AN NMR APPROACH TO FOLLOW THE STRUCTURAL MODIFICATION OF NATIVE APPLE PECTIN DURING DIGESTION

Dietary fiber (DF) is involved in many biological functions. These can be attributed not only to the native polymers but also to the oligomers formed during metabolic events. Since DF bioactivity is mainly carried out at the intestinal level, understanding if and to what extent modifications can occur during its journey throughout the gastrointestinal tract is crucial to correlate biological functions with DF composition and structural characteristics. Here an NMR approach to qualitatively and semi-quantitatively follow the degradation pathway of a bioactive polysaccharide under simulated gastrointestinal conditions is proposed. The method was applied to pursue the gastrointestinal fate of Golden Delicious apple pectin contained in apple tissues characterized by different levels of mechanical disintegration, i.e., intact pulp, puree, and homogenate. Experiments were also performed on model systems of native pectin extracted from the fruit. One and two-dimensional NMR experiments (1H, 13C, COSY, HSQC, TOCSY, HSQC-TOCSY, HMBC, and NOESY) were collected to gain insight into the structural modification of the heteropolysaccharide as affected by different gastrointestinal parameters (i.e., pH, bile salts, enzymes). The results indicated that the extent of pectin degradation was influenced by the intensity of mechanical disintegration of the vegetable matrix. Results also suggest a crucial role of upper gastrointestinal parameters in inducing pectin degradative reactions.