative high-performance liquid chromatography and identified by spectral data as the two diastereomers of N⁶-[2-(N²-2-deoxyguanosyl)propionyl]lysine. In this structure, the -amino group of lysine and the exocyclic amine group of 2-deoxyguanosine are linked via a carboxyethyl group, derived from the carbohydrate component. The binding sites and the binding types were confirmed by synthesis of the analogous products from N²-(1-carboxyethyl)guanosine and N-acetyllysine methyl ester.Dedicated to Professor Th. Severin on the occasion of his 75^th birthday     

Analysis of volatile components of Petite Arvine wine

Petite Arvine is a white grape variety that grows exclusively in the canton of Valais in Switzerland and is used to produce a typical regional wine. In order to elucidate the nature of the flavour compounds that contribute to the characteristic aroma of this wine, the organic extracts were analysed by gas chromatography and olfactometry. The olfactometrically detected zones were further compared with the odour of extracts of vegetal material. 3-Mercaptohexanol, -ionone and other compounds were identified as main contributors to the characteristic aroma of Petite Arvine wine.     

Determination of <Emphasis Type="SmallCaps">l</Emphasis>-lactic acid in yoghurt by a bienzyme amperometric graphite–Teflon composite biosensor

l-Lactic acid was determined in cows milk, goats milk and whey protein concentrate (WPC)-enriched goats milk yoghurts by using an amperometric graphite–Teflon biosensor in which peroxidase (HRP), l-lactate oxidase (L-LOD) and the mediator ferrocene were immobilized. The correlation between the l-lactic acid results obtained using the bienzyme biosensor method and a standard colorimetric enzymatic method was 0.95. One- and two-way analyses of variance indicated that the biosensor method was able to discriminate between WPC supplemented and non-supplemented yoghurts, whereas this discrimination could not be accomplished with the colorimetric enzymatic method. The biosensor described in this paper offers considerable advantages to industry because it provides rapid, direct and economical analysis of yoghurt quality.     

Influence of processing on the generation of γ-aminobutyric acid in green coffee beans

A determination of the concentrations of free amino acids in differently processed green coffees indicated the nonprotein amino acid -aminobutyric acid (GABA), a well-known plant stress metabolite, to be present in raw coffee beans (Coffea arabica L.) in significantly varying amounts. The GABA content of unwashed Arabica beans (green coffee produced by the dry processing method) was always markedly higher than that of washed Arabicas (wet processing method) as well as that of untreated seeds. This result underlined the assumption that during postharvest treatment a significant metabolism occurs within coffee seeds. A putative relation between drought stress of the coffee seeds and postharvest treatment methods is discussed. The GABA content of green coffee beans may serve as a potent tool to characterize the type of postharvest treatment applied in coffee processing.