Comparison of two alternatives of combined drying to process blueberries (O'Neal): Evaluation of the final quality

Abstract

In this work, we examined and compared two combined alternatives for the drying of blueberries (O´Neal). Pretreatments of osmotic dehydration (60°Brix sucrose solution, at 40°C for 6h) and hot air drying (60°C, 2.5 m/s for 90 min) were performed to reach the same water content. Pretreated blueberries were then dried by microwave at different microwave output power values: 562.5W, 622.5W and 750W. The combined drying processes were also compared with hot air drying alone (control). The effects of the processes over blueberries were studied in terms of decrease in water content, drying rate, mechanical properties (firmness and stiffness), optical properties (L*, a* and hue angle (h)), antioxidant capacity and rehydration capacity. The hot air-microwave drying decreased the process time and presented a high drying rate compared with the osmotic dehydration-microwave processes and the control drying. In terms of quality, the antioxidant and rehydration capacities were the most affected. The results showed that the best drying method to obtain the desired final product was the hot air-microwave drying (750W).

Experimental study of dehydration processes of raspberries (Rubus Idaeus ) with microwave and solar drying

“…The same extract was used to all determinations. The DPPH radical scavenging activity assay and ABTS cationic radical scavenging activity were determined according to the method described by Rodriguez et al (2015).…”

“…was determined. The concentration required to obtain a 50% antioxidant capacity, is typically used to express the antioxidant activity and to compare the antioxidant capacity of various samples (Rodriguez et al, 2015). ABTS + (2,2-azino-bis-(3-ethylbenzo-thiazoline-6-sulphonic acid)) was produced by mixing ABTS stock solution (7 mM) with potassium persulfate (2.45 mM).…”

“…Total polyphenols content was determined using the Folin-Ciocalteu method (Rodriguez et al, 2015). An aliquot of 0.5 mL of the extract was mixed with 2.5 mL of Folin-Ciocalteu´s reagent, (previously diluted 10-fold with distilled water) and 4 mL of Na 2 CD 3 solution (75 g/L).…”

“…Several studies have been reported on solar drying (Hassanain, 2010;Hossain et al, 2008;Rajkumar et al, 2007) and microwave drying (Zhao et al, 2016;Rodriguez et al, 2017a;Rodriguez et al, 2015;Bruijn & Bórquez 2014;Ghanem et al, 2012) of fruits and vegetables. However, there are limited studies on drying of raspberries.…”

Combined drying of Nopal pads ( Opuntia ficus‐indica ): Optimization of osmotic dehydration as a pretreatment before hot air drying

“…However, its main disadvantage is that it takes a long time, even at high temperatures, damaging the main attributes of the dry product (Sharma & Prasad, ). For this reason, the synergistic and additive effects of the combined drying would allow improving the drying performance and preserving the food quality (Rodríguez, Zaro, Lemoine, & Mascheroni, ).…”