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Study of the effects of fruit maturity on Argan oil quality through its mineral

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Abstract

Day by day, Argan oil is gaining an increasing importance in many areas, especially in the food field and the cosmetic and pharmaceutical industry. Due to this importance, the aim of this work was to study the effect of fruit maturity through the color of fruit on the mineral composition of oil in order to determine the optimum maturity. The samples of this study were collected at different degrees of maturity (color). The quality of the oil was assessed by determining the concentrations of eleven elements including seven dietary elements and four heavy metals. The results of this study show that the Argan oil has an unstable metal composition. Difference in the mineral composition was due to the difference in the maturity of the fruit. Argan oil obtained from green fruit grains showed less metal concentrations than the oil obtained from maturity (yellow), rip (brown) fruit grains, which provided a close or more stable metal composition. This maintains the stability of the quality of the oil. Therefore, maturity should be considered (color) of fruit, and there is a preferred color or degree of maturity for all fruit in order to prepare high quality Argan oil.

Keywords: Fruits maturity level, Edible Argan oil, Beauty Argan oil, Mineral composition, Chemometrics

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Materials and methods

Samples collection

Argan fruits at different maturity levels (unripe mature, and rip) (figure1) (20 kg) were collected from five geographical locations (Essaouira, Taroudant, Ait Baha, Tiznit, Agadir) (figure 2). Harvest Year was 2018. Care was taken to collect a representative sample, fruits were depulped manually, nuts were separated; shells were then manually broken, and kernels separated, extracted Argan oil press and determined the mineral content.

Apparatus

ICP-AES spectrometer (JobinYvon, Ultima 2) with axial viewed plasma was used for the mineral contents determination in each argan oil sample. The operating conditions were set as follows: power 1.15–1.2 kW, plasma flow gas 12–14 L/min, auxiliary gas flow 1.5 L/ min and nebulizer gas flow 0.2 L/min. The wavelengths used for the quantification were: Cadmium 214.440 nm, Chromium 205.560 nm, Zinc 213.857 nm, Copper 324.752 nm, Iron 238.204 nm, Potassium 766.490 nm, Magnesium 279.077 nm, Manganese 257.610 nm, Tin 235.848 nm, Phosphorus 178.287 nm and lead 220.353 nm.

Minerals

For mineral analysis, 0.25 g of argan oil was accurately weighed in vessel tubes, 10 mL of concentrated HNO3 (69.5%) and 8 mL of H2O2 (35%) were added and the tubes were heated on at 140 °C for 4 h. During all of the tests, the pressure was kept at 45 bar, and the ventilation was 3 min. After cooling, 1 mL of HNO3 (1%) was added and the final volume was adjusted to 25 mL with deionized water and measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

Results and discussion

Mineral composition

Mineral composition in vegetable oils, even in low quantities, has a significant impact on the quality of vegetable oils. Some elements play an important role in human physiology and some elements unfortunately contribute to the change in the quality of edible oil by igniting a series of oxidative reactions that result in the development of negative sensory factors (Agarwal et al., 2011; Benedet et al., 2008). Therefore, metal content represents important quality standards for vegetable oils.

In this study, the effect of maturity (color of fruit) on the mineral content of Argan oil was studied. Argan fruit was collected from five regions. The oil was extracted before and after the roasting of the Argan grain at different maturity levels.

Tables 1 and 2 contain the content of eleven elements (mg /l) presenting in the samples of the food oil and cosmetics extracted from the Argan fruit at different degrees of maturity. In general, the data showed sufficient variance in the concentration of nutrients in all Argan oil samples based on the degree of maturity or color of the fruit. Moreover, the data showed that the content of heavy metals (Cd, Cr, Zn, Sn) was close in all samples of oil extracted from Argan grains with different degrees of maturity. The content of Potassium, Calcium, Iron, Copper and Magnesium in the oil extracted from the most mature fruits of yellow and brown color is higher than the oil extracted from the less mature fruits of green color. This increase was due to quantity of water in the less mature fruits (green) which is more than in mature fruits. During the oil extraction process, the water is retained with the pulp resulting from extraction, which in turn retains significant concentrations of mineral content. Table 1 and 2 show that the increase in calcium concentration in the oils extracted from the more mature fruits (yellow and brown color) was higher compared with the other dietary elements. This increase is due to that the kernels of more mature fruit absorb calcium at higher rates to become more mature and hardness. Whereas, the Manganese content in all the oil samples was low (0.01 mg/l) and did not change during a period of this study. This result was also similar to those reported in an independent study (Ennoukh, et al., 2017). Our study showed that the degree of fruit maturity has a significant effect on mineral content in edible and cosmetic oil.

Chemometrics

Statistical analysis of data showing the elemental profile is a strong approach to assurance continuous improvement of quality control. In this study, principal component analysis and linear discriminate analysis have been used to evaluate the quality of Argan oil. This evaluating has been done on seven dietary elements that showed significant differences in the mineral content of Argan oil over different maturity stages.

Principal Component Analysis (PCA)

Principal component analysis (PCA) is an important technique to understand in the fields of statistics and data science and uses an orthogonal transformation to convert a set of observations of possibly correlated variables into a set of values of linearly uncorrelated variables called principal components.

In this work we used PCA to determine the effect of the degree of fruit maturity on dietary element content of Argan oil. Figure 1 shows the PCA values of the dietary elements (Ca, K, Mg, Mn, Fe, Cu, P) was collected by using a data set of edible argan oil from five regions of Argan and PCA score plot analysis was run. After rigorous analyses, a separation of 77.68%. While, a separation of 76.46% on the basis of concentration levels of Ca, K, Mg, Mn, Fe, Cu and P in beauty Argan oil shown in Fig.4. Through the values of of total inertia in the experimental data of figures (3, 477.68%, 76.46%, respectively, the visual PCA separation results were not as impressive. For this reason, we will be use the linear discriminant analysis (LDA) because he represents a reliable criterion according to Martin et al. (1999) and Grembecka et al. (2007).

Linear Discriminant Analysis (LDA)

Linear Discriminant Analysis (LDA) is most commonly used as dimensionality reduction technique in the pre-processing step for pattern classification applications. The goal is to project a dataset onto a lower-dimensional space with good class-separability in order avoid overfitting (“curse of dimensionality”).

The table 3 summarizes the reclassification of the observations, and allows to quickly seeing the % of well classified observations, which is the ratio of the number of observations that have been well classified over the total number of observations. It is here equal to 100%.

Figure represents the observations on the factor axes. It allows confirming that the species are very well discriminated on the factor axes extracted from the original explanatory variables.

Through the data of analysis, the samples introduced obtained from five regions of Argan were 100% successfully separated and grouped into three groups as illustrated by Fig. 5,6. From the figures 5 and 6, it can be seen that Argan oil obtained from unripe fruits are clearly separated from Argan oil obtained from ripe and fully ripe fruits. From the figures 5 and 6, it can be seen that Argan oil obtained from unripe fruits are clearly separated from Argan oil obtained from ripe and fully ripe fruits. for it, linear discriminant analysis proved to be the most successful to co confirm the effect of fruit maturity on metal composition of Argan oil.

Conclusion

Our study show that the mineral composition of edible and beauty Argan oil extracted from fruits at different levels of maturity harvested from the five locations vary according to maturity degree. It is through a detailed investigation of oil mineral composition clearly showed that the level of dietary elements in Argan oil prepared from unripe fruits less than level of dietary elements in Argan oil prepared from maturity and fully ripe fruits. While that the mineral content was more stable in Argan oil prepared from ripe and fully ripe fruits. Given the important role played by nutrients in quality of vegetable oils our results can be useful to recommend the most suitable maturity degree of Argan fruits

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