Method of optical-electrochemical biotesting in assessment of antibiotic properties of various essential oils

A biotesting technique is described that provides for periodic recording of changes in the intensity of elastic light scattering, pH, and electrical conductivity of a liquid nutrient medium incubated in the presence and absence of viable test microorganisms and test samples. With the use of the technique, the results of a comparative analysis of Lactobacillus acidophilus antibiotic activity on various concentrations of «essential oils» (EO, which can be used as functional additives to various food, feed, pharmaceutical, cosmetic and other products) obtained from 11 different types of plant raw materials are presented. Studies have shown that among the plant extracts studied, the most active prolonged antibiotic properties are those of EO obtained from Citrus aurantium flowers, Melaleuca alternifolia leaves, and Illicíum verum seeds. The initial antibiotic activity of the tested extracts (TE) in most cases was greater than their prolonged activity. At the same time, the mid-term (in terms of the time of TE interaction with test microorganisms) antibiotic activity of TE, as a rule, was intermediate in value between their initial and prolonged activity. At the same time, with a decrease in TE concentrations in the test medium, their antibiotic activity decreased monotonically. Thus, it is obvious that the biological activity of food and other products, including various plant extracts, is largely determined by the choice of not only the raw material and the method of extracting biologically active substances from it, but also the concentration of the extract in the product. Moreover, the exact nature of these dependencies in most cases can be established only empirically, with the help of a significant number of tests. And the latter can be conveniently carried out using the methodology presented in this work, which allows a much more rapid, objective and informative, as well as much less laborious and material-intensive, than by standard visual microbiological methods, to assess the effect on the dynamics of the vital activity of microorganisms of various samples of food, feed, pharmaceutical, cosmetic and other products, as well as individual ingredients and additives to them. The technique presented allows evaluating pro and antibiotic properties of various samples, individual ingredients, and additives in food, pharmaceutical and other industries in less material intensive and time consuming, as well as in more informative, objective, and expressive way.