Use of RAPD-PCR as a method to follow the progress of starter cultures in sauerkraut fermentations

Abstract DNA fingerprinting methods were used to follow the progress of unmarked starter cultures in laboratory sauerkraut fermentations (1.2 and 13 l). Random prime PCR (RAPD-PCR) was used for strain-specific identification of Leuconostoc mesenteroides cultures. A comparative analysis of RAPD banding patterns for fermentation isolates and starter cultures was carried out using both genetically marked and unmarked cultures. While some variation in the RAPD patterns was observed, the results showed that the starter cultures dominated the fermentation during early heterofermentative stage for up to 5 days after the start of fermentation. Results from marked and unmarked starter cultures were confirmed by intergenic transcribed spacer (ITS)-PCR, and strain identify was confirmed by pulse field gel electrophoresis (PFGE) patterns. The results demonstrate the utility of RAPD to follow the progression of unmarked starter cultures of L. mesenteroides in sauerkraut fermentations.

Energy-Based Dynamic Model for Variable Temperature Batch Fermentation by Lactococcus lactis

We developed a mechanistic mathematical model for predicting the progression of batch fermentation of cucumber juice by Lactococcus lactis under variable environmental conditions. In order to overcome the deficiencies of presently available models, we use a dynamic energy budget approach to model the dependence of growth on present as well as past environmental conditions. When parameter estimates from independent experimental data are used, our model is able to predict the outcomes of three different temperature shift scenarios. Sensitivity analyses elucidate how temperature affects the metabolism and growth of cells through all four stages of fermentation and reveal that there is a qualitative reversal in the factors limiting growth between low and high temperatures. Our model has an applied use as a predictive tool in batch culture growth. It has the added advantage of being able to suggest plausible and testable mechanistic assumptions about the interplay between cellular energetics and the modes of inhibition by temperature and end product accumulation

Isolation and characterization of a Lactobacillus plantarum bacteriophage, phiJL-1, from a cucumber fermentation

Abstract A virulent Lactobacillus plantarum bacteriophage, AJL-1, was isolated from a commercial cucumber fermentation. The phage was specific for two related strains of L. plantarum, BI7 and its mutant (deficient in malolactate fermenting ability) MU45, which have been evaluated as starter cultures for controlled cucumber fermentation and as biocontrol microorganisms for minimally processed vegetable products. The phage genome of AJL-1 was sequenced to reveal a linear, double-stranded DNA (36.7 kbp). Sodium dodecyl sulfate-polyacryamide gel electrophoresis (SDS-PAGE) profiles indicated that AJL-1 contains six structural proteins (28, 34, 45, 50, 61, and 76 kDa). Electron microscopy revealed that the phage has an isometric head (59 nm in diameter), a long non-contractile tail (182 nm in length and 11 nm in width), and a complex base plate. The phage belongs to the Bradley group B1 or Siphoviridae family. One-step growth kinetics of the phage showed that the latent period was 35 min, the rise period was 40 min, and the average burst size was 22 phage particles/infected cell. Phage particles (90%) adsorbed to the host cells 20 min after infection. Calcium supplementation (up to 30 mM CaCl 2 ) in MRS media did not affect the first cycle of phage adsorption, but promoted rapid phage propagation and cell lysis in the infection cycle subsequent to adsorption. The D values of AJL-1 at pH 6.5 were estimated to be 2.7 min at 70 jC and 0.2 min at 80 jC by a thermal inactivation experiment. Knowledge of the properties of L. plantarum bacteriophage AJL-1 may be important for the development of controlled vegetable fermentations.