# Characteristics and Vaporization Potential of Fermentation Waste of Greengage (_Prunus mume_)
## 3 Results  
### Total Phenolic and Flavonoid Contents  
Phenolic compounds are the primary secondary metabolites in plants and can act as natural antioxidants. They reduce free radical formation caused by different kinds of stress and thus they show their protective effects in plants, and reports show that they could have similar effects in humans [5; 23]. The total phenolic contents obtained from the fresh greengage and the fermentation waste are shown in Figure 2.  
Compared to the fresh fruit, an obvious decrease in the phenolic compound content in the fermentation waste was revealed. The exact values are 3.32 mg GAE/g EPW for fresh greengage against 1.34 mg GAE/g EPW for fermentation waste, about 59.6% less. As one of the main products of secondary metabolism, phenolic compounds are often enriched after fermentation since various kinds of secondary metabolism occur during fermentation [24]. However, phenolic compounds are mostly polar compounds and their polarity is close to that of esters and alcohols [25] which means that they are more easily dissolved in ester or alcohol solutions than water. Moreover ethanol is a better organic solvent for extracting phenolic compounds in plants compared to methanol and acetone [26]. Therefore, at the end of greengage wine production, the phenolic compounds were dissolved into the phase of ethanol (wine), resulting in their depletion in the fermentation waste.  
Phenolic compound content is one of the important factors in the fruit-based investigation. [PERSON], [PERSON] and [PERSON] [5] reported 1.88 and 1.08 mg GAE/g FW(Fresh Weight) for red and yellow plums, respectively. In research into edible wild fruit, [PERSON] et al. [27] reported 1.13 mg GAE/g FW from round plums. Compared with this relevant research in the literature, the content of phenolic compounds in the fermentation waste was still high enough to be valorized.  
Figure 3 demonstrates the total flavonoid content of both fresh fruit and the fermentation waste. The results show 1.70 mg RE/g EPW for fresh fruit and 1.17 mg RE/g EPW for fermentation waste, a decrease of 31.45%, indicating lower depletion compared to that of total phenolic compounds. The results may be explained by the fact that flavonoids are semi-polar compounds: their non-polar core structure is modified by various polar hydroxyl groups and carbohydrate moieties, and flavonoids can readily be extracted using polar organic solvents such as methanol, ethanol, acetonitrile and acetone [11; 28]. Consequently, larger amounts of flavonoids than other phenolic compounds may remain in the fermented marc. Clearly, the flavonoid content in the fermentation waste was far from exhausted as previous examples from the literature show. [PERSON] et al. [29] reported a value of 1.49 mg/g DW (Dry Weight) from Chinese plum, and another study obtained a  
Figure 2: Total phenolic contents of fresh greengage and its fermentation waste. The data are shown as the mean values of three determinations (n = 3) \(\pm\) standard deviation (error bars). Different letters indicate that they are significantly different at \(p<0.05\) according to ANOVA analysis.  
value of 2.5 mg QE (Quercetin Equivalent)/g FW for yellow plum and 2.3 mg QE/g FW for red plum [18].