Manipulation of growth characteristics of yogurt culture by application of an electromagnetic field.

摘要

The effect of applied electromagnetic fields on the metabolism of a commercial yogurt culture was assessed by measuring pH, titrated acidity, plate counts of viable microorganisms, and high performance liquid chromatography analysis of organic acids produced during the initial 4 hr of fermentation. A significant increase in titrated acidity was observed in the treated culture exposed to an electromagnetic field of 60 Hz, 4.3 G, a 1% duty cycle and square waveform. Analysis of organic acids by high performance liquid chromatography attributed the elevation in titrated acidity to a 5.9% increase in the concentration of lactic acid; a primary fermentation product of Streptococcus thermophilis during the initial 4 hr of yogurt development. The enhancement of lactic acid production was determined to be frequency sensitive, over a frequency range of 50-70 Hz. No significant elevation in the numbers of viable bacteria or the ratio of rods:cocci was observed through plate count methods, suggesting a change in culture metabolism rather than an elevation in the overall bacterial population was caused by the electromagnetic field. (Abstract shortened by UMI.)