Application of Mid- and Near-Infrared Spectroscopy for the Control and Chemical Evaluation of Brine Solutions and Traditional Sea Salts

Mid- and near-infrared spectroscopy methodologies were explored for the analysis of brine solutions and traditional sea salt samples. Brine solutions from different salt pans, corresponding to different stages of sodium chloride crystallisation, were collected. A total of 61 dried and non-dried traditional sea salts were also analysed. Partial least squares regression with leave-one-out cross-validation strategy was applied for the calibration of inorganic constituents Ca²⁺, Mg²⁺ and K⁺, alkalinity as HCO ₃ ^? , SO ₄ ^2? , NO ₂ ^? and NO ₃ ^? and phosphate in brine solutions. Promising results were obtained with the near-infrared (NIR) methodology for brine solutions with coefficients of determination R ²?>?0.90 for Mg⁺², K⁺, HCO ₃ ^? and SO ₄ ^2? . Using mid-infrared, the calibration for H₂PO ₄ ^? was R ²?=?0.85. In relation to the sea salt samples, the strategy adopted was the re-sampling based cross-validation using different spectral pre-processing treatments. In this case, the calibrations using the two IR methodologies fell bellow acceptable levels for the techniques; however, by comparing the R ² coefficient, the results were slightly better when using the NIR spectra of dried sea samples. In general, these results open a new possibility for the IR applications and also bring an opportunity for continuing with the NIR characterization for dried sea salt samples.     

Moisture movement in wood polypropylene composites

Moisture movement in an extruded wood polypropylene composite was evaluated by exposure to high humidity and immersion of the material in both fresh and seawater. The saturation moisture content was approximately 20 and 19% when exposed to distilled water and seawater, respectively. The moisture diffusion coefficient (D _m) of thin specimens exposed to high humidity was 3.4?×?10^?8?cm² $ / $ s. The D _m of small cubic specimens with extruded surfaces removed submerged in distilled water and seawater were estimated to be 3.1 and 2.3?×?10^?8?cm² $ / $ s, respectively. Use of these diffusion coefficients overestimates the rate of moisture movement in larger extrusion profiles indicating the role of transport phenomenon other than diffusion.     

Postharvest BTH treatment induced disease resistance and enhanced reactive oxygen species metabolism in muskmelon (Cucumis melo L.) fruit

Benzo (1, 2, 3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) is a novel synthetic elicitor capable of inducing disease resistance in many plants. Fruits were dipped in BTH at 100?mg/L for 10?min, and then stored at room temperature (22?±?2?°C, relative humidity 55–60?%). The results showed that BTH significantly (P?<?0.05) reduced the lesion area of fruits inoculated with Trichothecium roseum and the natural disease incidence of fruits during storage at room temperature. The treatment effectively maintained cell membrane integrity and decreased the production of lipid peroxidation and malondialdehyde. BTH treatment markedly enhanced the accumulation of hydrogen peroxide, (H₂O₂) while decreased the rate of superoxide anion (O ₂ ^·? ) production. Furthermore, BTH observably increased the activities of NADPH oxidase (NOX, EC1.6.3.1), superoxide dismutase (SOD, EC1.15.1.1), peroxidase (POD, EC1.11.1.7), ascorbate peroxidase (APX, EC1.11.1.11), and glutathione reductase (GR, EC1.6.4.2), while inhibited the catalase (CAT, EC1.11.1.6) activity. These results indicated that BTH treatment increased the disease resistance of muskmelon fruits by enhancing their antioxidant system activity after harvest, and suggested that postharvest treatment with BTH could be promising in reducing decay and reducing or/and substituting chemical fungicides to control postharvest diseases in fruits.     

Beer Clarification Using Ceramic Tubular Membranes

In this work, laboratory-made green beers were produced using a commercial hopped malt extract and used to study their cross-flow microfiltration (CFMF) performance in a bench-top plant, appropriately designed and equipped with ceramic tubular membrane modules with nominal pore size of 0.4, 0.8, or 1.2 μm, under different values of the initial green beer turbidity (H?≡?0.7–61.9 European Brewery Convention (EBC) unit), feed superficial velocity (v _S?≡?2–6 m s^?1), and transmembrane pressure difference (TMPD?≡?0.97–4.73 bar) under constant temperature (~10 °C). Whatever the membrane pore size and rough beer turbidity, the minimum quasi-steady-state value of the overall membrane resistance \( \left({\mathrm{R}}_{\mathrm{T}}^{*}\right) \) was obtained at TMPD of 3 to 4 bar and v _S?=?6 m s^?1. The 0.8-μm pore membrane was selected for the loss in the permeate density, and color was limited, while the volumetric permeation flux was high enough. Then, it was used to assess a double logarithmic trend between the quasi-steady-state permeation flux (J*) and beer turbidity with a limiting flux of 63?±?6 L m^?2 h^?1 for H?>?21 EBC units. Precentrifuged beer feeding resulted in 2.7- to 4.1-fold increase in J* with respect to the above limiting flux, provided that the haze level of rough beer had been reduced to 1.0 or 0.7 EBC unit, respectively. The cake filtration fouling mechanism was identified as the main reason for flux decline by analyzing mathematically the time course of both the experimental permeate volume and permeation flux data. By operating with the aforementioned clarified green beers at TMPD of 3.73 bar, v _S of 6 m s^?1, and periodic CO₂ backflushing, the average permeation flux (300–385 L m^?2 h^?1) resulted to be from three to five times higher than that (80–100 L m^?2 h^?1) at 0–2 °C claimed by the three commercial CFMF processes currently available.     

Effect of controlled atmospheres with varying O2/CO2 levels on the postharvest senescence and quality of broccoli (Brassica oleracea L. var. italica) florets

Controlled atmosphere (CA) has been widely used to help extend the shelf life and maintain the quality of horticultural products. In the present study, broccoli (Brassica oleracea L. cv. Youxiu) florets were stored under CA with high levels of O₂/CO₂ at 15 °C, including 100 % O₂, 80 % O₂ + 20 % CO₂, 60 % O₂ + 40 % CO₂, 40 % O₂ + 60 % CO₂, and air (control), to determine the effects of CA on storage period and on some physiological properties during storage. The results showed that compared with the control, the treatments combining O₂ and CO₂ effectively extended the storage period and inhibited respiration rate, ethylene production, and reductions in weight loss, chlorophyll, and ascorbic acid levels. Moreover, the CA treatments inhibited the increases in both superoxide radicals (O ₂ ^?· ) production rate and hydrogen peroxide (H₂O₂) level and reduced malondialdehyde accumulation, which could be beneficial in delay of senescence by alleviation of oxidative damage. In addition, broccoli florets exposed to CA conditions maintained lower activities of superoxide dismutase and peroxidase that are responsible for scavenging of O ₂ ^?· and H₂O₂ and alleviating lipid peroxidation. Among the treatments, the maximum efficacy was observed with a CA of 40 % O₂ + 60 % CO₂, which prolonged the storage period of broccoli heads to 17 days (d) compared with 4 d under air treatment. Conversely, 100 % O₂ treatment accelerated senescence and deterioration in the quality of broccoli, resulting in a shorter storage period. These results suggest that the establishment of an appropriate CA condition with high levels of O₂/CO₂ may be an ideal strategy for maintaining the quality of broccoli florets during storage.     

Changes in Structure, Rheology, and Water Mobility of Apple Tissue Induced by Osmotic Dehydration with Glucose or Trehalose

The impact of osmotic dehydration to water activity (a _w) at 0.97 or 0.94 with glucose or trehalose solutions on structure (optical and transmission electronic microscopy observations), rheological properties (small-scale dynamic oscillatory and creep/recovery measurements and large-scale compression force-deformation testing) and water mobility (¹H-NMR spectra) of parenchymatous apple tissue was investigated. In general, the nature and the concentration of sugar employed significantly affected the material properties and the structure of apple tissue. A dramatic loss in rigidity (E _d); an increase in deformation at rupture (?? _R ^R ), creep compliances (J ₀, J ₁, and J ₂), and fluidity (1/?? ₀) and a decrease in storage (G??) and loss (G??) moduli, true rupture stress (?? _R ^R ), and proton transverse relaxation times (T _2i) were induced by osmotic treatments. ?? _R ^R , C ₁, and T _2i parameters allowed to discriminate between the sugars used as osmotic agents while the different a _w levels for each sugar resulted in changes in ?? _R ^R , W, and T _2i values. Loss of turgor due to plasmolysis or rupture of membranes and desorganization/degradation of walls allowed explaining, at least partially, the changes in material parameters.     

Bacterial reporter strains for d-xylose content analysis in arabinoxylans

A pair of ice nucleation and fluorescence reporter strains induced specifically by d-xylose were developed and optimized, to monitor d-xylose content in hydrolyzed arabinoxylans samples. Reporter strains were developed by fusing the Escherichia coli xylose isomerase promoter P _xylA to the promoterless native inaZ gene of Pseudomonas syringae and synthetic gfp gene of Aequorea victoria and transferring final constructs to E. coli DH5α. Because of relatively low initial response toward the target analyte, signal improvement by promoter region length adjustment has been implemented. In both cases, this approach proved to be successful, although the manner in which reporter strains have responded to it was dissimilar. The specificity and quantitative response of obtained reporter strains have been confirmed, and the response ranges for NIxylA100 and gfpxylA300 have been established as 9 × 10^?6–9 × 10^?1 g l^?1 and 9 × 10^?3–9 g l^?1, respectively. The performance of developed reporter strains has been assessed in comparison with high-performance anion-exchange chromatography and demonstrated 15–18 % difference between data obtained with reporter strains and chromatography analysis, which for microbial sensors is an acceptable dissimilarity. The developed microbial reporter strains present an alternative for other analytical methods used for monosaccharide quantification and enable quantification of d-xylose in arabinoxylans samples.     

Proposal for visual grading criteria of structural timber of sweet chestnut from Spain

Bending strength, modulus of elasticity and density were obtained for 981 specimens of Spanish Sweet Chestnut (Castanea sativa Mill.) sawn timber from five provenances. Four-point bending tests were made with three sizes (40 × 100 × 2,500, 40 × 150 × 3,500 and 70 × 150 × 3,500 mm) according to EN 408 (CEN EN 408:2011). Visual grading criteria were established, resulting in 82 % of the samples being classified as one structural quality, namely MEF. Characteristic values of the density and the mechanical properties were determined according to EN 384 (CEN EN 384:2010a): E _0,mean  = 12.3 kN mm^?2; f _m,k  = 28 N mm^?2 and ρ _k  = 510 kg m^?3. Therefore, a strength class D24 was assigned according to EN 338 (CEN EN 338:2010b). The relationship between the modulus of elasticity and bending strength was lower (R² = 0.26) than for Spanish coniferous species.     

Rapid and Simple Determination of Sarafloxacin in Egg by Time-Resolved Chemiluminescence

A new chemiluminescence method for the determination of the fluoroquinolone sarafloxacin is described. The method is based on the measurement of the chemiluminescent (CL) radiation emitted in the reaction of sarafloxacin with Ce (IV) in sulfuric acid medium and in the presence of $ \mathrm{Ru}(\mathrm{bipy})_3^{2+ } $ as sensitizer. Since the method allows the recording of the whole CL intensity-versus-time profile, the use of measurement parameters such as the maximum CL emission is possible, which is proportional to the analyte concentration. The optimum chemical and experimental conditions for the CL emission of the reaction were researched. The calibration graph was lineal in the concentration range from 5.0 to 30.0 mg?L^?1 of sarafloxacin. The limit of detection, according to Clayton et al. (Anal Chem 59:2506–2514, 1987), was 1.17 mg?L^?1. After analyzing a series of ten solutions of 10.0 mg?L^?1 of sarafloxacin, the estimated average concentration was 10.30 mg?L^?1 with a standard deviation of 0.42 mg?L^?1 (confidence level, 95 %). The effect on the sarafloxacin CL signal of some common excipients (sucrose, lactose, and starch) used widely in pharmaceutical preparations was also tested, as well as that of others fluoroquinolones (namely, enrofloxacin and ciprofloxacin). Finally, the proposed method was applied to the determination of sarafloxacin in different spiked egg samples by using the standard addition methodology, obtaining excellent recoveries in all cases (close to 100 %).     

Microwave treatment of dietary gelatin does not generate cis-4-hydroxy-l-proline, an inhibitor of collagen biosynthesis

Aqueous solutions (5?g/100?ml) of commercial preparations of (a) an enzymatic partial hydrolysate of gelatin and (b) type A gelatin were subjected to threefold heating to boiling in a domestic microwave oven at 750?W and to conventional heating. Then samples were totally hydrolyzed (6?M hydrochloric acid, 110??°C, 24?h) and investigated for the presence of eight possible stereoisomers of 3- and 4-hydroxyproline (Hyp) using capillary gas chromatography. Amino acids were analyzed as N(O)-trifluoroacetyl 2-propyl esters on Chirasil-l-Val and detected by selected ion monitoring mass spectrometry. Blanks of (a) and (b) were analyzed in parallel. Relative amounts of 5.0±0.2% cis-4-d-Hyp were generated from native trans-4-l-Hyp as a result of total hydrolysis in all samples and independent of previous treatment. Notably, neither cis-3-l-Hyp nor cis-4-l-Hyp could be detected in either of the gelatin samples. Thus a report on the generation of antifibrotic and therefore potentially hazardous cis-3-l-Hyp and cis-4-l-Hyp from protein-bonded native trans-3-l-Hyp and trans-4-l-Hyp on microwave heating of infant formulae could not be confirmed.     

Electron Spin Resonance Spectroscopy for the Identification of Irradiated Foods with Complex ESR Signals

Electron spin resonance (ESR) spectroscopy for the detection of irradiated food could provide complex spectra due to the presence of different nonirradiation-specific paramagnetic species in the sample. Particularly, ESR signals from naturally present Mn²⁺ could limit the ESR-based detection of irradiated foods of plant origin. In this study, the effects of different concentrations of Mn²⁺ on the radiation-specific ESR spectral features of radiation-induced crystalline sugar or cellulose radicals were examined. Soy sauce powder with Mn²⁺ was irradiated at 10 kGy and its effect on the identification of radiation-induced sugar (pak choi, 10 kGy) and cellulose (red pepper powder, 10 kGy) radicals was evaluated. In the blends of red pepper and soy sauce, the left (g ₁?=?2.025) and central (g ₂?=?2.005) peaks of the cellulose signal significantly decreased with the decline of red pepper content (R ²?=?0.9384, g ₁; 0.8819, g ₂). However, the right peak (g ₃?=?1.988) significantly increased (R ²?=?0.9353, g ₃) with an escalation in the soy sauce content. The cellulose radical signals were identifiable from the blends containing more than 50 % red pepper powder. In the blends of soy sauce and pak choi, the ESR intensity of crystalline sugar radicals significantly decreased with the decline in pak choi content (R ²?=?0.9887). However, Mn²⁺ signal didn’t overlap with the sugar radical signals. The ESR signals from radiation-induced crystalline sugar remained unaffected; however, the signals from cellulose radicals provided a reduced detectionability depending upon the concentration of Mn²⁺ in the sample.     

Evaluation of Optimal Conditions for Determination of Low Tin Content in Fresh and Canned Tomato Samples Using Hydride Generation Inductively Coupled Plasma Optical Emission Spectrometry

We propose a procedure for the determination of tin in tomatoes after wet digestion of the samples in HNO₃ using hydride generation inductively coupled plasma optical emission spectrometry. The effect of acidity from HCl and HNO₃ (0.01–4.0 mol L^-1) as well as the presence of l-cysteine on the efficiency of SnH₄ generation by reaction with the NaBH₄ reductant was investigated. Optimal conditions were evaluated in terms of precision, accuracy (by recovery test) and limit of detection. The best results were obtained with l-cysteine and nitric acid for sample acidificitation. Addition of 1 % (m/v) l-cysteine enhanced the Sn signal and expanded the optimal range of HNO₃ concentrations towards higher values; hence, strict control of the acidity could be avoided, up to 1.0 mol L^-1. Under the optimized conditions, a detection limit of 1.2 ng mL^-1 was achieved. The applicability of the proposed method was demonstrated by the determination of low tin contents in digests of fresh and canned tomato samples with satisfactory results.     

Turbidimetric Behavior of Colloidal Particles in Beer Before Filtration Process

The effect of colloidal particles and yeast on turbidity of Pilsen beer before the filtration process was studied in this work. The colloidal particles are mainly composed of polysaccharides, representing 96.89 %, in second place proteins with a concentration close to 2 %, and polyphenols less than 0.3 %. There is also a very low concentration of yeast (<0.25 %). The presence of different types of particles in the sample caused multimodal histogram in the particle size distribution and four distinct zones were identified: (1) very small individual particles ( $ \overline D = 0.0{\text{6}}\mu {\text{m}} $ ), (2) yeast ( $ \overline D = {\text{3}}\mu {\text{m}} $ ), (3) colloidal aggregates ( $ \overline D = {\text{17}}\mu {\text{m}} $ ), and (4) a zone with a high dispersion of size, with two $ \overline D $ values (101 and 200 μm). Particles size counts well correlate with both the scanning electron microscopy (SEM) digital image analysis, and the turbidity determination. The fractal dimension (D _f) of the aggregates was determined by analyzing the SEM images with the Variogram method, obtaining D _f?>?2.4 values. Those values are typical of aggregates formed by rapid flocculation or diffusion limited aggregation. Results of this study support the formulation of a model valid for the prediction of colloidal particles concentration in beer.     

An investigation into gamma-ray treatment of shellfish using electron paramagnetic resonance spectroscopy

BACKGROUND: Gamma irradiation is a safe method for the decontamination of shellfish, and its technical feasibility and safety have been endorsed (FAO/IAEA/WHO). In order to implement proper food‐processing regulations, the identification of radiation treatment is required. In this study, electron paramagnetic resonance (EPR) spectroscopy was employed to identify the irradiation of seven different types of commonly consumed shellfish. RESULTS: Characteristics (g factor and signal intensity) of the EPR spectra of control and irradiated samples were recorded in order to clarify the gamma‐ray treatment of shellfish. Radiation‐specific signals around g = 2.0038 ± 0.0006 (g₁) and g = 1.9996 ± 0.0002 (g₂ and g₃) were observed for all shellfish samples irradiated with absorbed doses of 3 and 6 kGy. The X‐ray diffraction (XRD) spectra of some shellfish samples were recorded to investigate their mineral profiles. CONCLUSION: The EPR spectroscopic results indicated that carbonate minerals were the source of the paramagnetic species that were produced upon irradiation, entrapped in the shellfish and showed radiation‐specific asymmetric signals whose intensities increased quantitatively with the absorbed radiation dose. The XRD analysis revealed that aragonite and calcite minerals were present in the shells of shellfish. Copyright © 2011 Society of Chemical Industry     

Application of Analytical Methods for the Determination of Bioactive Compounds in Some Berries

Fluorometry, ESI-MS, FTIR, and radical scavenging assays were used for characterization of bioactive compounds and the levels of their antioxidant activities. Polyphenols, flavonoids, anthocyanins, and ascorbic acid and the level of antioxidant activity of water extracts of “Murtilla-like” [Myrteola nummularia (Poiret) Berg.], and other widely consumed berries were determined and compared. The contents of bioactive compounds and the levels of antioxidant activities in water extracts differed significantly in the investigated samples (P?<?0.05). “Murtilla-like” extracts contained polyphenols (mg GAE/g)—19.13?±?0.9, flavonoids, (mg CE/g)—3.12?±?0.1, anthocyanins (mg CGE/g)—120.23?±?5.4, and ascorbic acid (mg/g)—2.20?±?0.1; and antioxidant activities (μmolTE/g) by ABTS and CUPRAC assays were 200.55?±?8.7 and CUPRAC 116.76?±?5.7, respectively. Chemometrical processing was done on the basis of kinetic data of two variables (concentration and reaction time) by DPPH scavenging reaction. Polyphenol content highly correlated with antioxidant capacity (R² from 0.96 to 0.83). The quenching properties of berries were studied by the interaction of water polyphenol extracts with a small protein such as BSA by 3-D fluorescence and FTIR spectroscopy. These methods were used as additional tools for the characterization of polyphenols. Wild-grown non-investigated berries were compared with widely consumed ones, using their bioactive composition, antioxidant activities, and antiproliferative and fluorescence properties. In conclusion, the antioxidant properties of “Murtilla-like” can be used as a new source for consumption. The bioactivity of “Murtilla-like” is comparable with blueberries and raspberries. 3-D fluorescence and FTIR spectroscopy can be applied as additional analytical tools for rapid estimation of the quality of food products.

Thermal transition and thermo-physical properties of potato (<Emphasis Type="Italic">Solanum tuberosum L</Emphasis>.) var. Russet brown

Potatoes are an important food in many regions of the world and are commonly used in a variety of food products. Thermal transition and thermo-physical properties of potatoes are important in order to design efficient food processes and select appropriate storage conditions. In this study, we determined the thermal transitions and thermophysical properties of raw and blanched/par-fried potato for a temperature range of ??32 to 21.1 °C. Using differential scanning calorimetry, we found an initial freezing point (T_f) at ??1.8?±?0.1 °C, an onset of melting (T_m^′) at ??9.9?±?0.2 °C and an unfreezable water content (X^′_w) for maximally freeze-concentrated raw potato at 0.21 kg water/kg potato. Corresponding values for blanched/par-fried potatoes were ??0.9?±?0.1 °C, ??11.0?±?0.2 °C and 0.18 kg water/kg potato. Results show that an increase in solids content decreased T_f of both raw and blanched potatoes. We modelled the relationship between them using the Chen model. The apparent specific heat (C_app) increased around T_f to 31.7?±?1.13 kJ/kg K for raw potato and 26.7?±?0.62 kJ/kg K for blanched/par-fried potato. For frozen raw potato at ??32 °C, thermal diffusivity (α) was 0.89?±?0.01?×?10?^?6 m²/s and thermal conductivity (k), 1.82?±?0.14 W/m K, respectively. These values were higher for frozen raw potato than for the unfrozen raw potato (0.15?±?0.01?×?10?^?6 m²/s and 0.56?±?0.08 W/m K, respectively at 21.1 °C). The apparent density (ρ) of frozen raw potato (992?±?4.00 kg/m³ at ??32 °C) was less than that for unfrozen raw potato (1053?±?4.00 kg/m³ at 21.1 °C), and a similar trend was obtained for blanched/par-fried potato (993?±?2.00 kg/m³ at ??32 °C and 1188?±?7.00 kg/m³ at 21.1 °C, respectively). This study established a correlation between thermo-physical properties and temperature. Findings may be used to inform the design and optimization of freezing processes and frozen storage for potato products.     

Micellar Electrokinetic Chromatography Method for Determination of the Ten Water-Soluble Vitamins in Food Supplements

The separation and determination of the ten water-soluble vitamins by using capillary electrophoresis in the micellar electrokinetic chromatography in a single run are proposed. The method uses low toxicity and cost solvent (ethanol) as modifier of background electrolyte (BGE) attending to the Green Chemistry principles. The electrophoretic method uses 10.0 % (v/v) ethanol, 2.0 % (w/v) SDS, 0.02 mol?L^?1 borate at pH 8.70 as BGE. The standard and real sample solutions were injected in the eletrophoretic system by hydrodynamic injection under pressure of 0.80 psi for 8 s, and the separation was carried out in a fused silica capillary under a potential of 28 kV at 25 °C; the analytical signals were monitored at 214 nm. The analytical method is precise (r.s.d.?<?6 %), accurate (better than 9 %), selective, sensitive, robust, simple, and presents high analytical frequency as ten water-soluble vitamins were separated in only 18 min, with migration times of 5.75?±?0.02, 6.81?±?0.02, 8.13?±?0.04, 8.80?±?0.07, 8.98?±?0.06, 11.10?±?0.08, 11.34?±?0.05, 13.85?±?0.15, 14.82?±?0.04, and 17.85?±?0.30 min. Detection and quantification limits of 0.34, 0.32, 0.27, 0.20, 2.50, 4.98, 4.92, 0.30, 0.86 and 0.28 mg?L^?1 and 1.02, 0.97, 0.83, 0.62, 7.56, 15.09, 14.91, 0.90, 2.59 and 0.83 mg?L^?1, for vitamins PP (nicotinamide), B₁₂ (cyanocobalamin), B₂ (riboflavin), B₆ (pyridoxine), B₈ (biotin), C (ascorbic acid), B₅ (pantothenic acid), B₃ (nicotinic acid), B₁ (thiamine), and B₉ (folic acid), respectively. Excellent recoveries (intra and inter-day) were obtained and, when the method was applied to food supplement analyses the results were in agreement with the conventional HPLC methods.     

Fast and isocratic HPLC-method for steviol glycosides analysis from Stevia rebaudiana leaves

A fast isocratic HPLC method for analysis of steviol glycosides from Stevia rebaudiana leaves was developed with a high selectivity for nine known steviol glycosides and low eluent consumption. The analytical method was performed on a Purospher^? STAR RP-18 endcapped 3???m Hibar^? RT 250-4.6 column at 50?°C with an eluent composition of water (65 vol.?%) and acetonitrile (35 vol.?%). With a flow rate of 1?mL?min^?1, nine known steviol glycosides were detected selectively after 15?min. Method validation for rebaudioside A showed a LOD of 0.0004?mg?mL^?1 and a LOQ of 0.0038?mg?mL^?1. Particularly with regard to moderate solubility, the method is linear up to a concentration of rebaudioside?A of 4.8?mg?mL^?1. The linear calibration curve was obtained with a coefficient of determination of 0.9997?±?0.0002 and a total error of 2.01?% RSD (n?=?12). The accuracy of the method was determined by the percentage mean recovery rate to 100.99?±?2.01?%. The intra-day precision was in a range of 0.12 to 1.96?%?RSD and the inter-day precision varies from 0.02 to 1.89?% RSD. Small changes in operating conditions like eluent composition (65?±?2 vol.?%), temperature (50?±?10?°C) or flow rate (1?±?0.2?mL?min^?1) do not affect the performance of the analytical method. The reliable and robust proposed HPLC method can be applied for quantification of steviol glycosides in Stevia rebaudiana Bertoni leaves in laboratories and quality control in industry.     

Correlations of carbon isotope ratios of wine ingredients for the improved detection of adulterations I. Organic acids and ethanol

The δ¹³C-values of organic acids and their correlations to those of the sugar and ethanol, respectively, from 57 EU data bank wines of the Rheinpfalz area (years 1991?–?1993) and from some of their corresponding musts have been determined. In addition to the well established difference between fermented sugar and ethanol (Δδ¹³C = –1.7±0.2‰), a new constant correlation was found in wine for ethanol and citric acid (Δδ¹³C = +2.4±0.4‰). From this result a fixed δ-value difference for citric acid in wine to the fermented sugar of +0.7±0.6‰ can be deduced. The δ¹³C-values of L-malic acid and L-tartaric acid in must were not altered by the alcoholic fermentation; they should therefore directly provide access to the δ¹³C-value of the natural sugar in must. However, in non-adulterated wines the expected δ¹³C-value differences between these acids and ethanol showed unsatisfactory correlation coefficients. For L-malate this is attributed to the secondary (partial) degradation of this acid by the malolactic fermentation; a corresponding correction is envisaged in order to make L-malate available as an internal standard. As a reason for the unsatisfactory correlation between L-tartaric acid and ethanol, it is supposed that the time of its maximum biosynthesis period does not coincide with that of glucose in the grape ripening period.     

L-Ascorbic acid in nonenzymatic reactions

The influence of the water content, molar ratio, time and temperature on the formation of nondialysable melanoidins produced by the interaction ofl-ascorbic acid and glycine has been studied. The isolated polymers have been characterized by spectrum analysis and fractionated using gel chromatography. The rate constants of the reaction for temperatures of 90°C, 100°C and 110°C have been calculated and are (0.84±0.29) x 10^?5 x s^?1, (1.33±0.14) x 10^?5 x s^?1 and (5.30±0.37) x 10^?5 x s^?1 respectively. The activation energy of the reaction has been determined to be 106.07±32.47 kJ/mol.