Comparative effects of freeze-drying, fluidized bed-drying and heat moisture treatment on the in vitro digestibility of dry matter, starch and protein of corn grain

There is some evidence that the chemical composition and nutritional value of corn is variable and may be influenced by heat treatment. This study compares the modifications induced by freeze-drying (as control), fluidized-bed drying and heat-moisture treatment (at 54, 90 and 130°C) of a flint corn grain and flour harvested at two different moisture content (33 and 28%, wet basis) on its digestibility assessed through in vitro methodologies. High temperature applied during fluidized-bed drying and heat-moisture treatment lead to the increase of the in vitro digestibility of dry matter. This is associated to a partial gelatinization of corn starch granules during heat treatments making them more suitable for digestion by porcine pancreatic amylase. This assumption is demonstrated by the increase of the in vitro digestibility of starch recorded with the increase of drying and heat-treatment temperature. It must be noted however, that at the same time, the digestibility of corn proteins decreased, probably because of denaturation undergo by proteins during heat treatment. It seems that there is an interaction between digestion of starch and protein, the corn starch granule being tightly embedded in a protein matrix. The extent of all of these phenomena strongly depends on availability of water which play a key but non clear role in the effect thermal history of corn grain in its nutritive value.