Tropical fruits contribute substantially to human mineral intake worldwide, and banana, mango, pineapple and watermelon rank among the most widely consumed species in this category. Each fruit accumulates a distinct mineral profile that depends on species, cultivar, growing conditions and the specific plant fraction examined, since minerals distribute unevenly between the flesh, peel, rind and seed of a single fruit [1]. Calcium, potassium, iron, phosphorus, magnesium and zinc constitute the most nutritionally significant minerals supplied by fruit, and these elements play essential roles in human metabolic pathways, from electrolyte balance and bone formation to enzyme cofactor activity [1].

Nutritive composition of fruits differs not only between species but also across the different anatomical parts of the same fruit. For example, the flesh, peel and seeds of the same fruits have been shown to vary in terms of nutritional content. However, most of the available research focuses on the edible flesh and tends to leave out the nutritional contribution made by peels and seeds. These parts, mostly discarded as waste, can hold significant amounts of dietary fibre, natural sugars, minerals and other nutrients. Detailed analysis of nutrient content across every fruit fraction would give researchers a more complete grasp of a fruit’s true nutritional value [2]. Therefore, this study aimed to determine the mineral composition of not only the edible flesh but also the peel and seed fractions of four tropical fruits namely, Banana (Musa spp.), Mango (Mangifera indica), Pineapple (Ananas comosus) and Watermelon (Citrullus lanatus).

The mineral composition of the various fractions in the four selected tropical fruits is presented in Table 1 below.

Table 1. Mineral composition of fruit fractions (mg/100g).

Potassium was the dominant mineral, reaching almost 67 mg/100 g dry weight in banana peel, while iron concentrations were generally low (Table 1). Magnesium concentrations were moderate throughout. Zinc concentrations remained relatively constant among fractions. Peels generally accumulated more calcium than flesh (Table 1), and this calcium pattern held for every fruit examined; the potassium, zinc and iron patterns, discussed further below, did not hold for every fruit (Table 1).

Considering all five minerals collectively, Mango exhibited the highest mean magnesium (9.85 mg/100g) and iron (4.73 mg/100g) concentrations while maintaining moderate potassium and calcium contents therefore ranking best in mineral concentrations (Table 2). On the other hand, Watermelon had generally lower concentrations of most minerals except calcium where the lowest concentration was recorded in banana fruit averaging 1.97 mg/100g. Banana ranked second due to exceptionally high potassium (mean = 52.08 mg/100g) and zinc concentrations (mean = 9.8 mg/100g), although its calcium and iron contents were comparatively low, while Pineapple ranked third because of its high calcium concentration (mean = 5.14 mg/100g) and moderate iron content as shown in Table 2 below.

Table 2. Mean mineral composition in the four fruits (mg/100g).

Values are means ± standard deviation.

Peels exhibited the greatest accumulation of potassium (mean = 30.04 mg/100 g dry weight), zinc (mean = 6.01 mg/100g), calcium (mean = 5.90 mg/100g) and magnesium (mean = 7.62 mg/100g) at the fraction-mean level shown in Table 3, and flesh generally contained lower mineral concentrations than peel at this aggregated level. Three fruit-mineral combinations in Table 1 depart from this general pattern and are reported here explicitly rather than absorbed into the aggregate mean: mango flesh potassium (37.23 mg/100g) exceeded mango peel potassium (15.565 mg/100g); mango flesh iron (5.574 mg/100g) exceeded both mango peel iron (4.4355 mg/100g) and mango seed iron (4.177 mg/100g); and pineapple flesh zinc (4.5155 mg/100g) exceeded pineapple peel zinc (3.1695 mg/100g). Seed fractions carried the fraction-mean highest iron concentration (mean = 3.22 mg/100g, Table 3); at the level of individual fruits. However, this held for only one of the two fruits bearing a seed fraction, with watermelon seed iron (2.261 mg/100 g dry weight) exceeded watermelon flesh and peel iron, whereas mango flesh iron exceeded mango seed iron. Pineapple does not carry a reported seed fraction, and banana likewise does not carry a reported seed fraction, so this seed-level comparison applied only to mango and watermelon.

Table 3. Mean mineral composition in fruit fractions (mg/100g).

Values are means ± standard deviation.

ANOVA was used to test for statistical significance at p ≤ 0.05. It was determined that there is no significant differences in the mineral composition among the fruits (p = 0.1698) as well as the different fruit fractions (0.4623) as shown in Table 4 below.

Table 4. ANOVA table on mineral composition.

The dominance of potassium across all four fruits, with the highest concentration recorded in banana peel, agrees with reports on banana and plantain by-products, in which potassium consistently forms the most abundant mineral in both flesh and peel fractions [4]. Potassium accumulates in greatest amounts in peel because the peel portion contains more vascular and phloem tissue. This is because potassium translocates in fruits via phloem tissue during development. The mean amount recorded in this study for banana was less than concentration reported in fresh banana peel by Tsado et al., [4], this is due to cultivar selection, mineral nutrition of the soil and stage of maturity at harvest of sample.

Mango has the highest mean for Mg and Fe. It has also been observed in numerous studies that mango pulp can be an important supply for major minerals and some trace minerals namely magnesium, iron and zinc [5]. Since they play a major role in metabolism such as chlorophyll synthesis and respiration, iron and magnesium is high because of greater period of maturation of mango compared to watermelon, which also had lowest mean concentration in almost every mineral apart from Ca. The concentrations for Calcium, Potassium, Zinc and Magnesium were found in corresponding peel to be higher compared to the flesh in each of the four tropical fruits.

Table 3 therefore concurs with the findings concerning the separation of elements in Musa tissue which shows high concentration of mineral element in the peel (and in the peel extract) rather than in the pulp [6]. Peel tissue are known to accumulate nutrients at the exterior of fruit tissues since it’s closer to the epidermis and the cuticle. Therefore, they receive minerals from the vascular tissues as they are transferred from the rest of the plant to the various fruit tissues before a portion reaches the flesh during ripening processes [7].

Seeds, in contrast, recorded the highest iron concentration among the fractions, which corresponds with findings on mango seed which showed the significant concentration of essential elements in mango seed kernel with high fat and protein concentration [8]. The lack of a statistically significant difference in mineral composition between fruits and in fraction in present study showed general consistency in the overall elemental makeup.

The minerals concentrated in these four fruits carry direct relevance for addressing global micronutrient deficiencies, particularly given that calcium, iron, zinc, copper and magnesium deficiencies remain prevalent worldwide [9]. Potassium, the dominant mineral across all four fruits examined, supports blood pressure regulation, nerve function and muscle contraction, and adult potassium requirements range from approximately 2600 to 3400 mg per day [10]. Calcium, Iron and zinc, though present in comparatively modest amounts in the fruit flesh, reach considerably higher concentrations in the seed and peel fractions. This observation positions the underutilized fruit parts as potential targets for future food fortification or nutraceutical development strategies aimed at addressing micronutrient malnutrition, particularly in regions where these fruits are cultivated at large scale [11][12].

This study concludes that the four fruits, along with their flesh, peel and seed fractions, differ appreciably in their mineral content. These differences, however, did not reach statistical significance (p > 0.05) at either the fruit or fraction level. Potassium dominated the mineral profile across all samples, particularly in banana peels. Peels also consistently outperformed flesh in mineral composition in all the fruits.

This study recommends that peel and seed fractions of banana, mango, pineapple, and watermelon be considered for further evaluation toward valorisation into flour, animal feed, or nutraceutical extracts, on the basis of the measured potassium, zinc, calcium, magnesium and iron concentrations reported here, which are comparable to, or in several instances higher than, the corresponding flesh concentrations for these five minerals. Food safety, contaminant levels such as pesticide residues or heavy metals beyond the five minerals measured, the effect of processing steps on mineral retention, and the bioavailability of these minerals to a human consumer were not evaluated in this study and requires dedicated assessment before a practical valorisation is acted upon. Discarding peel and seed fractions as waste without such assessment nonetheless represents an avoidable loss of measured nutritive value.

All data generated or analyzed during this study are included in this published article.

All authors have read and agreed to the published version of the manuscript.