Oil extraction from Macadamia Integrifolia kernels using combined Convective circulating drying and Thermal pressing: Experimental study and bioactivity evaluation

Abstract

Macadamia integrifolia (M.I) is a high-value crop, primarily due to its kernels, which are rich in vegetable oil containing a high proportion of unsaturated fatty acids and antioxidant compounds. However, current oil extraction methods for M.I often overlook the importance of pre-drying and drying processes, which may result in reduced oil yield and compromised quality. This study aims to develop and optimize an oil extraction process for M.I using hot-air convective drying combined with hot pressing, and to compare the oil yield and quality with conventional methods such as sun drying and standard thermal drying. M.I kernels were subjected to moisture reduction and convective drying treatment. The oil was extracted using a hot pressing technique, followed by analyses including chemical composition (GC-MS), physicochemical parameters, quality indicators, and evaluations of bioactivity, such as antioxidant capacity (EC₁, ABTS, TEAC) and anti-tyrosinase activity. The results indicated that the convective drying method significantly improved oil yield, reaching up to 95.8%, and produced oil with higher contents of palmitoleic acid (20.1%), oleic acid (58.6%), and other beneficial compounds. The extracted oil also exhibited enhanced antioxidant activity and oxidative stability. This study highlighted the crucial role of controlled pre-drying and drying conditions in the post-harvest phase to optimize both the yield and quality of M.I oil, thereby promoting its potential applications in the functional food, cosmetic, and natural pharmaceutical industries.