Coating pretreatment of banana slices using carboxymethyl cellulose in an ultrasonic system before convective drying

Abstract

Drying is one of the oldest methods of food preservation. However, this method requires careful promotion and maintenance of the quality of the dried products. In this paper, Carboxymethyl cellulose (CMC) coating and sonication pretreatments were employed as a new approach to improve the efficiency of convective drying and produce dried banana slices with acceptable quality in a short period. To achieve these goals, the effects of ultrasonic power (at three levels of 0, 500, and 1000 W) and sample to CMC coating solution ratio (with three levels of 1:2, 1:3, and 1:4), as well as the mutual effect of these two independent variables, were evaluated. The results showed that increasing the ultrasonic power from 0 to 1000 W decreased the drying time (P ≤ 0.001), energy consumptions of the convective drier (P ≤ 0.001), total energy consumption (P ≤ 0.001), shrinkage (P ≤ 0.001), apparent density (P ≤ 0.001), shear stress (P ≤ 0.001), and the total color change (P ≤ 0.001); it also increased energy consumptions of the ultrasonic system (P ≤ 0.001), porosity (P ≤ 0.001), and TPC (P ≤ 0.001) of the dried banana slices significantly. Moreover, changing the sample to coating solution ratio from 1:2 to 1:4 reduced the shrinkage (P ≤ 0.001), apparent density (P ≤ 0.001), shear stress (P ≤ 0.001), and total color change (P ≤ 0.01); this also led to remarkable increase in the porosity (P ≤ 0.001) and TPC (P ≤ 0.05) of the dried samples. With respect to the cross-sectional scanning electron microscopy (SEM) images of the dried banana slices, it was found that the CMC coating pretreatment in an ultrasonic system, especially with an ultrasonic power of 1000 W and a sample to coating solution ratio of 1:4, enhanced the porosity of the dried banana slices. Overall, the combined application of ultrasonication and Carboxymethyl cellulose coating pretreatments could be considered as an effective approach to improve the quality of the dried products through convective drying.