Value-addition of sunburned pomegranate fruit to reduce postharvest losses: A cosmeceutical perspective

Sunburn renders 15% of pomegranate fruit production unmarketable in fresh fruit and juice industries. Uses for these fruit are scarce and their disposal represents an environmental problem. This work presents a comparative study on the composition and bioactivities of oils extracted from pomegranate seeds of sunburned fruit (SBF) and healthy fruit (HF) for value-adding potential of fruit representing postharvest losses. Oil samples were extracted with petroleum ether by ultrasonification after drying using different drying techniques (freeze-, sun- and oven-drying). Compositional analysis included p-anisidine value, total phenolic content (TPC) as well as essential oils and sterols while the investigated bioactivities included DPPH radical scavenging ability (RSA) and tyrosinase enzyme inhibition ability. Results showed that oven-dried seeds, regardless of seed source (SBF or HF), yielded higher oil ranging from 20.20 to 24.35% of dry matter. However, regardless of drying method, oil obtained from SBF contained higher TPC (1.4-2.8 mg g^-1 of oil GAE) than those obtained from HF. A total of 17 compounds were identified by GC-MS analysis with the predominant being 9,12,15-Octadecatrienoic acid, a conjugated linolenic acid, constituting 70-72% of total essential oils. Gamma-tocopherol constituted 95% of total tocopherol while β-sitosterol constituted between 85-87% of total sterols. Overall, good RSA was exhibited by all the investigated oil samples with IC₅₀ ranging from 34.77 to 59.29 µg mL-1 AAE. RSA was influenced by seed source (p=0.006) and drying method (p=0.025). All the oil samples showed good ability to inhibit tyrosinase enzyme regardless of seeds source and drying method, with monophenolase and diphenolase IC₅₀ ranging between 0.31 and 0.49 mg mL-1 and 0.64 and 2.43 mg mL^-1, respectively. This study indicates that seeds of sunburned pomegranate fruit can be exploited for high quality oil due to similar yield and bioactive composition compared to oil extracted from healthy fruit. In general, regardless of drying method, oils from seeds of SBF and HF both had good antioxidant activity and tyrosinase enzyme inhibition ability, which is applicable in skin care and nutraceutical industry.