Enhancement of bioactivity and bioavailability of wild oregano (Coleus amboinicus Lour.) phenolic extract through zein nanoencapsulation

Wild oregano phenolic extract (WOPE) was encapsulated in zein by simple conservation and yielded yellow green loose powder (ZWOPE) which, upon analysis through atomic force microscopy, consisted of closely packed spheres with an average size of 34.51 +- 11.56 nm. The encapsulation efficiency of 70.41 +- 6.41%, while the loading efficiency and payload of the nanoparticle were found to be at 14.08 +- 1.28% and 16.41 +- 1.75%, respectively. After 90 days of storage, the retention ratio of ZWOPE was 91% under refrigeration and 80% at room temperature. In vitro releasing profile showed that only 8% of WOPE was released from ZWOPE in simulated gastric fluid (SGF), while 79% was released in simulated intestinal fluid (SIF), thus suggesting that nanoencapsulation in zein protected WOPE from degradation in the stomach and allowed a sustained release in the intestines. ZWOPE and WOPE showed similar inhibition of lipid peroxidation of chick liver microsomes via ferric thiocyanate assay (P less than 0.0001). In ABTS radical cation decolorization assay, ZWOPE had an EC 50 of 448.86 +- 12.94 ug/mL, which was lesser than that of WOPE (523.41 +- 3.12 ug/mL, P=0.0156); and trolox equivalent of ZWOPE were greater than that of WOPE (P=0.0204). Antimicrobial assay using agar-cup method showed that nanoencapsulation in zein resulted in three-fold increase in inhibition of growth of E. coli and C. albicans, and two-field for P. aeruginosa and S. aureus. Further testing of the antifungal activity against banana, anthracnose and crown-tip disease revealed that by spraying 50 ppm of ZWOPE, the fungal infection in banana was prevented until after the 15th day compared to untreated banana which is manifested infection on the 2nd day, and to banana sprayed with 50 ppm of WOPE which manifested infection on the 3rd day. Inclusion of ZWOPE in broiler diets over a period of 21 days showed no significant improvement in average weight and daily gain (ADG) but enhanced the feed conversion, suggesting its potential use as a beneficial feed additive.