Effects of Different Roasting Degrees on the Quality of Lujiu Made with Macadamia Shells

To utilize the unique flavor of macadamia shells, we explored the effects of macadamia shells with different roasting degrees on the quality and flavor of Lujiu. In this study, the quality and key volatile flavor compounds of Lujiu made with differently roasted macadamia shells were analyzed by sensory evaluation, electronic nose, and headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) combined with relative odor activity value (ROAV) and multivariate statistical analysis. The sensory evaluation results showed that Lujiu made with macadamia shells roasted at 180 ℃ had the highest sensory score and was more popular. Lujiu samples made with differently roasted macadamia shells differed in alcohol content, pH, titratable acidity, L^*, a^*, and b^* values. A total of 66 aroma components were identified by HS-GC-IMS, including 30 esters, 3 aldehydes, 10 ketones, 16 alcohols (excluding ethanol), 1 acid, 2 ethers and 4 other compounds. Among these, the relative content of esters was the highest, followed by alcohols, ketones, and aldehydes. As the roasting temperature increased, the proportion of total volatile alcohols decreased, while the proportion of total volatile esters significantly increased. Six key odor markers, butanoic acid propyl ester, ethyl heptanoate, ethyl propanoate, isoamyl acetate, propyl propanoate and acetic acid ethyl ester, were selected by orthogonal partial least squares discriminant analysis and ROAV using the cutoff of variable importance in projection (VIP) ≥ 1 with ROAV ≥ 1. Among these compounds, isoamyl acetate, ethyl enanthate, butanoic acid propyl ester and propyl propanoate were abundant in base liquor. In contrast, the relative contents of ethyl propanoate and acetic acid ethyl ester were the lowest in base liquor and were higher in Lujiu samples made with macadamia shells roasted at 180 and 195 ℃; both compounds conferred Lujiu nutty and woody aromas. Lujiu made with differently roasted macadamia shells had their own unique aroma characteristics, which could be well separated by electronic nose and HS-GC-IMS. This study provides a theoretical basis to promote the development of the macadamia shell Lujiu industry.