The yellow pigment showed “perfect chemical stability”, report Chinese researchers in the International Journal of Food Science and Technology. “These results may be helpful for the further application investigations into its commercial prospects in food pigment industry,” wrote the researchers, led by Dr. Xiaohong Wang from the Huazhong Agricultural University in China
Natural pigments
Pigments are commonly used as food additives to improve colour and stimulate appetite.
Synthetic pigments are widely used in industry as they generally have brighter colour, better stability, and lower costs than natural pigments. However, research has suggested some synthetic pigments may have negative effects, causing hyperactivity in children, and having pro-inflammatory properties.
Natural pigments are generally considered safe, and offer nutritional and pharmacological benefits such as anti-oxidative and anti-inflammatory properties. But the use of natural pigments in food processing is narrow due to their lower stability, higher costs, and problems with storage.
The flower bud of Sophora japonica L. (known as Huaimi) has long been used in traditional Chinese medicine.
Extracts from Huaimi include a natural yellow pigment that is known for its benefits in Chinese ‘folk-law’ – but has never been researched for its chemical properties, say the researchers.
Systematic analysis
The new study extracted yellow pigment from Hauimi and – for the first time – studied its chemical structure, assessing its stability and potential for use in food processing.
Huaimi yellow pigment extracts (HYPE) were systematically studied using spectrophotometric analysis to test its stability related to pH value, temperature and metallic ions.
The main component of HYPE was seen to be flavonoid compounds, with rutin found to constitute over 40 per cent of the pigment.
The effects of pH were assessed at pH values between 2.0 to 9.0. HYPE was seen to remain a similar yellow at pH values between 2.0 and 6.0, whilst values over pH 7.0 resulted in HYPE solutions becoming a brighter yellow.
Mathematic modelling revealed HYPE to good thermal stability, with a half-life of 918.9 hours at room temperature.
Metallic ions displayed co-pigmentation influences on HYPE that may be beneficial for applications in the food industry, reported the authors.
Perfect stability
The researchers concluded that HYPE “displays perfect chemical stability” for potential food applications - acknowledging their results to be consistent with the pigments widespread use in Chinese herbal medicine.
The researchers confirmed the potential of HYPE as a natural pigment in food products, stating that whilst further research is required to assess the stability of the pigment in a food matrix, the potential for its use as a natural pigment are boosted by the high levels of rutin shown to be contained in the pigment.
“Flavonoids compounds are currently used as antioxidants in food industry, [the high flavonoids content] will undoubtedly promote the application of HYPE in future,” added the researchers.
Source: International Journal of Food Science and Technology
Published online ahead of print, doi: 10.1111/j.1365-2621.2010.02322.x
“Chemical stability of yellow pigment extracted from the flower bud of Sophora japonica L. (Huaimi)”
Authors: W. Chen, P. Li, X. Wang