The researchers looked at how quickly the sweetener degraded when tested in stevia in water, citric and phosphate solutions to mimic real-life beverage applications, and as a function of ultraviolet light intensity.
Under dark conditions, reb-A in phosphate buffers was more susceptible to breakdown than in water and citrate buffers at both pH levels, they write, however, when exposed to UV light the reb-A molecules degraded around 10 times faster in citrate than in phosphate buffers at both pH levels.
The sensitivity of reb-A to UV light was greater in citrate solutions than in water or phosphate solutions.
“Light exposure has an adverse effect on the stability of rebaudioside A. Proper formulations, light-protective packaging, and cool storage conditions are strategies that will improve the stability of rebaudioside A in food products,” write the researchers based at the US Auburn University.
The safety of stevia has not been called into question. A 2010 study tested its stability and found that although up to 70% of the compounds could be lost under extreme conditions (they looked at reb A and stevioside in soft drinks after 24, 48, and 72 hours of storage at 80 °C), at no point was the potentially toxic steviol aglycone detected.
Source: Journal of Food Science
Published online ahead of print20 February 2017 doi: 10.1111/1750-3841.13667
“Stability of the Stevia-Derived Sweetener Rebaudioside A in Solution as Affected by Ultraviolet Light Exposure”
Authors: Jiewen Zhang and Leonard N. Bell