Application of Image Processing to Analyze Shrinkage and Shape Changes of Shrimp Batch during Drying

Abstract

In this article, variations in the top-view area and lateral-view area, average area, perimeter, Feret diameter, roundness, elongation, shape of the edge, and diameters of the shrimp in the batch parallel and perpendicular to the drying medium flow were investigated in defined intervals during drying. For this purpose, a thin-layer dryer based on machine vision was fabricated and image analysis techniques were used. Drying experiments were conducted in triplicate at five drying temperatures of 50, 70, 90, 110, and 120°C and three drying medium velocities of 1, 1.5, and 2 m/s. Purely near-atmospheric superheated steam drying (SSD) was used for the temperatures above the boiling point of water (110 and 120°C). Drying at the other temperatures was done using a hot air convective method. Analysis of batch area shrinkage, average area shrinkage, normalized Feret diameter, dimensionless perimeter, and diameters parallel and perpendicular to the drying medium flow showed that there are almost linear relations with moisture content. Drying medium temperature and velocity had a significant effect on all measured morphological parameters (P < 0.01). There was a significant difference between shrinkage of diameters parallel and perpendicular to the drying medium flow in all studied drying conditions, which implies that shrinkage of shrimp samples was nonisotropic. Moreover, comparing the top- and lateral-view areas of the shrimp batch showed that there was nonisotropic shrinkage in the shrimp samples during drying process. More regular and irregular edges of shrimp were obtained at low and high temperatures, respectively. Drying took place entirely in the falling rate period. Drying medium velocity had no significant effect on drying time. No regular trend regarding the effect of the studied drying medium velocities on the roundness and elongation of shrimp samples was found. More porous shrimp samples with a lower degree of shrinkage were obtained in superheated steam drying in comparison to hot air drying at high temperatures.