When is the right time to harvest shikuwasa (Citrus depressa) ?
In 2008 Yamamoto Masashi et al. gave the answer, in 2010 Miyagi Kazuna et al. completed it but in a misleading way.
Miyagi Kazuna says that the juice is good to drink from late November to early December, when the sugar/acid ratio is close to that of regular mandarins.
In October, the fruit is moderately sweet (9° Brix) and still acidic (4%).
Which simply means that it should be treated like a regular mandarin. But a Shikuwasa it is not a regular mandarin at all. It is a left over wild-cultivated fruit , an ancestor of mandarins. The Chinese custom of consuming this fruit when green as a condiment including the peel is linked to its richness in flavonoids, which health benefits have now been demonstrated.
This was clearly shown by Yamamoto Masashi et al. Shikuwasa peel (in μg./0.1g) is a bomb of sinensetin, nobiletin and tangeretin. At least 0.5% PMF Poly Methoxy flavones) if it harvested up until the end of September. This level drops from October, it is divided by 2 by January.
Explanation : the CitOMT gene of small wild mandarins saturates the zest of the young fruit with nobiletin by methylation at the beginning of fruit development. This action is lost in domesticated mandarins. Nobelitin is first present in the green stage. It then decreases because CitOMT is no longer active.
October is the month when the fruit is transformed, it increases in size, increases in juice content and the peel becomes less dark green. Mid-October its taste is excellent, its full of juice and... nobelitin. There is a notable decrease in nobiletin as Shikuwasa ripen (Miyagi Kazuna, 2010)
The reason I'm so interested in the quantity of nobiletin is because of its demonstrated role in preventing and treating Alzheimer's disease (and neurodegenerations, Parkinsons etc.) - there were 4 important publications this year on the subject.
I was also fascinated by Jiafeng Li's demonstration of its effects on osteoarthritis by injection of nanoencapsulated nobiletin (this time we know that it is nobiletin that acts in osteoarthritis and cartilage lesions)
So that's why you need to harvest Shikuwasa in October !
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