Assembly of chitooligosaccharide-citrate-pectin complexes and use in fruit juice.

When chitooligosaccharide (COS) is added to fruit juice as a functional ingredient, citrate in the juice causes undesirable precipitation of a COS-pectin is complex. We assessed the interaction of COS, pectin, and citrate in fruit juice to provide a reference for the use of chitooligosaccharide in fruit juices. A high COS concentration and a small amount of citrate caused formation of a precipitate; at 10 mM citrate, the turbidity of the solution was highest, 59.96% ( = 0.6;  < 0.05). By Fourier-transform infrared spectroscopy and scanning electron microscopy, we determined that there were electrostatic interactions and hydrogen bonds between COS, citrate, and pectin, with competition between citrate and pectin for COS. To minimize precipitation, the data showed that COS should not exceed 0.2% in solution with 0.2% pectin at pH 4. Precipitation could be reduced by addition of 30 ~ 50 mM citrate, and COS should be less than 0.06% (w/v) when used in commercial juice. The taste of the juice will be maintained without affecting the antibacterial and antiseptic properties of COS. Our findings will promote the development of functional COS fruit juice.