A microwave multi-flash drying process for producing crispy bananas

• Microwave vacuum drying is an emerging technology of great interest for drying fruits.
• Multi-flash drying is a procedure reported as suitable for producing crisp fruits.
• Multi-flash drying coupled with microwave heating has not reported by literature.
• Microwave multi-flash drying is a suitable process for producing dried-and-crisp fruits.

A comparative study of different drying strategies to produce dried bananas with controlled microstructure and texture properties was conducted. The result of applying microwave heating coupled with vacuum pulses on the crispness of dried bananas was investigated. Banana slices were dehydrated by microwave vacuum (MWVD), a microwave multi-flash drying process (MWMFD) and freeze drying. Drying kinetics for MWVD and MWMFD showed three drying periods, i.e. i) a very short heating period, ii) constant drying rate period and iii) falling rate period. The higher nominal microwave power led to larger drying rates. The three different magnetron powers applied to the fruits did not result in different microstructures and textures, for a same drying procedure. On the other hand, MWMFD resulted in dried fruits with larger pores and porosities 20–50% higher than those produced by MWVD. Furthermore, puncture tests of MWMFD samples resulted in more irregular force–strain curves (jagged curves) that are characteristic of crisp products. The results show that it is possible to create dried-and-crisp fruits by applying successive cycles of heating and vacuum pulses in a microwave field. The MWMFD process is more effective than the MWVD process for producing dried-and-crisp bananas, with very short drying times when compared to freeze-drying times.