The study, published online in the Journal of Agricultural and Food Chemistry, is important for establishing the stability of the Stevia rebaudiana (Bertoni)-derived sweetener rebaudioside A.
The results also challenge an earlier study from the 1980s that reported significant degradation of rebaudioside A on exposure to sunlight, equivalent to one week of sunlight during the summer (J. Agric. Food Chem., 1983, Vol. 31, pp. 409-412).
Rebiana is the common name for high-purity Rebaudioside A, which is derived from the South American plant stevia rebaudiana. It is a natural non-calorie sweetener said to be 200 times sweeter than sugar and is said to provide zero calories without undesirable taste characteristics.
If it is ultimately as easy to use in food and beverage formulations as it claims to be, stevia's 'natural' label could see it take prime spot as the holy grail of sweeteners, as manufacturers increasingly try to adapt their formulations to the demands of the more health conscious consumer.
“A very carefully controlled study was performed using validated analytical methods where all analytes present at significant levels (greater than 0.5 per cent) were known or identified and where all analytes greater than 0.1 per cent were quantified with primary reference standards,” wrote Coca-Cola’s John Clos, Grant DuBois, and Indra Prakash.
“With this study, we have demonstrated that rebaudioside A, as well as stevioside, is stable to sunlight exposure.”
Clos, DuBois, and Prakash formulated cola and lemon-lime beverages sweetened with rebaudioside A or stevioside or no sweetener. The beverage formulations were intended to simulate those used in the 1983 study.
Samples were exposed to sunlight (3,000 langleys) or protected from sunlight (control sample). At the end of the exposure period, a detailed analysis of the beverages was undertaken. Levels of rebaudioside A and stevioside in the light-exposed were within 3 to 7 per cent and 1 to 7 per cent of the control samples, respectively.
“The fact that these degradation products are formed in similar amount in both control and sun-light exposed samples suggests that they are acid-promoted rather than sunlight-promoted degradation products,” wrote the researchers.
“Our findings on rebiana light stability refute those of an earlier study that suggested rebaudioside A to be unstable to sunlight exposure, while the structurally homologous stevioside is stable,” wrote the researchers.
“We replicated the earlier study and found no significant photodegradation for either rebaudioside A or stevioside,” they concluded.
In an attempt to explain the differences between the earlier study and the new one, Clos, DuBois, and Prakash stated that analytical methods were different, with the earlier study using techniques that may have distorted readings. Moreover, the Coca-Cola researchers note that the 1983 study used different sample preparation methods for beverages made with rebaudioside A and stevioside.
Coca-Cola has teamed up with Cargill to use its rebiana brand, called Truvia.
Cargill is already selling Truvia online as a table-top sweetener but the beverage companies are yet to sell drinks with the sweetener in the US.
Source: Journal of Agricultural and Food ChemistryPublished online ahead of print, ASAP Article, doi: 10.1021/jf801343e“Photostability of Rebaudioside A and Stevioside in Beverages”Authors: J.F. Clos, G.E. DuBois, I. Prakash