Crunchiness of Osmotically Dehydrated Freeze-Dried Strawberries

Consumers expect snacks that are tasty, healthy, and crunchy. However, optimizing crunchiness using sensory methods is time-consuming and expensive. Therefore, this paper proposes a new approach to measuring instrumental crunchiness. Whole strawberries of the "Honeoya" variety were osmotic dehydrated in a solution of sucrose and chokeberry juice concentrate for 1, 2, and 3 hours before freeze-drying. Texture was measured using acoustic emission (AE) and a compression test. The crunchiness index was calculated taking into account the number of AE events and mechanical energy. The content of bioactive substances, water activity, and porosity of the freeze-dried products were also assessed. Freeze-dried fruits after dehydration in chokeberry juice concentrate were characterized by lower final water activity and higher content of bioactive substances, but their crunchiness was the lowest. The crunchiest, loudest, and least hard were freeze-dried strawberries, dehydrated in a sucrose solution. The tested freeze-dried strawberries differed in the range of sound frequencies generated, which indicates a different cracking mechanism.