Effect of freezing on microstructure and degree of syneresis in differently formulated fruit fillings

•Degree of syneresis was inversely correlated to the amount of hydrocolloids.•Freezing enhanced syneresis while gellan gum increased water-holding capacity.•Microstructure was modified according to changes in formulation of fruit fillings.•NMR data was in agreement with the degree of syneresis.

This study describes the syneresis and its effect on microstructure in fruit fillings within a wide range of the total soluble solids content and with or without hydrocolloids upon freezing. Linear models showed the relevance of the addition of pectin and gellan gum to fillings to prevent syneresis, increasing the water-holding capacity especially after freezing. Microstructural experiments by means of NMR spin–spin relaxometry combined with fluorescence microscopy allowed to observe that the continuous hydrocolloid gel, containing the dispersed solution of native fruit parts with the addition of inulin and sugars, changed its structure/distribution according to the amount of each ingredient and due to the freezing process. Relaxometry results confirmed that hydrocolloids strength was correlated (R2 > 0.92) with water-holding capacity, due to a relationship between the signal given by the water chemically exchanging with biopolymers, and the changes in the degree of syneresis.