2Dairy Technology Department, Animal Production Research Institute, Agricultural Research Center, Dokki, Giza, Egypt
3Independent Scholar, Damietta, Egypt
Fresh goat’s milk was obtained from El-Serw Animal Production Research Station, Animal Production Research Institute, Agricultural Research Center, Egypt. The chemical composition of milk was. ABT culture (ABT-5) with mixed strains of S. thermophilus (as sole fermenting organism) and LA+ B. bifidum (as probiotic organisms) (Chr. Hansen’s Lab A/S Copenhagen, Denmark) were used. The starter culture was in freeze-dried direct-to-vat set form. After procurement, the starter cultures were stored at –18°C in the absence of atmospheric air. Saidy variety of date (P. dactylifera L) at the Tamr stage of maturity and honey were obtained from local market in Damiette Governorate, Egypt.
Preparation of Tamr
Tamr of good quality were carefully selected and washed with tap water after removing of the kernels. The flesh was cut into small pieces, soaked in hot water (90°C) for 3 min and directly soaked in previously heat treated milk.
Tamr and honey were added to goat’s milk as follow:
Sample A: Goat’s milk (control)
Sample B: Goat’s milk + 5% Tamr
Sample C: Goat’s milk + 10% Tamr
Sample D: Goat’s milk + 15% Tamr
Sample E: Goat’s milk + 20% Tamr
Sample F: Goat’s milk + 25% Tamr
Sample G: Goat’s milk + 10% Tamr + 1% Honey
Sample H: Goat’s milk + 10% Tamr + 2% Honey
Sample I: Goat’s milk + 10% Tamr + 3% Honey
Sample J: Goat’s milk + 15% Tamr + 1% Honey
Sample K: Goat’s milk + 15% Tamr + 2% Honey
Sample L: Goat’s milk + 15% Tamr + 3% Honey
Total solids, fat and total nitrogen contents of milk samples were determined according to AOAC . Titratable acidity in terms of % lactic acid was measured by titrating 10g of sample mixed with 10ml of boiling distilled water against 0.1 N NaOH using a 0.5% phenolphthalein indicator to an end point of faint pink color. pH of the sample was measured at 17 to 20°C using a pH meter (Corning pH/ion analyzer 350, Corning, NY) after calibration with standard buffers (pH 4.0 and 7.0). Redox potential was measured with a platinum electrode [model P14805-SC-DPAS-K8S/325; Ingold (now Mettler Toledo), Urdorf, Switzerland] connected to a pH meter (model H 18418; Hanna Instruments, Padova, Italy).
The curd tension was determined using the method of Chandrasekhara., et al.  whereas the susceptibility to syneresis (STS) was measured as given by Kpodo., et al. . For test of starter coagulation time during Rayeb milk making, milk was inculcated with starts and incubated at 40°C then coagulation was noticed at 30 min intervals. Water holding capacity (WHC) was measured according to Yousef., et al. .
Samples of goat’s milk mixed with Tamr and honey were organoleptically scored by the staff of the Dairy Department, Faculty of Agricultural, and Damietta University. The score points were 50 for flavour, 35 for body and texture and 15 for colour and appearance, which give a total score of 100 points.
Titratable acidity, pH, redox potential (Eh), total solids, fat and total protein values of goat’s milk mixed with various Tamr and honey amounts were showed in Table 1. The chemical composition of goat’s milk was within the normal range. The values of above mentioned properties corresponded to the results reported by other research workers [9,10]. Mixing various concentrations of Tamr with goats milk markedly increased acidity and Eh while decreased pH values. With increasing of Tamr amounts added to goat’s milk, total solids (TS) and total protein contents raised but fat concentrations slightly lowered.
|Treatments||Acidity (%)||pH values||Eh (mV*)||TS (%)||Fat (%)||TP (%)|
As it is expected, a gradual increase of titratable acidity and redox potential values in all milk treatments were noticed during fermentation period (Figures 1-6). Values of pH had the opposite trend of acidity and redox potential. The changes in acidity, Eh and pH changes could be attributed to the number and/or metabolic activity of acid producing micro-organisms. As starter grows, they produce acid which causes an increase in acidity and Eh and a decrease in pH. These results are in agreement with those previously reported for fermented milk “Lebens” .
Data in Table 2 refer to samples of goat’s milk contained Tamr coagulated faster than control. Adding 15, 20 and 25% Tamr to goat’s milk possessed the same effect on coagulation time which was more obvious as compared with that of addition 5 or 10%. Coagulation times were reduced by 9.03, 12.90, 16.13, 16.13 and 16.13% for samples B, C, D, E and F respectively. Addition of honey had the same trend of Tamr adding where coagulation times of samples contained honey were lower than that of other treatments. This may be attributed to the stimulation effect of honey on starter bacteria. These results are generally in harmony with those reported by Abd El-Salam., et al. .
The impact of incorporation of Tamr and honey with goat’s milk on curd tension is illustrated in Table 2. Because mixing Tamr or honey with milk increased total solids contents, it is normal to increase curd tension values in fermented treatments comparing with control. After 7 or 14 days of storage period, curd tension values of all samples slightly increased which may be due to moisture evaporation and total solids increasing during cooling storage. These findings are in line with those of EL-Boraey., et al. . De Jong  stated that slight differences in moisture may cause major differences in rheological parameters. Also Murad., et al.  and El-Nemer., et al.  showed that the hardness related to dry matter of the product. In contrast to our results Ayad., et al.  stated that supplementation of yoghurt with honey and talbina (cooked barley bran flour) or with molasses and talbina decreased the hardness which could be due to the ability of polysaccharides in honey and molasses to bind with significant amount of free water.
|Properties||Treatments||Storage period (day)|
|Coagulation time (min)||A||310||-||-|
|Curd tension (gm)||A||36.71||37.85||37.80|
As can be seen in Table 3, syneresis was determined by means of both drainage (susceptibility to syneresis) and centrifugal (water holding capacity) methods. Values of susceptibility to syneresis (STS) were markedly low in fermented goat’s milk samples contained Tamr or honey. Further, with increased level of incorporation, the values of STS in milk decreased. Treatments F and L recorded very low STS levels at the beginning and during storage time. Values of STS for fresh A, B, C, D, E and F samples were 19.20, 16.90, 9.70, 6.42, 4.75 and 1.88% respectively. In all samples, STS values decreased during storage period. These outcomes are similar to that reported by Zidan .
|Properties||Treatments||Storage period (day)|
to syneresis (%)
|Water holding capacity (%)||A||81.45||83.43||83.12|
Sensory Evaluation is defined as “A scientific discipline used to evoke, measure, analyze, and interpret those responses to products that are perceived by the senses of sight, smell, touch, taste, and hearing” . Table 4 illustrates the average scores of various sensory properties of goat’s milk mixed with different Tamr and honey levels. Because the white color of milk is preferred for Egyptian consumers so goat’s milk gained the highest color and appearance scores. Adding Tamr colored goat’s milk with light brown which slightly lowered the color and appearance grades. On the contrary, adding 5, 10 or 15% Tamr and 1 or 2% honey improved the body and texture of goat’s milk which may be attributed to total solids increasing. However, raising the amounts added of Tamr (20 or 25%) and honey (3%) negatively affected on the body and texture scores of goat’s milk because of very high thickness. Goaty flavor undoubtedly are the principal reasons for the declining of goat’s milk scores. This flavour is non-favorite for the majority of Egyptians. Addition Tamr (5, 10 or 15%) and honey (1 or 2%) succeeded to change flavour of goat’s milk to wanted sweetened flavour.
The authors declare no conflict of interest.
|Treatments||Color& Appearance (15)||Body& Texture (35)||Flavor (50)||Total (100)|
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