الفهرس 
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Abstract
Casein, the major milk protein component and its caseinate derivatives have physicochemical, functional and nutritive properties which make them useful worldwide. Caseins serve as food supplementation serving as functional additivies contributing adhesive, emulsion, coagulation or viscoelastic properties to foods. Thus, the aim of the present research was to modify of the physico-chemical and functional properties of buffalo’s casein through glycosylation with food – additives, i.e. ribose, glucose, galactose and lactose. The glycation was generated at 60 Cº, pH 6.5 for 72 h and then dialysed for 36 h. Lysine side chain; Histiden and Arginine in control casein were used as a marker for glycosylation. These results indicate that lysine glycation may be occurred within the ratio of 45 to 75%. The results indicated that histidine glycation may be occurred within the ratio of about 40 to 100 %. The results indicated that arginine glycation may be occurred within the ratio of about 57 to 64 %. The determination of functional properties of modified casein in comparison with those unmodified ones were assessed.
1. Ethanol stability (ES) of glycated buffaloe casein:
Ethanol stability was improved as a result of carbohydrate binding. It is well known that, the technological properties of milk are strongly influenced by the stability of the casein micelle system or rather by the fact that this stability can be lost as a result of any severe treatment such as addition of ethanol. The precipitation of glycated casein isolated from buffaloe’s milk by ethanol upto 95% concentration was examined. Ribose, glucose, galactose and lactose, as the most carbohydrate sugars consumed by humanbeing, were used for glycation of casein solution. It can be seen from the obtained data that unmodified casein (control) was precipitated at pH 2 by using alcohol concentration from 50 % to 95 %. At pH 4.0 precipitation started from 65 % alcohol. Above isoelectric point, at pH 6.0 precipitation was observed at 75 % alcohol and above, i.e, 95 %. At pH 8.0, the precipitation was observed by using 95% alcohol concentration only. No precipitation was detected at pH 10.0.
Riboglycation, glucoglycation, galactoglycation and lactoglycation of casein resulted in increasing of ethanol stability. The precipitations of alcohol test were detected only by using both 75 % and 95 % alcohol concentrations and at pH 4.0 only (around isoelectric point of casein).
2. Calcium sensitivity of glycated buffalo casein with different
sugars:
The casein solubility in calcium solutions for modified and unmodified casein was determined at different calcium concentrations ranging from 0 to 100mM of CaCl2 at pH value of 7.0. The casein solubility was expressed as a percentage of soluble casein at each calcium concentration. The influence of adding calcium ions on the solubility of buffalo casein and casein glycated with ribose, glucose, galactose, and lactose was studied. The results of unmodified casein indicate that increasing the CaCl2 concentration resulted in a decrease of protein solubility to reach a value of 62.2% of the original concentration at the highest Ca2+ concentration used (100 mM). More or less, same figures could be detected in the case of ribose and lactose casein glycation regarding solubility in calcium solutions. Generally speaking, glucose and lactose showed the higher solubility when comapared to unmodified casein whereas galactose showed less solubility, but ribose showed more similar solubility as control sample. On the other side, the effect of Ca2+ concentration on solubility of all casein samples showed significantly differences with all Ca2+ concentrations except with 10 mM concentration which showed no significant difference with zero concentration
3. Effect of environmental pH on the solubility of glycated buffalo casein:
Its determination under a variety of environmental conditions, such as environmental pH, can give valuable information on the processing and potential value in applications where solubility is a prerequisite. A typical solubility at different pH values for modified casein with glucose showed that at pH close to its isoelectric pH, i.e., 4.0, control casein was almost insoluble while at pH values > 4.0 it converted to the cationic salt and was almost soluble at pH 10.0. At pH < 4.0 control casein was also about 38.8% soluble. When casein was modified with glucose, galactose, lactose or ribose casein showed less solubility at pH 2 than the unmodified one. On the other hand at pH values from 4 to 10, all modification treatments of casein showed positive protein solubility than the unmodified casein. The statistical analysis of the results indicate that the differences were significant due to either casein glycation or pH changing.
4. Foaming properties of glycated buffalo casein with different sugars:
The foaming volume capacity was increased by modification of casein with ribose, glucose, galactose and lactose at all pH values. Modification of casein with glucose display the highest foaming capacity out of all the modification of casein treatments, being 78.6% at pH 2 and reached to 150% at pH 10.0.
For the foam stability, the results indicate a gradual decrease up to 60 min of experimental time. With all pH values used, increasing the time of setting, the foam volume stability percentage generally decreased up to 60 min. The foam volume after the first 5 min decreased to one third the original volume, and after 10 min it decreased to one fifth only. After that the decrease was slower and reached about 1/10 from initial volume between 40 - 45 min.
5. Emulsifying Properties:
. Emulsifying properties of buffaloe casein and modified glycated casein with ribose, glucose, galactose and lactose were studied at different pH values. A significant difference between type of carbohydrate and emulsion properties shows glucoglycation the highest significantly value of casein then lactose, ribose and galactose. Control casein shows the least value.
The emulsion stability decreased by increasing the time of storage. All sugars increased the EAI of glycated caseins at pH 2, and the glucose attained the highest value. At pH 4, i.e. near the isoelectric point of casein, the EAI curves declined with all used sugars as well as the control sample. Over this pH, namely at pH values 6, 8 and 10, all EAI curves took ascending direction and up to their highest EAI.
6. Buffer capacity of glycated buffalo casein with different sugars:
Buffering capacity can be seen that casein glycated with galactose showed the highest buffer index, followed with glucose, then ribose and the lowest was with lactose. It seems that the changes in casein composition and structure as a result of glycation could cause significant changes in the buffer capacity of casein solution at the same pH range (pH 7.0 – 8.0).
7. Rheological properties of casein solution chemically modified by reductive alkylation with reducing sugars:
The viscosity of the glycosylated and especially of the glactosylated casein was found to be increased. The increase of viscosity reported to be due to an increase in the net negative charge. Galactose had a higher intial rate of utilization of ε- amino groups of lysine residues. At all pHs used (pH 2- pH 10), the highest values were obtained with galactoglycated, lactoglycated, riboglycated casein and the lowest with glucoglycated then control casein. On the other hand, the changes in pH of the solutions affect the value of apparent viscosity. It can be seen from the results reported above that increasing the pH values resulted in decreased values of apparent viscosity. Increasing shear rates resulted in decreasing apparent viscosity. Increasing shear rates resulted in increasing shear stress of solutions. The relation of shear rate and shear stress at the protein concentration of unmodified and modified buffalo casein at 0.1%, 0.5% and 1% was studied. At 1% protein concentration was the highest correlation. Increasing shear stress resulted in higher increase with the increase of protein concentration. The results show that increasing shear rate resulted in an increase in shear stress.
The improvement of rheological characteristics of buffalo casein could produce an equivalent functionality with a smaller amount of added protein, helping to reduce product costs, as well as to promote its use as fever ingredient with a dilution value to develop customer-favored products with a competitive edge in the marketplace.
8. Surface tension:
The surface tension of 0.1% solutions in control buffalo casein as well as various glycated caseins (with ribose, glucose, galactose and lactose) at different pH values from pH 2 to pH 10. The surface tension value for the control casein at pH 2.0 was the lowest whereas the highest value was at pH 10.0. Increasing the pH value resulted in significantly increase in the surface tension except at pH 4.0 which showed significant decrease in all modified caseins as well as control casein and glycosylation with lactose gave the least value of surface tension whereas the glycosylation with galactose showed the highest value.
9. General comment:
The obtained results revealed that the functional properties of buffalo casein could be positively modified through glycosylation with food – safe additives. Further, the improvement of functional properties of buffalo casein could produce an equivalent functionality with a smaller amount of added protein, helping to reduce costs as well as to promote its use as high- active ingredient with a dilution value to develop customer- favored products with a competitive edge in the marketplace.