Effect of Flaxseed Mucilage and Gum Arabic on Probiotic Survival and Quality of Kefir during Cold Storage.

This study aimed to assess the survival of probiotic cultures in kefir. Kefir is a fermented dairy product, and in this study we incorporated nutritionally rich flaxseed mucilage and gum arabic as a prebiotic, then monitored for improvement in the the viability of Lactobacillus acidophilus and Bifidobacterium lactis. In addition, some physicochemical variables of kefir were investigated. The addition of flaxseed mucilage and gum arabic significantly (p ˂ 0.05) increased the growth of both Lactobacillus acidophilus and Bifidobacterium lactis compared to the control. Samples enriched with flaxseed mucilage and gum arabic had significantly (p ˂ 0.05) reduced pH and increased viscosity. Flaxseed mucilage and gum arabic significantly (p ˂ 0.05) changed the color parameters L*, a*, and b*. However, as the concentration of flaxseed mucilage increased, the L* value decreased. Moreover, adding flaxseed mucilage and gum arabic into kefir increased (p ˂ 0.05) the protein content. These results showed that flaxseed mucilage and gum arabic could be used to increase the survival of probiotic cultures in kefir without changing its physicochemical properties.

Effect of ultrasound and temperature on tomato peroxidase.

Tomato peroxidase (POD) was inactivated by heat and ultrasound. Thermal inactivation of tomato POD was performed at temperatures of 63, 64, 65, 66 and 67°C. Thermal inactivation of POD in tomato showed apparent first-order kinetics. E(a) was calculated from the slopes of Arrhenius plot and found as 14.9×10(4) J/mol. The effect of ultrasound on tomato peroxidase inactivation was investigated at 15%, 25%, 40%, 50% and 75% ultrasonic powers for 20-150 s. It was observed that as the ultrasonic power increased, inactivation rate increased. 100% POD inactivation was observed at 50% power for 150 s and at 75% power for 90 s of ultrasonication. Regeneration of POD activity was investigated for the samples exposed to ultrasound at different ultrasonic powers. It was observed that at 15% and 25% ultrasonic powers, residual enzyme activity increased linearly, whereas at powers of 40%, 50% and 75% residual enzyme activity increased nonlinearly. There was no regeneration in the samples which 100% enzyme inactivation obtained by ultrasound. A significant decrease in vitamin C content of tomato extract was observed as a function of temperature and treatment time, whereas ultrasonic treatment had no significant effect on vitamin C content of tomato extract.