Bitterstoffe beim Erhitzen von Saccharose, Maltose und Prolin 2. Mitteilung

Summary In addition to the mono- and dipyrrolidinohexosereductones described recently (Z Lebensm Unters Forsch (1984) 178:356) two further bittertasting compounds were isolated from heated mixtures of proline and sucrose (molar ratio 3: 1, 190 °C, 30 min) and also synthesized, namely 2,3-bis-(1-pyrrolidinyl)2-cyclopenten-l-one and 2,3-bis(1-pyrrolidinyl)-5methyliden-2-cyclopenten-l-one. The recognition thresholds (mmol/1) are 0.15–0.25 and 0.06–0.12 respectively. Both compounds have a burning bitter taste character. From a maltose-proline reaction mixture 2--glucosyl-5-hydroxy-5-methyl-4-piperidinyl-2-cyclopenten-1-one was isolated. When the dihydroxypyranone VI was heated with proline, 2,5-dihydroxy-5-methyl-4-prohnyl-2-cyclopenten-1-one and the cyclopent(b)azepinones XI and XII were among the compounds formed. These compounds also have a bitter taste character.Zusammenfassung Zusätzlich zu den kürzlich beschriebenen Mono- and Dipyrrolidinohexosereduktionen (Z Lebensm Unters Forsch (1984) 178:356) wurden zwei weitere bittere Verbindungen aus erhitzten Mischungen von Prolin and Saccharose (Molverhältnis 3:1, 190 °C, 30 min) isoliert and synthetisiert. Es handelt sich um 2,3-Bis-(1-Pyrrolidinyl)-2-cyclopenten-1-on und 2,3-Bis-(1-Pyrrolidinyl)-5-methyliden-2-cyclopenten-1-on. Die Erkennungsschwellenwerte (mmol/1) sind 0,15-0,25 and 0,06-0,12. Beide Verbindungen haben einen brennend-bitteren Geschmack. Aus einem Maltose-Prolin-Umsetzungsgemisch gelang die Isolierung des 2--Glucosyl-5-hydroxy-5-methyl-4-piperidinyl-2-cyclopenten-1-ons. Bei der Reaktion des Dihydropyranons VI mit Prolin wurden u. a. das 2,5-Dihydroxy-5-methyl-4-prolinyl2-cyclopenten-1-on sowie die Cyclopent(b)azepinone XI and XII gebildet. Diese Verbindungen sind ebenfalls mehr oder weniger stark bitter.     

Sediment dilution method to determine sorption coefficients of hydrophobic organic chemicals

Sorption coefficients of hydrophobic organic chemicals (HOC) to sediments and soils can easily be underestimated in traditional batch experiments, especially because analysis of the aqueous concentration often includes compounds sorbed to colloidal organic matter. In this work, a "sediment dilution approach" has been combined with measurements of freely dissolved concentrations to determine sorption coefficients of five chlorobenzenes and two chloroanilines in spiked sediment and of two unknown chemicals in field-contaminated sediment. A range of sediment suspensions with different sediment-water ratios was made. Freely dissolved concentrations in these suspensions were measured by negligible depletion solid-phase microextraction (nd-SPME). Sediment-water sorption coefficients (KD) were derived from the decrease of the freely dissolved concentrations as a function of the "dilution factor" (DF = volume water/mass sediment). The determined sorption coefficients were very similar to literature values. The experimental setup provides sorption coefficients without the need for total extractions, and the negligible depletion SPME technique does not require phase separation. The proposed method might be an alternative for batch equilibrium experiments to determine sorption coefficients.     

Influence of defined milk products on the flavour of white coffee beverages using static headspace gas chromatography–mass spectrometry/olfactometry and sensory analysis

The influence of milk processing and ingredients on the sensory properties of white coffee beverages has, as yet, not been thoroughly investigated, so in this study analysed milk products processed in a defined manner were added to a standardized, fresh coffee beverage; the resulting odour, taste and retronasal odour perception were measured by intensity tests, and selected volatiles were analysed by static headspace gas chromatography/mass spectrometry. After adding pasteurized consumers’ milk, the effects of a different fat content (3.5 and 1.5%) and fat dispersion were studied. The milk with the lower fat content and with smaller fat globules, resulting from double homogenization (each 250/50 bar), induced a more intense coffee-related retronasal odour perception, whereas the milk-related impression was nearly the same. The addition of casein increased the creamy and milky retronasal odour perception and reduced the coffee-related taste and retronasal odour. These correlations may result in a custom-made development of milky coffee beverages controlled in their nasal and retronasal odour and taste by the defined processing of the milk component. With instrumental analysis it was observable that the effect of the addition of twice-homogenized, twice-pasteurized low-fat milk and of the addition of whole milk was similar. In both cases more volatiles were released from the beverage than with the addition of low-fat milk that was homogenized once. This is an unexpected result, because the whole milk has a higher fat content than the low-fat milk and therefore a greater retention of the flavour compounds was expected. Is it possible that the flavour compounds are not dissolved in fat and that interactions happen only with fat globule membrane constituents?     

Fluorescence tracking of dissolved and particulate organic matter quality in a river-dominated estuary

Excitation-emission matrix (EEM) fluorescence was combined with parallel factor analysis (PARAFAC) to model base-extracted particulate (POM) and dissolved (DOM) organic matter quality in the Neuse River Estuary (NRE), North Carolina, before and after passage of Hurricane Irene in August 2011. Principle components analysis was used to determine that four of the PARAFAC components (C1-C3 and C6) were terrestrial sources to the NRE. One component (C4), prevalent in DOM of nutrient-impacted streams and estuaries and produced in phytoplankton cultures, was enriched in the POM and in surface sediment pore water DOM. One component (C5) was related to recent autochthonous production. Photoexposure of unfiltered Neuse River water caused an increase in slope ratio values (S(R)) which corresponded to an increase in the ratio C2:C3 for DOM, and the production of C4 fluorescence in both POM and DOM. Changes to the relative abundance of C4 in POM and DOM indicated that advection of pore water DOM from surface sediments into overlying waters could increase the autochthonous quality of DOM in shallow microtidal estuaries. Modeling POM and DOM simultaneously with PARAFAC is an informative technique that is applicable to assessments of estuarine water quality.     

Comparison of Rapid Methods for Detection of Giardia spp. and Cryptosporidium spp. (Oo)cysts Using Transportable Instrumentation in a Field Deployment

Reliable, sensitive, quantitative, and mobile rapid screening methods for pathogenic organisms are not yet readily available, but would provide a great benefit to humanitarian intervention units in disaster situations. We compared three different methods (immunofluorescent microscopy, IFM; flow cytometry, FCM; polymerase chain reaction, PCR) for the rapid and quantitative detection of Giardia lamblia and Cryptosporidium parvum (oo)cysts in a field campaign. For this we deployed our mobile instrumentation and sampled canal water and vegetables during a 2 week field study in Thailand. For purification and concentrations of (oo)cysts, we used filtration and immunomagnetic separation. We were able to detect considerably high oo(cysts) concentrations (ranges: 15-855 and 0-240 oo(cysts)/liter for Giardia and Cryptosporidium, respectively) in 85 to 300 min, with FCM being fastest, followed by PCR, and IFM being slowest due to the long analysis time per sample. FCM and IFM performed consistently well, whereas PCR reactions often failed. The recovery, established by FCM, was around 30% for Giardia and 13% for Cryptosporidium (oo)cysts. It was possible to track (oo)cysts from the wastewater further downstream to irrigation waters and confirm contamination of salads and water vegetables. We believe that rapid detection, in particular FCM-based methods, can substantially help in disaster management and outbreak prevention.     

Determination of a kinetic factor influencing the vaporescence of flavour components from wort

The current article considers the question of whether vaporescence during wort boiling affects evaporation via the vapour side mass transport. Thereby the vaporization of unwanted flavour components (such as dimethyl sulphide or benzaldehyde) can be influenced negatively or positively, which affects the amount of energy needed. The question is pursued by pre‐calculation and experimental validation of the vapour side mass stream at the evaporation surface: for that purpose vaporescence trials were carried out in a plant trial, with both benzaldehyde and water as pure substances and a mixture of benzaldehyde and water in an infinite solution (x_i < 10^?6). Trial parameters were process temperature and volume stream of the gas phase. The results obtained by the trials with pure substances enable pre‐calculation of vapour side mass transport. Then, pre‐calculation is compared with the results of the mixture trials and thus verified. As a result it has to be stated that vaporescence in the brew houses is pre‐calculable and that the mass transport has an impact on the vaporescence at the vapour side boundary layer. Copyright © 2016 The Institute of Brewing & Distilling     

Liquid chromatographic quantification of synthetic colorants in fish roe and caviar

According to the directive 94/36/EC of the European Union (EU), quantities of synthetic colorants added to foods are restricted by upper limits and, therefore, reliable methods for their quantification have to be established. Approved colorants, defined by so-called E numbers, are permitted for dying fish roe (commonly named caviar). We developed a chromatographic method for the quantitation of colorants in roe. The recovery rates of 14 synthetic food colorants from solid materials (Al₂O₃, XAD-2, anion exchangers, and polyamide-6) were tested, and polyamide powder was selected as adsorbent for quantitative determination of colorants in fish roe. The most effective sample preparation comprises extraction of colorants from roe with 1 M aqueous ammonia, defatting of the solution with n-hexane, adjustment of pH 2 of the extract, adsorption of dyes on the polyamide and desorption with a mixture of aqueous ammonia (25%) and methanol (1:9 v/v). The isolated colorants were analyzed by RP-HPLC with diode-array detection. In several caviars, the maximum of individual colorants regulated by EU were exceeded or colorants declared on food labels were not detected. Presented at 25th International Symposium on Chromatography, Paris, France, October 4–8, 2004.     

Characterization of high molecular weight coffee fractions and their fermentation by human intestinal microbiota

To investigate the structure and fermentability of high M(r) components of coffee brews by human gut bacteria Arabica coffee samples of three different degrees of roast (light, medium, and dark) were used for drip brew preparations and fractionation by ultrafiltration with different M(r) cut-offs. Total carbohydrates of the fractions ranged from 28.6 g/100 g to 56.7 g/100 g. Galactomannans and arabinogalactans were the main polysaccharides and made up between one-fourth and one-half of the respective coffee fraction. After 24 h of incubation with a human fecal suspension the polysaccharides of all fractions were extensively degraded. A decrease in the absorbance values at 405 and 280 nm, respectively, indicated that also chemically noncharacterized UV-active components such as Maillard reaction products, had been partially degraded or modified by the human gut bacteria. The remainder after 24 h of fermentation still showed antioxidant activity. Bacterial cells belonging to the Bacteroides-Prevotella group increased 2- to 40-fold during fermentation depending on the M(r) range of the fraction and the degree of roast. The production of high amounts of acetate and propionate is in accordance with a role of these bacteria in the degradation of high M(r) components from coffee.     

Synthesis and Evaluation of Molecularly Imprinted Polymers (MIP) with Affinity for the Polypeptide Nisin

The method of hierarchical imprinting was used for the first time in order to synthesize polymers with a high affinity for nisin. The concept of this approach is demonstrated by filling the pores of silica particles, which contain immobilized peptidic templates, with a mixture of monomers/initiator, followed by polymerization and subsequent dissolution of the silica template. This method leaves imprinted polymers with binding sites located at the surface that are capable of recognizing larger molecules with the same immobilized epitope. The results of the high-performance liquid chromatography analyses illustrate that the highest retention factors and imprinting factors of nisin on nisin C-terminal analogously imprinted polymers could be obtained with acetonitrile/water mixtures containing more than 80% water. Furthermore, nisin was strongly retained on polymers that were imprinted with a longer amino acid sequence because of better sterical accessibility of the binding sites for the C terminus of nisin. The retention of nisin (k = 21.65) under aqueous elution conditions results from selective ionic interactions and hydrophobic interactions. Furthermore, the polymers exhibited selectivity for the template Lys-Ala and the structurally related dipeptide Ala-Lys. The results of the present work show that these hierarchically imprinted polymers could be used for the chromatographic separation of the polypeptide nisin in aqueous solutions.