الفهرس 
Biopreservation of Domiati Like Cheese Using Protective Lactic Acid Bacterial CultureOnly 14 pages are availabe for public view
 |  | from | 117 |  |  |
| | | from | 117 | | |
Abstract
Lactic acid bacteria (LAB) are used in the manufacture of many food products, mainly in the manufacture of fermented dairy and cheese. Their applications in these products are aimed at producing lactic acid and flavor compounds and improving texture of the final
product. In addition, the importance of LAB in fermented food industry is increased when they are able to produce inhibitory compounds against pathogenic and spoilage species in food. This
kind of biologyical competition is being exploited to develop protective microbial cultures,
which have many applications in food preservation. This approach is known as biological food preservation.
On the other hand, Domiati cheese is considered one of the most important dairy products in Egypt. It is made from buffalo or cow milk, or a mixture of both. It is usually made from salted (5-12%) raw milk. Thus, some bacterial species, especially salt tolerant such as Staphylococcus aureus, can be found in the final cheese.
The general objective of this study is to evaluate the ability of some LAB isolates to inhibit the growth of Staphylococcus aureus in order to use some of them as a preventive culture in the production of whey less Domiati-like cheese. This goal was accomplished as described below.
1-Evaluation of the ability of some LAB isolates to produce antimicrobial
compounds against Staphylococcus aureus
The ability of 542 LAB isolates, previously isolated from raw milk and different milk products from many regions in Egypt, were screened for the production of evaluated to produce
inhibitory compounds against Staphylococcus aureus using DROP test, micro-dilution technique and agar diffusion method.
The results indicated that cell free extract supernatants of 8 isolates were able to inhibit growth of Staphylococcus aureus, suggesting the possible production of inhibitory compounds.
The thermal stability of the inhibitory compounds was evaluated and they found to be thermally stable even after treating the growth filtrate at 121°C for 20 min. The highest inhibitory effect against Staphylococcus aureus was observed at pH 3-4. Among 8 isolates, 3 produced inhibitory substances that have proteinaceous (peptide) nature.
77
2- Genetic identification of isolates that are capable of producing
antimicrobial compounds against Staphylococcus aureus Eight isolates of LAB with importante activity against Staphylococcus aureus were
identified genetically by sequencing 16S r-DNA gene and identified as follows:
Lactobacillus plantarum FFNL593
Lactobacillus plantarum FFNL158
Lactobacillus plantarum FFNL188
Lactobacillus plantarum FFNL190
Enterococcus faecium FFNL 417
Lactobacillus plantarum FFNL 94
Lactobacillus plantarum FFNL739
Lactobacillus plantarum FFNL1810
These strains were assessed to evaluate their safety in order to be used in the manufacture of some milk products. The evaluation included the ability to hydrolyze gelatin, DNA and blood
and to produce histamine production as well as their resistance to various antibiotics. The results indicated that these strains were not able to hydrolyze gelatin, DNA, or blood, and none
of had the ability to produce histamine. Also, these strains did not show resistance to the tested antibiotics.
3- Evaluation of the protective effect of some strains of Lactobacillus
plantarum for the control of Staphylococcus aureus in wheyless Domiati-like cheese
The ability of Lactobacillus plantarum strains FFNL1810 and FFNL739 to inhibit
Staphylococcus aureus in whey-less Domiati-like cheese was studied. As these strains had the highest antagonistic activity against Staphylococcus aureus, shown by in vitro assessments, they were selected to challenge the pathogen in Domiati-like cheese. The cheese was made
using a mixture composed of dried skimmed milk, concentrated milk proteins (70%) and dried, butter, which were reconstituted in water. This reconstituted milk mixture (RMM) was
homogenized and divided into 2 equal parts. The first part was salted (8%). Following pasteurization of salted and un salted parts, they were cooled to 40ºC and unsalted part was
inoculated with a commercial yogurt culture and further divided into 2 parts. Staphylococcus 78 aureus was added to the first part at a concentration of 105 cfu/ml.