Changes of Chemical and Physical Quality Attributes of Macadamia Nuts during Hybrid Drying and Processing

Abstract

Macadamia nuts are well known for their unique flavor and taste. They contain a high level of monounsaturated fatty acids such as oleic acid, which is claimed to have an effect on reducing blood cholesterol. This study focuses on monitoring the changes in the physical and chemical qualities of macadamia nuts during drying, roasting, and storage. A combination of heat pump drying and tunnel drying was selected for this study to provide a comparison with convectional hot air drying. After completion of all drying treatments, the dried nuts were subjected to roasting at 125°C for 20 min and storage in ethylene vinyl alcohol copolymer (EVOH) bags at 4°C for 3 months. After each stage of processing, nut samples were taken to assess the quality in terms of fatty acids, moisture content, water activity, peroxide value, free fatty acids, color, and volatile compounds. The experimental results showed that drying treatments using heat pump combined with tunnel drying can reduce drying time significantly. It appears that the combination of heat pump and tunnel drying resulted in maintaining the commercially accepted chemical and physical quality characteristics of macadamia nuts in terms of key fatty acid contents, peroxide value, free fatty acid content, and color. Moreover, drying with a heat pump dryer combined with tunnel drying did not increase the content of undesirable volatile compounds in dried macadamia nuts after processing.

Keywords:

• Drying
• Flavor
• Heat pump drying
• Lipids
• Macadamia nuts

ACKNOWLEDGMENTS

The authors thank the Commission on Higher Education of Thailand for funding this research; the Department of Food Science and Technology, School of Chemical Engineering, Faculty of Engineering, University of New South Wales, Australia, for the facilities and laboratory; and Denham Plantation, Knock row, northern New South Wales, for providing macadamia nut samples.

Notes

^a–e Values are means ± SD/√N. Statistical analysis was done separately for each drying method because the raw materials used in each batch were not the same. Means separation within columns based on probability of significant difference (p ≤ 0.05).

^nsNo significant difference (p > 0.05).

C12:0 = lauric acid, C14:0 = myristic acid, C16:0 = palmitic acid, C16:1 = palmitoleic acid, C18:0 = stearic acid, C18:1 = oleic acid, C18:2 = linoleic acid, C18:3 = linolenic acid, C20:0 = arachidic acid, C20:1 = eicosenic acid, and C22:0 = behenic acid.

Values are means ± SD/√N. Statistical analysis was done separately for each drying method because the raw materials used in each batch were not the same. Means separation within columns based on probability of significant difference (p ≤ 0.05).

^a–e Values are means ± SD/√N. Statistical analysis was done separately in each drying method because the raw materials in each batch were not the same.

Means separation within columns based on significant differences (p ≤ 0.05).