**Author details**

478 The Complex World of Polysaccharides

Besides, calcium existing in yoghurt or the added iron could interact with free chitosan molecules and those complexes. In our work, yoghurts with chitosan are subjected to gastrointestinal simulations. In the first step, our food passes through the simulated stomach (pH = 1.0–2.0) and it could be expected that casein peptidic fragments, chitosan, iron or calcium, all remain in solution. While the food passes through the first portion of the simulated small intestine, changes in pH can lead to formation of chitosan-casein peptidic complexes and iron or calcium could be interacting with them. At pH 6.8–7.0, free chitosan molecules and chitosan-casein-peptidic complexes precipitate forming flocculus. The force of the coagulum formed is high and can be seen in Figures 1 and 2. The results reported by Ausar et al. [162] indicate that hydrophobicity of the casein-chitosan complex is the main

Chitosan is essentially a positively charged polysaccharide. Iron and calcium are cations. Anal et al. [153] measured zeta potential of chitosan solutions, sodium caseinate solutions and chitosan-caseinate mixtures in a range of pH (3.0–6.5). They found that the pure chitosan solutions were strongly positively charged between pH 3.0 and 6.0. The zeta potential values of chitosan solutions decreased with increasing pH and were slightly negative (approximately − 2.5 mV) at pH 6.5. In our study, in the range of pH 3.0–6.0, isolated molecules of chitosan were probably interacting with iron or calcium by adsorption rather than by electrostatic forces. Besides, Anal et al. [153] observed that the zeta potentials of the chitosan–caseinate solutions were negative at pH > 5.5. In this range of pH, in our work, electrostatic interaction could exist between chitosan-caseinate complexes and iron or calcium. However, when chitosan precipitates, it captures the iron or calcium either by

The behavior of chitosan with calcium and iron in the digestive simulations were similar and can be explained in the same manner. However, the behavior between the other fibers used and the same micronutrients in the digestive simulations were significantly different. The flocculus formation by chitosan is a very strong kind of behavior which is independent of the use of the dialysis membrane. Evidently other types of interactions are brought into

Results showed that the different plant fibers decreased glucose, calcium and iron availabilities whereas the effect of chitosan (fiber from animal source) was more pronounced. These findings could be positive or negative depending on the nutrient and the nutritional stage or health of the population who would receive the food under study. However, the *in vitro* digestive chemical experimental model may be used to increase the understanding of the interactions between animal and plant fibers with nutrients and micronutrients. This knowledge is very important from the point of view of health and for

mechanism by which the casein-chitosan flocculation is produced.

play for the other fibers that need further studies to determine them.

electrostatic forces or by adsorption [138,139].

**11. Conclusion** 

food industry and technologists.

Marina Dello Staffolo

*CIDCA (Centro de Investigación y Desarrollo en Criotecnología de Alimentos), CONICET–CCT La Plata, Fac. Cs. Exactas, Universidad Nacional de La Plata, La Plata, Argentina* 

Alicia E. Bevilacqua *CIDCA (Centro de Investigación y Desarrollo en Criotecnología de Alimentos), CONICET–CCT La Plata, Fac. Cs. Exactas, Universidad Nacional de La Plata, La Plata, Argentina Departamento de Ingeniería Química, Facultad de Ingeniería, UNLP* 

María Susana Rodríguez and Liliana Albertengo *Instituto de Química del Sur (INQUISUR), CO NICET–UNS Bahía Blanca, Departamento de Química, Universidad Nacional del Sur, Argentina* 
