The antioxidant properties of milk casein subunits (alpha-casein, beta-casein and kappa-casein) were evaluated in liposomal models. All the subunits of casein are able to inhibit Fe-induced peroxidation of arachidonic acid inserted into multilamellar liposomes of dipalmitoylphosphatidylcholine (0.2 mM and 0.8 mM, respectively). The peroxidation was monitored as thiobarbituric acid reactive substances, and the strongest inhibitory effect occurred when 500 micrograms of alpha-casein were added to 0.5 ml of liposomal suspension. At this concentration, peroxidation was completely inhibited in our experimental conditions (incubation for 2 h at room temperature, with a mixture of ferrous sulfate and ascorbate, 50 and 500 microM final concentration, respectively). The mechanisms of antioxidant action are complex, but the strongest effect is achieved by modifying the Fe2+/Fe3+ equilibrium; in fact, caseins seem to favour the autoxidation of iron, and thus inhibit lipid peroxidation.
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"Dairy products and their fractions have been found to be antioxidative, e.g. milk, skim milk, whey, casein and lactoferrin (Steijins and Van 2000; Tong et al. 2000; Cervato et al. 1999; Colbert and Decker 1991; Taylor and Richardson 1980). Whey protein, a by-product recognized as valuable food ingredient with important nutritional and functional properties is gaining acceptance as functional food ingredient. "
[Show abstract][Hide abstract] ABSTRACT: The aim of the present study was to evaluate the antioxidant activity of flavoured milk enriched with antioxidative whey protein hydrolysates (WPHs) by radical scavenging method. Whey protein concentrate (WPC) was hydrolyzed by using three commercial proteases; flavouzyme, alcalase and corolase PP and these WPHs were analyzed for degree of hydrolysis and antioxidant activity. The antioxidant activities of these WPHs were evaluated using ABTS method. Trolox equivalent antioxidant activity of all the hydrolysates i.e. flavourzyme (0.81 ± 0.04), alcalase (1.16 ± 0.05) and corolase (1.42 ± 0.12) was higher than the WPC (0.19 ± 0.01). Among these, whey protein hydrolysates prepared using corolase showed maximum antioxidant activity. Total 15 β-lactoglobulin, 1 α-lactoalbumin, and 6 β-casein derived peptide fragments were identified in the WPHs by LC-MS/MS. Due to their size and characteristic amino acid composition, all the identified peptides may contribute for the antioxidant activity. The strawberry and chocolate flavoured milk was supplemented with WPC and WPHs and 2 % addition has shown increase in antioxidant activity upto 42 %. The result suggests that WPH could be used as natural biofunctional ingredients in enhancing antioxidant properties of food products.
"Nearly all fluid milks in the United States and Canada are fortified with vitamin D; fluid milk is a predominant food source of vitamin D. Another important feature of β-LG is its antioxidant activity. Several studies have described the antioxidant activity of proteins from animal and plant sources, including milk proteins (Cervato et al., 1999; Tong et al., 2000). Enhancement of the body's antioxidant defenses through dietary supplementation would seem to be a reasonable and practical approach to reduce the level of oxidative stress, and increasing evidence exists to support the effectiveness of such a strategy in vitro (Finkel and Holbrook, 2000). "
[Show abstract][Hide abstract] ABSTRACT: Heating is necessary for processing milk in the dairy industry, which evidently produces a conformational change in beta-lactoglobulin (beta-LG). beta-Lactoglobulin, a major protein that accounts for approximately 10 to 15% of total milk proteins, is a globular protein consisting of 162 AA with a relative molecular mass of 18.4 kDa. The purpose of the present study was to determine the antioxidant role of beta-LG in milk and the possible mechanism involved. We showed that beta-LG is a mild antioxidant whose potency is less than that of vitamin E and probucol (the latter being an antioxidant used for clinical therapy). The conversion of the beta-LG monomer to dimer was responsible, in part, for the mode of action in protecting low-density lipoproteins against copper-induced oxidation. Cross-linking the free thiol groups of beta-LG by heating (100 degrees C for 2 min), or chemically modifying the beta-LG by carboxymethylation to block the thiol groups resulted in a substantial loss of antioxidant activity. The data suggest that Cys-121 plays an essential role in the antioxidant nature of beta-LG. By using an anti-LG antibody affinity column to deplete the beta-LG from milk, we observed from the lost antioxidant activity that beta-LG contributes approximately 50% of the total activity. Because beta-LG is extremely sensitive to thermal denaturation, to maintain its antioxidant nature, dairy products consumed daily should not be overheated in order to maintain its antioxidant nature.
"Several studies have described the antioxidant activity of proteins from several animal and plant sources, such as milk protein (Cervato et al. 1999; Chen et al. 2003), barley hordein (Chiue et al. 1997a) and maize zein (Chiue et al. 1997b). Furthermore, some peptides derived from hydrolysed food proteins have been shown to have noteworthy antioxidative activities against the peroxidation of lipids or fatty acids (Saiga et al. 2003; Dávalos et al. 2004). "
[Show abstract][Hide abstract] ABSTRACT: To investigate the production of antioxidant activity during fermentation with commonly used dairy starter cultures. Moreover, to study the development of antioxidant activity during fermentation, and the connection to proteolysis and bacterial growth.
Antioxidant activity was measured by analysing the radical scavenging activity using a spectrophotometric decolorization assay and lipid peroxidation inhibition was assayed using liposomal model system with a fluorescence method. Milk was fermented with 25 lactic acid bacterial (LAB) strains, and from these six strains, exhibiting the highest radical scavenging activity was selected for further investigation. Leuconostoc mesenteroides ssp. cremoris strains, Lactobacillus jensenii (ATCC 25258) and Lactobacillus acidophilus (ATCC 4356) showed the highest activity with both the methods used. However, the radical scavenging activity was stronger than lipid peroxidation inhibition activity. The development of radical scavenging activity was connected to proteolysis with four strains. Molecular distribution profiles showed that fermentates with high scavenging activity also possessed a higher proportion of peptides in the molecular mass range of 4-20 kDa, while others had mostly large polypeptides and compounds below 4 kDa. In addition, the amount of hydrophobic amino acids was higher in these fermentates.
The development of antioxidant activity was strain-specific characteristic. The development of radical scavengers was more connected to the simultaneous development of proteolysis whereas, lipid peroxidation inhibitory activity was related to bacterial growth. However, high radical scavenging activity was not directly connected to the high degree of proteolysis.
To the best of our knowledge, this seems to be the first report, which screens possible antioxidant activity among most common dairy LAB strains. Use of such strains improve nutritional value of fermented dairy products.