Mulberry fruit's pharmacological potential requires more human evidence: Review
Generally consumed as fresh fruits, jams and juices, mulberry fruits are widely planted in Asia. Mulberry contains significant amounts of biologically active ingredients associated with potentially beneficial pharmacological effects on health, and has thus been used in traditional medicine.
Previous studies have found bioactive components such as alkaloids and flavonoids in mulberry, making it a possible antioxidant.
But more prominent in the fruit are water-soluble bioactive polyphenols called anthocyanins, with its purported health benefits including anti-cholesterol, anti-obesity and hepatoprotective effects.
A study led by the University of Otago was therefore conducted to review the pharmacological effects of the mulberry fruit.
Mulberry's multiple minerals
The researchers found that several studies had reported that multiple phytochemical compounds could be isolated from the fruit, including epigallocatechin, epigallocatechin gallate, gallocatechin, and gallocatechin gallate.
In addition, it was found to contain essential amino acids such as isoleucine, leucine, methionine and cysteine, and seven non-essential amino acids, including arginine, glutamic acid, glycine and aspartic acid.
Minerals such as potassium, calcium, magnesium, iron, sodium, zinc and copper were also detected, alongside organic acids like citric, tartaric and acetic acids.
While mulberry fruit was also found to be high in anthocyanins, purple mulberry fruit extract was reported as containing higher contents of total sugars and anthocyanins than red and purple-red mulberry fruit extracts.
The researchers wrote: "This is because sugars are needed as the precursors to synthesis anthocyanins. However, red mulberry fruit had a higher ascorbic acid and ß-carotene than purple and purple-red mulberry fruit extracts."
Furthermore, another study showed that there were more phenolic compounds in mulberry fruits than in blackberry, blueberry, raspberry and strawberry.
Anthocyanins in mulberry fruits have been known to "inhibit the oxidation of low-density lipoprotein (LDL) and scavenge free radicals".
One of the studies reviewed reported that rats on a high-fat diet, given 5% or 10% mulberry fruit powder, experienced a significant decrease in the concentration of serum and liver triglycerides, total cholesterol and serum LDL cholesterol, as well as an increase in serum HDL cholesterol.
An RCT involving 58 hypercholesterolaemic adults between 30 and 60 years old, consuming 45g of freeze-dried mulberry fruit for six weeks lowered the level of total and LDL cholesterol in the intervention group.
Other effects reported by the studies reviewed included improved resistance of insulin and leptin, modulation of obesity-induced oxidative stress and inflammation, prevention of gastric carcinoma formation, reduction in physical fatigue, and neuroprotective activity.
Lacking the human touch
Despite the generally positive health effects of mulberry fruit consumption, the limited number of human studies in this area meant it was difficult to determine its safety, as well as the appropriate dosage and treatment duration.
The researchers wrote: "The majority of the studies that reported beneficial effects of mulberry fruits on health are animal-based studies.
"Moreover, these studies used different varieties of mulberry fruits, types of solvents and methods of preparation, which cause the evaluation of activity of mulberry fruits to be difficult."
They then concluded: "Larger, well-designed, randomised controlled trials are needed to examine the effects of mulberry fruit consumption on human health.
"Similar to other plants and food products, the fate of polyphenol compounds in the body — especially after undergoing intestinal transformations by enzymes produced by gut microbiota — should also be addressed.
"The elucidation of some active ingredient structures in mulberry fruits and their mechanisms in promoting pharmacological properties are also worthy of further research."
"Effects of Mulberry Fruit (Morus alba L.) Consumption on Health Outcomes: A Mini-Review"
Authors: Hongxia Zhang, et al.