Characterization of Oxidative Stability of Fish Oil- and Plant Oil-Enriched Skimmed Milk

The objective of this research was to determine the oxidative stability of fish oil blended with crude plant oils rich in naturally occurring antioxidants, camelina oil and oat oil, respectively, in bulk and after supplementation of 1 wt% of oil blends to skimmed milk emulsions. Ability of crude oat oil and camelina oil to protect fish oil in bulk and as fish oil-enriched skimmed milk emulsions was evaluated. Results of oxidative stability of bulk oils and blends assessed by the Schaal oven weight gain test and by the rancimat method showed significant increase in oxidative stability when oat oil was added to fish oil in only 5 and 10 %, whereas no protective effect of camelina oil was observed when evaluated by these methods. Moreover, fish oil blended with oat oil conferred the lowest PV and lower amounts of volatile compounds during the storage period of 14 days at 4 °C. Surprisingly, skimmed milk supplemented with fish-oat oil blend gave the highest scores for off-flavors in the sensory evaluation, demonstrating that several methods, including sensory analysis, should be combined to illustrate the complete picture of lipid oxidation in emulsions.     

Improving the Oxidative Stability of Krill Oil-in-Water Emulsions

A positively charged protein (fish gelatin) or a negatively charged protein species (heat-treated milk protein–carbohydrate mixture) was added to a primary krill oil (KO) emulsion stabilized by the phospholipids inherent in KO, with the aim of improving the oxidative stability of KO-in-water emulsions at pH 8.0 (10 % KO). The positively charged fish gelatin deposited on the primary interface of the oil droplets in the primary KO-in-water emulsion improved the oxidative stability of the KO-in-water emulsion as evidenced by the higher eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) remaining and lower propanal produced after accelerated oxidation (40 °C, 25 days). The addition of the negatively charged heat-treated milk protein–carbohydrate mixture containing Maillard reaction products (MRP) to the bulk phase of the emulsion also enhanced the oxidative stability of the KO-in-water emulsion. The addition of MRP to the aqueous phase of phospholipids stabilized emulsion droplets offered more protection to EPA and DHA of the KO emulsions compared to the formation of an additional layer at the interface of the KO emulsion droplet. This suggests that interventions based on addition of antioxidant species to the formulation were more effective for arresting oxidation than increasing the thickness of the droplet interface. The addition of proteins into KO containing emulsion formulations is a promising strategy for protecting omega-3 marine phospholipids against oxidation.     

Physico-chemical Properties of Marine Phospholipid Emulsions

Many studies have shown that marine phospholipids (PL) have better bioavailability, better resistance towards oxidation and contain higher polyunsaturated fatty acids such as eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) than triglycerides (TAG) present in fish oil. The objective of this study was to investigate the emulsifying properties of various commercial marine PL and the feasibility of using them to prepare stable emulsions prepared with or without addition of fish oil. In addition, this study also investigated the relationship between chemical composition of marine PL and the stability of their emulsions. Physical stability was investigated through particle size distribution (PSD), zeta potential, microscopy inspection and emulsion separation (ES); while the oxidative and hydrolytic stability of emulsions were investigated through peroxide value (PV) and free fatty acids value (FFA) after 32?days storage at room temperature and at 2?°C. In conclusion, marine PL showed good emulsifying properties and it was possible to prepare marine PL emulsions with and without addition of fish oil. Emulsion with both good oxidative stability and physical stability could be prepared by using marine PL of high purity, less TAG, more PL, cholesterol and higher antioxidant content.     

Stabilization of highly unsaturated fatty acids and delivery into foods

Highly unsaturated fatty acids derived from fish or algal oils, particularly EPA and DHA, are in high demand as healthy food ingredients in fortified foods. Due to their oxidative instability most food products incorporate stabilized microencapsulated EPA and DHA oils to avoid negative sensory impact associated with oxidation of these fatty acids. Complex coacervation has been particularly successful in stabilizing fish oil and providing an ingredient with a sensory shelf‐life consistent with that of the food product. Overcoming the technical challenges associated with the instability of these oils will help drive growth of the omega‐3 fortified healthy food ingredient market.     

Delivery of Omega-3 Fatty Acids into Cake Through Emulsification of Fish Oil-in-Milk and Encapsulation by Spray Drying with Added Polymers

Fortification of cakes with fish oil encapsulates was performed to enhance the consumption of health-beneficial polyunsaturated fatty acids like eicosapentaenoic acid and docosahexaenoic acid. Fish oil-in-milk emulsions prepared by ultrasonication at different amplitudes were encapsulated by spray drying using different wall materials. The oxidative stability of fish oil encapsulates was determined for 32 days at room and refrigerated temperatures. Oxidatively stable encapsulates and organoleptic quality of fortified cakes reveal that emulsification of fish oil-in-milk and encapsulation by spray drying are potential processes to produce fish oil encapsulates suitable for fortification of bakery products with omega-3 fatty acids.     

Effect of ingredients on oxidative stability of fish oil‐enriched drinking yoghurt

The oxidative stabilities of fish oil‐enriched milk and fish oil‐enriched drinking yoghurt were compared by following the development of lipid oxidation in plain milk, plain yoghurt and yoghurt to which ingredients present in drinking yoghurt were added one by one. All samples were enriched with 1 wt‐% fish oil. After 3 weeks of storage, development of peroxide values, volatile secondary oxidation products and fishy off‐flavors were much more pronounced in the milk compared to any of the yoghurt samples, irrespective of any added ingredients used to prepare flavored drinking yoghurt. Thus, pectin, citric acid or glucono‐delta‐lactone did not affect the oxidative stability of fish oil‐enriched yoghurt emulsions. Furthermore, the fruit preparation and added sugar did not lead to increased antioxidative activity. It is concluded that yoghurt as the dairy component in the fish oil‐enriched emulsion was responsible for the remarkably high oxidative stability and was able to protect the n‐3 PUFA against oxidative deterioration. It should be considered that this strong antioxidative effect of yoghurt might mask potential antioxidative effects of the other ingredients in the drinking yoghurt.     

Antioxidant properties of individual phospholipids in a salmon oil model system

The antioxidant properties of phospholipids (PL) in a refined salmon oil model system were measured by determining changes in the 2-thiobarbituric acid number and decreases in the ratio of docosahexaenoic acid (DHA)/palmitic acid (22:6/16:0) of a fish oil system incubated at 180°C for up to 3 h. The more phosphatidylcholine (PC) added to the oil system, the higher the oxidative stability obtained. The order of effectiveness of commercial phospholipids in inhibiting oxidation and the loss of polyunsaturated fatty acids was as follows: sphingomyelin (SPH)=lysophosphatidylcholine (LPC)=phosphatidylcholine (PC)=phosphatidylethanolamine (PE)>phosphatidylserine (PS)>phosphatidylinositol (PI)>phosphatidylglycerol (PG)>control salmon oil. Nitrogen containing PL, including PE, PC, LPC and SPH, were equally effective in exerting greater antioxidant properties than PS, PG and PI. The inverse relationship observed between the oxidation index (C22:6/C16:0) and color intensity for treatments following 2 h of heating suggests that Maillard-type reaction products may have contributed to the oxidative stability of PL-supplemented fish oils.     

Thermal Stability of Rapeseed Oil Fortified with Unsaturated Fatty Acid Sterol Esters

The thermal stability of rapeseed oil fortified with 3 % sterol linolenate, sterol linoleate, and sterol oleate was investigated using the Rancimat accelerated oxidation method. The results indicated that the sterol ester content in fortified oil displayed positive correlations (P < 0.05) with total phenols and tocopherols and significant negative correlations (P < 0.05) with acid value (AV), peroxide value (POV), conjugated diene value, \(\varDelta E\) value, viscosity, and polyphenols and γ-tocopherol levels. The sterol ester content in fortified oil was found to significantly decrease when the oil was heated at 110 °C. The rate of increase of the AV, POV, \(\varDelta E\) value, and viscosity, and the rate of decrease of polyunsaturated fatty acid, tocopherol, and polyphenol contents were accelerated with the increase of the degree of unsaturation of fatty acid sterol esters in rapeseed oil during heating. Therefore, the oxidative stability is further reduced by increasing the degree of unsaturation, as the instability of fortified oil is mainly due to the decomposition of unsaturated fatty acid sterol esters. The addition of lipid-soluble polyphenols is an effective method to improve the stability of rapeseed oil fortified with unsaturated fatty acid sterol esters.     

Monitoring fish oil volatiles to assess the quality of fish oil

The fish oil industry is continuously growing; however there is a lack of analytical methods to assess fish oil quality that correlate with the results obtained through sensory testing. Solid phase microextraction (SPME) provides a means to monitor the concentration of oxidative volatiles in fish oil. Because volatile oxidation products are responsible for the off‐flavours found in oxidized fish oil, this technique may be used as a substitute for sensory panels. Principal component analysis (PCA), combined with sensory panels, can be used to determine the oxidation products that are most correlated with degradation of the sensory properties of the oil. This creates the potential for development of methods that can determine when the sensory qualities of oil have deteriorated beyond an acceptable level.     

Microencapsulation of fish oil

Fish oil is susceptible to oxidative degradation generating undesired lipid peroxides, secondary and tertiary oxidation products. These products pose health risks, reduce shelf‐life stability and cause fishy odor and taste leading to decreased sensory quality. Microencapsulation of fish oil using spray drying, coacervation, ultrasonication and membrane emulsification techniques is employed to overcome these problems.     

Possibilities of Fisherman’s Friend Type Lozenges Fortification with Omega-3 LC PUFA by Addition of Microencapsulated Fish Oil

The aim of this study was to evaluate the influence of fish oil powder addition on sensory quality and oxidative stability of Fisherman’s Friend type lozenges. Microencapsulated fish oil (MFO) was used for lozenge formulation. Sensory quality of the moderate and strong mint flavored lozenges was not significantly affected by fish oil powder addition up to 60 and 80 g kg⁻¹, respectively. Higher MFO addition resulted in significant reduction in the sensory quality and increases in fishy off-flavor intensity. During 4 months of storage in air permeable packages, a gradual decrease in sensory quality and an increase in fishy off-flavor were detected in lozenges containing MFO, which were more significant in moderately flavored than in strongly flavored ones. The peroxide value increased significantly during air storage. However, the peroxide value of vacuum stored samples increased slightly whereas sensory scores remained stable. A recommendation to pack and store the MFO lozenges under limited oxygen is suggested due to the low stability of the MFO product. A dose of 5 lozenges fortified with MFO might provide 40 mg of omega-3 LC PUFA elevating its average level in the diet.     

Homogenization Pressure and Temperature Affect Protein Partitioning and Oxidative Stability of Emulsions

The oxidative stability of 10 % fish oil-in-water emulsions was investigated for emulsions prepared under different homogenization conditions. Homogenization was conducted at two different pressures (5 or 22.5 MPa), and at two different temperatures (22 and 72 °C). Milk proteins were used as the emulsifier. Hence, emulsions were prepared with either a combination of α-lactalbumin and β-lactoglobulin or with a combination of sodium caseinate and β-lactoglobulin. Results showed that an increase in pressure increased the oxidative stability of emulsions with caseinate and β-lactoglobulin, whereas it decreased the oxidative stability of emulsions with α-lactalbumin and β-lactoglobulin. For both types of emulsions the partitioning of proteins between the interface and the aqueous phase appeared to be important for the oxidative stability. The effect of pre-heating the aqueous phase with the milk proteins prior to homogenization did not have any clear effect on lipid oxidation in either of the two types of emulsions.     

Sensory Assessment of Microencapsulated Fish Oil Powder

The aim of the study was to investigate the influence of microencapsulation by spray drying on fish oil sensory quality. Evaluated fish oil powders were coated with modified cellulose, skim milk powder and a mixture of fish gelatin and cornstarch. Samples were stored in the presence of air and under vacuum and then sensory evaluated. It was shown that fish oil powders were very susceptible to oxidation resulting in off-flavor formation. Odor profiles of samples stored in the presence of air were unstable and showed increases in undesirable odor attributes, which were significantly correlated with peroxide value, especially in the case of samples formed by spray drying. Elimination of air from the packaging improved stability of all samples during storage in both odor profile and peroxide value. The main conclusion of this study is that microencapsulation, especially by spray drying, provokes strong changes in fish oil sensory quality. Microencapsulated fish oil powder is not stable and rapidly oxidizes in the presence of air. However, its stability may be improved when stored under vacuum.     

Oxidative flavour deterioration of fish oil enriched milk

The oxidative deterioration of milk emulsions supplemented with 1.5 wt‐% fish oil was investigated by sensory evaluation and by determining the peroxide value and volatile oxidation products after cold storage. Two types of milk emulsions were produced, one with a highly unsaturated tuna oil (38 wt‐% of n‐3 fatty acids) and one with cod liver oil (26 wt‐% of n‐3 fatty acids). The effect of added calcium disodium ethylenediaminetetraacetate (EDTA) on oxidation was also investigated. Emulsions based on cod liver oil with a slightly elevated peroxide value (1.5 meq/kg) oxidised significantly faster than the tuna oil emulsions, having a lower initial peroxide value (0.1 meq/kg). In the tuna oil emulsions the fishy off‐flavour could not be detected throughout the storage period. Addition of 5—50 ppm EDTA significantly reduced the development of volatile oxidation products in the cod liver oil emulsions, indicating that metal chelation with EDTA could inhibit the decomposition of lipid hydroperoxides in these emulsions. This study showed that an oxidatively stable milk emulsion containing highly polyunsaturated tuna fish oil could be prepared without significant fishy off‐flavour development upon storage, provided that the initial peroxide value was sufficiently low.     

Influence of interesterification on the oxidative stability of marine oil triacylglycerols

To understand the relationship between triacylglycerol structure of marine oils and their oxidative stability, peroxide values and absorbed oxygen levels of whale, sardine, cod liver and skipjack oils, interesterified by lipase and NaOCH₃, were compared with those of native oils during storage at 40°C. Triacylglycerol structures of marine oils were characterized by high-performance liquid chromatography and differential scanning calorimetry analyses. Enzymatically interesterified fish oils were more stable than native oils because the level of highly unsaturated triacylglycerols was decreased. However, the oxidative stability of interesterified whale oil was more susceptible to oxidation than the native oil.     

Comparison of the oxidative stability of chemically and enzymatically interesterified fats

A mixture of low erucic acid rapeseed (LEAR) oil and tallow (6:4, w/w) was used for enzymatic interesterification using Lipozyme IM – a sn-1,3-specific lipase of Rhizomucor miehei, or for chemical interesterification using sodium methoxide. The starting mixture and the products of interesterification were separated by column chromatography into pure triacylglycerols (TAGs) and a non-TAG fraction containing free fatty acids, mono- and diacylglycerols. Subsequently, the starting mixture, the products of chemical and enzymatic interesterification and the pure triacylglycerols were oxidized and their oxidative stability was examined by means of DSC. The investigation showed that the pure triacylglycerols isolated from the product of enzymatic interesterification have a comparable oxidative stability to that of the TAGs prepared from the starting mixture. In contrast, the TAGs obtained from the products of chemical interesterification had inferior oxidative stability. The presence of non-TAG fraction in the interesterification products lowers their resistance to oxidation. The starting mixture had the highest oxidative stability.     

Characterization and Oxidative Stability of Human Milk Fat Substitutes Enzymatically Produced from Palm Stearin

Production of human milk fat substitutes (HMFSs) from three types of palm stearin with palmitic acid (PA) of 91.3, 70.3 and 62.6 %, respectively, was scaled up to a kilogram scale. The physiochemical properties of these products including fatty acid profiles, triacylglycerol compositions, tocopherol contents, oxidative stability and melting and crystallization profiles were compared with those of HMFSs from lard, butterfat and tripalmitin and fats from infant formulas. Based on their chemical compositions, HMFSs from palm stearin with PA contents of 70.3 and 62.6 % produced by enzymatic acidolysis were found to have the highest degree of similarity to human milk fat, which indicated that these HMFSs were the most suitable for use in infant formulas. However, HMFSs from palm stearin with PA content of 91.3 % had the highest tocopherol contents. By investigation of the primary and secondary oxidation products during accelerated oxidation, the oxidative stability of HMFSs was found to be positively correlated to the contents of tocopherols, and the volatile oxidation compounds with the highest relative contents in HMFSs were aldehydes analyzed by solid-phase microextraction-GC–MS. All HMFSs had final melting points lower than body temperature.     

Characterization and Oxidative Stability of Structured Lipids: Infant Milk Fat Analog

Structured lipids (SLs) for infant milk formulation were produced by enzymatic interesterification of tripalmitin with vegetable oil blends and fish oil. The SLs were characterized by fatty acid content and structure, melting profiles, oxidative stability index, free fatty acid (FFA) concentration, and tocopherol content. Oxidative stability was studied using accelerated methods by quantifying FFA, peroxides (peroxide value) and aldehydes (p-anisidine value) production. Total oxidation (TOTOX value) was calculated as 2 × (peroxide value) + (p-anisidine value). The structured lipids after purification by distillation and addition of antioxidants had melting profiles, oxidative stability index, and initial FFA concentration that were similar to that of the starting oil blends, while the fatty acid composition and structure of the SLs were similar to that of human milk fat. Oxidative stability of the SLs was improved with tocopherol addition as antioxidants and was comparable to that of the vegetable oils and oil blends.     

Zusammenfassung von Versuchen über die Wirkung bestimmter Futterkomponenten auf die Stabilität der Milch und des Schweinespecks

Summary of Investigations Concerning the Effect of Certain Feed Components on Stability of Milk and Bacon Even if lipidoxidations in metabolism are necessary, on spontaneously running autoxidations in the body must be kept a close watch. In animal products oxidative damages can occur as a consequence and simultaneously sensoric changes. Finally men will have advantages and disadvantages of the stability or instability of food. The effect of feed on milk and bacon quality has been investigated in a series of feeding trials. Oxidation of milk leads to a taste of oxidation or metallic savour. Oxidation of bacon causes because of getting rancid a shorter stability, which can be tested by an acceleration of the oxidative progress in laboratory. An extrapolation of the results in milk and bacon should be carefully transferred to the oxidation of the cell membrane. Investigations of cows and pigs have demonstrated that the unsaturated fat of the feed diminishes the stability of the animal products. Antioxidants, having been taken up, and vitamin E improve them facing the oxidations in milk and bacon. Hardened fish oil, added to the feed, had a favourable effect on milk and bacon stability as on the savour. Mineral substances, fed to animals, had no significantly oxidative effect. Additions of copper showed that the fat in the porc liver was of greater stability against oxidation. An addition of molybdenum did not change the activity of xanthineoxidase in milk either. This enzyme had an activity which correlated with the antioxidative properties of milk.     

Analysis of EPA and DHA and distinction between fish oils and concentrates

Fish oil is the major dietary source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Adequate dietary intake of these n‐3 PUFA is beneficial to reduce the risks of cardiovascular mortality, prostate cancer, and neurological disorders in children and adults. There is a surge in demand for fish oil in the functional food market. Microencapsulation of fish oil is the trend to improve its stability and sensory quality. The EPA and DHA content of the fish oil products may vary markedly from the label due to their susceptibility to oxidation. Quick and reliable methods other than the AOAC BF₃ method have been exploited to quantify EPA and DHA in the encapsulated fish oil and the microencapsulated powdered products such as infant formula. This article describes a method to differentiate the ethyl‐ester form from the TAG form of EPA and DHA in encapsulated fish oil which may be a mixture of natural triacylglycerol enriched with ethyl esterified EPA and DHA. A method is recommended due to the difference in apparent potency of these two esterified forms, which may be a concern in infant formula and elsewhere.