Tayseer Abd Elrahim Suleiman and Mohammed Osman Mohammed
SUMMARY
This study was carried out to evaluate the chemical quality of imported processed cheese.
The study was based on collecting twenty seven samples of one type of processed cheese, nine from Khartoum, nine from Khartoum North and nine from Omdurman. Samples were collected from groceries of three different areas according to the income level of the majority of residents in the area. The chemical composition (fat, protein, total solids, titratable acidity and ash) of the processed cheese were estimated.
The results indicated that there was a significant difference (P<0.01) in total solids and a significant difference (P<0.05) in titratable acidity, while there was no significant difference (P>0.05) in fat, protein and ash contents of cheese samples obtained from the three cities.
Protein and fat were high in Omdurman (8.87 ± 0.093 and 29.50 ± 0.148 respectively), while the titratable acidity and ash were high in Khartoum (0.669 ± 0.002 and 2.67 ± 0.056 respectively).
Total solids content was high in Khartoum North (50.22 ± 0.116 respectively). Fat and protein contents were high in high income area (29.61 ± 0.203 and 8.95 ± 0.007 respectively), while total solids and ash content were high in low income area (47.87 ± 0.264 and 2.72 ± 0.091 respectively).
INTRODUCTION
Processed cheese is made by further processing of finished cheese usually a blend of hard rennet varieties with different aromas and degrees of maturity (Bylund, 1995). Processed cheese performance shines brightly in the food industry. This product combine flavour and function with long shelf life to help the food processing industry to find the unique combination of melt, flow, shred and flavour to serve their needs (Turner, 2003).
However, while processed cheese popularity is growing, it will likely grow even faster if dairy processors can more easily customize and control it’s characteristics (Haines, 2004). Traditionally, processed cheese was made by heating and stirring mixture of natural cheese, chelating salts, fat and water at temperature between 70 and 95oC for short time about 5 to 10 minutes (Siew, 2004). The modern manufacture of natural cheese consist of four basic steps: coagulating, draining, salting and ripening. Processed cheese manufacture incorporates extra steps, including cleaning, blending and melting. Dairy products such as milk or butter may also be added to the processed cheese especially if it is intended for spreading (Dallas, 1997).
There are two main types of cheese in Sudan namely Sudanese white cheese (Gibna bayda) and braided semi hard cheese (Mudaffarra). Other types of cheese provided recently by Sudanese industries, are Mozzarella and Rome. However the processed cheese is not yet produced by the Sudanese industry; as cheese could be stored for longer periods and excess milk could be converted into processed cheese (Nour Eldaeim, 2005).
Pasteurized processed cheese food must contain at least 51% cheese, no more than 44% moisture and less or equal to 23% fat. Pasteurized processed cheese spread may have moisture content between 44 and 60% but must include at least 51% cheese and at least 20% milk fat. Processed cheese products do not comply with the previous standards such as product with more than 50% moisture, or substantial levels of non dairy products (Glass and Doyle, 2005).
Recently, processed cheese is imported fro neighboring countries according to standards set by the government. This study attempted to highlight on the ability of cheese to retain it quality during storage.
MATERIALS AND METHODS
Twenty seven samples of one type of processed cheese were collected from Khartoum State, nine from Khartoum, nine from Khartoum North and nine from Omdurman. From each town the samples were collected from groceries of three different areas according to the income level (high, middle and low income) and hygiene measures. From each area three samples were collected.
The groceries of high and middle income areas had proper cooling system, while groceries of low income areas had no cooling system.
The samples were put in the refrigerator for preservation till analysis.
The samples were analyzed for protein, fat, total solids, ash, titratable acidity according to AOAC,(2003).
Protein content:-
The protein content was determined by Kjeldahal method.
Fat content:-
The fat content was determined by Gerber method.
Total solids content:-
Total solids content was determined according to the modified method of AOAC (2003).
Two grams of cheese samples were weighed and placed in a clean dry porcelain dish and heated on a steam bath for 10 – 15 minutes. The dishes were then placed in an oven at 100oC for three hours, then cooled and weighed quickly. Heating, cooling and weighing were repeated until the difference between two successive readings was less than 0.1 mg.
The total solids content was calculated from the following equation:
| T.S. (%) = | W1 | x 100 |
| W2 |
Where:
W1 = Weight of sample after drying
W2 = Weight of sample before drying
Ash content:-
The ash content was determined according to the method described in AOAC (2003).
Titratable acidity:
Titratable acidity was determined according to AOAC (2003).
Statistical analysis:
Statistical analysis was performed using the MSTATC (1990). General Linear Models (GLM) were used to determine the quality of cheese.
RESULTS
Chemical composition of processed cheese as affected by city:-
Table (1) presents the chemical composition as affected by city from which the samples were collected. Data showed that there was no significant difference (P>0.05) between the three cities in fat content, protein content and ash content. However, fat content was high in Khartoum (29.50 ± 0.148) and low in Khartoum North (29.22 ± 0.148). The protein content was high in Khartoum (8.87 ± 0.093) and low in Omdurman and Khartoum North with value (8.75 ± 0.093). The ash content was high in Omdurman and low in Khartoum North. Total solids contents was high in Khartoum North (50.22 ± 0.116) and low in Khartoum (46.28 ± 0.116).
Titratable acidity showed a significant difference (P<0.05) between the three cities with higher values in Omdurman (0.698 ± 0002) and lower values in Khartoum (0.619 ± 0.002).
Table (1). The chemical composition of processed cheese as
affected by city.
| Chemical Composition (%) | City | Grand mean | S.L. | ||
| Khartoum North | Omdurman | Khartoum | |||
| Fat content | 29.22±0.148 | 29.33±0.148 | 29.50±0.148 | 29.35±4.423 | N.S. |
| Protein content | 8.75±0.093 | 8.75±0.093 | 8.87±0.093 | 8.79±2.420 | N.S. |
| Total solids content | 50.22±0.116a | 48.78±0.116b | 46.28±0.116c | 48.43±5.681 | ** |
| Titratable acidity | 0.659±0.007b | 0.698±0.002a | 0.619±0.002c | 0.659±0.662 | * |
| Ash content | 2.63±0.056 | 2.67±0.056 | 2.64±0.056 | 2.65±1.328 | N.S |
Means in each row bearing the same superscripts
are not significantly different( P>0.05).
** = (P< 0.01).
* = (P<0.05).
S.L.= Significant level.
N.S = Non significant (P>0.05).
Chemical composition of processed cheese as affected by income level
areas:-
Table (2) presents the chemical composition of processed cheese as affected by area from which the samples were collected. No significant difference was observed between the three areas (P>0.05) in fat, protein, total solids and ash contents. However, the fat content (29.61 ± 0.203), protein content (8.95 ± 0.077) and total solids content (48.72 ± 0.265) were high in high income area compared to other areas. The ash content was high in low income area (2.72 ± 0.091).
The titratable acidity was significantly high (P<0.001) in high income area (0.692 ± 0.007) and low in low income areas (0.632 ± 0.007).
Table (2). The chemical composition of processed cheese as
affected by income level areas.
| Chemical Composition (%) | Income area | Grand mean | S.L. | ||
| High | Middle | Low | |||
| Fat | 29.61±0.203 | 29.33±0.204 | 29.11±0.203 | 29.35±4.423 | N.S. |
| Protein | 8.95±0.077 | 8.79 ±0.077 | 8.73±0.077 | 8.82±2.426 | N.S. |
| Total solids | 48.72±0.264 | 48.67±0.264 | 47.89±0.264 | 48.43±5.681 | N.S. |
| Titratable acidity | 0.692±0.007a | 0.653±0.007b | 0.632±0.007b | 0.659±0.662 | *** |
| Ash | 2.62±0.091 | 2.60±0.091 | 2.72±0.091 | 2.65±1.328 | N.S |
Means in each row bearing the same superscripts
are not significantly different( P>0.05).
*** = (P< 0.001).
S.L.= Significant level.
N.S = Non significant.
Chemical composition of processed cheese as affected by income level area within each city:-
Table (3) presents the chemical composition of processed cheese as affected by area within each city. In Khartoum North the income level did not significantly affect (P>0.05) the chemical composition of processed cheese in terms of fat, protein, total solids and ash contents. However, cheese collected from low income area tended to be slightly acidic (0.590 ± 0.013) compared to cheese collected from other areas.
In Omdurman no changes was observed (P>0.05) in fat, total solids and ash contents with regard to income level. The protein content was slightly higher in cheese collected from high income area (8.90 ± 0.134). Cheese collected from middle income area tended to be slightly acidic (0.688 ± 0.013).
In Khartoum the income level did not significantly (P>0.05) affect the fat, protein, total solids, ash contents and titratable acidity.
DISCUSSION
The research of this kind might give the authorities a chance to evaluate the unfavourable conditions and make the right decision.
Processed cheese is a product of other types of cheese which might be of low quality from the start, and if the manufacturing conditions are not ideal the contamination might happen to the processed cheese.
The present study found that the fat content was high in process cheese under study and the percentage of fat in all samples fulfills with the standards of Alimentarius (2000).
The protein content of processed cheese was lower than the other varieties of cheese and this is due to the added water that reduced the total solids content. This result is in agreement with Nour Eldaeim (2005).
Hamed et al., (1997) mentioned that the protein content of the process cheese decreased by storage time a result that might be due to limited degradation or assimilation of protein in cheese.
The variation of total solids content between examined samples might be due to the variation of different percentages of moisture contents in the examined process cheese. However, the total solids content of processed cheese under study was agreement with the standards of Alimentarius (2000).
The samples collected from some low income areas are slightly acidic, that might be due to the storage conditions, meaning that high temperature conditions were favourable to lactic acid bacteria that produced lactic acid from the remaining lactose in the cheese curd.
This result is in disagreement with the findings of Nour Eldaeim (2005) who reported a decrease in the acidity of processed cheese during processing. However, although the result does not agree with Nour Eldaeim (2005), but there might be some thermophilic lactic acid bacteria survived processing heat treatment.
Nour Eldaeim (2005) mentioned that the ash content increased in processed cheese due to the addition of emulsifiers.
ACKNOWLEDEMENTS
The authors would like to acknowledge the Department of Dairy Production, Faculty of Animal Production, University of Khartoum for allowing them to conduct this research.
REFERENCES
Alimentarius, C. (2000). Food standards programme for milk and milk products. Food and agriculture organization and world health organization .00100 Rome, Italy.
AOAC (2003). Official Methods of Analysis. Association of Official Analytical Chemists, Washington, DC, USA.
Bylund, G. (1995). Dairy processing. Published by Tetra Pak Processing Systems AB, 5 – 221, 86, Lund, Sweden.
Dallas, S. (1997). Natural and processed cheese, Emission Factor and Inventory Group, Research Triangle Park, AP. 42, USA.
Freed, R. (1990). MSTATC. Package 384 plant and soil science. Michigan State, University of East Lansing, MI 48824, USA.
Glass, K. and Doyle, E.M. (2005). Safety of processed cheese. Food Research Institute, University of Wisonsin, Madison, WI 53706. Available at www.wise.edu.
Glass, K. and Doyle, E.M. (2005). Safety of processed cheese. Food Research Institute, University of Wisonsin, Madison, WI 53706. Available at www.wise.edu.
Hamed, A.; Khader, A.F; El Garawany, G.A. and Abdelsalam, M.H. (1997). Effect of storage on the composition, rheological properties and organoleptic quality of commercial processed cheese. Egyptian Journal of Dairy Science, 25 (4): 113 – 122.
Nour Eldaeim, A.S.M. (2005). Manufacture and evaluation of processed cheese made from Sudanese white cheese. M.Sc. Thesis, University of Khartoum, Sudan.
Siew, K.L.; Sketle, A. and Henning, K. (2004). The influence of moisture content on the reheological properties of processed cheese spreads. International Journal of Food Science and Technology, 39 (7): 763 – 769.
Turner, J. (2003). Developing processed cheese. Published by Santiago Publishing. Available www.furl.net.
Authors:
TAYSEER ABD ELRAHIM SULEIMAN
MOHAMMED OSMAN MOHAMMED
| Khartoum | Omdurman | Khartoum North | City | Table (3): Chemical composition of processed cheese as affected by income level area within each city. | |||||||||||
| S.L. | Grand mean | Low income area | Middle income area | High income area | S.L. | Grand mean | Low income area | Middle income area | High income area | S.L. | Grand mean | Low income area | Middle income area | High income area | |
| N.S. | 29.50±4.435 | 29.17±0.352 | 29.50±0.352 | 29.83±0.352 | N.S. | 29.34±4.422 | 29.17±0.352 | 29.67±0.352 | 29.17. ±0.352 | N.S. | 29.22±4.414 | 29.00±0.352 | 28.83±0.352 | 29.83±0.352 | Fat (%) |
| N.S | 8.87±2.432 | 8.62±0.134 | 8.95±0.134 | 9.05±0.134 | *** | 8.75±2.415 | 8.73±0.134 | 8.62±0.134 | 8.90±0.134 | N.S. | 8.91±2.437 | 8.83±1.34 | 8.82±0.134 | 9.07±0.134 | Protein (%) |
| N.S. | 46.28±2.432 | 45.50±0.458 | 46.83±0.013 | 46.50±0.458 | * | 48.61±5.693 | 48.00±0.458 | 49.83±0.458 | 48.0±0.458 | N.S. | 50.22±5.786 | 50.17±0.458 | 49.33±0.458 | 51.17±0.458 | Total solids (%) |
| N.S. | 0.636±0.651 | 0.612±0.013 | 0.620±0.013 | 0.677±0.013 | N.S. | 0.698±0.682 | 0.693±0.013 | 0.688±0.013 | 0.713±0.013 | * | 0.668±0.661 | 0.590±0.013c | 0.652±0.013b | 0.737±0.013a | Titratable Acidity (%) |
| N.S. | 2.64±1.325 | 2.70±0.158 | 2.68±0.158 | 2.53±0.158 | N.S. | 2.67±1.335 | 2.92±0.158 | 2.52±0.158 | 2.58±0.158 | N.S. | 2.63±1.323 | 2.53±0.158 | 2.60±0.158 | 2.75±0.158 | Ash (%) |
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