A novel lignan compound with tyrosinase inhibitory activity in the peel of passion fruit
Passiflora edulis Sims is a herbaceous vine plant belonging to the Passifloraceae family, also known as passion fruit, egg fruit, Brazilian fruit, etc. In 2018, the planting area of passion fruit in China exceeded 60000 hectares, of which Guangxi had a cultivation area of nearly 33350 hectares and a yield of 300000 tons, accounting for 70% of the country’s total, with an output value of about 2 billion yuan. The skin of passion fruit accounts for about 50% to 55% of the weight of fresh fruit, but during the processing, the skin is often discarded, which not only causes serious pollution to the environment, but also results in a great waste of resources. Therefore, the study of the composition and activity of passion fruit peel can provide basic data for the resource utilization of passion fruit.

Studies have shown that the peel of passion fruit contains not only polysaccharides, flavonoids, and anthocyanins, but also alkaloids, terpenes, and other substances. Peng et al. isolated three anthocyanins from the skin of purple fruit passion fruit. Zhu et al. identified 5 anthocyanins in the skin of purple fruit passion fruit. He et al. reported 12 anthocyanins in the peel of Fujian’s “Purple Fragrant No.1” purple fruit passion fruit. From this, it can be seen that the research on the composition of passion fruit peel mainly focuses on anthocyanins, while there are relatively few reports on lignans. The aim of this study is to further explore the bioactive components of passion fruit peel, except for anthocyanins, and to screen their activity through tyrosinase activity assay kit and molecular docking, in order to increase the utilization value of passion fruit peel.

The yield of passion fruit in Guangxi increased from 68500 tons in 2015 to 312800 tons in 2019, and the planting area has grown at an average annual rate of 35.6% since 2015, reaching 28280 hectares in 2019. During the production of fruit juice, over 75% of waste from passion fruit is not fully utilized. How to recycle bioactive compounds from passion fruit peel for use in pharmaceuticals, cosmetics, and food industries is a problem worthy of in-depth research.
Three compounds were obtained by purifying and isolating the skin of passion fruit, including two simple phenylpropanoids, namely sophocarpin and syringin, and one new compound, inositol lignan, which is a new lignan. Pine bark glycoside is a type of glucoside of pine bark alcohol that can inhibit fungal growth and blackening reactions. Liu et al. found that syringin has a strong anti osteoporosis effect on ovariectomized mice, and its molecular mechanism may be related to the NF – κ B and PI3K/Akt signaling pathways. Li et al. found that syringin alleviates angiotensin II induced hypertrophy of H9c2 cardiomyocytes by activating AMPK α and autophagy related signaling pathways. Based on this, we conducted anti-inflammatory and anti-tumor activity tests on inositol lignans, but did not show good activity (data not published). By detecting the tyrosinase inhibitory activity of three compounds, it was found that compound 1 has tyrosinase inhibitory activity. But after screening three compounds for tyrosinase inhibitory activity, it was found that inositol lignan has tyrosinase inhibitory activity. At the same time, molecular docking studies on tyrosinase proteins have found that inositol lignin has the lowest binding energy with tyrosinase, indicating a strong binding effect between the two. Molecular dynamics simulations have further verified the degree and stability of their binding. In summary, this study has delved into the bioactive components of the skin of purple fruit passion fruit, which is beneficial for increasing the utilization value of the skin and further expanding the economic added value of passion fruit.