## 3 Processing and Extraction
### Microwave-Assisted Extraction (MAE)  
Microwave-assisted extraction employs microwaves--non-ionizing electromagnetic waves--which cause changes in plant cell structure. The phenomena of heat and mass transfer which proceed in one direction occur in this type of extraction. The microwave energy is applied directly to material due to molecular interactions with the electromagnetic field through the conversion of electromagnetic energy to thermal energy. The heat must be then dissipated volumetrically inside the sample. These phenomena improve cell penetration and the internal and external diffusion of compounds is what finally leads to improved extraction yields [124]. The examples of microwaves applied in bioactive compound extraction processes for berry fruit wastes are presented in Table 8.  
[PERSON] et al. [125] studied the optimum conditions for MAE of anthocyanins from black-currant pomace. Variable values for power, time, solid-liquid ratio and the pH of the solvent were applied. Results have shown that the highest power (700 W) and solid-liquid ratio (1:20) but the shortest time (10 min) and the lowest pH (2) values were the most efficient conditions for anthocyanin extraction. In a HPLC study, delphinidin-3-rutoside turned out to be the most abundant anthocyanin. [PERSON] et al. [126] applied various types of solvents and levels of power in MAE of pectin and polyphenolic rich extracts from cranberry pomace. The highest yields of polyphenols were obtained with an alkaline extraction process with a power value of 36 W/g. When SLE and MAE used with different solvents of cranberry press residues were compared, MAE resulted in a higher yield of extraction in every variant of the experiment. Values of quercetin equivalents of powdered cranberry residues were highest for MAE with 100% acetone used as a solvent and were significantly increased compared to water and ethanol extraction processes [127]. [PERSON] et al. [128] compared different methods of extraction of phenolic compounds from cranberry pomace: SLE, UAE and MAE, using ethanol and trifluoroacetic acid as a solvent mixture. The extract obtained in MAE featured the lowest anthocyanin and polyphenol contents across all the studied samples. Impact of Processing Conditions  
Power: Inconclusive results of applied microwave power impact on efficiency were observed. A higher power value applied in MAE improved the extraction of anthocyanins from black-currant pomace [125] and also led to lower phenolic content in extracts from cranberry pomace [126]. These results are associated with the temperature increase when extended power is applied. The efficiency of MAE increases with increasing microwave power till the optimum temperature point is reached, after which it starts to decrease while the power (and temperature) is still rising [124]. Time: The shorter the time of microwave input, the better MAE efficiency was observed [125]. This may be related to the destructive impact of microwaves and the increased \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multicolumn{3}{c}{**PEF Conditions**} & \multirow{2}{*}{**Antioxidant Composition**} & \multirow{2}{*}{**Antioxidant Activity *} & \multirow{2}{*}{**Reference**} \\  & **(E—Equipment, F—Power, FS—Field Strength, & & & & \\  & **f—Frequency, W—Pulse Width, I—Energy Input, S—Solvent, L–Liquid-Liquid Ratio)** & & & & \\ \hline \hline  & E: PEF system & & & & \\  & Pulse duration: 2 μs & & & & \\  & S: acidic ethanol & & & & \\  & L/L: 15/1:6/17 & & & & \\  & PS: 15/20/25 kV/cm & & & & & \\  & No of pulses: 8/10/12 & & & & \\  & Flow rate: 7 mL/min & & & & \\ \hline \hline \end{tabular}
* Results are expressed as written in the bracket after first given result.  
\end{table} 
Table 7: _Cont._temperature on the structure of bioactive compounds. A prolonged duration of microwave power applied to a sample can promote the degradation of antioxidants [124]. Solvent type: The solvent influence on the MAE process is similar to that described in SLE.