Microwave hydrodiffusion and gravity pretreatment of Camellia japonica flowers for the extraction of bioactives

The valorization of Camellia japonica flower varieties through the green extraction of their bioactive components is addressed. Microwave hydrodiffusion and gravity (MHG) can be an efficient and rapid pretreatment to dry the petals; for example, in the Royal Velvet variety, the energy consumption was 16 times lower compared to air drying. The hydrolates obtained in this stage represented only 0.5 mg gallic acid equivalents/g flower, but some of the fractions contained up to 10 times higher and a Trolox equivalent antioxidant capacity (TEAC) value equivalent to 0.4 g Trolox/g extract. The dried solids were extracted using 96% ethanol to yield around 30% solubles, which was 50% higher than the extraction yield from the air-dried samples. The MHG dried solids were treated with supercritical CO₂ to yield up to 2.4% of an extract containing phenolics and lipids with a favorable omega-3 to omega-6 ratio. The residual solids from supercritical extraction were further processed with microwave heated pressurized hot water for 5 min at various temperatures. The 200 °C extract achieved a solubilization of 50% of the material, obtaining a product with 22% phenolic content, almost 30% of the antiradical capacity of Trolox, a minimum inhibitory concentration (MIC) value of 8 mg/mL against Staphylococcus aureus, and contained mainly organic acids, tannins like (epi)catechin gallate and B-type (epi)catechin oligomers, and prodelphinidins like (epi)gallocatechin-O-hexoside and (epi)catechin-(epi)gallocatechin gallate. The obtained extracts were proposed for incorporation onto starch films. The results confirm the potential of non-toxic solvents to achieve a complete valorization of this resource.