Interlaboratory study on lipid oxidation during accelerated storage trials with rapeseed and sunflower oil analyzed by conjugated dienes as primary oxidation products

11 Páginas.-- 5 Figuras.-- 2 Tablas.-- Material suplementarioAccelerated storage tests are frequently used to assess the oxidative stability of foods and related systems due to its reproducibility. Various methods and experimental conditions are used to measure lipid oxidation. Differences between laboratories make it necessary to determine the repeatability and reproducibility of oxidation tests performed under the same conditions. The objective of the present interlaboratory study was to evaluate the outcome of a storage test for two different bulk oils, sunflower oil (SFO) and rapeseed oil (RSO), during a period of 9 weeks at 20°C, 30°C, 40°C, and 60°C. Sixteen laboratories were provided with bottled oils and conducted the storage tests according to a detailed protocol. Lipid oxidation was monitored by the formation of conjugated dienes (CD) and the activation energy (Ea) was determined for comparative purposes and statistically evaluated. An increase in CD formation was observed for both oils when the storage temperature was increased in all laboratories. The Ea,1 ranged from 47.9 to 73.3 kJ mol−1 in RSO and from 27.8 to 62.6 kJ mol−1 in SFO, with average values of 58.2 and 46.8 kJ mol−1, respectively. The reproducibility coefficients were 10.9% and 18.2% for RSO and SFO, respectively. Practical applications: In order to compare results on oxidative stability of foods derived from different studies, the reproducibility of storage tests and methods employed to evaluate the oxidation level should be considered. This study provides fundamental data on the reproducibility of lipid oxidation under accelerated storage conditions and defines important parameters to be considered for the conduction of experiments.Open access funding enabled and organized by Projekt DEAL. We thank Brökelmann + Co – Oelmühle GmbH + Co for the donation of the vegetable oils. The authors gratefully acknowledge Lina Stuthmann from the Food Technology Division, Kiel University and Inge Holmberg from the National Food Institute, Technical University of Denmark for their skillful help.Peer reviewe

Rapid Quantitative Profiling of Lipid Oxidation Products in a Food Emulsion by 1H NMR

Lipid oxidation is one of the most important reasons for the compromised shelf life of food emulsions. A major bottleneck in unravelling the underlying mechanisms is the lack of methods that provide a rapid, quantitative, and comprehensive molecular view on lipid oxidation in these heterogeneous systems. In this study, the unbiased and quantitative nature of 1H NMR was exploited to assess lipid oxidation products in mayonnaise, a particularly oxidation-prone food emulsion. An efficient and robust procedure was implemented to produce samples where the 1H NMR signals of oxidation products could be observed in a well resolved and reproducible manner. 1H NMR signals of hydroperoxides were assigned in a fatty acid and isomer specific way. Band-selective 1H NMR pulse excitation allowed immediate and precise (RSDR = 5.9%) quantification of both hydroperoxides and aldehydes with high throughput and large dynamic range at levels of 0.03 mmol/kg. Explorative multivariate data modeling of the quantitative 1H NMR profiles revealed that shelf life temperature has a significant impact on lipid oxidation mechanisms

DATA

Supplementary, raw data, and code

Quantitative spatiotemporal mapping of lipid and protein oxidation in mayonnaise

Lipid oxidation in food emulsions is mediated by emulsifiers in the water phase and at the oil–water interface. To unravel the physico-chemical mechanisms and to obtain local lipid and protein oxidation rates, we used confocal laser scanning microscopy (CLSM), thereby monitoring changes in both the fluorescence emission of a lipophilic dye BODIPY 665/676 and protein auto-fluorescence. Our data show that the removal of lipid-soluble antioxidants from mayonnaises promotes lipid oxidation within oil droplets as well as protein oxidation at the oil–water interface. Furthermore, we demonstrate that ascorbic acid acts as either a lipid antioxidant or pro-oxidant depending on the presence of lipid-soluble antioxidants. The effects of antioxidant formulation on local lipid and protein oxidation rates were all statistically significant (p < 0.0001). The observed protein oxidation at the oil–water interface was spatially heterogeneous, which is in line with the heterogeneous distribution of lipoprotein granules from the egg yolk used for emulsification. The impact of the droplet size on local lipid and protein oxidation rates was significant (p < 0.0001) but minor compared to the effects of ascorbic acid addition and lipid-soluble antioxidant depletion. The presented results demonstrate that CLSM can be applied for unraveling the roles of colloidal structure and transport in mediating lipid oxidation in complex food emulsions.</p

³¹P NMR assessment of the phosvitin-iron complex in mayonnaise

Lipid oxidation is the main reason for the limited shelf life of mayonnaise. One of the main catalysts of this process is iron, which is introduced in its ferric (Fe(III)) form via phosvitin, an egg yolk phosphoprotein rich in phosphoserines. The binding of Fe(III) to phosvitin and its ability to establish a redox couple with Fe(II) is believed to determine the oxidation rate of unsaturated lipids. In this work, a 31P NMR based method was developed to quantify loading of phosvitin with Fe(III) and its reductive release. Both features could be quantified in model phosvitin solutions by exploiting the paramagnetic broadening of 31P NMR signal of phosphoserine residues by Fe(III). This method was then successfully applied to quantify the phosvitin-Fe(III) loading in mayonnaise water phase by liquid NMR, whereas 31P NMR MAS could only provide a qualitative measure. The 31P NMR method showed a direct relation between loading of the Fe(III)-phosvitin complex and lipid oxidation.</p

TEMPO/NaClO₂/NaOCl oxidation of arabinoxylans

TEMPO-oxidation of neutral polysaccharides has been used to obtain polyuronides displaying improved functional properties. Although arabinoxylans (AX) from different sources may yield polyuronides with diverse properties due to their variable arabinose (Araf) substitution patterns, information of the TEMPO-oxidation of AX on its structure remains scarce. We oxidized AX using various TEMPO:NaClO2:NaOCl ratios. A TEMPO:NaClO2:NaOCl ratio of 1.0:2.6:0.4 per mol of Ara gave an oxidized-AX with high molecular weight, minimal effect on xylose appearance, and comprising charged side chains. Although NMR analyses unveiled arabinuronic acid (AraAf) as the only oxidation product in the oxidized-AX, accurate AraA quantification is still challenging. Linkage analysis showed that > 75 % of the β-(1→4)-xylan backbone remained single-substituted at position O-3 of Xyl similarly to native AX. TEMPO-oxidation of AX can be considered a promising approach to obtain arabinuronoxylans with a substitution pattern resembling its parental AX.</p

Quantitative and predictive modelling of lipid oxidation in mayonnaise

Food emulsions with high amounts of unsaturated fats, such as mayonnaise, are prone to lipid oxidation. In the food industry, typically accelerated shelf life tests are applied to assess the oxidative stability of different formulations. Here, the appearance of aldehydes at the so-called onset time, typically weeks, is considered a measure for oxidative stability of food emulsions, such as mayonnaise. To enable earlier assessment of compromised shelf-life, a predictive model for volatile off-flavor generation is developed. The model is based on the formation kinetics of hydroperoxides, which are early oxidation products and precursors of volatile aldehydes, responsible for off-flavor. Under accelerated shelf-life conditions (50◦C), hydroperoxide (LOOH) concentration over time shows a sigmoidal curvature followed by an acceleration phase that occurs at a LOOH-concentration between 38-50 mmol/kg, here interpreted as a critical LOOH concentration (CCLOOH). We hypothesize that the time at which CCLOOH was reached is related to the onset of aldehyde generation and that the characterization of the LOOH-generation curvature could be based on reaction kinetics in the first days. These hypotheses are tested using semi-empirical models to describe the autocatalytic character of hydroperoxide formation in combination with the CCLOOH. The Foubert function is selected as best describing the LOOH-curvature and is hence used to accurately predict onset of aldehyde generation, in most cases within several days of shelf-life. Furthermore, we find that the defining parameters of this model could be used to recognize antioxidant mechanisms at play.</p

Evaluation of PBN spin-trapped radicals as early markers of lipid oxidation in mayonnaise

Quality deterioration of mayonnaise is caused by lipid oxidation, mediated by radical reactions. Assessment of radicals would enable early lipid oxidation assessment and generate mechanistic insights. To monitor short-lived lipid-radicals, N-tert-butyl-α-phenylnitrone (PBN), a spin-trap, is commonly used. In this study, the fate of PBN-adducts and their impact on lipid oxidation mechanisms in mayonnaise were investigated. The main signals detected by Electron Spin Resonance (ESR) were attributed to L[rad]-radicals attached to 2-methyl-2-nitrosopropane (MNP), one of three degradation products of the PBN-peroxy-adduct. The second degradation product, benzaldehyde, was detected with Nuclear Magnetic Resonance (1H NMR), in line with MNP-L adduct generation. For the third class of degradation products, LO[rad]-radicals, their scission products were detected with 1H NMR and indicated that LO[rad]-radicals have a major impact on downstream oxidation pathways. This precludes mechanistical studies in presence of PBN. Degradation products of PBN-adducts can, however, be used for early assessment of antioxidants efficacy in oil-in-water emulsions

³¹P NMR assessment of the phosvitin-iron complex in mayonnaise

Lipid oxidation is the main reason for the limited shelf life of mayonnaise. One of the main catalysts of this process is iron, which is introduced in its ferric (Fe(III)) form via phosvitin, an egg yolk phosphoprotein rich in phosphoserines. The binding of Fe(III) to phosvitin and its ability to establish a redox couple with Fe(II) is believed to determine the oxidation rate of unsaturated lipids. In this work, a 31P NMR based method was developed to quantify loading of phosvitin with Fe(III) and its reductive release. Both features could be quantified in model phosvitin solutions by exploiting the paramagnetic broadening of 31P NMR signal of phosphoserine residues by Fe(III). This method was then successfully applied to quantify the phosvitin-Fe(III) loading in mayonnaise water phase by liquid NMR, whereas 31P NMR MAS could only provide a qualitative measure. The 31P NMR method showed a direct relation between loading of the Fe(III)-phosvitin complex and lipid oxidation.</p