Studies on the utilization of vegetables protein have been given considerable attention due to the imbalance between the world food supply and the number of population. Also there is a worldwide need for more dietary protein, particularly for low income groups. Soymilk and mung bean milk are the most thoroughly plant protein studied and used in different dairy products such as ice cream  ; yoghurt   ; yoghurt from mung bean  , and Domiati cheese  .
Maize (Zea Mays) is a common staple tropical crop with very low protein and poor amino acid profile  . For corn to be efficient in a melio rating malnutrition, it must be supplemented with high grade protein-soybean can provide a useful complement to cereals and tubers to give a balanced diet that could prevent protein energy malnutrition (PEM)  . Chemically corn contains sugars content (1% - 3%) (consisting of glucose, fructose and sucrose), protein (8% - 11%), Fat, vitamins and minerals  . Milky stage corn on the cob is the most suitable as a raw material for soy corn milk production with good quality  . Omueti and Ashaye  reported that soy corn milk produced from white corn grains that had higher acceptability and digestibility than soy milk for both adults and children.
In literature no much information was available about the using of corn milk in dairy products, so this research aimed to study the possibility of producing acceptable, low cost and highly nutritional yoghurt using various ratios of soy bean milk and corn milk added to buffalo milk.
2. Materials and Methods
Milk supply: Buffalo milk was obtained from the farm of Faculty of Agriculture, Sohag University, Egypt.
Soybean: Soybean Giza 22 was obtained from the Agriculture Administration, Minia governorate.
Corn grains: Corn cob grains (milky stage) of freshly harvested green were obtained from a private field situated of Girga, Sohag governorate.
2.2. Preparation of Soybean Milk
Whole soy beans were washed and soaked overnight in distilled water. After decanting the soaking water, the soybeans were blended with 10 times their weight of distilled water for 3 minutes. The resultant slurry was filtered through double-layered cheese cloth to obtain soy milk  .
2.3. Preparation of Corn Milk
White cob corn grains were harvested at milky stage of maturity when grains most milky and Juicy (milky). The grains were separated from the cob and cleaned to remove hairs and other extraneous materials. Corn-grains were mixed in tap water in the ratio of 1:2 (w/w) using blender and finally the mixture was filtered through cheese cloth.
2.4. The Details of the Tow Experiment are given in the Following Sup Sections
2.4.1. The First Experiment
Yoghurt was made from buffalo’s milk and mixtures of soy milk and corn milk ratios as following:
B1 (100 ml buffalo milk + 90 ml Soy milk + 10 ml Corn milk).
C1 (100 ml buffalo milk + 80 ml Soy milk + 20 ml Corn milk).
D1 (100 ml buffalo milk + 70 ml Soy milk + 30 ml Corn milk).
E1 (100 ml buffalo milk + 60 ml Soy milk + 40 ml Corn milk).
F1 (100 ml buffalo milk + 50 ml Soy milk + 50 ml Corn milk).
2.4.2. The Second Experiment
Yoghurt was made from buffalo s milk and corn milk ratio’s as following:
B2 (90 ml buffalo milk + 10 ml Corn milk).
C2 (80 ml buffalo milk + 20 ml Corn milk).
D2 (70 ml buffalo milk + 30 ml Corn milk).
E2 (60 ml buffalo milk + 40 ml Corn milk).
F2 (50 ml buffalo milk + 50 ml Corn milk).
G2 (40 ml buffalo milk + 60 ml corn milk).
The above mentioned mixtures were heated to 85˚C for 15 min., cooled to 40˚C and inoculated with 2% of starter (Streptococcus thermophilus and Lactobacillus delbrueckii sub sp. bulgaricus 1:1). The inoculated mixture was carefully stirred, filled in cups and then incubated at 40˚C until complete coagulation and stored at 7˚C.
2.5. Chemical Analysis
Total solids (TS), Total protein (TP), Fat content, ash content and pH values were measured according to A.O.A.C  . Curd firmness was carried out by method described by Ibrahim  .
2.6. Sensory Evaluation
Twenty one trained panelists included staff members, graduated and undergraduated student of Dairy Department of Faculty of Agriculture, Sohag university were selected for evaluating the yoghurt samples using a quality rating score card the evaluation score was performed in duplicate and included different properties viz. flavor (50 points), body and texture (30 points) and appearance and color (20 points) as described by El-Sayed and El-Sayed  .
3. Results and Discussion
Data presented in Table 1 show some chemical composition of soy milk and corn milk compared with buffalo’s milk. Data indicated that specific gravity for corn milk (1.056) was higher than that in buffalo milk and soy milk. The high value of specific gravity is related to increasing total solids content. Buffalo milk contained 17.99% TS, 4.09% Total protein, 7.30% Fat and 0.83% Ash. pH value
Table 1. Some physical and chemical properties of buffalo milk, soy milk, corn milk and mixture buffalo milk with different ratios of soy milk and corn milk (%).
A = control (100% buffalo milk), B1 = (100 ml buffalo milk + 90 ml soy milk + 10 ml corn milk), C1 = (100 ml buffalo milk + 80 ml soy milk + 20 ml corn milk), D1 = (100 ml buffalo milk + 70 ml soy milk + 30 ml corn milk), E1 = (100 ml buffalo milk + 60 ml soy milk + 40 ml corn milk), F1 = (100 ml buffalo milk + 50 ml soy milk + 50 ml corn milk).
was 6.80. Data shown that soymilk contained 6.99% TS, 2.98% Total protein, 2.00% Fat and 0.43% Ash, while corn milk contained 15.62% TS, 1.58% Total protein and 0.54% Ash.
The pH values for the two types of milk were 7.03 and 7.04 respectively. According to the results obtained by Bikheet  soy milk had 9.1% total solids, 4.2% total protein and 1.5% fat. The differences between obtained results and the others studies may be due to the differences of water content and the filtration method  . The pH values of buffalo milk with different ratios of soy milk and corn milk for all treatments were between 7.02 - 7.09 (Table 1). The specific gravity and total solids increase with increasing level of corn milk. However, increasing the level of corn milk in the mixture led to decrease the percentage of total protein and fat. Whereas, there was unclear changes were found in ash content for all treatment.
Data presented in Table 2 showed the chemical composition of different ratios of buffalo milk and different ratios of buffalo milk with corn milk. The pH values for all treatment were between 6.8 and 6.9. Specific gravity increased with increasing the level of corn milk. The treatment B2 has the lowest values of Specific gravity (1.033), while the treatment G2 had the highest (1.046). As regarding to the% of TP, Fat and ash content decreased with increasing the level of corn milk. Also it was observed that no changes in the total solids for all treatments.
The tabulated data in Table 3 showed the physicochemical characteristics of buffalo milk with different ratio of soy corn Yoghurt. The pH value for buffalo milk (control) was 4.8. The values for all treatments were ranged from 4.80 to 4.50. The pH values obtained in the present study were in agreement with that obtained by Angelia et al.  , who reported that yoghurt made from buffalo milk with soy milk: corn milk (80:20), (70:30), (60:40), and (50:50) has pH values
Table 2. Chemical composition of buffalo milk with different ratios of corn milk (%).
A = control (100% buffalo milk), B2 = (90% buffalo milk + 10 % corn milk), C2 = (80% buffalo milk + 20% corn milk), D2 = (70% buffalo milk + 30% corn milk), E2 = (60% buffalo milk + 40% corn milk), F2 = (50% buffalo milk + 50% corn milk), G2 = (40% buffalo milk + 60% corn milk).
Table 3. Chemical composition of yoghurt made from buffalo milk with different ratios of soy milk and corn milk.
A = Control Sample (100% buffalo milk), B1 = 100 ml buffalo + 90 ml soy milk + 10 ml corn milk, C1 = 100 ml buffalo + 80 ml soy milk + 20 ml corn milk, D1 = 100 ml buffalo + 70 ml soy milk + 30 ml corn milk, E1 = 100 ml buffalo + 60 ml soy milk + 40 ml corn milk, F1 = 100 ml buffalo + 50 ml soy milk + 50 ml corn milk.
4.638 , 4.582 , 4.556 , and 4.539 respectively. Higher ratio of corn milk decreased the pH value and this may be due to the fructose of sweet corn. Corn can be used as substrate converted to lactic acid. The pH of soy corn yoghurt had lower than the dairy yoghurt. This might be due to the different kind of substrate in soy corn milk such as fructose and sucrose as compared with sugar addition  . The total protein, fat and ash content were decreased with increasing of corn milk ratio (Table 3). There was a gradual decrease in level of protein as observed in all treatment. Sample B1 has 4.63% while samples C1, D1, E1 and F1 have 4.38%, 4.21%, 3.97% and 3.56% respectively. Comparative level of protein in sample B1 and C1 were nutritionally significant in terms of the potentials. These products can contribute to increase protein intake of consumers  . Fat content were a gradual decrease in all treatments, Sample (B1) has 5.8% and reached to 5% in sample (F1). These results were higher than that obtained by Makanjuola  . Ash content in all treatments was 0.72 - 0.74. The obtained data were higher than that obtained by Makanjuola  , who found that the ash contents were 0.60 and 0.62% for samples contained 80% soy milk plus 20% corn milk and 70% soy milk plus 30% corn milk respectively. The curd firmness was affected by decreasing level of soy milk; the values were gradually increased with increasing corn milk. These results those obtained by Schmidt et al.  who found that isolated soy protein used to fortify yoghurt resulted a product having a weak texture. The highest value of curd firmness was observed for treatment F1 (50 soy milk: 50 corn milk) compared to other treatments. Generally, composition of milk especially its total solids and pH have a paramount influence on curd firmness and gel structure  .
Results in Table 4 indicate the changes in chemical composition of yoghurt made from different ratio of buffalo’s milk and corn milk. It is clear that the pH values in all treatment decreased with increasing the corn milk level to buffalo’s milk may be due to the effect of corn milk. Same results were reported by Magdoub et al.  for yoghurt produced by mixing soy milk. Data presented in Table 4 indicated that the pH values were well agreement with those obtained by Hosny and Angelia et al.   explained that the acidic nature of maize protein could be responsible for high titratable acidity and the lower of pH value. Total solids content in control sample (A) was 21.9%, while that for all treatments ranged from 25.01% - 15.06%. The decrease of TS for treatments was due to the lower total solids content of corn milk (15.62%) as shown in Table 1. It is obviously noted that total protein, fat and ash content decreased as corn milk ratios increased, this is attributed due to the lower content of protein and ash content in corn milk than buffalo milk.
The curd firmness was affected by the level of corn milk addition. It was shown that treatments C2 (80:20), D2 (70:30) and E2 (60:40) resulted yoghurt have high value of curd firmness compared to the other treatments. Generally increasing level of corn milk led to increasing curd firmness.
Results obtained in Table 5 shown that the decreasing amount of soy milk in the mixtures led to increase in the acceptability of the product. Treatments E1 (60:40) and F1 (50:50) have higher scores in flavor, body and texture and appearance and color than that of the other treatments. The obtained data were in full agreement with results given by Angelia et al.  , who found that the different ratio of soy milk and corn milk cause high difference of the preference score of appearance, aroma, texture and taste. High corn milk ratio resulted in higher score of appearance and aroma. Soy corn yoghurt with (50:50) ratio was the most acceptable. Corn milk has some volatile substance such as acetaldehyde which can contribute to reduce beany flavor of soy milk  . Treatments E1 (60:40) and F1 (50:50) had higher level of curd firmness (Table 4) and total sensory scores Table 5 than that the other treatments. However, addition of up to (60:40) and (50:50) of soy corn milk can be used in the manufacture of yoghurt without negative effect on the sensory properties.
Results in Table 6 indicated that increasing the amount of corn milk in the mixtures led to decrease in the acceptability of the product. However, addition of
Table 4. Chemical composition of yoghurt made from different ratios of buffalo milk and corn milk.
A = Control (100 % buffalo milk), B2 = (90% buffalo + 10% corn milk), C2 = (80% buffalo + 20% corn milk), D2 = (70% buffalo + 30% corn milk), E2 = (60% buffalo + 40% corn milk), F2 = (50% buffalo + 50% corn milk), G2 = (40% buffalo + 60% corn milk).
Table 5. Organoleptic scores of yoghurt made from buffalo milk and different ratios of soy milk and corn milk.
A = Control Sample (100% buffalo milk), B1 = 100 ml buffalo + 90 ml soy milk + 10 ml corn milk, C1= 100 ml buffalo + 80 ml soy milk + 20 ml corn milk, D1 = 100 ml buffalo + 70 ml soy milk + 30 ml corn milk, E1 = 100 ml buffalo + 60 ml soy milk + 40 ml corn milk, F1 = 100 ml buffalo + 50 ml soy milk + 50 ml corn milk.
Table 6. Sensory Scores of yoghurt made from different ratios of buffalo milk and corn milk.
A = Control (100 % buffalo milk), B2 = (90% buffalo + 10% corn milk), C2= (80% buffalo + 20% corn milk), D2 = (70% buffalo + 30% corn milk), E2 = (60% buffalo + 40% corn milk), F2 = (50% buffalo + 50% corn milk), G2 = (40% buffalo + 60% corn milk).
corn milks up to 10% - 30% can be used in the manufacture of yoghurt, which had good curd firmness and accepted to the consumers.
From the above mentioned results it could be concluded that addition of corn milk and soy milk for the production, added value to the product through increased its nutrient content and sensory properties, also, being cheap and readily available to low income families in the developing country. Corn milk was generally acceptable organoleptically than soy milk, so corn milk could be incorporated with buffalo or cow milk to manufacture of some dairy products.
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