Propolis Sample Collection, Extraction, and Processing

Propolis samples were collected in September of 2018 in Liaocheng Apiculture Research Institute, Shandong province, China. The ethanolic extract was prepared as reported by Almeida et al. (19). Ten grams of the powder was mixed with 100 ml of 75% ethanol in a sealed container protected from light (to avoid loss of volatile and photosensitive compounds) under agitation in a water bath at 70°C for 30 min. After extraction, the mixture was filtered. The filtrated liquid was combined with the original liquid. The ethanol was recovered by rotary evaporation and left overnight to obtain the crude propolis extract in the upper layer and the crude propolis extract in the lower layer.