Does Passion Flower Help Anxiety?

The Passifloraceae family consists of 18 to 23 genera and over 500 to 700 species, with over 70 species considered edible varieties [1-3]. Among these, the Passiflora genus is the most important, due to its rich species diversity and significant economic value [4-6]. Passionflower is native to Brazil and is now widely distributed in tropical and subtropical regions [6]. 

Brazil remains the world's largest producer and consumer of passionflower [1,7], with an annual production exceeding 920,000 tons and a cultivation area of approximately 61,842 hectares. With the gradual expansion of passion fruit cultivation area in China, production has also been steadily increasing. Currently, the cultivation area is approximately 44,466 hectares, with an annual output of nearly 600,000 tons and a total value of 3 billion yuan [8]. Passiflora plants are primarily vine-like plants, most of which have auxiliary tendrils. Their fruits are indehiscent ellipsoidal or spherical capsules. Many varieties are cultivated as ornamental plants due to their unique and vibrant flower shapes [3-6,8-9].

In recent years, some passion fruit varieties have gained significant attention due to their diverse fruit flavors and rich content of bioactive compounds, which are believed to promote human health. Passiflora plants are a rich source of vitamins, phenolic compounds, flavonoids, and minerals, and can be used as medicinal drugs for treating certain diseases, exhibiting anti-tumor, anti-anxiety, anti-insomnia, anti-inflammatory, anti-oxidative, anti-hyperlipidemic, and antispasmodic effects [1,3,8-11]. 

With the growing research interest in passionflower in China, understanding its chemical composition and genetic characteristics can help improve its yield and quality through cultivation management and breeding techniques, thereby enhancing its commercial value. This study analyzes the development trends in passion fruit quality research, summarizes the nutritional and functional component composition of passion fruit both domestically and internationally, and evaluates their development and utilization potential. The aim is to provide a reference basis for improving its nutritional and medicinal quality, thereby promoting the comprehensive utilization and product development of passion fruit.

1 Current Status of Nutritional Quality Research on Passion Fruit

This study conducted a literature search using the Web of Science database with the keywords "Passiflora * Nutritional * Quality,""Passion fruit * Functional component,""Passiflora * Volatile compound,"and "Passion fruit * Volatile compound,"covering the years 1900–2021, and excluding duplicate or overlapping literature. A total of 270 documents were retrieved, and a statistical analysis was conducted on the literature related to the quality and functional components of Passiflora species (Figure 1). From the first relevant literature in 1967 until the late 1990s, the number of publications appeared in a discontinuous manner and showed almost zero growth. Subsequently, it exhibited a fluctuating growth trend. Since 2010, research on the quality of Passiflora plants has developed rapidly, with cumulative publications accounting for 67.8% of the total.

From a national distribution perspective, Brazil leads significantly in the number of publications, accounting for 48.5% of the total publications from the top 10 countries. China ranks second with 9.3%, but the gap with Brazil remains substantial. Although China has gradually recognized its nutritional and medicinal value, the number of papers published in SCI-indexed journals in the first tier remains relatively low, necessitating increased research investment and improved research standards. 

Using VOS viewer software to analyze international research directions on passion fruit nutritional quality and functional components (Figure 2), the results indicate that research on passion fruit nutritional quality primarily focuses on five aspects: 1) mineral nutrition and yield (yield, mineral elements, magnesium, potassium, and sodium, etc.); 2) clinical medicine-related (flavonoids, phenolic acids, dietary fiber, leaves, plants, and potential applications, etc.); 3) Volatile compounds and related products (aroma, wine, deep fermentation, terpenes, and peel, etc.); 4) Sensory quality and processed products (sensory quality, appearance, formulated products, and flour, etc.); 5) Diet and nutrition (carbohydrates, seeds, crude protein, and by-products, etc.).

2 Research Progress on the Nutritional Quality of Passion Fruit

2.1 Factors Influencing the Nutritional Content of Passion Fruit

The range values and average values of conventional nutritional indicators for passion fruit pulp, peel, seeds, and juice are shown in Table 1. This study selected purple-fruited and yellow-fruited varieties commonly available in the Chinese market as examples. It can be seen that the average vitamin C content per 100 g of passion fruit pulp is 19.86 mg (range: 16.00–57.76 mg), According to "The Natura Food Hub,"foods containing 15–30 mg of vitamin C per 100 g of edible portion can be considered an excellent source of vitamin C, and those exceeding 30 mg are considered an excellent source of vitamin C [5]. Therefore, passion fruit pulp can be considered one of the excellent sources of vitamin C. The fat content of different parts of passion fruit is as follows: seeds > peel > flesh. Passion fruit flesh is low in fat [1]; the peel and seeds have higher cellulose content than the flesh; and the seeds have higher protein content than the peel and flesh.

Passion fruit belongs to the high-acid type of fruit. When consumed fresh, the appropriate acid content is approximately 2%. Adding passion fruit juice during juice production can reduce the addition of acidifiers in the juice [12-13]. Studies have shown that pasteurization processing methods can effectively maintain the levels of soluble solids, total acidity, total sugar, and total vitamin C in passion fruit, with little change [14-15]. Based on research results from various countries [16-19], the growth and fruit quality of passion fruit are influenced by conventional nutritional indicators, which are affected by variety genetic characteristics, altitude, climatic conditions (light intensity, temperature, humidity, and precipitation), soil conditions (soil type and soil fertility), cultivation management (irrigation and fertilization), harvest timing (maturity and time), and storage conditions (storage temperature).

Conventional nutritional indicators vary among different passion fruit varieties. Among P. quadrangularis (Yellow), P. maliformis (Purple), and P. edulis (Frederick), P. maliformis has the highest vitamin C content in its fruit pulp, while P. edulis (Frederick) has the lowest [5]. The vitamin C content in the peel of P. quadrangularis is approximately three times that in its juice. The vitamin C content in the flesh of P. setacea is higher than that in P. quadrangularis and similar to that in P. maliformis [20]. The soluble solids content of naturally matured fruits of these three varieties was significantly higher than that of P. edulis (Pink) and P. edulis f. flavicarpa.

The juice acidity of P. edulis f. flavicarpa was higher, while the acidity of the middle peel of P. quadrangularis was lower. P. caerulea (Orange) has sweeter flesh, higher soluble solids content, and lower acidity; P. edulis (Yellow) has lower soluble solids content and stronger acidity, resulting in a slightly sour taste [17].

Cultivation methods and environmental conditions significantly influence the nutritional quality of passion fruit. The organic acid content in passion fruit varies with the altitude of the planting location [21]. Research on the minimum accumulated temperature (ATmin) for passion fruit cultivation in Japan indicates that when ATmin reaches 1,350°C, fruit quality meets fresh-market standards, and higher ATmin values correlate with better fruit quality [13]. Under trellis cultivation, the vitamin C content in the flesh of P. setacea was significantly higher than that in cultivation; moreover, the highest vitamin C content in the flesh occurred during the dry season, which may be related to light and water stress [20]. However, other studies have found that different cultivation methods do not significantly affect the vitamin C content of the fruit flesh of P. edulis Sims f. flavicarpa Deg. [22].

The quality of passion fruit also varies under different storage conditions. At room temperature, the acidity of passion fruit decreases gradually with prolonged storage time; however, extending the storage period or increasing the temperature reduces the commercial value of the fruit peel [14]. As storage time increases, the soluble solids content and pH of P. edulis Sims f. flavicarpa fruit, but the titratable acidity showed no significant changes [15]. High oxygen modified atmosphere packaging effectively maintains the levels of vitamin C, soluble solids, total phenols, and total flavonoids in passion fruit, as it inhibits the respiratory activity of passion fruit, maintains the fruit's good physical characteristics and nutritional properties [23]. PLA/PBAT "polyethylene/adipic acid-terephthalic acid-butyric acid copolymer [Poly(lactic acid)/Poly(butylene adipate-co-terephthalate ) packaging is more effective than PE (polyethylene) in reducing passion fruit aging, delaying the reduction of total acidity and the oxidation of vitamin C, and maintaining the best quality of passion fruit fruit [24].

2.2 Nutritional Components of Passion Fruit and Influencing Factors

The soluble sugars in passion fruit are primarily glucose, fructose, and sucrose. The proportions of these sugar components vary among different varieties and growing regions, and are also influenced by the fruit's maturity stage, growth conditions, and environmental factors [18]. The proportion of soluble sugar components directly affects the sweetness of the fruit, with sweetness values in the following order: fructose > sucrose > glucose [13].

Currently, there is some controversy regarding the proportions of sugar components. Some studies suggest that sucrose is the most abundant sugar component, followed by glucose and fructose [17, 27]; however, other studies indicate that glucose and fructose are the most abundant sugar components [18, 28]. Additionally, reports have shown that glucose accounts for a larger proportion of total sugars, followed by fructose [5]. This may be due to differences in cultivation environments and soil nutrient conditions. Harvesting fruits at different stages of maturity can also affect the distribution of sugar component ratios. In P. edulis (Purple) fruits harvested 60–80 days after flowering, glucose and fructose content was higher, while sucrose content was lower [5]; in P. edulis (Pink) and P. edulis f. flavicarpa had a higher sucrose content and lower glucose and fructose content in unripe passion fruit pulp; however, the sucrose content in P. edulis (Purple) fruits harvested 52 days after flowering was nearly twice that of glucose or fructose.

The composition of organic acids in passion fruit is an important component influencing juice flavor, and its content is closely related to fruit quality [29]. However, research results on the organic acid composition of passion fruit vary significantly. In addition to being influenced by factors such as variety, growth conditions, environmental conditions, and fruit maturity, different analytical methods also yield varying results for organic acid components. Using reverse-phase high-performance liquid chromatography to determine the organic acid content in passion fruit, the results showed citric acid > L-malic acid > L-lactic acid > succinic acid > L-ascorbic acid > tartaric acid > fumaric acid [30]. Using ion exchange chromatography to determine the organic acid components in passion fruit, the results showed that citric acid and malic acid were the main components, with relatively low levels of succinic acid [29].

The organic acid components of passion fruit vary slightly among different varieties. In P. foetida, the organic acids include citric acid, oxalic acid, tartaric acid, malic acid, and ascorbic acid, with citric acid and oxalic acid being the primary organic acids in the fruit, while the concentrations of other organic acids are very low [28]; purple passion fruit fruits contain organic acids including malic acid, succinic acid, lactic acid, citric acid, and succinic acid, with significant differences among the organic acids, and citric acid having the highest content [31]. Based on the above research findings, passion fruit belongs to the citric acid-dominant fruit category.

Passion fruit contains abundant amino acids, with 17 amino acids detected in the fruit pulp and 16 amino acids detected in the seeds (with isoleucine not detected), while only 6 amino acids were detected in processed juice, and their concentrations were relatively low. The amino acid component with the highest proportion in the fruit pulp and seeds is glutamic acid, followed by arginine. In juice, glutamic acid also has the highest proportion [28, 31-32]. Among amino acid components, glutamic acid is an important source of delicious taste, while glycine is the primary source of sweetness. In passion fruit pulp, flavor-related amino acids (glutamic acid, glycine, and aspartic acid) account for more than one-third of the total amino acids in the fruit, and the content of essential amino acids such as histidine, threonine, isoleucine, leucine, lysine, and valine is higher than the nutritional requirements for humans [13, 28].

The amino acid content of P. subpeltata fruits, compared with FAO/WHO reference values, shows the highest content of leucine, followed by phenylalanine, threonine, and valine [33]. In protein synthesis, leucine plays a crucial role in the growth and maintenance of the body. Therefore, consuming passion fruit can provide amino acids at dietary nutrient levels and also aid in normal metabolism.

3 Study on the aromatic components of passion fruit

Aroma is one of the most important attributes influencing the sensory quality of fresh and processed passion fruit products. Previous studies [22,24,34-37]have found that the main volatile compounds in passion fruit are esters, with common volatile components including ethyl butyrate, ethyl caprylate, ethyl acetate, and hexyl caprylate (Figure 3). The primary volatile components responsible for the sweet, fruity, and floral aromas of passion fruit are esters (ethyl butyrate and ethyl caprylate) and terpenes (α-pinene, β-myrcene, limonene, and γ-isopimaric acid); while the chemical components primarily responsible for its green aroma are aldehydes (hexanal and octanal) [1].

The variety, growing region, cultivation system, storage time, and detection methods of passion fruit can all influence the volatile compounds identified. Using GC-O and GC-MS analysis of P. mollissima (Kunth) L. H. Bailey fruits, 19 volatile compounds were identified, primarily including linalool, hexyl acetate, 1,8-cineole, and butyl acetate; the aroma precursors were identified as (Z)-3-hexenyl b-D-glucopyranoside and linalyl b-D-glucopyranoside [36]. Using HS-SPME and GC-qMS, the volatile compounds in P. edulis were identified as glucopyranoside [Linalyl b-D-glucopyranoside][36]. Using HS-SPME and GC-qMS, 51 volatile compounds were identified in the fruits of P. edulis Sims, 24 in those of P. edulis Sims f. flavicarpa, and 21 in P. mollissima fruits, with ethyl esters being the most abundant components in the volatile compounds of all these varieties [37]. In the fruits of P. edulis Sims fo edulis, 19 odor compounds were identified, with the main aromatic components being ethyl butyrate, ethyl hexanoate, and b-ionone, which exhibit fruity and floral aromas [35].

Fresh passion fruit fruits were identified as containing 39 flavor compounds, including esters, terpenes, ketones, aldehydes, and other categories. However, during the entire storage process, a total of 140 flavor components were identified, primarily consisting of six types of compounds: esters, alcohols, ketones, alkenes, and aldehydes. Ethyl acetate, propionyl acetate, methyl butyrate, ethyl hexanoate, hexanol, and methyl heptanone were present throughout the storage period. The primary volatile compounds were esters, with ethyl butyrate and ethyl acetate being the most significant [24]. Research has also found that fresh passion fruit does not contain ethyl butyrate, which is produced gradually as the fruit matures and ages. In the future, it may be possible to use the detection of ethyl butyrate content to determine the storage time.

Under organic and traditional cultivation methods, the volatile components of passion fruit are basically the same, but there are also some differences. Under organic cultivation, the content of ethyl 2-propenoate, 2-methyl-1-propanol, diethyl carbonate, and ethyl hexanoate in passion fruit was three times higher than that in conventional cultivation. However, under conventional cultivation, the content of butyl acetate, hexanal, butyl acetate, and trans-3-hexenyl butyrate are three times higher than those in fruits grown under organic cultivation. In organic cultivation, the content of hexanoates, acetates, and saturated alcohols is higher, resulting in more pronounced fruit flavor, sweetness, and citrus notes, which enhance the overall taste of passion fruit.

Additionally, trans- and cis-butyric acid-3-hexenyl esters, α-phellandrene, α-pinene, D-limonene, trans-β-caryophyllene, and δ-thujene contribute more to the aroma of passion fruit fruits grown organically, while unsaturated alcohols, β-myrcene, and β-linalool (which have grassy and sulfur-like odors) account for a higher proportion of the aroma in passion fruit fruits under traditional cultivation methods [22]. α-Linolenic acid metabolism, metabolic pathways, and secondary metabolic pathways are the primary pathways involved in the synthesis of important volatile organic compounds in passion fruit fruits, the phenylpropanoid and fatty acid metabolic pathways are crucial metabolic pathways in passion fruit growth for resisting environmental stress [32]. In a study of P. edulis Sims (Purple) fruits in Hainan, China, 13 important gene families in fatty acid pathways and 8 important gene families in terpenoid pathways were identified (Figure 4), including the ACX, ADH, ALDH, and HPL gene families, particularly ACX13/14/15/20, ADH13/26/33, ALDH1/4/21, and HPL4/6, are key genes for ester synthesis, while the TPS gene family, particularly PeTPS2/3/4/24, are key genes for terpenoid synthesis [8].

4. Recent Advances in the Functional Quality of Passion Fruit

In recent years, the bioactive properties and chemical characteristics of passionflower plants and their crude extracts have garnered increasing attention worldwide. Different varieties, climatic conditions, geographical locations, cultivation years, maturity levels, and storage conditions all influence the content and composition of bioactive compounds such as phenolic compounds, anthocyanins, flavonoids, and carotenoids in passionflower plants [17,20,34,38].

4.1 Research on Phenolic Compounds in Passion Fruit

Currently, the primary methods for identifying the structures of phenolic compounds in passion fruit plants include nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) [6,39]. Methods for qualitative or quantitative analysis of phenolic compounds include high-performance thin-layer chromatography (HPTLC) [4], high-performance liquid chromatography-ultraviolet spectrophotometry (HPLC-UV) [6], and liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) [3,39], among others. The most commonly used solvent for extracting phenolic compounds from leaves, fruit pulp, and fruit peel is methanol, while ethanol is commonly used for seed extraction [6]. Analysis of phenolic compound content in 34 Passiflora species revealed that leaves contained the highest levels, followed by peel, seeds, and pulp [6].

4.1.1 Study of Phenolic Compounds in Leaves

Passiflora leaves contain abundant phenolic compounds, primarily flavonoids (including luteolin, isosorbide, morin, isomorin, apigenin, and carotene, among others) [34,39-42]. Metabolites from the leaves of 17 Passiflora species were identified, yielding a total of 49 flavonoids, including 20 C-flavonoids, 8 O-flavonoids, and 21 C,O-flavonoids. Among these, the bioactive components of P. caerulea and P. incarnata were the most similar, but studies have reported slight differences in the composition and content of phenolic compounds in the leaves of different Passiflora species [39].Incarnata were most similar, but other studies have reported slight differences in the composition and content of phenolic compounds in the leaves of different Passiflora species [39].

Extracts from the leaves of Passiflora alata and P. edulis exhibit strong in vitro antioxidant activity, and P. alata has higher total antioxidant activity than P. edulis [43]. Crude extracts from P. alata and P. incarnata leaves exhibit strong inhibitory activity against human acute lymphoblastic leukemia cells (CCRF-CEM), while P. caerulea shows weaker inhibitory activity [34]. Although P. caerulea and P. incarnata extracts share similar properties, differences in extract content may account for their distinct pharmacological effects; P. alata extracts may also serve as adjunctive therapeutic agents for cancer patients. The leaves and stems of Passiflora plants are traditional medicinal plants in many countries, exhibiting anti-inflammatory, anti-diarrheal, and antispasmodic activities [41], sedative and anxiolytic effects [45], and antioxidant and antitumor activities [34, 40, 42].

4.1.2 Study of phenolic compounds in fruits

Passionflower fruit pulp contains abundant phenolic compounds. Direct consumption of P. subpeltata fruit pulp provides natural secondary metabolites, including protocatechuic acid, ferulic acid, vanillic acid, epicatechin, p-coumaric acid, cinnamic acid, santol, and quercetin-3-glucoside, among 15 polyphenolic compounds [33]. However, their composition and content are influenced by variety [20], maturity [3], and cultivation practices [22]. Organically cultivated passion fruit had higher total polyphenolic compound content and total antioxidant activity than conventionally cultivated passion fruit [22]. In P. cincinnata fruits, the concentrations of gallic acid, coumaric acid, ferulic acid, and caffeic acid increased gradually with increasing maturity, while the content of isoquercitrin decreased with increasing maturity, while rutin content increases with increasing maturity [3]. Preliminary identification of polyphenolic compounds in wild passion fruit P. foetida fruits yielded 75 components, including 39 free phenolic compounds, 14 insoluble glycoside phenols, and 22 insoluble ester phenols [28].

Flavonoids are important phenolic compounds in passion fruit pulp, with the main components being isorhamnetin, rhamnetin, morin, and isomorin, though these may vary depending on the variety. The most abundant flavonoid in P. setacea fruit pulp is hesperetin-7-O-rutinoside [20], P. caerulea (Orange) fruit pulp is rich in lycopene, and P. edulis (Yellow) fruit pulp contains relatively high levels of quercetin [17], P. edulis Sims (purple) fruits have significantly higher levels of flavonoids, anthocyanins, and flavanols than yellow fruits, while P. edulis Sims (yellow) has significantly higher levels of flavonoids and their carbon-based derivatives than purple fruits [10]. The biosynthetic pathways of phenylpropanoids and flavonoids in the fruit pulp and their potential metabolic products are important factors influencing the nutritional components, color, and antioxidant activity of passion fruit (Figure 5).

Passiflora fruit peel can serve as an important source of antioxidant substances, with its antioxidant active components primarily consisting of flavonoids, chalcones, and phenolic acids [44]. The phenolic composition and content vary among different Passiflora fruit peel varieties. The antioxidant capacity and phenolic content of P. mollissima and P. edulis have higher antioxidant capacity and phenolic content than P. ligularis and P. edulisflavicarpa [44]. P. edulis (Purple) peel contains higher anthocyanin content, while P. caerulea (Orange) peel is rich in β-carotene and phenolic compounds [17]. Therefore, passion fruit peel can be processed further and added to food formulations to enrich food nutrition, not only benefiting human health but also reducing the environmental impact of residues, thereby generating higher economic benefits and promoting positive effects on both the environment and the economy.

Comparing data from the U.S. Department of Agriculture (USDA) database, the naringin content in fresh passion fruit juice is similar to that in fresh lemon juice, higher than in fresh orange juice, and lower than in orange juice [20]. Naringin has anti-inflammatory and anti-cancer properties, and studies have reported that passion fruit juice, after pasteurization, exhibits stable physicochemical properties, with no significant changes in color parameters, phenolic compounds, flavonoids, carotenoids, and antioxidant capacity [15,45]. Therefore, passion fruit juice is a highly important functional food that warrants further development and research.

4.2 Other bioactive compounds

The fruits of Passiflora plants contain various bioactive compounds, such as polysaccharides, carotenoids, terpenoids, biogenic amines, and alkaloids. Plant polysaccharides have immune-modulating, antibacterial, radioprotective, hypoglycemic, and gut microbiota-regulating effects. Through hot water extraction of the sugar components from Passiflora fruits, it was found that the main component of polysaccharides is galacturonic acid, accounting for approximately 44% (Figure 6). Additionally, it was confirmed that passionflower fruits contain neutral sugars such as arabinose, glucose, rhamnose, mannose, and fucose, with trace amounts of xylose and ribose detected [46].

P.edulis (Yellow) fruit pulp contains high levels of cryptoxanthin, α-carotene, β-carotene, vitamin A, quercetin, and kaempferol [17]. Orange passion fruit pulp has high levels of lycopene, lutein, zeaxanthin, total carotenoids, and some phenolic compounds are relatively high. Australia has conducted a relatively comprehensive study on carotenoids in passion fruit, identifying β-cryptoxanthin, α-carotene, β-carotene, zeaxanthin, violaxanthin, citroxanthin, γ-carotene, α-cryptoxanthin, β-citraurin, antheraxanthin, neoxanthin, phytoene, and phytofluene. Additionally, using 1H and 13C nuclear magnetic resonance (NMR) and fast atom bombardment mass spectrometry (FABMS) techniques, the following steroidal triterpenoids were identified in Passiflora plants: Passiflorine, Cyclopassiflosides I–VI, and Cyclopassifloic acids A–D. In addition to triterpenoids, another compound belonging to the indole alkaloid family was isolated and identified from Passiflora fruit, namely Harman, Harmine, Harmaline, and Harmalol [47].

In plants, polyamines participate in cellular processes such as cell division, root formation, embryo development, organogenesis, flower differentiation, aging, fruit development, and maturation. They also play a role in controlling and regulating plants' tolerance to abiotic stress [38]. Biogenic amines such as histamine, tyramine, serotonin, and putrescine play important roles in regulating neural or vascular activity. In food, the presence of amines can also serve as an indicator of product quality or hygiene conditions. However, excessive consumption of amines may have adverse health effects, such as nausea and headaches [19,48]. Spermine, spermine, guanidine, putrescine, and tryptophan are present in all four species: P. alata, P. edulis, P. nitida, and P. setacea [38,48]. During the entire developmental process of the fruit, the levels of spermidine, putrescine, and guanidine in P. setacea decrease, while the level of spermine remains unchanged; P. alata has the highest polyamine content among the four species; and in P. setacea and P. nitida, putrescine content is relatively high; in P. setacea, guanidine content is the highest; indoleamine and tyramine are present at relatively low levels in all four varieties [38].

5 Application Research on Passiflora Plants

Passiflora plants are valuable in their entirety and have a wide range of applications. First, in terms of ornamental value, they are highly valued for their unique flower shapes and vibrant colors, and can be developed into bonsai products using techniques such as dwarfing and potting, for use in landscape design. Currently, as the global market for passion fruit concentrate juice continues to expand, passion fruit plants, which can adsorb and mitigate the harmful effects of heavy metals and other toxic substances in soil on plants, are being utilized by many countries to process waste from juice production for petroleum processing [11], wastewater treatment, and environmental restoration.

For example, the flavonoids such as quercetin in passionflower plants can form complexes with metals, playing a beneficial role in chelation for plants exposed to industrial toxins including fluoride [9]; additionally, the soluble dietary fiber in passionflower peel exhibits adsorption effects on heavy metals such as Cu²⁺ and Cd²⁺ [49]. Furthermore, passionflower plants have found extensive applications in food processing. Pb²⁺, and Cd²⁺ [49].

Secondly, Passiflora plants have also found extensive applications in food processing. Currently, in addition to common products such as juice, wine, dried fruit, and jam, the pectin, natural pigments, and flavor compounds in passion fruit peel can be used as food additives in yogurt, bread, cakes, and puffed foods. Due to the high content of dietary fiber and polysaccharides in passion fruit peel powder, many countries such as Brazil use passion fruit powder as a food additive to replace wheat flour in bread and other foods. These products are used to assist in the treatment of diabetes, as they can lower blood sugar, triglycerides, cholesterol, and insulin levels, while also increasing satiety and improving digestive system function. They are also an excellent companion for weight loss and body shaping.

Passion fruit flesh contains a high amount of antioxidant active compounds and is classified as a high-acid fruit. Under pasteurization processing methods, its nutritional components can be well preserved. Therefore, many European countries often use passion fruit flesh or powder as a common additive in juice beverages, not only reducing the addition of acidifiers but also providing the human body with minerals and amino acids at dietary nutrient levels, and also help maintain normal metabolic functions in the human body. Passion fruit seeds have a high total dietary fiber content [17], and the two types of fiber they contain, PFSP and PFA, exhibit excellent antioxidant, antibacterial properties, and processing performance [50], making them widely applicable for oil extraction or as raw materials in manufacturing. Passionflower seeds are an important source of essential fatty acids for the human body. Due to their high linoleic acid content, they are considered a high-quality edible oil, capable of lowering cholesterol and blood lipid levels in the human body, and can be used as a therapeutic agent for atherosclerosis; they can also be used as raw materials for margarine, essential oils, and beauty oils, and are being developed for use in the food and cosmetics industries [51-52].

Finally, Passiflora plants have extensive applications in clinical medicine. In addition to its seeds being used for medicinal purposes, the roots, stems, leaves, and fruits of Passiflora all possess significant medicinal value, as they are rich in various bioactive compounds such as phenolic compounds, flavonoids, terpenoids, alkaloids, dietary fiber, glycosides, peptides, and proteins. Passiflora plants are medicinal plants with antibacterial, anti-inflammatory, sedative, analgesic, anthelmintic, and anxiolytic effects, and can be used as drugs for the treatment or adjunctive therapy of insomnia, hypertension, asthma, pneumonia, dysmenorrhea, epilepsy, and gastric cancer [1,9,53-54].

Passiflora plants have been included in the British Herbal Pharmacopoeia (1983), the American Homeopathic Pharmacopoeia (1981), the Indian Homeopathic Pharmacopoeia (1974), the Swiss Pharmacopoeia (1987), the German Pharmacopoeia (1997), the French Pharmacopoeia (1965), and the Brazilian Pharmacopoeia (1959) [1,9], among numerous national pharmacopoeias or official works on medicinal plants. This indicates that Passiflora species have widespread clinical applications. Due to their role in female estrogen replacement therapy, Passiflora plants were recognized by the U.S. Food and Drug Administration (FDA) in the 1994 Dietary Supplement Health and Education Act (DSHEA) as an exempt herb, and they are also used worldwide as over-the-counter (OTC) formulations. Additionally, Passiflora plants are recognized by the U.S. government and the European Commission as dietary supplements and flavorings.

6 Outlook

Passiflora plants are nutritionally rich, containing a variety of bioactive compounds throughout their entire plant, making them a highly valuable plant for further development. Future research on the nutrition and applications of Passiflora should focus on the following areas (Figure 7): 1) Studies on improving the nutritional quality of fresh Passiflora fruits and the bioactive components that can be purified and utilized through cultivation methods such as nutrient management, tailored to different application needs (e.g., pharmaceutical, edible, or food processing), and establish corresponding cultivation technical guidelines and fruit nutritional quality grading standards; 2) Conduct in-depth research on the pharmacological activities of Passiflora plants, which currently focus on the inhibitory effects of bioactive compounds such as phenolic acids and flavonoids on the central nervous system, and gradually identify Passiflora plant varieties with potential for development in clinical medicine; and conduct in-depth studies on the antioxidant activity and mechanisms of action of their bioactive compounds; 3) Given that research on the uses and deep processing of Passiflora plants in China is still in its infancy, there is an urgent need to accelerate the development of Passiflora by-products, the extraction of natural products, and the research and development of related products, as well as the in-depth exploration of natural products; It is recommended to expedite the development of the entire industrial chain of Passiflora plants in China, with a focus on the development of deep-processed products and their application in clinical medicine.

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