Impact of Drying Processes on Strawberry (Fragaria var. Camarosa) Texture: Identification of Crispy and Crunchy Features by Instrumental Measurement

The aim of this study was to evaluate the effect of hot air drying, freeze drying and swell drying (which is a coupling of hot air drying to instant controlled pressure drop DIC) on strawberry to compare and contrast its quality in terms of texture, such as crunchy and crispy features, correlated with the expansion ratios and the microstructure's modification. The obtained results showed that swell-dried strawberry had a high crispness behavior. Also, its relative expansion ratio was thrice more than air-dried samples. Moreover, it was observed that saturated steam pressure of DIC texturing operation compared with the thermal holding time had a significant effect on the maximum penetration distance and the average of microruptures force on crunchiness and crispness, respectively. Hence, these structural changes provide a versatile swell-dried strawberry as highly functional snack that was able to be evaluated instrumentally by puncture test. Practical Applications Puncture test is an instrumental measurement that helps to describe the crispness of snacks, biscuits, extruded products, etc. Swell-drying process is defined as instant controlled pressure drop (DIC)-assisted hot air drying. The thermomechanical effects of DIC are mainly induced by the abrupt pressure drop toward a vacuum (about 5kPa) after shortly subjecting the material to saturated steam pressure (from 0.1 up to 0.6MPa). The abrupt pressure drop rate (P/t>0.5MPa/s) causes an autovaporization of product's water, promoting instant cooling of the product, which immediately decrease the product's temperature under its Tg allowing to cross the glass transition Tg, which immediately stops the thermal effects avoiding any resulting degradation. The impact of DIC on strawberry can be observed in expansion ratio and much better through texture content as crispy and/or crunchy snacking. Hence, it is necessary to instrumentally describe the mechanical behavior of such a brittle-dried strawberry. The texture measurements allow using it as one of multicriteria optimization of DIC texturing processing parameters.