A study has found key differences between durian grown in China compared with South-East Asia. - Photo: Sun Yeung
BEIJING (SCMP): Durians grown in China could be missing or extremely low in some key nutrients, according to a study into the nutritional profile of the tropical fruit taking root in Hainan.
In the first study of its kind, scientists found that, compared with durians grown in Southeast Asia, the Chinese-grown fruit displayed a surprisingly different nutritional profile.
For example, Monthong, or golden pillow, durian grown in China did not contain the antioxidant quercetin at all, while its Thai counterpart contained huge amounts, researchers at the Hainan Academy of Agricultural Sciences found.
In fact, the only Hainan durian variety that was found to have quercetin was the long-stemmed Kan Yao, but it was at a level 520 times lower than the same variety grown overseas and 540,000 times lower than the levels in the Thai Monthong.
As for gallic acid, a compound with antioxidant, anti-inflammatory and anticancer properties, the team said it was not detected in Kan Yao, a result that was consistent with previous studies. But its levels in Monthong were “significantly lower than the levels previously reported”.
A 2008 study of Thai durians reported 2,072 micrograms of gallic acid per 100 grams in Monthong, 906 times higher than the 22.85 nanograms per gram of the Chinese-grown fruit.
“The differences in climate and content of minerals and nutrients in the soil could affect the accumulation of nutrients during the durian growth process,” said lead author Zhang Jing at the Sanya Nanfan Research Institute of the Hainan Academy of Agricultural Sciences.
“This could lead to higher levels of certain substances, while others might be absent,” she added.
In a paper published in the Chinese-language journal Food and Fermentation Industries on December 12, the researchers said the main antioxidants found in the three durian types studied – Monthong, Kan Yao and Musang King – were procyanidin B1, catechin and quercetin.
“The results ... indicated that Kan Yao has the strongest in vitro antioxidant activity [of the three],” the scientists said.
China is the world’s biggest importer of the pungent, prickly fruit, buying 95 per cent of global exports. In 2018, it began large-scale cultivation of durian in Hainan province, the country’s only tropical island with a climate suited to growing the fruit.
Durian is a nutritious fruit high in Vitamin C, potassium, dietary fibre and other nutrients. Unlike most other fruit, it is also high in fat.
The study focused on polyphenols, natural plant compounds that can act as antioxidants to neutralise harmful free radicals which increase the risks of cancer, diabetes and heart disease.
To evaluate the antioxidant functions of domestically grown durians, the team collected samples which were 90 per cent ripe on trees from a farm in Baoting Li and Miao autonomous county in the south of Hainan.
The team detected a total of 26 polyphenolic compounds in the Monthong, Kan Yao and Musang King varieties, which were found to have 19, 22, and 18 different compounds respectively.
Catechin, an antioxidant also found in green tea, was unique to Monthong, according to the study. Kan Yao uniquely contained quercetin, nicotiflorin, procyanidin B1 and trans-cinnamic acid.
Procyanidin B1 is also found in grape seeds, apples, peanut skin and cranberries, and is being studied as an anticancer drug.
The team said the types and concentrations of polyphenolic compounds were closely related to the farming location, variety and ripeness of durian.
The scientists cited the 2008 study that found Monthong durian in Thailand had the highest variety of polyphenolic compounds among five varieties analysed, with quercetin being one of the dominant bioactive substances.
“This differs from our results,” they wrote. “Kan Yao had the highest variety of detected polyphenolic compounds. While quercetin was not detected in Monthong, it was found to have esculin, catechin and 4-hydroxybenzoic acid,” they said, referring to other polyphenols. Esculin, for example, has been found to be antidiabetic.
Zhang said nutritional analyses of durian from Southeast Asia provided reference ranges, but there were no clear thresholds indicating what levels were good or bad.
Zhang also said the results did not yet fully represent durian cultivation in Hainan.
“Our current results are preliminary with samples from one farm. To build a big picture of nutritional values, we will extend sample gathering to more plantations in different areas in Hainan.”
The team also aims to identify nutrients that could be improved, such as substances that could promote ovarian health. Previous studies have shown that durians could be used to create a supplement to help treat infertility in polycystic ovary syndrome.
“By identifying one or several substances that help with ovary recovery and protection, we could further study how they are synthesised and regulated at the genetic level,” she said.
“Once we understand which genes control the accumulation of these compounds, we can enhance those genes through breeding to increase the levels of beneficial substances in durian.” - SOUTH CHINA MORNING POST
