Effect of in vitro gastrointestinal conditions on the structural and conformational properties of oat β-glucan

Abstract

The physicochemical properties of oat β-glucan have been shown to govern its health benefits by a plethora of studies. However, the effect of the passage through the gastrointestinal tract on the conformational and structural characteristics is not fully explained. The aim of the present study was to elucidate the effect of in vitro gastrointestinal conditions on the structure and conformation of oat β-glucan utilizing Asymmetric Flow Field-Flow Fractionation (AF4) coupled with multiple detectors and in conjunction with NMR. Oat β-glucan was gently extracted from oat flour and its conformational characteristics before and after in vitro gastric and gastrointestinal digestion was investigated with AF4. The contribution of digestive enzymes and bile acids on the conformation of β-glucan was also explored. Moreover, the structural features and the bile acid-binding capacity of oat β-glucan were analyzed with NMR spectroscopy. Oat β-glucan without digestion presented a fringed micelle structure for primary aggregates of single β-glucan chains, and other supramolecular secondary aggregates of primary aggregates were detected for the high molar mass species. Under gastric conditions, the apparent density of β-glucan increased over the molar mass distribution, suggesting more compact secondary aggregates. An interaction of β-glucan and pepsin at low pH cannot be excluded. The completion of the whole gastrointestinal digestion restored the apparent density to the same levels as before digestion. No effect of the digestive enzymes on the conformation of β-glucan was shown, except from a temporary effect of pepsin only under gastric conditions. On the other hand, the presence of bile acids induced an increment to the apparent density of the secondary aggregates indicating conformation-dependent bile acid binding mechanism. This interaction was further confirmed with NMR spectroscopy by observing numerous changes in the resonance of bile acids’ carbons in presence of β-glucan. In conclusion, the examination of oat β-glucan under in vitro gastrointestinal conditions with AF4 and NMR sheds light on the aggregation behaviors and binding mechanisms and enables a rich gain of knowledge for its physiological effects.

Popular Abstract

β-Glucan is good for health!! But why?

Oat is a very common cereal and its consumption has been linked with numerous health benefits. One of the main components of oat that is responsible for these health-promoting properties is β-glucan. It is proven that a daily consumption of 3 grams of β-glucan can effectively reduce the blood cholesterol levels and prevent cardiovascular disease, which causes the death of thousands of people annually. β-Glucan can also enhance the blood glucose levels and blood pressure. β-Glucan is a dietary fiber. That means that our body cannot digest β-glucan. So, the most interesting property of β-glucan that influences the physiological effects is that increases the viscosity inside the gastrointestinal tract. In other words, when we consume β-glucan in a meal, the digested food content in the intestines is more viscous. This thicker composition of the digested food components may lower the rate for the absorption of other macronutrients, such as carbohydrates and fat. Therefore, the glucose and lipids levels after a meal are low. In order to better understand how β-glucan acts in the gastrointestinal tract, we should analyze β-glucan in a molecular level.
The aim of the present study was to understand how β-glucan molecules behave during the digestion. The first step was to extract β-glucan from oat. The use of pure β-glucan helps us to focus only on β-glucan molecules, and not to other components that exist at oat. Then, the digestion of β-glucan was simulated at the lab. If we precisely “copy” the exact conditions that exist in our gastrointestinal tract, we can run the experiments without human subjects and get similar results to the “real” digestion in humans. Then, the β-glucan molecules were analyzed in a molecular level using several advanced techniques which can provide a lot of information about the structure of β-glucan molecules and the way they interact with each other. It was shown the β-glucan molecules interact with each other and they form some super big molecules which can explain the increased viscosity in the gastrointestinal tract after the consumption of β-glucan. Another interesting finding was that β-glucan can interact with bile acids. Our body produces bile acids using cholesterol. So, if β-glucan binds bile acids, then our body has to produce more of these bile acids. Therefore, blood cholesterol may be decreased. It was shown that the way that β-glucan molecules interact with each other affects its ability to bind bile acids.
In conclusion, the present study shows that the understanding of the properties of β-glucan in a molecular level can explain some of each nutritional properties. And by knowing how β-glucan acts, we can produce food products with the greatest health benefits!

• author: Korompokis, Konstantinos
• supervisor: Claudia Zielke
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLGM01 20152
• year: 2016
• type: H2 - Master's Degree (Two Years)
• subject: Agriculture and Food Sciences; Technology and Engineering
• keywords: Bile acids, Aggregation, Oat β-glucan, in vitro digestion, Asymmetric Flow Field-Flow Fractionation, NMR, food technology, livsmedelsteknologi
• language: English
• id: 8892516
• date added to LUP: 2016-10-07 15:15:21
• date last changed: 2016-10-07 15:15:21