Influences of Pretreatments and Drying Process Including Fluidized Bed Puffing on Quality Attributes and Microstructural Changes of Banana Slices

Abstract

Healthy snacks have received more attention because of their low fat content. Color and texture are important to snack quality. Effects of chemical pretreatment, thickness, blanching, and puffing temperature on quality of banana slices were therefore investigated. Banana slices (2.5 and 3.5 mm thickness) were chemically treated by citric acid and sodium metabisulfite, blanched, and dried at a temperature of 90 C to an intermediate moisture content of 25% db. They were then puffed in a fluidized bed dryer at 160 and 180 C for 2 min and dried again at the same drying temperature as the first drying step. Blanching, puffing temperature, and thickness strongly affected the degree of shrinkage, effective moisture diffusivity, morphology, textural properties such as hardness and crispiness, and color, but the chemical treatment did not affect those qualities. Blanching can improve the product appearance; the color was uniform and shiny throughout the surface and golden yellow. However, the textural attributes of the blanched sample had higher hardness and less crispiness than those of unblanched sample.

Comparative study of the effects of thermal blanching pretreatments and puffing temperature levels on the microstructure and qualities of crisp banana slices

“…Starch gelatinization can limit the moisture movement during drying, thereby extending drying time of the first predrying step. Similar findings were reported byAbano (2020) andRaikham et al (2015).…”

“…In comparing the hot water and steam pretreatments, the difference between them in the volume ratio of their bananas was negligible (not significant). Both type of pretreatments could be applied successfully to increase the volume for crisp Namwa bananas; however, the decreased volume ratio was observed in crisp blanched Homtong bananas (Raikham et al, 2015).…”

“…The crisp banana samples were analyzed for their texture properties by the Instron texture analyzer (TA-XT plus, Stable Micro Systems, Surrey, UK) which used a 5 N load cell. A cutting probe (HDP-BSK type) was used to fracture crisp banana samples with a blade speed of 2 mm/s (Raikham et al, 2015).…”

“…This study revealed a wide range of pore sizes in banana microstructure and corresponding to the morphological structure of crisp bananas under various thermal blanching pretreatments at a puffing temperature of 170 C as shown in Figure 6. Similarly, the microstructure of the crisp Homtong banana slices that were processed by HTST (Raikham et al, 2015), as well as that of the crisp durian slices that were processed by microwave vacuum drying (Paengkanya et al, 2015) also contained widely range of pore sizes throughout their cross-sectional area. In contrast, for crisp mango and papaya processed via freeze drying or freeze drying combined with explosion puffing, they both featured uniform pore sizes in their structure (Yi, Lyu, Bi, Zhou, & Zhou, 2017).…”

“…Nevertheless, the banana slices often undergo browning and are partially scorched on their surface after puffing. This brown color on dried food may be due the enzymatic browning (Liu, Mujumdar, Zhang, & Jiang, 2015) and nonenzymatic browning that takes place during the high-temperature processing of starchy foods (Raikham, Prachayawarakorn, Nathakaranakule, & Soponronnarit, 2015;Tabtiang et al, 2012). The brown coloring on the dried product can produce acrylamide in the starchy food product (Mustafa, Anderson, Rosen, Eldin, & Åman, 2005).…”