# The Influence of Processing on the Bioactive Compounds of Small Berries
## 4 Processing of Small Berries and Their Effects on Bioactive Compounds
### Drying  
Drying is one of the most common processing operations used to transform perishable fruits and vegetables into stable products available for consumption throughout the year [65; 69]. Berry drying can be achieved by using conventional or alternative methods. The advantages and disadvantages of each drying method are presented in Figure 3. Conventional methods include convective drying (hot air drying, convective multi-flash drying, fluidized bed drying), spray drying, freeze drying, and osmotic drying. Often, the combination of alternative technologies, like pulsed electric fields (PEF) or US, exhibits good potential for the drying of berries while offering superior protection of bioactive compounds. The most used alternative drying methods are presented in Figure 3.  
Convective drying is a simple and cheap method, easy to operate, and frequently used when processing solid berries and pomace [70]. Most of the time, the use of these convective drying methods requires high temperatures and long drying times, which frequently exert a negative effect on most of the bioactive compounds present in berries [69]. For instance, the convective drying of strawberries at 50 \({}^{\circ}\)C for 360 min decreased the antioxidant activity, anthocyanins, and total phenolic content by about 75%, 26%, and 61%, respectively [71]. Thus, many efforts have been made in an attempt to preserve the phytochemicals from berries by combining convective drying with other conventional drying methods, or replacing it with alternative methods [70]. Heat pump drying represents a good alternative to convective drying, being able to reduce energy losses, and reducing the costs of drying while providing enhanced quality. Another alternative to the convective drying of berries is vacuum drying. It uses lower temperatures, a high drying rate, and a low-oxygen environment while providing superior protection of bioactives [72]. [PERSON] et al. [73] applied vacuum drying (at 50 \({}^{\circ}\)C and 60 \({}^{\circ}\)C) on murta berries and obtained higher contents of bound flavonoids and polyphenols than from fresh berries. These results were attributed to the changes in the tissue structure during vacuum drying, which improved the extraction yield of the bound total flavonoids. Freeze drying is another vacuum drying technique that uses low temperature and low pressure, able to retain most of the biologically active components present in fresh berries, such as vitamins and antioxidants. When used alone, freeze drying requires up to six times more operating costs than hot air drying. However, the advantage of maintaining the bioactive properties of the berries almost intact compensates for the high costs. A combination of freeze drying with vacuum drying or microwave drying was shown to be a good alternative to hot air drying for obtaining berries with high vitamin C, total anthocyanin, and total polyphenol content, while improving the drying time and efficiency [70; 74]. For example, [PERSON] et al. [75] found that the microwave-assisted freeze drying of raspberry pure ensured high retention of anthocyanins, representing a promising alternative to conventional freeze drying. Far-infrared radiation heating assisted by vacuum drying was recently reported to possess excellent potential for drying berries with a waxy layer such as blueberries with a high content of bioactive constituents [76]. Compared to conventional drying techniques, the equipment used for far-infrared radiation is simple and requires a shorter drying duration and reduced energy consumption [70]. Spray drying is used for liquids, such as juices, to obtain powders with high shelf life, good solubility, and dispersibility. On the other hand, it uses high temperatures that may result in the degradation of bioactive compounds. [PERSON] et al. [77] showed that this drawback can be limited by applying ultrasound treatment prior to spray drying.