FUNCTIONAL PROPERTIES OF GOAT AND BUFFALO MILK PROTEINS

د. محمود ابرهيم باحث بمعهد بحوث تكنولوجيا الاغذية 

ملخص رسالة الماجستير ( جامعة الاسكندرية )

SUMMARY AND CONCLUSIONS

The physicochemical properties of food proteins affect their functional properties of the food as texture, colour, flavour, water binding and stability. Probably the most important physicochemical properties are solubility, hydration, rheology, surface activity and gelation. Milk proteins, either caseins or whey proteins, due to their heterogeneity, range of physical properties and amphipolar characteristics, were used in food processing for multiple functions.  Most of research was focused on bovine milk proteins due to the dominance of such type of milk all over the world. However, little attentions were directed to evaluate the functional properties of non-bovine milk proteins.Therefore, this study was conducted to study different functional properties of both goat and buffalo milk proteins in order to gain some knowledge to evaluate these proteins for further application in food industry. To achieve such goals, various caseins (HCl, lactic, rennet) and casein- coprecipitate preparations were prepared by different methods. Meanwhile, the effect of some factors as concentration of protein, pH of the medium, trypsin treatment on functional properties of prepared proteins was studied. The obtained results revealed the following:

1. Goat milk proteins have higher significant (P≤ 0.05) degree of solubility than those of buffalo milk.
2. The solubility of both goat and buffalo milk proteins was protein concentration and pH dependent, i.e. the higher the concentration and pH value, the higher the solubility.
3. Goat and buffalo HCl-casein showed the highest solubility at pH 8 followed by lactic casein then rennet casein. But casein co-precipitate was characterization by very low solubility at all pH values comparing to the other caseins.
4. The emulsifying capacity (EC) of goat and buffalo caseins was concentration and pH dependent, i.e, the higher the concentration and pH value, the higher the EC.
5. Goat HCl-casein showed the highest EC at pH 8 and there was no significant (p≤ 0.05) change between lactic casein and rennet casein. But casein co-precipitate was characterization by very low EC at all pH values comparing to the other caseins.
6. Buffalo lactic -casein showed the highest EC at pH 8 followed by HCl-casein, and then casein co-precipitate. But rennet casein was characterization by very low EC at all pH values comparing to the other caseins.

7. Goat milk proteins (HCl- , lactic -, rennet casein and casein co-precipitate )  have higher significant (P ≤ 0.05) degree of EC than those of buffalo milk at all concentrations and pH values.
8. The viscosity of different goat and buffalo milk casein preparations as affected by concentrations. The viscosity of all casein preparations was significantly   increased by concentration increase. Meanwhile the two types of goat and buffalo milk casein preparations were not affected by the increase of pH from 7 to 8.
9. Goat milk casein coprecipitate is the proper preparation for the food application in order to obtain high viscous mixture followed by lactic casein. The viscosity of all goat milk casein preparations except rennet casein was pH independent.

10. At all pH values, the ascending order of   viscosity of goat and buffalo proteins  was HCl-casein, rennet casein, lactic casein and casein coprecipitate.
11. Over all results revealed that goat milk rennet casein and casein coprecipitate have significantly (p≤0.05) higher viscosity values than those of buffalo milk caseins but there were no significant differences between lactic casein and HCl-casein of both types of milk. Both types of casein preparations are similar in that HCl-casein had the lowest viscosity, while casein co-precipitate had the highest viscosity value.
12. The foaming capacity FC and foam expanded FE of goat and buffalo HCl-casein increased with the concentration increase. Meanwhile the FC and FE of buffalo HCl-casein were higher significant than that of goat HCl-casein at all concentrations and pH value.
13. The highest foam volume of buffalo HCl-casein was obtained at pH 7.0 for all casein concentrations. On the other side the highest FC of goat HCl-casein was obtained at pH 7.5.
14. The foam volume stability FVS of buffalo HCl-casein was higher than that of goat casein. The higher FVS was found at buffalo HCl-casein, concentration 1.00% and pH 8.0.
15. The FC and FE of goat and buffalo lactic casein were increased with the concentration increase at all pH value. The FC, FE and FVS of buffalo lactic-casein were higher than that of goat casein. The higher FVS was found at buffalo lactic casein, at pH 7.0 and concentration 1.00%.
16. The FC and FE of goat and buffalo rennet casein were increase with the concentration increase at all pH values. The FC, FE and FVS of buffalo casein were higher than that of goat casein.
17. The behaviour of buffalo rennet casein is different than that of goat rennet casein because the best foam stability of the former casein can be obtained at higher pH value and concentration than the latter casein.
18. The behaviour of goat and buffalo casein co-precipitate CCP is similar, the foam capacity of buffalo CCP is better than that of goat milk at higher concentrations and pH values.

19. The obtained  results revealed that the FVS of goat casein co-precipitate is higher than that of buffalo at  both pH 7.5 and 8.0.
20. The solubility of both goat and buffalo milk HCl-casein was significantly (p ≤ 0.05) increased then decreased by trypsin treatment for 5and 15 min, respectively.
21. The solubility of native and trypsin treated goat milk HCl-casein, lactic casein and casein co-precipitate was significantly higher than these of buffalo milk.
22. Trypsin hydrolysis at pH 7.0 for 5 min enhances the EC of goat HCl-casein and lactic casein as well as buffalo lactic casein and no HCl-casein. But the EC of casein co-precipitate of goat and buffalo milk is retarded by the same treatment under the same conditions.
23. The behaviour of HCl-casein of buffalo milk is different than any other casein preparations whether buffalo or goat milk. Meanwhile, the tryptic products of most of casein preparations in both goat and buffalo milk have lower viscosity than native proteins.

24. Trypsin treatment for 5 min of both types of casein resulted a significant increase in foam volume; followed by another significant increase after 15 min. the FC of buffalo HCl- and lactic casein hydrolysate was higher than that of goat casein.
25. The behaviour of foam stability of goat milk HCl-casein is completely different than that of buffalo milk, since the tryptic treatment enhanced the foam stability of the former but reduced that of the latter.
26. Trypsin treatment for 5 min of both types of casein resulted a significant increase in foam volume, followed by another significant increase after 15 min. The rate of foam volume increase was significantly  higher  in case of buffalo lactic casein than that of goat milk.
27. The behaviour of foam stability of goat milk lactic casein is completely different than that of buffalo milk, since the tryptic treatment enhanced the foam stability of the former but reduced that of the latter.
28. After trypsin treatment for 5 min of both types of casein co-precipitate have a significant increase in foam volume, followed by another significant increase after 15 min in case of goat but there was no significant change in case of buffalo milk casein co-precipitate.
29. The trypsin treatment had no effect on FVS of goat and buffalo casein co-precipitate.
30. Results showed also that goat and buffalo milk casein preparations were completely different in their electrophoretic behaviors due to the differences in charges and molecular weights. B) The behaviour of goat and buffalo milk casein preparations towards trypsin hydrolysis was entirely different. Since, buffalo lactic casein and casein coprecipitate were higher in proteolysis by trypsin than those of goat proteins, while goat HCl-casein has the opposite behaviour.

Conclusions

1. Goat and buffalo milk protein preparations are highly different in their functional properties.
2. All goat milk protein preparations are characterized by their higher solubility, emulsifying capacity than buffalo milk proteins, therefore they can be used in food application as beverages, baking, candy, soups, sausage and ice cream making.
3. Buffalo milk protein preparations are characterized by their higher foaming capacity and stability than those of goat milk, therefore they can be used in ice cream making, coffee whitener, foam milk, spongy cakes and whipped toppings.
4. To improve the functional properties of either goat and buffalo milk protein preparations, trypsin treatment for 5 min is recommended.