Chemical, microbiological and organoleptic studies on onion slices dehydrated by steam and microwave techniques

Abstract EN

The objective of this analysis was to determine the effects of various dehydration technologies (steam and microwave) on the chemical, microbiological and organoleptic effects of onion slices (Allium cepa L.).

Specimens for onion cutouts were dried by using a three-phase microwave power from 290 W to 800 W and a steam dehydration method from 4 hours in 3 parts (130 °C/60 min, 100 °C/60 min and 80 °C/120 min) on the microwave floor.

Dehydrated onion strips have decreased to a humidity value of 4.91 -5.78% equivalent to 86.14% of fresh onion pieces due to substantial moisture loss.

Other nutrients such as crude fat , total protein, crude fiber , ash and carbohydrate contents of dehydrated onion slices have been concentrated.

As a result, their nutritional values improved compared to fresh pieces of onion.

The discrepancies between the chemical composition content of steam and microwave dried onion slices were not statistically important, but other variables like pungency and sugar levels as well as microbial parameters were significant (p<0.05).

In addition, the production power levels in the microwave oven used in the test did not impact the main components (total protein, crude fat , ash, crude fibre and carbohydrate) and other nutrients (vitamins, pungency and sugar) of the dried samples, but had a substantial impact on the organoleptic and microbial parameters.

As regards the physical appearance, the dehydrated samples showed that microwave dehydrated slices at 480 W and 800 W had discolored to brownish tint, but the transition was slightly more pronounced in the case of steam dehydrated and microwave dehydrated slices at 210 W.

However, the steam-dehydrated slices were lighter in colour and appropriate in appearance.

In conclusion, more research will be required on microwave food dehydration and the implementation of such technology in Egyptian factories to reduce the loss of water-soluble components during dehydration, minimize drying time and energy consumption, and have no significant effect on the sensory characteristics of dried onion slices.