Citric acid and heating on gelatin hydrolysis and gelation in confectionery gels

Acids hydrolyze gelatin and weaken its gelling capacity in water, which raises concerns about the use of food acids in gelatin-based confections (gummies). This study aimed to understand the effects of citric acid (CA) and heat treatment on the molecular weight (MW) of gelatin and, most importantly, the changes in gelling power in water versus sugar-rich confectionery solutions. The MW distributions of gelatin (6 wt%) in both plain (sweetener-free) and confectionery gels (with up to 80% sweetener solids) were analyzed using gel electrophoresis (SDS-PAGE), and the gelling kinetics and gel properties were characterized using rheology, differential scanning calorimetry, and texture and color analyses. In both plain and confectionery gels, the extent of hydrolysis increased with the CA concentration (0–2%) and the extent of heat treatment (up to 110 °C), which caused the depression of gelling temperature. However, despite CA-catalyzed hydrolyses having detrimental effects on plain gels, some limited hydrolysis with up to 1.5% CA was found to increase gel strength, hardness, and renaturation rate (melting enthalpy) of the confectionery gels, potentially due to the enhanced molecular mobility of gelatin in high viscous gelling matrices. Nonetheless, excessive hydrolysis induced by heating the acidified (1% CA) gummi mixtures to over 100 °C caused a reduced renaturation rate and weakened gel strength. The thermal treatment also promoted sucrose inversion and the Maillard reaction, leading to the development of yellow to brown colors in the final products.