FACTORS AFFECTING MACADAMIA NUT STABILITY. 3. Effects of Roasting Oil Quality and Antioxidants

SUMMARY– Chemical and physical changes in roasting oil from a commercial processing plant and the relationship of these changes to quality and shelf‐life of roasted macadamia kernels were investigated. Oil was sampled initially and after 2, 4 and 13 weeks of roasting. Generally, free fatty acid, color (absorbance at 550 nm), refractive index and viscosity of the roasting oil increased with use. Changes in iodine number and fatty acid composition indicated there was considerable oil exchange between roasting oil and macadamia kernels. Antioxidant loss in the roasting oil was rapid. No flavor differences were observed in kernels immediately after roasting in the various oil samples, and shelf‐life was not appreciably affected by continuous use of the oil for as long as 13 weeks. A second study investigated the effects of vacuum‐packing (0, 15 and 24 in.) and direct antioxidant application (approximately 76 ppm butylated hydroxyanisole and butylated hydroxy‐toluene) on the stability of dry‐roasted macadamia kernels. Stability of antioxidant‐treated kernels was greater than that of untreated kernels, regardless of vacuum level. Vacuum packing had no effect on antioxidant‐treated kernels, but showed some benefit for untreated kernels.