HKBU develops more accurate way to inspect sulphur-treated food, Chinese herbal medicine

This approach uses tryptophan sulphonate.

Researchers from the Hong Kong Baptist University (HKBU) have discovered a new approach for the inspection of sulphur-treated food and Chinese herbal medicinal products through a new chemical marker called tryptophan sulphonate, a chemical compound formed when tryptophan, a naturally occurring amino acid in many foods, reacts with sulphite.

In a statement, HKBU said the team led by Xu Jun, assistant professor of the teaching and research division of the School of Chinese Medicine, conducted comparative experiments on 20 food products using the tryptophan sulphonate test. They found that the compound is present in sulphur-fumigated food samples but not in non-fumigated samples. 

The researchers applied tryptophan sulphonate and sulphite tests to 50 food and Chinese herbal medicines samples collected from markets for their evaluation. 

“The tryptophan sulphonate test result was positive in corn starch, dried star fruit, dried mango and snow fungus, but negative in garlic and onion; sulphite test yielded opposite results,” HKBU said. 

Since garlic and onion contain sulphur-containing components, it can be concluded that the positive sulphite test result is not a consequence of treatment. The tryptophan sulphonate test is therefore more reliable for detecting sulphur-treatment for food items with intrinsic sulphur-containing constituents, HKBU said. 

The researchers noted that the sulphite test may produce false-negative results due to the instability of sulphites caused by high temperature and prolonged storage of the food samples.

Furthermore, the tryptophan suphonate test is quicker and more automated, with a one-hour ultrasonic extraction and two-minute mass spectrometry, allowing for batch processing. In comparison, the sulphite test takes 2.5 hours of manual work per sample, HKBU said. 

The research team hopes to develop the tryptophan sulphonate test for commercial application.