Richard K. Creveling

Occurrence of cyclic fatty acid monomers in frying oils used for fast foods

Cyclic fatty acid monomers were analyzed by gas chromatography in commercial frying oils, obtained in this country and in the Middle East. Samples were obtained from food outlets in California and Illinois after varying periods of usage. The samples from Egypt and Israel were collected from street vendors frying vegetable patties (known as “fallafel”) in open-air stands. The United States samples ranged from 0.1 to 0.5% cyclic monomers, and from 1 to 8% polar +noneluted thermal oxidation materials. The Middle Eastern samples showed significantly more heat abuse, with values for cyclic monomers from 0.2 to 0.7% and polar materials ranging from 2 to 22%.

Changes in physical and chemical properties of shortenings used for commercial deep-fat frying

This study evaluated some of the changes that occur in shortenings used for commercial deep-fat frying in fast-service restaurants. Foods cooked in partially hydrogenated soybean oil were battered chicken parts and french fries. Sixty-five samples of fresh and used shortenings were collected from nine restaurants on three occasions over a three-month period. Frying periods varied from 0 to 300 hr, and most samples were taken just before the used fat was discarded. For fresh shortenings, percentages of polar materials, free fatty acids (FFA), materials not eluted by gas chromatography, and fatty acid profiles differed only slightly. For used samples, there were marked variations in these analyses and in increases of dielectric constant measurements. Frying times were highly correlated with increases in dielectric constant, polar materials and FFA. The greatest change in fatty acid profiles occurred intrans-C18 monoenes which decreased from over 40% to as low as 13%. Due to lipid exchange with chicken fat, both oleic and linoleic acids increased in the shortenings with hours of use, whereas stearic acid decreased. There were high correlations, among increases in dielectric constant, percentages of polar materials and FFA, demonstrating that each of these methods could predict degradation of the shortening. However, the increase in dielectric constant, as measured by a Foodoil Sensor (FOS), was the most convenient for quality control in restaurant situations. In most cases, used shortening was discarded before 100 hr of frying time; and only a few of these samples had FOS readings near 4.0, FFA over 1.00%, or percentages of polar materials over 27%. These values have been suggested as discard criteria. However, a number of samples used between 100 and 300 hr exceeded these limits. There is a need to specify suitable limits, related to quality and health factors, to determine at what point a cooking fat should be discarded.

Lipid content and fatty acid profiles of various deep-fat fried foods

Forty-one brands of nine different types of snack and convenience foods were purchased from food stores and fast service restaurants in the Sacramento area of California. All samples had been prepared by deep-fat frying. They included potato chips, corn chips, tortilla chips, cheese chips, cheese puffs, cake donuts, french fries, chicken pieces and fish pieces. These samples were analyzed in duplicate for total fat and fatty acid composition. The total lipid content of each type of food varied among different commercial sources; the average percentages were as follows: potato chips, 40; cheese puffs, 38; corn chips, 35; cheese chips, 25; tortilla chips, 24; cake donuts, 22; chicken thighs, 14; french fried potatoes, 14, and fish pieces, 10. The fatty acid profiles of the total lipids in several brands of potato chips were relatively constant. The fatty acid profiles of the total lipids in the corn and cheese snack foods varied widely. Fatty acid compositions of donuts, chicken and fish pieces and french fries were influenced by the amount and fatty acid profile of the lipids in each uncooked food, as well as by the composition of the cooking fat.

Effects of selected chemical treatments on quality of fats used for deep frying

Maintaining quality of fats and oils used for deep frying is important in food preparation. In this study, commercially used shortenings were treated with various adsorbents and/or additives with a view to extending their useful life. Quality parameters monitored were increases in dielectric constant, free fatty acids, color (absorbance at 420 nm) and total polar materials. Bleaching clay, charcoal, magnesium oxide and Celite, and their mixtures, effectively reduced one or more of these parameters in used vegetable and animal-vegetable shortenings. However, when the treated fats were used to fry more french fried potatoes in the laboratory, they often deteriorated more rapidly than the untreated control fats. The daily addition of 200 ppm ascorbyl palmitate to fresh, partially hydrogenated soybean oil shortening used to fry french fries retarded free fatty acid development but increased color development and dielectric constant. Treatments employed to extend the useful life of frying fats improved quality parameters, but continued frying after treatment led to greater deterioration than occurred in the untreated control samples.

Cleavage of l-cystine by soluble enzyme preparations from Brassica species

Abstract The decomposition of l -cystine to pyruvate and the persulfide, thiocysteine, is catalyzed by soluble enzymes obtained from tissues of brassica species. the enzyme, called trivially cystine lyase, requires pyridoxal-5′-PO4 for activity; however, the stimulation of activity by exogenous cofactor is dependent on the species. Partial purification of the enzyme from the root of B. napobrassica (rutabaga) was accomplished. The rutabaga lyase was completely inactive in the absence of added pyridoxal-5′-PO4. The PH optimum was between 8.5 And 8.9. The lyase was specific for the l -configuration of the amino acid and was only slightly inhibited by equimolar concentrations of The D -Form. The km for l -cystine was 1 mm and was 0.5 μm for pyridoxal-5′-PO4. There was a severe competitive inhibition by thiol compounds such as cysteine and reduced glutathione. The ki for both of these compounds was 1.5 × 10−4 m . The enzyme preparation was capable of utilizing s-Methyl- l -cysteine sulfoxide and l -cysteine-s-Sulfate as substrates. It was completely inactive toward l -cystathionine and dl -allocystathionine. The stoichiometry of the reaction was one mole of thiocysteine and one mole of pyruvate produced per mole of cystine.

l-proline dehydrogenase of Triticum vulgare germ: Purification, properties and cofactor interactions

Abstract The enzyme catalysing the l -proline-dependent reduction of NAD + has been purified over 600-fold from wheat germ acetone powder extracts. l -Proline, 3,4 dehydro- dl -proline, thiazolidine-4-carboxylate were the only substrates utilized readily. The K m for l -proline was 1·0 mM and for NAD + 0·8 mM. The enzyme was highly specific for NAD + with NADP + and NADPH acting as effective competitive inhibitors with a K i of 1·8 and 0·4 μM, respectively. All ribonucleoside triphosphates tested were good non-competitive inhibitors, in particular UTP. The purified enzyme could reduce pyrroline-5-carboxylate, either chemically synthesized or generated in a linked assay system from ornithine by a highly-purified ornithine transaminase. In the latter case both NADH and NADPH were utilized equally well as the reductant. With chemically synthesized dl -pyrroline-5-carboxy-late as the substrate. NADPH was used at only 25% the rate of NADH, and NADPH strongly inhibited the oxidation of NADH.

Stereochemistry of the β-cyanoalanine synthetase and S-alkylcysteine lyase reactions☆

Abstract The stereochemistry of the replacement of the SH-group of cysteine by CN catalyzed by β-cyanoalanine synthetase was studied using cysteine stereospecifically tritiated at C-3. Analysis of the resulting β-cyanoalanine by conversion into fumarate via aspartate and malate showed that the reaction had occurred with retention of configuration at C-3. Using cystine stereospecifically labeled at C-3 with tritium or with tritium and deuterium, it was found that the α,β-elimination reaction catalyzed by S-alkylcysteine lyase involves stereo-specific replacement of the β-substituent of the substrate by a hydrogen derived from the solvent, D2O or H2O, with retention of configuration to give pyruvate containing a chiral methyl group. The results are discussed, particularly in the light of mechanistic proposals by Braunstem and co-workers.