Free radical generation assays: new methodology for accelerated oxidation studies at low temperature in complex food matrices

A novel method for the rapid screening of antioxidant efficacy and oxidative stability in food and feed matrices has been developed. The analyses are described as free radical generation (FRG) assays. The new procedure combines the use of azo-initiators with analytical equipment that is widely used for antioxidant research such as the oxidative stability instrument and the oxygen bomb. The use of initiators instead of high temperatures as a driving force to increase the rate of oxidation improves the correlation between the accelerated screening of foodstuffs and real shelf life. The improved correlation can be mainly explained by the fact that food products are analyzed in their original status, maintaining all interfacial phenomena of the food matrix. Furthermore, the lower temperature of analysis reduces differences between the reaction kinetics of the assay and those of the oxidation during actual shelf life. Consequently, the correlation between the accelerated analysis and shelf life is improved, particularly when compared to accelerated oxidation at high temperatures. The FRG assays could be used successfully to evaluate the efficacy of natural antioxidants in heat-sensitive food products such as emulsions and meat products. A good correlation was observed between the accelerated tests and the oxidation parameters obtained from standard shelf-life evaluation. It was possible to successfully compare the efficacy of several antioxidants and to predict shelf life for these heat-sensitive food matrices.     

Lipoxygenase inactivation in green beans (Phaseolus vulgaris L.) due to high pressure treatment at subzero and elevated temperatures

The kinetics of lipoxygenase (LOX) inactivation in green beans due to high-pressure treatment were studied in the pressure-temperature area of 0.1 up to 650 MPa and -10 up to 70 degrees C for systems with different levels of food complexity, i.e., in green bean juice and intact green beans (in situ study). For both systems, LOX was irreversibly inactivated by high-pressure treatment combined with subzero and elevated temperatures and the inactivation could be described as a first-order reaction. At ambient pressure, in situ LOX was less thermostable than in the juice at temperatures below 68 degrees C whereas the stability ranking was reverse at temperatures above 68 degrees C. At temperatures below 63 degrees C, sensitivity of the inactivation rate constants to temperature changes was on the same order of magnitude in the juice and in situ, while at higher temperature it was lower in situ. The pressure needed to obtain the same rate of LOX inactivation at a given temperature was lower in situ than in the juice. Application of high-pressure treatment at low/subzero temperature resulted in an antagonistic effect on LOX inactivation for both systems, whereas no such effect was found above room temperature. The pressure-temperature dependence of the LOX inactivation rate constants in green beans was successfully modeled.     

δ34S variations in vegetation and soil exposed to intense biogenic sulphide emissions near Paige mountain,N.W.T., Canada

Sulphur isotope abundances demonstrate that natural emissions of biogenic H₂S and its oxidation products from springs near Paige Mountain, N.W.T., Canada, can be incorporated into surrounding soil and vegetation. δ³⁴S values as low as ? 33‰ for soil and vegetation are the result of dominant uptake of biogenic atmospheric compounds. In contrast, vegetation on a gypsum outcrop remote from the springs, has δ³⁴S values as high as + 26‰ indicating nearly exclusive derivation of S from the soil. Near the springs, soil with vegetative cover is less depleted in ³⁴S than soil lacking cover. Lower needles on a Black Spruce were found to be less depleted in ³⁴S than the upper needles. These observations suggest that upper foliage exerts a canopy effect on lower foliage and in turn, interception by vegetation reduces the flux of atmospheric S compounds to the soil. Clearly, natural emissions of S compounds can interfere in studies of long range transport of industrial emissions; S isotope analyses might identify such interferences and reduce the chance of misinterpretation.     

Species-specific earthworm population responses in relation to flooding dynamics in a Dutch floodplain soil

Earthworms dominate the animal biomass in moist floodplain soils. They are known to survive long periods in aerated water, but little is known about earthworm population dynamics in floodplain systems with changing inundation frequencies. This study determined earthworm population dynamics in a floodplain system, in relation to frequency and duration of flooding events. From October 2000 to May 2003 earthworms were hand sorted in the ‘Afferdensche en Deestsche Waarden’, a floodplain on the south bank of the river Rhine, near Druten, The Netherlands. Earthworm numbers and biomasses per age class (adult, subadult, juvenile) were recorded. Numbers and biomasses tend to decrease during flooding. Lumbricus terrestris was found in high numbers (>10/m²) only at the end of a flooding period. Allolobophora chlorotica was hardly affected by flooding; their biomass remained stable during the year. Aporrectodea caliginosa showed fluctuating numbers and biomasses during the sampling period that did not correlate with flooding frequency. Numbers and biomasses of Lumbricus rubellus were strongly reduced at the end of each flooding event, but their population densities fully recovered until next flooding event. Earthworm populations in floodplains fluctuate in time, depending on the season and on the time, duration and frequency of flooding. Different earthworm species react differently towards these flooding dynamics.     

Tylosin detection in animal feed by liquid chromatography-tandem mass spectrometry with enzymatic hydrolysis of the tylosin urea adduct

When the use of tylosin as a feed additive was forbidden by Council Regulation 2821/98, the necessity of a chemical confirmation method for the monitoring of the ban was created. Recently a method was developed for the detection of tylosin in animal feed by means of LC-MS/MS. During the validation high deviating values for the decision limit, detection capability, and repeatability for tylosin in cattle feed were observed, and the presence of urea and the formation of a tylosin urea adduct (TUA) were suggested as possible explanations. In this study two hydrolysis approaches for the TUA adduct were compared, namely, a chemical hydrolysis and an enzymatic hydrolysis with urease. The latter yielded a more complete hydrolysis of urea and was used for further validation. The recovery increased by approximately 15-25% depending on the amount of urea present in the feed (0.5-2%). The decision limit and detection capability were hardly influenced by the enzymatic hydrolysis.     

Determination of total folate in plant material by chemical conversion into para-aminobenzoic acid followed by high performance liquid chromatography combined with on-line postcolumn derivatization and fluorescence detection

A procedure involving chemical conversion of all forms of folate present in plant material into para-aminobenzoic acid (PABA) and a liquid chromatographic-fluorimetric determination with on-line postcolumn derivatization is reported. All folates are cleaved with liberation of PABA by hydrogen peroxide followed by acid hydrolysis using concentrated hydrochloric acid (37%) at 110 degrees C for 6 h. The reaction yield for individual folates conversion to PABA ranged from 44.4 to 97.3%. PABA could be determined sensitively by on-line postcolumn derivatization with fluorescamine, the detection limit for PABA being 3.02 nM. On the basis of this principle, a method for the determination of total folate in plant material, including a purification step on an affinity column, is presented, which offers a sufficient sensitivity and selectivity for routine analysis of total folate in natural samples. The total folate contents of tomatoes, carrots, white cabbage, and spinach were determined, and the results were quite comparable to the data reported. The recovery of PABA and the comparison of total folate analysis in spinach on different occasions (over 6 months) are also reported. The method is reliable, universal for all folates, including polyglutamate and monoglutamate forms, and eliminates the need for a deconjugation step and multiple conversion reactions.     

Effect of Al hydroxide polymers on cation exchange of montmorillonite

Al hydroxide polymers (AlHO) can significantly influence the cation exchange behaviour of clays. We have determined the effect of synthesized AlHO on Ca–Na, Zn–Na and Pb–Na exchange for a series of exchanger compositions and two Al loadings at pH 6.0 and an ionic strength of 0.01  m . The preference for Ca on the siloxane surface of the clay–AlHO system (CAlHO) was greater than for the pure clay, and the average K _V (Vanselow selectivity coefficient) was determined to be 2.16 and 1.24, respectively. The selectivity coefficients for the exchange reactions Zn–Na and Pb–Na were not directly determined in CAlHO systems, because heavy-metal ions bind as well to the clay surface as to the AlHO over a wide range of pH. We have estimated the effect of the presence of AlHO on the selectivity coefficients of Zn–Na and Pb–Na exchange by extrapolation of the experimental results of Ca–Na, Zn–Na and Pb–Na exchange for pure clay and Ca–Na exchange for CAlHO. The average K _V was increased by the presence of the AlHO from 1.23 to 2.16 for Zn–Na exchange and from 1.59 to 2.77 for Pb–Na exchange. The increase in the preference for the divalent cations is probably caused by parallel alignment of clay platelets by sorption of AlHO. Increasing the amount of AlHO did not change the selectivity for Ca–Na exchange, and probably the structure of the system or the arrangement of the clay platelets and AlHO particles was not substantially changed. This was supported by the linear reduction of the cation exchange capacity with amount of AlHO present at pH 6.6. It seems likely that the selectivity coefficients for Ca–Na, Zn–Na and Pb–Na exchange that we found apply in naturally occurring montmorillonite–AlHO systems.     

Coriander essential oil composition from two genotypes grown in different environmental conditions

The objective was to study the essential oil composition of coriander fruits in plants growing in environments differing in soil conditions and weediness level. Factorial field experiments were conducted in two locations from the Rolling Pampas, Argentina, and two coriander landraces (European and Argentinean) were tested under two levels of nitrogen fertilization and weediness. Data were evaluated with uni- and multivariate techniques. The variation in the oil composition was related to the relative proportion of the constituents and not to the presence/absence of a particular component. Weather conditions in 1997 favored linalool and camphor in both landraces. Location, fertilization, and weediness also affected the chemical profile. The European landrace showed a more stable concentration of the major components than the Argentinean landrace. These results, which show the relationships between some environmental conditions and the essential oil composition, are useful in the development of innovative strategies aimed to improve oil composition and to manage crop pests.     

Displacement imaging in porous media using the line scan NMR technique

Displacement imaging is a recent, powerful NMR method with which distributions of displacements can be acquired of e.g. fluids within a porous medium. Both motion parallel and perpendicular to the flow direction may be observed within a time window of a few milliseconds to several seconds. By combining displacement imaging with the line scan technique, one-dimensionally resolved measurements with a high temporal resolution ( < 1 min) of the spatial dependency of motion can be obtained. Here we present displacement images of flow through two simple model systems for soil: an unconsolidated glass bead water system and a sintered glass bead filter. It is demonstrated that the combination of displacement imaging and spatial resolution along a line is important to access both bulk displacement and local displacements in relation to the local porosity.