Claude Hasselmann

Determination of folates in foods by high-performance liquid chromatography with fluorescence detection after precolumn conversion to 5-methyltetrahydrofolates.

A liquid chromatographic-fluorimetric determination of folates in foodstuffs including their extraction, without or with deconjugation, chemical conversion to 5-CH3-H4PteGlu(n) and purification of the extract by affinity chromatography is reported. The conversion enables the analysis of total folates and also of the contents of the different mono- and polyglutamate forms of the folates. The method has a satisfactory day-to-day repeatability (never,more than 10%) and a very low detection limit (0.02 pmol per injection). Depending on the folate studied, the recovery rates varied from 78% (10-CHO-PteGlu) to 98% (5-CHO-H4PteGlu). Furthermore it has been possible to show that the deconjugation of the folates by rat plasma conjugase was incomplete in foodstuffs whereas chicken pancreas conjugase effectively converted the different folate polyglutamates into folate diglutamates. It could not be demonstrated that prior hydrolysis with a protease and amylase was useful for the analysis of the different foodstuffs studied (yeast, spinach, beef liver, beef fillet and peas) when deconjugation was performed with the chicken pancreas conjugase.

Smearing of soft cheese with Enterococcus faecium WHE 81, a multi-bacteriocin producer, against Listeria monocytogenes.

Enterococcus faecium WHE 81, a multi-bacteriocin producer, was tested for its antimicrobial activity on Listeria monocytogenes in Munster cheese, a red smear soft cheese. The naturally delayed and superficial contamination of this type of cheese allowed the use of E. faecium WHE 81 at the beginning of the ripening as a surface culture. A brine solution inoculated at 10(5)CFU of E. faecium WHE 81 per mL was sprayed on the cheese surface during the first smearing operation. On day 7, smearing of cheese samples with a brine solution at 10(2)CFU of L. monocytogenes per mL yielded initial cell counts of approximately 50 CFU g(-1) of the pathogen on the cheese surface. Although, in some instances, L. monocytogenes could survive (<50 CFU g(-1)) in the presence of E. faecium WHE 81, it was unable to initiate growth. In control samples however, L. monocytogenes counts often exceeded 10(4) CFU g(-1). In other respects, E. faecium WHE 81, which naturally existed in Munster cheese, did not adversely impact on the ripening process.

Inhibition of Listeria monocytogenes in a Smear-Surface Soft Cheese by Lactobacillus plantarum WHE 92, a Pediocin AcH Producer

The anti-Listeria monocytogenes activity of Lactobacillus plantarum WHE 92, a pediocin AcH producer, was investigated in Munster cheese, a smear-surface soft cheese. The appearance of L. monocytogenes in the cheese, which naturally occurs solely in the crust and never before 1 week of ripening, could be prevented by spraying a cell suspension of L. plantarum WHE 92 (ca. 10(5) CFU/ml) on the cheese surface at the beginning of the ripening period. L. monocytogenes was sometimes detected at low levels (<5.0 x 10(1) CFU/g) after 7 to 11 days of ripening. However, this pathogen not be able to grow, nor did it survive the presence of L. plantarum WHE 92 in any of the samples examined until the end of the ripening not be able to grow, nor did it survive the presence of than 10(4) CFU/g in control samples. In other respects, L. plantarum WHE 92, which exists naturally in Munster cheese, did not adversely affect the evolution of the ripening process. This procedure has allowed manufacturers to successfully put an antilisterial treatment into practice in their ripening rooms.

Supercritical fluid extraction of hydrocarbons and 2-alkylcyclobutanones for the detection of irradiated foodstuffs

Supercritical carbon dioxide can be used to carry out a selective and fast extraction (30 min) of volatile hydrocarbons and 2-alkylcyclobutanones contained in irradiated foods. After elimination of the traces of triglycerides still contained in the extracts on a silica column, the compounds were analysed by gas chromatography-mass spectroscopy (2-alkylcyclobutanones) and gas chromatography-flame ionization detection (volatile hydrocarbons). The present method was applied successfully to freeze-dried samples (1 g or less) of cheese, chicken, avocados and to various ingredients (chocolate, liquid whole eggs) included in non-irradiated cookies. It was faster (4-5 h) than the reference methods EN 1784 (volatile hydrocarbons) and EN 1785 (2-alkylcyclobutanones), which take 1.5 days each. The minimal dose detectable by this method is, in addition, slightly lower than those of the reference methods.

2-Alkylcyclobutanones as markers for irradiated foodstuffs. III. Improvement of the field of application on the EN 1785 method by using silver ion chromatography

The inclusion of a purification step by silver ion chromatography in the EN 1785 analytical protocol for 2-alkylcyclobutanones (validated by the European Committee for Standardization for the detection of ionizing radiation treatment) has considerably improved the quality of the chromatograms obtained, allowing the detection of food samples irradiated at very low doses (0.1 kGy) or irradiated ingredients included in low proportions in non irradiated foodstuffs. This analytical modification of the protocol EN 1785 ought thus to permit a very considerable extension of its current field of application.

Supercritical fluid extraction for the detection of 2-dodecylcyclobutanone in low dose irradiated plant foods.

Supercritical carbon dioxide extraction [152 bar (15,200 kPa), 80 degrees C, 4 ml min(-1), 60 min], performed on lipids (2 g) previously extracted from irradiated plant foods, allowed a selective extraction of 2-dodecylcyclobutanone and its further detection by gas chromatography-mass spectrometry in 50 Gy irradiated cowpeas and 100 Gy irradiated rice. However, because of the higher quantities of lipid impurities in these test samples compared to those present in meat samples, a longer and slightly more polar capillary column than the one proposed in the official standard EN 1785 method should be used to obtain a satisfactory resolution.

2-Alkylcyclobutanones as markers for irradiated foodstuffs—I. Synthesis of saturated and unsaturated standards

The reaction scheme suggested for the synthesis of 2-alkylcyclobutanone standards, the key step being a Wittig reaction between a protected ketoaldehyde and phosphoranes with alkyl chains of variable length, has made it possible to prepare different 2-alkylcyclobutanones with saturated alkyl chains (C6 to C14) (in yields varying from 27 to 36%) as well as 2-alkylcyclobutanones with monounsaturated chains (C12 and C14) (in yields of 23 and 17%). In addition, the 2-alkylcyclobutanones synthesized with an odd number of carbon atoms in the saturated alkyl chain, especially 2-undecylcyclobutanone (C11), might be utilized as internal standards when assaying these chemical compounds by GC/MS.

Influence of 3-Substitution on Excited State Properties of Indole in Aqueous Solutions

Considerable attention has been paid to the excited states of the indole ring in the past two decades, since as, the aromatic moiety of tryptophan, it is the major near-ultraviolet chromophore of proteins where it can play the role of a fluorescent probe. Nevertheless photophysical and photochemical properties of indole are rather particular and remain largely unelucidated (Longworth, 1971).

Feasibility for the setting up of a multipurpose food irradiation facility in Senegal

Abstract The setting up of a cobalt 60 (activity 300 kCi) irradiation facility in the highest populated region of Senegal (Dakar district), to treat a wide range of foodstuffs destined for local consumption, can be considered as immediately profitable for a private investor and a Senegalese food producer (or trader), on the condition that the annual tonnage of foodstuffs treated is adequate, more than 20,000 t kGy −1 , i.e. a total tonnage of above 115,000 t, taking into account the irradiation doses used for the various foodstuffs.