Thin layer drying kinetics of Banana var. Monthan (ABB): Influence of convective drying on nutritional quality, microstructure, thermal properties, color, and sensory characteristics
Authors: Kumar Paramasivam Suresh , Nambi Eyarkai , Shiva Karur Nallappagounder , Vaganan Muthu Mayil , Ravi Iyyakkutty , Jeyabaskaran Kandallu Jayaraman , Uma Subbaraya 
Published: February 2019

Banana with good amount of resistant starch (RS) offers greater benefit to human health. Studying the dehydration mechanism of the raw banana slice is very important for subsequent processes and quality of the product. Thus the study was aimed to investigate the influence of varying temperatures viz., 45, 55, and 65°C in a convective dryer on thin layer drying kinetics and to infer their influence on the rheological properties coupled thermal and sensory quality. Time for reducing the moisture content from the initial 71.2 ± 0.2% to a final 4.66–6.13% was found to be 270, 210, and 150 min for the drying temperatures 45, 55, and 65°C, respectively. Moisture ratio decreased exponentially with an increase in drying time. Page and logarithmic models obtained highest r2, lowest chi‐square values and least root mean square error and better reflected drying mechanism of banana slices. Improved rehydration ratio (1:2.4) and RS content (36.26%) was observed with the drying temperature of 55°C. Higher water absorption capacity (WAC) was observed in 55°C (4.86%). Swelling power of the flour was maintained to 4–6% till 70°C but it reached to 22% with the increase in temperature to 90°C. Thermal properties and microstructure of flour differed significantly with the temperatures. The lower value for whiteness index with low temperature drying reflected the better drying than at higher temperatures. Dehydration at 55°C was superior with nutrients like ascorbic acid. The banana flour had the rod shaped starch granules and traces of protein in its surface as evidenced. Irregular spherical shape, surface dents, and shrinkages were observed in powders dehydrated with high temperature (>65°C). Equilbrium relative humidity (ERH) studies revealed that 13.27 and 15.23% were the danger and critical point, respectively, for the banana flour. Descriptive sensory scores of the banana flour endorsed that dehydration at 65°C was found superior to other temperatures.

Practical applications

Banana flour offers greater potential to increase the resistant starch (RS) content in the food products besides adding minerals and basic nutrients. Drying process should retain the characteristics of fresh fruits by minimizing the cellular and structural changes during the drying. Mathematical modeling offers scope to set the variables which are influencing the drying of banana slices. The dried banana flour could be a replacement or supplement for various formulations. With the better physical properties like swelling capacity and enthalpy along with high RS, banana flour allow the formation of low bulk, high‐fiber products like pasta, noodles, and healthy functional foods with improved sensory descriptors. Banana flour‐based enterprises could be started in places where banana is cultivated and large sum of produced bananas are getting wasted due to poor postharvest management.