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Validation of DIDGI® for the Digestion of Infant Formula

The DIDGI® system is a very recent one. Although several matrices (dairy, meat, fruits and vegetables, emulsions) have been submitted to digestion using the DIDGI® system, only data obtained on the digestion of infant formulas have been published so far (Ménard et al. 2014). In order to demonstrate that this system was physiologically-relevant, a comparison of the in vitro and in vivo digestion of an infant formula was performed. The in vivo trial was conducted on 18 piglets that were fed the infant formula for which the concentration in lipids and proteins was increased compared to a standard one, but the ratio lipids/proteins was kept constant. In parallel, in vitro gastro-intestinal digestion was performed on this enriched infant formula using the newly developed system and the extent of milk proteolysis was monitored and compared to the one obtained in vivo.

Protocol for the In Vitro Dynamic Digestion of Infant Formula Using the DIDGI® System

Infant formula (150 ml) was introduced into the gastric compartment within a pre-set period of time, i.e. 10 min. The pH values were controlled via the computer by secreting either 0.5 M HCl to decrease the pH in the stomach or 0.1 M Na2CO3 to neutralize the pH in the small intestine.

The dynamic digestive system was set up using parameters taken from the literature that are listed in Table 8.1. The pH curve in the stomach was obtained by combining data from different in vivo experiments on piglets (Moughan et al. 1991; Chiang et al. 2008; Bouzerzour et al. 2012) whereas intestinal pH was kept constant at 6.5. Other parameters like the transit time of the formula in the stomach (determination of t1/2 and β) was obtained from an exhaustive review on human infant gastrointestinal physiological conditions (Bourlieu et al. 2014) and fixed at t1/2 = 70 min or 200 min and β = 1.23 or 2.2 for gastric or intestinal transit time, respectively. Volumes, flow rates of secretions, nature and quantity of enzymes in the different stages of the gastro-intestinal model have been described previously (Minekus et al. 1995; Blanquet et al. 2004; Bouzerzour et al. 2012) based on results of in vivo experiments. Digestive enzymes and bile were diluted in 150 mM NaCl, pH 6.5. After rehydration, all the digestive enzymes were kept on ice throughout the experiment in order to avoid autolysis. Digestion experiments were performed in triplicates. Samples were collected during the digestion in each compartment at 30, 60, 90, 120 and 210 min after ingestion. Before being frozen at −20 °C, phenylmethanesulfonyl fluoride was added at 0.37 g/kg of digested sample in order to inhibit proteolysis.

Table 8.1 Parameters of in vitro gastro-intestinal conditions Gastric conditions

Secretions

Pepsin flow

1,250 U/mL

0.25 ml/min

Lipase flow

60 U/mL

0.25 mL/min

Transit time

t1/2(min)

70 min

β

1.23

Intestinal conditions

Fasted volume

5 ml of bile solution (1 %)

+5 ml of pancreatin solution (10 %)

pH

Maintained at 6.5

Secretions

Bile flow

1 %

0.5 mL/min

Pancreatin flow

10 %

0.25 mL/min

Transit time

t1/2(min)

200

β

2.2

 
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