Release kinetic study of encapsulated probiotic Lacticaseibacillus rhamnosus strain NCDC 347 in double-layer matrix encapsulated by spray drying

Probiotics are living microorganisms that, when consumed in the right amounts, offer health benefits to the human body. They are often added to foods like yogurt and supplements to support digestion and boost the immune system. However, these tiny helpers face a perilous journey before they can reach their destination. To be effective, they must survive the harsh environment of the stomach, where strong acids and digestive enzymes are designed to break down food and kill bacteria. If the probiotics die before reaching the intestines, the food or supplement provides little benefit. Scientists have long sought ways to protect these delicate cells, much like building a shield around a fragile traveler, ensuring they arrive alive and ready to work.

One promising method for this protection is microencapsulation, a process where bacteria are coated in a protective layer. A common technique used to create these coatings is spray drying, which turns a liquid mixture into a fine powder. While this method is efficient and scalable, the heat and stress involved can sometimes damage the bacteria. To solve this, researchers are exploring combinations of different materials to create stronger, more resilient shields. In this study, scientists at the National Institute of Food Technology Entrepreneurship and Management in India investigated a specific blend of two food-grade materials: skim milk powder and carrageenan. Skim milk powder contains proteins and sugars that can cushion bacteria against heat and drying stress, while carrageenan, a substance extracted from red seaweed, is known for its ability to form gels and hold onto water. The researchers wanted to see if mixing these two would create a double-layered shield that could not only protect the bacteria during the drying process but also control exactly when and where the bacteria are released inside the body.

The team focused on a specific strain of probiotic bacteria called Lacticaseibacillus rhamnosus NCDC 347. They mixed the bacteria with solutions of skim milk powder, carrageenan, and a combination of both, then used a spray dryer to turn the mixtures into a fine powder. To test how well this new shield worked, they simulated the journey through the human digestive system. They placed the powder in liquids that mimic the stomach's acidic environment and the intestines' more neutral, enzyme-rich environment. They also tested the powder in plain water to see how it behaved without digestive fluids. By measuring how much of the bacteria leaked out of the powder over time, they could determine if the shield was holding up or breaking down.

The results showed that the blend of skim milk and carrageenan created a highly effective barrier. When the powder was placed in plain water, the bacteria were released very slowly, indicating that the shield remained intact and did not simply dissolve. However, when the powder was moved into a fluid mimicking the intestines, the release rate increased significantly. This suggests the shield is smart; it stays closed in the stomach but opens up when it reaches the intestines, which is exactly where the bacteria need to be. In contrast, when the researchers tested the powder in a highly acidic liquid meant to mimic the stomach, the release was much slower than in the intestines, confirming that the bacteria were protected from the harsh acid.

The researchers also looked at how the shield itself changed shape and size as it absorbed water. They found that the material swelled significantly when it entered the intestinal fluid, absorbing more than twice its own weight in water. This swelling was a key part of the process, as it helped push the bacteria out of the shield. Interestingly, the way the bacteria moved out of the shield was not a simple, steady flow. Instead, the release was driven by the material relaxing and changing its structure after soaking up water. This is different from how a sponge might simply let water drip through; here, the material itself had to expand and shift to let the bacteria escape. This mechanism ensures that the bacteria are not dumped all at once but are delivered in a controlled manner.

Perhaps the most important finding was how well the bacteria survived the journey. When the researchers exposed the unprotected bacteria to the acidic stomach fluid, their numbers dropped dramatically, with most of them dying within two hours. However, the bacteria hidden inside the skim milk and carrageenan shield remained much stronger. After two hours in the same acidic fluid, a large majority of the protected bacteria were still alive. The shield also proved effective against bile salts, a substance found in the intestines that can be toxic to bacteria. Again, the protected bacteria survived much better than those without a shield. Even after two hours in a solution with high levels of bile salts, the protected bacteria maintained high survival rates, whereas the unprotected ones suffered heavy losses.

The study concludes that this specific combination of skim milk and carrageenan is a powerful tool for delivering probiotics. It successfully protects the bacteria from the heat of the manufacturing process and the harsh conditions of the stomach. Most importantly, it allows the bacteria to survive the trip and release them in the intestines, where they can do their job. The researchers suggest that this double-layer system could be used to create new functional foods and supplements that reliably deliver live probiotics to the human gut, turning a difficult biological challenge into a manageable engineering solution.