Michal Voldřich

Changes of properties of polymer packaging films during high pressure treatment

Abstract The effect of high pressure on the polymer packaging materials was studied. Seven single material films as well as seven laminates suitable for high pressure preservation of food or commonly used as food contact layer were pressurized using the pressure 600 MPa for 60 min. The effect of pressure treatment on the change of following film parameters were evaluated: mechanical properties (tensile strength and seal strength), transparency (absorbance at 450 and 600 nm), water vapour permeability, global migration characteristics into fat food simulants (95% ethanol and isooctane) and the transfer of food simulants (water and olive oil) into packaging materials. The obtained results confirmed the influence of high pressure treatment on functional properties of tested films, in some cases in rather significant level (loss of heat sealability, changes of migration levels, etc.). The obtained results need further confirmation by tests done in closer cooperation with packaging materials producers, which enables better understanding of film changes.

Resistance of vegetative cells and ascospores of heat resistant mould Talaromyces avellaneus to the high pressure treatment in apple juice

Thermoresistant moulds including Talaromyces avellaneus are frequent microbial contamination of fruit juices and purees, which are supposed as food products suitable for pressure pasteurisation. The effect of high pressure treatment on survival of vegetative cells and ascospores of T. avellaneus was studied. The vegetative cells T. avellaneus were very sensitive to high pressure, the sufficient pressure treatment for the reduction by six orders was 200 MPa at 17 °C for 60 min or 300 MPa at 17 °C for 5 min. In apple juice the ascospores of T. avellaneus were relatively resistant to the high pressure treatment, the treatment of 600 MPa at 17 or 25 °C for 60 min reduced their concentration by two or three orders, respectively. Sufficient inactivation rate was obtained when the combination of pressurisation and gentle heating was used, the total reduction (by six orders) was reached at 600 MPa and 60 °C after 60 min.

Determination of fumaric acid in apple juice by on-line coupled capillary isotachophoresis–capillary zone electrophoresis with UV detection

An on-line coupled capillary isotachophoresis-capillary zone electrophoresis (cITP-CZE) method for the determination of the fumaric acid content in apple juice is presented. A clear separation of fumaric acid in real samples is achieved within 20 min. The leading, terminating and background electrolyte of the employed system consist of 10 mM HCl+beta-alanine+5 mM beta-cyclodextrin+0.05% hydroxypropylmethylcelullose (HPMC), pH 3, 10 mM citric acid and 20 mM citric acid+beta-alanine+5 mM beta-cyclodextrin+0.1% HPMC, pH 3.3, respectively. The linearity, recovery, repeatability and detection limit of the developed method are 25-1000 ng/ml, 1.07%, 95.4+/-3.5 (+/-s)% and 10 ng/ml, respectively. Low laboriousness (no sample pretreatment), sufficient sensitivity and low running cost are the important attributes of the cITP-CZE method which was successfully applied to analyses of real samples of apple juices.

Rapid determination of 5-hydroxymethylfurfural by DART ionization with time-of-flight mass spectrometry

DART (direct analysis in real time), a novel technique with wide potential for rapid screening analysis, coupled with high-resolution time-of-flight mass spectrometry (TOF-MS) has been used for quantitative analysis of 5-hydroxymethylfurfural (5-HMF), a typical temperature marker of food. The DART/TOF-MS method was optimised and validated. Quantification of 5-HMF was achieved by use of a stable isotope-labelled 5-HMF standard prepared from glucose. Formation of 5-HMF from saccharides, a potential source of overestimation of results, was evaluated. Forty-four real samples (honey and caramelised condensed sweetened milk) and 50 model samples of heated honey were analysed. The possibility of using DART for analysis of heated samples of honey was confirmed. HPLC and DART/TOF-MS methods for determination of 5-HMF were compared. The correlation equation between these methods was DART = 1.0287HPLC + 0.21340, R2 = 0.9557. The DART/TOF-MS method has been proved to enable efficient and rapid determination of 5-HMF in a variety of food matrices, for example honey and caramel.

Determination of phenolic acids by capillary zone electrophoresis and HPLC

Selected phenolic acids are determined by capillary zone electrophoresis and HPLC, each using UV detection. The optimised CZE background electrolyte contained 50 mM acetic acid, 95 mM 6-aminocaproic acid, 0.1% polyacrylamide, 1% polyvinylpyrrolidone, and 10% methanol. Twelve phenolic acids (gallic, p-hydroxybenzoic, 3,4-dihydroxybenzoic, vanillic, syringic, o-coumaric, p-coumaric, caffeic, sinapic, ferulic, salicylic and chlorogenic) were separated within 10 minutes. Chromatographic separation of these phenolic acids was carried out on an Eclipse XBD C8 column using a mobile phase gradient (acetonitrile / methanol / water / 0.1% phosphoric acid); all were separated within 25 minutes. Electrophoretic and chromatographic determinations of ferulic and chlorogenic acids were compared on barley, malt, and potato samples. The methods’ characteristics were: linearity (1–20 mg ml and 0.2–4 mg ml−1), accuracy (recovery 94 ± 5% and 96 ± 4%), intra-assay repeatability (4.1% and 3.5%), and detection limit (0.2 and 0.02 mg ml−1).

Electrophoretic determination of calystegines A3 and B2 in potato

Potatoes, members of the Solanaceae plant family, contain calystegines, water-soluble nortropane alkaloids, which are biologically active as glycosidase inhibitors. The content of calystegines A(3) and B(2) in different varieties of potato and in various parts of the tubers (whole potato, peel, flesh, and sprouts) were analysed by new capillary zone electrophoresis and capillary isotachophoresis methods and by the routine GC method. The optimized background electrolyte for capillary zone electrophoretic analysis was mixture of 20 mM histidine, 20 mM N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid and 20% (v/v) methanol in demineralized water. Calystegines were detected by indirect UV detection at 210 nm. A clear separation of calystegines from other components of the methanolic sample extract was achieved within 4 min. The electrolytes for isotachophoretic analysis consisted of 5 mM NH(4)OH, 10 mM N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid, 0.1% hydroxyethylcellulose and 20% (v/v) methanol in demineralized water (leading) and 5 mM histidine+10 mM acetic acid+20% (v/v) methanol in demineralized water (terminating). Calystegines were separated within 20 min and detected by a conductimeter. Method characteristics of both zone electrophoresis and isotachophoresis, i.e., linearity (10-100 ng/microl and 1-10 ng/microl), accuracy (recovery 96+/-5% and 98+/-4%), intra-assay repeatability (4.2% and 3.5%), and detection limit (3 and 0.4 ng/microl) were evaluated. Simple sample preparation, sufficient sensitivity, speed of analysis, and low running cost are important attributes of the electrophoretic methods. The overall results of electrophoretic methods were comparable with GC.

Isotachophoretic determination of creatinine in meat and meat products.

A capillary isotachophoretic method (CITP) to determine the creatinine concentration in meat and meat products is described. A clear separation of the creatinine from other components of an acidic extract of sample was achieved within 20 min. Method characteristics (linearity, accuracy, precision and detection limit) were determined. The developed method was successfully applied to analyze real samples and to determine creatinine and creatine content (indirect determination after acidic hot extraction) in meat and meat products.

Determination of aristolochic acid by capillary zone electrophoresis

A simple and rapid capillary zone electrophoresis (CZE) method for the determination of aristolochic acid (AA) in dietary supplements and selected herbs is described. A clear separation of AA from other sample constituents was achieved within 5 minutes without any sample clean up. A mixture of 20 mM-morpholinethanesulphonic acid+10 mM-BisTrisPropane+0.2% hydroxyethylcelullose in 10% methanol serves as a background electrolyte. The linearity, accuracy, intra-assay and detection limit of the developed method are 200–6000 ng/mL, 95–103%, 3.5%, and 50 ng/ml, respectively. Ease of use, sufficient sensitivity and low running cost are the most important attributes of the CZE method. The proposed CZE method was compared with HPLC.

Determination of phytic acid and inositolphosphates in barley

Phytic acid (PA) and lower inositolphosphates (InsPn) is the main storage form of phosphorus in grains or seeds. The content of PA and InsPn in different varieties of barley was analyzed by capillary isotachophoresis and online‐coupled capillary isotachophoresis with CZE. The electrolytes (in demineralized water) for the isotachophoretic analysis consisted of 10 mM HCl, 14 mM glycylglycine, and 0.1% 2‐hydroxyethylcellulose (leading) and 10 mM citric acid (terminating). The optimized electrolytes for the online coupling isotachophoresis with zone electrophoresis analysis were mixtures of 5 mM HCl, 7 mM glycylglycine, and 0.1% 2‐hydroxyethylcellulose (leading), 20 mM citric acid, 10 mM glycylglycine, and 0.1% 2‐hydroxyethylcellulose (background) and 10 mM citric acid (terminating). PA and all studied InsPn were separated within 25 min and detected by a conductivity detector. Simple sample preparation (acidic extraction), sufficient sensitivity, speed of analysis, and low running cost are important attributes of the electrophoretic methods. The method was used for the determination of PA and InsPn in barley varieties within an ongoing research project.

HPLC determination of thiol-containing anti-browning additives in fruit and vegetable products

The HPLC determination of residual thiol-containing anti-browning additives (cysteine, N-acetyl-cysteine and reduced glutathione) in treated fruit and vegetable products using the Ellmans reagent (5,5′-dithiobis(2-nitrobenzoic acid); DTNB) is described. The thiols were isolated by extraction with solvent containing NaF, EDTA, acetic and ascorbic acids and derivatized with the Ellmans reagent in an aqueous medium at pH 8.0. The resulting disulphides were determined by reverse phase HPLC with mobile phase consisting of methanol and phosphate buffer pH 7.5. The UV-detection at 330 nm was used. The optimal extraction and derivatization conditions were found and the method was used to determine the residual concentrations of thiols in potato, avocado, apple and banana purees, sliced mushrooms and frozen basil treated with cysteine.