# The Influence of Processing on the Bioactive Compounds of Small Berries
## 4 Processing of Small Berries and Their Effects on Bioactive Compounds
### Drying
The combination of the two drying methods allowed dried raspberries, blackcurrants, and elderberries with improved bioactive constituents to be obtained [77]. Figure 3: The drying methods used for drying berries: mechanisms, advantages, and disadvantages (adapted from [70]). Osmotic drying is a method based on the use of hypertonic solutions, where fresh berries are immersed, enabling water transfer from the food matrix to a solution due to an osmotic pressure difference [70]. Frequently, the hypertonic solutions used as drying agents include sugars, sodium chloride, polyols, or concentrate juices. For example, the osmotic treatment of strawberries using concentrated chokeberry juice was shown to be very effective in improving the polyphenol content and antioxidant activity of dried strawberries [78]. The high moisture, sugar, or salt content of the final product, which does not allow the chemical composition at the end of the drying process to be predicted, is considered the main disadvantage of the osmotic dehydration process [70]. The drying of berries using microwaves (MWs) represents an attractive alternative as it provides high drying rates and limits the oxidation process, while the product quality, in terms of mechanical properties and phytochemical content, is enhanced [79]. The main disadvantages of using MW drying are associated with the difficulty of assuring uniform temperature, the limited penetration depth of the microwave radiation, and high initial costs [79]. When processing berries, combining MW with another drying method showed excellent potential for limiting these drawbacks. Often, MW drying is assisted by convective or vacuum drying. For example, [PERSON] and [PERSON] [69] tested the influence of freezing, convective, and MW-vacuum drying on the bioactive components of cranberries. The authors showed that MW-vacuum drying was able to better protect the total phenolic content of cranberries compared to convective drying. Moreover, compared to freeze drying, the antioxidant activity of the cranberries subjected to MW-vacuum drying was significantly higher. However, the phytochemical content was dependent on the MW power; the contents of polyphenols, flavonoids, and anthocyanins of cranberries were significantly reduced at powers above 300 W. Similar observations were reported for blueberries; the degradation of total polyphenols and anthocyanin components was lower during MW-vacuum drying compared to hot air convective drying. During MW-vacuum drying, the exposure of the blueberries to oxygen was lower compared to hot air convective drying, causing minor changes in the phytochemical components [80]. [PERSON] et al. [81] compared the effect of freeze drying, vacuum drying, vacuum-MW drying, and convective drying on the phytochemicals of strawberries. Among the tested methods, vacuum-MW drying at a microwave power of 240 W was the most efficient in the retention of heat- and oxygen-sensitive phenolic components and ascorbic acid in strawberries. A comparative study on strawberry drying using radio frequency, MW, freeze drying, and hot air was performed by [PERSON] et al. [82]. Compared to MW drying and hot air drying, radio frequency and freeze drying favored the retention of more anthocyanins and phenolic compounds. The pretreatment of berries by sonication, followed by MW-vacuum-assisted drying, showed good potential for the drying of cranberries while ensuring superior retention of bioactive compounds, as recently reported by [PERSON] et al. [39]. cranberries pretreated with a combination of blanching, ultrasound, and pulsed electric field, followed by MW-vacuum drying, presented a higher content of anthocyanins compared to control samples (without blanching, ultrasound, or pulsed electric field treatment) [65]. The use of explosion puffing drying as a pretreatment, followed by freeze drying, resulted in dried mulberries and raspberries with a high content of anthocyanins and antioxidant activity, as shown by several authors [83; 84]. [PERSON] et al.