Effect of glucose, pH and lactic acid on Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens within a commercial heat-shrunk vacuum-package film.

Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens are common spoilage organisms found within the microbiome of refrigerated vacuum-packaged (VP) beef. Extending and predicting VP beef shelf-life requires knowledge about how spoilage bacteria growth is influenced by environmental extrinsic and intrinsic factors. Multifactorial effects of pH, lactic acid (LA) and glucose on growth kinetics were quantified for C. maltaromaticum, B. thermosphacta and S. liquefaciens within a heat shrink-wrapped VP commercial film containing a simulated beef medium. LA, pH, and undissociated lactic acid (UDLA) significantly affected bacterial growth rate (p < 0.001), whereas 5.55 mM glucose produced a marginal effect. At 1.12 mM UDLA, growth rate and maximum population density decreased 20.9 and 3.5%, 56 and 7%, and 11 and 2% for C. maltaromaticum, B. thermosphacta, and S. liquefaciens, respectively.

qPCR quantification of Carnobacterium maltaromaticum, Brochothrix thermosphacta, and Serratia liquefaciens growth kinetics in mixed culture.

Quantifying growth kinetics of specific spoilage microorganisms in mixed culture is required to describe the evolution of food microbiomes. A qPCR method was developed to selectively amplify individual meat spoilage bacteria, Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens, within a broth medium designed to simulate the composition of beef. An optimized method of DNA extraction was produced for standard curve construction. Method specificity was determined by individual single peaks in melt curves. Reaction efficiency for standard curves of C. maltaromaticum, B. thermosphacta and S. liquefaciens was high (R2 = 0.98-0.99), and linear quantification was achieved over a 5 log CFU/ml range. Coefficient of variation was calculated considering both threshold cycle (Ct) and bacterial concentration; the value did not exceed 14% for inter- or intra-runs for either method. Comparison of growth kinetic parameters derived from plate count and qPCR showed no significant variation (P > .05) for growth rate (GR) and maximum population density (MPD); lag phase duration (LPD) was not included in this comparison due to high innate variability. Log quantification of each isolate was validated in a mixed-culture experiment for all three species with qPCR and plate count differing less than 0.3 log CFU/ml (average 0.10 log CFU/ml, R2 = 0.98).

Optimization and partial characterization of culture conditions for the production of alkaline protease from Bacillus licheniformis P003.

Proteolytic enzymes have occupied a pivotal position for their practical applications. The present study was carried out under shake flask conditions for the production of alkaline protease from Bacillus licheniformis P003 in basal medium containing glucose, peptone, K2HPO4, MgSO4 and Na2CO3 at pH 10. The effect of culture conditions and medium components for maximum production of alkaline protease was investigated using one factor constant at a time method along with its characterization. Maximum level of enzyme production was obtained after 48h of incubation with 2% inoculum size at 42°C, under continuous agitation at 150 rpm, in growth medium of pH 9. Highest enzyme production was obtained using 1% rice flour as carbon source and 0.8% beef extract as organic nitrogen source. Results indicated that single organic nitrogen source alone was more suitable than using in combinations and there was no significant positive effect of adding inorganic nitrogen sources in basal medium. After optimization of the parameters, enzyme production was increased about 20 fold than that of in basal medium. The crude enzyme was highly active at pH 10 and stable from pH 7-11. The enzyme showed highest activity (100%) at 50°C, and retained 78% relative activity at 70°C. Stability studies showed that the enzyme retained 75% of its initial activity after heating at 60°C for 1h. The enzyme retained about 66% and 46% of its initial activity after 28 days of storage at 4°C and room temperature (25°C) respectively. Mn(2+) and Mg(2+) increased the residual activity of the enzyme, whereas Fe(2+) moderately inhibited its residual activity. When pre-incubated with Tween-20, Tween-80, SDS and H2O2, each at 0.5% concentration, the enzyme showed increased residual activity. These characteristics may make the enzyme suitable for several industrial applications, especially in leather industries.

Production and partial characterization of extracellular amylase enzyme from Bacillus amyloliquefaciens P-001.

Amylases are one of the most important enzymes in present-day biotechnology. The present study was concerned with the production and partial characterization of extracellular amylase from Bacillus amyloliquefaciens P-001. The effect of various fermentation conditions on amylase production through shake-flask culture was investigated. Enzyme production was induced by a variety of starchy substrate but corn flour was found to be a suitable natural source for maximum production. Tryptone and ammonium nitrate (0.2%) as nitrogen sources gave higher yield compared to other nitrogen sources. Maximum enzyme production was obtained after 48 hrs of incubation in a fermentation medium with initial pH 9.0 at 42°C under continuous agitation at 150 rpm. The size of inoculum was also optimized which was found to be 1% (v/v). Enzyme production was 2.43 times higher after optimizing the production conditions as compared to the basal media. Studies on crude amylase revealed that optimum pH, temperature and reaction time of enzyme activity was 6.5, 60°C and 40 minutes respectively. About 73% of the activity retained after heating the crude enzyme solution at 50°C for 30 min. The enzyme was activated by Ca(2+) (relative activity 146.25%). It was strongly inhibited by Mn(2+), Zn(2+) and Cu(2+), but less affected by Mg(2+) and Fe(2+).