Thea Aukrust

Purification and amino acid sequence of sakacin A, a bacteriocin from Lactobacillus sake Lb706.

Sakacin A, a bacteriocin produced by Lactobacillus sake Lb706 and which inhibits the growth of Listeria monocytogenes, was purified to homogeneity by ammonium sulphate precipitation and ion-exchange, hydrophobic-interaction and reversed-phase chromatography. The complete amino acid sequence of sakacin A was determined by Edman degradation. The bacteriocin consisted of 41 amino acid residues and had a calculated M(r) of 4308.7, which is in good agreement with the value determined by mass spectrometry. The structural gene encoding sakacin A (sakA) was cloned and sequenced. The gene encoded a primary translation product of 59 amino acid residues which was cleaved between amino acids 18 and 19 to yield the active sakacin A. Sakacin A shared some sequence similarities with other bacteriocins.

Transformation of Lactobacillus strains used in meat and vegetable fermentations

Abstract For transformation of Lactobacillus plantarum and Lactobacillus sake strains of meat and vegetable origin, electroporation using the electroporation solutions 952 m m sucrose with 3·5 m m MgCl2 or 30% polyethylene glycol (PEG 1500) was found to be efficient. The highest transformation efficiencies for all the meat strains and most of the vegetable strains were obtained using PEG 1500. Although the transformation efficiencies varied, the strains tested showed essentially the same response pattern to different electrical pulses, as illustrated by response surface plots. For screening purposes a setting of 1·5 kV and 400 ohm pulse control resistance is recommended. For optimization of transformation efficiency for specific strains, selected combinations of voltage and pulse control resistance along the optimum shown in the plots can be used. Transformation efficiencies can be further improved by using medium shift from MRS without dextrose to MRS, and by including a magnesium solution in the washing procedure. The combined effect of these pre-treatments has raised the transformation frequency of previously low transforming strains with a factor of 103, giving transformation efficiencies sufficient for most practical applications.

Lactic acid fermentation influence on sugar content and colour of deep-fried carrot chips

Abstract Carrot chips with a light red-yellow colour were obtained by lactic acid fermentation of carrot slices in a brine prior to deep-frying. The fermentation process decreased the content of reducing sugars up to 75%, thereby restricting the extent of Maillard reactions during heating. Rinsing the slices after fermentation but prior to deep-frying enhanced sugar removal. Three strains of Lactobacillus were tested. Strain NCIMB 40450 reduced sugar levels faster than strains NCDO 1193 and NCDO 1752. The best colour properties were obtained when carrot slices were deep-fried after 24 h fermentation.

Influence of brine composition on yield and quality of deep-fried fermented carrot chips

Deep-fried fermented carrot chips are a new product produced by including a fermentation step prior to the traditional deep-frying process. Composition and osmolarity of the brine used in the fermentation stage of carrot chips production were shown to be of importance for frying time, fat content, yield and texture of the chips. In hypotonic brines the water content of the carrot increased resulting in a prolonged frying time and a darker product. When calcium was used in the brine a lower final pH was observed, and the fat absorption of the carrot during frying was reduced. NaCl gave better colour and higher yield of chips. The yield increased with increasing amounts of salt in the brine even though the fat content decreased. Prolonged fermentation decreased the yield of carrot chips. No simple relationship between brine composition, texture, colour and yield could be described.