Investigating the effect of thermal processing on biochemical composition and kernel shelf-life of macadamia (macadamia integrifolia).

Abstract

Rancidity is a major limiting factor affecting the postharvest quality and consequently, the storability and market value of macadamia nuts. Initial high moisture content accelerates the primary stages of rancidity where hydroperoxides accumulate as main oxidation products, eventually breaking down to form low molecular weight oxygenated constituents such as alcohols, aldehydes, ketones and free fatty acids, eventually resulting in the development of off-odours and off-flavours. Hydroperoxides can also react with amino acid residues in the Maillard reaction, thereby initiating excessive browning. Kernel browning may be evident as surface discolouration or internal as ‘concealed damage’ of nuts. Internal browning may be accompanied by off-odours and off-flavours and is impossible to detect during processing, often with no visible signs. Such kernels are unacceptable to both the export and local market. The aim of this chapter was to review the potential of thermal processing on delaying the onset of rancidity and therefore, improving kernel shelf life and nutritional quality of macadamia nuts; and to review the reliability of visible to near infrared spectroscopy (Vis/NIRS) to non-invasively predict kernel rancidity. Keywords: Rancidity, browning, free fatty acids, near infrared spectroscopy