Research progress on the structure and biological activity of phenolic compounds in edible passion fruit
Passiflora is a perennial herbaceous or woody vine species belonging to the Passiflora Linn. family, native to South America and mainly distributed in tropical and subtropical regions. Its fruit is rich in nutrients and is often consumed fresh or processed into juice for consumption. There are six popular varieties of edible passion fruit worldwide, as detailed in Table 1.

In some tropical production areas such as Europe and America, purple skinned passion fruit, winged stem passion fruit, yellow fruit passion fruit, large fruit passion fruit, and blue passion fruit (P.caerulea L.) are traditional folk medicinal plants used for diuresis, cough relief, anti-inflammatory and analgesic effects, blood pressure reduction, sedation, anticonvulsant effects, and anti addiction. Multiple extracts of passion fruit are approved for use in the pharmacopoeias of countries such as the United States, Brazil, and the United Kingdom. China introduced purple skin passion fruit in 1901, and now there are multiple cultivated varieties in Guangxi Province, Yunnan Province, Fujian Province, and Chongqing City. Local people have discovered that consuming passion fruit has detoxifying and beautifying effects, eliminating inflammation, and resisting aging. The “Yunnan Traditional Chinese Medicine Resource List” also records that “passion fruit has a bitter taste and a warm nature. Roots, vines, flowers, and fruits can be used as medicine, with the effects of dispelling wind and dampness, promoting blood circulation and relieving pain, clearing heat, stopping cough, and dissolving phlegm. It is used to treat rheumatic bone diseases, hernias, dysmenorrhea, neuralgia, insomnia, wind heat dizziness, nasal congestion and runny nose, and is also used topically to treat fractures. As of 2020, there are 2980 patents related to passion fruit in China, of which 8.29% are patents for medical preparations and 6.07% are patents for specific therapeutic activities of compounds or drug preparations. These patents indicate that passion fruit has health benefits such as clearing heat, detoxifying, calming the mind, and calming the nerves. With the increasing recognition and demand for passion fruit among people, its planting areas in China have gradually expanded. Taking Guangxi Province, which was the first to introduce passion fruit, as an example, in 2020, the planting area of purple skin passion fruit and yellow fruit passion fruit reached over 20000 hectares, with an annual output of about 300000 tons, and has become one of the local characteristic poverty alleviation industries.

Phenolic substances are an important class of secondary metabolites in plants, with over 8000 species discovered in nature. Modern research on passion fruit has shown that this plant genus contains chemical components such as phenols, alkaloids, and triterpenoids. Phenolic substances are its characteristic secondary metabolites, exhibiting beneficial physiological effects such as antioxidant, anti-inflammatory, antibacterial, and hypoglycemic effects on the human body. Previously, research on the genus Passionfruit mainly focused on the analysis of passion fruit and its components, and there has been no comprehensive summary of phenolic compounds in edible Passionfruit plants to date. Therefore, this article systematically reviews the content, types, chemical structure characteristics, and activities of phenolic substances in edible passion fruit, aiming to help people find and develop more natural and excellent sources of phenolic substances, and promote scientific research and rational development of China’s edible passion fruit industry.

Eating passion fruit is a natural treasure trove of phenolic compounds, which have benefits such as preventing diseases and enhancing physical fitness after ingestion. Previous studies have shown that in addition to direct consumption, these phenolic compounds have the potential to be developed to meet personalized choices of related drugs and functional foods for different populations. Domestic and foreign researchers have paid attention to the phenolic components of edible passion fruit, and have measured the total phenols, total flavonoid content, and biological activity. However, existing research is insufficient, and further exploration is needed on the following issues: 1) The active compounds found in edible passion fruit are mainly flavonoid carbon glycosides and oxygen glycosides, but currently their total flavonoid or total phenolic content is determined using rutin or kaempferol as standard samples, which cannot fully represent and reflect the phenolic compound content of edible passion fruit. Therefore, it is necessary to study and establish a method for determining the total phenolic content based on the main flavonoid carbon glycosides such as paeoniflorin and kaempferol as standard samples. At the same time, the determination of these flavonoid carbon glycosides or oxygen glycosides themselves in passion fruit should also be established. The content determination method provides scientific data support for the cultivation of high-quality edible passion fruit and the development of related products; 2) The current research on the activity of phenolic compounds in edible passion fruit mainly focuses on crude extracts, which cannot clarify the specific material basis and regulatory pathways of biological activity. Therefore, it is necessary to pay attention to the separation and purification of compounds, deeply explore the mechanism of their activity, and determine their structure-activity relationship, in order to provide a basis for the scientific utilization of edible passion fruit; 3) The whole fruit of edible passion fruit is rich in phenolic compounds, and existing research is mostly focused on its pulp, with low processing and utilization of stems, leaves, and skin. In the future, attention should be paid to the study of phenolic substances in these parts to achieve efficient utilization of natural resources.