Study On Lactoperoxidase System Components In Goat Milk

Goat milk is a sort of natural food, which is full of nutriments, easy tobe digested, and higher in nutrition. There are many nutriments in goat milk, such asprotein, amino acid, vitamin, mineral and so on, which makes it to be the goodcondition for the growth and reproduction of microorganisms. Under proper conditions,microorganisms will proliferate quickly and result in deterioration of goat milk andcertain economical loss. Therefore, it is so important to keep the goat milk fresh.Lactoperoxidase system is one of the natural antibacterial activity system in goatmilk. The three components of lactoperoxidase system are lactoperoxidase(LPO),thiocyanate(SCN^-) and hydrogen peroxide(H₂O₂). Previous studies showed thatconcentrations of 1μg/mL (LPO), 15μg/mL (SCN^-) and 8.5μg/mL (H₂O₂) would beadequate for activation of the natural lactoperoxidase system. However, thelactoperoxidase content in goat milk is far more than which is required, there is no needto add more. In fact, there are only 1-3μg/mL (SCN^-) and 0.03-0.5μg/mL (H₂O₂) in rawgoat milk, which evolve as the main limiting factors for activation of the naturallactoperoxidase system. So addition of SCN^- and H₂O₂ is needed.The thesis makes a comparatively systematic research on the components oflactoperoxidase system, which is the basics for activation of lactoperoxidase system ingoat milk, including the properties of lactoperoxidase, effects of physiological factorson lactoperoxidase system components and effect of adding antistaling agents onIactoperoxidase system components. The resuIts of the studies are listed as follows:1. Lactoperoxidase possesses good hot stability, and its optimal temperature is55℃. In the temperature range of 50-60℃, the lactoperoxidase activity is high.2. The lactoperoxidase activity was relatively stable in the pH range of 3.0-8.0,and the lactoperoxidase activity residual is higher than 97%. The optimal pH is 5.5,and in the pH range of 5.0-6.0, the lactoperoxidase activity is also high.3. Lactoperoxidase is rather sensitive to light. The study in the thesis indicates thatlactoperoxidase activity of the group exposed to light declines by 31.73% in thecondition of 25℃through 3h, while the group kept away from the light shows thatlactoperoxidase activity only declines by 7.74%.4. With a rise in fetal times, lactoperoxidase activity and OSCN^- concentration rebase evidently, while the concentration of OSCN^- and H₂O₂ present rising current.5. The lactation of goats has a great effect on the components of LPS, The changeof which present to be the curves. Lactoperoxidase activity and OSCN^- concentrationhoist evidently, reaching to 3.96U/mL and 3.16μg/mL at the seventh lactation, whilethe concentration of OSCN^- and H₂O₂ present descending curve, keeping the highestlevel of 5.58μ/mL and 1.64μg/mL at the first lactation.6. With a rise in lactation capacity, LPO activity, SCN^- and OSCN^- concentrationsdecrease evidently, keeping the highest level of 2.68U/mL, 2.97μg/mL and1.34μg/mL at the lactation capacity of 1.6kg/d; the change of H₂O₂ concentration isjust on the contrary, reaching to 0.14μg/mL at the lactation capacity of 2.3kg/d.7. Addition of thiocyanate(SCN-) has a great effect on LPS components in goatmilk. With a rise in time, LPO activity and OSCN concentration rise evidently, whilethe concentrations of SCN^- and H₂O₂ decrease.8. After adding hydrogen peroxide(H₂O₂), LPO activity increases by 6.88% and thelevel of SCN^- concentration decrease. Contemporary, SCN^- concentration increases by25.64%. With a rise in time, OSCN^- concentration decrease quickly, which hardly tobe detected in the condition of 25℃through 7h.9. Addition of sodium percarbonate has a great effect on the LPS components ingoat milk. LPO activity increases by 10.11%, reaching to 1.96U/mL after 7h. And thelevel of SCN^- concentration decrease, the change of OSCN^- concentration is just onthe contrary. With a rise in time, H₂O₂ concentration decreases, which hardly to bedetected in the condition of 25℃through 7h.10. After adding solid antistaling agents or liquid antistaling agents, LPO activityin trial groups increases compared with the control group, and LPO activity in trialgroup with solid antistaling agents is the highest. With a rise in time, SCN^-concentration decreases, while OSCN^- concentration increases; H₂O₂ concentrationcontinues to reduce in the whole process. However, H₂O₂ concentration in trial groupwith solid antistaling agents declines slowly.