Multifilm Mass Transfer and Reaction Rate Kinetics in a Newly Developed In Vitro Digestion System for Carbohydrate Digestion

Abstract

Multifilm mass transfer theory has been used in conjunction with developing a new in vitro starch digestion model and applied to assessing starch digestion kinetics. One significance of this research is that this in vitro model has similar dynamics, such as similar Reynolds numbers for both in vivo and in vitro systems. In the in vitro intestine model, when the flow rate changes from 5.9 × 10^-6 m³ s^-1 to 1.0 × 10^-5 m³ s^-1 inside the intestine wall (inside the sausage casing), the Re number changes from 362 to 615. An oral digestion model, a stomach model, and an intestine model have been built to quantitatively understand reaction rate kinetics and two-film (or multifilm) mass transfer for carbohydrate digestion. This in vitro digestion system represents the oral mastication process to reduce the length scale of the test food, amylase inhibition in the stomach, and glucose generation and transport through the intestine wall according to the various emptying rates from stomach. Another dimensionless group, the Damköhler number (Da), has been calculated based on glucose measurements from this in vitro model, which show similar glycemic responses of the hydrolysis for banana and carrot with in vivo results. Another significance of this research is to distinguish a low GI food from a high GI one in this in vitro system and the possibility to estimate the GI value based on the glucose measurements.

Keywords: carbohydrate digestion; in vitro digestion; intestine model; mass transfer; mass transfer resistance; oral digestion model.

Figure 1

Diagram of two-film mass transfer in carbohydrate oral digestion. The internal mass transfer resistance decreases after mastication (shown in black arrow lines), while the external mass transfer resistance (shown in green arrow lines) keeps constant at the same mastication rate (in vivo).

Figure 2

Diagram of two-film mass transfer in carbohydrate intestine digestion.

Figure 3

Diagram of the oral digestion model mimicking the mastication in the oral digestion process.

Figure 4

Diagram of the stomach digestion model mimicking the residence of food bolus in the stomach and carbohydrate digestion inhibition.

Figure 5

Schematic diagram of the intestine digestion model designed to replicate glucose generation and transport dynamics. The orange lines indicate the flow inside the intestine (the sausage casing), and the blue lines indicate the flow outside the intestine.

Figure 6

Images of the oral digestion model including a molar tooth model to mimic the mastication and food bolus formation and a beaker and stirrer system to mimic the transport phenomena after swallowing.

Figure 7

Glucose content data from banana and carrot oral processing using the oral model and the beaker and stirrer system at 50 rpm and a pH of 6.9.

Figure 8

Glucose content data from banana and carrot stomach processes using the beaker and stirrer system at 50 rpm.

Figure 9

Performance qualification using glucose in the lab-built intestine model. The glucose transfers from inside the sausage casing to the outside of the casing, mimicking the in vivo glucose transport through the intestine wall to the blood steam. The glucose contents inside the casing decrease, and the glucose contents outside the casing increase.

Figure 10

The lab-built intestine model (B) using the sausage casing (A) and the SEM images of the dry casing (A1,A2), and the soaked casing (B1,B2) showing the villi on the intestine wall, which increases the surface area after soaking.

Figure 11

Glucose contents outside the sausage casing during single foods (bananas and carrots) digestion in the lab-built in vitro system (oral model and intestine model). Some error bars are smaller than the symbols on the figure.

Figure 12

Glucose contents for banana GI estimation using the area under the curve (AUC).

Figure 13

Glucose contents for carrot GI estimation using AUC.