Insights on the chemical basis of the astringency of Spanish red wines

The main goal of the present study is to provide an insight on the role played by non-volatile molecules on the different in-mouth attributes, particularly astringency. For achieving such goal, the main in-mouth sensory attributes of 34 oaked Spanish red wines were measured by a trained panel. The wine content in 30 sensory-active molecules was analysed by different HPLC based methodologies together with classical enological parameters and two proanthocyanidin indexes. Fourteen compounds (aconitic acids, polymeric proanthocyanidins, caftaric, caffeic and coutaric acids and seven quercetins) were found to be at concentrations above reported taste thresholds and to have a reasonably high range of occurrence. Two highly statistically significant models for astringency were built with those compounds. Even if the models could not be fully validated by sensory addition experiments, the research has demonstrated that wine astringency is driven by polymeric proanthocyanidins and by certain phenolic acids, the rate trans/cis-aconitic acid and flavonol profiles. The research has highlighted the existence of extremely complex interactions between non-volatile compounds on the in-mouth sensory perception. Particularly remarkable is the lack of additivity and potential antagonism found between the pairs cis/trans-aconitic acids, between aconitic and caffeic acids and between quercetin-3-O-galactoside and quercetin-3-O-glucoside. Also remarkable was the sweetness × astringent interaction and the matrix-dependence of the sensory responses elicited by flavonols. These results suggest the need for new paradigms and experimental procedures for fully decoding the real sensory relevance of individual non-volatile compounds in the overall wine flavour.     

Erosion-corrosion mapping of Fe in aqueous slurries: some views on a new rationale for defining the erosion-corrosion interaction

In studies of erosion-corrosion of materials in aqueous conditions, there have been various attempts to define regimes of interaction. Such regimes indicate whether erosion or corrosion may dominate the wastage mechanism. However, intermediate regimes in which corrosion and erosion interact with each other may lead to situations where the wastage is far greater than the sum of the processes acting separately.A common method of defining erosion-corrosion interactions has been to distinguish between the regime in which erosion enhances the corrosion rate (the so called “additive effect” because the corrosion contribution can be measured electrochemically and thus added to the erosion contribution to assess the overall wastage rate) and the regime where corrosion enhances erosion (the so-called “synergistic” effect). However, regimes of erosion-corrosion, where corrosion impedes the erosion are also of great importance mechanistically, and usually these are termed as exhibiting “negative synergism”. Defining the conditions in which a transition from “positive” to “negative synergism” occurs, is useful in order to optimize the parameters to minimize the wastage rate.This paper reviews the rationale that has been used to define erosion-corrosion regimes in aqueous conditions as part of a study of the erosion-corrosion of Fe at various pHs. The mathematical definitions are discussed in relation to practical erosion-corrosion problems. In addition, a new “antagonistic” erosion-corrosion regime is proposed to properly define the concept of “negative synergism”.     

Inverse relationships between selenium and mercury in tissues of young walleye (Stizosedion vitreum) from Canadian boreal lakes

The concentrations of total mercury (Hg), methylmercury (MeHg) and total selenium (Se) were determined in muscle, liver and brain tissues of young-of-the-year walleye (Stizosedion vitreum) specimens collected from 8 boreal lakes that are located within 107 km around the Sudbury smelters in Ontario, Canada. Dry weight basis concentrations of Hg were highest in muscle and lowest in brain (p < 0.05), those of MeHg were higher in muscle than in liver and brain but there was no significant difference between liver and brain (p < 0.05). The highest Se concentrations were found in liver and the lowest in brain (p < 0.05). Considering the biomass of the studied tissues, muscle was the part of the body where most of Hg, MeHg and Se were accumulated. In fish muscle, the percentage of MeHg over Hg was the highest and this percentage was the lowest in liver. The concentrations of Hg, MeHg and Se in the studied tissues were closely related to the concentrations of total dissolved Se in lake waters which vary with the distance of the lakes from the smelters. Thresholds of Se concentrations in tissues were revealed (6.2, 12.0 and 3.5 mg kg^− 1 dry wt., for muscle, liver and brain, respectively), above which a significant reduction of MeHg concentrations was observed in all studied tissues compared to lower Se levels in the same tissues. Based on the collected information and data analysis, possible mechanisms for the biological processes behind the observed inverse relationships between Se and Hg in fish tissues are discussed.     

The inhibitory effect of natural microflora of food on growth of Listeria monocytogenes in enrichment broths

The aims of this study were to (i) compare the inhibitory effects of the natural microflora of different foods on the growth of Listeria monocytogenes during enrichment in selective and non-selective broths; (ii) to isolate and identify components of the microflora of the most inhibitory food; and (iii) to determine which of these components was most inhibitory to growth of L. monocytogenes in co-culture studies. Growth of an antibiotic-resistant marker strain of L. monocytogenes was examined during enrichment of a range of different foods in Tryptone Soya Broth (TSB), Half Fraser Broth (HFB) and Oxoid Novel Enrichment (ONE) Broth. Inhibition of L. monocytogenes was greatest in the presence of minced beef, salami and soft cheese and least with prepared fresh salad and chicken pâté. For any particular food the numbers of L. monocytogenes present after 24 h enrichment in different broths increased in the order: TSB, HFB and ONE Broth. Numbers of L. monocytogenes recovered after enrichment in TSB were inversely related to the initial aerobic plate count (APC) in the food but with only a moderate coefficient of determination (R²) of 0.51 implying that microbial numbers and the composition of the microflora both influenced the degree of inhibition of L. monocytogenes. In HFB and ONE Broth the relationship between APC and final L. monocytogenes counts was weaker. The microflora of TSB after 24 h enrichment of minced beef consisted of lactic acid bacteria, Brochothrix thermosphacta, Pseudomonas spp., Enterobacteriaceae, and enterococci. In co-culture studies of L. monocytogenes with different components of the microflora in TSB, the lactic acid bacteria were the most inhibitory followed by the Enterobacteriaceae. The least inhibitory organisms were Pseudomonas sp., enterococci and B. thermosphacta. In HFB and ONE Broth the growth of Gram-negative organisms was inhibited but lactic acid bacteria still reached high numbers after 24 h. A more detailed study of the growth of low numbers of L. monocytogenes during enrichment of minced beef in TSB revealed that growth of L. monocytogenes ceased at a cell concentration of about 10² cfu/ml when lactic acid bacteria entered stationary phase. However in ONE Broth growth of lactic acid bacteria was slower than in TSB with a longer lag time allowing L. monocytogenes to achieve much higher numbers before lactic acid bacteria reached stationary phase. This work has identified the relative inhibitory effects of different components of a natural food microflora and shown that the ability of low numbers of L. monocytogenes to achieve high cell concentrations is highly dependent on the extent to which enrichment media are able to inhibit or delay growth of the more effective competitors.     

Investigation of antioxidant synergisms and antagonisms among thymol, carvacrol, thymoquinone and p-cymene in a model system using the Briggs-Rauscher oscillating reaction

Auto-oxidation of lipids has been recognised as a major deterioration process affecting both the sensory and nutritional quality of foods; the application of antioxidants is one of the technically simplest ways of reducing this process. Previous reports showed that these compounds were found in selected aromatic plants and that thymol, carvacrol, thymoquinone and p-cymene as constituents of different essential oils possess substantial antioxidant activity. In the present study their antioxidant capacities were evaluated using the Briggs-Rauscher oscillating reaction method.Our results indicate that the majority of the antioxidant mixtures demonstrated some level of discrepancy in antioxidant capacity when compared to individual values of their constituents. The strong antagonistic effect was found only when thymoquinone was paired with p-cymene. All other combinations of two antioxidants clearly showed some degree of synergistic effect. The mixtures of three antioxidants showed a decrease in antioxidant capacity when compared to their individual values. The results obtained for more complex mixtures of four antioxidants showed a decrease in antioxidant capacity, indicating and confirming that the antagonistic effect between thymoquinone and p-cymene overrides the synergistic effect of other pairs.     

Interactions of antioxidants isolated from tart cherry (Prunus cerasus) fruits

Tart cherry produces various kinds of polyphenolics in its fruits that include cyanidin derivatives (mostly cyanidin 3-glucosylrutinoside, cyanidin 3-rutinoside, cyanidin sophoroside), peonidin 3-glucoside; kaempferol, quercetin, and isorhamnetin and their derivatives, as well as the alkaloid, melatonin. The antioxidant capacities of these constituents were analysed using the TEAC antioxidant assay. Kaempferol, quercetin, isorhamnetin 3-rutinoside, cyanidin 3-rutinoside, and melatonin showed significant antioxidant capacities; of these, kaempferol proved to be the most active. In order to determine how these constituents interact in terms of expression of their antioxidant action, we performed an isobolographic analysis. Using different dose ratios (e.g., 1:1, 1:2, 1:4) for the selected polyphenol constituents, we found evidence that three types of interactions may occur: synergistic, additive, and negative. The most important and new finding here was that pairs of compounds with the highest antioxidant capacity (e.g., kaempferol and melatonin at a dose ratio of 2:1, respectively, and cyanidin 3-rutinoside and isorhamnetin 3-rutinoside at a dose ratio of 1:4, respectively) showed strong synergistic types of interactions. Additive or negative types of interactions occurred for pairs of compounds that had lower antioxidant capacities. Thus, not all polyphenols in tart cherry fruits are equally effective in alleviating oxidative stress. Those which are most effective are likely to be acting synergistically.     

Role of nitrogen in tribochemical interaction between Zndtp and succinimide in boundary lubrication

Tribochemical interactions between zinc dithiophosphate (Zndtp) and polyisobutene succinimide (PIBSI) were studied in the mild wear regime by a dual analysis approach. Both TEM analyses of wear fragments and inside wear scar XPS on tribofilms were obtained in the same location of the wear track. In presence of the succinimide, there are notable modifications in the composition of the zinc polyphosphate tribofilm which is classically formed in presence of Zndtp alone. Apart from amorphous zinc polyphosphate glass, the film contains also large amounts of oxidised species (oxides, sulphates and nitrates) together with residual succinimide function groups. The atomic ratio N/P is about 0.3. Moreover, compared to Zndtp, less tribofilm is produced due to some competition in adsorption process. The results highlight the role of the tribochemical reaction to explain the antagonism between the two additives. The presence of some iron oxide in the tribofilm material indicates that the anti-abrasive wear mechanism of Zndtp is hindered by the presence of the succinimide. The lower content of the tribofilm in sulphide species also suggests a lower efficiency to control the anti-seizure properties of the mixture of the two additives.     

Contributions of phenolics and added vitamin C to the antioxidant capacity of pomegranate and grape juices: synergism and antagonism among constituents

The aim of this study was to examine the contribution of sugar, organic acid, neutral phenol, and anthocyanin fractions and added ascorbic acid to grape and pomegranate‐nectarine juice total phenol, oxygen radical absorbance capacity (ORAC), ferric reducing antioxidant power (FRAP) and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) values. Neutral phenol and anthocyanin fractions contributed ≥75% of the total antioxidant capacity (TAC) for both juices. Intrinsic synergy and antagonism among the fractionated constituents occurred inconsistently in each assay. Sugars and organic acids antagonised pomegranate juice neutral phenols and anthocyanins in the DPPH assay by 50% and the grape juice ORAC value by 21%, but were synergistic to the grape juice FRAP value. The added ascorbic acid was dose‐dependently synergistic with pomegranate and grape juice total phenol, DPPH and FRAP assays, but less so in the ORAC assay. Thus, the interactions between grape and pomegranate juice constituents determine TAC and total phenol values, and synergy in these assays could not be attributed solely to polyphenols.     

菜园土壤高磷条件对油菜磷、锌含量的影响

采用盆钵试验研究了菜园土高磷条件下对油菜磷、锌颉颃作用的影响。结果表明,随着土壤有效磷含量的升高,油菜植株体内的含磷量也在不断升高,但上升的趋势逐渐减缓,其中,茎叶的含磷量始终大于根中的含磷量。而植株的含锌量则有很大的不同,随着土壤有效磷含量的增加,植株根中的含锌量也在不断的增加,直到趋于平稳,而茎叶中锌的含量随土壤有效磷含量的升高而增加到一定程度后表现出下降的变化趋势。这说明油菜的磷、锌颉颃作用是发生在植株体内的一种生理机制。