Hard to replace
Only isabgol comes close as an alternative to Gelidium IN THE 1950s, Xanthan gum, a gelling agent made from a plant bacterium known as Xanthomonascampestris, was discovered as a substitute to agar as it is stable over a wide range of temperatures. However, it does not form good gels on its own. Xanthan remains a viscous liquid. It is not a gel, says Shashi Bhushan Babbar, a professor at the Department of Botany, Delhi University, adding that its efficacy increases only when it is used in combination with agar. This can at least limit, if not completely restrict, our consumption of agar, he says.
In 1978, gellan gum, made from the bacterium, Sphingomonassp, was introduced as a reagent. Gellan gum gels faster and is of higher quality than agar. But it came in the line of fire because of its hyperhydracity— tissues cultured on gellan gum tend to retain water. It is also costlier than agar.
Then in 1997, isabgol, a husk derived from the seeds of Plantago ovata, was tested as a gelling agent. It melts at a temperature greater than 1000 C. However, the problem with isabgol is that it is highly viscous at high temperatures and forms a gel even with cold water. Moreover, the isabgol available in the market is not pure and impurities can affect the quality of culturing.
Most recently, guar gum, the ground endosperm of guar beans, was proposed as a reagent. But guar gum is highly viscous at high temperatures. It has less clarity because of the presence of impurities. But the problem with guar gum is that it cannot be poured from one vessel to another. It has to be lifted by a spatula, making the process of transfer of culture medium extremely cumbersome, othing works as well as agar. At the same time, I believe that isabgol is the best substitute available at present, adds Babbar.