Antioxidant Activity of Whey in a Salmon Oil Emulsion

ABSTRACT: The antioxidant capabilities of whey in a Tween20 TM -stabilized salmon emulsion were investigated.Whey fractions inhibited formation of thiobarbituric acid reactive substances (TBARS) and lipid peroxides in a 10% salmon oil emulsion in the order of whey > high-molecular-weight (HMW) fraction > low-molecular-weightfraction. Heating the HMW fraction exposed sulfhydryls, with optimum exposure at 80 °C. Heating the HMW frac-tion above 80 °C increased antioxidant activity. The HMW fraction of whey (80 °C) alone, a-tocopherol (40 ppm)alone, and their combination inhibited TBARS 59, 19 and 86%, respectively, at 21 d of storage. Sulfhydryls oxidizedbefore a-tocopherol, suggesting that sulfhydryls are the primary antioxidant. Results indicate that whey proteinscould be useful antioxidants in food emulsions.Keywords: lipid oxidation, fish oil, a-tocopherol, whey, sulfhydryls Introduction T HE HEALTH BENEFITS OF DIETARY OMEGA -3 ( W -3) FATTY ACIDS include reduced susceptibility to malignant tumors, protec-tion against heart disease, and improved brain and eye functionin infants (Simopoulos 1991; Innis 1991). It is of great interest tofood manufacturers to use v-3 fatty acids as physiologically func-tional ingredients to improve the nutritional profile of food prod-ucts. However, oxidation of v-3 fatty acids is very rapid, thuscausing rapid flavor deterioration, loss of nutrients, and forma-tion of potentially toxic compounds (Kubow 1992; Frankel 1998). These problems have been major barriers to utilizing oils thatcontain high concentrations of v-3 fatty acids in foods.Oxidative stability of v-3 fatty acids can be increased usingfree radical scavengers. Tertiary-butylhydroquinone (TBHQ,0.02%) has been successfully employed to slow oxidation of men-haden oil for up to 40 days, compared to approximately 3 d forthe control (Farkas and others 1997). ty of skim milk, an observation that was partially attributed to ex-Alpha-Tocopherol and bu-tylated hydroxytoluene (BHT) alone or in combination increasedthe oxidative stability of octadecatetraenoic acid (ODTA), eicosa-pentaenoic acid (EPA), and docosahexaenoic acid (DHA), inhibit-ing malonaldehye (MA) formation upon addition of Fenton’s re-agent (Ogata and others 1996). Alpha-Tocopherol inhibited MAformation from ODTA and DHA 67 and 28 % respectively, buthad no activity toward EPA. BHT inhibited MA formation fromODTA, DHA, and EPA 80, 58 and 93 %, respectively (Ogata andothers 1996). A combination of ascorbic acid (200 ppm) solubi-lized in lecithin reverse micelles and d-tocopherol (4000 ppm)was also tested for its ability to decrease autoxidation of sardineoil, with the carbonyl value of the control reaching 45 at day 36and the carbonyl value of the antioxidant-treated sample reach-ing 1.0 during the same period. (Han and others 1997). If v-3 fatty acids are to be successfully incorporated into pro-cessed foods, it will most likely be in the form of a lipid disper-sion. While lipid-soluble free radical scavengers may be effectivein minimizing oxidation for a limited amount of time in bulk oils,their effectiveness seems to be dependent on fatty acid type andthey are not likely to be effective for the shelf-life required formost processed foods. In addition, the effectiveness of lipid-sol-uble free radical scavengers in oil-in-water emulsions can be dif-ferent if they partition into both the continuous phase and emul-sion droplet (Huang and others 1997). Therefore, if v-3 fatty acidoils are to be successfully utilized in food emulsions, additionalantioxidant hurdles must be utilized, such as continuous phasemetal chelators and free radical scavengers.Proteins are well known mediators of lipid oxidation. A num-ber of antioxidative proteins and protein products exist, includ-ing soy and yeast protein hydrolysates (Bishov and Henick 1972and 1975), gelatin (Kawashima 1979), and blood plasma proteins(Wayner and others 1987; Halliwell 1988). Mechanisms of the an-tioxidative effects of proteins include chelation of prooxidanttransition metals by proteins such as lactoferrin (Gutteridge andothers 1981) and serum albumin (Meucci and others 1991) andfree radical scavenging by amino acid residues such as cysteineand tyrosine (Wayner and others 1987; Ostdal and others 1996). Taylor and Richardson (1980) explored the antioxidant activi-ty of heated skim milk in a methyl linoleate emulsion catalyzedby hemoglobin. They found that heat treatment (70 to 130 °C ina silicone oil bath, up to 30 min) increased the antioxidant activi-posure of proteinaceous sulfhydryl groups. Heat treatment re-sulted in an increase in reactive sulfhydryls (48 mM sulfhydrylswith no heat to 71 mM sulfhydryls after a 130 °C, 30 min heattreatment), but a decline in total sulfhydryls (146 mM sulfhydr-yls with no heat to 39 mM sulfhydryls after a 130 °C, 30 min heattreatment). Milk fractions were also evaluated, with both wheyand casein being antioxidative, although casein showed muchgreater activity. The activity of casein was hypothesized to bemostly due to a physical binding of prooxidants, while the activi-ty of whey was thought to be chemical in nature. While this studyyielded interesting results concerning the antioxidant capabili-ties of skim milk and whey, it is difficult to predict how milk couldimpact oxidation in food systems since the research of Taylor andRichardson did not use prooxidants typical of a food emulsion(for example, hemoglobin), nor did they use lipids (methyl li-noleate dispersion with Tween 80