الفهرس 
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Abstract
Soft cheese is one of the oldest dairy products with the best nutritive value and health keeping function. It is popular in many countries worldwide with palatable taste and various flavor.
Salt is an important component and it affects various aspects of cheese including the shelf life, enzyme activity, flavor and microbial proliferation during ripening. Many consumers prefer low salt soft cheese due to health issues such as hypertension, obesity, and heart attacks.
Therefore, there is an increasing requirement in the dairy industry to prolong product shelf life of low salt cheese and inhibit spoilage caused by aerobic spore formers by natural preservatives and/or new methods of conservation.
Some samples of low salt soft cheese were collected randomly from different localities in Alexandria and El Behera governorates for quality evaluation (Physicochemical examination) and studying the incidence of aerobic spore forming bacteria in these samples.
In the second part of the study, the antimicrobial agents (protective culture, nisin, lysozyme and natamycin) were studied to inhibit the activity of 28 isolates of spore forming bacteria (28 strains were isolated from commercial low soft cheese collected from Egyptian market) to evaluate their effectiveness.
In the third experimental part of the study, low salt soft cheese was manufactured in the lab and examined for physicochemical properties and studying the effect of natural antimicrobial additives (protective culture, nisin, natamycin and lysozyme) on the growth of these bacteria and their effect on physicochemical properties and sensory characteristics.
7.1. Compositional Quality Evaluation:
7.1.1. pH value: The mean pH value of examined low salt soft cheese samples was 5.83±0.52 in Alexandria while in El-Behera was 5.40±0.70.
7.1.2. Acidity percent: The acidity percent of examined low salt soft cheese samples had mean value of 0.53±0.31% in Alexandria while in El-Behera was 0.67±0.35%.
7.1.3. Moisture content: The mean value of moisture percent of examined low salt soft cheese samples was 57.95±3.54% in Alexandria while in El-Behera was 56.76±4.91%.
7.1.4. Fat/DM: The mean value of fat/DM percent of examined low salt soft cheese samples was 23.72±5.76% in Alexandria while in El-Behera was 25.45±12.99%, these results compared with Egyptian standards.
7.1.5. Salt percent: Salt percent of examined low salt soft cheese samples was 1.80±0.49% in Alexandria while in El-Behera was 1.78±0.62%.
7.2. Incidence of aerobic spore forming bacteria in the examined low salt soft cheese samples:
Incidence of aerobic spore forming microorganisms in samples collected from Alexandria governorate was 95.83% with mean value of 8.63×102± 7.87×10² while the incidence in samples of El-Behera governorate was 100% with mean value of 5.71×102± 4.10×10².
7.3.Antibacterial activity of natural additives against isolated aerobic spore forming bacteria using agar well diffusion test :
Lysozyme showed the highest inhibition zone of 32.90±19.30 followed by protective culture which showed inhibition zone of 26.10±10.20 then nisin inhibition zone was 25.30±11.9,while natamycin showed no effect against aerobic spore forming bacteria.
7.4. Effect of natural antibacterial additives with various concentrations on physicochemical examination of laboratory manufactured low salt soft cheese during storage period (30 days) at 4±1°C.
7.4.1. Pattern of pH value of laboratory manufactured soft cheese treated with different concentrations of natural additives:
pH value of control cheese samples at 1st day of analysis was 6.50±0.141 then decreased to 6.44±0.007 at 30th day of analysis, pH of cheese treated with protective culture (40 mg kg -1) at 1st day of analysis and 30th day of analysis were 6.17±0.007, 5.18±0.141, respectively, pH of lysozyme treated cheese at 1st day of analysis was 6.70±0.007 then decreased to 6.50±0.007 at 30th day of analysis. pH of cheese treated with nisin (25 mg kg-1) at 1st day of analysis ,and 30th day of analysis were 6.53±0.007, 6.42±0.14 in a respective way, pH of cheese treated with combined nisin and lysozyme (25 mg kg -1/100 mg kg -1) at 1st day of analysis was 5.83±0.007 then decreased 5.73±0.028 at 30th day of analysis.
7.4.2. Pattern of Acidity content of laboratory manufactured soft cheese treated with different concentrations of natural additives :
Acidity content of cheese free (control) was 0.23±0.028 at 1st day of analysis then increased at 30th day of analysis to reach 0.32±0.028. Acidity of cheese treated with protective culture (40 mg kg -1) at 1st day of analysis 0.42±0.014 then increased at 30th day of analysis to reach 0.52±0.014. Acidity content of lysozyme treated cheese (100 mg kg -1) at 1st day of analysis was 0.23±0.042 then increased to 0.31±0.007 at 30th day of analysis. Acidity content of cheese treated with nisin (25 mg kg -1) at 1st day of analysis 0.23±0.007 then increased to 0.27±0.028 at 30th day of analysis. Acidity results of cheese treated with combined nisin and lysozyme (25 mg kg -1/100 mg kg -1) at 1st day of analysis 0.27±0.007 then increased at 30th day of analysis to 0.57±0.014. Acidity content of cheese treated with combined protective culture and natamycin (40mg kg -1/25 mg kg -1) at 1st day of analysis was 0.40±0.007 then at 30thday of analysis was 0.52±0.007.
7.4.3. Pattern of moisture content of laboratory manufactured Soft cheese treated with different concentrations of natural additives:
Data presented that moisture content of cheese free (control) was 55.23±1.28 at 1st day of analysis then became 51.36±1.32 at 30th day of analysis. Moisture percent readings for cheese treated with protective culture (40 mg kg-1) at 1st day of analysis,30th day of analysis were 58.26±0.29, 57.20±0.00 in a respective way. Moisture percent readings of lysozyme (100 mg kg-1) at 1st day of analysis, 30th day of analysis were 53.03±0.67, 50.13 ±0.27 in a respective way. Moisture percent readings of nisin (25 mg kg-1) at 1st day of analysis 63.18±0.01 then decreased to 60.36±3.16 at 30th day of analysis .Moisture content of cheese treated with nisin and lysozyme (25 mg kg-1/100 mg kg-1) was 67.56±0.15 at 1st day of analysis then became 64.79±0.22 at 30th day of storage. Moisture content of cheese treated with protective culture and natamycin (40 mg kg -1/25 mg kg -1) at 1st day of analysis was 65.09±0.55 then decreased to 60.04±0.03 at 30th day of analysis.
7.4.4. Pattern of fat content of laboratory manufactured soft cheese treated with different concentrations of natural additives:
Fat content of cheese free (control) at 1st day of analysis was 14.95±0.071 and finally became 15.05±0.071 at 30th day of storage. Cheese treated with protective culture (40 mg kg-1) fat content at 1st day of analysis, 30th day of analysis were 14.95±0.071,15.05±0.071, respectively. Fat content of cheese treated with nisin and lysozyme (25 mg kg-1/100 mg kg-1) at 1st day of analysis 14.95±0.007 then decreased at 30th day of storage. Fat content of treated cheese with protective culture and natamycin (40 mg kg -1/25 mg kg -1) at 1st day of analysis 14.95±0.141 then became 14.90±0.071 at 30th day of storage.
7.4.5. Pattern of salt content of laboratory manufactured soft cheese treated with different concentrations of natural additives:
Salt content of cheese free (control) was 1.46±0.00 at 1st day then increased at 30th day of storage to reach 1.56±0.14.. Salt content of cheese treated with protective culture (40 mg kg-1) at 1st day of analysis, 30th day of analysis were 1.46±0.141, 1.80±0.00 respectively. Salt content of cheese treated with lysozyme (100 mg kg-1) was 1.46±0.00 at 1st day then increased at 30th day of storage. Salt content of cheese treated with nisin and lysozyme (25 mg kg-1/100 mg kg-1) was 1.47±0.283 at 1st day of analysis then increased to 1.87±0.283 at 30th day of storage.
7.5. Growth pattern of aerobic spore forming bacteria in laboratory manufactured Soft cheese treated with different concentrations of natural additives during storage period (30 days) at 4±1°C.
Results illustrated that all-natural antibacterial additives have a vital role in reduction of aerobic spore forming bacteria in soft cheese principally cheese treated with combination of nisin and lysozyme reduced the count from 419±0.71 at initial analysis to 46±0.71at 30th day of storage. Also cheese treated with lysozyme alone the count decreased from 573±0.71 to 46±0.71 at last analysis. Cheese treated with nisin, the count decreased from 591±0.71 to 73±0.71 at the end of storage period also the usage of protective culture had a principal role in reduction of spore formers, but cheese made without any additives, spore forming bacterial count was in continuous increment as increased from 864±0.71 to 2109±0.71 at the end of storage period.
7.6. Effect of different concentrations of natural antibacterial additives on Sensory evaluation of examined laboratory made Soft cheese during storage period (30 days) at 4±1°C:
7.6.1. Pattern of appearance of laboratory manufactured soft cheese treated with different concentrations of natural additives :
Appearance of cheese treated with protective culture (40 mg kg -1) at 1st day of analysis was 7.93±1.28 then increased gradually to 8.12±0.19 at 30th day of analysis. Appearance of cheese treated with combination between protective culture plus natamycin ( 40 mg kg -1/25 mg kg -1) was 7.67±1.23 at 1st day then increased to 7.98±0.16 at 30th day of storage .
7.6.2. Pattern of taste and flavor of laboratory manufactured soft cheese treated with different concentrations of natural additives:
Flavor and taste of cheese treated with protective culture (40 mg kg-1) was 8.40±0.828 at 1st day of analysis then increased to 8.66±0.13 at 30th day of storage. Flavor and taste values for cheese treated with nisin and lysozyme (25 mg kg -1/100 mg kg -1) at 1st day of analysis, 30th day of analysis were 7.13 ±1.51, 6.10±0.53 in a respectively, these treatments affected positively on taste of soft cheese.
7.6.3. Pattern of Texture of laboratory manufactured soft cheese treated with different concentrations of natural additives:
Texture values of cheese free (control) increased from 5.20±2.68 at initial day of analysis to 7.89±1.41 at 30th day of storage .Texture readings decreased was 8.40±0.632 at 1st day and finally became 7.67±0.39 at 30th day of storage in cheese treated with protective culture (40 mg kg-1), this considered the best effect on texture of soft cheese compared to other additives.
7.6.4. Pattern of Aroma / smell of laboratory manufactured soft cheese treated with different concentrations of natural additives:
Aroma / smell of cheese treated with protective culture (40 mg kg-1) was 7.33±2.13 at initial analysis then increased sharply to 7.98±0.34 at last analysis (30th day of storage). This considered the best improvement of smell of soft cheese. Aroma / smell of cheese treated with nisin and lysozyme (25 mg kg -1/100 mg kg -1) at 1st day of analysis was 7.00±1.73 then increased to 7.89±0.45 at 30th day of storage.
7.6.5. Pattern of overall acceptance of laboratory manufactured soft cheese treated with different concentrations of natural additives:
Overall acceptance of cheese treated with protective culture (40 mg kg-1) decreased from 8.13±0.99 at 1st day to 8.03±0.07 at 30th day of storage. Overall acceptance of cheese treated with protective culture + Natamycin (40 mg kg -1/25 mg kg -1) at 1st day of analysis, 30th day of analysis were 8.00±1.13 ,7.28±0.41 respectively. These additives improve the overall acceptance compared to other additives.
Finally, to improve the safety of these product, efforts should be raising awareness of the importance of hygiene barriers and raw milk quality as well as improved process control can be suggested. We can recommend that the receiving of raw milk should be carefully monitored and only obtained from suppliers apply good manufacturing practices. from the other hands, the strict hygienic measures of cleaning and sanitization of all food contact surfaces as well as prevention of environmental contamination.