GSG is steviol glycoside with between one and twenty glucose units attached to the molecule. Its international number is INS 960d and its EU number is E 960d.
It is a mixture of materials at different glycosylation levels, not a single compound - which is where it differs from single components such as Reb A or Reb M. Attaching glucose units raises water solubility and brings the sweetness curve closer to sucrose, while sweetness intensity falls.
How it is made
Purified steviol glycoside is used as the substrate and cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) as the catalyst, with dextrin as the glucose donor; α-1,4-linked glucose units are transferred onto the C4 hydroxyl of the glycoside molecule. The process conditions recorded in the EFSA opinion of 2022 are: liquefied donor mixed with substrate, reaction at 60 °C for 48 hours, enzyme inactivation by heating at 100 °C for 15 minutes, then decolourisation, demineralisation, dextrin removal, concentration and spray drying. The reaction runs in water under mild conditions and the steviol skeleton is unchanged.
Figure 1 - Finished GSG is the same white powder as the starting glycoside. What changes is the glucose chain attached to it, and with it the solubility.
The Melis series from Xinghua GL Stevia uses a low-temperature dual-enzyme process that attaches 2-3 glucose units per molecule, with dextrin as the donor. The enzyme source is the same as the strain named in the EU specification, and the difference lies only in reaction temperature and the order in which enzymes are added - so under EU rules the product is still E 960d. Different grades are built from intermediates of different purity; component content, sweetness conversion and in-house limits follow the specification agreed between both parties.
Grades differ by glycosylation level and intermediate purity, so always compare on the agreed specification rather than on the product name.
Primary sources: JECFA specifications (INS 960d); (EU) 2023/447; EFSA opinion 2022
Related products: GSG Series