An overview of the nutritional value, health properties, and future challenges of Chinese bayberry

Organic acids and sugars

CB fruits exhibit a please sweet and sour taste. Prior reports have indicated that these fruits contain soluble solid levels ranging from 8.4–15.0% (Cheng et al., 2016; Liang et al., 2019; Liang et al., 2020; Liu et al., 2020; Zhang et al., 2016a; Zhang et al., 2018a; Zhang et al., 2021; Yan et al., 2016), with total sugar and total acid contents of 8.4% and 1.2%, respectively. While the data herein were from multiple sources and were derived from different analytical approaches, we have converted these data into the same units to reduce variability and permit statistical analyses. Sucrose, fructose, and glucose are the main sugars in CB fruits fruit, with respective content levels of 3.8–15.9 g/100 g, 0.9−1.9 g/100 g, and 0.9−1.6 g/100 g, respectively. Organic acids in these fruits primarily include citric acid, malic acid, oxalic acid, tartaric acid, and vitamin C (ascorbic acid), with respective content levels of 7.2–14.0 g/kg, 0.8 g/kg, 25.3 mg/kg, 438.5 mg/kg (Li et al., 2017), and 11.9–114.6 mg/100g (Table 1, values measured on a fresh weight basis), with vitamin C levels being similar to those in strawberries (25.08–108.1 mg/100 g) (Kim et al., 2015; Urün et al., 2021) and citrus fruits (110 mg/100 g) (Elkhatim, Elagib & Hassan, 2018; Rey, Zacarías & Rodrigo, 2020).

Flavonoids

CB fruits contain high levels of flavonoids (13.6–294.3 mg/100 g fresh weight [FW]) (Sun et al., 2013a; Xia et al., 2021a; Zhang et al., 2018a). Flavonoids are key bioactive CB derivatives, with the number of detected polyphenols 38 reported by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS), where proanthocyanidins, as well as flavonols, including myricitrin and quercetrin, were the predominant ingredients in a previous study (Liu et al., 2020). CB-derived flavonoids are thought to exhibit beneficial anti-cancer and anti-diabetes activities (Zhang et al., 2018b). The most abundant flavonoid in these analyzed fruits was the cyanidin-3-O-glucoside (6,322–1,1846 mg/kg dry weight [DW]), followed by the epicatechin (82.25–111.87 mg/kg DW), quercetin (5.98–36.47 mg/kg DW), myricetin-3-O-rhamnoside (21.2–91.6 mg/kg DW), kaempferol-3-O-rhamnoside (279.14 mg/100 g DW), quercetin-3-O-rutinoside (0.07−1.39 mg/kg DW), quercetin-3-O-galactoside (30.8 mg/g DW), quercetin-3-O-glucoside (8.2 mg/g DW) (Liu et al., 2020; Zhang et al., 2016a; Zhang et al., 2021). The total relative anthocyanin levels in these fruits are 2.80−5.12 mg/kg (DW) (Zhang et al., 2021). These substances account for the majority of secondary metabolites present in CB fruits, offering a valuable resource for future studies of the association between flavonoids and physiological function.

Phenolic acids

Total phenolic content levels in CB fruits range from 61.6–498.94 mg/100 g FW (Sun et al., 2013a; Xia et al., 2021a). These polyphenols exhibit anti-oxidant and anti-proliferative activities, as well as bacteriostatic properties which have led to interest in their use as natural preservatives (Tao et al., 2020). In prior analyses of secondary metabolites, 15 CB-derived phenolic acids were identified (Liu et al., 2020). The content of protocatechuic acid, caffeic acid, and p-coumaric acid levels in CB fruits are 32.12–133.84 mg/kg (DW), 0.39−4.45 mg/kg (DW), and 0.05−0.57 mg/kg (DW) (Zhang et al., 2021), and these compounds have been ascribed beneficial pharmacological activities including the ability to prevent platelet aggregation, reduce myocardial oxygen consumption, increase myocardial oxygen tolerance, and slow the heart rate. In addition, they exhibit bacteriostatic, neuroprotective, analgesic, anti-tumor, and anti-oxidant activity (Song et al., 2020).

CB fruits also contain a variety of other compounds including gallic acid and ellagic acid. Total levels of gallic acid and ellagic acid are 19.81–102.30 mg/kg (DW) and 2.58–10.06 mg/kg (DW), respectively (Zhang et al., 2016a). Studies have shown that these compounds may be of value in the context of treating liver disease, and for preventing retinal diseases associated with oxidative damage, arteriosclerosis, and cerebrovascular diseases (Fu et al., 2014; Liang et al., 2021; Mizuno et al., 2017).

In this review, we summarized 38 flavonoids and 15 phenolic acids that can be detected in CB fruit, and analyzed the content of some of them, which provides a reference for the separation, purification and functional research of secondary metabolites in future research.

Anti-cancer properties

Some researchers have demonstrated that CB extracts exhibit anti-cancer activity (Wang et al., 2016), with many flavonoids (cyanidin-3-O-glucoside, myricanol, prodelphinidins, proanthocyanidins, and isoquercitrin) having been shown to inhibit apoptosis in a variety of tumor cells (Zhang et al., 2018b).

Many studies have explored the mechanistic basis for the anti-tumor activity of CB extracts. For example, CB fruit-derived cyanidin-3-O-glucoside was shown to suppress gastric adenocarcinoma xenograft growth in a dose-dependent fashion in mice (Wang et al., 2016). Myricanol extracted from CB bark can similarly suppress A549 lung cancer cell growth in a dose-dependent fashion (Dai et al., 2014), while myricitrin (myricetin-3-O-rhamnoside), quercitrin (quercetin-3-rhamnoside), and proanthocyanidins derived from CB leaves inhibited the growth of A2780/CP70 ovarian cancer cells (Zhang et al., 2018b; Zhang et al., 2018c). CB leaf-derived prodelphinidin and proanthocyanidins can further suppress the growth of OVCAR-3 human ovarian cancer cells (Fu et al., 2017; Zhang et al., 2018d). Isoquercitrin extracted from CB fruits was also able to inhibit the viability and colony formation activity of the HepG2 and Huh7 human liver cancer cell lines, activating apoptosis and autophagy dysregulation in these cells (Shui et al., 2020) (Table 2). CB extracts may thus be a valuable resource for natural compounds with anti-tumor activity.

Anti-oxidant, anti-inflammatory, and anti-aging properties

CB extracts exhibit potent anti-oxidant and free radical scavenging activity within treated cells (Xia et al., 2021b). Both myricitrin and quercetin-3-rhamnoside extracted from CB leaves, as well as anthocyanin extracted from CB fruits, function as potent anti-oxidants (Zhang et al., 2016b; Huang et al., 2014). Similarly, proanthocyanidins derived from CB leaves exhibit pronounced anti-oxidant potency (Fu et al., 2014), while cyanidin-3-O-glucoside extracted from CB fruit can protect neonatal porcine islets against reactive oxygen species-induced injury (Li et al., 2017a). Cyanidin-3-O-glucoside and myricetin additionally exhibit anti-inflammatory activity when used to treat P. acnes-stimulated human SZ95 sebocytes, making them promising modulators of inflammatory signaling pathways in the treatment of skin acne (Chen et al., 2019). Phenolic-rich extracts derived from CB can additionally prevent protein glycation and advanced glycation end-products formation, in addition to exhibiting anti-aging properties (Zhang et al., 2021) (Table 2). CB fruits and leaves are an important source of therapeutically useful flavonoids and polyphenolics. These extracts possess strong anti-oxidant anti-inflammatory, and anti-aging properties, and may thus be developed as natural anti-oxidants to benefit public health.

Anti-diabetic and anti-obesity properties

A number of natural products that exhibit hypoglycemic activity have been identified in recent years (Dong et al., 2021; Hung et al., 2012; Chukwuma et al., 2019), and these compounds are reported to be safe and to additionally possess promising anti-oxidant, anti-tumor, and lipid-lowering activities. As such, they hold promise as alternative therapeutic tools with the potential to alleviate pharmacological dependence upon hypoglycemic and lipid-lowering drugs (Boath, Stewart & McDougall, 2012). Extracts from different CB tissues have been found to exhibit these properties. For example, CB fruit extracts contain high levels of flavonols and proanthocyanidins, and were found to significantly lower fasting blood glucose while increasing glucose tolerance and insulin sensitivity in diabetic KK-A^y mice (Liu et al., 2020; Zhang et al., 2016a). Moreover, the expression of the insulin 1 and glycogen synthase kinase 3 β genes were notably suppressed whereas hepatic AMPK α phosphorylation was significantly increased in treated mice, suggesting that these CB fruit extracts can exert anti-diabetic efficacy at least in part via an AMPK-dependent pathway (Wang et al., 2020b). Cyanidin-3-glucoside-rich fruit extracts can further protect pancreatic β cells against oxidative stress-induced injury and associated hypoglycemic effects in diabetic mice (Sun et al., 2012). CB fruits are an excellent natural anti-diabetic food, suggesting their potential application as a functional food ingredient or for further drug discovery use in the prevention and control of diabetes mellitus and its complications.

Myricanol extracts derived from CB bark have been shown to suppress lipid accumulation in zebrafish fed a high-fat diet by inhibiting peroxisome proliferator-activated receptor γ, CCAAT/enhancer-binding protein α, and other adipogenic factors (Shen et al., 2019a). Moreover, proanthocyanidin extracts derived from CB leaves can exhibit anti-obesity activity owing to the upregulation of SIRT1 and the consequent deacetylation of PPAR- γ together with C/EBP- α downregulation and BMP4 upregulation to increase brown fat levels in a high-fat diet-induced rat model of obesity (Zhou, Chen & Ye, 2017). CB extracts exhibit significant anti-obesity efficacy, and may thus offer value as a potential therapeutic agent for the treatment of obesity.

The neuroprotective properties of CB and its therapeutic use in the treatment of cerebrovascular and cardiovascular diseases

CB extracts have also been shown to exhibit neuroprotective activity and to be effective in the treatment of cerebral and cardiovascular diseases. Anthocyanin-rich CB fruit extracts can protect against cerebral ischemia-reperfusion injury in Male ICR mice (Cui et al., 2018), while flavonoids derived from these fruits exert cardioprotective activity by decreasing the severity of oxidative damage in 8-week-old Sprague-Dawley rats (Wang et al., 2019). Moreover, an in vivo analysis of ApoE^−/− model mice and Sprague-Dawley rats found that myricitrin was able to significantly attenuate Dox-induced myocardial damage, protecting against vascular endothelial cell damage and inhibiting the formation of early atherosclerotic plaques (Sun et al., 2013b; Sun et al., 2016). Myricitrin was also found to be neuroprotective (Shen et al., 2019b). The development of myricitrin and anthocyanin-based flavonoids as novel drugs for treating cerebrovascular and cardiovascular diseases is thus an important area for future research, and CB extracts are a valuable source of such compounds and a food supplement with natural neuroprotective properties.

CB trees grow rapidly and need to be trimmed 2–3 times a year, resulting in a large number of discarded leaves and branches. In traditional production contexts, these leaves and branches will be crushed into slag and serve as raw materials for cheap organic fertilizer. However, in light of this review of the various functions of CB extracts, it is clear that valuable compounds can be extracted from non-fruit tissues including leaves, bark, and roots, highlighting novel production opportunities for these discarded leaves and branches. In the future, these safe to eat, these extracts can be applied for dietary use for the prevention of tumor growth and the enhancement of immunity, offering further economic benefits and extending the value and applications of CB.

Harvesting, preservation and storage

CB fruits are susceptible to mechanical damage and water loss, physiological deterioration, and microbial decay, making them poorly suited to storage and transportation , such that they have a post-harvest life of just 1–2 days under ambient temperatures, resulting in severe post-harvest losses (Arbol et al., 2016; Wang et al., 2009). As such, high-quality fresh fruits are most often picked by hand, while processed fruits are gathered using auxiliary harvesting tools. Experienced pickers can harvest intact CB fruits at rates of 8–10 kg per hour.

The storage, preservation, and transportation of these fruits are thus essential to their commercial dissemination. Current approaches to the storage of these fruits include chemical preservation, hot air treatment, cold storage, and controlled atmosphere storage. Controlled atmosphere storage primarily consists of the filling of closed packaging containers with ∼15% CO₂ or NO₂ to inhibit ethylene release and fruit respiration, followed by storage at 5−8 ° C, allowing fruits to be preserved for approximately 20 days. Under traditional cold storage (5−8 °C), fruits can generally be preserved for 7 days. Chemical preservation can be achieved by treating fruits with preservatives non-thermal plasma-activated water, methyl jasmonate, and 1-MPC, allowing for preservation for up to 13 d (Wang et al., 2009; Ma et al., 2016). CB fruits can also be treated with hot air (48 °C) for 3 h, followed by storage at 4 °C for about 15 days (Wang et al., 2010; Dai et al., 2021).

Chinese bayberry juice processing

CB fruits consist of 90–95% flesh and just 5–10% core by weight. Following harvesting, CB fruits can be stored at low temperatures (4 °C or −20 ° C), after which fruits are pressed, filtered, and the core and remaining residues are removed (Fang et al., 2006; Fang et al., 2009), resulting in a juice yield of 73.50–84.00%. The total sugar content in prepared CB juice ranges from 2.32−9.46 g/100 mL, while total acid levels range from 0.57−1.36 g/100 mL. total amino acid levels range from 0.057−1.672 g/L, and total phenolic acid and flavonoid contents range from 1.149−2.243 mg/L and 286-907 mg/L, respectively (Tian et al., 2019; Wang et al., 2012; Xu et al., 2014). Polypropylene membrane-filtered CB juice can then be pasteurized, processed, and drunk directly following dilution to taste or stored at −20 °C for up to 180 days.

Chinese bayberry wine processing

According to prior reports, to prepare CB wine, fresh or frozen CB fruits are crushed using a juice extractor and sucrose is used to adjust the total soluble must content to 15.0° Brix. Musts are then pasteurized for 5 min at 100 °C followed by rapid cooling to 20 °C (Zhang, Li & Fan, 2019). Fermentation is performed using a wild yeast strain isolated from a natural CB mash and identified as Pichia kluyveri (Du et al., 2016; Li et al., 2017b), with fermentation being conducted for 4–7 days at 28 °C until the total weight loss is less than 0.2 g/d. After fermentation, wine is clarified for 1 h with 0.20 g/L poly-vinylpyrrolidone and 0.06 g/L chitosan. Following centrifugation, wines are bottled with equal headspace volume and stored for 70 days in the dark at room temperature (Xu et al., 2014). The resultant wine exhibits a total anthocyanin content of 51.1–116.6 mg/L, as well as an ester content of 25.713 mg/L. The primary esters in the resultant wine include ethyl decanoate (9.166 mg/L), ethyl octanoate (6.245 mg/L), ethyl acetate (3.462 mg/L), diethyl butanedioate (2.741 mg/L), and ethyl dodecanoate (2.219 mg/L), respectively. Total acid levels range from 0.323–0.907 mg/L (Cao, Wu & Weng, 2020), while total phenols and flavonoids range from 90.10–510 mg/L following fermentation.

Culinary and commercial applications

CB fruits exhibit a sugar/acid ratio of approximately 7–15, accounting for their sweet and sour taste. These fruits can promote digestion and control the composition of the gut microbiome (Tao et al., 2020), and have long been used to produce a range of food products and other commercial items. Broadly, these products can be classified into two main categories: beverages, and foods. Beverages include CB juice (Fang et al., 2006), wine (Zhao et al., 2019; Zhang et al., 2020), and sparkling water, while CB fruit-derived foods (Fang, Zhang & Wang, 2007) include dried CB fruits, CB jam, canned CB fruits, candies, ice cream, yam cake, steamed cake, and moon cake.

CB fruit dry powder

In one proof of concept study, frozen CB juice was thawed and mixed at a 1:1 ratio with a maltodextrin solution (11° Brix), yielding a total solids content in the final solution of 11° Brix. This solution was then fed through a mini spray-dryer (aspirator rate: 100%, 35 m³/h; atomization air rotameter: 30 mm, 439 L/h with a co-current flow; drying air inlet temperature: 150 ° C) with the pump rate being adjusted to maintain an 80  °C outlet temperature. When air inlet temperatures were below 50 °C at the end of the experiment, samples were collected (Fang & Bhandari, 2012). These spray-dried protects exhibited stable polyphenol content and anti-oxidant activity over a 6-month storage period (Fang & Bhandari, 2011). Dry powders are the most effective means of preserving the active substances in CB fruits at present, and can also be directly leveraged for further processing into health products or additives.