Microbial stability, phytochemical retention, and organoleptic attributes of dense phase CO2 processed muscadine grape juice

Dense phase CO2 processing (DP-CO2) is a promising alternative to thermal pasteurization potentially inactivating microorganisms without affecting food phytochemicals or organoleptic characteristics. To demonstrate these effects, studies were conducted by changing processing pressure and CO2 concentration in relation to microbial destruction. Subsequent storage stability (10 weeks at 4 degrees C) of muscadine grape juice processed by DP-CO2 (34.5 MPa at 8% or 16% CO2) was evaluated and compared to a heat-pasteurized juice (75 degrees C, 15 s). Thermal pasteurization decreased anthocyanins (16%), soluble phenolics (26%), and antioxidant capacity (10%) whereas no changes were observed for both DP-CO2 juices. DP-CO2 juices also retained higher anthocyanins (335 mg/L), polyphenolics (473 mg/L), and antioxidant capacity (10.9 micromol of Trolox equivalents/mL) than thermally pasteurized juices at the end of storage. Insignificant differences in sensory attributes (color, flavor, aroma, and overall likeability) were observed between unprocessed and DP-CO2 juices, while significant differences were observed between unprocessed and heat-pasteurized juices. Panelists preferred DP-CO2 over heat-pasteurized juices throughout the first 6 weeks of storage, whereby the growth of yeast and mold adversely affected the juice aroma. Comparable microbial counts were observed between DP-CO2 and thermally pasteurized juices during the first 5 weeks of storage. DP-CO2 protected phytochemicals in muscadine juice during processing and storage without compromising microbial stability or sensory attributes over 5 weeks of storage.     

Enhancing the retention of phytochemicals and organoleptic attributes in muscadine grape juice through a combined approach between dense phase CO2 processing and copigmentation

This study evaluated the phytochemical stability and organoleptic attributes of an ascorbic acid-fortified muscadine grape juice as affected by dense phase CO2 processing (DP-CO2) and addition of thyme polyphenolic cofactors (Thymus vulgaris; 1:100 anthocyanin-to-cofactor molar ratio) in efforts to prevent phytochemical losses that occur during storage of anthocyanin-containing beverages, especially in the presence of carbonyl compounds commonly produced during thermal processing and storage. DP-CO2 processing insignificantly altered initial juice phytochemical and antioxidant content, whereas thermal pasteurization reduced anthocyanins (263 mg/L), ascorbic acid (42 mg/L), soluble phenolics (266 mg/L), and antioxidant capacity (6 microM Trolox equivalents/mL). Similar trends were observed during storage, and data showed that increasing the CO2 level from 8 to 16% during DP-CO2 was instrumental in reducing juice phytochemical and antioxidant degradation. Copigmentation was instrumental in retaining higher anthocyanin, soluble phenolics, and antioxidant capacity during storage without affecting initial juice aroma and flavor characteristics. Moreover, on the basis of overall likeability scores, panelists preferred copigmented juices, which had increased juice color intensity and masked the detrimental color fading that occurred during storage, especially when compared to thermally pasteurized juices. DP-CO2 and copigmentation were effective strategies to reduce phytochemical and color deterioration that occurred in muscadine juice during storage without affecting their organoleptic attributes.     

Influence of elevated CO2 and GM barley on a soil mesofauna community in a mesocosm test system

We hypothesized that the combined effect of rising levels of atmospheric carbon dioxide (CO₂) and increasing use of genetically modified (GM) crops in agriculture may affect soil food-webs. So we designed a study for the assessment of the effects of elevated CO₂ (eCO₂) concentrations and GM barley on a soil-mesofauna community employing a 2nd tier mesocosm test system. The GM barley, Hordeum vulgare cv. Golden Promise, had a modified content of amino acids and it was compared with three non-GM barley cultivated varieties including the isogenic line. Our mesocosm experiment was conducted in a greenhouse at ambient (aCO₂) and eCO₂ (+80 ppm) levels and included a multispecies assemblage of Collembola, Acari and Enchytraeidae with either a GM or conventional spring barley varieties. To detect food-web changes we added dried maize leaves naturally enriched in δ¹³C and δ¹⁵N relative to the soil substrate. Soil, plants and animals were collected after five and eleven weeks. We found that the eCO₂ concentration did not affect the plant biomass, but the predatory mite and two collembolan species showed significantly lower abundances at eCO₂. The densities of three collembolan species (Folsomia fimetaria, Proisotoma minuta and juveniles of Mesaphorura macrochaeta) was significantly lower in the GM treatment compared to some of the non-GM varieties. F. fimetaria was less abundant in presence of GM barley compared to the cultivated barley variety “Netto” at both CO₂ levels, while the density of P. minuta was significantly reduced with the GM barley compared to variety “Netto” at aCO₂ and the isogenic variety at eCO₂. Maize litter acted as a food source for the community, as it was revealed by δ¹³C values in microarthropods. Microarthropod δ¹³C decreased over time, which indicates a diet change of the species towards carbon derived from barley, due to maize litter decomposition. The industrially produced CO₂ gas also had a role as an isotopic marker, as the different δ¹³C values were reflected in the barley and in the collembolan species. GM barley did not affect δ¹³C and δ¹⁵N values of soil animals indicating that the overall trophic structure of the mesofauna community was not changed compared to the non-GM cultivated varieties. The mesocosm methodology integrating stable isotope analysis demonstrates the potential of the multi-species mesocosm as a tool to detect and track changes in the soil trophic interactions in response to environmental pressures, climate and novel agricultural crops.     

Aeration effects on CO2, N2O,and CH4 emission and leachate composition of a forest soil

The availability of O₂ is one of the most important factors controlling the chemical and biological reactions in soils. In this study, the effects of different aeration conditions on the dynamics of the emission of trace gases (CO₂, N₂O, CH₄) and the leachate composition (NO₃^‐, DOC, Mn, Fe) were determined. The experiment was conducted with naturally structured soil columns (silty clay, Vertisol) from a well aerated forest site. The soil monoliths were incubated in a microcosm system at different O₂ concentrations (0, 0.001, 0.005, 0.01, 0.05, and 0.205 m³ m^‐3 in the air flow through the headspace of the microcosms) for 85 days. Reduced O₂ availability resulted in a decreased CO₂ release but in increased N₂O emission rates. The greatest cumulative N₂O emissions (= 1.6 g N₂O‐N m^‐2) were observed at intermediate O₂ concentrations (0.005 and 0.01 m³ m^‐3) when both nitrification and denitrification occurred simultaneously in the soil. Cumulative N₂O emissions were smallest (= 0.05 g N₂O‐N m^‐2) for the aeration with ambient air (O₂ concentration: 0.205 m³ m^‐3), although nitrate availability was greatest in this treatment. The emission of CH₄ and leaching of Mn and Fe were restricted to the soil columns incubated under completely anoxic conditions. The sequence of the reduction processes under completely anoxic conditions complied with the thermodynamic theory: soil nitrate was reduced first, followed by the reduction of Mn(IV) and Fe(III) and finally CO₂ was reduced to CH₄. The re‐aeration of the soil columns after 85 days of anoxic incubation terminated the production of CH₄ and dissolved Fe and Mn in the soil but strongly increased the emission rates of CO₂ and N₂O and the leaching of NO₃^‐ probably because of the accumulation of DOC and NH₄⁺ during the previous anoxic period.     

Effect of Assessment Scale on Spatial and Temporal Variations in CH4, CO2, and N2O Fluxes in a Forested Wetland

Emissions of methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) from a forested watershed (160 ha) in South Carolina, USA, were estimated with a spatially explicit watershed-scale modeling framework that utilizes the spatial variations in physical and biogeochemical characteristics across watersheds. The target watershed (WS80) consisting of wetland (23%) and upland (77%) was divided into 675 grid cells, and each of the cells had unique combination of vegetation, hydrology, soil properties, and topography. Driven by local climate, topography, soil, and vegetation conditions, MIKE SHE was used to generate daily flows as well as water table depth for each grid cell across the watershed. Forest-DNDC was then run for each cell to calculate its biogeochemistry including daily fluxes of the three greenhouse gases (GHGs). The simulated daily average CH₄, CO₂ and N₂O flux from the watershed were 17.9 mg C, 1.3 g C and 0.7 mg N m⁻², respectively, during the period from 2003–2007. The average contributions of the wetlands to the CH₄, CO₂ and N₂O emissions were about 95%, 20% and 18%, respectively. The spatial and temporal variation in the modeled CH₄, CO₂ and N₂O fluxes were large, and closely related to hydrological conditions. To understand the impact of spatial heterogeneity in physical and biogeochemical characteristics of the target watershed on GHG emissions, we used Forest-DNDC in a coarse mode (field scale), in which the entire watershed was set as a single simulated unit, where all hydrological, biogeochemical, and biophysical conditions were considered uniform. The results from the field-scale model differed from those modeled with the watershed-scale model which considered the spatial differences in physical and biogeochemical characteristics of the catchment. This contrast demonstrates that the spatially averaged topographic or biophysical conditions which are inherent with field-scale simulations could mask “hot spots” or small source areas with inherently high GHGs flux rates. The spatial resolution in conjunction with coupled hydrological and biogeochemical models could play a crucial role in reducing uncertainty of modeled GHG emissions from wetland-involved watersheds.     

Emissions of CH4, CO2, and N2O from soil at a cattle overwintering area as affected by available C and N

Relationships between CH₄, CO₂, and N₂O emissions were studied in soil that had been freshly amended with large deposits of cattle wastes. Dynamics of CH₄, CO₂, and N₂O emissions were investigated with flux chambers from early April to late June 2011, during the 3 months following cattle overwintering at the site. This 81-day field study was supplemented with soil analyses of available C and N content and measurement of denitrification activity. In a more detailed field investigation, the daily time course of emissions was determined. The field research was complemented with a laboratory experiment that focused on the short-term time course of N₂O and CH₄ production in artificially created anoxic soil microsites. The following hypotheses were tested: (i) a large input of C (and N and other nutrients) in cattle manure creates conditions suitable for methanogenesis, and therefore overwintering areas can produce large amounts of CH₄; (ii) N₂O is produced and emitted until the level of mineral N decreases, while the level of CH₄ production is low; and (iii) production of CH₄ is greater when N immobilization decreases the level of NO₃⁻ in soil. N₂O emissions were relatively large during the first 3 weeks, then peaked (at ca. 4000 μg N₂ON m⁻² h⁻¹) and soon decreased to almost zero; the changes were related to the mineral and soluble organic N content in soil. CH₄ fluxes were large, though variable, in the first 2 months (600–3000 μg CH₄C m⁻² h⁻¹) and were independent of C and N availability. Although time courses differed for CH₄ and N₂O, a negative relationship between N₂O and CH₄ emissions was not detected. Contrary to CH₄ and N₂O fluxes, CO₂ emissions progressively increased to ca. 300 mg CO₂C m⁻² h⁻¹ at the end of the field study and were closely related to air and soil temperatures. Diurnal measurements revealed significant correlations between temperature and emissions of CH₄, N₂O, and CO₂. Addition of C to soil during anaerobic incubation increased the production and consumption of N₂O and supported the emission of CH₄. The results suggest that rapid denitrification significantly contributes to the exhaustion of oxidizing agents and helps create microsites supporting methanogenesis in otherwise N₂O-producing upland soil. The results also indicate that accurate estimate of gas fluxes in animal-impacted grassland areas requires assessment of both diurnal and long-term changes in CH₄, CO₂, and N₂O emissions.     

Repeated drying–rewetting cycles and their effects on the emission of CO2, N2O,NO, and CH4 in a forest soil

Prolonged summer droughts due to climate change are expected for this century, but little is known about the effects of drying and wetting on biogenic trace‐gas fluxes of forest soils. Here, the response of CO₂, N₂O, NO, and CH₄ fluxes from temperate forest soils towards drying–wetting events has been investigated, using undisturbed soil columns from a Norway spruce forest in the “Fichtelgebirge”, Germany. Two different types of soil columns have been used for this study to quantify the contribution of organic and mineral horizons to the total fluxes: (1) organic horizons (O) and (2) organic and mineral soil horizons (O+M). Three drying–wetting treatments with different rewetting intensities (8, 20, and 50 mm of irrigation d^–1) have been compared to a constantly moist control to estimate the influence of rainfall intensity under identical drying conditions and constant temperature (+15°C). Drought significantly reduced CO₂, N₂O, and NO fluxes in most cycles. Following rewetting, CO₂ fluxes quickly recovered back to control level in the O columns but remained significantly reduced in the O+M columns with total CO₂ fluxes from the drying–wetting treatment ranging approx. 80% of control fluxes. Fluxes of N₂O and NO remained significantly reduced in both O and O+M columns even after rewetting, with cumulative fluxes from drying–wetting treatments ranging between 20% and 90% of the control fluxes, depending on gas and cycle. Fluxes of CH₄ were small in all treatments and seem to play no significant role in this soil. No evidence for the release of additional gas fluxes due to drying–wetting was found. The intensity of rewetting had no significant effect on the CO₂, N₂O, NO, and CH₄ fluxes, suggesting that the length of the drought period is more important for the emission of these gases. We can therefore not confirm earlier findings that fluxes of CO₂, N₂O, and NO during wetting of dry soil exceed the fluxes of constantly moist soil.     

Groundwater level controls CO2, N2O and CH4 fluxes of three different hydromorphic soil types of a temperate forest ecosystem

Hydromorphic soils should exhibit higher climate change feedback potentials than well aerated soils since soil organic matter (SOM) losses in them are predicted to be much larger than those of well aerated soils. To evaluate a combined feedback relationship between groundwater level (GWL) and total greenhouse gas (GHG) emission, a greenhouse microcosm experiment was performed by exposing three hydromorphic forest soil types that differed in carbon content to three water levels (?40, ?20 and ?5 cm) while plants were excluded. Net GHG fluxes were measured continuously. GHG concentrations plus oxygen were measured in soil air and soil water at different depths. In this study, soil type hardly affected GHG emissions but GWL did. CO₂ emissions peaked at GWL of ?40 cm and declined on average to 65 and 33% during GWL at ?20 and ?5 cm, respectively. CH₄ emissions showed the opposite pattern having the highest emission rates at GWL of ?5 cm and compared to that on average only ?3 and ?8% during GWL at ?20 and ?40 cm, respectively. The highest mean N₂O emissions were detected at the intermediate GWL of ?20 cm, whereas it is reduced on average to 18% for GWL at ?40 cm and at ?5 cm. The highest greenhouse gas emissions (in CO₂ equivalents) were calculated for GWL at ?20 cm. During GWL at ?40 cm, CO₂ equivalent fluxes were only insignificantly lower. CO₂ equivalent fluxes reduced explicitly in mean to 35% with GWL at ?5 cm. The outcome emphasizes that anaerobic SOM decomposition apparently produces a lower warming potential than aerobic SOM decomposition. Undoubtedly, hydromorphic soils have to be considered for climate–carbon feedback scenarios.     

Analysis of a model reaction system containing cysteine and (E)-2-methyl-2-butenal, (E)-2-hexenal, or mesityl oxide

Cysteine conjugates, resulting from the addition of cysteine to alpha,beta-unsaturated carbonyl compounds, are important precursors of odorant sulfur compounds in food flavors. The aim of this work was to better understand this chemistry in the light of the unexpected double addition of cysteine to two unsaturated aldehydes. These reactions were studied as a function of pH. When (E)-2-methyl-2-butenal (tiglic aldehyde, 4) was treated with cysteine in water at pH 8, the major product formed was the new compound (4R)-2-(2-[[(2R)-2-amino-2-carboxyethyl]thio]methylpropyl)-1,3-thiazolidine-4-carboxylic acid (6). Under acidic conditions (pH 1), we also observed a double addition, but the second cysteine was linked by a vinylic sulfide bond to form the previously unreported major product, (2R,2'R,E)-S,S'-(2,3-dimethyl-1-propene-1,3-diyl)bis-cysteine (7). When (E)-2-hexenal (12) was treated with cysteine under acidic conditions, the major product was the novel (4R,2' 'R)-2-[2'-(2' '-amino-2' '-carboxyethylthio)pentyl]-1,3-thiazolidine-4-carboxylic acid (13), and the formation of an vinylic sulfide compound analogous to 7 was not observed. Reduction of the acidic crude reaction mixture with NaBH(4) afforded 13 and the cysteine derivative (R)-S-[1-(2-hydroxyethyl)butyl]cysteine (14) in 14% yield. Treating (E)-2-hexenal with cysteine at pH 8 followed by NaBH(4) reduction yielded the new product (3R)-7-propylhexahydro-1,4-thiazepine-3-carboxylic acid (15). Addition of cysteine to mesityl oxide (16), at pH 8, followed by reduction with NaBH(4) furnished (R)-S-(3-hydroxy-1,1-dimethylbutyl)cysteine (3) and the new compound (3R)-hexahydro-5,7,7-trimethyl-1,4-thiazepine-3-carboxylic acid (18).     

Tracer studies on the incorporation of [2-14C]-DL-mevalonate into chlorophylls a and b, alpha-chaconine, and alpha-solanine of potato sprouts

Chlorophyll and glycoalkaloids are synthesized in different parts of the potato plant including leaves, tubers, and sprouts. Although light stimulates the biosynthesis of both constituents, the question of whether the two biosynthetic pathways are under the same genetic control has not been resolved. This study investigated the dynamics of incorporation of labeled [2-(14)C]-DL-mavalonate into chlorophyll a, chlorophyll b, and the glycoalkaloids alpha-chaconine and alpha-solanine in potato sprouts after 7 and 14 days of storage in the light and in the dark. No chlorophyll synthesis occurred in the dark. Fractionation of the "glycoalkaloid" extract followed by high-performance liquid chromatography produced four peaks. The fractions were collected and analyzed for radioactivity. About 80% of the radioactivity resided in fraction 1, the composition of which is unknown. Two of the fractions, with 1-14% of the original label, were alpha-chaconine and alpha-solanine. The radioactivity derived from mevalonate largely resides in unidentified compound(s) eluting as a single peak on the HPLC column before the peaks associated with the glycoalkaloids. The specific radioactivity of alpha-chaconine and alpha-solanine increased approximately 2-fold in going from 7 to 14 days of exposure in the light and in the dark. These and additional observations point to the near identity of the dynamics of biosynthesis of the two glycoalkaloids. These data also implicate a non-mevalonate pathway for the synthesis of both chlorophylls and the glycoalkaloids and are consistent with independent genetic control of the concurrent formation of the two classes of compounds during greening of potatoes.     

Identification of 9(E),11(E)-18:2 fatty acid methyl ester at trace level in thermal stressed olive oils by GC coupled to acetonitrile CI-MS and CI-MS/MS, a possible marker for adulteration by addition of deodorized olive oil

The olive oil market is suffering from sophisticated illegal treatments. One common adulteration process consists of the addition to virgin olive oil of lower quality oils, such as "lampante" oil, an inexpensive oil and with some organoleptic defects, which is then submitted to thermal deodorization under vacuum processes for removal of the undesired flavor components. Such a blending may not have a huge influence on the chemical composition and may not significantly affect the parameters usually checked as quality indicators, although the organoleptic properties may change. As a consequence, a major effort is being devoted to find reliable markers able to unmask such adulterations. We report here the complete characterization of a compound, detected at trace levels exclusively in thermal stressed oils, which could be a candidate marker for adulteration. The investigation, carried out by GC-MS and GC-MS/MS, provided its complete structure, including the stereochemistry, shown to be a 9(E),11(E)-18:2 fatty acid methyl ester. Experimental data also confirmed the influence of both temperature and heating time on formation and concentration of this compound.