*3.2.3 Effect of vinegar residue on blueberry fruit quality*

The reducing sugar of fruits of VR1 and VR2 increased by 8.12 and 9.65% (**Table 3**) with the application of vinegar residue, and the titratable acidity content decreased by 14.28 and 7.14% compared with the control. At the same time, the soluble solid content of fruits increased significantly as soluble solid content of fruits of VR2 increased by 11.60% compared with the control. The accumulation of total phenols and ketones in blueberry fruits was significantly promoted by the application of vinegar residue (**Table 3**), and the content of total phenols and total flavonoids of VR2 increased by 71.42 and 100.00%, respectively, compared with the control. The results showed that the application of vinegar residue could significantly improve the quality of blueberry fruits.
