Several yoghurt-cream formulations as carriers for probiotic bacteria

INTRODUCTION The storage conditions i.e. temperature, moisture content and composition of powders, relative humidity, oxygen content, light exposure and packaging materials, have significant influences on probiotic survival as dried powders, and the correct storage conditions are essential to maintain viable populations of probiotic bacteria. An alternative means to increase the viability of probiotic bacteria is the microgranulation technology where an innovative matrix surrounding the bacteria protects the viable microorganisms. Moisture content and water activity have been long recognized as important for evaluating product stability and predicted shelf-life, especially of dry powders and intermediate moisture solids. In this study different formulations of yoghurt-cream were tested as carrier for probiotic bacteria in order to increase the shelf-life in new food products (such as biscuits and cakes). The stability of probiotic bacteria in yoghurt-cream formulations was compared with the stability of probiotic bacteria in microgranules. We also established the best method for preparing a new probiotic yoghurt-cream with a view to upgrading production to an industrial scale. MATERIALS AND METHODS Several formulations of yoghurt-cream were prepared in this way: butter or margarine or hydrogenated vegetable oil, dextrose, freeze-dried whole milk yoghurt, skimmed milk powder are mixed well. The two probiotic bacteria, Lactobacillus rhamnosus IMC501® and Lactobacillus paracasei IMC502®, are added as lyophilized powder or microgranules in order to obtain 107 CFU/g of yoghurt-cream. The homogenized yoghurt-creams were distributed in aluminium bags, tightly closed and stored at 25°C and 4°C. The viability of the probiotic bacteria mixture was tested at the lab production time and at different time intervals. Viable cell count expressed as CFU/g of mixed L. rhamnosus IMC501® and L. paracasei IMC502® were determined by the standard count method. Colonies randomly selected from each product were subjected to morphological and molecular analysis (RAPD). Water activity (aw), moisture content and pH of ingredients and final yoghurt-creams were measured. At each analysis point a product sensory profile was defined. The same tests were performed on microgranules made of a vegetable fats matrix containing the two probiotic bacteria. RESULTS The stability of the probiotic concentration was excellent at 4°C for all the formulations. No major changes of the bacterial concentration during time for most formulas of probiotic yoghurt-cream proposed in this study was observed at 25°C. The products absorb little or no moisture during storage, causing a slight change in aw. The probiotic microgranules however lasted for a long time than lyophilized powder maintaining the bacterial concentration much stable. Total evaluation in term of colour, texture and taste of all samples were good and did not have any marked off-flavour during the storage period. DISCUSSION The study demonstrated that these new formulations of yoghurt-cream used as carriers of probiotic bacteria prolong their shelf-life. The possibility to widen the probiotic consumption producing new food products and to prolong their shelf-life at room temperature represents an important impact on the market of functional foods. The comparison of probiotic stability between yoghurt-cream formulations and microgranules itself gives similar results.