Comparative study of microwave assisted extraction and ultrasound assisted-extraction for the maximum recovery of phenolic compounds from Camellia japonica var Eugenia de Montijo

Camellia japonica is an underexplored medicinal plant with associated bioactivities (Pereira et al., 2022). Innovative approaches to the large-scale application of C. japonica are proposed, with one of the main lines being the extraction of phenolic compounds (Cho et al., 2009). Significant efforts are taken in order to develop rapid technological progress with low costs, labor and time. Green extractions, and among them microwave and ultrasounds assisted extraction (MAE and UAE), are popular and relatively inexpensive extraction techniques (Hanula et al., 2020). Therefore, the purpose of this study was to find the optimal green extraction method of C. japonica var. Eugenia de Montijo flowers´ (ultrasound or microwaves) able to isolate extracts containing the highest yields and amounts of phenolic compounds. Both processes were optimized by response surface methodology using a five-level central composite design combining the independent variables of processing time (t, 5-25 min), temperature (T, 50-180ºC) and solvent (S, acidify ethanol 0-100%) for MAE and ultrasound power (P, 150-400 W), t (0-45 min) and S (acidify ethanol 0-100%) in the case of UAE. The main extracted compounds were identified and quantified by LC-MS/MS. Two responses were studied: extraction yield and content of phenolic compounds. The results showed that the maximum yields (80%) were obtained with MAE at high temperatures and low times (180ºC, 5 min). The main family of phenolic compounds were flavonols (i.e., kaempferol 3-o-acetyl-glucoside, dihydroquercetin). Based on these results, the current study contributes to the valorization of underutilized flower species common in Spain's North-West region by obtaining rich extracts in phenolic compounds that can potentially be used as ingredients in various industrial fields.