Lipid oxidation in oil-in-water emulsions: Iron complexation by buffer ions and transfer on the interface as a possible mechanism.

Lipid oxidation is the main hurdle for omega-3 fatty acid enrichment in food and beverages. Fat oxidation reduces the quality and safety of supplemented products. A tuna oil-in-water emulsion (20%v/v) was exposed to iron-induced oxidation. Emulsions with changing emulsifiers and buffers were analyzed under different storage conditions (argon purging, pH variation) using Conjugated Dienes and Thiobarbituric acid reactive substances assays. The results showed that free iron ions cannot interact with oxygen. However, buffers (Citrate and phosphate) chelate iron ions (Fe (II)). Depending on the pH value and the type of buffer-Fe (II) complex, its prooxidant activity and spatial distribution are influenced. The complex charge defines the interactions with the oil-water interface, i.e., positively charged interfaces repel positively charged complexes which keeps the prooxidant away. The mechanistic understanding of this work will help formulators and product developers to choose the right buffer and emulsifier combination for oxidation sensitive emulsions.

Detection of Lipid Oxidation in Infant Formulas: Application of Infrared Spectroscopy to Complex Food Systems.

 Fish- or algal oils have become a common component of infant formula products for their high docosahexaenoic acid (DHA) content. DHA is widely recognized to contribute to the normal development of the infant, and the European Commission recently regulated the DHA content in infant formulas. For many manufacturers of first-age early life nutrition products, a higher inclusion level of DHA poses various challenges. Long-chain polyunsaturated fatty acids (LC-PUFAs) such as DHA are very prone to oxidation, which can alter the organoleptic property and nutritional value of the final product. Traditional methods for the assessment of oxidation in complex systems require solvent extraction of the included fat, which can involve harmful reagents and may alter the oxidation status of the system. A rapid, efficient, non-toxic real-time method to monitor lipid oxidation in complex systems such as infant formula emulsions would be desirable. In this study, infrared spectroscopy was therefore chosen to monitor iron-induced oxidation in liquid infant formula, with conjugated dienes and headspace volatiles measured with GC-MS as reference methods. Infrared spectra of infant formula were recorded directly in mid- and near-infrared regions using attenuated total reflectance Fourier-transform (ATR-FTIR) and near-infrared (NIRS) spectrophotometers. Overall, good correlation coefficients (R2 > 0.9) were acquired between volatiles content and infrared spectroscopy. Despite the complex composition of infant formula containing proteins and sugars, infrared spectroscopy was still able to detect spectral changes unique to lipid oxidation. By comparison, near-infrared spectroscopy (NIRS) presented better results than ATR-FTIR: prediction error ATR-FTIR 18% > prediction error NIRS 9%. Consequently, NIRS demonstrates great potential to be adopted as an in-line or on-line, non-destructive, and sustainable method for dairy and especially infant formula manufacturers.

Fast, direct and in situ monitoring of lipid oxidation in an oil-in-water emulsion by near infrared spectroscopy.

Lipid oxidation has implications on food, cosmetics and other fat containing products. Fatty acid autoxidation alters both the quality and safety of these products. Efficient and fast methods are needed to track lipid oxidation in complex systems. In this study, an oil-in-water emulsion (20% v/v of fish oil stabilized with high oleic sunflower lecithin) was subjected to iron-initiated oxidation. Conjugated dienes (CDs) were measured after fat extraction using a standardized method. Near infrared spectroscopy (NIRS) has been used to record chemical changes occurring during oxidation directly in the emulsion. Variations were noticed in different spectral regions. Partial least squares regression (PLSR) revealed correlations between conjugated diene values and NIRS spectra. High coefficients of determination (R2 = 0.967 and 0.996) were found for calibration and prediction respectively. The CD value was predicted from NIRS spectra with an error of 7.26 mmol eq. LH kg-1 oil (7.8% error). Limits of detection (LOD) and quantification (LOQ) of 4.65 and 15.5 mmol eq. LH kg-1 oil were estimated. NIRS is a rapid and simple method for measuring lipid oxidation (CD value) in an emulsion without prior fat extraction. NIRS can replace the reference methods that use hazardous solvents and consume time. Therefore, NIRS enables in-line monitoring for process and quality control.

Impact of Oak Wood Barrel Tannin Potential and Toasting on White Wine Antioxidant Stability.

Wines aged in oak wood barrels with various uniform tannin contents (which were classified according to their total ellagitannins contents as predicted by Near Infrared Spectroscopy on the untoasted wood) and different toasting levels (high precision toasting by radiation) were distinguished according to their overall abilities to resist against oxidation. Wine trials were carried out on two different vintages (2015, 2016) and three grape varieties (Sauvignon blanc, Sémillon, Chardonnay). Regardless of the vintage and the wine matrix, a relationship was established between wine oxidative stability (based on EPR spin trapping methodology) and oak barrel tannin potential. The extraction kinetic of ellagitannins by wines appeared linear during barrel aging and achieved its maximum at six or eight months, in a grape variety dependent manner. Oak wood barrel tannin potentials and toastings had no effect on wine glutathione and polyphenols contents. However, wines aged in new barrels with both low and medium tannin potentials, preserved at the end of aging and important number of S-N containing compounds, which was in addition to the known ellagitanins, revealed wines better antioxidant stability.

Fast and direct analysis of oxidation levels of oil-in-water emulsions using ATR-FTIR.

Oxidation of omega-3 fatty acids is a major limitation on its enrichment in food and beverages. An efficient and simple method to monitor lipid oxidation in complex systems is essential to limit lipid oxidation during formulation and processing. Fish oil-in-water emulsions (20% v/v) were exposed to iron or free radical initiated oxidation. Conjugated dienes (CDs) were rapidly measured using a previously developed fat extraction method. Fourier transform infrared (FTIR) spectroscopy has been used to directly record chemical changes occurring during oxidation. Variations were noticed in different spectral regions despite the presence of broad water bands near 3400 and 1640 cm-1. Partial least squares regression (PLSR) revealed correlations between CD values and full FTIR spectra (4000-600 cm-1), and different spectral regions (e.g., 1800-1500 cm-1, 1500-900 cm-1). These correlations confirm that FTIR spectroscopy is a rapid and simple method for measuring lipid oxidation in complex foods without prior fat extraction.