Physical stability and antioxidant ability of a sustainable oil-in-water emulsion containing perilla skin extract and upcycled Aquasoya powder

Abstract

As a response to global concerns regarding environmental issues, upcycling has become one of the expanding trends in the food industry. Perilla has been widely used for edible and medicinal purpose in Asian countries. The seeds of perilla are consumed as oil and powder, while perilla skin and pomace are usually discarded. However, they still contain high contents of polyphenol. In order to take advantage of this, phenolic compounds were extracted from perilla skin to make perilla skin extract (PSE), and an oil-in-water (O/W) emulsion containing PSE (PO) was formulated using small black bean (Rhynchosia nulubilis) Aquasoya powder as an emulsifier. O/W emulsion without PSE (PX) was also formulated and the physicochemical characteristics were compared with PO. Nulsaemi (Perilla frutescens (L.) Britton var. frutescens) was used to prepare PSE due to its rich contents of rosmarinic acid (RA). Highperformance liquid chromatography result showed that perilla skin still possessed more than one-third of RA (0.53 ± 0.12 mg/g dried perilla skin) contents in perilla powder (1.21 ± 0.28mg/g dried perilla powder). Also, as the RA contents in PSE (31.06 ± 2.57 mg/g PSE) and perilla powder extract (PDE) (34.82 ± 0.50 mg/g PDE)showed less than 10% of difference, the validity of perilla skin as a RA source was verified. Subsequently, the physical properties and the antioxidant effects were assessed. As a result, diminutions of particle size and emulsion stability enhancement were observed in PO. The mean droplet diameter of PO was 350.57 ± 9.60 nm, which is approximately one-third of that from PX. And during the 30 days of storage, PO showed no statistical change in particle size. Also, centrifugal photosedimentometry results showed that the physical stability of the emulsion was significantly improved after incorporation of PSE. For this reason, it was concluded that PSE can stabilize the emulsion system, and this stability can be maintained at 4 °C for 30 days of storage. No statistical difference between DPPH radical scavenging ability of PO and PX was observed for the first 10 days. After then, DPPH radical scavenging ability of PX gradually decreased for another 20 days, whereas PO maintained its value. On the other hand, ABTS results revealed that PO had higher antioxidant ability than PX, and initial lipid oxidation was delayed in PO according to peroxide value results. Taking these into account, it was concluded the phenolic compounds from perilla skin can still work as the antioxidant reagents and slacken the rate of lipid oxidation. These results suggest that the application of PSE in soybean protein-based emulsions can be considered as it can stabilize the emulsion systems and still possess the antioxidant ability after the incorporation into the emulsion.