PRESERVATION OF FRESH FOOD WITH PHYTOCHEMICAL LOADED NANOEMULSIONS

The objective of this study was to develop and test a food grade nanoemulsion as an improved delivery medium for applying phytochemicals to extend the shelf life of fresh foods. The hypothesis was that phenolics, which have both hydrophilic and hydrophobic structures, can bind at the interface of an oil-water solution. Nanoemulsions, with high surface areas, should therefore have a high interfacial absorption capacity for otherwise less soluble phytochemicals and act as a universal solvent to deliver the antimicrobial and antioxidant effects into fresh foods. The food grade nanoemulsion was developed from 10% (v/v) vegetable oil and 5% (w/v) modified starch HI-CAP100 using a microfluidizer at 95 MPa pressure for more than two processing cycles. These nanoemulsion ranged in particle size from 180 to 220 nm. The developed nanoemulsion was stable for more than a year at -80°C and 8 weeks at room temperature. The solubility enhancement of phenolics using nanoemulsion was determined with respect to their solubilities in oil and water. The nanoemulsion acted as a universal solvent for phenolics with a wide range of log P phase partitioning values. The solubility enhancement of phenolic compounds in nanoemulsion, compared to their solubility in water was ascorbyl palmitate > quercetin > rutin > vanillic acid > vanillin > caffeic acid > gallic acid with a solubility enhancement factor of 40, 27, 15, 4, 3.2, 2.3 and 0.63 times increased solubility respectively. The solubility enhancement of the emulsion compared to oil was in the order ascorbyl palmitate > rutin > quercetin > vanillic acid > caffeic acid > curcumin > vanillin with an increase of 19.5, 15, 10, 7, 3.6, 3.5 and 2.3 fold respectively. The nanoemulsion was also able to dissolve 6477 ± 276, 3533 ± 314 and 519 ± 4 µg/mL of tea, apple and grape seed extracts. However, these solubilities were lower than the aqueous solubilities of these extracts. The ability of nanoemulsions to deliver various phenolic compounds to fish fillets dipped in nanoemulsions diluted into aqueous solutions was measured. Gallic acid was tested as a model for delivery onto fresh fish fillets at various concentrations ranging from 200-1200 µg/mL. A fourfold increase in the binding of gallic acid by fish muscle was observed after a 30 minute dip in the nanoemulsion compared to uptake from a water control at the same concentration. Similarly all other tested compounds showed absorption to fish muscle when delivered as a nanoemulsion. The extent of absorption was time and concentration dependent, though most of the absorption occurred in the first 10 minutes. (+)-Catechin was the only exception where the aqueous delivery of catechin to fish fillet was superior compared to nanoemulsion delivery. The ability of the nanoemulsion to suppress fish off flavours, particularly trimethylamine (TMA), was tested as a criterion for the effectiveness of the nanoemulsion as a preservative delivery medium. A screening trial with phytochemicals showed variable suppression effects of TMA production. Selected phytochemicals and their combinations were then tested in quadruplicate for their ability to suppress TMA levels in treated fish. All the phytochemicals added to nanoemulsions showed significant (p < 0.05) effects on production of TMA when compared with their aqueous solutions. TMA levels in the control fish rose from 4mg/100 g fish on day 0 to 12mg/100 g fish on day 10 of storage at 8°C. The most effective results were achieved by synergies of two compounds such as vanillin/β-carotene and β-carotene/curcumin where final TMA values 1.5 mg/100 g and 3.4 mg/100 g fish on day 10 of storage were achieved respectively. The nanoemulsion without phytochemicals was also partially effective in reducing the TMA level. These suppression effects of diluted blank nanoemulsion were related to the level of water added to blank nanoemulsions when used as dip mediums. The present findings present new information on the development of water dilutable, stable food grade nanoemulsions with the ability to dissolve and deliver a variety of phytochemicals. The use of hydrophobic phenolics as a dip medium was made possible by solubilization of phytochemicals into nanoemulsion. Similarly combinations of hydrophobic/hydrophilic and hydrophobic/hydrophobic phenolics as preservatives have been made possible extending the shelf life of fish beyond that achievable by water soluble combinations