Acid beverage floc: protein-saponin interactions and an unstable emulsion model

The occurrence of acid beverage floc (ABF) in acidified carbonated beverages has long been attributed to the presence of saponins. We have examined this assertion and have found evidence to suggest that traces of protein may also be a key factor, along with lipid material present in the floc. Turbidity levels of beet sugar protein (0.001 wt.%) and saponin (0.001 wt.%) solutions were examined over time using spectrophotometry. At neutral pH, no change in turbidity was observed in any combination (individually or mixed). Furthermore, acidified (pH 2) saponin and protein solutions, considered separately, also exhibited no change. However, a mixture of equal concentrations at pH 2 showed an initial increase in turbidity up to 2 h after mixing, followed by a decrease over the ensuing 12 h. Interfacial tension measurements also indicated interactions between the protein and saponin at pH 2. Photon correlation spectroscopy (PCS-Malvern Zetasizer 4) was used to quantitatively examine the particle size distributions and aggregation of a model, highly dilute dispersion, of bromohexadecane in 20 wt.% sucrose solution, prepared with a jet homogenisor. Beet sugar saponin (0.001 wt.%) and protein (0.001 wt.%) were added to the dispersion, and their emulsion-stabilising effects examined via oil droplet size measurement over time. At neutral pH, the size of oil droplets in the dispersion was unaffected by the addition of saponin or protein. At pH 2, the presence of saponin again caused no effect on droplet size. However, in acid conditions, protein appeared to destabilise the dispersion. The results indicate that the key to controlling the ABF problem may be the ratio of saponin to protein in the product, which may or may not stabilise dispersed lipid, depending on their interactions.