Puddings, custards, and other foods containing starch often lose their consistency when frozen and thawed. This is because, during the freezing and thawing process, starch paste undergoes separation into solid and liquid phases.
The resulting deterioration in product quality is a problem for the food industry, which routinely freezes merchandise during storage and transport.
However, in the March issue of Nature Biotechnology, researchers have used a genetic technology called "antisense" to alter the starch composition and structure in a potato, creating a starch that can withstand up to 5 freeze-thaw cycles.
Potato starch is made up of two glucan polymers. These are amylose, a long and essentially unbranched chain of glucose molecules, and amylopectin, a relatively short and more highly branched glucose chain.
Building on knowledge gained from the manipulation of various genes involved in starch synthesis, Stephen Jobling and colleagues hypothesized that a potato with mostly short-chained amylopectin would reduce separation in potato starch during the freeze-thaw process.
The researchers modified the starch structure by removing the long chains of amylose and reducing the branch length of short-chain amylopectin.
| The new starch strain contained amylopectin with shorter branches and very little amylose.
| Nature Biotechnology |
They did this by simultaneously inhibiting three starch synthase enzymes: one responsible for synthesizing amylose, and two that affect branch chain length of amylopectin.
This was achieved by introducing DNA sequences into potatoes. The DNA encoded messenger RNA in opposite orientation (antisense) to natural RNA produced by the three corresponding starch synthase genes, thereby inhibiting formation of the three enzymes.
The result was a potato strain containing amylopectin with shorter branches and very little amylose.
After 5 freeze-thaw cycles, the starch from this strain remained clear - a sign that separation had not occurred.
Stabilizing starch this way is environmentally friendly and potentially more economical than chemical modification, the current alternative.