Water chestnut adds crunch to vegetables

LIMP, soggy vegetables and over-soft fruit could soon be a thing of the past following a breakthrough study of plant-based food texture by the Institute of Food Research.

For the first time, researchers at the IFR's multidisciplinary Bio-material Science Group have identified the components which give the Chinese water chestnut its characteristic "crisp and crunchy" properties. And they believe the same components can be manipulated in other plant-based foods - with widespread implications for the food industry.

The key to the texture of fruit and vegetables is the way their cell walls break up when eaten. Processing, canning and cooking often weaken the cell structure, causing cells to separate too easily on eating - giving the unwelcome soft texture. "The water chestnut maintains its unique crunchy texture as its cells do not separate easily, even on cooking," explained research leader Keith Waldron.

With a new technique of chemical extraction unique to the IFR, the research team found unusually high levels of ferulic acid in the cell walls of the water chestnut. When the acid was extracted from the cell walls, the cells separated more easily. High levels of the same chemical "glue" were also found in beetroot and sugar beet, other vegetables renowned for maintaining their texture.

"But more exciting was that we also found lower levels of ferulic acid in other fruit and vegetables," he added. "We have discovered the acid in carrots and apples, so we know the biochemistry is already in place to enhance their crunchiness if we can find a way to crank up that biochemistry."

Conventional industry research into fruit and vegetable texture has focused on genetic manipulation of enzymes and the addition of calcium during canning.

Research at the IFR is aimed at learning how to control ferulic acid levels. Funding has been secured from the Biotechnology and Biological Sciences Research Council.

The discovery is also expected to have wider implications for the food industry. "Plant cell walls can affect the food's resistance to pesticides, as well as taste and juiciness," said Dr Waldron.