Effect of Processing Parameters on Trypsin Inhibitor and Lectin Contents of Tortillas from Whole Raw Corn‐Soybean Mixtures
Authors: DEL VALLE F. R. , PICO M. L. , CAMACHO J. L. , BOURGES H. 
Published: August 2006

Trypsin inhibitor and lectins in raw corn‐soybean blends (92/8 and 84/16 w/w, dry basis) cooked in limewater decreased with cooking time and increasing lime concentration, with total inactivation occurring, in all cases, after 30 min. These factors, determined in raw corn‐soybean (92/8 and 84/16 w/w, dry basis) tortillas decreased with increasing hot plate contact time; total inactivation of both occurred only with 92/8 tortillas after 60 sec. Antinutritional factor inactivation rates were considerably higher for hot plate cooking than for limewater boiling. Soaking cooked blends in liquor after turning off the heat and allowing to cool, followed by grinding into a dough had little effect on antinutritional factors, while washing cooked blends with water resulted in some reduction of both factors. Corn‐soybean tortillas prepared with normal heat treatment had no residual factors, while those prepared with minimum heat treatment had insignificantly low residual trypsin inhibitor and no lectins.

SUMMARY & CONCLUSIONS

EFFECTS of processing parameters on trypsin inhibitor and lectin contents of corn‐soybean tortillas prepared by lime cooking of whole raw corn‐soybean mixtures may be summarized as follows.

Cooking time in boiling limewater and on the hot plate produces the largest reduction of both trypsin inhibitor and lectins. Due to higher temperature and higher initial blend moisture content involved, hot plate cooking exhibits higher inactivation rate than limewater boiling. Total reduction of antinutritional factors is higher when boiling in limewater, however, due to considerably longer processing time employed as compared with hot plate cooking.

Trypsin inhibitor and lectin inactivation rates on boiling in limewater appear to increase with increasing lime concentration due, probably, to additional protein denaturation by higher pH's.

Soaking in cooking liquor after boiling in limewater and turning off the heat results in relatively little reduction of trypsin inhibitor and lectins, because temperature begins to drop after the heat has been turned off.

Some trypsin inhibitor and lectins appear to be leached out into the liquor during cooking and removed by subsequent washing. This effect, however, produces relatively little reduction of both antinutritional factors.

Grinding of cooked corn‐soybean mixtures into a dough involves relatively low temperatures and produces very low temperature rise; consequently, this process probably results in negligible change in trypsin inhibitor and lectins.

In all experiments performed, lectin agglutinating activity to human blood was appreciably lower and more easily destroyed by heat treatment or increasing lime concentration, than to rabbit blood.

Tortillas prepared by limewater cooking of whole raw corn‐soybean mixtures by the traditional method would probably be free from trypsin inhibitor and lectins if normal heat treatment, resulting from employment of usual processing conditions (i.e., boiling in limewater for 30 min and cooking 45 sec on a hot plate, alternating sides, 15 sec each side) were applied. In this case most antinutritional factor activity would be destroyed by limewater cooking, with additional heat treatment applied on the hot plate serving as a safety factor. If, on the other hand, a heat treatment lower than normal were applied, tortillas with residual trypsin inhibitor, but no lectins, could result. Trypsin inhibitor level, however, would probably be too low to be of any significance.

It can be concluded that, because of the reduction of the concentration of trypsin inhibitor and lectins, corn‐soybean tortillas prepared by the method described in this paper would probably be suitable for human consumption.