Novel conjugative plasmids from the natural isolate Lactococcus lactis subspecies cremoris DPC3758: a repository of genes for the potential improvement of dairy starters

A collection of 17 natural lactococcal isolates from raw milk cheeses were studied in terms of their plasmid distribution, content, and diversity. All strains in the collection harbored an abundance of plasmids, including Lactococcus lactis ssp. cremoris DPC3758, whose 8-plasmid complement was selected for sequencing. The complete sequences of pAF22 (22,388 kb), pAF14 (14,419 kb), pAF12 (12,067 kb), pAF07 (7,435 kb), and pAF04 (3,801 kb) were obtained, whereas gene functions of technological interest were mapped to pAF65 (65 kb) and pAF45 (45 kb) by PCR. The plasmids of L. lactis DPC3758 were found to encode many genes with the potential to improve the technological properties of dairy starters. These included 3 anti-phage restriction/modification (R/M) systems (1 of type I and 2 of type II) and genes for immunity/resistance to nisin, lacticin 481, cadmium, and copper. Regions encoding conjugative/mobilization functions were present in 6 of the 8 plasmids, including those containing the R/M systems, thus enabling the food-grade transfer of these mechanisms to industrial strains. Using cadmium selection, the sequential stacking of the R/M plasmids into a plasmid-free host provided the recipient with increased protection against 936- and c2-type phages. The association of food-grade selectable markers and mobilization functions on L. lactis DPC3758 plasmids will facilitate their exploitation to obtain industrial strains with enhanced phage protection and robustness. These natural plasmids also provide another example of the major role of plasmids in contributing to host fitness and preservation within its ecological niche.     

Environmental monitoring of hydrocarbons: a chemical sensor perspective

Assessing the environmental impact of organic pollutants requires reliable analytical tools that can rapidly screen them with minimal sample handling. Chemical sensors are expected to play an increasing role in environmental monitoring, and recent technological advances are certain to facilitate the application of chemical sensing devices. The search for highly selective, sensitive, low cost, stable, and robust sensors for hydrocarbons is an area of interest that is reflected by many publications on this topic. This report surveys some of the work that has been undertaken using sensors to detect hydrocarbons in the gas and liquid phase. The analytical capabilities of various sensors are compared and discussed in terms of their selectivity, sensitivity, and detection limit. It was found that the sensitivity is highly dependent on the experimental conditions used in the preparation of the sensing surface. Many sensors display acceptable sensitivity under controlled laboratory conditions; however, very few are selective enough to distinguish among several hydrocarbons in complex mixtures. Selectivity is still a challenge that is hindering the widespread application of chemical sensors for environmental monitoring of hydrocarbons and a number of strategies have been proposed to help overcome some of these problems.     

An instrumental variable method for model order identification

The paper describes a simple instrumental variable method for identifying the structure of a wide class of time-series models. The method is aimed at providing a parametrically efficient (parsimonious) model structure which will lead to a combination of low residual error variance, i.e. a good explanation of the data, and low parametric estimation error variance (as measured by some norm associated with the covariance matrix of the estimation errors). It can be applied to single input-single output and multivariable systems using either discrete or continuous-time series models. It can also function as a recursive (on-line) test for reduction in model order.     

APPLICATION OF THE POLYMERASE CHAIN REACTION TO THE RAPID ANALYSIS OF BREWERY YEAST STRAINS

The rapid discrimination of closely-related Saccharomyces cerevisiae strains can pose a significant problem to breweries, in particular where closely related strains are being used simultaneously to manufacture different products. In this study, two PCR approaches have been examined to assess their usefulness for the discrimination of brewery ale and lager yeast strains. PCR using arbitrary primers (RAPD PCR) was found unsuitable for such an application since the DNA profiles generated from brewery strains were generally found to be identical, due presumably to the close genetic relatedness of these yeasts. In contrast, PCR using δ sequence primers could rapidly differentiate between many ale and lager strains and characteristic profiles for these were generated. This method could also be applied directly to yeasts isolated from brewery worts or from active dried yeast preparations. Results of such analyses were available within the working day.     

Influence of heating on the polyphenolic content and antioxidant activity of grape seed flour

Abstract: The production of grape seed flour (GSF) from a waste product generated during winemaking, is of interest in product development applications due to its potential health benefits. However, before GSF can used in baking as a source of additional antioxidants, research on its heat stability is required. The overall objective of this study was to assess changes in phenolic content and antioxidant activity of GSF during heating. Merlot GSF was heated at 5 temperatures (120 to 240 °C) for 0 to 90 min. At each time/temperature combination, total phenolic content (TPC), total flavanoid content (TFC), Trolox equivalent antioxidant capacity (TEAC), 2,2 diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging, and ferric ion reducing antioxidant power (FRAP) of the extracts were determined. Specific polyphenolic compounds, including catechin, gallocatechin, epicatechin, and gallic acid were also measured. Results showed that when Merlot GSF was heated to ≥180 °C, significant decreases in the TPC and antioxidant activity, measured using FRAP, DPPH, and TEAC, were observed. Longer heating times also caused a reduction in antioxidant capability. Catechin and epicatechin content decreased with increasing heating temperature while gallocatechin and gallic acid content increased. Both catechin and epicatechin content had strong positive correlations (r > 0.91) with TPC and TFC, as well with FRAP and TEAC, suggesting that the GSF antioxidant activity is related to the presence of these particular compounds. Overall, while a decrease in antioxidant content was observed during heating, this occurred at higher baking temperatures. Thus GSF may be suitable for use as an ingredient in baked goods to bolster antioxidant content. Practical Application: In order for Merlot grape seed flour (GSF) to be used in baking as a source of additional antioxidant compounds, the impact of heating on the polyphenolic compounds in the GSF needed to be examined. Thermal treatment of Merlot GSF caused significant decreases in the TPC, antioxidant power, and specific polyphenolic compounds when heated ≥180 °C. Thus while antioxidant content decreased with higher heating temperatures, this occurred at higher baking temperatures. Thus, GSF may be suitable for use as an ingredient in baked goods to bolster antioxidant content.     

Total phenolic content, consumer acceptance, and instrumental analysis of bread made with grape seed flour

Grape seed flour (GSF) from grape pomace, a waste product generated during winemaking, was explored for use in bread production due to its potential health benefits. This study evaluated the consumer acceptance and physical properties of bread, including total phenolic content (TPC), made with varying levels of GSF. Dough and breads were prepared using different levels of replacement of hard red spring wheat flour (HRS) with GSF (0 to 10 g GSF/100 g HRS) and stored for 0, 2, or 6 wk at -20 °C. Replacement of 10 g GSF/100 g HRS increased the bread TPC from 0.064 mg tannic acid/g dry weight to 4.25 mg tannic acid/g dry weight. Consumer acceptance and instrumental analyses were used to investigate changes in sensory and texture properties due to GSF replacement. Replacement above 5 g GSF/100 g HRS decreased the loaf brightness and volume, with an increase in the bread hardness and porosity. Generally, breads containing ≥ 7.5 g GSF/100 g HRS were characterized by lower consumer acceptance. A reduction in overall and bitterness acceptance was observed in bread at 10 g GSF/100 g HRS, with decreased acceptance of astringency and sweetness at 7.5 and 10 g GSF/100 g HRS. Based on these results, the replacement of 5 g GSF/100 g HRS is recommended for the production of fortified breads with acceptable physical and sensory properties and high TPC activity compared to refined bread. PRACTICAL APPLICATIONS: This study shows that grape seed flour (GSF) can be used to replace hard red spring wheat flour (HRS) in bread production, with moderate impact on the physical and sensory properties of the bread. Replacement of up to 10 g GSF/100 g HRS significantly decreased overall consumer acceptance of the bread, with lower consumer acceptance of sweetness and astringency at 7.5 and 10 g GSF/100 g HRS. Thus, a replacement value of 5 g GSF/100 g HRS is recommended for the production of fortified breads.     

Stormwater and fire as sources of black carbon nanoparticles to Lake Tahoe

Emitted to the atmosphere through fire and fossil fuel combustion, refractory black carbon nanoparticles (rBC) impact human health, climate, and the carbon cycle. Eventually these particles enter aquatic environments, where they may affect the fate of other pollutants. While ubiquitous, the particles are still poorly characterized in freshwater systems. Here we present the results of a study determining rBC in waters of the Lake Tahoe watershed in the western United States from 2007 to 2009. The study period spanned a large fire within the Tahoe basin, seasonal snowmelt, and a number of storm events, which resulted in pulses of urban runoff into the lake with rBC concentrations up to 4 orders of magnitude higher than midlake concentrations. The results show that rBC pulses from both the fire and urban runoff were rapidly attenuated suggesting unexpected aggregation or degradation of the particles. We find that those processes prevent rBC concentrations from building up in the clear and oligotrophic Lake Tahoe. This rapid removal of rBC soon after entry into the lake has implications for the transport of rBC in the global aquatic environment and the flux of rBC from continents to the global ocean.     

Role of soil freezing events in interannual patterns of stream chemistry at the Hubbard Brook Experimental Forest,New Hampshire

Soil freezing is a disturbance of the below ground environment, potentially resulting in increased losses of NO3- and surface water acidification. Here, we report the effects of soil freezing on interannual variation in stream chemistry at the Hubbard Brook Experimental Forest, New Hampshire. Data from 1970 to 1997 of soil frost depth, snow cover, precipitation, air temperature, and stream discharge and chemistry were used in a stepwise linear regression model to select the variables that best predicted deviations of annual stream concentrations from 4-year running averages. Variables quantifying soil freezing severity were selected as significant predictors of short-term fluctuations in stream K+, NO3-, Ca2+, and Mg2+ concentrations from 1970 to 1989, explaining 59 and 47% of the short-term variability in K+ and NO3-, respectively. Fine-root mortality and disturbance of root-soil-microbe interactions, with subsequent effects on decomposition and nutrient uptake, likely contributed to the mobilization of K+ and NO3- to streamwater following severe soil freezing events. The relationship between soil freezing and stream chemistry, however, weakened during the period 1990-1997. Because soil freezing has had inconsistent effects on stream chemistry during the period 1970-1997, it is unclear whether future changes in the frequency, duration, and depth of soil freezing events as the result of changes in the snow cover regime under a warmer climate will have significant impacts on the losses of NO3- and nutrient-base cations from temperate northern ecosystems.     

Salmonella carriage in an Irish pig herd: correlation between serological and bacteriological detection methods

Salmonella carriage in pigs represents a serious health problem that undoubtedly contributes to the spread of human disease. Thus, the efficient and reliable testing of farm animals for bacteria such as Salmonella is an important aspect of any efficient control strategy. Serological analysis of 15 meat juice samples detected antibodies against Salmonella in some. but not all, of the animals identified bacteriologically as harboring the pathogen, indicating a lack of correlation between the bacteriological and serological methods used for Salmonella detection. The results suggest that testing by enzyme-linked immunosorbent assay is appropriate at the herd level, with culture methods preferable for individual animal analysis. A novel culture protocol detected Salmonella in the cecal contents of 15 pigs, whereas a method based on the European Standard identified only 9 pigs as being Salmonella-positive. During the study, an unusual finding was the relatively high incidence of Salmonella London carriage in the pigs tested.     

Assessment of iron bioavailability from twenty elite late‐maturing tropical maize varieties using an in vitro digestion/Caco‐2 cell model

An in vitro digestion/Caco‐2 cell model was used to assess iron bioavailability of twenty elite late‐maturing tropical maize varieties grown in three diverse agroecologies in West and Central Africa (WCA). Kernel‐iron concentration of the varieties, averaged across locations, varied from 19.2 to 24.4 mg kg^?1, while mean kernel‐zinc concentration ranged between 19.4 and 24.6 mg kg^?1. Significant differences in iron bioavailability were observed among varieties, but the environment had no significant effect. Mean bioavailable iron ranged between 14% below and 43% above the reference control variety, TZB‐SR. Variety DMR‐LSR‐Y with the highest concentrations of kernel‐iron and ‐zinc of 24–25 mg kg^?1 across the three locations had a similar quantity of bioavailable iron as the reference control, TZB‐SR. In the long run this variety could be potentially effective in reducing iron deficiency because of its high kernel‐iron. The most promising varieties were Mid‐altitude STR synthetic and ACR91SUWAN‐1‐SRC1. They had kernel‐iron and ‐zinc levels of 22–24 mg kg^?1 and bioavailable iron 24–36% higher than the reference control, TZB‐SR. Additional research is necessary to determine if the increases in kernel‐iron concentration and bioavailable iron observed in this study can significantly improve the iron status of individuals in WCA at risk for iron deficiency. Copyright © 2004 Society of Chemical Industry