Lactic acid bacteria are indispensable in pharmaceutical and food industries. They produce lactic acid, which is used in the production of yogurts, cheese, and other fermented dairy products, and serves as a natural preservative for many other food products. What’s more, lactic acid is used in creams, serums, and other skin products.
In order to ensure stable quality of products, it’s essential to control the processes associated with the production of lactic acid and the activity of lactic acid bacteria. Typically, this is done with the use of titrimetry, and gas or high-performance liquid chromatography. Such methods call for special laboratory equipment and the associated conditions. Biosensors provide an alternative, but most of those are aimed at detecting pathogenic organisms and are not designed for analyzing lactic acid cultures.
Scientists from ITMO’s Infochemistry Center have developed Russia’s first smartphone-based system that can evaluate the growth of Streptococcus thermophilus lactic acid bacteria based on photographs. It can help quickly assess microbiological parameters, especially in labs that need to occasionally conduct such analyses but weren’t designed for that purpose. Being easy to use and not dependent on stationery lab equipment, the system is accessible to users who haven’t received any special training.
“During the Streptococcus thermophilus growth process, the pH of the medium gradually changes, which is visually reflected by a change in the color of the indicator added to the sample. The user photographs the bacteria-filled Petri dish with their smartphone, then uploads the image to our Telegram bot. The color analysis algorithm, which uses a hexadecimal color code, automatically identifies the outline of the Petri dish and deletes the background and noise. Then, it calculates the medial color values of the uploaded image and compares them with an earlier created color gradient of 25 reference images that are stored in our local database. In several seconds, our system returns the pH value with a margin of error at just 0.01”, comments Olga Osmak, the first author of the research and engineer at ITMO’s Infochemistry Center.
Researcher Olga Osmak photographs a lactic bacteria sample. Photo by Alina Fedorova / Megabyte Media
The technology’s main advantage is its ability to monitor the growth of lactic acid bacteria while they are being prepared for the production process. Such a system makes it possible to control the entry parameters of a bacterial culture before it is introduced into the production line, thus ensuring the stability and reproducibility of the resulting fermented dairy product in small-batch production. It can also be used for school experiments in microbiology. Students can grow bacteria in a Petri dish and use the Telegram bot to study the fermentation of lactic acid bacteria and the production of lactic acid.
In the future, the system could also help observe oral hygiene. Pathogenic Streptococcus mutans lactic acid bacteria are among the causes of dental caries. They produce lactic acid, which decreases the pH of the media and causes the dental enamel to deteriorate. In order to check their dental health, users could apply a special gel and take a smartphone photo that the system will assess for acidity.
Researcher Mikhail Volodarsky conducts experiments with lactic acid bacteria. Photo by Alina Fedorova / Megabyte Media
Scientists at ITMO aim to further expand the system’s functions. As of today, it can analyse the growth of Streptococcus thermophilus using bromocresol purple as a pH indicator. But it can also be adapted to work with other cultures and strains of lactic acid bacteria as well as different indicators: for example, bromothymol blue.
Researchers Olga Osmak and Mikhail Volodarsky. Photo by Alina Fedorova / Megabyte Media
What’s more, the scientists plan to add a precise focus mode for cases in which researchers need to analyze a specific area in a Petri dish, as well as automatic assessment of the stage of bacteria growth and the amount of lactic acid produced. The latter will make it possible to learn about bacterial growth and pH changes, as well as control the quality of produce during production. As a step towards these goals, the team has already conducted a series of spectrophotometry experiments and formed a database of changes in the optical density of bacterial cultures.
The research was conducted as part of the Russian Science Foundation grant No. 23-16-00224.
