Nutraceutical and medicinal property of Mulberry fruits: A review on its pharmacological potential

Cytogenetics & Plant Biotechnology Research Unit, Department of Sericulture, Raiganj University, Uttar Dinajpur, 733134, India Insect Ecology and Conservation Biology Laboratory, Department of Sericulture, Raiganj University, Uttar Dinajpur, 733134, West Bengal, India Laboratory of Organic Synthesis, Department of Chemistry, Raiganj University, Raiganj–733134 Chemical Biology Laboratory, Department of Sericulture, Raiganj University, Uttar Dinajpur, 733134, West Bengal, India Department of Biotechnology, Institution of Health Sciences, University of Health Sciences, Istanbul, 34668, Uskudar, Istanbul, Turkey Centre for Nanotechnology Sciences, Raiganj University, North Dinajpur, West Bengal, 733134, India


INTRODUCTION
Sericulture is one leading agriculture-based industry that practiced worldwide due to its revenue-generating capacity (1). Bombyx mori produces high-quality silk yarn in the form of the cocoon, which has high demand in textile as a monophagous insect B. mori is solely dependent on the leaves of a single host plant known as Mulberry (2). Mulberry (Morus) plants belong to the family Moraceae which cultivated from tropical to temperate region with diverse topographical and meteorological conditions (3). Mulberry includes 68 species and 1 subspecies with at least 100 known varieties of which most of them cultivated in Asia (4,5). In India Mulberry cultivation laevigata are the most dominating species (5).
Recently, the demand for mulberry fruit is increasing as a healthy natural product because of its good taste, dietetic value, and biological activities (7). In conventional Chinese folk medicine, mulberry fruits have been used in to treat diabetes, hypertension, anemia, and arthritis (8). Natural products are always enriched with bioactive compounds (9)(10)(11). These bioactive ingredients of mulberry fruits have drawn the attention of many researchers due to their nutritional and therapeutic properties that reduce the risk of developing some chronic diseases (12,13). About 50% of the approved drugs present in the market are made up of natural products (10). At present, about 80% of the world population uses the plant-derived drug, and this phytomedicine industry is expected to attain approximately $35 billion market value up to 2020 (14). Due to the presence of many natural bioactive compounds, mulberry fruits have an immense opportunity to be useful therapeutic products. In the present review, we mainly focused on understanding the nutritional and phytochemical properties of mulberry fruit along with its efficacy towards various metabolic disorders and other life-threatening diseases.

PHYTOCHEMICAL COMPOSITION
In comparison to mulberry leaves, records of traditional use of mulberry fruits are very limited due to a lack of awareness of its nutritional and medicinal value (15). At present, isolation and characterization of the phytochemicals from mulberry fruits are imperative, as these fruits are consumed in many countries for dietary enhancement (10). Mulberry fruits harbor a diverse array of biological elements that have elite nutritional value and, many of them decorated with antioxidant properties due to the presence of polyphenolic groups (16).

Nutrients
Mulberry fruits are excellent in tastes with sour flavor (pH < 3.5) and low-calorie content (17,18). This fruit contains plentiful primary metabolites (Table 1) in the form of carbohydrate, protein, lipid, vitamins, minerals, and fiber that provide a healthy dietary option to the consumers. The principal carbohydrates are found in the form of monosaccharide and polysaccharides whose amount increases during ripening (19)(20)(21). The monosaccharide of mulberry fruits is comprising of glucose, arabinose, galacturonic acid, and galactose (22). While the immense majority of the polysaccharide reported from mulberry fruits ( Table 2) are acid heteropolysaccharides, which are the primary source of α, β-glycosidic linked glucans, these mulberry fruit polysaccharides (MFPs) exert remarkable medicinal effects on human health (23).
Mulberry fruit (M. alba) contains a higher amount of proteins (1.44g/100g) in comparison to strawberries, raspberries, and blackberries (0.67g/100g, 1.20 g/100g, and 1.39g/100g respectively) (7). Interestingly higher protein content was revealed from the Indian subcontinent with a value of 1.73g/100g in M. laevigata (large black fruit) fruiti (24). Mulberry fruit contain 18 amino acids, out of which nine are belong to essential amino acids group that obligatory for humans. The ratio between the essential amino acid and total amino acid (EAA/TAA) of mulberry fruit is 42%, that is quite akin to milk and fish (25). World Health Organization recommended mulberry fruit as an excellent dietary product as its essential amino acid score is more than 100 (26).
The most predominant essential amino acid in mulberry fruit is linoleic acid (C18:2), which has high nutritional and therapeutic value for a human being (27).
Mulberry fruit contains more abundant polyunsaturated fatty acids are in comparison to monounsaturated and saturated fatty acids. Many researchers have been isolated 14 different fatty acids from mulberry fruit extract (MFE), and they suggested that profile of these fatty acids are varying due to difference in environmental conditions and genetic factors (3,4,28). This fruit is an excellent source of different minerals and vitamins. Minerals include calcium, sodium, potassium, iron, zinc, and magnesium. Vitamin C (ascorbic acid), vitamin A, vitamin B, vitamin E (αtocopherol, β -tocopherol, δ -tocopherol and γ-tocopherol), and vitamin K are the most abundant vitamins present in mulberry fruit (29,30). Ascorbic acid has a direct effect on antioxidant activity.
Out of the four mulberry species predominantly cultivated in the Indian subcontinent, M.
laevigata (large black fruit) possesses the highest level of ascorbic acid (17.03 mg/100g), followed by M. indica, M. nigra and M. alba (24). These reported nutrients have a decisive role in human health.

Bioactive components
In recent days many researchers are focusing on the pharmacological property of mulberry fruit as it possesses various bioactive phytochemicals. Bioactive components of mulberry fruit are preciously categorized in polyphenol, alkaloid, and melatonin (Table 3, Fig. 1).

Polyphenols
Polyphenols of mulberry fruit represented a substantial and diversified family that includes flavonoids (anthocyanins, flavanol, and flavonols) and phenolic acids (benzoic acid and hydroxycinnamic acid)(10). Bae and Suh(31) revealed that total phenols and total flavonols in the alcoholic extract of mulberry fruit were equivalent to the range of 6-65 µg/g catechins, 137-2057µg/g malvidin-3-glucoside and 960-2570µg/g gallic acid. These phenolic contents of mulberry are quite higher than other berries and vary among different species and variety (32,33).

Anthocyanins
Anthocyanins belong to the subfamily of flavonoids and responsible for red to blue and  (32,35,36). Out of the 20 components, the chief anthocyanin isolated from mulberry fruit is Cyanidin 3-O-glucoside (301.75 mg/ g of mulberry anthocyanin extract), which exerts antidiabetic and antitumor activity (23,37).

Flavanols and Flavonols
These compounds also belong to the flavonoid subfamily.

Phenolic acids
Phenolic acids extracted from mulberry fruit are mainly present as benzoic acid and hydroxycinnamic acid (10). Benzoic acid derivatives reported in MFE are vanillic acid, gallic acid, hydroxybenzoic acid, and protocatechuic acid.
Hydroxycinnamic acid derivatives in MFE were identified as cinnamic acid, chlorogenic acid, ocoumaric acid, p-coumaric acid, ferulic acid, and caffeic acid. Mahmood et al. (19) revealed that mulberry fruit contain chlorogenic acid as most teeming phenolic acid derivative, while Butkhup, Samappito, and Samappito(33) quantified that cinnamic acid was the most abundant phenolic acid derivative extracted from the mulberry fruit. This deference observed due to differences in the genetic constituent and agro-ecological condition of the cultivars (28,32).

Melatonin
Melatonin is a neurohormone which regulates circadian rhythms and sleeping disorder in has been reported in MFE of setting the stage, but melatonin content then decreased in the ripening stage. The optimal level of melatonin (31.59 ng/ml) recorded during ethanol fermentation of mulberry fruit extract at 250 °C(49).

MEDICINAL PROPERTIES
As discussed earlier, mulberry fruit is enriched with the different bioactive components, which has a therapeutic effect on human health(50,51). Out of these bioactive components, anthocyanins of mulberry fruits can restrain low density lipoprotein (LDL) oxidation and scavenge the free radicals(52,53). Experiments conducted with MFE in animal models as dietary supplements improve health and a wide array of pharmacological benefits.

Antioxidant Activity
Antioxidant activity of MFE has shown a significant difference between mulberry cultivars with the definite correlation between the polyphenolic content and antioxidant activity (31,54). of human and proposed its probable mechanism(63,66) (Fig. 2). They advocated MFE act as a robust anti-diabetic agent by accelerating the synthesis of glycogen, promoting gluconeogenesis, and remodeling of insulin resistance via AKT/PI3K pathway. These experimental studies showed that MFE could improve insulin sensitivity, decrease gluconeogenesis, amplify skeletal muscle glucose transporter-4 (GLUT4). It shows that mulberry fruits decrease phosphoenolpyruvate carboxykinase and glucose 6-phosphatase levels in the liver to exert an anti-diabetic effect.

Much evidence suggests that MFP decorated with immunomodulating action that has been examined on T-cells, B-cells, dendritic cells, and macrophages. Mulberry fruit glycoprotein named
MP can significantly increase T and/or B cell proliferation at a dose of 125-2000μg/ml (67,68).

Anti-atherosclerosis Activity
Atherosclerosis is a cardiovascular disease associated with the buildup of lipids (mainly oxidative low-density lipid) in the innermost layer of the artery (72). Consumption of natural antioxidant reduces the risk of atherosclerosis development (73,74). Anthocyanins, rutin, protocatechuic acid, caffeic acid, and naringenin are the main polyphenolic compounds that could reduce atherogenesis ( Fig. 1 and 3 They also advocated that anthocyanin extract of mulberry fruit was tenfold higher effective than mulberry water extract. Chan et al. (76) proposed that polyphenolic extract could arrest cells of smooth muscle in thoracic aorta of A7r5 rat through induction of NO production and p53/AMPK activation at the G0/G1 phase to diminish atherosclerosis.

Anti-Obesity activity
Hypolipidemic activity of MFE was investigated high lipid diet-induced obese rat. MFE significantly reduces fasting blood sugar and body weight gain in a dose-dependent mode (77). HUVECs. These findings revealed that phytochemicals of mulberry fruit may be advantageous in anti-angiogenesis therapy for the treatment of cancer. In future, the molecular mechanisms of the anti-tumor activity exerted by MFE need to be further illuminated.

Hepatoprotective activity
Hepatoprotective protective activity of MFPs was studied in acute and sub-acute alcoholic-

CONCLUSIONS AND FUTURE RESEARCH
The present study has highlighted the nutrients content and bioactive phytochemicals of mulberry fruits that exert health benefits to the human being. The bioactive compounds such as polysaccharides, polyphenols, and alkaloids present in mulberry fruits are dependent on the variable cultivars and agro-ecological conditions. Although these bioactive phytochemicals may work synergistically with each other and with chemical drugs to promote health benefits and to cure many diseases, there are insightful gaps in our understanding regarding the molecular mechanism of such biological activities. Extensive studies were done to isolate and characterize MFE, but still, there is a bottleneck to relate the bioactive components of MFE with biological activities.
Moreover, there are very few reports on the molecular mechanism and metabolic pathway of such bioactive components. Thus, it is crucial to understand the mechanism of how these