Aqueous extracts from agrocybe cylindracea and pleurotus ostreatus as source of antioxidant coatings

Agrocybe cylindracea and Pleurotus ostreatus mushrooms are rich in polysaccharides and phenolic compounds with antioxidant and antimicrobial properties. Therefore, these mushrooms can be a good source of natural food preservatives and edible coatings. The main goal of this study was to develop an edible coating with antioxidant activity. Edible coatings are composed of biopolymers and may be carriers of additives with bioactive properties. This study developed an aqueous extraction process that allows the extraction of biopolymers and bioactive compounds (eg. phenolic compounds) from A. cylindracea and P. ostreatus mushrooms, with antioxidant activity, which can be used as preservative edible coating. To accomplish this, after a pre-treatment by maceration of frozen mushrooms two consecutive aqueous extractions were applied, where the first was at room temperature (A) and the second (B) was hot extraction (90ºC; 1h; 5 000rpm). Extracts were lyophilized and the extraction yields were determined. Total phenolics content was determined through Folin Ciocalteu and antioxidant activity through ABTS method. The yields of extracts A and B from P. ostreatus were 33.60% ± 0.39 and 15.18% ± 0.70. The yields of extracts A and B from A. cylindracea were 30.91% ± 0.89 and 14.77% ± 1.49, respectively. These results are in agreement with yields of A. cylindracea hot-water extracts reported by Tsai, Huang and Mau,2006. Phenol content of extracts from A. cylindracea (extract A: 13.35 ± 0.55; extract B: 12.79 ± 0.67 mg gallic acid equivalent (GAE) per g of dry extract) were higher than phenol content of extracts from P. ostreatus (extract A: 10.28 ± 0.70; extract B: 11.52 ± 0.62 mg GAE per g of dry extract). The ABTS radical cation-scavenging activity was also higher in extracts from A. cylindracea (extract A: 12.04 ±1.26; extract B: 6.78 ± 0.44mg ascorbic acid equivalent (AAE) per g of dry extract) than extracts from P.ostreatus (extract A: 6.39 ± 1.45; extract B: 5.75 ± 0.49mg AAE per g of dry extract). Results of this study indicate that A. cylindracea has more antioxidant activity than P. ostreatus, but both mushrooms are potential sources of natural antioxidant preservatives and polysaccharides to produce bioactive edible coatings.