The effect of water, brine and ethanol flotation on the quality and shelf life of macadamia kernels. I. Whole kernels

Abstract

Flotation in water, salt or ethanol solution is a method for separating macadamia nuts with different oil contents. Effects on quality and shelf life of macadamia nuts of immersing them in water (sp. gr. 1.00 g/cm3), brine (sp. gr. 1.02 g/cm3) or ethanol solution (sp. gr. 0197 g/cm3) were investigated. Whole macadamia nuts were dipped in each solution for 0, 30 or 60 s, redried to 1.0-1.5% moisture content (wet basis) and stored under a partial vacuum for 0, 4 or 12 months. After storage, whole macadamia nuts were evaluated for physical and sensory properties (hardness, colour, flavour, rancidity, sweetness and overall quality), and macadamia nut oil was extracted by cold pressing and analysed for peroxide value and free fatty acid content. Immersion in water had no effect on quality or shelf life of macadamia nuts. Immersion in brine or ethanol significantly (P < 0.05) changed the flavour of the nuts, but had no significant (P > 0.05) effect on shelf life or nut oil stability after 12 months of storage. It is concluded that water flotation is a feasible method to separate and grade macadamia nuts, although further microbiological investigations are suggested.