Lipid oxidation in milk, yoghurt, and salad dressing enriched with neat fish oil or pre-emulsified fish oil.

This study compared the oxidative stabilities of fish-oil-enriched milk, yoghurt, and salad dressing and investigated the effects on oxidation of adding either neat fish oil or a fish-oil-in-water emulsion to these products. Milk emulsions had higher levels of a fishy off-flavor and oxidized faster, as determined by the peroxide value and volatile oxidation products, than fish-oil-enriched yoghurt and dressing, despite the fact that dressings had a higher fish oil content and were stored at room temperature. Additionally, fish-oil-enriched yoghurt generally had higher oxidative stability than fish-oil-enriched dressings, irrespective of the mode of fish oil addition. Yoghurt thus seemed to be a good delivery system of lipids containing n-3 polyunsaturated fatty acids. Different effects of adding fish oil either as neat fish oil or as a fish-oil-in-water emulsion were observed for milk, yoghurt, and dressing. Yoghurt and dressing enriched with neat fish oil were more stable than those enriched with a fish-oil-in-water emulsion, whereas milk enriched with neat fish oil was less stable than milk enriched with the fish-oil-in-water emulsion. Overall, it seemed that application of neat fish oil was a good option for preserving the final quality in yoghurt and dressings, but a pre-emulsion may still be considered for the fish oil enrichment of certain food products, for example, milk.

Ascorbyl palmitate, gamma-tocopherol, and EDTA affect lipid oxidation in fish oil enriched salad dressing differently.

The aim of the study was to investigate the ability of gamma-tocopherol, ethylenediaminetetraacetate (EDTA), and ascorbyl palmitate to protect fish oil enriched salad dressing against oxidation during a 6 week storage period at room temperature. The lipid-soluble gamma-tocopherol (220 and 880 microg g-1 of fish oil) reduced lipid oxidation during storage by partly retarding the formation of lipid hydroperoxides (PV) and by decreasing the concentrations of individual volatile oxidation products by 34-39 and 42-66%, respectively. EDTA (10 and 50 microg g-1 of dressing) was the most efficient single antioxidant, and overall peroxide values and volatiles were reduced by approximately 70 and 77-86%, respectively. Conversely, prooxidant effects were observed with a high concentration of ascorbyl palmitate (300 microg g-1 of fish oil), whereas a low concentration was slightly antioxidative (50 microg/g of fish oil). Finally, a combination of all three antioxidants completely inhibited oxidation during storage, indicating that the prooxidant effects of ascorbyl palmitate were reverted or overshadowed by EDTA and gamma-tocopherol.

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: lipid oxidation.

In this study fish oil was incorporated into commercial homogenized milk using different homogenization temperatures and pressures. The main aim was to understand the significance of homogenization temperature and pressure on the oxidative stability of the resulting milks. Increasing homogenization temperature from 50 to 72 degrees C decreased droplet size only slightly, whereas a pressure increase from 5 to 22.5 MPa decreased droplet size significantly. Surprisingly, emulsions having small droplets, and therefore large interfacial area, were less oxidized than emulsions having bigger droplets. Emulsions with similar droplet size distributions, but resulting from different homogenization conditions, had significantly different oxidative stabilities, indicating that properties of significance to oxidation other than droplet size itself were affected by the different treatments. In general, homogenization at 72 degrees C appeared to induce protective effects against oxidation as compared to homogenization at 50 degrees C. The results thus indicated that the actual composition of the oil-water interface is more important than total surface area itself.

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: oxidation linked to changes in protein composition at the oil-water interface.

Fish oil was incorporated into milk under different homogenization temperatures (50 and 72 degrees C) and pressures (5, 15, and 22.5 MPa). Subsequently, the oxidative stability of the milk and changes in the protein composition of the milk fat globule membrane (MFGM) were examined. Results showed that high pressure and high temperature (72 degrees C and 22.5 MPa) resulted in less lipid oxidation, whereas low pressure and low temperature (50 degrees C and 5 MPa) resulted in faster lipid oxidation. Analysis of protein oxidation indicated that especially casein was prone to oxidation. The level of free thiol groups was increased by high temperature (72 degrees C) and with increasing pressure. Furthermore, SDS-PAGE and confocal laser scanning microscopy (CLSM) indicated that high temperature resulted in an increase in beta-lactoglobulin adsorbed at the oil-water interface. This was even more pronounced with higher pressure. Less casein seemed to be present at the oil-water interface with increasing pressure. Overall, the results indicated that a combination of more beta-lactoglobulin and less casein at the oil-water interface gave the most stable emulsions with respect to lipid oxidation.

Protease-assisted clarification of black currant juice: synergy with other clarifying agents and effects on the phenol content.

Conventional clarification with gelatin and silica sol removes a considerable amount of antioxidant phenolics from berry juices. This study examined the clarification and haze-diminishing effects of alternative clarification strategies on black currant juice including centrifugation and addition of acidic protease and pectinolytic enzyme preparations and gallic acid. Centrifugation of freshly pressed juice (10,000 g for 15 min) resulted in a approximately 95% reduction of immediate turbidity and had a decreasing effect on haze development in the juice during cold storage without significantly compromising the total phenols levels. The extent of clarification and haze diminishment varied after individual treatments with five different acidic proteases, but one of the protease preparations, Enzeco, derived from Aspergillus niger, consistently tended to perform best. The individual and interactive effects on juice turbidity, total phenols, and total anthocyanin contents of clarification treatments involving the use of two selected acid proteases (Enzeco and Novozyme 89L), a pectinase (Pectinex BE 3-L), and gallic acid were evaluated in a full factorial 2(4) experimental design. Haze development during cold storage decreased when gallic acid or any of the enzyme preparations were employed individually, but negative interaction effects resulted when the pectinase was employed in combination with any of the proteases. After 28 storage days at 2 degrees C, the lowest levels of haze formation were achieved when the Enzeco protease preparation, added at 0.025 g/L, was added with 0.050 g/L of gallic acid and allowed to react in the juice for 90 min at 50 degrees C. The corresponding anthocyanin reduction was approximately 12% (compared to approximately 30% with gelatin silica sol treatment). The data support the hypothesis that phenol-protein interactions are involved in juice turbidity development during cold storage of berry juices and demonstrate that precentrifugation and protease-assisted clarification show promise as an alternative, phenolics-retaining clarification strategy in black currant juice processing.

Protection against oxidation of fish-oil-enriched milk emulsions through addition of rapeseed oil or antioxidants.

The ability of rapeseed oil and/or different antioxidants (alpha- and gamma-tocopherol mixture, ascorbyl palmitate, and EDTA) to protect fish-oil-enriched milk emulsions against oxidation was investigated. Tocopherol isomers in concentrations similar to those found in natural rapeseed oil were added to rapeseed oil stripped of natural tocopherols. The rapeseed oil with added tocopherols significantly inhibited oxidation in the fish-oil-enriched milk emulsions. In contrast, the emulsions with only fish oil and added alpha- and gamma-tocopherol were less stable than the emulsions with fish oil alone. When added individually, the gamma-tocopherol seemed to inhibit oxidation more efficiently than alpha-tocopherol. Ascorbyl palmitate (AP) almost completely retarded oxidation in the fish-oil-enriched milk emulsions, as determined by PV, volatile oxidation products, and sensory evaluation. AP also prevented the otherwise prooxidant effect of tocopherols added to fish oil before emulsification. No interactions between AP, tocopherols, and EDTA were observed, and EDTA added alone to fish oil did not show antioxidant properties in the milk emulsions. Overall, the results showed that addition of AP or rapeseed oil containing natural tocopherols to fish oil was equally efficient in inhibiting oxidation in the fish-oil-enriched milk emulsions.

Rye bran bread intake elevates urinary excretion of ferulic acid in humans, but does not affect the susceptibility of LDL to oxidation ex vivo.

BACKGROUND: Rye bread contributes an important part of the whole grain intake in the Scandinavian diet. Ferulic acid is the major phenolic compound in rye bran and is an antioxidant in vitro and may, therefore, contribute to cardioprotective effects of whole grain consumption. AIM OF THE STUDY: Firstly, to evaluate the bioavailability and potential antioxidative effects in humans of ferulic acid from rye. Secondly, to evaluate urine levels of ferulic acid as a possible biomarker of the ordinary dietary intake of ferulic acid. METHODS: We determined the urinary excretion of ferulic acid in 18 postmenopausal women after a dietary intake of rye bran or an inert wheat bran (control) in a crossover study (2 x 6 weeks with 4 weeks washout). The potential antioxidative effect of the rye bran intervention was investigated by measuring low-density lipoprotein (LDL) susceptibility to copper oxidation ex vivo. The subjects ingested rye bran enriched breads equivalent to approximately 10.2 mg ferulic acid per day. RESULTS: The urinary excretion of ferulic acid averaged approximately 4.8 mg per day during intervention with rye bran breads and approximately 1.9 mg per day on the control breads (P = 0.002). Rye bran intervention had no influence on lag time or propagation rate of the LDL oxidation ex vivo. CONCLUSIONS: The present study demonstrated that ferulic acid from rye bran is bioavailable and that the urinary concentration of ferulic acid reflects the dietary intake of this hydroxycinnamic acid. Within the period of intervention, the elevated ferulic acid did not produce a measurable antioxidative effect on the subjects' LDL. It is suggested that the determination of ferulic acid in urine is a useful biomarker to assess the intake of ferulic acid from a regular diet.

Modeling the sensory impact of defined combinations of volatile lipid oxidation products on fishy and metallic off-flavors.

The volatiles (E,Z)-2,6-nonadienal, 1-penten-3-one, (Z)-4-heptenal, and (E,E)-2,4-heptadienal were added to milk containing 1.5% fat according to a central composite design, to evaluate the individual and combinatory effects of these volatiles on sensory properties. The milk samples with added volatiles were subjected to sensory descriptive analysis for fishy and metallic off-flavors. The data were analyzed using partial least-squares regression and multiple linear regression to develop mathematical models. The models revealed significant main effects of (E,Z)-2,6-nonadienal and 1-penten-3-one and highlighted the importance of two-factor interactions for contribution toward off-flavors. The results suggest that (E,Z)-2,6-nonadienal and 1-penten-3-one could be useful markers for fishy and metallic off-flavors in fish oil and fish oil enriched foods. Within the addition levels of the volatiles there was a curvature effect of (E,Z)-2,6-nonadienal, a compensatory effect of (Z)-4-heptenal and (E,E)-2,4-heptadienal, and a synergistic effect of (E,Z)-2,6-nonadienal and (Z)-4-heptenal in the development of fishy off-flavors.

Chemical and olfactometric characterization of volatile flavor compounds in a fish oil enriched milk emulsion.

Development of objectionable fishy off-flavors is an obstacle in the development of fish oil enriched foods. Only little is known about the sensory impact of specific volatile fish oil oxidation products in food emulsions. This study examined the volatiles profiles of fish oil enriched milk during cold storage (2 degrees C) for 14 days by dynamic headspace sampling followed by gas chromatography-mass spectrometry analyses. Different volatiles (n = 60) comprising alkenals, alkadienals, alkatrienals, and vinyl ketones were identified in the fish oil enriched milk. The potent odorants identified by gas chromatography-olfactometry were 1-penten-3-one, (Z)-4-heptenal, 1-octen-3-one, (Z)-1,5-octadien-3-one, (E,E)-2,4-heptadienal, and (E,Z)-2,6-nonadienal, but despite their potency, none of the separated volatiles imparted a fishy or metallic odor. Two isomers, (E,Z,Z) and (E,E,Z) of 2,4,7-decatrienal were identified in fish oil enriched milk emulsions with peroxide values 0.8 and 3.4 meq/kg, respectively. To our knowledge, this is the first report on appearance of these decatrienals in food emulsions having a relatively low peroxide value.