Whey protein isolate (WPI), soy protein isolate (SPI), and sodium caseinate (CAS) can inhibit lipid oxidation when they produce a positive charge at the interface of emulsion droplets. However, when proteins are used to stabilize oil-in-water emulsions, only a fraction of them actually absorb to the emulsion droplets, with the rest remaining in the continuous phase. The impact of these continuous phase proteins on the oxidative stability of protein-stabilized emulsions is not well understood. WPI-stabilized menhaden oil-in-water emulsions were prepared by high-pressure homogenization. In some experiments WPI was removed from the continuous phase of the emulsions through repeated centrifugation and resuspension of the emulsion droplets (washed emulsion). Unwashed emulsions were more oxidatively stable than washed emulsions at pH 7.0, suggesting that continuous phase proteins were antioxidative. The oxidative stability of emulsions containing different kinds of protein in the continuous phase decreased in the order SPI > CAS > WPI, as determined by both hydroperoxide and headspace propanal formation. Iron-binding studies showed that the chelating ability of the proteins decreased in the order CAS > SPI > WPI. The free sulfhydryls of both WPI and SPI were involved in their antioxidant activity. This research shows that continuous phase proteins could be an effective means of protecting omega-3 fatty acids from oxidative deterioration.

The antioxidant activity of carnosine, a β‐alanine‐histidine dipeptide found in skeletal muscle, was investigated. Carnosine (25 mM) inhibited the catalysis of lipid oxidation by iron, hemoglobin, lipoxidase and singlet oxygen from 35–96% suggesting that the antioxidant mechanism of carnosine is not solely due to metal chelation. Heating the carnosine at 100°C for 15 min had no effect on its ability to inhibit these lipid oxidation catalysts, and the activity of carnosine was not affected over the pH range of 5.1–7.1. Studies using tocopherol‐containing liposomes suggest that carnosine and tocopherol do not act synergistically to inhibit lipid oxidation. These data indicate that carnosine has excellent potential for use as a natural antioxidant in processed foods.

No abstract

A yogurt mix (2 g fat and 17g solids/100 g) was supplemented with an algae oil emulsion to provide 500 mg omega-3 fatty acids per 272 g serving of yogurt white mass. The emulsion was added to the yogurt mix either before or after the homogenization step and prior to pasteurization. It was then flavoured with a strawberry fruit base and fermented and stored for up to three weeks. The oxidative deterioration of the products was determined by hydroperoxide measurements and by trained and consumer sensory evaluations. The hydroperoxide content of the supplemented yogurts increased over the storage treatment and was unaffected by the stage of addition. The trained panel could distinguish a stronger fishy flavour in both of the supplemented yogurts after 22 days storage, but the consumer panel rated both control and supplemented samples similarly, as 'moderately liked'.

Staphylokinase (SAK) as the third generation thrombolytic molecule is a promising agent for the treatment of thrombosis. SAK variant of SAKфC was expressed in Pichia pastoris strains KM71H and GS115. The codon adaptation index of SAK was improved from 0.75 to 0.89. The expression of recombinant SAK (rSAK) reached to its maximum (310 mg/L of the culture medium) after 48-hr stimulation with 3% methanol and remained steady until day 5. The maximum activity of the enzyme was at pH 8.6 and 37°C. It was highly active at temperatures 20-37°C and pH ranges of 6.8-9 (relative residual activity more than 80%). It was determined that rSAK was 73.8% of the total proteins secreted by P. pastoris KM71H into the culture media. The specific activities of rSAK were measured as 9,002 and 21,042 U/mg for the nonpurified and purified proteins, respectively. The quantity of the purified protein (>99% purity) was 720 µg/mL with a purification factor of 2.34. Western blot analysis showed two bands of nearly 22 and 18.6 kDa. It was concluded that P. pastoris is a proper host for expression of biologically active and endotoxin-free rSAK due to its high expression and low protein impurity in culture supernatant.