Evolution of the physicochemical properties of oil-free sweet potato chips during microwave vacuum drying

Abstract

The demand for healthy and convenient foods is a worldwide trend. Sweet potato attracted great attention due to its carbohydrates with a low glycemic index. Dehydrated sweet potatoes can be an excellent alternative for using and adding value to this raw material. The objective of this study was to evaluate the physicochemical properties of sliced sweet potato during the microwave vacuum drying (MWVD) for producing crispy oil-free chips. Fresh sweet potato samples were selected, peeled, sliced, blanched, and then dehydrated using a microwave oven adapted with a vacuum chamber and a rotation system to operate under vacuum. It was measured the evolution of moisture, water activity, temperature, color, apparent specific mass, porosity, and acoustic/mechanical analysis of the texture during the MWVD. Crispy sweet potato chips were obtained in <30 min, presenting low moisture (0.028 g g−1 db) and water activity (0.262). The dehydrated samples showed high porosity (67.5%) and a low apparent density (0.456 g cm−3). Optical micrographs and acoustic/mechanical properties showed an expanded (puffed) product structure with large pores, which resulted in irregular acoustic/mechanical signals, characteristics of a crispy food matrix. Colorimetric analyses indicated a little change between fresh and dried samples, with an absence of burnt spots. In conclusion, MWVD is a suitable process to produce highly porous sweet potato chips, adding value, and extending the vegetable's shelf life.