Ultrasound-assisted extraction of total anthocyanins from Rubia sylvatica Nakai fruit and radical scavenging activity of the extract

Ultrasound-assisted extraction (UAE) of total anthocyanin (TA) and total phenolics (TP) from Rubia sylvatica Nakai fruit (RSF) was optimized using response surface methodology. On the basis of a single-factor experiment, six factors were screened using a Plackett-Burman experimental design to determine the variables that significantly influence the extraction yield of TA and TP, namely ultrasound power, liquid: solid ratio, ethanol concentration, pH value, extraction temperature, and extraction duration. Based on statistical significance analysis, ethanol concentration, pH value, and extraction temperature were selected for further optimization of the extraction process using a Box–Behnken design. Under the optimum conditions, yields of TA and TP were 22.50 ± 0.89 mg cyanidin-3-glucoside/g RSF and 36.20 ± 0.11 mg gallic acid/g RSF, respectively. The extract prepared under UAE exhibited excellent DPPH radical scavenging activity (IC 50 1.21 ± 0.04 mg/mL). The results demonstrate that R. sylvatica fruit are rich in anthocyanins and show considerable potential as a source of colorants for use in the food industry.