Nese Basaran

ABSTRACT:  The dielectric properties must be defined to design efficient radio frequency (RF) and microwave (MW) processes by the food manufacturers. The objective of this study was to understand how frequency, temperature, and muscle fiber orientation influence the dielectric properties. The eye of round ( Semitendinosus ) muscle was selected because it contains large, relatively uniform muscle cells with similar muscle fiber orientation and relatively uniform chemical composition throughout the tissue. Dielectric properties were measured using an open‐ended coaxial probe technique at 27, 915, and 1800 MHz and temperatures between −5 and 130 °C. Power penetration depth was calculated. Since many commercially prepared, thermally processed, ready‐to‐eat entrees are made with frozen meat, dielectric property measurements were started from −5 °C. The dielectric constant and dielectric loss factors were often higher for muscle with the muscle fiber measured in a parallel orientation to the probe compared to samples of the same treatment (for example, fresh or frozen) in a perpendicular tissue orientation at the same frequency and temperature. Dielectric constant and loss values for frozen beef tended to be higher than fresh beef at the same temperature and frequency. Tissue orientation appeared to have a greater effect on dielectric loss values at lower frequencies. Penetration depth tended to be greater when the direction of propagation was perpendicular to the muscle fiber.

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 K_m values for non-glycosylated and glycosylated xylanases were 1·4 mg ml⁻¹ and 4·2 mg ml⁻¹, respectively, and V_max 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.

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.