Heat adaptation of Escherichia coli K12: Effect of acid and glucose

AbstractThe objective of this work is to investigate the effect of the (possible) acid adaptation during growth in a glucose rich environment on the heat resistance of Escherichia coli K12 MG1655. E. coli cells were grown in TSB and/or TSB dextrose free broth until they reached the stationary phase. Afterwards, the stationary phase cells were added in TSB and/or TSB dextrose free broth and inactivation took place at 54oC and 58oC. It was observed that growth in a glucose rich environment leads to an increased heat resistance, most likely due to a certain level of acid and further heat adaptation via cross protection

In situ production of prebiotic AXOS by the hyperthermophilic xylanase B from Thermotoga maritima in high quality bread

In situ enrichment of bread with arabinoxylan-oligosaccharides (AXOS) through enzymic degradation of wheat flour arabinoxylan (AX) by the hyperthermophilic xylanase B from Thermotoga maritima (rXTMB) was studied. The xylanolytic activity of rXTMB during breadmaking was essentially restricted to the baking phase. This prevented problems with dough processability and bread quality that generally are associated with thorough hydrolysis of the flour AX during dough mixing and fermentation. rXTMB action did not affect loaf volume. Bread with a dry matter AXOS content of 1.5% was obtained. Further increase in bread AXOS levels was achieved by combining rXTMB with xylanases from Pseudoalteromonas haloplanktis or Bacillus subtilis. Remarkably, such a combination synergistically increased the specific bread loaf volume. Assuming an average daily consumption of 180 g of fresh bread, the bread AXOS levels suffice to provide a substantial part of the AXOS intake leading to desired physiological effects in humans.status: publishe

A predictive model for the growth/no growth boundary of Zygosaccharomyces bailii at 7°C and conditions mimicking acidified sauces

The spoilage potential of Zygosaccharomyces bailii has been widely recognized within the food industry. However, few data are available on the growth characteristics of this yeast at low temperature and in the absence of chemical preservatives. In this study, the growth/no growth boundary of Z. bailii was defined at refrigeration temperature (7 degrees C) and at conditions relevant to high-sugar, low-pH foods (such as ketchup and salad dressing), i.e. pH 3.0-5.0 (five levels), a(w) 0.93-0.97 (five levels) and acetic acid concentration 0-2.5% (v/v; six levels). Yeast growth was followed during 90 days by optical density measurements, and logistic regression models were used to describe the data. Acetic acid had a significant effect on the relation between a(w) and NaCl concentration and this interaction had important consequences for the model development. When data were modelled as a function of a(w) or NaCl concentration, a stimulatory effect by acetic acid was observed. In contrast, as a function of (toxic) Na+ ions, no evidence was found of such a phenomenon. These results indicate that in cases where the relationship between a(w) and solute concentration is not straightforward such as in the presence of acid preservatives, one must be critical towards the interpretation of data and correspondingly, the development of predictive models. On a practical note, the developed models, especially the one incorporating Na+ ions, may be used (1) to assess the stability of shelf-stable acidified foods stored under chilled conditions after opening or (2) to formulate new additive-free products intended for storage at 7 degrees C