Hard to re­place

Down to Earth - - SCIENCE -

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.

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