The influence of extrusion on loss and racemization of amino acids.

The influence of the operation conditions (temperature and residence time) of a thermic treatment on the total amount (free and protein-bound) of amino acid enantiomers of dry fullfat soya was investigated. Total amino acid content was determined using conventional ion-exchange amino acid analysis of total hydrolysates and chiral amino acid analysis was performed by HPLC after precolumn derivatization with o-phthaldialdehyde and 1-thio-beta-D-glucose tetraacetate. Contrary to corn that was investigated previously, notable racemization was detected even at lower temperatures. At 140 degrees C the ratio of the D-enantiomer was 0.87% for glutamic acid, 2.81% for serine, and 1.92% for phenylalanine; at 220 degrees C the ratios of the D-enantiomer of the above amino acids were 1.43, 4.61, and 4.68%, respectively. The concentration of several L-amino acids decreased. At 220 degrees C there was 10% less L-glutamic acid, 17% less L-serine, 5% less L-phenylalanine, 6.6% less L-aspartic, acid and 21% less L-lysine than in the control; their loss can be assigned to different degrees of L - D conversion. While nearly complete transformation of L-phenylalanine can be attributed to racemization, the main cause of the loss of L-lysine is not racemization. The treatments in the same order of magnitude resulted in the formation of more D-amino acids and greater extent of racemization of amino acids in fullfat soya than that of maize.

The influence of manufacture on the free D-amino acid content of Cheddar cheese.

The changes in the concentration and those of composition of alanine, aspartic acid and glutamic acid enantiomers were investigated during manufacture of Cheddar cheese. The amount of D-alanine increased continuously during ripening following the liberation of L-alanine originated from the proteolysis of milk proteins. There was slightly more D-aspartic and D-glutamic acid in the dry matter of curd after pressing than before pressurization. The D-amino acid content and the ratio of the D-enantiomers related to the total amount of free amino acids differed significantly among cheeses produced with different single-strain starters. The D-amino acid composition changed during manufacture, but the influence of the strain selection was not significant on the D-amino acid pattern.

Comparison of extraction methods to monitor pesticide residues in surface water.

A regular monitoring program to study the pesticide concentration in surface waters has been carried out since 1976 in Hungary by the National Plant Protection Organization of the Ministry of Agriculture and Regional Development jointly with the Regional Water Authorities. At the beginning of this program a liquid-liquid partition method is used to extract the pesticides from water samples. After checking the pH value, one sample aliquot is extracted to analyze the basic and neutral compounds. Another aliquot is acidified to pH 2 and extracted to analyze acidic compounds. Disadvantages of this method are high solvent consumption and the need to apply solvents (methylene chloride and diethyl ether) that are harmful to human health. Therefore, the solid-phase extraction method has been introduced. This method has another advantage in that by using the vacuum manifold a number of samples can be extracted simultaneously depending on the capacity (number of ports) of the manifold. Three types of cartridges (LiChrolut EN, ISOLUTE ENV+, and Carbograph) are tested. The suitability and reproducibility of the extraction on various cartridges is studied and compared through recovery experiments. Recoveries are done for 22 active ingredients at spiking levels of 1-5 times the limit of determination (in the range of 0.05-2.5 microg/L) with each extraction method. Individual recovery values as well as average recoveries for all methods are between 70% and 100%, with the relative standard deviation generally below 20%. Carbograph is the only cartridge among those studied that can be used to extract both neutral and acidic compounds in one sample loading step using two different consecutive elution steps.

Determination of residues of endosulfan and five pyrethroid insecticides in virgin olive oil using gas chromatography with electron-capture detection.

A simple, fast and economical method has been developed for the determination of endosulfan and five pyrethroid insecticides, cypermethrin, deltamethrin, fenvalerate, lambda-cyhalothrin and permethrin, in virgin olive oil. The method uses a Sep-Pak alumina-N column cleanup after a liquid-liquid extraction or low-temperature precipitation step, and gas chromatography (GC) with electron-capture detection. The matrix effect was assessed for the GC systems used. Recoveries were 71-91% with RSD values of 6-17%. The method was applied to 338 virgin olive oil samples for monitoring of residues of these pesticides. Cypermethrin and lambda-cyhalothrin were detected at the limit of quantification in one sample each, while 22% of samples contained endosulfan residues, mostly at very low levels ranging from 0.02 to 0.57 mg/kg.