苹果汁纳滤过程的膜污染机制及多酚截留特性

Fouling Mechanisms during Nanofiltration of Apple Juice and Rejection Properties of Polyphenols

果蔬汁纳滤过程的膜污染及其关键成分的变化是该技术在果蔬加工领域应用的关键问题。为明确苹果汁纳滤过程中的膜污染机制和多酚物质的截留特性,本文研究了跨膜压力、流速和浓缩倍数等关键参数对纳滤过程膜污染和多酚截留率的影响。结果表明:3个关键参数对膜通量的影响较大,跨膜压力和流速越高,浓缩倍数越低,膜通量越大,最大值可达26.25 L/(m2·h)。通过Resistance-in-series模型和SEM分析,各参数对总污染阻力(Rtot)、可逆污染阻力(Rrev)和不可逆污染阻力(Rirr)具有较大的影响与差异性,其中Rrev是关键阻力,占85%以上。受流体剪切力等因素影响,流速越低,压力越小,浓缩倍数越高,膜阻力越大。多酚的截留率随流速增大而减小,压力增大而增大,浓缩倍数增大先降低后上升。控制关键参数可使多酚截留率提高至95%以上。通过对可溶性固形物、总酚、总糖、总酸和维生素C等关键营养成分分析,苹果汁浓缩液中各成分含量提高比例分别为56.57%,98.54%,59.62%,68.75%和49.56%,80%以上的营养成分得到保留。

Membrane fouling and loss of key components during nanofiltration（NF） are critical problems in fruit and vegetable processing. To investigate membrane fouling mechanism and rejection properties of polyphenols, the influence of three key parameters contained transmembrane pressure（TMP）, velocity and concentration ratio on NF of apple juice were determined. Results showed that all the three parameters had great influence on permeate flux. Higher TMP and velocity as well as lower concentration ratio resulted in a higher permeate flux and the maximum flux was 26.25 L/（m2·h）.According to resistance-in-series model and SEM, these three parameters significantly influence on total fouling resistances（Rtot）, reversible fouling resistance（Rrev） and irreversible fouling resistance（Rirr）. Rrev was the dominate resistance accounting for 85% because fluid shear force, fouling resistance increased with the velocity and TMP decreasing,and concentration ratio increasing. Retention rate of polyphenols decreased with velocity, increased with TMP and first decreased then increased with concentration ratio. The retention rate of polyphenols could be more than 95% by optimization. Contents of key nutritional components in concentrated apple juice, including soluble solids, total phenol, total sugar, total acid and vitamin C increased to 56.57%, 98.54%, 59.62%, 68.75% and 49.56%, respectively. Finally,more than 80% of nutrient contents in apple juice retained after NF.