What Is Passion Flower and Its Extract?

Passiflora L., also known as passion fruit, passion fruit, Brazilian fruit, is a herbaceous vine plant of the genus Passiflora in the Passifloraceae family, native to South America, and is now widely planted in tropical and subtropical regions, with Brazil, Ecuador, Peru, Thailand, Malaysia and Indonesia as the main production areas [1]. It was introduced to Qinzhou, Guangxi, China in 1988 and has been cultivated in Guangdong, Hainan, Fujian, Yunnan, Taiwan, Jiangxi, Sichuan and Guizhou since then [2]. Passion fruit can emit banana, pineapple, lemon and other more than 10 kinds of fruits of the rich flavor, sweet and sour, and rich in a large number of total sugar, protein and other nutrients, as well as the human body needs seven kinds of amino acids and calcium, iron, potassium and other kinds of minerals, there is a "fruit juice king,"the beauty of the name.

The whole body of passion flower is a treasure, roots, stems and leaves can be used as medicine, with anti-inflammatory and pain relief, blood circulation and strengthening the body, lowering fat and blood pressure and other therapeutic effects. The fruit can be made into juice, fruit wine, dried fruit and other products; peel can be extracted pectin, used as food processing stabilizer and thickener; seed oil content of 28.2% [3], the oil content of 28.2%. 2% [3], the oil quality is comparable to sunflower oil, can be used as edible oil.

Passion flower is planted in the same year, harvested in the same year, can be harvested continuously for 2~3 years, with low investment, fast income, wide adaptability, and has become a "new star"in the fruit market in recent years. This paper reviews the research progress of passion flower at home and abroad in recent years from the aspects of germplasm resources and breeding, cultivation status, nutritional components, functional active ingredients and their effects, and processing and utilization, and proposes directions for in-depth research on variety selection and breeding, field cultivation technology, functional active components and their mechanisms of action, and post-harvest preservation technology, with a view to providing references to the in-depth development and utilization of passion flower. The purpose is to provide reference for the deep development and utilization of passion flower.

1 Germplasm resources and breeding

Passiflora is recognized as the most abundant genus in the Passifloraceae family, with about 520 species, mainly in the Americas, Colombia and Brazil [5]. There are 19 species in China, and six species are currently edible as fruits: the purple-fruited species (P. edulis Sims), the yellow-fruited species (P. edulis Sim. F, flavicar pa Deg.), the camphor-leafed passion flower (P. laurifolia L.), the large-fruited passion flower (P. quadrangularis L.), and the sweet-fruited species (P. ligustralis L.). P. quadrangularis L., P. ligularis Juss and P. mollis-sima [6]. The majority of Passiflora plants are diploids, typical hermaphrodites, but the pistils and stamens do not develop at the same time, resulting in a low self-pollination rate. This dioecy ensures that the plants are cross-pollinated, which contributes to their genetic diversity and adaptability to the environment [7].

The genetic diversity of passion flower is very important for the breeding of passion flower, but more research is needed to promote the development of this diversity as a natural resource. In recent years, only a few papers have reported the application of SSR, SRAP, ITS sequence analysis and gene cloning techniques to genetic diversity and breeding studies. At present, the study and conservation of germplasm resources of Passiflora is still in the initial stage. It has been reported that the most prominent obstacle in the current passion flower breeding process is the low representation of passion flower in germplasm banks, the number of genetic resources available for breeding is lower than the total genetic resources registered in active germplasm banks (AGBs), and most of the materials lack biological and agronomic information due to the lack of technological and financial support for the maintenance and identification of AGB genetic resources [8].

Yield and quality are the two most important indicators in passion flower breeding. Leng Yanfeng [9] found that there is a certain correlation between yield and quality traits, but the correlation is not significant, and the improvement of these two traits can be synchronized in the breeding process. In recent years, there have been few reports of new varieties of passionfruit cultivated at home and abroad. "Pingtang No. 1"(purple fruit species) is a cold-resistant species from the local wild passion flower by natural domestication and artificial selection of Guizhou Mountain Resource Research Institute, with a semi-lethal low temperature of -3.59℃, and it can survive at the lowest temperature of -3.5℃ and the lowest temperature of -4.5℃. The half-lethal low temperature is -3.59 ℃, and it can overwinter smoothly in the karst mountainous areas of Guizhou where the lowest temperature is below 0 ℃, and at the same time, its fruit quality and nutritional value are higher [10], which is a new variety worth promoting.

2 Cultivation status

2 . 2.1 Distribution

According to Wang Yu[11] , the cultivation history of passion flower in China can be traced back to 1901, when purple-fruited passion flower was introduced from Japan to Taiwan. In 1956, Xiamen, Fujian introduced passion flower from Indonesia. At present, there are three major types of passion flower cultivars in China, namely, purple-fruited passion flower, yellow-fruited passion flower and its hybrids [12]. Although passion flower was introduced earlier in China, large-scale commercial cultivation has only begun to develop in recent years.

As of 2018, the national planting area of passion flower reached 9,400hm2 , of which Guangxi has the largest planting area of 4,667hm2 , mainly distributed in Nanning, Liuzhou, Beiliu, Qinzhou, Guilin and Guigang, etc.; Chongqing 733.3hm2 , mainly distributed in Chongqing and Chongqing, etc., and Chongqing 733.3hm2 , mainly distributed in Chongqing and Chongqing. Chongqing 733.3hm2 , mainly distributed in Dianjiang; Yunnan 3,333hm2 , mainly distributed in Dehong and Xishuangbanna; Fujian 333hm2 , distributed in Zhangzhou, Longyan, etc.; Guizhou 333hm2 , mainly distributed in Songtao, from the river, Yanhe, Jinsha, Huishui, Pu'an, and Zhenning, etc., and the planting varieties are mainly TANON 1, Zixiang 1, and JINWANG 2 [9]. Hainan belongs to the tropical region, and the climatic conditions are very suitable for the growth of passion flower. In 2018, the planting area of passion flower in Hainan Province was about 333hm2 , mainly concentrated in Dongfang City (about 100hm2 ) and Wuzhishan City (about 86.7hm2 ), while the others were mainly in Dongfang City (about 100hm2 ). 7hm2 ), while other cities and counties are still in sporadic and scattered planting [13]. At the beginning of 2019, with the expanding market demand for passion flower, the planting area of passion flower in the country has been greatly increased [4].

2 . 2.2 Characteristics of main plant varieties

Passion flower likes light, suitable for cultivation in tropical and southern subtropical areas, where the average annual temperature is above 18 ℃ and the average temperature of the coldest month is above 8 ℃. At present, the main cultivars of passion flower are "Tainong No. 1", "Zixiang No. 1", "Golden Passion Flower"and "Full Star". "The main cultivars of passion flower are The growth characteristics of these varieties are different. TIANNONG No. 1"is a hybrid between yellow and purple fruit varieties, which has the advantages of self-seeding affinity, abundant and stable yields, etc. Compared with "Golden Passionfruit", "Zixiang No. 1" has the advantages of self-seeding affinity, abundant and stable yields.

Compared with "Golden Passion Flower"and "Fruit of the Sky", "TANO-1"is more cold-resistant, and their cold-resistant sizes are "TANO-1"> "Fruit of the Sky", "Fruit of the Sky"> "Fruit of the Sky"and "Fruit of the Sky". The cold resistance of the three plants was as follows: "TANO-1"> "TENA-1"> "TENA-1"> "TENA-1"> "TENA-1"> "TENA-1"> "TENA-1"> "TENA-1"> "TENA-1"[14]. "Golden passion flower"is less cold-tolerant, and is susceptible to frost damage in winter, and the plant will be severely frozen or even die when it is below 0 ℃ [15]. However, golden passion flower is more resistant to stem rot than purple fruit passion flower, so it is often used as rootstock for grafting seedlings. The "Star of Heaven"is sensitive to low temperature, susceptible to stem rot and green spot virus, and difficult to manage, so it should be carefully selected for planting. "Zixiang No. 1"is a new variety of fresh food developed from "Tainong No. 1", with a ripening period from late June to February of the following year. Dong Wanpeng et al.[16] pointed out that the semi-lethal low temperature of "Zixiang 1"was -2.5 ℃, and the adaptability and resistance of "Zixiang 1"was -2.5 ℃. 5 ℃, adaptability and cold resistance than the "sky star"and "golden passion flower"are stronger.

Zhang Xijuan et al.[17] investigated the fruit characters of four varieties, namely, "Mantianxing", "Tainong No. 1", "Zixiang No. 1"and "Golden Passionflower", and found that the fruit characters of these four varieties were better than those of the other varieties. Evaluation of the fruit traits of the four varieties found that the flesh color of the four varieties was orange-yellow, and the fruit shape index was close to 1, except for the "golden passion flower", which was nearly round, and the fruit shape of the other varieties was elliptical.

The average single-fruit mass of the "sky star"is the largest, 134.82 g, and its single-fruit mass, longitudinal and transverse diameter of the fruit, peel thickness are significantly higher than the other three varieties, suitable for integrated processing and utilization; "purple fragrance 1"single-fruit mass, longitudinal and transverse diameter is the smallest, and the soluble solids content is the lowest (the lowest), the lowest (the lowest), and the lowest (the lowest). Zixiang 1"has the smallest single fruit mass, longitudinal and transverse diameter, and the lowest soluble solids content (12.11%). The "Zixiang 1"has the smallest single fruit mass, longitudinal and transverse diameter, and the lowest soluble solids content (12.11%) but sweet flavor. The fruit of "Golden Passionfruit"is sweet and sour, and has the highest soluble solids content (17.43%), while the fruit of "Golden Passionfruit"has the lowest soluble solids content (12.11%). 43%), "Golden Passionfruit"and "Purple Fragrance No. 1"have better taste and flavor, and both are suitable for fresh eating. The "Tainong No. 1"performs well in all indexes and can be eaten freshly or utilized in processing.

2 . 2.3 Cultivation and management techniques

2.3.1 Breeding technology

Currently, there are three main breeding techniques for passion flower seedlings: seed propagation, cuttings propagation and grafting propagation. Seedling propagation is the direct sowing of passion flower seeds, which produces seedlings with well-developed root systems that do not carry viruses, but they are gradually being eliminated because of the problems of high variability, long growth period, uneven fruit size, low yield and poor quality; cuttings propagation is the asexual reproduction of plants using roots, stems and other nutrient organs, which maintains the parent's traits, but with undeveloped root systems, weak resistance to diseases, and susceptibility to infection by germs and viruses; grafting propagation is the asexual propagation of plants using roots, stems and other nutrient organs. Grafting propagation is to select the scion from the good mother plant as the scion and graft it onto the rootstock for propagation, which has the advantages of developed root system and resistance to stem rot, but it requires strict screening of the rootstock and scion.

Tissue culture technology is another asexual propagation technology, its advantage is that the growth of seedlings in tissue culture is neat and consistent, easy to manage, and the application of detoxification technology can better make the seedlings grow healthily, but it is seldom applied in passion flower seedling, which may be related to the lack of maturity of the tissue culture technology of passion flower, the long breeding cycle, and the large variation among varieties. Therefore, it is necessary to choose suitable methods for seedling breeding according to local conditions to ensure the healthy growth of seedlings.

2.3.2 Field planting management technology

2.3.2.1 Planting mode

Passiflora belongs to trailing plants, in order to ensure sufficient photosynthesis in the late stage of growth and enough growing space, it is necessary to build a trellis for its growth. There are three common types of trellis: flat trellis, fence and drape. The flat trellis type is the most commonly used type at present, which is more resistant to wind and collapse, but also has the shortcomings of high cost of erection, and pruning in the later stage may easily lead to poor ventilation and air permeability, and the problem of pests and diseases. Hedge type is also a widely used model for planting passion flower.

This planting mode is more flexible and can be planted on flat land, mountainous land and hilly areas, with good ventilation and lighting, which is convenient for agricultural operation, but it is laborious in pruning and is not resistant to typhoon. The drape planting model is an innovative planting model based on the canopy model, with the advantages of good pruning, ventilation and air permeability, so more and more farmers are willing to try this model. In order to enable plants to be put on the shelves earlier, branching, flowering and fruiting earlier, so that the products can be marketed earlier and the yield and economic benefits can be increased, Zou Jing et al [18] studied a new planting model - the short trellis dense planting, which has a trellis of only 1.3m high and a planting density of 120m. The trellis is only 1.3m high and the planting density is 120 plants/667m2 .

2.3.2.2 Water and Fertilizer Management

Passiflora root system is shallow, mainly distributed in the soil layer of 2~20cm depth, aerobic, moisture-loving, afraid of flooding, cultivation should be done before the drainage measures, open a good drainage ditch, to prevent water accumulation in the garden and the base of the plant. At the same time, the new shoots sprouting and differentiation period, flower bud differentiation and fruit expansion period is the key period of water demand, pay attention to the water supply in place.

Passiflora has a special growth characteristic, which is a fruit with both nutritive and reproductive growth. Due to its large growth, it has a high demand for water and fertilizer. In recent years, there have been few reports on the fertilizer requirements of passionfruit in various periods of growth in China and abroad, and most of the fruit growers grow passionfruit based on their experience.

The amount of nitrogen fertilizer applied is 5.6~8.0kg/667m2 , the amount of phosphorus fertilizer applied is 6.0~7.0kg/667m2 , the amount of potassium fertilizer applied is 12.0~15.0kg/667m2 . 6.0~7.8kg/667m2 of phosphorus fertilizer and 12.0~15.6kg/667m2 of potassium fertilizer, the yield increase of passion flower was greatest. This shows that passion flower has a high demand for phosphorus and potassium fertilizers. However, the quality of passion flower was not analyzed under this fertilization condition, so whether it is the optimal fertilization rate or not needs to be further researched.

2.3.2.3 Disease and pest control

The main diseases of passion flower include basal rot, virus disease, blight, leaf spot, and seedling blight, while insect pests include thrips, aphids, fruit flies, ants, and other subterranean pests, etc. The main diseases of passion flower include basal rot, virus disease, blight, leaf spot, and seedling blight. Stem rot and virus diseases are common diseases of passion flower. Fusarium solani is the causal agent of stem rot [13], the infected plants start to rot from the rhizome, initially appearing as watery spots, then turning brown and gradually spreading upwards, the disease can reach up to 0.5 m of the plant. The disease can reach up to 0.5 m of the plant. In general, the diseased stems and leaves wither and die. The disease has a high incidence in May-August and can be prevented by watering every 20d with diclosan or pca + potassium permanganate. In the early stages of the disease, the soil at the base of the stems should be peeled back, the diseased parts scraped off, and the roots should be irrigated with methomyl, copper complex, chlorobromoisocyanuric acid, and oxadiazepam-fumonisin, and the diseased parts should be coated. If stem rot has already occurred, scrape off the rotted parts and then apply Rimox + copper thiessence to the diseased parts and the surrounding area. The control of Phytophthora infestans requires attention to the ventilation and drainage of the planting environment, and the diseased plants should be burned as soon as they are found.

At present, 26 kinds of plant viruses infecting passion flower have been reported in China and abroad, but most of the diseases caused by these viruses only occur sporadically in a few countries [20], among which, lignifying virus of the genus Potato Y virus is a common problem seriously jeopardizing the cultivation of passion flower worldwide, and lignifying virus and cucumber mosaic virus are more common in Hainan [14]. In addition to prevention and control of the source of infection, no effective methods have been found. Xie Wei-han [21] suggested that tazaril has a good therapeutic effect on passionflower virus disease, with low toxicity, and is a completely non-polluting, zero pesticide residue anti-pest agent, but this is only a summary of the experience of local farmers, and no research has been carried out to verify this. For insect pests, a combination of physical and chemical control is usually adopted. Physical control is mainly done by hanging yellow boards, green boards, insecticidal lamps, and the use of sexual attractants. Studies have reported that yellow boards can be used for aphids and fruit flies [22], while green boards are more effective for thrips [23].

3 Nutritional composition

The color of passion fruit juice is bright, known as the "king of juice"and "king of vitamin C", which is loved by people. Guo Yanfeng et al.[24] studied the nutrient composition of "golden passion flower", "Tainong No. 1", "purple fruit No. 1 (i.e., purple fragrance No. 1)"respectively, and found that: passion fruit juice contains 8.6~9.7 g of protein and 8.6~9.7 g of vitamin C. The juice of passion fruit is also a good source of nutrients. 8.6~9.7 g/kg, total acid 36.50~42.43 g/kg, total sugar 5.85~7.53 g/kg, vitamin C 0.12~0.13 g/kg, minerals 3.79~4.81 g/kg, total amino acids 5.29~8.06 g/kg, and superoxide dismutase 184.23~238.67 U/mL; among the mineral elements, potassium was the highest. The content of potassium is the highest among all kinds of mineral elements, which is 3.52~4.48 g/kg.

There are some differences in the nutritional composition of different varieties of fruit juice, among which the protein, mineral and total amino acid contents of golden fruit juice are significantly higher than those of the other two varieties. The content of reducing sugar of "Star"juice is the highest, 13.60%. 60%. Reducing sugars can be directly absorbed by the body and help to raise blood glucose, therefore, Mantianxing is particularly suitable for correction of hypoglycemia in patients with hypoglycemia [25]. He Jie et al.[26] analyzed the amino acid composition of six kinds of fruits, such as "purple fruit passion fruit", banana, fruit and others, and found that the total amino acid content of "purple fruit passion fruit"was the highest, and the content of sweet amino acid, lysine and other amino acids was higher than that of other five kinds of fruits. It was found that the total amino acid content of "purple passion fruit"was the highest, and the contents of sweet amino acids, lysine and other amino acids were higher than those of the other five fruits. The results showed that passionfruit is very nutritious.

The fruit juice rate of passion fruit is about 40%, and about 50% is the rind. The passion fruit peel contains a large amount of crude fiber (3.0%) and pectin (1.0%). 0%) and pectin (1.41%). It also contains protein, polysaccharide carbohydrates, polyphenolic antioxidant components and a little fat, which have high nutritional and health values [27]. At present, the processing of passion fruit mainly focuses on the utilization of fruit juice, and the peel is mostly used as feed or waste, resulting in the nutritional value of the peel not being fully developed and applied.

4 Functional active ingredients and their efficacy

Passion flower is not only rich in nutrients, but also contains a variety of functionally active ingredients, which have a variety of physiological functions that are beneficial to the human body. With the rapid development of the passion flower market, passion flower, especially its by-products such as rind, seeds, stems and leaves, has been studied in various aspects. It has been found that the common functional active ingredients in passion flower extracts include flavonoids, flavonoid glycosides, alkaloids and other small molecular compounds such as cyanogenic compounds and phenols, as well as monoterpenes, triterpenes and saponins [28]. In many European countries, passionflower is widely used as a common folk medicine in the development of anxiolytic and sedative drugs [29].

4 . 4.1 Polyphenolic compounds

The polyphenolic compounds in passion flower mainly include phenolic acids and flavonoids. Polyphenolic compounds are distributed in the juice, peel and leaves of passion flower, of which the content of polyphenols in passion flower peel is 15.096 mg/g [30]. The polyphenol content of passion fruit peel was 15.096 mg/g[30] , and the total phenol content of the leaf was 2.20 mg/g[31] . The polyphenol content of passion fruit peel was 15 .096 mg/g [30], and the total phenol content of leaf was 2.20 mg/g [31]. The flavonoids were found in different parts of the fruit, including 37.55mg/g in the juice, 37.5mg/g in the juice, and 2.20mg/g in the leaf [31]. The content of flavonoids in different parts of fruits was 37.55 mg/g in juice, 6.89 mg/g in cuticle, and 6.5 mg/g in pericarp [32]. The content of flavonoids in different parts of the fruit was 37.55mg/g in the juice, 6.89mg/g in the cuticle of the pericarp, 4.82mg/g in the spongy layer of the pericarp and 70.04mg/g in the seeds. 04 mg/g in the seed, and 102.37 mg/g in the oil meal after seed extraction [32].  37 mg/g [32].

Gomes et al. [33] and García-Ruiz et al. [34] isolated and identified flavonoids from passion flower fruits with different levels of composition. Gomes et al. identified lignans and derivatives of apigenin as the main flavonoids in passion flower, whereas García-Ruiz et al. identified 18 flavonoids, mainly flavonoid-triol monomers and proanthocyanidins. Thus, the flavonoids in Passiflora fruits are not only rich in content, but also diverse, with significant differences in content among different parts.

Peng Yaling [35] also found flavonoids in the stems and leaves of Passiflora, mainly four kinds of flavonoids such as lignans, isoorientin, isomonocerotin, and ouabain. These four flavonoids have different degrees of inhibitory effect on α-glucosidase, and the strongest inhibitory effect is lignans. At the same time, Peng Yaling also pointed out that luteolin and isoorientin can down-regulate the mRNA and protein expression of SGLT1 and GLUT2, thus delaying the absorption of glucose, which undoubtedly provides a basis for diabetic patients to reduce the blood glucose content in the body. It has also been reported that the flavonoid compounds in the stems and leaves of Passiflora purpurea have protective activities on the nervous system [36]. Araujo et al.[37] , based on the previous study that flavonoids extracted from passion flower have the potential to inhibit the production of nitric oxide and tumor necrosis factor a as well as its antioxidant potential, analyzed the antimycobacterial activity and anti-inflammatory effect of flavonoids, and suggested that flavonoids in passion flower have the potential to treat tuberculosis.

4 . 4.2 Polysaccharides

The pericarp of passion flower is rich in polysaccharides, mainly composed of six monosaccharides, including glucose, xylose, galacturonic acid, rhamnose, galactose, and arabinose [38], of which polygalacturonic acid is the main component of polysaccharides in subcritical aqueous extracts [39].

Microwave-assisted extraction [40] and ultrasonic-assisted extraction [41] are two new methods for extracting the polysaccharides from the pericarp in recent years, and these two methods are characterized by short extraction time and high efficiency compared with the traditional acid extraction method, and the polysaccharides of passion fruit pericarp were obtained at the rates of 14.12%, 10.6% and 10.6%, respectively.  The extraction rate of polysaccharides from passion fruit peel was 14.12% and 10.36%, respectively. The extraction rate of passion fruit peel polysaccharides was 14.12% and 10.36% respectively. In recent years, the role of passion flower pericarp polysaccharides has gradually become the focus of academic research. The results of Zheng Mingluan [42] showed that the crude polysaccharides of passionflower have good inhibitory effects on bacteria and yeasts. According to a recent study, passion flower pericarp polysaccharides not only have antioxidant, immunomodulatory, and lipid-lowering effects, but also relieve traveler's fatigue, and can be used in eco-tourism through the development of health care beverages and other products [41].

4 . 4.3 Carotenoids

In addition to polyphenolic compounds and polysaccharides, the main bioactive components of passion flower are carotenoids. The β-carotene content of passion flower juice was (1,362.07±136.221).  The β-carotene content in passion fruit juice was (1,362.07±136.221) μg/100 g FW, which was second only to West Indian cherry and papaya; β-carotene was also detected in seeds, with a content of (57.93±5.80) μg/100 g FW. 93±5.80) μg/100 g FW [43]. Wang QF et al. [44] compared the contents of lutein and β-carotene in the fruits of purple-fruited passionflower, yellow-fruited passionflower and double-flowered passionflower and found that double-flowered passionflower had the highest content, followed by yellow-fruited passionflower, and purple-fruited passionflower had the lowest content. The content of carotenoids in passion flower was not only related to the variety, but also affected by the cultivation method. Pertuzatti et al.[45] analyzed the carotenoid content of "golden passion flower"fruits under conventional and organic cultivation, and found that the carotenoid content of conventional cultivation was nearly twice as much as that of organic cultivation.

4 . 4.4 Other

In addition, passionflower contains functional active ingredients such as alkaloids, triterpenoids [28], and cedrol [46], but the mechanism of these substances is not clear, and their biological activities need to be further investigated.

5 Processing and utilization

Passiflora fruits can be processed and utilized from inside to outside, from seeds, juice to peel. At present, the processing and utilization of passion flower is mostly done with purple fruits, while yellow fruits are mainly eaten fresh. Primary processed products such as juice drinks, wine, vinegar and dried fruit are also becoming more common.

5.1 Seeds 5.1 Seeds

A passion flower fruit contains about 160 seeds, accounting for about 10% of the total fruit weight, and the oil content of the seeds can reach 28.2%. The oil content of the seeds can reach 28.2%, and the oil content of the seed kernel is more than 60%. The unsaturated fatty acid content of the seed oil is over 80%, which not only helps the human body to remove free radicals and slow down the aging process, but also promotes the absorption of many kinds of vitamins, which is beneficial to health. At the present stage, the development and utilization of passion flower seeds mainly focuses on the extraction and processing of seed oil. The most primitive methods for extracting oil from passion flower seeds are the pressing method and the raw milling method, both of which do not have a high oil yield. With the advancement of science and technology, people gradually developed the ultra-critical interface extraction method and microwave extraction method, which further improved the oil yield.

Compared with the traditional methods, these two methods have the advantages of shorter extraction time, higher solvent recovery and higher unsaturated fatty acid content, and the resulting seed oil is bright in color and elegant in taste. Ma Jinkui et al.[3] and Wu Yuchun et al.[47] used supercritical CO2 extraction and microwave-hexane extraction to extract passion flower seed oil successively, and the oil yield was not the same. The oil yield obtained by microwave-hexane extraction was higher, 27.68%, and the extracted passionflower seed oil was not the same. In particular, the oil yield of the microwave-hexane extraction method was higher, at 27.68%, and the extracted passion flower seed oil was more antioxidant, with a scavenging rate of 80.43% of DPPH radicals. 43%. The research on the processing and utilization of passion flower seeds has made some progress, but the research is not deep enough and comprehensive, and the processed products are relatively single. Passiflora seeds are often discarded as by-products of processing, and only a small amount of them are processed into seed oil or feed, with a very low utilization rate.

5 . 5.2 Fruit Juice

Passiflora fruit juice is not only rich in nutrients, but also has a unique flavor and special taste, making it a high-quality raw material for food processing. However, passion fruit juice has a high acidity, pH 2.4 ~ 2.6 [48], and is not suitable for direct processing and consumption, but must be processed into a complex product with other additives with higher sugar content to have higher edibility. Currently, passion fruit juice is often processed into juice drinks, fruit wine, fruit vinegar, fruit tea and other products.

As the quality of life improves, people are demanding more and more fruit juices and beverages. Instead of using passionfruit to prepare single fruit juices, compound juice beverages are prepared by adding sweeter juices such as poppy seed[49] , satsumas[50] and dragon fruits[51] , which are moderately sweet and sour, and are more in line with people's tastes. Juice stabilization and sterilization are two important aspects in the production of passion fruit juice.

Zhu Xianghao [52] found that the stability of juice was poor when using a single stabilizer, but when xanthan gum and CMC were combined at a ratio of 4:1, the juice was stabilized better, with a centrifugal sedimentation rate of only 0.09%. The centrifugal sedimentation rate was only 0.09%. At the same time, the use of ultrahigh-pressure sterilization of passionfruit juice could effectively extend the supply period of the juice. The shelf life of the ultrahigh-pressure sterilized passion fruit juice can reach 97d at 4 ℃, which is 27d longer than that of the pasteurized passion fruit juice, and the quality and taste of the juice basically remain unchanged during the storage period, and the nutrients of the juice drink are better preserved.

Because of the high acid and low sugar characteristics of passion fruit, fermentation is difficult in the preparation of passion fruit wine, and how to reduce acidity is the key to research. It has been reported that calcium carbonate is more effective as an acid-reducing agent in the preparation of passionfruit wine, and the resulting wine can obtain a better sensory evaluation, with an alcoholic strength of 12% Vol after fermentation [53]. The brewing of passion fruit vinegar is a new research object in recent years, and it is still in the stage of research on the fermentation process. The preparation of passion fruit tea is usually combined with some Chinese herbs to make a tea beverage with health benefits. For example, when passion flower juice is used to make tea, it is combined with chrysanthemum, honeysuckle [54] and orange blossom [55], which not only has a good flavor and quality, but also has rich health effects, which is very popular among people.

5 . 5.3 Pericarp

The peel of passion fruit accounts for about 40%~50% of the fruit weight, but it is often discarded as an accessory product during the production process, which not only pollutes the environment but also wastes resources. As a result, some researchers have started to study the utilization of the peel. The passion fruit rind is rich in pectin and can be processed into preserved fruits that are not only tasty but also chewy. Zeng Fan [56] used the best process for the production of passion fruit preserves: cleaning, scooping pulp, boiling, separation, salting and acid cooking, pickling and drying, which resulted in a high yield of preserved fruits, not astringent and not bitter, moderately sweet, and delicate and non-fibrous in the mouth.

Du Lijuan et al [57] used ultrasonic sugar infiltration method to prepare passionfruit preserves on the basis of previous researchers, which not only shortened the curing time, but also effectively removed the bitter, astringent and other undesirable flavors of passionfruit peels by adding salt to the hot soup of the peels. Peel powder is the process of processing fresh fruit peels into a nutrient-rich powder that is easy to store and transport. It was reported that spray drying method was effective in preparing passion fruit peel powder with a collection rate of 34.7%. It was reported that the spray-drying method was effective in preparing passion fruit powder, with a collection rate of 34.7%, and the resulting powder was light red in color, aromatic in taste, creamy and dry, and with good solubility [58]. It has also been suggested that passion flower pericarp can be used to extract essential oil as a raw material for flavor, which can be applied in food and cosmetic industries [59].

5 . 4 Post-harvest preservation technology

Fruit harvesting and processing and utilization will face a freshness storage problem, passion flower belongs to the respiratory leap type fruit, in the third day of postharvest storage will appear in the peak respiratory period, fruit appearance, quality began to decline [60]. Zhang Zhaokun et al. [60] pointed out that passion fruit harvested at seven maturity is suitable for longer distance storage and transportation and marketing, while eight maturity is suitable for short distance marketing. Currently, the preservation techniques of passion flower in China and abroad mainly involve the treatment of hot water combined with CaCl2 solution[61] , film treatment[62] , 1-MCP treatment[63] , and the treatment of different packaging materials[64] . However, these preservation techniques have not been widely applied so far.

6 Summary and Prospects

Germplasm resources are the material basis of crop breeding, and the richness of crop germplasm resources and the depth of related research work will determine the advantages of crop breeding. Passiflora is rich in species, but the relatives between species are relatively close and the genetic base is narrow [65], and the varieties cultivated on a large scale commercially at present are extremely limited, and many resources have yet to be developed and utilized. Nowadays, many industrial projects and public utility projects are causing more and more serious damage to the agricultural environment, and many wild species are on the verge of extinction, so the collection and preservation of germplasm resources are becoming more and more urgent. At present, the breeding level of passion flower is still in the initial stage, and many excellent characteristics such as resistance to stress, disease and high yield will be the direction of future research.

Although the area under passion flower cultivation has expanded greatly in recent years, most of the growers lack management techniques for large-scale cultivation, resulting in low yields and low quality fruits that are not competitive in the market. In order to develop the passion flower industry in the long run, the planting link at the beginning of the industrial chain must first ensure the quality of seedlings, and at the same time establish a set of standardized and efficient planting and management technical procedures is also very necessary.

Tissue culture technology can produce a large number of seedlings in a relatively short time, which is of great significance to the development of the passion flower industry. However, the tissue culture technology of passion flower is still in the experimental stage, and cannot be applied to actual production due to the immaturity of the detoxification technology and the imperfect evaluation of the cultivation performance in the field. In the process of cultivation and management, many key technologies have not yet made breakthroughs, such as how to fertilize accurately and efficiently, and how to prevent and control key pests and diseases (e.g., stem rot and virus disease), etc., which have become bottlenecks for large-scale cultivation of passion flower, and we have not yet found good preventive and curative measures for them.

In terms of nutrients and pharmacological activities, although there is a large amount of literature proving that passionflower fruits, seeds, stems and leaves are rich in nutritional and medicinal values, the effectiveness of the extraction process of many active ingredients is still not obvious and needs to be further optimized. The mechanism of some functional active ingredients such as alkaloids, anthocyanosides, and betulinol is still unclear, and the structural characteristics of the extracts and their regulatory mechanisms in specific pathologies need to be further studied. At present, some progress has been made in the study of nutrients, active substances and physiological activities in some of the accessory products of passion flower processing, such as the skin and fruit residue, but the study of physiological activities is mostly based on the extracted composites, and it is not possible to determine which kind of substance is specific, what kind of physiological activity it has, and the mechanism of its action is not clear either. Further studies on the nutrients and bioactive components and their mechanisms of action are conducive to the development of passion flower products.

In recent years, most of the processed products of passion flower are primary processed products, and there is a lack of high value-added food and health products. As people's living standard is increasing, they are pursuing higher and higher quality of life, and the demand for research and development of high value-added products will become more and more urgent. In addition, there is an urgent need for research and promotion of convenient and quick preservation and storage techniques for passion fruit. How to delay the respiratory transition peak of passion flower, improve the freshness preservation technology of fresh fruits, and prolong the shelf life of fruits are especially important for the circulation and processing utilization of passion flower in the market.

To sum up, basic research and comprehensive utilization of passion flower has a long way to go. In recent years, the demand for passion flower juice in the international market has been growing at a rate of 15%~20% per year[5] , and it is also favored by consumers in the fresh food market, which makes the passion flower industry an industry with great potential for development and broad prospects. However, the planting and processing industry of passion flower in China started late, the production and operation are scattered, the planting management level is low, the planting management technology system is insufficient to integrate and promote the application of germplasm resources, the collection and development of germplasm resources is relatively lacking, and science and technology to support the development of the industry needs to be improved, and it should be strengthened in the breeding of varieties, field planting technology, disease and pest control and post-harvest preservation of freshness technology and so on.

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