Low methoxyl pectin/sodium caseinate interactions and composite film formation at neutral pH

- Phase diagram of sodium caseinate and low methoxyl pectin was established at pH 7.
- Complexes were formed suggesting the existence of attractive interactions between the two negatively charged biopolymers.
- Composite films were formed from sodium caseinate and LM pectin mixtures at pH 7.
- Obtained films were characterized for their mechanical and morphological properties.
- Films containing higher amounts of protein had less interactions with water.

The behavior of mixed negatively charged sodium caseinate (CAS) and low methoxyl pectin (LMP) at pH 7.0 was presented by phase diagram. The existence of interactions between CAS and LMP as a function of increasing protein concentration at neutral pH was studied by turbidity and zeta potential measurements. The observed significant increase of turbidity value for higher CAS/LMP ratios as well as the obtained zeta potential profile confirmed the formation of complexes at pH 7.0 at which the two macromolecules are negatively charged. Then, composite films were elaborated from CAS and LMP mixtures by increasing protein to polysaccharide ratio at neutral pH. The results revealed that the incorporation of protein to pectin-based films significantly increased the stiffness of films (Young's modulus) and decreased their flexibility (p < 0.05). Water content of composite films decreased significantly as the concentration of CAS increased (p < 0.05) and reached its lowest value for CAS/LMP ratios of 2 and 5 (7.50 ± 0.10% and 7.63 ± 0.19%) compared to LMP film (19.82 ± 0.19%). The prepared films, having tunable properties by varying the ratio of CAS/LMP, seem to be adequate for the packaging of moist foods.

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