This study examined the effect of different apple cultivars upon the UV inactivation of Escherichia coli O157:H7 strains within unfiltered apple cider. Apple cider was prepared from eight different apple cultivars, inoculated with approximately 10 6 to 10 7 CFU of three strains of E. coli O157:H7 per ml (933, ATCC 43889, and ATCC 43895), and exposed to 14 mJ of UV irradiation per cm 2 . Bacterial populations for treated and untreated samples were then enumerated by using nonselective media. E. coli O157:H7 ATCC 43889 showed the most sensitivity to this disinfection process with an average 6.63-log reduction compared to an average log reduction of 5.93 for both strains 933 and ATCC 43895. The highest log reduction seen, 7.19, occurred for strain ATCC 43889 in Rome cider. The same cider produced the lowest log reductions: 5.33 and 5.25 for strains 933 and ATCC 43895, respectively. Among the apple cultivars, an average log reduction range of 5.78 (Red Delicious) to 6.74 (Empire) was observed, with two statistically significant (␣ < 0.05) log reduction groups represented. Within the paired cultivar-strain analysis, five of eight ciders showed statistically significant (␣ < 0.05) differences in at least two of the E. coli strains used. Comparison of log reductions among the E. coli strains to the cider parameters of°Brix, pH, and malic acid content failed to show any statistically significant relationship (R 2 > 0.95). However, the results of this study indicate that regardless of the apple cultivar used, a minimum 5-log reduction is achieved for all of the strains of E. coli O157:H7 tested.
Twenty-five strains of Lactococcus lactis subspecies lactis and subspecies cremoris obtained from dairy industry and environmental collections were examined by 16S RNA automated ribotyping profiles and site-specific PCR (S-PCR). By automated ribotyping, the majority of strains were classified in accordance with phenotypic characterization, with the exception of one lactis (220) and two cremoris (BO32 and 140) strains. A complete differentiation of subspecies lactis and cremoris in agreement with conventional phenotypic methods was achieved by S-PCR with a set of site-specific primer pairs (PR1, RM4, and F3) designed particularly from a deletion region found in subspecies cremoris, but not in lactis. Therefore, S-PCR with primers (PR1, RM4, and F3) is a rapid and very sensitive method for the distinction of lactis and cremoris subspecies in dairy production.
P. BASARAN, Y.D. HANG, N. BASARAN AND R.W. WOROBO. 2001.
Aims: The main goal of this study was to characterize the xylanase (xynA) gene from Pichia stipitis NRRL Y‐11543.
Methods and Results: The xylanase gene was cloned into pUC19 in Escherichia coli DH5αF′ and selected by growth on RBB‐xylan. All functional clones contained a recombinant plasmid with an insert of 2·4 kbp, as determined by restriction mapping. The nucleotide sequence of the P. stipitis xylanase gene consisted of 1146 bp and encoded a protein of 381 amino acids with a molecular weight of 43 649 Da. The sequence contained a putative 20‐amino acid N‐terminal signal sequence and four N‐linked glycosylation sites. The Km values for non‐glycosylated and glycosylated xylanases were 1·4 mg ml−1 and 4·2 mg ml−1, respectively, and Vmax values were 0·8 and 0·082 μmol min−1 mg−1 protein, respectively.
Conclusions: Xylanase, a rarely found enzyme in yeast species, has been characterized in detail.
Significance and Impact of the Study: The results of this study can be used to develop better xylanase‐utilizing yeast strains.
Obesity is a global epidemic effecting the health and life style of millions of people in both developed and developing countries. In this article, current medical treatments, recent scientific progresses toward understanding obesity, and future potentials in biotechnology applications in pharmaceutical research are reviewed in detail.
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