الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
 |  | from | 160 |  |  |
| | | from | 160 | | |
Abstract
In the present study two hundred and eighty random samples of raw milk and pasteurized milk, Kareish, Domiati, Ras and Mozzarella cheese and butter (40 samples each) were collected from various districts in Assiut Governorate, Egypt. The samples were tested for the presence of Pseudomonas spp. The isolated strains were identified by conventional method and then by PCR using 16S rDNA gene. Also, the obtained isolates of P.aeruginosa were examined three virulence genes (toxA, exoS and phzM) by PCR. Moreover, nanoemulsions of N.sativa and C.cyminum EOs were prepared and then characterized by Zeta sizer, FTIR and TEM. Finally, the effect of N.sativa and C.cyminum EOs and their nanoemulsions on the growth and multiplication of P.aeruginosa during manufacture and storage of Kareish cheese was studied.
The obtained results revealed that 37 (92.5%), 19 (47.5%), 25 (62.5%), 7 (17.5%), 25 (62.5%), 22 (55%) and 26 (65%) of raw milk, pasteurized milk, Kareish cheese, Domiati cheese, Ras cheese, Mozzarella cheese and butter were contaminated with Pseudomonas spp., respectively. Using conventional method, the obtained results revealed that 11 different species of Pseudomonas were identified from the obtained isolates that were recovered from the examined samples as 7 (4.22%), 53 (31.93%), 45 (27.11%), 26 (15.7%), 14 (8.4%), 7 (4.22%), 3 (1.81%), 4 (2.41%), 5 (3.01%), 1 (0.60%) and 1 (0.60%) were P.aeruginosa, P.fluorescens, P.fragi, P.putida, P.stutzeri, P.alcaligens, P.pseudoalkaligens, P.lundensis, P.veronii, P.mandelii and P.brenneri, respectively.
Using PCR, the obtained results showed that 7 (2.5%) of the examined samples were contaminated with P.aeruginosa with 4 (10%) from raw milk, 2 (5%) from Kareish cheese and 1 (2.5%) from butter. The confirmed P.aeruginosa strains were then examined for the presence of toxA, exoS and phzM virulence genes by PCR. Results revealed that 6 out of 7 strains (85.71%) had virulence genes from which 4 (57.1%), 6 (85.71%) and 4 (57.1%) harbored toxA, exoS and toxA plus exoS, respectively. The highest incidence of virulence genes was observed in the isolates recovered from the examined raw milk samples.
In the present study, MIC of N.sativa and C.cyminum EOs and their NEs was determined against P.aeruginosa by measuring zones of inhibition. Results showed that MIC of N.sativa and C.cyminum EOs was 0.03%. In addition, MIC of N.sativa NE was 0.1% and C.cyminum NE was 0.25%.
Furthermore, results showed that count of inoculated P.aeruginosa decreased gradually during manufacture and storage of Kareish cheese till the 4th week (9.2×〖10〗^5 cfu/ml). On the other hand, the count decreased slightly earlier (at the 3rd week) when EOs of N.sativa and C.cyminum in concentrations (0.06 and 0.03% for each EO) was added during manufacture of such cheese and became <100 cfu/g at the 4th week of storage.
Meanwhile, the count was clearly decreased in the 3rd week when MIC of N.sativa (0.5 and 0.25%) and C.cyminum (0.25 and 0.1%) NEs were added during manufacture of such cheese and when 1% NE of the two EOs was added, the organism became <100 cfu/g at the 3rd week of Kareish cheese ripening, but for other concentrations of NEs, the microbe was <100 cfu/g at the 4th week of storage.
Furthermore, the sensory evaluation of fresh Kareish cheese manufactured by adding different concentrations of N.sativa and C.cyminum EOs and NEs revealed that manufactured cheese acquired higher score for flavor, body and texture and appearance than control. As adding of EOs to Kareish cheese produced soft and moist cheese texture and flavor.
Also the study included preparation and characterization of NEs of N.sativa and C.cyminum. Results of NEs characterization showed that the prepared N.sativa NE had droplet size 20.1 nm with PDI 0.689 while prepared C.cyminum NE had droplet size 34.24 nm with PDI 0.459 by Zeta sizer. But, TEM results revealed that the prepared N.sativa NE had droplet size 25.4 nm while prepared C.cyminum NE had droplet size 30.5 nm. Thus, TEM is more accurate in measuring droplet size of NEs. In addition to, FTIR analysis of the prepared NEs suggested that there were changes occurred in the functional groups of EOs which were due to NE formation.