Influence of Drying Methods on Apple Pectin Content and Quality Characteristics

Objective: To study the content and quality characteristics of three types of apple pectin (WSP, NSP, CSP) treated by different drying methods. Methods: Apple pectin was dried by hot air drying (60, 75, 90 ℃), vacuum freeze dryingn (−50 ℃) and natural drying. The effects of different drying methods on the browning degree of apple and the pectin content, protein content, total sugar content, antioxidant capacity and pectin structure of three types of apples were studied. Results: The browning degree of apple slices was the smallest under hot air drying at 60 ℃. The content of three different types of pectin was different. The content of WSP was the most, ranging from 58.06% to 77.09%, followed by NSP, ranging from 30.57% to 54.98%, and the content of CSP was the least, ranging from 14.64% to 27.06%. Among them, the content of three types of pectin after hot air drying at 60 ℃ was the most. The total sugar content of WSP, CSP and NSP was 34.56%~6.92%, 11.02%~4.04% and 15.46%~8.75%, respectively. The total sugar content of WSP dried at 75 ℃ was the highest. The total sugar content of NSP and CSP under hot air drying at 90 ℃ was also the highest. The protein content of three different types of pectin was different. The range of WSP, NSP and CSP was 2.92%~5.73%, 1.39%~4.27% and 1.50%~5.40%, respectively. Fourier transform infrared spectroscopy analysis showed that there was little difference in the structure of apple pectin under different drying conditions. The drying method had a significant effect on the antioxidant capacity of pectin. The antioxidant capacity of WSP and NSP ranged from 91.27% to 78.54% and 8.15% to 2.14%, respectively. The antioxidant capacity of CSP was very weak. Among them, the antioxidant capacity of WSP and NSP under 90 ℃ hot air drying was the strongest, which was 91.27% and 8.15%, respectively. The antioxidant capacity of WSP and NSP under freeze drying was the weakest, which was 78.54% and 2.14%, respectively. Conclusion: After apples were treated by different drying methods, the contents and properties of three different types of pectin in apples were different. The apple pectin dried at 60 ℃ was the best, and the apple pectin content, total sugar content, protein content and antioxidant capacity were 50.69%, 15.27%, 3.61% and 31.33%, respectively. This study would provide theoretical support for the extraction process of apple pectin and the antioxidant capacity of different types of pectin, and also provide some reference value for further study on the effect of different drying methods on pectin drying.