Porosity, color, texture, and microscopic structure of russet potatoes dried using microwave vacuum, heated air, and freeze drying.

Microwave vacuum drying (MVD) provides an alternative drying method for making dried products with a puffed, porous texture. This article describes the porosity, color, texture, and microscopic analysis of potatoes dried using MVD, heated air (HAD), and freeze drying (FD). The porosity was calculated from a ratio of apparent density and true density. A mathematical model for calculating true density from moisture content and apparent density was derived. Potatoes dried using MVD had 20 times the porosity compared to HAD potatoes; but FD had the highest porosity. Puncture tests and SEM images supported indirect and direct confirmation for the experimental porosity. Texture measurements indicated that MVD potatoes were crispy and porous, HAD potatoes were hard and brittle, and FD potatoes were spongy and subject to shatter. MVD potatoes retained more fresh-like color compared to HAD and FD potatoes.