In 1982, the Fifth International Conference on Exercise Biochemistry proposed fatigue is that a particular intensity of activity during the course of physiological activities can’t be initiated or maintained by the body (F. Li, Han, Wu, Ma, Zhang, Guo, et al., 2016). Fatigue can generally be categorized into three types, including physiological fatigue, pathological fatigue and psychological fatigue. The peripheral fatigue, one type of physiological fatigue, also named as muscle fatigue and sports fatigue, primarily caused by muscle factors, including energy deficiency, metabolite accumulation and metabolic disorder in skeletal muscle (Jiameng & Hongyan, 2017; Neu, Mairesse, Montana, Gilson, Corazza, Lefevre, et al., 2014; Taylor, Amann, Duchateau, Meeusen, & Rice, 2016). Although peripheral fatigue is not a clinical symptom, it will have major negative consequences on the body and result in a number of diseases if it is not actively and successfully treated (Le-le MA, LIN, LIU, LIU, HUANG, TAN, et al., 2020). Under today’s fast-paced living conditions, phenomena like unreasonable diet, lack of exercise, irregular work and rest, lack of sleep, mental tension, high psychological pressure, and long-term bad mood are widespread. As a result, more and more people are in sub-health state (a special state between health and illness) and facing "unexplained fatigue". (C. Luo, Xu, Wei, Feng, Huang, Liu, et al., 2019). At the same time, in recent years, sports fatigue has received an increasing amount of study and attention in the disciplines of athletics, the military, and aerospace. The rapid eradication of fatigue has become a focus of global study. And the dietary supplements or natural anti-fatigue products are gaining popularity.
Phyllanthus emblica L. (PE) is a tropical fruit of Euphorbiaceae, which is sweet, sour, crisp and slightly astringent. With a history spanning thousands of years, it is extensively dispersed in tropical and subtropical nations like India, Southwest China, Vietnam, Thailand, and Indonesia. PE is frequently utilized as both a fruit and a medication, and typically used in the form of a decoction and pill powder as a medication. PE was initially introduced to China from Ayurvedic medicine in India, which then developed in Chinese medicine and was widely used. Traditional Chinese medicine conside the use of PE for a prolonged period of time can strengthen qi and lighten the body. At the same time, Triphala powder, which is made up of PE, terminalia chebula and myrobalan, is often used to treat fatigue in the early and late stages of plague fever (Jaiswal, Liang, & Zhao, 2016; Prasad & Srivastava, 2020). Additionally, current pharmacological study demonstrates PE's blatant anti-fatigue action. For instance, the swimming time of normal mice can be significantly extend by gavag 0.3 and 0.5 g·kg− 1 of PE water extract for 30 days (Cui, Huang, & Lin, 2008). Rats undergoing high-intensity endurance training can have their fat decomposition promoted and their glycogen consumption reduced by the administration of 3.5 g·kg− 1 PE with 49 days (LIN, 2007). Numerous polyphenols, including as cheleric acid, corilagin, Gallic acid (GA) and ellagic acid (EA), are abundant in PE (Bhatt, Rawat, Badhani, & Rawal, 2017-z. HUANG, RAN, TAN, ZHANG, LI, FAN, et al., 2019; H. Huang, Tan, Li, Tan, Gao, Bao, et al., 2022). It has the effects of anti-oxidation, anti-cancer, hypoglycemic, lipid lowering, anti-bacterial, anti-virus, anti-inflammatory, cardiovascular and cerebrovascular protection, liver protection, reduction of renal ischemia-reperfusion injury, anti-hypersensitivity, skin protection, nerve protection, etc (Kahkeshani, Farzaei, Fotouhi, Alavi, Bahramsoltani, Naseri, et al., 2019; Ríos, Giner, Marín, & Recio, 2018). At present, studies have proved that polyphenols have anti-fatigue effects, which are mainly related to their ability to resist oxidative stress, maintain mitochondrial function and energy metabolism, regulate bone, sugar, lipid and protein metabolism (Ríos, Giner, Marín, & Recio, 2018; ZHAO, 2021; Zhou & Jiang, 2019). At the same time, there are relevant reports that the metabolite urolithin A produced by EA through the action of gut microbiota has the ability to protect mitochondria and enhance muscles(Ghosh, Das, Biswas, Gnyawali, Singh, Gorain, et al., 2020). The polyphenols in PE may be the material basis for its anti fatigue effect.
The polyphenols in PE, however, are unstable and easily change when heated during processing. Such as drying and extraction. Polyphenols primarily experience hydrolysis, oxidation and polymerization that greatly affect their composition and activity. For instance, when tea soup was heated, the higher the temperature is, the longer the heating period, and the quicker the polyphenols are transformed, the more obvious the changes in the appearance, flavor and activity of tea soup will be (Kim, Liang, Jin, Sun, Lu, Du, et al., 2007). Similar phenomena are reported in wine and coffee (Del Pino-García, González-SanJosé, Rivero-Pérez, García-Lomillo, & Muñiz, 2017; Pettinato, Casazza, & Perego, 2019). But now, there is no report on the composition change law in the drying and extraction process of PE and no concern regarding the impact of this process on the anti-fatigue effect, making it challenging to choose a suitable processing method and processing time of PE. This is the main cause of the inconsistent and unstable nature of PE products, which prevents the high-quality growth of the PE relevant sectors. In light of the aforementioned issues, this paper explored PE's chemical composition variations and transformation laws using various drying and extraction methods. And reserch the impact of various processing methods on PE's anti-fatigue properties. The goal of this study was to better understand the connection between PE's anti-fatigue properties and its heat transformation law during the drying and extraction processes. This is significant in terms of investigating the physical basis of PE's anti-fatigue properties, improving PE's production method, and creating associated dietary supplements.