Analysis of volatile compounds and their changes during liquor aging of Chinese liquor 'Gujing Gongjiu'.

摘要

Chinese liquor "Gujing Gongjiu" is a traditional Chinese distilled alcoholic beverage that is categorized into a strong-aromatic fragrance liquor. It has a strong mixed floral, fruity, and sweet flavor with a smooth taste. Volatile compounds were extracted by headspace solid-phase microextraction (HS-SPME) from Gujing liquors that were aged for 1, 5, 10, and 20 years. Optimization of HS-SPME method was performed to determine the best experimental condition for extraction of liquor volatiles. Gas chromatography-mass spectrometry (GC-MS) was used for quantitative and qualitative analysis of liquor volatiles. Volatile compounds were identified by Kovat's retention indices and their mass spectrum. The influence of extended aging time on the composition of liquor volatiles was investigated.;The general volatile profiles of the four aged liquors were similar. The major volatile group in the Gujing liquor was esters that comprised over 96% of total volatiles. Ethyl hexanoate was the dominant compound in all four liquors and accounted for approximately 50% of the total volatile amount. Ethyl hexanoate is easily characterized by its floral and fruity smell and served as the main contributor to the liquor's flavor. Ethyl acetate (0.69-2.07%), ethyl butanoate (4.05-5.11%), ethyl pentanoate (0.94-3.68%), ethyl heptanoate (4.20-7.11%), ethyl octanoate (8.32-17.74%), and hexyl hexanoate (1.69-3.81%) were other characteristic esters recognized by their high detective intensities. The effect of aging time did not cause a significantly different percentage of composition of ester compounds. Alcohols were the second largest volatile group and provided sweet, fruity flavors. Unlike the ester class, the concentration of detected alcohols was reduced as aging time increased. The amount of volatile organic acids is important since they are associated with sweaty off-flavors. Hexanoic acid was the major organic acid and reached its highest concentration after aging of 10 years. Besides, acetals provided floral and fruity flavors for the liquor. Their total amount significantly decreased at the beginning of aging and then became stable as aging time increased. Other identified chemical classes included phenolic compounds, sulfur-containing compounds, anhydrides, ketones and aldehydes. However, only one or two compounds were identified from these groups, and their concentrations were relatively low to the predominant compounds.