沙漠研究 19-1, 197- 200 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Mineral Characterization of Some Tunisian Apple Cultivars
Manel BOUDABOUS1, Abessalem MRABET1, Ali FERCHICHI1
Abstract: The content of major (Na, K, Ca, Mg and P) and minor elements (Fe, Cu, Zn andMn) in apple consumed in the Tunisian arid land has been determined by using flame atomic
absorption and spectrophotometer method. Significant differences were observed in themineral contents of the apple samples. This difference between mineral contents and varieties
is reported in the literature and a comparison has been carried out with diverse fruits. Ingenerally, apples are rich in macroelements (P, Na, K, Ca and Mg) while the microelements (Cu,Zn, Fe and Mn) are in the form of traces.
Keywords: Apple cultivars, Mineral composition, Tunisia

1. Introduction
Apples are one of the most frequently consumed fruits in the world after citrus, banana and grapes.
In Tunisia, commercial apple production in recent years amounted to 130 thousand tones and apples coveran area of 34 thousand hectares (FAOSTAT, 2005).
Apples constitute an important part of the human diet, as they are a source of monosaccharides,minerals, dietary fibre, and various biologically active compounds, such as vitamin C, and certain phenolic
compounds which are known to act as natural antioxidants (Wu et al., 2006).
Many factors affect the elemental contents of fruits, for example, variety, state of ripeness, soil type,soil condition, fertilization, irrigation and weather (Tahvonen, 1993). In this study we used four apple
cultivars grown in Tunisian arid land, which have not been studied before, in order to evaluate thevariability of elemental composition.
2. Materials and Methods
2.1. Plant material
Four apple cultivars (Douce de Djerba, Anna, Chahla and Arbi) grown in Tunisian arid land (Djerbaand Zarzis) were used for this study. The apples were harvested based on industry standards.
2.2. Mineral analysis
Plant materiel was dried at 70 ˚C. Four grams of sample (apple pulp), placed in a porcelain capsule,was calcined then by the muffle furnace at 550 ˚C/4h. After cooling, ashers were washed by 5 ml ofdeionised water and 1 ml of hydrochloric acid and were brought to boiling. The capsule content wasfiltered. The filtrate was brought to volume using deionised water to 100 ml. This solution will be usedfor mineral analysis.
A Shimadzu AA 6800 was used to determine the sodium, potassium, calcium, magnesium, copper,zinc, iron and manganese concentrations by atomic absorption spectrophotometry method. The element
concentration was calculated according to the equation: % Na, % K, % Ca, % Mg, % Cu,% Zn % Fe and %Mn = C × V /(104 × m) × % MS, where C featured value (ppm), V extract volume (ml), m mass (g), % MS
Percentage of dry material.
A Secomam spectrophotometer was used to determine the phosphorus concentration. Standard
solutions of P 0, 2, 4, 8 mg/ l were prepared by diluting basic solution of P 100 mg/l, and 10 ml of eachstandard. The diluted extract was placed in 25 ml tubes with 10 ml of the vanadomolybdic reagent.
After 10 min, the absorbencies were measured at 430 nm. Extracts were diluted as needed. P
concentrations were calculated according to the formula: % P = (C × Df)/(100 × m), where C Phosphorus
Concentration (mg/l), Df Dilution factor, m extract mass (g).

1Arid and Oases cropping laboratory, Arid Area Institute (IRA), 4119 Medenine, Tunisia.
E-mail: modoboudabous@yahoo.fr

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2.3. Statistical analysis
All analysis was carried out using SPSS software 12.0 version. Data were analyzed statistically(ANOVA) using analysis of variance and means separated using Duncan’s multiple range test at the P<0.05
level of significance. Results were expressed also in dendrogram form using the order TREE. Thistechnique was founded on the Euclidean distance.
3. Results and Discussion
Statistical analysis show the existence of a highly significant difference (p<0.01) between the varieties
for the character tenor of minerals (Table 1). In this communication, we will treat results of mineral
analyses one by one.
Table 1. Elemental composition (mg/g) of selected categories of apples.

Varieties
Anna
ChahlaArbi
Douce
Djerba

Na
3.47a
3.43a
3.69a
18.46b

K
53.59a63.22b134.72c139.96c

Ca
1.78a
3.80b
2.83c
2.56d

Mg
1.73a
2.47b
5.82c
4.68d

Cu
0.00a0.02a
0.09b
0.07b

P
1.73a
3.46b
7.40c
9.52d

Zn
0.09a
0.08b
0.13c
0.10d

Fe
0.16a
0.36b
0.47c
0.26d

Mn
0.03a
0.05a
0.07b
0.03c

Different superscript in each column indicates the significant differences in the mean at P<0.05.

3.1. Potassium
Results show that the four varieties studied are very rich in this mineral element. Potassium (K) was
the most predominant element present in all categories of apples. Indeed, its content varies from 53.59"Anna" to 139.96 mg/100 g "Douce de Djerba".
Similar results were found by Eisele and Drake (2005), during their tests to identify the mineralcomposition of 175 varieties of apples trade from 12 countries and several regions of the United States.
Indeed, the potassium content in all varieties is very high and peaked at 2712.3 ppm, a content that is very
high in comparison with our varieties (21.43 to 55.98 ppm). In contrast, Emaga et al. (2007) showed thatbanana is characterized by potassium levels ranging from 5.52 to 6.35 mg/100 g, relatively low incomparison with our results.
Ercisli and Orhan (2007) demonstrated that potassium is the predominant element founded in threevarieties of mulberry studied. Indeed, the levels of K vary from 834 mg/100 g (Morus rubra) to 1668
mg/100 g (Morus alba). In the same case, Vasantha and Clegg (2007) have shown that potassium is themost dominant mineral in ten varieties of grapes analyzed.
Potassium promotes the growth of the fruit; in general, a high K content of fruit is correlated with anincrease in fruit size. In contrast to nitrogen, potassium has a positive effect on the formation of organic
acids and accelerates the development of color (Huguet et al., 1971).
3.2. Sodium
The variation of the sodium content at the various studied varieties is shown in Table 1. Values
oscillate between a maximum recorded at the Douce de Djerba variety (18.46 mg/100 g) and a minimum at
the Chahla variety 3.43 mg/100 g. Results from this study indicates these varieties are characterized bylow levels of sodium compared with the results given by Eisele and Drake (2005) which refer to levels
between 0.5 and 73.4 ppm with an average of 11.8 ppm.
3.3. Calcium
Calcium is an essential element to the cohesion of the cells. It has a role in the conservation of fruit.
Present in sufficient quantity, it slows the ripening process by slowing breathing and loss of firmness(Fallahi et al., 1985). It participates in maintaining cellular integrity stiffen its action on membranes andalso in maintaining protein synthesis (Hopfinger and Poovaiah, 1979).

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Table 1 shows that the variety Chahla presents the highest level of calcium (3.8 mg/100 g), while
Anna presents the lowest content (1.78 mg/100 g). In generally, we can say that our varieties are not richin this element, values range from 0.71 to 1.52 ppm with an average of 1.09 ppm, in comparison with thefindings of Eisele and Drake (2005) who found values which range from 18.7 to 80.3 ppm with an averageof 41.9 ppm.
3.4. MagnesiumHigh levels of magnesium in fruit results in an increase in tissue firmness and total acidity (Huguet etal., 1971; Papp and Aziz, 1989). This significantly influences photosynthesis, on the one hand, because it
enters the composition of chlorophylls and on the other hand because it acts as cofactor on a certain
number of enzymes and in particular on the key enzymes of the cycle of pentose phosphates, controlling
the photosynthetic CO2 fixation.
For the different varieties studied, magnesium content varies between a minimum of 1.73 mg/100 gregistered with Anna variety and a maximum of 5.82 mg/100 g in Arbi. It’s the Douce de Djerba whichcontains the most important value of Mg (Table 1).
Hopfinger et al. (1984) highlighted the role of magnesium and calcium on the enzymatic browning ofapple tree. Indeed, these authors showed that the enzymatic tanning due to the polyphenoloxydase, wasstimulated by the addition from 0.8 to 10 mM of MgCl2 whereas the addition of CaCl2 to the same
concentration has an opposite effect. This leads to the supposition that the enzymatic tanning of apple isstimulated by an imbalance in the ratio Mg/Ca of tissue.
3.5. Phosphorus
The phosphorus has a beneficial effect on root growth and fruit set. Phosphorus fertilization allows anincrease in the circumference of trunks and productivity of trees.
The decline in P content of fruits is correlated with an increase in fruit size and an increase of total
acidity (Travers, 2004).
For the studied varieties, Table 1 shows that the phosphorus concentrations oscillate from 1.73
mg/100 g (Anna) and 9.52 mg/100 g (Douce de Djerba).
Compared to other fruits such as blackberries or dates whose concentrations respectively range from226 to 247 mg/100 g (Ercisli and Orhan, 2007) and from 57.4 to 91.6 mg/100 g (Mrabet, 2005) we can saythat apple is classified as one of the fruits which are not very rich in phosphorus.
3.6. Microelements
The concentrations of Cu, Fe, Mn and Zn are very low and at times at on trace levels. Despite this low
level, the difference between the varieties is significant. This variability may be due to the fact thatvarieties are not analyzed from the same source and therefore they were not grown under the same soil andenvironmental conditions. This assumption is advanced by Hakala et al. (2003) during their tests toidentify the chemical composition of mulberry and Youssef et al. (1982) to identify the date composition.
4. Comparison of the studied varieties according to their mineral content
Results of apple mineral composition permit to discuss two groups (Fig. 1).

G1
G2Fig. 1. Dendrogram obtained in the basis of mineral content of the different apple cultivars.

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Group 1: Contains the majority of the varieties (Anna, Chahla and Arbi) which are characterized by:• A mean content of sodium (3.43 to 3.69 mg/g);• A high content of calcium (1.78 to 3.8 mg/g);• A high content of magnesium (1.73 to 5.82).
Group 2: This group contains only one variety (Douce de Djerba) which is characterized by:• A high content of sodium (18.46 mg/g);• A high content of potassium (139.69 mg/g);• A high content of phosphorus 9.52 mg/g).
5. Conclusions
The mineral composition results showed that our varieties are relatively rich in macroelements (P, Na,K, Ca and Mg) whereas the microelements (Cu, Zn, Fe and Mn) are in the form of trace. Potassium was
the most abundant mineral found in all apple categories. Calcium was significantly higher in Chahla thanin the other apples while magnesium was higher in Arbi variety. It is quite clear that the Douce de Djerba
variety makes the difference as long as it contains the most important content of sodium, potassium, andphosphorus.
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