Explain the pH Meter - Food Microbiology?

pH is a negative logarithm of H+ ion concentration. Its value remains between 0 and 14. Pure water has a pH of 7 (neutral). pH value less than 7 is acidic and more than 7 is basic. The measurement of pH can be done by using pH meter. pH meter is used to measure and set the pH of culture media or reagents used for microbiological and biochemical assays. It is important as different microbes have different pH requirements for growth. Most of the bacteria, in general, have optimum pH for growth between 6.5 to 7.5, though there are certain exceptions.

Some bacteria are acidophiles (grow at acidic pH) or alkalophiles (needs high pH in alkaline range for growth). Most fungi have pH optima around 4 to 6 and yeasts need pH around 3 to 5. The pH meter has a glass electrode for measuring the pH. During determination of pH, first the instrument is calibrated with standard buffers of pH 4, 7 and 9. Then the pH of the sample solution is determined by dipping the glass electrode in the solution and pH is read directly from the pH meter scale.