Effect of three acid-reducing methods on the physicochemical property and active substance of red raspberry juice

To solve the problem of sharp sourness in raspberry juice, using red raspberry juice as the research object, the acid-reducing treatment was carried out by biological, physical and chemical methods respectively to adjust its pH value to 3.5, and the physicochemical indexes, antioxidant activity and sensory quality were analyzed. The results showed that the acid reduction rates of red raspberry juice treated by biological, physical and chemical methods were 59.4%, 55.5% and 27.3%, respectively. After acid reduction by biological methods, the contents of total sugar, soluble solids, titratable acid, pH, total phenols, total flavonoids and total anthocyanins in red raspberry juice were 9.28 g/L, 4.94 °Bx, 7.09 g/L, 3.55, 1.21 g/L, 0.90 g/L and 40.56 mg/L, respectively. It could reduce the contents of citric acid and malic acid to 5.01 g/L and 0.57 g/L, respectively. Its main monomer phenolic compounds were chlorogenic acid, cryptochlorogenic acid and arbutin (with content of 140.77 mg/L, 67.54 mg/L and 89.34 mg/L, respectively), which could better retain the contents of arbutin, ellagic acid and eugenic acid in red raspberry juice, and increase the contents of monomer phenolic compounds such as gallic acid and p-coumaric acid. The half maximal inhibitory concentration (IC₅₀) values of DPPH and ABTS⁺ free radical scavenging ability were 1.83 and 19.16, respectively. It had the highest sensory score (88.4), with well-balanced and pleasant sweet and sour taste. Overall, the quality of red raspberry juice treated with biological methods for acid reduction was the optimal.