Effects of different roasting temperatures on the flavor characteristics of shelled macadamia kernels: Analysis based on HS-GC-IMS and HS-SPME-GC-MS.

This study aimed to evaluate the effect of roasting temperature on the flavor characteristics of shelled macadamia kernels (SMKs) employing quantitative descriptive sensory analysis, color analysis, and two volatile compound profiling techniques, namely headspace-solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). Sensory and color analyses showed that roasting at 140 °C yielded a desirable roasted macadamia product, exhibiting a rich balsam flavor, creamy aroma, and uniform, harmonious faint yellow color. HS-SPME-GC-MS and HS-GC-IMS identified 107 volatile organic compounds (VOCs). Aldehydes, pyrazines, and furans increased with increasing roasting temperature, and these compounds were key contributors to the nutty aroma. Lipid oxidation dominated flavor formation during low-temperature roasting, while Strecker degradation prevailed at high temperatures. Among the VOCs, 23 with relative odor activity values (ROAV) of ≥1 contributed significantly to the overall aroma of roasted SMK. Furthermore, HS-SPME-GC-MS and HS-GC-IMS identified 10 and 16 key VOCs, respectively, including 2-methylpyrazine, 2,5-dimethylpyrazine, 2-ethylpyrazine, nonanal, and propanal. Interestingly, ethanol content showed a significant negative correlation (p < 0.05) with "bitter," and "burnt", as well as with a*, b*, and c, whereas most pyrazine compounds exhibited positive correlations with these sensory attributes (p < 0.05). Altogether, the findings of this study present roasting as an effective approach for enhancing macadamia nut aroma and provide valuable insights for flavor control in nut products.