The transitioning feature between uncooked and cooked cowpea seeds studied by the mechanical compression test

摘要

Mechanical tests can allow for the mimicking of the textural attributes of foods as perceived by humans. Here we report on the use of the mechanical compression test to study the reactions underlying the cooking of the cowpea seeds (beans) until doneness. The creep test was applied to deal with the time-dependence of the strain, epsilon(t), at a constant force and to derive the elasticity, K-e and viscosity, K-v indices for the different heating times. The results, epsilon(t), were fitted using mostly a stretched exponential with a linear asymptotic (time) function. The flow rate (omega) and the strain (epsilon) are the constants of the asymptotic function. Both viscoelasticity indices decreased strongly before the first 30 min (from 562 N to 14 N for K-e and from 5.4 x 10(6) N s to 0.11 x 10(6) N s for K-v), but from 30 to 75 min + 3 min, K-e remained almost constant (similar to 14 N) while K-v increases (from 0.11 x 106 to 0.24 x 10(6) N s). Both viscoelasticity indices decreased strongly again after 75 min +/- 3 min (from 14 N to 0.24 x 10(6) N s for K-e and K-v respectively). The heating time-dependence of the viscoelasticity indices clearly reflects the cowpeas beans transitioning to the cooked state and this may be correlated directly to the kinetic of water absorption, starch gelatinization and protein denaturation. This would correlate not only to the cooking time but also to the nutrient quantity balance. The results from this study shows that the samples mechanical properties with the simmering time correlate with the cooking reaction transitioning.