Does in vitro protocol predict the nutritional value of thermally treated cereals?

Several in vitro protocols were proposed to rapidly evaluate the nutritional value of cereal and food ingredients. These In vitro protocols are based on restricted parameters and may involve results differing to the reality once assessed in vivo. Moreover, information about some in vitro parameters is sometimes insufficiently described.
In the present study, a three steps in vitro digestion simulation developed by Tervila-Wilo et al. (1996) to mimic digestion in poultry digestive tract was assessed and compared with in vivo digestibility of corn grain harvest at two moisture contents and dried at three temperatures. In vitro digestion simulation showed that increasing drying temperature led to an increase in in vitro digestibility of dry matter (IVDMD) while in vivo digestibility of dry matter (DM) measured on force fed broilers chickens decreased in the same conditions.
To improve this in vitro digestion model, the effect of amylase activity of pancreatin, substrate concentration, corn flour particles reduction and agitation were investigated. Results showed that increasing amylase activity of pancreatin and decreasing substrate concentration improved DM digestibility through starch digestibility while corn flour particles reduction had little effect on its final DM digestibility. Rotational agitation greatly improved starch digestibility and therefore DM digestibility, even at low speed. This increase in DM digestibility reached 20% and was attributed to the better contact between substrate and enzymes and a reduction in solution viscosity under constant agitation. A good adjustment of these parameters would improve the ability of in vitro digestion simulation to accurately predict nutritional value of thermally treated cereals. They have to be taken into account on the implementation of in vitro digestion simulation aiming to predict in vivo performances of consumers.