Involvement of flavanoids in beer color instability during storage

Besides Maillard reactions, structural rearrangements of flavan-3-ol monomers cause color changes in beer during storage. Acetone/water-soluble fractions (70/30, v/v) of three lager beers of the same batch, differently stabilized before bottling in glass or poly(ethylene terephthalate) (PET) bottles, were monitored by normal-phase HPLC-ESI(-)-MS/MS over a 1-year period of storage at 20 degrees C. In parallel, beer color was monitored by the European Brewery Convention assay. The evolution of color was similar in the silica gel-filtered beer to that in identically bottled and stored poly(vinylpolypyrrolidone)-treated samples, despite the high flavanoid dimers content of the former. On the other hand, color evolved more rapidly in the PET bottle, suggesting a key role of oxygen. The kinetics was still increased in model media containing (+)-catechin, while no color was detected when normal-phase HPLC-fractionated dimers or trimers were investigated. (+)-Catechin emerged as the precursor of less polar products, characterized by a yellow-brown color. MS/MS enabled us to identify these products as issued from the oxidation and intramolecular additions of dehydrodicatechin B4. Similar structures were found in aged beers spiked with (+)-catechin. Beer storage in the absence of oxygen and at low temperature is recommended so as to minimize the synthesis of such pigments.     

Clinical field study to evaluate the efficacy and safety of the amino-acetonitrile derivative, monepantel, compared with registered anthelmintics against gastrointestinal nematodes of sheep in Australia

Objective   To determine the efficacy of monepantel, a developmental compound from the amino-acetonitrile derivative class of anthelmintics, against field infections of gastrointestinal nematodes in sheep.
Procedures   Comparisons of efficacy (using standard faecal worm egg count reduction tests) and safety (on the basis of visual observations) were made in a large-scale field study in Australia, between groups of sheep treated with either an oral solution of monepantel or a registered anthelmintic. The sheep were naturally infected with the major gastrointestinal nematode genera present in Australia.
Results   The post-treatment efficacy results for monepantel were: at 7 days (±1 day) efficacy was >98%; at 14 days (±1 day) it was generally close to or >99%; and at 21 days (±1 day) efficacy was consistently >99%. A high proportion of the targeted nematode populations were confirmed as being resistant to one or more of the currently available anthelmintic classes.
Conclusions   Monepantel when used under field conditions at a minimum dose rate of 2.5 mg/kg was highly effective against mixed-genus natural field infections of the major gastrointestinal nematode genera including Haemonchus , Teladorsagia ( Ostertagia ), Trichostrongylus , Nematodirus , Chabertia and Oesophagostomum . This result included efficacy against some populations resistant to the currently available broad-spectrum anthelmintics. Few Cooperia spp. were present to allow confirmation of efficacy against this genus. On no occasion after treatment did any commercial anthelmintic-treated groups have significantly lower faecal egg counts than the monepantel-treated groups. Monepantel was safe for the target animals and human operators when used in a field situation.     

Androgenesis in a Lolium multiflorum × Festuca arundinacea hybrid to generate genotypic variation for drought resistance

The pentaploid hybrid of Lolium multiflorum and Festuca arundinacea (2n = 5x = 35) combines the high growth rate of L. multiforum with the drought resistance and freezing-tolerance of F. arundinacea. Unfortunately, it also displays the deleterious traits associated with Festuca, namely those associated with high leaf fibre content giving rise to poor palatability and digestibility. To access different combinations of these characters, anther cultures were initiated and regenerated into single embryo derived plants. The anther culture method was very productive since out of a total of 2349 androgenic plants derived from the same parent plant, 57% were green plantlets, although only 507 (22%) subsequently established into plants following transfer to soil. Chromosome counts of randomly selected lines showed that plants with euploid chromosome numbers (14, 21, and 28) would appear to have selective advantage during regeneration. There was wide variation between mature androgenic plants grown under field conditions in plant height, leaf length, leaf width, tiller number and herbage dry matter. The variation between genotypes in response to drought stress was assessed by placing replicate clones under rain-out shelters or under irrigated control conditions in the field. Herbage dry matter under drought was higher in a number of androgenic lines than either parents, but not higher than the pentaploid hybrid. Androgenesis was shown to be a highly effective procedure to expose diverse phenotypic variation all derived from the same Lolium × Festuca hybrid genotype. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of weathering on metal releases from an engineered deposit for alum shale leaching residues

A pile of ca 15,000 t of crushed alum shale leaching residues from uranium refining was deposited in Ranstad, Sweden, in 1972 as a part of a pilot study of various waste storage concepts. A field study has been performed in order to evaluate the efficiency of the engineered barriers (bentoniteltill or crushed limestone) for the prevention of weathering of the leaching residues and subsequent release of metal rich leachates. The concentration levels of Fe (from pyrite in the alum shale) as well as metals associated with the pyrite (e.g. Cu and Ni) indicate that the weathering of leaching residues underneath the cover has progressed to less than 4 cm in 15 yr. No breakthrough of precipitation is indicated from the composition of the percolation water coming from the deposit. Thus, the weathering rate is reduced by ca 3 orders of magnitude in comparison with leaching residues freely exposed to air and precipitation.     

Combinatorial synthesis and sensorial properties of polyfunctional thiols.

Over the past few years, polyfunctional thiols present as trace components have been found to play a major role in many food flavors, due to their exceptionally low odor thresholds. Unfortunately, their presence in minute concentration (in ng/kg to a few microg/kg) and their high reactivity make it very difficult to extract and identify them. Furthermore, most of them are not yet commercially available. The aim of this work was to characterize the chromatographic and sensorial properties of 10 synthetic mercaptoketones and mercaptoalcohols. Combinatorial chemistry proved to be a very useful way to synthesize them rapidly. Sulfur-selective sulfur chemiluminescence detection chromatograms coupled with mass spectroscopy enabled the target compounds to be identified. Flavor profiles and best estimate gas chromatography lowest amount detected by sniffing (BE-GC-LOADS) values were further determined by GC-olfactometry. As expected, new, exceptionally odorant molecules (BE-GC-LOADS < 0.1 ng) were revealed by this unusual approach.     

Release of deuterated (E)-2-nonenal during beer aging from labeled precursors synthesized before boiling

Although lipid autoxidation in the boiling kettle is a key determinant of the cardboard flavor of aged beers, recent results show that mashing is another significant source of wort nonenal potential, the well-known indicator of how a beer will release (E)-2-nonenal during storage. Although unstable, deuterated (E)-2-nonenal nitrogen adducts created during mashing can in some cases partially persist in the pitching wort, to release deuterated (E)-2-nonenal during beer aging. In the experiment described here, the relative contributions of mashing and boiling were estimated at 30 and 70%, respectively. The presence of oxygen during mashing and, to a lesser extent, high lipoxygenase activity can intensify the stale cardboard flavor.     

Evidence of Strecker aldehyde excretion by yeast in cold contact fermentations

A medium containing labeled leucine-d(10) has been used to show that Saccharomyces cerevisiae was able to produce deuterated 3-methylbutanal in a cold contact fermentation. Whereas residual unreduced Strecker aldehydes bound to polyphenols were considered until now as the main defect of alcohol-free beers, yeast emerges from this work as an additional source of worty flavor. When the same experiment was conducted without leucine, 3-methylbutanal excretion also occurred, indicating that valine could be used by yeast as precursor.