ARS | Publication request: SUGAR COMPOSITION AND COLOR DEVELOPMENT DURING DRYING AND ROASTING OF MACADAMIA NUTS

Submitted to: Hawaii Macadamia Nut Association
Publication Type: Proceedings
Publication Acceptance Date: September 14, 2005
Publication Date: September 14, 2005
Citation: Wall, M.M., Gentry, T.S. 2005. Sugar composition and color development during drying and roasting of macadamia nuts. Proceedings of the Hawaii Macadamia Nut Association 45th Annual Conference. P11-19.

Technical Abstract: Research was conducted to determine the variability in moisture content and sugar composition among macadamia cultivars at harvest, and to determine whether this variability contributes to kernel browning after processing. Also, immature kernels were compared to mature kernels for color quality and sugar content. Moisture content was lowest in nuts harvested from the low-rainfall district of Kau, and in early-maturing cultivars [Kau (HAES 344) and Keaau (HAES 660)] harvested during the drier months of July to September. Moisture content of fresh kernels was positively correlated with total sugar content. Total sugar content of fresh macadamia nuts varied from 2.9% to 5.6% when averaged over 4 cultivars from 3 regions during 2 years. Macadamia nut cultivars at harvest differed in sucrose concentrations, but not reducing sugar concentrations. For all cultivars, reducing sugars decreased during drying, and kernel centers darkened slightly. The centers of roasted kernels were not darker than dried kernels, except for Keauhou (HAES 246) nuts. Variability in sugar composition had a minimal impact on color quality when processing conditions were optimal. Kernels with internal or external browning had higher reducing sugar contents (0.24 to 0.27%) than cream-colored kernels (0.3%). Immature kernels had higher levels of sucrose and reducing sugars, and more internal and external browning after roasting, than mature kernels. The presence of immature kernels may impact the final color of macadamia kernels, depending on processing conditions.