Studying semi-dynamic digestion kinetics of food: Establishing a computer-controlled multireactor approach.

In this work, a multireactor system to study digestion (MuReDi) kinetics is introduced. For this, a custom-made automated system with four independent syringe pumps (BioXplorer 100, H.E.L Group) was acquired. This system consists of multiple, small-scale reactors allowing to study digestion as a function of time and thus to determine digestion kinetics. The different digestion conditions used in the oral, gastric, and small intestinal phase were based on the digestion protocols published by the INFOGEST consortium. We showed that the minimum working volume of a reactor is 30 mL. Besides, repeatability of the digestion kinetics was shown for two food systems: a liquid Ensure® Plus Vanilla drink, and a solid, cooked lentil sample. When comparing static digestion kinetics with semi-dynamic ones, a significantly different digestion pattern was observed. In the static case, a relatively fast hydrolysis rate was observed until a clear plateau was reached. Oppositely, for the semi-dynamic case, a delayed start of the hydrolysis process was noticed. In the gastric phase, this was explained by the decreasing pH and the large pH dependency of pepsin activity. In the small intestine, the lag phase was relatively shorter, yet clearly present. Here we related it to the gradual enzyme (and bile salt) secretion that had to diffuse towards the substrate before hydrolysis could start. Generally, this work showed that the MuReDi system could be used to perform a semi-dynamic digestion approach which largely impacted the overall digestion kinetics. This is important to consider in future in vitro food digestion simulation work to come closer to physiologically relevant digestion kinetics.

Digestion kinetics of lipids and proteins in plant-based shakes: Impact of processing conditions and resulting structural properties.

In this work, plant-based shakes were prepared (5% oil, 6% protein, 1% lecithin, 88% water) (w/w) using two processing techniques (i) only mixing versus (ii) mixing followed by high pressure homogenisation, as well as two processing sequences (i) adding all ingredients together versus (ii) stepwise addition of ingredients. Shakes only mixed consisted of large, irregular particles (1-100 µm). Eventually, this resulted in a relatively low lipid and protein digestion extent after 2 h of gastric pre-digestion (9% and < 1%, respectively). In contrast, shakes that were subjected to high pressure homogenisation displayed small, homogeneous particles (<10 µm). Besides, lipids and proteins were digested to a high extent in the stomach (40% and 10%, respectively). The small intestinal digestion kinetics indicated a significant impact of proteins on lipid digestion kineticsbutno significant effect of lipids on protein digestion kinetics. The results highlighted the relevance of food processing on macronutrient (micro)structure and further gastrointestinal functionality.

Enzymatic and chemical conversions taking place during in vitro gastric lipid digestion: The effect of emulsion droplet size behavior.

This investigation reports the effect of droplet size behavior on the overall lipolysis profile and molecular lipolysis mechanisms under in vitro gastric conditions. O/W emulsions (5% triolein, 1% sodium taurodeoxycholate) with different initial droplet sizes (fine: 0.58 µm; medium: 1.82 µm; and large: 4.00 µm) were subjected to static in vitro digestion. For the first time, multiple lipolysis products including diolein and monoolein regioisomers were quantified within a single HPLC run. An inverse relation was found between the droplet size and the initial rate and final extent of lipolysis based on the digested triolein. Furthermore, a mechanistic gastric lipolysis model was established based on a reaction scheme including enzymatic and chemical isomerization conversions. The estimated rate of the sn-1/3 hydrolysis was around two- to thirty-fold faster compared to the rates of sn-2 cleavage and isomerization, respectively. These findings resulted in a profound insight in in vitro gastric molecular lipolysis mechanisms.