There are multiple Morus sp. fruits (about 2 to 3 cm long); they form together and are arranged longitudinally around the central axis, similar to blackberries, and are low in calories, but rich in nutrients and antioxidants, so they can ensure good overall health [4]. The fruits contain a high-water content (over 70%), and the pH values differ between species: M. alba presents the highest value of pH (5.6), while the M. rubra and M. nigra have values of 4.04 and 3.52, respectively [5]. Based on values of pH, total soluble solid and total dry weight, the M. alba could be recommended for processing, while M nigra may be recommended for fresh fruit production [5][6].
The taste is better in the case of black fruits, which is due to the lower pH value compared to white fruits, which are sometimes characterized as tasteless. All these own connections, together with the nutritional and medicinal ones, make the black mulberry fruits increasingly sought after and studied
[2][5][3][7][8][9][10][11].
The mineral content of mulberry fruits depends on the species, fruit maturity and composition of soil and environmental conditions (light, humidity, temperature, altitude)
[5][12][13][14]. In the study of Ercisli & Orhan, 2007
[5], ten elements were determined from mulberry fruits collected from Turkey, where potassium was predominant.
Iron, an essential mineral and very rare in berry fruits, has a high value of 4.2 mg/100 g in
M. alba and
M. nigra. In another study
[12] of the macroelements, N, K and P are found in large levels, while sodium is present in a very low concentration (0.01 mg) in
M. alba and
M. nigra grown in Spain. The levels of iron varied between 28.20 to 46.74 mg/kg and 23.92 to 37.09 mg/kg in
M. alba and
M. nigra, respectively, demonstrating good sources of non-heme iron. In the black mulberry, grown in Western Serbia at different altitudes, the highest amount of minerals was determined for phosphorus and potassium, with a significant difference depending on altitude. Additionally, the authors showed that black mulberries are a good source of iron, with the highest content (1.95 mg/100 g) found at 187 m altitude
[13]. The form of iron in foods is ferric iron (Fe
3+), which is less bioavailable than ferrous iron (Fe
2+).
In vivo, the increase in iron bioavailability was attributed to ascorbic acid’s chelating and reducing properties
[15]. The high content of vitamin C and iron from mulberry resulted in the better bioavailability of iron and can be used to treat anemia
[16].
In the mulberries fruits grown in Xinjiang region, China, potassium was the dominant macronutrient, followed by calcium and magnesium. Due to the high Fe content of Russian mulberry and black mulberry from China (11.4–11.9 mg/100 g fw), they can be used as dietary supplements to treat the iron deficiency, anemia
[16].
In terms of the fatty acids profile of mulberry fruits, linoleic acid is dominant, followed by palmitic acid and oleic acid, the latter being detected only in
M. alba and
M. nigra [5][6][17]. Additionally, the high level of linoleic acid (52.3%) was found in white mulberry cultivated from Xinjiang region, China
[16].
Regarding protein content, the mulberry fruits grown in southeastern Spain are a good source of protein;
M. alba had a higher protein content than
M. nigra [12]. In the mulberries cultivated in China, the ratio between essential amino acids (EAA) and total amino acid (TAA) was 44%, 42% and 29% for Russian, white and black mulberries, respectively. Foods with EAA/TAA ratio 40% are an ideal protein source, suggesting that the Russian and white mulberries cultivated in China could be used as an important quality protein source
[16].
Ascorbic acid (vitamin C), a powerful water-soluble antioxidant compound, was quantified with the reflectometer in the mulberry fruits (
n = 30); the highest value was recorded in
M. alba (22.4 mg/100 mL), followed by
M. nigra and
M. rubra with 21.8 and 19.4 mg/100 mL, respectively
[5]. Black mulberries had the highest content in ascorbic acid (48.4 mg/100 g fw), compared with Russian and white mulberry fruits (5.64 mg/100 g fw and 6.01 mg/100 g fw, respectively) grown in China
[16].
Nguyen et al., 2008, mentioned that unripe mulberry, i.e., the green parts of fruits, contain a white sap that may be toxic, stimulating, or mildly hallucinogenic
[3].