The development of encapsulated probiotic bacteria with prebiotics incorporated into cereal beverages

Most probiotic products are dairy-based and require refrigeration, but there are currently no spray dried probiotic powders sold commercially today. The aim of this research is to develop instant cereal beverage using an oat-based formulation containing the probiotic organism Lactobacillus acidophilus. Escherichia coli K12 was initially used as a reference Gram negative microorganism to compare with the Gram positive L. acidophilus. The work started with the examination of growth to determine the timings required to harvest cells in the mid-log phase and the early-stationary phase of both bacteria. Spray only experiments were then performed which showed that atomisation itself did not cause any significant effect on cell survival of either cultures, either in the mid-log or early-stationary phases. The spray drying experiments found that cells harvested in the early-stationary phase had a greater heat resistance than those cultured in their mid-log phase at the same outlet temperature. It was also found that the higher the drying outlet temperature, the lower was the cell survival rate. The best survival rates were found when spray drying at drying outlet temperatures lower than 80 °C. E coli K12 was found to have a lower level of survival than L. acidophilus especially when spray dried with maltodextrin without culture broth components present. This can be attributed to the much thinner cell wall of the Gram negative E coli K12 bacterium. The optimal growth phase (early stationary) and spray drying outlet temperature (80°C) were then taken forward in to the next study for L. acidophilus when various combinations and ratios of proteins (either whey protein, isolated soy protein or skim milk) and sugars (either maltose, lactose or fructose), and maltodextrin were tested. Cell survival rates after spray drying were tested after rehydrating in phosphate buffer solution (PBS), simulated gastric juice (SGI) or 2% Bile solution for 1 hour, although significantly better survival was observed if left to rehydrate for 12 hours. By directly examining experimental data and also using Response Surface Methodology (RSM) it was found that in general increasing the protein level gave a higher cell survival rate after rehydrating in PBS, SGI and bile solution, while formulations containing no protein showed the lowest survival rate. It was strongly shown that the presence of protein above 50%, particularly milk protein, does protect cells in these harsher environments. The sugar contents were limited to a maximum value of 25% due to stickiness limitations. It was found that maltose produced better results than lactose or fructose. Incorporation of a liquid oat drink into the formulation to replace distilled water only produced a slight lowering of survival levels if protein levels were still maintained, but replacing the protein mixture by a prebiotic (Orafti®P95) produced adverse results. After storage for 3 months these spray dried cultures showed high stability when stored at refrigerator temperatures (4 °C) although acceptable levels of survival were also found when stored at room temperature. A simulated hydration/digestion was performed by which cells were hydrated in distilled water and exposed to SGI and bile solution in turn. These showed very good results and indicated that the bacteria could be transported to the gut in a viable state. The recommended formulation for spray dried L. acidophilus encapsulated with whey protein, maltose and maltodextrin incorporated into prebiotics and oat drink is 16%, 2%, 2%, 0% and 80% respectively.