Measurement of lipid oxidation in meat and meat products

Effects of Animal Diet and Processing Methods on the Quality Traits of Dry-Cured Ham Produced from Turopolje Pigs

The Turopolje pig (TP) is a local Croatian pig breed that almost became extinct in the second half of the 20th century. Today, the TP is still endangered, and a new conservation strategy based on products with higher added value is needed to preserve the breed. There is little information on the quality of TP meat products such as smoked and dry-cured ham, including the impact of natural feeds or processing innovations such as smoke reduction. This study, therefore, investigated the effects of the animal's diet (either conventionally fed or acorn-supplemented) and the processing method (standard or lightly smoked) on the quality traits of dry-cured TP ham. Twenty hams, evenly distributed among the treatments, were processed for 15 months and then analysed for physicochemical and textural traits, volatiles and sensory profile. The hams from acorn-supplemented pigs lost less weight during processing (p ≤ 0.05). Otherwise, the diet had no significant effect on most examined ham traits. The exceptions were protein content and the texture parameter hardness, which decreased (p ≤ 0.05), and the degree of proteolysis and colour parameters, which increased (p ≤ 0.05) as a result of acorn supplementation. However, these effects were generally small and varied between the inner (m. biceps femoris) and outer (m. semimembranosus) muscles. Furthermore, acorn supplementation was associated with less typical ham odour and lower sensory scores for sweetness and colour uniformity (p ≤ 0.05). The smoke reduction had no effect on the physicochemical and colour properties but resulted in a significant reduction (p ≤ 0.05) in the volatile phenolic compounds and an improved texture to the hams. This was reflected both in reduced (p ≤ 0.05) hardness, identified in the instrumental analysis, and in an increased (p ≤ 0.05) softness, solubility and moistness, identified in the sensory evaluation. To summarize, the quality of the TP ham under the conditions studied was only slightly affected by acorn supplementation, whereas reduced smoking had a more significant effect, which was mainly reflected in an improved texture.

Effect of Different Genotypes and Harvest Times of Sage (Salvia spp. Labiatae) on Lipid Oxidation of Cooked Meat

Lipid oxidation is the primary non-microbial reason for quality deterioration of meat and meat products. Lipid oxidation can be prevented or delayed by antioxidants. In this study, 15 sage (Salvia spp. Labiatae) extracts (five genotypes, three harvest times) were tested for their ability to reduce lipid oxidation (peroxide value (PV) and thiobarbituric acid reactive substances (TBARS)) in ground, uncured, cooked porcine and bovine meat (60%/40% mixture) during 14 days of refrigerated storage. Additionally, total phenolic content was determined, and the antioxidant capacity of the extracts was measured as radical scavenging activity (2,2-diphenyl-1-picrylhydrazyl assay), reducing power, and superoxide anion scavenging activity. All 15 sage extracts were able to reduce lipid oxidation, though showing expected differences depending on genotype and harvest time. The extracts of S. officinalis accession from Foggia, Italy performed better than the other genotypes when looking at the entire storage period and considering both PV and TBARS. Of the applied methods for determining antioxidant capacity, superoxide anion scavenging activity proved to be the best determinant of the ability of sage to reduce lipid oxidation in the meat sample.

Monitoring the lipid oxidation and flavor of Russian sturgeon fillets treated with low temperature vacuum heating: formation and relationship

BACKGROUND

Sturgeon is one of the most precious fish resources worldwide. Low temperature vacuum heating (LTVH) has been confirmed as a good way of maintaining food quality. However, there is a lack of in-depth studies assessing the impact of LTVH on lipid oxidation and flavor formation.

RESULTS

The present study compared the effect of LTVH and traditional cooking on lipid oxidation and flavor of sturgeon fillets. In total, 13 fatty acids were detected, of which polyunsaturated fatty acids content was the highest (P < 0.05). LTVH prevented the formation of conjugated diene and thiobarbituric acid reactive substances (P < 0.05), as manifested by an increased signal intensity of free radicals of electron spin resonance. The characteristic peaks intensity of lipid by Raman at 970 cm^-1 , 1080 cm^-1 and 1655 cm^-1 were reduced, whereas peaks at 1068 cm^-1 and 1125 cm^-1 displayed the opposite trend. Confocal fluorescence microscopy showed that the lipids particles were reduced and distributed more evenly with an increase in heating temperature. Principal component analysis of electronic nose cannot effectively separate all groups; however, gas chromatography-ion migration spectrometry showed that the volatile flavor compounds were relatively stable during LTVH. Correlation analysis of all the above lipid oxidation indices and characteristic flavor substances showed that each treatment group was located in different quadrants and demonstrated great differentiation.

CONCLUSION

Overall, the results of the present study support the view that LTVH is a healthier way of cooking. © 2022 Society of Chemical Industry.

The Evaluation of the Effects of Dietary Vitamin E or Selenium on Lipid Oxidation in Rabbit Hamburgers: Comparing TBARS and Hexanal SPME-GC Analyses

The effects and specificity of dietary supplementation of EconomasETM (EcoE), mainly consisting of organic selenium (0.15 or 0.30 mg/kg feed; Se) or of vitamin E (100 or 200 mg/kg feed; VE), on lipid oxidation were evaluated in rabbit hamburgers during refrigerated storage. Oxidation data obtained by thiobarbituric acid-reactive substances (TBARS) spectrophotometric analysis and solid-phase microextraction (SPME) coupled with gas chromatography (GC) to determine hexanal content were compared. The relationships between oxidation levels, colour and pH and the discriminability of EcoE- or VE-treatment compared with control were also examined. TBARS content decreased in both VE and EcoE groups, while hexanal showed lower values only in the VE100 dietary group. The colour parameters were compatible with acceptable product quality and seemed to parallel the TBARS values up to the second day storage. Both VE and EcoE improved oxidative stability without affecting the sensory properties, but the VE effect appeared to more specifically hamper lipid oxidation, as evidenced by the determination and quantification of hexanal, a specific product of fatty acid peroxidation.

Utilization of Astaxanthin as a Synthetic Antioxidant Replacement for Emulsified Sausages

The aim of this study was to evaluate the effect of astaxanthin (AX) on the quality and sensory characteristics of emulsified pork sausages during cold storage. The changes of Peroxide value (PV), 2-thiobarbituric acid-reactive substances (TBARS), thiol content, texture profile analysis, instrumental color, and sensorial qualities were assessed on specific storage days. The emulsified sausages with added AX exhibited significantly (p < 0.05) higher redness values and total color differences (ΔE) on all storage days. Sensory values recorded the reddest color and greater overall acceptability scores to the sample with AX. In addition, AX had a significantly (p < 0.05) greater effect on PV, TBARS, and thiol content of sausages, compared with the control (CON). AX showed higher oxidation stability than CON for regression coefficient, and the level of inhibition of malondialdehyde formation was similar to that of butylated hydroxytoluene (BHT) on storage days. Synthetically, AX had a desirable consequence on antioxidant activity and color of emulsified sausages; therefore, it can be used as a multifunctional additive in emulsified pork sausages.

Fatty Acid Characterization of Beef Longissimus from Steers Finished on Fodder Beet or Traditional Winter Forages in New Zealand Compared to US Grain-Fed Beef

Fatty acids were evaluated to characterize lipid profiles of beef from 3 feeding programs: New Zealand (NZ) fodder beet (FB), NZ grass/non-FB (NFB), and United States grain. Strip loins were selected within each program based on expected eating quality focusing on marbling, ossification, and pH. Selection resulted in 6 treatments: FB high quality, FB low quality, NFB high quality, NFB low quality, US Top Choice, and US Select. Samples were aged 21 d or 35 d postmortem. A subset of 152 samples (12–13 per treatment combination) were used for fatty acid characterization. Within the polar lipid fraction, US treatments had lower monounsaturated fatty acid (MUFA) and greater polyunsaturated fatty acid (PUFA) than NZ treatments (P &lt; 0.05). Within the neutral lipid fraction, concentrations of total neutral lipids and proportions of saturated fatty acid, MUFA, and PUFA were affected by treatment (P &lt; 0.05). Total neutral lipids were greatest in Top Choice (P &lt; 0.05) and greater in FB high quality than all other treatments (P &lt; 0.05). Proportions of satu- rated fatty acid in the neutral lipid fraction were greater in NFB treatments than US treatments (P &lt; 0.05); FB treatments were intermediate. Proportions of MUFA were greatest in Top Choice (P &lt; 0.05). Proportions of PUFA were greatest (P &lt; 0.05) in Select, greater in Top Choice than all NZ treatments (P &lt; 0.05), and greater in NFB treatments than FB treatments (P &lt; 0.05). No interactions occurred for any groups of fatty acids in either fraction ( P &gt; 0.05), and aging did not affect fatty acid composition. Lipid profiles were impacted by finishing diet; however, most differences were between US grain-fed beef and NZ treatments—with limited differences between FB and NFB samples—when product was selected based on quality descriptors. Therefore, FB could be substituted for grass forages to sustain the NZ beef industry through winter months and limit seasonality without detrimental effects on product quality.

A Comprehensive Review on Lipid Oxidation in Meat and Meat Products

Meat and meat products are a fundamental part of the human diet. The protein and vitamin content, as well as essential fatty acids, gives them an appropriate composition to complete the nutritional requirements. However, meat constituents are susceptible to degradation processes. Among them, the most important, after microbial deterioration, are oxidative processes, which affect lipids, pigments, proteins and vitamins. During these reactions a sensory degradation of the product occurs, causing consumer rejection. In addition, there is a nutritional loss that leads to the formation of toxic substances, so the control of oxidative processes is of vital importance for the meat industry. Nonetheless, despite lipid oxidation being widely investigated for decades, the complex reactions involved in the process, as well as the different pathways and factors that influenced them, make that lipid oxidation mechanisms have not yet been completely understood. Thus, this article reviews the fundamental mechanisms of lipid oxidation, the most important oxidative reactions, the main factors that influence lipid oxidation, and the routine methods to measure compounds derived from lipid oxidation in meat.

Effect of fermented blueberry on the oxidative stability and volatile molecule profiles of emulsion-type sausage during refrigerated storage

Objective

The aim of this work was to assess the effect of fermented blueberry (FB; 2%, 4%, and 6%) on the oxidative stability and volatile molecule profiles of emulsion-type sausage stored at 4°C for 28 days.

Methods

The antioxidant activity of FB was determined through radical-scavenging activity against 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals. Four formulations of sausage treatments with different FB levels (0%, 2%, 4%, 6%) were prepared, then peroxide value (POVs), thiobarbituric acid-reactive substances (TBARS) values, protein carbonyls and thiol groups were measured. The aroma profiles of sausages for each treatment was also determined.

Results

The half maximal inhibitory concentration indicated that FB had greater scavenging ability than ascorbic acid against DPPH and hydroxyl radicals. Sausages with FB significantly retarded increases in POVs and TBARS, as well as in the content of protein carbonyls during all storage days (p<0.05). Particularly, 4% and 6% FB-treated sausages had better oxidation inhibition effects. However, FB accelerated the reduction in thiol groups (p<0.05). Additionally, FB inhibits the excessive formation of aldehyde compounds; for example, hexanal, which may cause rancid flavors, decreased from 58.25% to 19.41%. FB also created 6 alcohols (i.e., 2-methyl-1-propanol, 3-methyl-1-butanol, and phenylethyl alcohol), 5 ester compounds (i.e., ethyl acetate, ethyl lactate, and ethyl hexanoate) and 3-hydroxy-2-butanone in the sausages that contribute to sausage flavors. The principal component analysis showed that the aroma profiles of sausages with and without FB are easily identified.

Conclusion

The addition of FB could significantly reduce the lipid and protein oxidation and improve oxidative stability for storage. Also, adding FB could inhibit rancid flavors and contribute to sausage flavors.

Palatability Characterization of Fresh and Dry-Aged Ground Beef Patties

Descriptive trained sensory attributes, fatty acids, and volatile compounds were determined to characterize the effects of dry-aging on ground beef. Beef shoulder clods were ground to include 100% fresh beef, 100% dry-aged beef, and a 50% fresh and 50% dry-aged ground beef blend. Samples comprised of 100% dry-aged beef were rated greatest (P < 0.001) for browned/grilled, earthy/mushroom, and nutty/roasted-nut flavors; however, panelists also detected greater (P ≤ 0.011) incidences of sour/acidic and bitter flavors. The addition of dry-aged beef increased (P < 0.001) hardness and reduced (P < 0.001) tenderness. Dry-aging also caused a shift in saturated fatty acids, where shorter chain saturated fatty acids (≤ 16:0) were reduced (P ≤ 0.034) compared to stearic acid (18:0). Meanwhile, increases of trans-octadecenoic acid (18:1 trans) and decreases of cis monounsaturated fatty acids were present in dry-aged beef. Concentrations of 18:2 conjugated linoleic isomers were greatest (P < 0.001) in fresh beef and decreased with the incorporation of dry-aged beef. Several lipid-derived volatile compounds were greater (P < 0.05) in dry-aged beef compared with fresh beef, implying a greater degree of lipid degradation among dry-aged beef. Increases (P ≤ 0.031) were determined for 3- and 2-methyl butanal with the addition of dry-aged beef. Intermediates of the Maillard reaction, 2,3-butanedione and acetoin, were determined to be greatest (P ≤ 0.046) from dry-aged beef. Alterations of fatty acids and volatile compounds with dry-aging were determined to be related with intensity of individual flavor attributes. Overall, it may be concluded that inclusion of dry-aged beef impacts flavor profile through altered fatty acid profiles and flavor related compounds. These results support the idea that dry-aging may be utilized to impart an altered ground beef flavor experience.

Non-Destructive Spectroscopic Techniques and Multivariate Analysis for Assessment of Fat Quality in Pork and Pork Products: A Review

Fat is one of the most important traits determining the quality of pork. The composition of the fat greatly influences the quality of pork and its processed products, and contribute to defining the overall carcass value. However, establishing an efficient method for assessing fat quality parameters such as fatty acid composition, solid fat content, oxidative stability, iodine value, and fat color, remains a challenge that must be addressed. Conventional methods such as visual inspection, mechanical methods, and chemical methods are used off the production line, which often results in an inaccurate representation of the process because the dynamics are lost due to the time required to perform the analysis. Consequently, rapid, and non-destructive alternative methods are needed. In this paper, the traditional fat quality assessment techniques are discussed with emphasis on spectroscopic techniques as an alternative. Potential spectroscopic techniques include infrared spectroscopy, nuclear magnetic resonance and Raman spectroscopy. Hyperspectral imaging as an emerging advanced spectroscopy-based technology is introduced and discussed for the recent development of assessment for fat quality attributes. All techniques are described in terms of their operating principles and the research advances involving their application for pork fat quality parameters. Future trends for the non-destructive spectroscopic techniques are also discussed.

Oxidative stability of blesbok, springbok and fallow deer droëwors with added rooibos extract

Abstract The addition of rooibos extract (RBE) (0%, 0.25%, 0.50%, 1.0% RBE) to improve the oxidative stability of blesbok, springbok and fallow deer droëwors (dried sausage) was studied. RBE treatments had no effects (p more than 0.05) on the lipid and protein oxidation of the dried product. With the addition of RBE 0.25%, lipid stability after drying showed the malonaldehydes decreased considerably. Haem-iron concentration increased after drying and differed (p less than 0.05) between RBE treatments within the dried stage within species. There were no differences (p more than 0.05) between the moisture, protein and fat contents between treatments within a specific processing stage. With the high polyunsaturated fatty acid content of the sausages, a high level of oxidation occurred. Even though RBE addition did not reduce oxidation significantly during the drying process, it could be a successful addition to the traditional South African meat product if it is shown to impart positive flavour attributes.

Preparation of organogel with tea polyphenols complex for enhancing the antioxidation properties of edible oil

Food-grade organogels are semisolid systems with immobilized liquid edible oil in a three-dimensional network of self-assembled gelators, and they are supposed to have a broad range of potential applications in food industries. In this work, an edible organogel with tea polyphenols was developed, which possesses a highly effective antioxidative function. To enhance the dispersibility of the tea polyphenols in the oil phase, a solid lipid-surfactant-tea polyphenols complex (organogel complex) was first prepared according to a novel method. Then, a food-grade organogel was prepared by mixing this organogel complex with fresh peanut oil. Compared with adding free tea polyphenols, the organogel complex could be more homogeneously distributed in the prepared organogel system, especially under heating condition. Furthermore, the organogel loading of tea polyphenols performed a 2.5-fold higher antioxidation compared with other chemically synthesized antioxidants (butylated hydroxytoluene and propyl gallate) by evaluating the peroxide value of the fresh peanut oil based organogel in accelerated oxidation conditions.

Quantitative study of the relationships among proteolysis, lipid oxidation, structure and texture throughout the dry-cured ham process

Temperature, salt and water contents are key processing factors in dry-cured ham production. They affect how proteolysis, lipid oxidation, structure and texture evolve, and thus determine the sensory properties and final quality of dry-cured ham. The aim of this study was to quantify the interrelationships and the time course of (i) proteolysis, (ii) lipid oxidation, (iii) five textural parameters: hardness, fragility, cohesiveness, springiness and adhesiveness and (iv) four structural parameters: fibre numbers, extracellular spaces, cross section area, and connective tissue area, during the dry-cured ham process. Applying multiple polynomial regression enabled us to build phenomenological models relating proteolysis, salt and water contents to certain textural and structural parameters investigated. A linear relationship between lipid oxidation and proteolysis was also established. All of these models and relationships, once combined with salt penetration, water migration and heat transfer models, can be used to dynamically simulate all of these phenomena throughout dry-cured ham manufacturing.

Hydroperoxide formation in different lean meats

Peroxide is one of the compounds that are indicated to be toxic in the human digestion system. Lean fresh meat samples were collected from beef, lamb, pork and chicken to investigate their hydroperoxide formation potential. Total peroxides of fresh comminuted raw meat were determined by analysing protein-bound peroxides and hydroperoxide compounds in water-methanol and chloroform extracted phases. The amount of total peroxides was ranked as: beef>pork>lamb>chicken. Hydroperoxide formation was examined at different pH values and at different incubation times, using beef and chicken samples. All peroxides were transient, with a maximum value after 2-4 h of incubation at 37 °C. When pH fell from 7 to 1.5, the different peroxides fell by 10-20%. Non-polar peroxide formation could largely (70%) be described by variation in fatty acid composition and hemin content of the meat, while protein-bound peroxide variation was less explained by these variables. Liposome addition increased (40%) the amount of protein-bound peroxides.

Relationship between histochemical, structural characteristics and oxidative stability of rhea limb muscles

Histochemical and structural characteristics were investigated in Gastrocnemius pars interna (GN) and Iliofiburalis (IF) limb muscles of Rhea americana. The average myofibre area cross-section was greater in GN than IF muscle (p<0.001), whereas the fibre density per section was higher in IF than GN muscle. The only type of myofibre found in both the rhea limb muscles analysed in this study was fast-twitch oxidative-glycolytic fibres (FOG). Immunolabelling analysis and ultrastructural observation of myofibres confirmed the contractile and metabolic characteristics of rhea myofibres, revealing the absolute fast isoform of myosin heavy chain and the abundance of glycogen and mitochondria inside the cells, mainly in IF muscle. These findings converged with previous results on the biochemical and physicochemical characteristics of rhea meat to provide further evidence that myofibre composition substantially influences the oxidative reactions of the muscle and therefore the meat quality, but more in-depth examination is needed to establish the links between myofibre characteristics, myofibre glycogen concentration and meat stability during storage.

Effect of frozen storage duration and cooking on physical and oxidative changes in M. Gastrocnemius pars interna and M. Iliofiburalis of Rhea americana

This study was conducted to evaluate the effect of frozen storage time (30, 60, 90 or 180 days) and cooking (100 °C, 30 min) on the physical characteristics and oxidative stability of M. Gastrocnemius pars interna (GN) and M. Iliofiburalis (IF) of rhea americana. Physical parameters measured included thawing and cooking loss, colour parameters (L*a*b*), while oxidation was assessed by determining the TBA-RS, carbonyl and aromatic amino acid content. Prolonged frozen storage of rhea meat decreased lightness (L*), yellowness (b*), and increased the discoloration parameter hue angle and redness a*. During storage, muscle IF was more prone to lipid and myoglobin oxidation than muscle GN. Cooking loss declined with the increase of storage time and was higher in GN than in IF muscle. With cooking, TBA-RS, carbonyl content, and aromatic amino acids (phenylalanine, tyrosine, and tryptophan) were highly affected, but the extent of oxidation ranged according to muscle and duration of frozen storage.

Chemistry and biochemistry of lipid peroxidation products

Oxidative stress and resulting lipid peroxidation is involved in various and numerous pathological states including inflammation, atherosclerosis, neurodegenerative diseases and cancer. This review is focused on recent advances concerning the formation, metabolism and reactivity towards macromolecules of lipid peroxidation breakdown products, some of which being considered as 'second messengers' of oxidative stress. This review relates also new advances regarding apoptosis induction, survival/proliferation processes and autophagy regulated by 4-hydroxynonenal, a major product of omega-6 fatty acid peroxidation, in relationship with detoxication mechanisms. The use of these lipid peroxidation products as oxidative stress/lipid peroxidation biomarkers is also addressed.

Use of meat fluorescence emission as a marker of oxidation promoted by cooking

Accumulation of fluorescent pigments in cooked bovine meat (M. Longissimus thoracis) was studied in relationship with the heating parameters (time and temperature). Muscles were aged at 4°C for 11days under vacuum before cooking. Meat cooking was performed by applying jets of steam. Three different heating treatments were tested: two with constant surface temperatures of 65 and 96°C for 300s, and one with a continuously increasing surface temperature up to 207°C. After extraction in water/dichloromethane/ethanol, fluorescence pigments were distributed between the apolar phase (emission 420-440nm after excitation at 360nm) and the polar phase, where two emission peaks were seen (emission 410-430 and 515nm after excitation at 360nm). Fluorescence in the two phases was little affected by heating at the two constant temperatures while it increased exponentially after 1min of treatment, as the varying temperature reached 141°C. The maximum fluorescence increases, measured in the extreme conditions of cooking (207°C/300s), were of 5000% in the apolar phase and 1700% in the polar phase. Thiobarbituric acid reactive substances (TBARS) and protein carbonyls were measured in parallel. The correlations between these two parameters and the fluorescence emission demonstrated that the interaction between proteins and aldehyde products of lipid peroxidation was mainly involved in the production of fluorescent pigments in cooked meat.

Contribution of mass spectrometry to assess quality of milk-based products

The vast knowledge of milk chemistry has been extensively used by the dairy manufacturing industry to develop and optimize the modern technology required to produce high-quality milk products to which we are accustomed. A thorough understanding of the chemistry of milk and its numerous components is essential for designing processing equipment and conditions needed for the manufacture and distribution of high-quality dairy products. Knowledge and application of milk chemistry is also indispensable for fractionating milk into its principal components for use as functional and nutritional ingredients by the food industry. For all these reasons, powerful analytical methods are required. Because of the complexity of the milk matrix, mass spectrometry, coupled or not to separation techniques, constitutes a key tool in this area. In the present manuscript, we review the contribution and potentialities of mass spectrometry-based techniques to assess quality of milk-based products.

Quantitative determination of dityrosine in milk powders by liquid chromatography coupled to tandem mass spectrometry using isotope dilution

An analytical method to quantify dityrosine (DiTyr) in milk powder samples is presented. The assay is based on isotope dilution liquid chromatography coupled to electrospray ionisation tandem mass spectrometry (LC-ESIMS/MS). The sample preparation entails acid hydrolysis of milk proteins followed by a solid phase-extraction (SPE) step. Neither artifactual formation nor degradation of DiTyr were observed during the proteolysis step. Mass spectral detection was performed in the positive ion mode by recording five transition reactions for DiTyr, in order to unambiguously confirm the presence of DiTyr by correct ion ratios. Under the analytical conditions used, the limit of detection (LOD) and limit of quantification (LOQ) for DiTyr were estimated at ca. 2 and 6 micromol DiTyr per mol of Tyr (using ca. 500 microg of milk proteins), with a mean recovery of ca. 90%. Quantification was conduced in eight different commercial milk powder samples, and the level of DiTyr ranged from below the LOQ up to 393.0 +/- 9.1 micromol DiTyr per mol of Tyr.

Study of protein modification by 4-hydroxy-2-nonenal and other short chain aldehydes analyzed by electrospray ionization tandem mass spectrometry

A convenient way to study lipid oxidation products-modified proteins by means of suitable model systems has been investigated. As a model peptide, the oxidized B chain of insulin has been chemically modified by either 4-hydroxy-2-nonenal (HNE) or hexanal and the extent, sites, and structure of modifications were assessed by electrospray mass spectrometry. A reduction step, using either NaCNBH(3) or NaBH(4), was also studied to stabilize the alkylated compounds. From the data gathered, it appeared that NaCNBH(3), when added at the beginning of incubation, dramatically influenced the HNE-induced modifications in terms of the addition mechanism (Schiff base formation instead of Michael addition) but also of the amino acid residues modified (N-terminal amino acid instead of histidine residues). However, by reducing the HNE-adducted species at the end of the reaction with NaBH(4), the fragment ions obtained in the product ion scan experiments become more stable and thus, easier to interpret in terms of origin and mechanism involved. With regard to hexanal induced modifications, we have observed that hexanal addition under reductive conditions led to an extensive modification of the peptide backbone. Moreover, as confirmed by "in-source" collision followed by collision induced dissociation (CID) experiments on selected precursor ions (pseudo-MS(3) experiments), N,N-di-alkylations were first observed on the N-terminal residue and further on Lys(29) residue. On the other hand, compared to the native peptide, no significant changes in MS/MS fragmentation patterns (b and y ions series) were observed whatever the basic site modified by the aldehyde-addition.

Comparison of analytical techniques to quantify malondialdehyde in milk powders

Several analytical methods were compared to quantify malondialdehyde (MDA) in milk powders. Modified thiobarbituric acid (TBA) methods, using either visible spectrophotometry (direct absorbance reading or after third derivative transformation of the spectrum) or HPLC, required derivatisation at elevated temperature, which appeared to catalyse artefactual MDA formation and thus overestimate the MDA content. In contrast to the TBA derivatisation method, the measurement of MDA as the dinitrophenylhydrazone derivative by HPLC or as the phenylhydrazone product by GC-MS with a deuterated internal standard resulted in lower estimates in the ranges of 2-17- and 3-30-fold, respectively; apparently due to the milder derivatisation conditions. The estimates of MDA determined by both HPLC-UV and GC-MS techniques result in lower values which are similar in magnitude even though the GC-MS technique is more sensitive.

Evaluation and comparison of two improved techniques for the on-line detection of antioxidants in liquid chromatography eluates

Two methods for the on-line detection in HPLC eluates of analytes possessing radical scavenging activity were improved and compared. The instrumental set-up of the method that is based on on-line inhibition of luminol chemiluminescence (CL) by antioxidants was improved using better quality syringe pumps, employing a diode array detector, and introducing a mixing/neutralisation coil and a pulse damper. Sensitivity of the HPLC-CL detection increased by a factor of 4. Post-column neutralisation of eluates improved compatibility of this detection method with acidified HPLC eluents. The second method, which is based on the post-column quenching of 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH*), was improved by readjusting composition and flow-rate of the reagent, mounting an additional pulse damper and detecting unreacted DPPH* with a detector equipped with a tungsten lamp. Purging of the DPPH* solution with He gas prior to analysis was introduced. This led to 30-fold better detection limits. The improved methods were compared with respect to limits of detection, the radical scavenging mechanism involved, compatibility with common HPLC solvents and pH range, and some technical aspects. The techniques described have high potential for the rapid identification of radical scavengers in complex samples like plant extracts.