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Articles by I. Nahvi
Total Records ( 2 ) for I. Nahvi
  I. Nahvi and H. Moeini
  In this study of twenty-five samples which were collected from dairy producing centers in the city of Isfahan, 30 yeast strains were isolated using Malt Extract Broth (MEB) containing 0.1 gl-1 chloramphenicol and Yeast Extract Glucose Chloramphenicol Agar (YGCA). Of the isolated strains, 11 with the ability to lactose fermentation were isolated (M1-M11). These strains were identified by morphological and physiological properties. From these 11 strains, six were identified as Kluyveromyces lactis, four as Kluyveromyces marxianus and one as Candida versatilis. In the next step, the amount of produced single cell protein, SCP, from whey; whey including nitrogen supplementation and whey with mixed yeast cultures in these strains was measured. Among these strains, M2 that was identified as K. lactis had the most SCP production from whey with 11.79 gl-1. It was found that the ammonium sulfate as a nitrogen source has a significant effect on biomass yield so that amount of produced biomass of the M11 strain (K. marxianus) increase from 11.54 gl-1 (from whey without nitrogen supplementation) to 15.75 gl-1 (in the presence of nitrogen source). The co-cultures of yeast strains with Saccharomyces cerevisiae were evaluated. In the mixed yeast cultures of these yeast strains and S. cerevisiae, the M2 strain which was identified as K. lactis had the most biomass production, 22.38 gl-1. ONPG assay of beta-galactosidase in yeast strains found that a strain of K. lactis (M2) has the highest enzyme activity (8103 Eu ml-1). These strains can be used for removal of whey pollutant, SCP & ethanol production and treatment of lactose in dairy food.
  M. Mirhosaini , I. Nahvi , R. Kasra Kermanshahi and M. Tavassoli
  Nisin is a bacteriocin produced by Lactococcus lactis strains and has been used internationally as food preservative. In this study bacteriocin producing bacteria were isolated from dairy products and milk by MRS agar. To identify the bacteriocin biochemical tests were carried out. Also the effected of pH, autoclaving temperature and proteases such as Pepsin and Proteinase k were studied. The results showed that the newly isolated bacteriocin has different stability in acidic pH in comparison to Nisin. Unlike Nisin it loses its activity in acidic pH. The molecular weight of isolated bacteriocin was determined by SDS-PAGE. It had the same molecular weight as Nisin. Also the inhibitory effects of new bacteriocin and Nisin on SDS-PAGE were compared. It had similar inhibitory effect as Nisin. For further identification, PCR was carried out with Nisin specific primers and control primers to 16s rRNA gene. Although, positive result was obtained for the control gene, no result was obtained with specific primer. The inhibitory effect of isolated bacteriocin on Bacillus cereus and Listeria monocytogenes was also studied. The growth of both strains was inhibited by the bacteriocin and more inhibition was observed on Listria monocytogenes than Bacillus cereus. Finally, to optimize the production of bacteriocin the effect of pH and temperature were studied. The optimum conditions for bacteriocin producing bacterium were pH 6 and 37°C.
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