Orange byproduct (flavedo and albedo) from juice extraction, was used as raw material for this study. Kinetics of total phenolic and total flavonoid contents and antioxidant activity was experimentally determined during both conventional (agitation at 80 rpm) and ultrasound assisted (at 520 and 790 W/L) aqueous extraction from orange byproduct at 5, 15, and 25 °C. An extraction mathematical model was also developed. Significant increase of biocompounds extraction yields was observed as temperature and acoustic power density increased. Ultrasound assistance allowed higher yields at lower temperatures and shorter times. Yields of total phenolic and total flavonoid contents and antioxidant activity obtained with ultrasound extraction (790 W/L, 25 °C, 3 min) were 29%, 39%, and 197% higher, respectively, than those obtained by conventional extraction. The extraction kinetics curves were properly represented by the Weibull model for both conventional and acoustic extraction (mean relative error lower than 5%). Naringin, neohesperidin, and hesperidin were the main phenolic compounds found in the extracts, followed by ferulic, sinapic, and cuomaric acids. Neohesperidin, hesperidin, coumaric acid, and sinapic acid presented the highest yields, especially when extraction was assisted by ultrasound. Meanwhile, naringin and ferulic acid were extracted in a lesser extent, most likely due to their lipophilic character.

Drying may alter the microstructure of vegetables and influence the release of bioactive compounds during digestion. The effects of convective drying (at 60 °C and 2 m s⁻¹; CD) and freeze-drying (at −50 °C and 30 Pa; FD) on the microstructure (evaluated using scanning electron microscopy (SEM) and image analyses with ImageJ software) of beetroot and the kinetics of biocompound release (total polyphenol content (TPC) and antioxidant activity (AA)) during 180 min of in vitro gastric digestion have been studied. Raw beetroot was used as the control. Drying promoted the collapse of cell walls causing volume shrinkage that resulted in a greater cell number per area unit; meanwhile in vitro digestion caused cell structure disruption, which resulted in a lower cell number per area unit. Drying promoted decreases of TPC (42% in CD and 29% in FD) and AA (66% in CD and 63% in FD) of beetroot. However, release of TPC and AA from dried samples during digestion was 82% (CD) and 76 (FD) % higher than from the raw sample. The Weibull model allowed the satisfactory modelling of the TPC and AA release kinetics (mean relative error of simulation lower than 8.5%).

The impact of cryogenic pretreatments on drying performance was studied in blueberries, seabuckthorn fruits and green grapes. The fruits were immersed in liquid nitrogen in 2 min freezing/thawing cycles (one to five). Untreated samples were used as the control. Drying experiments were carried out on treated and non-treated berries at 50 °C and 1 m/s (hot-air-drying), 50 °C and 25″ Hg vacuum (vacuum-drying), 30 mTorr total pressure and 25 °C shelf temperature (freeze-drying). The weight loss evolution of the foodstuffs was measured as a function of time. Microscopic (SEM and optical) determinations of the epicarp were performed. A visual inspection was performed and color changes and volume reductions were assessed before and after dehydration. The thickness of the berries’ epicarp decreased between 20 and 50% (depending on the fruit) after 3–5 immersions in liquid N2. The drying kinetics was accelerated significantly for the three tested drying processes (i.e., drying time decreased from 48 to 16 h for blueberry freeze-drying). The best quality of dried berries was observed for pretreated blueberries after freeze-drying, keeping their volume, shape and color after the process. This work shows that “tailor-made” dried berry products with desired properties can be achieved and drying performance can be improved by the application of ultra-low temperature pretreatments.