Showing papers by "J. Bruce German published in 1996"

Inhibition of in vitro human LDL oxidation by phenolic antioxidants from grapes and wines

Abstract: Current research suggests that wine contains substances that may reduce the mortality rate from coronary diseases. The oxidation of low-density lipoprotein (LDL) is thought to be a key step in the development of atherosclerosis. Phenolic fractions of a Petite Syrah wine were evaluated for their antioxidant activity in inhibiting LDL oxidation in vitro. The more active fractions contained components of the catechin family. The catechin oligomers and the procyanidin dimers (B 2 , B 3 , B 4 , B 6 , B 8 ) and trimers (C 1 , C 2 ) were extracted, isolated and purified from grapes seeds. These compounds were tested for their inhibition of LDL oxidation, along with other monomeric wine phenolics. The procyanidin dimers B 2 and B 8 , and trimer C 1 , and the monomers catechin, epicatechin and myricetin had the highest antioxidant activity. The procyanidin dimers B 3 , B 4 and C 2 and the monomers gallic acid, quercetin, caffeic acid, and rutin, and a group of compounds that included the dimer B 6 , ellagic acid, sinapic acid, cyanidin had lower antioxidant activity and α-tocopherol had the least activity. Thus, the numerous phenolic compounds found in wine are potent antioxidants in inhibiting LDL oxidation in vitro.

Effect of different lipid systems on antioxidant activity of rosemary constituents carnosol and carnosic acid with and without α-tocopherol

Abstract: The effect of oxidizing lipid substrate on the antioxidant activity of carnosol and carnosic acid were evaluated in bulk and emulsified systems. In bulk methyl linoleate, carnosic acid was a better antioxidant than carnosol on the basis of conjugated diene hydroperoxide formation, and both were more active than α-tocopherol. However, in linoleic acid carnosol was more active than carnosic acid. In bulk corn oil triglycerides, α-tocopherol exhibited the most antioxidant activity followed by carnosic acid and carnosol. In all emulsified systems, α-tocopherol consistently exhibited more antioxidant activity than carnosol and carnosic acid. In mixtures, carnosol decreased and carnosic acid increased the oxidative stability of α-tocopherol in corn oil. During oxidation carnosic acid and carnosol are converted to unknown compounds which exhibit antioxidant activity. The type and polarity of the lipid system used as a model substrate significantly affect the antioxidant activity of carnosol and carnosic acid. Ke...

Antioxidant Activity of Carnosic Acid and Methyl Carnosate in Bulk Oils and Oil-in-Water Emulsions

Abstract: This study was aimed at evaluating the antioxidant activities of carnosic acid and its methyl ester, methyl carnosate, in inhibiting the formation and decomposition of hydroperoxides in bulk and emulsified corn oil triglycerides at 60 °C. In both lipid systems, methyl carnosate was a better antioxidant than carnosic acid, and both were more active than α-tocopherol. The difference in antioxidant activity between methyl carnosate and carnosic acid was greater in emulsion than in bulk systems. Carnosic acid was less stable than methyl carnosate and α-tocopherol in bulk corn oil and 1% Tween 20 micelle solution. The partitioning of carnosic acid into the water phase may explain its low activity in emulsions. The measurement of antioxidant depletion may not be a valid method to evaluate antioxidant activities because the antioxidant activities of carnosic acid and methyl carnosate were not related to their oxidative stability in bulk oil and Tween 20 solution. Keywords: Antioxidants; carnosic acid; methyl car...

Determination of hydroperoxides and structures by high-performance liquid chromatography with post-column detection with diphenyl-1-pyrenylphosphine

Abstract: A high-performance liquid chromatographic method, using post-column detection with diphenyl-1-pyrenyl-phosphine (DPPP), was developed for the quantitative and qualitative determination of isomeric lipid hydroperoxides (OOH) The OOH eluted from a normal-phase column were passed through a photodiode array detector and then mixed with DPPP solution in a reaction coil heated at 80°C DPPP oxide formed by the reaction with OOH was determined by monitoring the fluorescence intensity at 380 nm and excitation at 352 nm The conjugated diene OOH (13-cis, trans- and 9-cis, trans-OOH) and nonconjugated OOH (12-cis-trans- and 10-cis, trans-OOH) from photosensitized oxidation of methyl linoleate were determined in a molar ratio of 31∶29∶19∶21, respectively However, only the two conjugated hydroperoxides were detected by ultraviolet absorption at 234 nm Further applications were carried out for the determination of OOH of methyl oleate and methyl linolenate This method proved to be useful for the determination of the OOH containing both conjugated and nonconjugated diene structures

Mechanical Properties and Water Vapor Permeability of Edible Films from Whey Protein Isolate and N-Ethylmaleimide or Cysteine

Abstract: The role of sulfhydryl/disulfide interchange in determining the water vapor permeability (WVP) and mechanical properties of edible films from whey protein isolate (WPI) was investigated. Nearly total inhibition of sulfhydryl/disulfide interchange by the sulfhydryl blocking agent N-ethylmaleimide (NEM) reduced protein solubility by 50%, but had no effect on WVP, Young's modulus, yield stress, or breaking stress. Breaking strain was reduced significantly at high levels of added NEM. Reduction of disulfide bonds with cysteine had no effect on WVP. The effects of hydrogen bonding far outweigh those of disulfide bonding in WPI films. Keywords: Edible films; biodegradable films; elastic modulus; tensile stress; sulfhydryl/disulfide interchange; thiol/disulfide interchange

Increased hepatic Δ6‐Desaturase activity with growth hormone expression in the MG101 transgenic mouse

Abstract: Growth hormone (GH) has many metabolic effects, but its mechanism(s) of action are not fully understood. We studied the short-term effects of endogenously produced GH on liver Δ6-desaturase activity and adipose and liver lipid fraction fatty acid composition in transgenic mice. MG101 transgenic mice ages 73–114 d received zinc to activate the ovine GH transgene for 7 d. Nontransgenic littermates, used as controls, also received zinc. Liver lipids were fractionated into phospholipids (PL), cholesteryl esters, and triglycerides (TG), and retroperitoneal adipose fractionated into PL and TG for fatty acid analysis. Liver microsomes were assayed for Δ6-desaturase activity. Animals expressing the ovine growth hormone transgene had a 2.5-fold higher liver Δ6-desaturase activity than controls. Arachidonate and docosahexaenoate were significantly higher in liver PL of GH transgenic animals compared to controls, but both were decreased in adipose PL in the GH animals. We conclude that increased production of GH affects both production and organ distribution of highly unsaturated fatty acids. The changes in arachidonate in various lipid pools following transgene expression may mediate the systemic actions of GH.

Diversity of the polar lipids of the food-borne pathogen Listeria monocytogenes.

Abstract: Listeria monocytogenes is a Gram-positive bacterium that can adapt to high salinity and cold. Because the membrane lipids may play a role in its survival and adaptation, we have examined the polar lipids of L. monocytogenes. Extraction of total lipids from L. monocytogenes yielded 7 +/- 1 mg/mL wet cells. Polar lipids represented 64% of total lipids and contained 9% lipid-phosphorus. Polar lipids were separated into 14 components by two-dimensional thin-layer chromatography. Eight components (88% of polar lipids) contained lipid-phosphorus; among these was one major component (34% of polar lipids). Two other phospholipids were ninhydrin-positive components and accounted for 15% of the polar lipids. Orcinol staining revealed two glyco- or sulfo-lipids accounting for 9% of polar lipids. Five components (4% of polar lipids) were amino components free of phosphorus. The major component contained 46% of its fatty acids as 15:0 anteiso, 24% as 17: 0 anteiso, and 11% as 15:0 iso. The fatty acid profile of the remaining polar lipids was variable, consisting primarily of 16:0, 18:0, 15:0 anteiso, and 17:0 anteiso. Their unsaturation level was < or = 20%; however, the major phosphoaminolipid component was 46% unsaturated. The ratios of 15:0 anteiso/17:0 anteiso and 15:0 anteiso/15:0 iso were similar in all classes, averaging 1.5 and 4.5, respectively. Since the adaptation process to stressful environments involves activation of a membrane transport system for the protectant glycine betaine, the membrane lipids may play a role in enabling transport.

Contribution of triglycerides from cocoa butter to the physical properties of milkfat fractions.

Abstract: Milkfat was separated into major chainlength fractions by solid-phase extraction. The effect on thermal behavior and texture of replacing both saturated and monounsaturated long-chain triglycerides from milkfat by long-chain monounsaturated triglycerides with an unsaturated fatty acid in thesn-2 position is reported. Increasing proportions of cocoa butter were added to fractions of short-to medium-chain triglycerides (C22−C44) and medium- to long-chain triglycerides (C36−C48) isolated from milkfat. Thermal behavior and texture of the mixtures were measured. Results indicated that long-chain monounsaturated triglycerides from cocoa butter enhanced co-crystallization and co-operative melting and did not induce polymorphic transitions upon crystallization and melting of the fractions. At 4°C, they acted as texture builder if present in proportions of more than 30%, whereas below this level, they acted as texture softeners. The effect of the long-chain monounsaturated triglycerides on the texture of fractions that melt at low temperature could not be predicted from the proportion of solid fat at that temperature.

Dietary modulation of phospholipid fatty acid composition and lipoxygenase products in mouse lung homogenates.

Abstract: This study investigated the potential of dietary fats to modulate the arachidonic acid content of mouse lung phospholipids and the formation of lipoxygenase products from arachidonic and eicosapentaenoic acids. Prior to breeding, female mice were fed for five months diets with 10 wt% of either olive oil, safflower oil, fish oil, or linseed oil. The same diets were fed to the females during gestation and to the pups from day 18 to day 42 postpartum. On day 42, the phospholipids were extracted from fresh lung tissue and separated into classes [phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylcholine (PC), and phosphatidylinositol (PI)] by thin-layer chromatography. Methyl esters of phospholipid fatty acids and unesterified fatty acids were analyzed by gas chromatography. At comparable dietary n-3/n-6 ratios, arachidonic acid was reduced 85 and 75% in lungs from mice fed linseed oil and fish oil, respectively, compared to lungs of safflower oil-fed mice. Dietary fats affected the proportion of arachidonic acid in phospholipids in the order: PE > PC > PS > PI. Following incubation of homogenized lung tissue, the total amount of 12-lipoxygenase products was lowest in lungs from mice fed olive oil, and 12-hydroxyeicosatetraenoic acid was lowest in incubated lungs from mice fed linseed oil. Comparison of the amounts of lipoxygenase substrate fatty acids in the individual phospholipids with the lipoxygenase products suggested that the major substrate pool for the 12-lipoxygenase pathway in mouse lung homogenates was PC.