Food researcher Lochan Singh happens to be a vegetarian but over a 12-week period she visited 20 restaurants across the National Capital Region ordering samples of tandoori chicken fresh from traditional ovens.

She processed the chicken samples in her lab at the National Institute of Food Technology Entrepreneurship and Management in Sonepat (Haryana) to measure chemical compounds called polycyclic aromatic hydrocarbons (PAH) ubiquitous in charred food and linked to cancer.

Her study has found that while the risk associated with PAH levels in the chicken samples were on average “within safe limits” set by European regulatory authorities, the PAH levels varied dramatically sample to sample — insignificantly low in some but high in others.

Singh and her research supervisor Tripti Agarwal also noted certain patterns in the PAH levels that they say appear to be influenced by the cooking method and ingredients in the marinade for the chicken.

“Our findings should be the starting point for more research — the samples we examined had variable PAH levels,” said Agarwal, an assistant professor in the agriculture and environmental sciences department at the NIFTEM. “This suggests that there are ways to cook tandoori chicken with low PAH. We need to determine exactly what factors help keep PAH low.”

Scientists have known for long that PAHs emerge when meat, including poultry or fish, is cooked using high-temperature methods such as frying, grilling, or heating in an oven. The chemicals form when fat from the meat drips on flames and smoke.

Lab studies on animals have suggested that PAH in the diet can increase the risk of cancers, including tumours of the gastrointestinal tract, and health experts have for years called on people to restrict or avoid charred food.

Agarwal too is vegetarian but the NIFTEM scientists said they chose tandoori chicken for their study because of a dearth of research on concentrations of PAHs in this food item popular across the country.

Their 20-sample study, published in Risk Analysis, a peer-reviewed research journal, has found that PAH levels were on average 440 micrograms per kg but varied from a low 25 micrograms per kg in one sample to 3,773 micrograms per kg in another.

They found that chicken that was cooked twice — half-cooked in the oven, hung outside, then cooked again before being served — had higher PAH levels than chicken placed in the oven only once until fully cooked.

The marinade appeared to influence PAH levels too. Chicken marinated in oil, spices, coriander and herbs, for instance, had an average 37 micrograms PAH, while chicken soaked in oil, turmeric and red chilli had 81 microgram PAH and a marinade of oil, curd and a special masala (a mix of spices) had 1,400 microgram PAH per kg chicken.

The study has also shown that PAH levels in tandoori chicken were on average much higher than those in grilled chicken and chicken shawarma measured earlier by scientists in Kuwait.

The NIFTEM researchers say their study could provide baseline data for future research aimed at tailoring cooking methods, ingredients, even oven designs for the lowest possible PAH levels. “Is it possible that certain chemicals in some marinades might reduce the PAH levels? Future studies should probe such questions,” Agarwal said. The two scientists are currently also working on a similar analysis of PAH levels in fish.