Leif H. Skibsted

High-oxygen packaging atmosphere influences protein oxidation and tenderness of porcine longissimus dorsi during chill storage

The effect of modified atmosphere packaging (70% O(2)/30% CO(2)) and skin packaging (no oxygen) on protein oxidation and texture of longissimus dorsi was investigated during storage for 14 days at 4°C. High oxygen atmosphere resulted in reduced tenderness and juiciness and SDS-PAGE revealed cross-linking of myosin heavy chain through disulfide bonding, and the content of protein thiols was reduced indicating protein oxidation. Myofibril fragmentation was reduced in meat stored in high oxygen atmosphere indicating less proteolysis and/or cross-linking of proteins. Protein carbonyl content was not affected by the packaging atmospheres. This study shows that packaging in modified atmosphere containing a high level of oxygen can result in protein cross-linking and reduced tenderness and juiciness of the meat.

Comparative mechanisms and rates of free radical scavenging by carotenoid antioxidants

The comparative mechanisms and relative rates of nitrogen dioxide (NO2 ⋅), thiyl (RS⋅) and sulphonyl (RSO2 ⋅) radical scavenging by the carotenoid antioxidants lycopene, lutein, zeaxanthin, astaxanthin and canthaxanthin have been determined by pulse radiolysis. All the carotenoids under study react with the NO2 ⋅ radical via electron transfer to generate the carotenoid radical cation (Car⋅+). In marked contrast the glutathione and 2‐mercaptoethanol thiyl radicals react via a radical addition process to generate carotenoid‐thiyl radical adducts [RS‐Car]⋅. The RSO2 ⋅ radical undergoes both radical addition, [RSO2‐Car]⋅ and electron abstraction, Car⋅+. Both carotenoid adduct radicals and radical cations decay bimolecularly. Absolute rate constants for radical scavenging were in the order of ∼107–109 M−1 s−1 and follow the sequence HO(CH2)2S⋅>RSO2 ⋅>GS⋅>NO2 ⋅. Although there were some discernible trends in carotenoid reactivity for individual radicals, rate constants varied by no greater than a factor of 2.5. The mechanism and rate of scavenging is strongly dependent on the nature of the oxidising radical species but much less dependent on the carotenoid structure.

The combined effect of antioxidants and modified atmosphere packaging on protein and lipid oxidation in beef patties during chill storage.

Effect of rosemary extract and ascorbate/citrate (1:1) in combination with modified atmosphere packaging (100% N(2), 80% O(2)/20% N(2)) on protein and lipid oxidation in minced beef patties during storage in the dark for up to 6 days at 4°C was investigated. A high level of oxygen in the packaging atmosphere was found to increase both lipid and protein oxidation during storage as evaluated by TBARS analysis of secondary lipid oxidation products and by 2,4-dinitrophenylhydrazine derivatization of protein carbonyls. Both antioxidant systems tested were found to inhibit lipid oxidation but not protein oxidation. In contrast, ascorbate/citrate was found to promote protein oxidation. Rosemary extract was found to regenerate or protect α-tocopherol whereas the packaging atmospheres had no effect on α-tocopherol stability. In high oxygen atmospheres both antioxidants protected the fresh red meat colour with ascorbate/citrate being more efficient than the rosemary extract, whereas no effect of antioxidant on meat colour was found in beef patties stored in 100% nitrogen.

Effect of heat treatment, water activity and storage temperature on the oxidative stability of whole milk powder

Abstract The oxidative status of high-heat, medium-heat and low-heat whole milk powder was investigated at moderately accelerated storage conditions, with exposure to atmospheric air at 25 or 45 °C and at three water activities (0.11, 0.23 and 0.33 at 25 °C, and 0.11, 0.17 and 0.31 at 45 °C) for 2 months using: (i) electron spin resonance spectrometry for measurement of the level of free radicals, (ii) determination of thiobarbituric acid reactive substances (TBARS) as a measurement of secondary lipid oxidation products, (iii) size-exclusion HPLC for measurement of fluorescent protein polymerization products, and (iv) sensory evaluation. Lipid oxidation was affected greatly by storage temperature, with a maximum level of free radicals being detected after 47 days at 45 °C, and with the highest level in low-heat powder, irrespective of water activity. The sensory quality dropped to an unacceptable level for low-heat powder within 33 days of storage, as confirmed by measurement of TBARS, and the increasing TBARS value was parallelled by a decrease of ‘free’ thiol groups to an unmeasurable level in low-heat powder, in contrast to medium- and high-heat powders, in which the initial level of free thiol groups was only reduced by one-third after 63 days of storage. In contrast to common beliefs, initial powder quality was retained best at water activities between 0.11 and 0.23, where powders showed no significant differences in sensory quality, irrespective of preheat treatment. No difference in sensory score was found for storage at different water activities at 25 °C, whereas storage at water activity 0.31 at 45 °C markedly affected all powders. This effect was ascribed to a combination of increased autoxidation rate and increased Maillard reaction rate giving rise to protein polymerization, in effect decreasing the powder solubility, as often seen during storage under tropical conditions.

The antioxidative activity of plant extracts in cooked pork patties as evaluated by descriptive sensory profiling and chemical analysis

Antioxidative efficiency of extracts of rosemary, green tea, coffee and grape skin in precooked pork patties was investigated during storage under retail conditions (10 days, 4 °C, atmospheric air), using descriptive sensory profiling following reheating and quantitative measurements of hexanal, thiobarbituric acid reactive substances (TBARS) and vitamin E as indicators of lipid oxidation. The initial oxidative status of pork patties (evaluated by ANOVA) showed a significant lower level of secondary oxidation products and higher levels of vitamin E in patties with extracts incorporated, indicating that the extracts retarded lipid oxidation during processing of the meat. Data analysis for the storage study was based on qualitative overview of sensory/chemical variation by principal component analysis (PCA) and quantitative ANOVA-PLSR for determination of the relationship between design variables (days of chill-storage, extract treatment) versus sensory-chemical variables and PLSR for elucidating the predictive ability of the chemical methods for sensory terms. Lipid oxidation was seen to involve a decrease in perception of meat flavour/odour and a concomitant increase in the off-flavour/odours linseed, rancid. TBARS, hexanal and vitamin E were all significant predictive indices (P<0.05) for the majority of the sensory terms, while vitamin E through negative correlation with TBARS and hexanal displayed its antioxidative effect and thus, its ability to preserve sensory fresh meat flavour/odour. The effect of the various extracts incorporated in the product was clearly related to the degree of lipid oxidation and an overall ranking of the antioxidative efficiency of extracts in declining order became apparent: Rosemary>Grape skin>Tea>Coffee>Reference. Furthermore, the relation between extracts and vitamin E indicated that the extracts, to some extent, interacted with the vitamin and prevented it from degrading. In conclusion, the rosemary extract displayed potential for maintaining sensory eating quality in processed pork products.

Dittany (Origanum dictamnus) as a source of water-extractable antioxidants

Extracts of dittany (Origanum dictamnus L.) made with solvents of varying polarity were evaluated (i) by electron spin resonance (ESR) spectrometry using the spin trapping technique for their efficiencies as scavengers of free radicals, and (ii) by measurement of oxygen depletion in a methyl linoleate emulsion for their efficiencies as chain-breaking antioxidants. Aqueous extracts of dittany most efficiently scavenged hydroxyl radicals as generated by the Fenton reaction and this extract also most efficiently reduced oxygen consumption when initiated by metmyoglobin. Ethanol and acetone extracts of dittany showed less activity in both assays with methanol extract being intermediate. The high efficiencies found in the aqueous (and methanol) extracts of dittany were closely related to a high content of phenolic compounds in these extracts, while the amounts of phenolics in the ethanol and acetone extract were lower. In aqueous extracts, the antioxidative activity was confirmed in a turkey thigh meat homogenate, where development of thiobarbituric reactive substances was increasingly inhibited by increasing additions from 0.0018 mg dittany/g meat to efficient inhibition for 0.011 mg dittany/g meat and higher additions. Dittany should be further explored as a source of water-extractable antioxidants.

Carotenoid scavenging of radicals : effect of carotenoid structure and oxygen partial pressure on antioxidative activity

ZusammenfassungEs wurde die Entfernung von freien Radikalen beim Carotenoid untersucht durch Peroxidation der Methylester der ungesättigten Fettsäuren unter Verwendung von Metmyoglobin in einem heterogenen Lipid/Wasser-System und azo-bis-Isobutyronitril wie ein freier Radikal-Initiator in einer homogenen Chloroform-Lösung. Für das heterogene System, unter Verwendung einer Kombination einer elektrochemischen Messung der Sauerstoffverminderung, der spektrophotometrischen Bestimmung der Lipidhydroperoxide und des Carotenoidabbaues wurde demonstriert, daß jedes der vier Carotenoide, Astaxanthin,β-Carotin, Canthaxanthin und Zeaxanthin, die Methylester gegen Oxidation schützt. Der antioxidative Effekt steigt mit fallendem Sauerstoffdruck (0,010<po2<0.50 atm); weiterhin ist er wenig abhängig von der Struktur des Carotenoids. Für das homogene System wurde der Einfluß der Struktur des Carotenoids weiterhin untersucht; und es wurde demonstriert, daß die Stabilität der vier Carotenoide in dem oxidierenden System verschieden ist, und zwar mit fallender Stabilität in der Reihe: Astaxanthin>Canthaxanthin>β-Carotin >Zeaxanthin. Jedes der vier Carotenoide kann die Lipidoxidation unterdrücken, der Grad der Unterdrükkung der Peroxidation des Methyllinolats entspricht dem Unterschied in der Stabilität.AbstractCarotenoid scavenging of free radicals has been investigated in peroxidizing methyl esters of unsaturated fatty acids using (i) metmyoglobin as a water-based freeradical initiator in a heterogeneous lipid/water system, and (ii) azo-bis-isobutyronitrile as a free-radical initiator in a homogeneous chloroform solution. For the heterogeneous system, using a combination of electrochemical oxygen depletion measurements, spectrophotometric determination of lipid hydroperoxides and carotenoid degradation, it was demonstrated that each of the four carotenoids astaxanthin,β-carotene, canthaxanthin, and zeaxanthin protects the methyl esters against oxidation. The antioxidative effect increases with increasing carotenoid concentration, increases with decreasing oxygen partial pressure (0.010< pO2 <0.50 atm), and shows little dependence on the structure of the carotenoid. For a homogeneous solution, the effect of the structure of the carotenoid was further investigated, and it was shown that the stability of the four carotenoids in the oxidizing system are different, with the order of decreasing stability being: astaxanthin>canthaxanthin>β-carotene>zeaxanthin. Each of the four carotenoids can suppress lipid oxidation and the degree of suppression of peroxidation of methyl linoleate corresponds to the difference in stability.

Screening of antioxidative activity of spices. A comparison between assays based on ESR spin trapping and electrochemical measurement of oxygen consumption

Abstract Spices belonging to the Labiatae family were used to develop assays for evaluation of antioxidative activity of spices and spice extracts. Two different principles for detection of antioxidative activity were used: (i) an ESR spin trapping technique in which hydroxyl radicals were generated by the Fenton reaction and trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in competition with spice extract constituents, (ii) electrochemical measurement of oxygen depletion rate in a heterogeneous lipid/water emulsion with lipid oxidation initiated by metmyoglobin. The ESR free radical method relates to the effect of antioxidant on the initiation of oxidation, while the oxygen depletion method relates to the effect of antioxidant on the propagation of oxidation. For both methods, marjoram and basil showed the lowest activity, while winter savory showed the highest activity as measured by the ESR method, and Turkish oregano and Chilean oregano showed the highest activity as measured by the oxygen depletion method. Total phenol content in the extract correlates linearly with the antioxidant activity as measured by oxygen depletion, but not with the free radical scavenging effect. It is concluded that extracts of the investigated spices contain components with at least two different antioxidative mechanisms.

Two-electron electrochemical oxidation of quercetin and kaempferol changes only the flavonoid C-ring

Bulk electrolysis of the antioxidant flavonoids quercetin and kaempferol in acetonitrile both yield a single oxidation product in two-electron processes. The oxidation products are more polar than their parent compounds, with an increased molecular weight of 16g/mol, and were identified as 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone and 2-(4-hydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone for quercetin and kaempferol, respectively. Two-electron oxidation of the parent flavonoid is suggested to yield a 3,4-flavandione with unchanged substitution pattern in the A- and B-ring, which may rearrange to form the substituted 3(2H)-benzofuranone through the chalcan-trione ring-chain tautomer. The acidity of the 3-OH group is suggested to determine the fate of the flavonoid phenoxyl radical, originally formed by one-electron oxidation, as no well-defined oxidation product of luteolin (lacking the 3-OH group) could be isolated despite rather similar half-peak potentials: Ep/2 = 0.97V, 0.98 V and 1.17 V vs. NHE for quercetin, kaempferol and luteolin, respectively, as measured by cyclic voltammetry in acetonitrile.

Regeneration of phenolic antioxidants from phenoxyl radicals: An ESR and electrochemical study of antioxidant hierarchy

Radicals from the flavonoids quercetin, (+)-catechin, (+/-)-taxifolin and luteolin, and from all-rac-alpha-tocopherol have been generated electrochemically by one-electron oxidation in deaerated dimethylformamide (DMF), and characterised by electron spin resonance spectroscopy (ESR) after spin-trapping by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Simulations of the ESR spectrum based on estimated coupling constants of the spin-trapped quercetin radical, confirmed that this antioxidant radical is oxygen-centered. The complex mixture of radicals, quinoid intermediates and stable two-electron oxidation products, were for each antioxidant allowed to react with each of the four other antioxidants, and the progression of reaction followed by ESR after addition of DMPO, and the product solution further analysed by HPLC. All-rac-alpha-tocopherol was found to be most efficient in regenerating each of the other antioxidants from their oxidation products with a regeneration index (defined as moles regenerated of the oxidised phenolic antioxidant divided with moles of all-rac-alpha-tocopherol consumed) of 0.90+/-0.16 for quercetin, 0.48+/-0.11 for (+)-catechin, 0.48+/-0.06 for (+/-)-taxifolin and 0.50+/-0.10 for luteolin in equimolar 1.00 mM solution. Quercetin was found to have the highest regeneration index among the flavonoids: 0.88+/-0.13 for (+/-)-catechin, 0.41+/-0.03 for (+/-)-taxifolin and 0.41+/-0.02 for luteolin. The antioxidant hierarchy based on the reduction potentials determined by cyclic voltammetry under similar conditions (0.93 V for all-rac-alpha-tocopherol, 1.07 V for quercetin, 1.15 V for luteolin, 1.16V for (+)-catechin and 1.20 V for (+/-)-taxifolin) is compared with the observed over-all regeneration (34% for quercetin, 34% for (+)-catechin, 52% for (+/-)-taxifolin and 43% for luteolin by all-rac-alpha-tocopherol).