الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Objectively, because of the conventional heating whether pasteurization, boiling or rather sterilization is the common procedure applied to control the load of microbes in milk. In spite of its very straightforward and efficient, but may lead to several sensory acceptability and nutritional losses in the resultant product, particularly when heat treatment is implemented in poor quality milk, which possesses a high load of microbes and hence more heating process (temperature degree and/or time) is needed. Accurate thermal treatment methods such as pasteurization may not be available in small cheese manufacturers, as it increases the clotting time and weakens both of the milk rennetability and the strength of the hardness of cheese curd. Therefore, many small cheese manufacturers resort to using unauthorized preservatives or illegal proportions instead of pasteurization Innovative, easy to implement, and rapid technologies are required for the modern food industry to meet the never ending demands of consumers (e.g. fresh and safe ready-to-eat products). Ozonation has several merits that make it a technology to be considered in the food industry; it is the most powerful sanitizer; it decomposes rapidly to oxygen leaving no residues. Low concentrations of ozone are quite enough to be effective. It acts strongly against extended spectrum of microorganisms, i.e. bacteria, fungi, viruses, protozoa, and bacterial as well as fungal spores. In addition, it may be considered a promising way because its reduced cost, which makes it affordable for small food producers, mini dairies especially small cheese manufacturers. Therefore, this research aims to assess the effect of different ozone dozes versus heat treatment on some chemical and microbiological properties including pathogens of raw milk, from which two of the most common white soft cheeses in Egypt, namely Domiati and Kariesh cheeses were chosen to be made.
Technically, to achieve these purposes the study was conducted into three parts as following:
Part I: Effect of ozonation treatment on the cow’s milk properties versus pasteurization
In this part, forty kilograms of raw cow’ milks were divided into eight equal portions, 1st portion was heat treated at 72°C for 15 sec then rapidly cooled to room temperature. Other 7 portions were treated with ascending ozonation times, namely, nil (served as a control), 5, 10 15, 20, 25 and or 30 min using an ozone generating device from the air )Electric Anion Ozonizer, Healthy Life, Model, AK-102, UK) at the rate of 400 mg O3/h.
On the other hand, twenty five kilograms of fresh skim milk were autoclaved at 115°C /15 min then cooled to room temperature. Thereafter, the sterilized milk was divided into equal five portions. Tow portions were separately inoculated with 0.1% of 24-h age broth cultured with Gram positive pathogenic bacterial strain of Staphylococcus aureus or Bacillus cereus. Other three portions were individually inoculated with 0.1% of 24-h age broth cultured with Gram negative bacterial strain of Escherichia coli, Salmonella typhimurium and Shigella flexneri. All inoculated milk samples were ozonized for nil, 5, 10 15, 20, 25 or 30 min using the same ozone generating device at the same previous rate and immediately tested for the survival count of the studied pathogenic strains.
The obtained results of the 1st part could be summarized as follow:
1. Microbiologically, initial enumerated log count in raw cow’s milk was 7.22, 3.11, 2.18 or 3.15 cfu/ml for total bacterial, yeasts and molds, Enterobacteriacae or psychrotrophes, respectively. Those required at least 15, 20, 20 or 30 min ozonation at the rate of 400 mg O3/h to be significantly equal or less than those of 4.32, 1.05, <1 or 1.60 of the heat treated one at 72°C for 15 sec towards these microorganisms in order.
2. Pathogenically, initial inoculated log counts of certain pathogenic strains including, Staph. aureus, B. cereus E. coli, S. typhimurium and Sh. flexneri were 8.3, 8.5, 8.4, 8.2 and 7.4 cfu/ml, in order. The corresponding log count reduced to <1 after 25, 25, 20, 20 and 30 min of ozonation at the rate of 400 mg O3/h, respectively.
3. Physiochemically, neither the heat treatment at 72°C for 15 sec nor the ozonation for any time at the rate of 400 mg O3/h led to any significant difference neither in the contents of total solids, fat, protein, lactose, ash, titratable acidity (TA) nor the pH value of cow’s milk.
Part II: Application of ozonation technique in Domiati cheese production
In this part, full cream cow’s milk was divided into 3 equal portions. The 1st portion (control) was heated at 72°C/15sec, cooled to 40o C. The 2nd and 3rd portions were ozonized for 20 and 30 min, respectively using the same ozone generating device at the same previous rate. Then the ozonized milks were warmed to 40o C. All three portions were salted to 5% NaCl, renneted at the rate of 5ml/10 kg milk and incubated at 40o C up to curdling. The curds were separately scooped in wooden frames lined with cheese cloth to drain whey and consolidated by a slight pressure for 24 h. After 24 h of whey drainage, the cheese curd was cut into pieces (~ 500g) and transferred to plastic containers. The obtained cheeses were pickled at room temperature (25 ± 2°C) for 3 months in their respective whey (previously heated to 85°C and then cooled to 25°C).
The obtained results of the 2nd part could be summarized as follow:
1. Physiochemically, Domiati cheese made from heat treated milk was significantly distinguished with higher yield, fat/dry matter (DM), protein/DM, lactose/DM and ash/DM as well as lower DM contents versus those made from ozonized milk. While the salt/moisture content of cheese was significantly influenced neither by the kind of milk treatment nor by prolonging of cheese pickling period, which led to increase all compositional components studied except of the lactose/DM, which thereby decreased.
2. Maturationally, Domiati cheeses made using ozonized milk ripened more rapidly, where they possessed higher levels of water soluble nitrogen/total nitrogen (WSN/TN), formol and Schilovich numbers versus those of heat-treated milk cheese, which however contained higher TA % and lower pH value compared with the former. Opposite to the pH value, the other ripening indices rose as the cheese ripening period progressive.
3. Rheologically, although Domiati cheese made from heat treated milk had the higher hardness value than those made using ozonized milk, those possessed higher gumminess and springiness. While the cohesiveness criterion was not varied either among the kind of cheese milk treatment or along pickling period, which caused significant increases in all other cheese textural parameters.
4. Microbiologically, heat treated-milk Domiati cheese contained the highest log count of total bacterial count (TBC) as well as yeasts and molds versus those of ozonized-milk cheese regardless the ozonation time. TBC increased in the 1st month then decreased gradually by prolonging the pickling period of cheese to the 3rd month. Log count of yeasts and molds in cheese declined along pickling period. Neither coliform bacteria, Staphylococcus aureus nor Salmonella typhimurium was detected in all Domiati cheeses whether made from heat treated or ozonized milks, whether when fresh or along the pickling period.
5. Organoleptically, ozonized-milk Domiati cheese gained appearance, body and texture as well as total scores higher than those of heat treated-milk cheese. The flavor score of 20 min-ozonized milk cheese was as high as that of heat treated one followed by that of 30 min-ozonized milk cheese. During pickling period, scores of all sensory criteria of Domiati cheeses, opposite to the appearance, increased gradually until the end of the pickling period (3 months).
Part III: Application of ozonation technique in Kariesh cheese production
In this part, skimmed cow’s milk was divided into three equal portions. The 1st portion (control) was heated at 72°C/15sec, cooled to 40o C. The 2nd and 3rd portions were ozonized for 20 and 30 min, respectively using the same ozone apparatus mentioned above at the same rate. Then the ozonized milks were warmed to 40o C. All three portions were inoculated with 2% of freshly activated YC starter culture and incubated at 40o C up to curdling. The curds were cut and filled into stainless steel molds lined with cheese cloth and consolidated by a slight pressure for 24 h. The blocks of curd were then cut, dry salted using 2% NaCl (w/w), packaged into plastic containers and kept for 21 days at refrigerator (5 ± 2°C).
The obtained results of the 3rd part could be summarized as follow:
1. Physiochemically, Kariesh cheese made from heat treated skimmed milk was significantly distinguished with higher yield, protein/DM and lower DM contents than those made using ozonized skimmed milk. While both of lactose/DM, fat/DM, ash/DM and salt/moisture contents were not exhibited any response towards the treatment of skimmed milk prior cheese making. The prolonging cold storage period (CSP) of cheese led to increase in DM, protein/DM as well as ash/DM contents and to decrease in lactose/DM content. While both of fat/DM and salt/moisture contents were not influenced.
2. Maturationally, Kariesh cheeses made using heat treated-skimmed milk was characterized with WSN/TN and TA contents lower than those of ozonized skimmed-milk cheese. Nevertheless, pH value did not vary. As the CSP of cheese progressed, both of WSN/TN and TA contents gradually increased, while the pH value decreased until the end of CSP (3 weeks).
3. Rheologically, Kariesh cheese made from skimmed milk ozonized for any time was particularized with hardness as well as gumminess values higher and springiness value lower than those made using heat treated skimmed milk. During CSP of cheese, both hardness and gumminess values gradually increased while that of springiness decreased. Whilst the cohesiveness criterion was not varied either among the kind of cheese milk treatment or along CSP of cheese.
4. Microbiologically, heat treated-milk Kariesh cheese contained the lowest log count of Streptococci and Lactobacilli as well as the highest log count of yeasts and molds versus those of ozonized skimmed-milk cheese. Both trending directions became more pronounced as the ozonation time of cheese skimmed milk rose. Log counts of Streptococci and Lactobacilli increased as well as that of yeasts and molds decreased as the CSP prolonged. Neither coliform, Staphylococcus nor Salmonella was detected in all Kariesh cheese treatments whether when fresh on at the end of CSP (3 weeks).
5. Organoleptically, although the appearance scores of Kariesh cheeses were not influenced, ozonized skimmed-milk cheese gained body and texture as well as total scores higher and flavor score lower than those of heat-treated skimmed milk cheese. The flavor score of 20 min-ozonized milk cheese was as higher than that of 30 min-ozonized milk cheese. During CSP, both of appearance, flavor and total scores of Kariesh cheese lowered while the body and texture score enhanced gradually until the end of the CSP (3 weeks).
Finally, this study provides a realistic solution to small laboratories for the manufacture of cheese, which controls most of the processed milk, a new idea applicable to the production of safe food instead of using preservatives, whether authorized or unauthorized, to cover its inability to acquire pasteurization devices in violation of the legislation.