Evaluation of Methods for Expansion Properties of Legume Extrudates

The expansion properties of extrudate such as diameter ratio, sectional expansion index, longitudinal expansion index, specific length, and specific density are used to describe the effect of extrusion processing as well as material parameters. In this study four types of extrudates namely lentil, lentil+starch, whole dry pea+starch, and split dry pea+ starch were evaluated for their expansion properties with N = 50. The effect of number of replicates and progressive values of the statistical parameters like mean, coefficient of variability (CV), standard deviation (SD), and standard error (SE) were compared graphically. It was determined that 30 replicates were sufficient for determining the expansion characteristics of the extrudates. The CV of the extrudates was lower than other engineering materials due to the homogeneity of the sample, obtained as effect of the mixing capacity of extrusion processing. A mathematical relationship was developed from the pooled data to predict the number of replicates required for desired CV from the advance estimate with five observations. The determination of specific density by dimensional measurement, as well as bulk density by glass bead displacement, was also compared. For measurement of bulk density, five replicates were found to satisfy low CV condition.