Effects of Temperature on the Quality of Vacuum Concentrated Pear Juice and Construction of Quality Evaluation Model

Objective: To compare the quality of vacuum concentrated pear juice at different temperatures and construct a quality evaluation method for concentrated pear juice. Method: Fresh pear juice was concentrated under decompression condition (vacuum degree 0.005 MPa) at concentration temperatures of 50, 60, 70 and 80 ℃, respectively. The evaluation model of concentrated pear juice was constructed based on the browning degree, pH, total phenolic content, total flavonoid content, Fe³⁺reducing power, soluble sugar, organic acid and volatile components of the concentrated pear juice. Results: The content of tartaric acid, fumaric acid and pH decreased significantly with the increasing temperature, while the browning degree, total phenolic content, total flavonoid content, Fe³⁺reducing power, quinic acid, malic acid, citric acid increased significantly. The content of alcohols was the highest in concentrated pear juice of 50 ℃ (4.753 μg/mL), the esters was the highest in concentrated pear juice of 70 ℃ (2.808 μg/mL), the aldehydes and ketones were the highest in concentrated pear juice of 70 ℃ (12.478 μg/mL). This study obtained a model for evaluating the quality of concentrated pear juice and found that 70 ℃ was best vacuum concentration temperature for pear juice. Conclusion: The vacuum concentration temperature could affect the quality of concentrated pear juice, which could be well distinguished by the quality evaluation model. This study would provide references for the quality control of vacuum concentrated pear juice.