Bio-preservation of chocolate mousse with free and immobilized cells of Lactobacillus plantarum D2 and lemon (Citrus lemon L.) or grapefruit (Citrus paradisi L.) zest essential oils.

Background: The bio-preservation of food products using various natural ingredients and metabolites from various types of beneficial microorganisms released during targeted fermentation is a method that simultaneously has a preservative effect on the food product and provides a model of its composition in order to ensure its functional and health properties. This double effect can be achieved by incorporating ingredients with proven preservative and functional effects into the food product, such as essential oils from various plant species and probiotic bacteria. The aim of the present research was to study the synergistic effect of selected probiotic lactic acid bacteria (LAB) and essential oils with high antimicrobial activity against pathogenic and spoilage microorganisms for the bio-preservation of chocolate mousse food emulsion.

Methods: The susceptibility of the selected probiotic strain Lactobacillus plantarum D2 to different concentrations of the selected lemon or grapefruit essential oil was examined using the disc-diffusion method. Nine chocolate mousse variants were prepared with the inclusion of free or immobilized cells of the probiotic strain L. plantarum D2 and/or lemon or grapefruit zest essential oils. The chocolate mousse variants were stored for 20 days in refrigerated conditions, and changes in the concentration of viable lactobacilli cells, the pH and the microbiological purity were monitored in accordance with standard requirements by taking samples on the 0th, 5th, 10th, 15th, and 20th days of storage. An organoleptic evaluation of the chocolate variants was performed on the 0th day.

Results: Concentrations of up to 1% lemon or grapefruit essential oil did not affect the growth of the probiotic strain L. plantarum D2, which revealed opportunities for their joint application for the bio-preservation of food emulsions. The obtained chocolate mousse variants were characterized by preserved organoleptic characteristics and microbiological safety. Free or immobilized probiotic L. plantarum D2 cells applied alone or in combination with lemon or grapefruit essential oils provided bio-preservation of the food emulsions, maintaining a high concentration of viable cells (106-107 cfu/g) during storage under refrigerated conditions for 20 days.

Conclusions: The combined application of free or immobilized probiotic LAB and lemon or grapefruit essential oils resulted in better bio-preservation results than in the use of probiotic LAB or essential oils alone, thus suggesting a synergistic effect between the two bio-preservative agents. Moreover, the obtained chocolate mousse emulsions can be classified as functional foods and the chocolate mousse food matrix can successfully be used as a vehicle for delivery of probiotic LAB to a wide range of food consumers. The obtained results and the developed successful bio-preservation strategy for the production of chocolate mousse food emulsions would provide grounds for the future selection of other probiotic lactobacilli strains, essential oils and synergistic combinations of them for the development of successful bio-preservation strategies for other types of food and beverage products.