Physicochemical and Rheological properties of fortified cocoa milk containing prebiotic lactulose and stevia for individuals with Dysphagia

Imagine a world where the simple act of taking a sip of your favorite drink feels like a high-stakes obstacle course. For millions of people, especially as they age or deal with certain health conditions, swallowing can be a dangerous game of "chance or choke." This is a condition called dysphagia, where the muscles and nerves needed to swallow don't work right. If a liquid is too runny, it can slip down the wrong pipe into the lungs, causing serious infections or even choking. To fix this, scientists and doctors use a special toolkit to thicken drinks, turning them from a fast-flowing river into a slow-moving honey. The goal is to find the "Goldilocks" consistency: thick enough to stay safe, but not so thick it feels like eating glue.

Enter the world of food science, where researchers act like culinary architects. They use special ingredients called hydrocolloids—think of them as microscopic building blocks that can hold water and create a gentle, stretchy net inside a drink. They also have to worry about temperature; a drink might be thick in the fridge but turn into a watery mess the moment it hits the warmth of your mouth. The big question is: Can we make a tasty, healthy drink that stays thick and safe, even when it gets warm, without using too much sugar? This is where the story of a new "super cocoa milk" begins.

The Mission: A Cocoa Milk That Plays by the Rules

In this study, a team of scientists set out to build a fortified cocoa milk specifically designed for people with swallowing difficulties. They wanted to create a drink that wasn't just safe to swallow, but also packed with health benefits. They aimed to hit specific "thickening levels" defined by the International Dysphagia Diet Standardisation Initiative (IDDSI), which are like traffic lights for drink consistency, ensuring the liquid flows at a safe speed.

To make this happen, they played with a few key ingredients. First, they used carrageenan, a seaweed-derived gum that acts like a structural engineer, building a scaffold to hold the liquid together. They tested different amounts, ranging from 0.03% to 0.25%, to see how much was needed to get the right texture. Then, they had to solve the "sugar problem." Many people with these conditions also need to watch their sugar intake or avoid lactose. So, instead of just using regular sugar, they tried swapping it out for stevia (a natural, zero-calorie sweetener) and maltodextrin (a starch-based filler), while also adding lactulose, a prebiotic that helps gut health.

The Experiment: Mixing, Heating, and Testing

The researchers brewed up batches of cocoa milk, heating them to 75°C to let the carrageenan soak up water and form its network. They added their sweeteners and prebiotics, then cooled the mixture down. But the real test was the temperature shift. They measured how thick the drinks were at 10°C (like a cold serving) and at 35°C (the temperature of a human mouth).

They found that as they added more carrageenan, the drink got thicker, just like adding more flour makes dough stiffer. However, there was a catch: when they warmed the drinks up to 35°C, the thickened liquids tended to thin out, losing their protective "honey-like" quality. This is a common problem; heat can break the weak bonds holding the thickener together.

Here is where the magic happened. The team discovered that adding maltodextrin acted like a thermal shield. When they combined carrageenan with maltodextrin and stevia, the drink stayed much thicker at mouth temperature compared to the versions made with regular sugar. For example, at the 0.10% carrageenan level, the maltodextrin-stevia version held a viscosity of 0.066 Pa·s at 35°C, while the sugar version dropped to just 0.033 Pa·s. That's a huge difference in safety! The maltodextrin helped the carrageenan network hold its ground even when things got hot.

The Flow: Not Just a Liquid, But a Smart Fluid

The scientists also looked at how the liquid flowed. They found that all their cocoa milk samples behaved like "shear-thinning" fluids. Imagine squeezing a tube of toothpaste: it's thick and stiff in the tube, but when you squeeze it (apply force), it suddenly flows easily. These drinks did the same thing. They were thick and slow when sitting in the cup, but when the tongue pushed them toward the throat, they became easier to swallow. This is exactly what dysphagia patients need. The data showed that the flow followed a predictable pattern, with a mathematical "fit" that was very strong (R² = 0.94–0.98), meaning the scientists could reliably predict how the drink would behave.

The Taste Test: Does It Actually Taste Good?

A safe drink is useless if no one wants to drink it. The team invited 15 trained taste testers to give the samples a rating from 1 to 5. The results were clear: the formulation with 0.10% carrageenan and stevia was the crowd favorite. It scored the highest for taste and overall enjoyment. Interestingly, the panelists didn't complain about a bitter aftertaste from the stevia, and the texture felt creamy and smooth. The sugar-based versions, on the other hand, didn't score as high, especially when the carrageenan level was low. The higher the carrageenan, the better the texture scores, because the drink felt more substantial and "safe" in the mouth.

Stability: No Sludge, No Spoilage

Finally, the team checked if the drinks would fall apart or go bad over time. They stored the samples in the fridge for 5 days.

• Sediment: The drinks with carrageenan stayed perfectly mixed. No cocoa powder sank to the bottom. The only sample that had visible sediment was the control group (the one with no thickener), proving that the carrageenan was doing its job as a suspension agent.
• Acidity and pH: The drinks with stevia stayed more stable in terms of acidity compared to the sugar versions. The sugar drinks became slightly more acidic over time, likely because bacteria feasted on the sugar and produced acid. The stevia drinks didn't give the bacteria a feast, so they stayed fresher.
• Microbes: After 5 days, all the drinks were still safe to drink, with bacterial counts well within the limits for pasteurized milk products. The stevia samples actually had slightly lower bacterial counts than the sugar ones, suggesting that stevia might even have a tiny bit of a natural preservative effect.

The Verdict

The study concludes that it is absolutely possible to create a cocoa milk that is both a functional medicine for swallowing safety and a delicious treat. By mixing carrageenan with maltodextrin and stevia, the researchers created a drink that stays thick and safe even when it hits the warmth of the mouth. It hits the right "traffic light" levels for dysphagia, tastes great, and doesn't separate or spoil quickly. While the prebiotic lactulose and the sweetener stevia didn't drastically change the thickness of the drink, they successfully added health benefits without ruining the texture or taste. It's a win-win: a drink that keeps people safe from choking while also feeding their gut health and satisfying their sweet tooth.