HONG
KONG, July 29, 2024 /PRNewswire/ -- A research
team at Hong Kong Baptist University
(HKBU) has developed a new approach for the inspection of
sulfur-treated food and Chinese herbal medicinal products through a
new chemical marker called tryptophan sulfonate. This approach is
more accurate, rapid and efficient for large sample quantities
compared to the current testing method. The study marks a potential
advancement in food safety and quality assurance, providing the
industry with a robust tool for inspecting sulfur-treated food and
Chinese herbal medicinal products.
The research findings have been published in the international
scientific journal Food Chemistry.
More accurate and efficient test in need
Sulfur treatment, including sulfur fumigation and the addition
of sulfites, is a common preservation method employed in the food
and Chinese herbal medicinal industries. However, excessive
consumption of preservative sulfites in food and Chinese herbal
medicinal products can lead to respiratory symptoms and compromised
nutritional value and safety.
Currently, sulfite test is the most commonly used method for
inspecting residual sulfites in sulfur-treated food. Nevertheless,
sulfites are chemically unstable, sometimes leading to inaccurate
results. Sulfite test is also labour-intensive and time consuming.
It can only analyse one sample at a time, making high-throughput
analysis challenging. Furthermore, sulfite test may yield
false-positive results for food rich in endogenous
sulfur-containing components such as garlic and onion.
Tryptophan sulfonate as a chemical marker
In search of a more accurate and efficient testing approach, Dr
Xu Jun , Assistant Professor of the
Teaching and Research Division of the School of Chinese Medicine at
HKBU, and his research team identified a chemical compound called
tryptophan sulfonate in sulfur-fumigated samples using
untargeted metabolomics. Tryptophan sulfonate is formed when
tryptophan, a naturally occurring amino acid in many foods, reacts
with sulfite.
The research team conducted comparative experiments on 20 food
products using the tryptophan sulfonate test. It was found that
tryptophan sulfonate is present consistently in all
sulfur-fumigated food samples but not in non-fumigated samples. The
finding demonstrated the potential of tryptophan sulfonate as a
specific chemical marker for distinguishing sulfur-treated and
non-sulfur-treated food products.
Tryptophan sulfonate test outperforms sulfite
test
To evaluate the applicability of tryptophan sulfonate in the
inspection of sulfur-treated food products and Chinese herbal
medicines, the team applied tryptophan sulfonate and sulfite tests
to 50 food and Chinese herbal medicinesamples collected from
markets. It was found that tryptophan sulfonate test and sulfite
test results were mostly identical except for six food samples,
including corn starch, dried star fruit, dried mango, snow fungus,
garlic and onion. The tryptophan sulfonate test result was positive
in corn starch, dried star fruit, dried mango and snow fungus, but
negative in garlic and onion; sulfite test yielded opposite
results.
As garlic and onion are known to contain endogenous
sulfur-containing components, it is evident that the positive
sulfite test result is not a consequence of sulfur-treatment.
Tryptophan sulfonate test is therefore a more reliable approach
for detecting sulfur-treatment for food items with intrinsic
sulfur-containing constituents.
False-negative due to instability of sulfites
For the discrepancies between the two tests on the other four
food samples, the research team hypothesised that the sulfite test
may produce false-negative results due to the instability of
sulfites caused by high temperature and prolonged storage of the
food samples.
In a separate experiment, the research team found that sulfite
levels in sulfur-fumigated ginger, yam and ginseng declined by
around 90% to 100% after nine months of storage, and reduced by
around 50% to 72% after heating, while the tryptophan sulfonate
levels remained stable. They concluded that the instability of
residual sulfites could lead to false-negative results. In
contrast, tryptophan sulfonate exhibited greater stability over
heat and storage, suggesting it serves as a better chemical marker
for sulfur-treatment inspection.
High throughput screening made possible
On the testing procedure, tryptophan sulfonate test is faster
and more automated. It involves a direct ultrasonic extraction for
one hour and mass spectrometry analysis for two minutes, allowing
the parallel handling of batches of samples. In contrast, sulfite
test requires 2.5 hours of manual operation, including reflux
extraction and titration for a single sample test.
Dr Xu Jun said: "Our research
showed that tryptophan sulfonate serves as a highly distinctive
chemical marker, enhancing the accuracy and efficiency of
sulfur-treated food and Chinese herbal medicine inspection. It is
especially suitable for high throughput screening of large samples
size. It demonstrates the potential in offering a more
cost-effective alternative for the existing test protocol adopted
by the industry."
Moving forward, the research team hopes to further develop the
tryptophan sulfonate test for commercial application.
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SOURCE Hong Kong Baptist
University