Effect of mild yeast fermentation on aroma compounds and functional components of Lycium ruthenicum Murray

Mild fermentation of Lycium ruthenicum Murray (LR) by yeast facilitates the leaching of nutrients from LR, increases the functional properties of the fermentation broth, and improves its aroma quality. Headspace solid phase microextraction was used to extract the volatile compounds from raw LR juice and fermented LR beverage samples. The volatile compounds were identified using gas chromatography-mass spectrometry (GC-MS), and analysed by relative odour activity value (ROAV). The contents of total flavonoids, polysaccharides, and anthocyanins were also determined. The results showed that the contents and types of volatile compounds changed significantly after fermentation. In total, 24 volatile compounds were identified in raw LR juice, and 39 volatile compounds were identified in fermented LR beverage. The relative content of esters increased from 20.65 to 72.59%, and alcohols increased from 2.05 to 5.72%. However, acids decreased significantly, from 70.76 to 1.74%. A total of seven volatile compounds with ROAV ≥ 0.01 were found in fermented and raw LR juices, most of which belonged to esters and aldehydes, and mainly provided strong fruity and slightly boozy and oily flavours to fermented LR beverages. For functional components, the content of total flavonoids increased significantly from 1.08 to 1.70 g/100 g (p < 0.05). However, the total polysaccharide content decreased significantly from 10.88 to 9.99 g/100 g (p < 0.05). The content of anthocyanins did not change significantly. The findings could provide theoretical guidance for improving the aroma quality and functional components of fermented LR beverages, and deliver new insights into the process of aroma production in this fermented juice.