Ascorbic acid mediated hydrolysis of galactomannans

Ascorbic acid (AA) is an antioxidant widely used in the food industry to prevent colour fade and spoilage. This study assesses the effect of 0.02 wt% AA on the rheology of common food thickeners – galactomannans (GM). GMs immediately exhibit a significant reduction in solution viscosity upon AA addition: guar gum (−67 % ± 7 %), locust bean gum (−47 % ± 5 %), and cassia gum (−58 % ± 4 %). Other food acids at 0.02 wt% showed no decline in viscosity, nor did another reducing agent, potassium iodide. GMs were then mixed with xanthan gum (XG) ± low acyl gellan gum (LAG) and AA's impact was assessed using small amplitude oscillatory shear rheology. As the temperature decreased, the storage modulus decreased in the presence of AA compared to without. The molecular weight (MW) of the GMs ± AA, was assessed using size exclusion chromatography – multi angle light scattering. The reduction in MW, was between 6 and 8 times for each GM, and was supported with analytical ultracentrifugation. This established the hydrolytic decomposition of GMs by AA, leading to a decrease in function due to a reduction in MW. This hydrolytic effect was observed regardless of pH, showing that acid hydrolysis isn't the primary mechanism. This study shows, for the first time, that AA causes extensive degradation of galactomannans, affecting their viscoelastic characteristics. These findings could affect many products; informing decisions on their quality and shelf life, as well as their cost-effectiveness and environmental life cycle.