Once upon a time, folk wisdom dictated the harvesting of certain herbs under the light of a full moon - now technology is taking over with the development of handheld devices that measure the potency of the plant in the field.

The old tales were based on the true phenomenon that plants with medicinal effects have maximum potency at particular times. Modern growers of plants which contain compounds beneficial to health also need to know when this is - if their products are to be effective.

Paul LaChance, Executive Director of the Nutraceuticals Institute at Rutgers University, told the annual meeting of the American Association for the Advancement of Science (AAAS) that his team was developing handheld bioassay devices that could measure the levels of a bioactive compound in just 20 minutes.

Perfect moment

"We've been developing rapid amino assays. With these, a farmer can know where in the field, what part of the plant and when best to pick it," he said.

"It also means he gets a better yield of his crop and a better price for it."

The key part, according to Dr LaChance, is that: "You have to agree on the biomarker - the chemical which signifies the presence of the active ingredient."

Bamboo to blueberry

The team is developing a number of bioassays. One spots the active ingredient of blueberries: "Blueberries have similar properties as cranberries in reducing urinary tract infections."

Another identifies a compound in bamboo shoots believed to lower blood cholesterol.

Some of the bioassays have other purposes such as the one that detects the presence of a virus in blueberry plants.

"It can tell you before the plant flowers - which is the way it is identified now - which plants have the problem and where," he said.