By Food Materials Research Team
At present, food product development focuses on the products that can deliver health and wellness function to consumers, so they will be in good health both physically and mentally through healthy eating. Delivering the healthy function to consumers, the manufacturers need to understand the process of food digestion in human digestive system, including relevant nutrients and all mechanisms involved from the oral process through other organs during the Gastrointestinal tract (GI tract), such as the esophagus, stomach, small intestine, large intestine, and ultimately excretes from the body as food residues, as shown in figure 1.
Figure 1: The mechanism and nutrients that are absorbed by the digestive process. (The image was adapted from the research by Norton and the team.)
Digestive process
In engineering, the digestive process is viewed as the transformation of food through 3 main mechanisms, namely disintegration, transport phenomena, and reaction. However, the sequence can be divided into 4 stages, as follows.
The oral processing
This stage transforms food into a bolus which is soft and sticky for easy swallowing into the esophagus. It also alters the food structure to be smaller and mingled with saliva, whereas saliva acts as a lubricant with the teeth and mucous membranes in the oral wall. The amylase and lipase will digest the starch and fat which are food constituents. It should be noted that the interaction between the organs’ surfaces in the oral cavity and the food particles can also affect the perception of food, such as smell, taste, and textures.
The digestion in the stomach
When a bolus is swallowed through the esophagus and entered the stomach, the stomach will act as a reactor by secreting the gastric juice and repeatedly tightening and relaxing (peristalsis) so that the food size to become smaller until chyme is produced. Afterward, chyme will then move further into the pyloric part of the stomach sphincter into the small intestine.
The digestion and absorption in the small intestine
Once chyme passes into the small intestine, the secreted digestive juice from the pancreas and the small intestine wall will transform its condition into an alkaline salt. Furthermore, the bile from the liver will act as an emulsifier and reduce the size of fat particles to increase the surface area, which partly assists the lipase enzyme to digest fats more efficiently. In the small intestine, there are various enzymes that digest proteins, peptides, starches, and sugars into smaller sizes so that they will readily be absorbed through the small intestine wall and enter the bloodstream.
The fermentation in the large intestine
The large intestine is the last organ in the digestive system that does not perform any digestive processes but acts as a fermentation area full of various bacteria (109-1012 CFU/ml). These bacteria are important agents that help digest food wastes and produce vitamins and some short-chain fatty acids that can be absorbed and beneficial to the body. Furthermore, the large intestine also absorbs the water and minerals left in food wastes and return them to the body before being excreted as the solid waste from the body.
The influence of food structure towards the absorption into the body
An understanding of all the processes occurring in the digestive system is critical to innovative food development. Vital nutrients, such as vitamins, minerals, and bioactive substances will properly be absorbed and performed within the body when the food is digested in the digestive system. After that, the substances will be released from the food structure and ready to be absorbed into the bloodstream. Most importantly, the capabilities of the digestion, absorption, and application of various nutrients and bioactive substances in food are very dissimilar depending on the structures and complexities of the food matrix, as well as the interaction between various elements in the food products.
Food is essential for human body and life. The human body can receive food or nutrients ranging in size from centimeters down to nanometers. For example, fruits and vegetables that have a large size in centimeters, but their interior structures of plant cells and plant cell walls are thousands of times smaller as shown in figure 2A. In plant cells and plant cell walls, there are various polysaccharides, such as cellulose, hemicellulose, pectin, or meat-based foods that contain small myofibrils binding together into a large bundle, as shown in figure 2B, which its characteristic of the structure is classified as a hierarchy structure. Therefore, when human consumes these kinds of food, their body will not absorb the nutrients directly until the digestive process transformed the food structure into a smaller molecule, which can be readily absorbed by the body.
Figure 2: The hierarchical structure in plant tissue and meat.
The nutrients in the form of carbohydrates, proteins, and fats also have a hierarchical structure as shown in figure 3. It can be seen that the nutrients’ size becomes smaller from left to right through the digestive process so that the body can absorb and use those nutrients.
However, the process of transforming the food structure into smaller molecules can create new structures or interactions, which leads to the endeavor of understanding the mechanism of nutrients release and its bioaccesibility become more challenging. For example, the formation of the insoluble properties of coagulated milk protein or the precipitation of polysaccharides, or a viscous suspension of fibers when in the gastric acidity environment, which helps retard the gastric emptying and satiety.
Figure 3: The hierarchical structure of the nutrients, such as carbohydrates, proteins, and fats that may find in food products.
The structure of food in digestive process has a great influence on the nutrition and wellbeing of consumers. Therefore, the study of changes in food structure during the digestion, the digestive capacity, and the release of nutrients and vital substances from food structure are important themes in the research and development of healthy food products and the reduction of pathogenesis of food diseases, such as obesity, diabetes, heart and cardiovascular disease.
Research guidelines of Food Materials Research Team, MTEC
Food Materials Research Team has developed its expertise by integrating science related to mechanics, rheology, and tribology to understand the mechanism of food occlusion. The research team has also expanded the research scope to cover the overall gastrointestinal tract by developing research capability and creating technology knowledge of gut simulation with Food Biotechnology Research Team of the National Center for Genetic Engineering and Biotechnology (BIOTEC).
Furthermore, the digestive simulator technology can help develop the performance testing capabilities, mechanism, and food safety, as well as various functional ingredients by stimulating the digestive conditions in the stomach and small intestine through the tiny-TIMagc system and the functional state of the large intestine through the TIM-2 system as shown in figure 4.
Figure 4: The study and understanding of the digestive mechanism by integrating the science of mechanism, rheology, and tribology for food occlusion and oral digestion, as well as the digestive simulation technology using the tiny-TIMagc and TIM-2 system for food digestion and absorption in the upper and lower digestive organs.
The tiny-TIMagc and TIM-2 system have been demonstrated in testing the digestive efficiency and studying of vital substances release along with the amount of nutrients and drugs that are left or absorbed in a feeding or fasting state. The research in digestive simulation, therefore, has become an advanced technology that will strengthen and create research expertise in efficacy and safety testing for food industries and other related industries in the near future.
Referrence
Norton, I.T., Moore, S., & Fryer, P. (2007). Understanding food structuring and breakdown: engineering approaches to obesity. Obesity Reviews, 8, 83–88.
Norton, I.T., Spyropoulos, F., & Cox, P.W. (2008). Rheological control and understanding necessary to formulate healthy everyday foods, Annual Transactions of The Nordic Rheology Society, 16, 9–14.
Norton, J.E., Wallis, G.A., Spyropoulos, F., Lillford, P.J., & Norton, I.T. (2014). Designing Food Structures for Nutrition and Health Benefits. Annual Review of Food Science and Technology, 5(1), 177–195.
Tang, D., & Marangoni, A.G., (2006). Quantitative study on the microstructure of colloidal fat crystal networks and fractal dimensions. Advances in Colloid Interface Science, 128-130, 257-
Troncoso, E., & Aguilera, J.M. (2009). Food microstructure and digestion. Food Science & Technology, 23(4), 24-27.
Parada, J., & Aguilera, J.M. (2007). Food microstructure affects the bioavailability of several nutrients. Journal of Food Science, 72(2), 21-32.
Turgeon, S.L., & Rioux, L.-E. (2011). Food matrix impact on macro-nutrients nutritional properties. Food Hydrocolloids, 25, 1915–19
Fiszman, S., & Varela, (2013). The role of gums in satiety/satiation. A review. Food Hydrocolloids, 32, 147–154.
Campbell, C.L., Wagoner, T.B., & Foegeding, E.A. (2017). Designing foods for satiety: The roles of food structure and oral processing in satiation and satiety. Food Structure, 13, 1–
Morell, P., & Fiszman, S. (2017). Revisiting the role of protein-induced satiation and satiety. Food Hydrocolloids, 68, 199–210.
Aguilera, M. (2019). The food matrix: implications in processing, nutrition and health, Critical Reviews in Food Science and Nutrition, 59(22), 3612-3629.
