Could salt-soluble proteins denaturation index (Promatest) of corn grain help to predict in vitro digestibility of dry matter?

The Promatest is a quick and reliable test which allows the assessment of the loss of solubility of salt-soluble proteins. It was used as a reference method for the assessment of the thermal shock suffered by grain and is frequently used by the starch industry to monitor starch quality. There is some evidence that protein solubility is associated with energy utilization. It was then believed that the Promatest could be used to predict the nutritional quality of corn grain
This study aims to determine if the Promatest could be used to predict the in vitro digestibility of dry matter of corn grain. Almost 80 samples of corn grain dried at different temperature were analyzed for their salt-soluble protein content. The in vitro digestibility of these corn samples was determined with three different in vitro methods which chiefly differ from each other in the time, the buffer and the amount of enzymes used.
Results show that there is a strong correlation between the three methods the in vitro digestibility of dry matter determination (r=0.7627, 0.767 and 0.9324). The promatest index seems to be inversely correlated with in vitro digestibility of samples (r = -0.5343, -0.6861 and -0.5921). However, analysis of plots displayed for the promatest index and all in vitro digestibility measures show that Promatest index values of some samples with close in vitro dry matter digestibility can drastically vary suggesting that others factors such as drying temperature and moisture content may be involved.