Ethanolic coconut husk extract: In vitro antioxidative activity and effect on oxidative stability of shrimp oil emulsion

Ethanolic coconut husk extract (ECHE) was characterized and its effect on lipid oxidation of shrimp oil-in-water emulsion was studied. Condensed tannin was abundant in ECHE (492.2 and 441.9 mg catechin equivalent/g extract as determined by vanillin and BuOH-HCl assays, respectively). The major free phenolics in ECHE were tannic acid and catechins (205.98 and 103.56 mg/kg dry extract, respectively). Antioxidative activities of ECHE at different levels (50-200 mg/L) tested by all in vitro assays increased as its concentration increased (P<0.05). 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging activity and metal chelating activity were decreased up to 50% when heated at temperature higher than 90 degrees C for longer than 60 min (P<0.05). Impact of ECHE (200 and 400 mg/L) on lipid oxidation of shrimp oil-in-water emulsion was monitored throughout 12 days of storage at 30 degrees C. Lipid oxidation of emulsion added with ECHE was retarded as evidenced by the lower conjugated diene (CD), thiobarbituric acid-reactive substances (TBARS) value, and rho-anisidine value (AnV). Eicosapentaenoic acid (EPA; C20:5 n-3) and docosahexaenoic acid (DHA; C22:6 n-3) were more retained in the sample added with ECHE (200 mg/L) at the end of storage (P<0.05). ECHE could therefore be used as a natural antioxidant, particularly in emulsion. Practical application: Coconut husk, the underutilized material from coconut processing, contains condensed tannin and free phenolic compounds with antioxidative activity. Coconut husk extract could therefore increase oxidative stability of lipids in food systems, particularly those rich in polyunsaturated fatty acid such as shrimp oil. Emulsion is generally prone to oxidation due to its large surface area of oil phase exposed to aqueous phase. Thus, coconut husk extract can be used as a natural antioxidant, which could maintain the quality of emulsion as well as other fat-based foods during the extended storage.