BACKGROUND: Kefir is a fermented milk product containing some anticarcinogenic organic compounds with nutritional benefits, which made it one of the natural dairy beverages extensively consumed. OBJECTIVES: The present study was conducted to assess the effect of two selective probiotics on the values of acidic criteria and probiotic survival in the kefir produced in this study. METHODS: In the first step, the cow milk, preheated at 90oC for 5 min, was inoculated with the commercial starter and divided into two groups. They were complemented with L. acidophilus LA-5 and L. paracasei 431 and incu-bated at 30oC for 6 h. They were then preserved at refrigerated temperature up to 14 days and then sampling was carried out to evaluate the changes of values of organic acids (lactic acid and acetic acid), pH, titratable acidity and survival of probiotic complemented bacteria on the 1st, 7th, and 14th days. RESULTS: The pH values of L. acidophilus LA-5 and L. paracasei 431 were 4.34 and 4.36 at the beginning of the cold storage and reached 4.27 and 4.31 at day 14. The acidity of L. acidophilus LA-5-complemented kefir on the 1st day was 0.80 gr/100 gr higher than L. paracasei 431-complemented kefir which showed 0.72 gr/100 gr. Lactic acid was ranging from 1.57 to 2.40 gr/100 mL or 2.17 to 2.42 gr/100 mL (from the 1st to the 14th day) in the kefirs complemented with L. acidophilus LA-5 and L. paracasei 431, respectively. In the kefirs complemented with L. acidophilus LA-5 and L. paracasei 431, the acetic acid was stable (from 0.11 to 0.13 gr/100 mL) during 14 days but increased in the later (from 0.11 to 0.23 gr/100 mL) .The survival of both bacteria was higher than 7 logs CFU/gr in the kefir. CONCLUSIONS: Adding L. acidophilus LA-5 and L. paracacei 431 can moderate the acidity of the kefir and extend the survival of complementary probiotics at a standard level during two weeks of cold preservation.

BACKGROUND: The probiotics must be alive in sufficient numbers and one of the main stress factors that probiotic strains should tolerate is food preservatives, like herbal essential oils (EOs). To provide a balance between sensory accept-ability and antimicrobial efficacy, the use of sub-lethal concentrations of EOs in combination with other preservation methods has been proposed. OBJECTIVES: The aim of this study was to evaluate the effect of sub-lethal level of Ziziphora clinopodioides essential oil (ZEO) stress on viability of microencapsulated Lactobacillus acidophilus, and Bifidobacterium bifidum, and examine physicochemical and sensory properties of probiotic yoghurt during 28 days of storage. Moreover, the survival of probi-otics was evaluated in gastrointestinal conditions. METHODS: The sub-lethal and lethal levels of ZEO were determined for Lactobacillus acidophilus and Bifidobacterium bifidum. Both probiotics (109 CFU/mL) were exposed to sub-lethal dose of ZEO on MRS broth for about 2 h and then microencapsulated with alginate-chitosan. First, viability of encapsulated probiotics was estimated in simulated gastrointestinal conditions. After preparation of yoghurt, enumeration of free and encapsulated probiotics in yoghurt was done. Finally, physicochemical and sensory properties of probiotic yoghurt were measured. RESULTS: According to the GC-MS, Thymol (41.70%), alpha-terpineol (7.31%) and carvacrol (5.39%) were the most commonly detected components in the ZEO. The lethal doses of ZEO for L. acidophilus and B. bifidum probiotic bacteria were 1750 and 1500 ppm, respectively. Encapsulation and exposure of probiotics to sub-lethal dose of ZEO increased significantly the survival of probiotics in both gastrointestinal conditions and during 28 days of yoghurt storage (p <0.05). Furthermore, encapsulation and exposure of probiotics to sub-lethal dose of ZEO did not significantly change the pH of yoghurt samples (p >0.05). On the other hand, syneresis was not significantly different in all samples (p >0.05). The group exposed to ZEO obtained the lowest score for flavor. However, significant differences were observed between the exposed and other groups in the term of flavor, texture and overall acceptability (p <0.05). CONCLUSIONS: Exposure to sublethal concentration of ZEO could be used as a prebiotic in probiotic yoghurt contain-ing probiotics so as to improve the survival and viability of microcapsulated probiotics and enhance some of the physico-chemical and sensory properties.

BACKGROUND: Staphylococcal foodborne intoxication is the most common cause of foodborne illnesses by Staphylococcus aureus strains and most are caused by the enterotoxins of S. aureus. Staphylococcal enterotoxin A (SEA) is the most frequently responsible for staphylococcal food poisoning outbreaks. From a food safety and human health point of view, lactic acid bacteria (LAB) may provide a promising strategy in the fight against S. aureus.OBJECTIVES: Increasing product shelf life, and enhancing the safety of food and human health using natural microflora are the aims of this study. METHODS: In this study we evaluate the inhibitory effects of three lactobacillus strains isolated from yoghurt, namely lactobacillus acidophilus, lactobacillus fermentum and lactobacillus paracasei, on the growth and enterotoxin production of Staphylococcus aureus by co-incubating each strain with enterotoxigenic S. aureus at two temperatures: 25 and 35°C. Expression of the SEA gene of S. aureus was assessed by real-time PCR. RESULTS: All the strains decreased the bacterial count at both temperatures compared to the control. This effect was greater at 25°°C than at 35°C. The production of SEA, SEC and SEE was inhibited by all the isolates tested. Furthermore, expression of the sea gene was significantly suppressed in S. aureus co-cultured with the lactobacillus isolates and the greatest impact was on Lactobacillus acidophilus at 35 ° C. CONCLUSINS: This research highlights the potential of lactic acid bacteria isolated from traditional foods for use as natural preservatives in foodstuffs and suggests a new approach for biocontrol of Staphylococcus aureus.