Abstract:The fermentation of blackberry pulp using Lacticaseibacillus paracasei PC18 was conducted， with continuous measurement of the nutritional chemical content and antioxidant activity throughout the processing.Ultra-high performance liquid chromatography-mass spectrometry （UPLC-MS） was used for the qualitative and quantitative analysis of polyphenolic compounds before and after fermentation. The results showed that the reducing sugar content of the blackberry fermentation liquid increased significantly from 51.79 mg/mL to 66.65 mg/mL after 24 h fermentation， and then fluctuated downwards. The total phenolic content gradually decreased， stabilizing after 48 h， from 1 006.81 μg/mL to 871.19 μg/mL（P＜0.05）. The antioxidant activity of the blackberry fermentation liquid increased from 3.82 mmol TEAC/L to 4.65 mmol TEAC/L over the first 48 h（P＜0.05）， reaching a peak of 5.13 mmol TEAC/L at 72 h. After 48 h fermentation， 13 polyphenolic compounds with significant changes were identified， with 12 showing an increase in concentration， except for chlorogenic acid， which decreased. The largest increases were observed in vanillic acid， protocatechuic acid， gentisic acid， and p-hydroxybenzoic acid， with increases of 85.07%， 72.79%， 29.33%， and 28.97%， respectively. Correlation analysis indicated that the fermentation of blackberry pulp with L. paracasei PC18 promotes the biotransformation of phenolic compounds in the blackberry， providing a rich material basis for enhancing the antioxidant activity of blackberry products.