A tea enthusiast in Shantou suffered from chronic constipation and had tried various remedies and health supplements with little success. Drinking tea is already a popular custom in the Chaoshan region, so he switched his usual oolong tea to aged raw Puer tea at home.
Surprisingly, after drinking it for a while, this tea enthusiast was able to naturally relieve himself, and his digestive function improved significantly. He was very grateful that Puer tea helped him overcome his embarrassing problem.
How did Puer tea help alleviate this tea enthusiast's constipation? Is there any specific scientific explanation for such health benefits associated with Puer tea? Why are Puer tea's functional properties more pronounced than those of other types of tea?
In today's feature article, Lu Li will continue to discuss with fellow tea enthusiasts the powerful substance contained within Puer tea – secondary metabolites.
Secondary Metabolites
In unfermented tea leaves, most of the plant nutrients are primary metabolites. However, during the fermentation process of Puer tea, these primary metabolites are transformed, degraded, and condensed into unique secondary metabolites.[1]
Secondary metabolites may be familiar to readers who have followed Lu Li's previous articles. This is a large family with over two thousand members, and there are still many categories yet to be discovered by current research.[2]
These compounds have very low relative molecular masses but are highly active. They often attach themselves to larger polymers in their small molecular state, providing numerous benefits to the human body.
The currently discovered functions of secondary metabolites include activating the lymphatic system, enhancing the immune system, controlling cholesterol levels, regulating hematopoietic functions, modulating the central nervous system and peripheral nerves, and reducing high blood pressure.[3]
Puer tea, which primarily ages over time, is rich in these secondary metabolites. Both the microbial fermentation process of ripe Puer tea and the natural fermentation process of raw Puer tea generate an abundance of secondary metabolites.
This is because the post-aging of Puer tea is a semi-anoxic fermentation process. During this process, the color of Puer tea gradually changes, and its plant nutrients transform from primary to secondary metabolites.
The most representative example of this transformation is the conversion of tea polyphenols. Research has found that the content of tea polyphenols in fresh Puer tea is generally above 25%, while after 50 years of aging, the content of tea polyphenols in aged Puer tea can drop below 5%.[4]
These tea polyphenols do not disappear; instead, they are transformed into more precious active ingredients. Due to space limitations, we will introduce here only two examples: γ-aminobutyric acid (GABA), which has a blood pressure-lowering effect, and thearubigins, which have anticancer properties.
γ-Aminobutyric Acid (GABA) is an effective blood pressure-lowering component that acts on the vascular motor center of the spinal cord, effectively promoting vasodilation.
The raw leaves used to make Puer tea, from Yunnan's large-leaf variety, spontaneously produce GABA in an anoxic, sealed environment. This component is not unique to Puer tea; Astragalus, a common ingredient in blood pressure-lowering drugs, also contains GABA as its active ingredient.[5]
Analysis of Thearubigins
Next, let's talk about thearubigins (TRS), a compound widely present in both Puer and black teas. Researchers consider it one of the most valuable substances in tea, capable of treating cancer and scavenging DPPH radicals.[6]
Research reports have pointed out that thearubigins, abundant in aged Puer and ripe Puer teas, can significantly improve hematocrit, plasma viscosity, and red blood cell electrophoresis, thus alleviating the symptoms of hyper-viscosity in hypertensive patients.[7]
From a physicochemical perspective, thearubigins are a collective term for heterogeneous phenolic acidic pigments, including various heterologous substances with relative molecular masses ranging from 700 to 40,000. They can be considered a mixture of tea pigments.
In the study of the formation mechanism of thearubigins, the scientific community previously relied on the fermentation model of Black Tea:
First, theaflavins are produced, then they convert to thearubigins, and finally, thearubigins convert to theabrowns.
However, subsequent studies have shown that thearubigins are extremely unstable and easily convert to theabrowns. In various tests of black tea, only the converted theabrowns could be found, while thearubigins were nowhere to be seen.
The appearance of theabrowns signifies the end of pigment evolution in black tea, leading to spoilage. This was one of the reasons some experts from Jiangsu and Zhejiang criticized the claim that Puer tea improves with age during the “Great Siege.”
When the research focus shifted from black tea to Puer tea, the study of thearubigins saw a breakthrough. However, the mechanisms of thearubigin formation in these two types of tea are entirely different. Here, Lu Li will briefly introduce them:
In the first half of pigment evolution, the performance of Puer and black teas is similar. The key difference lies in the second half. Unlike the direct conversion in black tea, thearubigins in Puer tea undergo a “reversionary evolution” process.[8]
The change in infusion color is even more evident. Initially, theaflavins predominate in Puer tea, giving the infusion an orange-yellow hue. After a period of aging, the appearance of thearubigins changes the infusion color to orange-red.
As Puer tea further transforms, thearubigins become dominant, and the infusion color turns dark red. When Puer tea reaches a certain critical point, the clarity and brightness of the infusion increase, becoming bright and clear.
This pigment evolution process can be summarized as: theaflavins → thearubigins → theabrowns → thearubigins. It is important to emphasize that during the later stages of Puer tea fermentation, theabrowns, through oxidation, release thearubigins again.
This is the unique mechanism of thearubigin formation in Puer tea. Not only does it validate the reasonableness of the phenomenon that the infusion of aged Puer tea is brighter than that of fresh Puer tea, but it also forms a large amount of thearubigins, which provide numerous benefits to the human body.
At this point, the functionality of Puer tea for the human body is further enhanced. It can not only boost the immune system but also aid in the treatment of hypertension, hyperlipidemia, diabetes, Gout, and other “rich diseases.”
However, it should be noted that although the “targeted” nature of secondary metabolites in Puer tea is very strong, they are mostly trace or micro-level amounts. Their effects on the human body are still not significant compared to targeted drugs.[9]
However, the types of these secondary metabolites are vast. Different medicinal components have different target actions. When all these forces come together, they truly form a definite “pharmacological effect.”[10]
Compared to drugs and health supplements, natural foods like Puer tea are harmless. Long-term consumption does not burden the liver and kidneys like taking medication, nor does it increase drug resistance and reduce immunity.
Moreover, this is not the full extent of Puer tea's benefits. Recent research proposes a new idea: Could advanced technologies such as supercritical extraction preserve a specific active component in Puer tea, thereby amplifying its functionality?
For example, L-EGCG-based anti-cancer teas, GABA-based blood pressure-lowering teas, yeast-based slimming teas, tea polysaccharide-based hypog