Compairson Of Pretreatments And Drying Method For Dried Apple Cubes

This work has focused on usage of application of ultrasound, which is one ofadvanced pretreatment techniques prior to fruit drying and new drying techniques orcombination of several techniques in improving quality of final products in order tosolve problems of drying such as long drying times and high cost.Ultrasound pretreatment is applied at ambient temperatures, producingmicroscopic channels in materials to improve drying rate and it is known to havedifferent effects on different fruits. Effects of ultrasound (water as medium) andmicrowave pretreatments on apple cubes prior to spouted bed drying wereinvestigated. Ultrasound pretreatment resulted in great loss of sugars (25.7%for15min) compared to microwave pretreatment where little rise in sugar content wasobserved (1.6%for300W). Ultrasound pretreatment improved drying rate better thanmicrowave pretreatment. Nevertheless, microwave pretreated dried apples wereharder and had lower water activity than ultrasound pretreated ones. Low FrequencyNuclear Magnetic Resonance (LF-NMR) analysis used to study water state it revealedthat all pretreatments promoted redistribution of water among apple cellcompartments and showed that most of water lost is from vacuole. If dried fruits oflow calories are required then ultrasound pretreatment would be preferred.Microwave pulse spouted vacuum drying (MPSVD) of apple was assessed soas to improve the quality of dried apple, especially the structural and texturalproperties. Comparison to other drying methods; microwave spouted bed drying(MSBD), microwave vacuum drying (MVD) and vacuum drying (VD) was donebased on color, texture, density, rehydration capacity and sensory evaluation of driedapple. Although MPSVD did not have the highest drying rate, it exhibited dried applecubes with best color characteristics and highest sensory evaluation scores. MPSVD isa promising technique for development of healthy snack food products withreasonable processing time.