Search

Acidity is one of the primary sensory elements in wine, and the balance of sugar and acidity is probably the strongest element affecting wine appreciation. However, little is known about how yeast strains and fermentation conditions will affect the production of fermentation-derived acids, including acetic, succinic and pyruvic acid. This study employs a multifactorial experimental design to provide a better understanding of how individual or simultaneous changes in environmental parameters such as pH, sugar and temperature influence the production of individual organic acids during fermentation in several yeast strains in synthetic must. Certain changes in environmental factors led to conserved trends between strains and treatments. Strains produced higher succinic acid levels when temperature was increased. Significant strain-dependent differences were observed when sugar concentrations were varied for both strains: the combinatorial impact of high initial sugars and fermentation temperature was more pronounced when increased pyruvic acid production was observed in yeast strain VIN13. On the other hand, while combinatorial influences are evident, higher sugar fermentation settings were largely characterised by high acetic acid concentrations for both strains. It is clear that simultaneous changes in sugar, pH and temperature affect organic acid trends in a variable manner, depending on the particular combination of environmental parameters and yeast strain. The study provides valuable information regarding the manner in which initial must parameters and environmental conditions throughout fermentation may affect wine acidity. Since many of these parameters can be controlled at least in part during the winemaking process, the data provide important background information for oenological strategies that aim to optimise the acid balance of wines.

The conversion of grape sugar to ethanol and carbon dioxide is the primary biochemical reaction in alcoholic wine fermentation, but microbial interactions, as well as complex secondary metabolic reactions, are equally relevant in terms of the composition of the final wine produced. The chemical composition of a wine determines the taste, flavour and aroma of the product, and is determined by many factors such as grape variety, geographical and viticultural conditions, microbial ecology of the grapes and of the fermentation processes, and the winemaking practices. Through the years, major advances have been made in understanding the biochemistry, ecology, physiology and molecular biology of the various yeast strains involved in wine production, and how these yeasts affect wine chemistry and wine sensory properties. However, many important aspects of the impact of yeast on specific wine-relevant sensory parameters remain little understood. One of these areas of limited knowledge is the contribution of individual wine yeast strains to the total organic acid profile of wine. Wine quality is indeed very directly linked to what wine tasters frequently refer to as the sugar-acid balance. The total acidity of a wine is therefore of prime sensory importance, and acidity adjustments are a frequent and legal practice in many wineries. However, the total acidity is the result of the sum of all the individual organic acids that are present in wine. Importantly, each of these acids has its own sensory attributes, with descriptors ranging from fresh to sour to metallic. It is therefore important not only to consider total acidity, but also the contribution of each individual acid to the overall acid profile of the wine. This review will summarise the current knowledge about the origin, synthesis and analysis of organic acids in wine, as well as on the management of wine acidity.

Over the 10-year period January 1976 - December 1985, 446 patients with histologically verified adenocarcinoma of the stomach were treated at Tygerberg Hospital. Coloured patients made up 63,4% of the study population and a significant increase in the annual proportion of this group was observed. Coloured men comprised 47,6% of the total group. The mean age of white and coloured patients differed significantly (68,9 v. 56,5; P < 0,001). The symptom complex was essentially similar in the two racial groups and in general the character of the symptoms had no bearing on the prevalence of resection. Although antral tumours were most common in whites and in coloureds, there was a significant increase in tumours located in the fundus in whites. The resection rate remained unchanged over the 10-year period. Only 4 cases of early gastric cancer were detected during this period without any signs of an increased yield of early lesions over time. This audit revealed no beneficial changes over time, which is in stark contrast with reports from Japan regarding the proportion of curable lesions.

One design strategy by which to iterate the photocatalytic efficiency of semiconducting nanomaterials for harvesting solar energy involves the synthesis of type-II heterostructured materials. In this article, a straightforward, facile and environmentally benign route to heterostructures in which SnO₂ nanospheres are capped by PbS nanocubes is reported. It offers to address current limitations to photocatalytic efficiency brought about by electron-hole recombination and narrow photoresponsive ranges in many existing systems. PbS nanocubes are grown in the presence of preformed SnO₂ nanospheres by functionalizing the surface of the latter using cetyltrimethylammonium bromide (CTAB). Heterostructure formation is confirmed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface area analysis, and transmission electron microscopy (TEM) analysis. Rietveld refinement has been exploited to simultaneously elucidate the atomic and microstructures of these materials, allowing the quantitative determination of particle structure and stability. The combination of narrow band-gap semiconductor (PbS) and wide band-gap semiconductor (SnO₂) endows the heterostructured nanomaterial with potential as a photocatalyst and, in the degradation of Rhodamine B (RhB) dye under solar simulation, it showed superior photocatalytic activity to that of its separate SnO₂ and PbS components. A strong type-II interaction is demonstrated by the heterostructure and a charge separation mechanism has been utilized to clarify this behaviour.

The γ′ strengthening phase in an advanced nickel-based superalloy, ATI 718Plus, was characterized using a blind source separation applied to a four dimensional X-ray microanalysis dataset obtained by scanning transmission electron microscopy. Selected patterns in the X-ray spectra identified by independent component analysis were found to be spatially and chemically representative of the matrix (γ) and precipitate phases (γ′) present in the superalloy, enabling their size, shape and distribution to be determined. The three dimensional chemical reconstruction of the microstructure may provide insight into the role of the various alloying elements in the evolution of the microstructure at the nano-scale.