Detection of self-propelling bacteria by speckle correlation assessment and applications to food industry

Bacteria are often associated with the insurgence of diseases and many efforts have been made to develop methods for accurate identification of bacteria in food for industry and new generation smart farms. On the other hand, there is a wide category of "good" bacteria that are used in food and pharmaceutic industry. In particular, probiotics are microbial species that have been demonstrated to confer benefits to health, acting against pathologies such as obesity, diabetes, etc. Probiotics have to maintain their viability during their transit through the gastro-intestinal apparatus in order to act to enhance the immune system. The use of alginate microcapsules is one of the most common methods of preservation, applicable to several biological matrices, including probiotics. Here we use bio-speckle decorrelation as a tool for the rapid assessment of microencapsulation effectiveness. Although speckles are often thought as a source of noise, these can be fruitfully used to increase the sensitivity of coherent imaging sensors. Thus, it is possible to characterize bacteria motion and to use it as a contrast agent for applications in food science and industry. Through bio-speckle decorrelation, we detect the presence of bacteria in food without any chemical analysis. Moreover, we quantify the shelf-time of alginate-encapsulated Lactobacillus rhamnosus and Lactobacillus plantarum probiotic bacteria and their survival rate under simulated gastro-intestinal conditions.