Internal discoloration of various varieties of Macadamia nuts as influenced by enzymatic browning and Maillard reaction

Abstract

© 2015 Elsevier B.V. Brown kernels or internal discolouration (IDC) in various varieties of Macadamia nuts (Macadamia integrifolia and Macadamia tetraphylla) occurred through three different pathways: (i) an enzymatic browning reaction, (ii) Maillard reaction and (iii) infection by microorganisms. The phenolic compounds and polyphenol oxidase (PPO) activities of macadamias were analysed. Brown sections of the same kernel had higher levels of bound phenolics compared to the white sections, indicating the participation of phenolic compounds in the formation of brown kernel. The Maillard reaction was studied by determining the sugar amount using HPLC. The reducing sugars during drying reacted with kernel proteins causing the formation of brown pigments. Among the various varieties studied, 'Daddow' variety showed the least degree of hydrolysis. When kernel was infected with Penicillium aurantiogriseum, the kernel turns brown. The internal discoloration in macadamias is the first report that has been explored in our study. The findings of this study have potential to improve the existing postharvest techniques used in the Macadamia processing industry.