Lycopen’s Stability in Watermelon Juice (Citrullus lanatus) Regarding to Technological Routes

Highly prized by consumers, watermelon is rich in water, but also in micronutrients including lycopene, pigment responsible for the red color. It is also a powerful antioxidant which has many virtues including the prevention and treatment of certain diseases. The transformation into nectar of watermelons combined with treatment could cause several modifications including the alteration of coloring. It is in this context that this study focuses on the variation of the lycopene content in nectars. Thus, nectars of 12  ̊Brix and 15  ̊Brix were prepared from three varieties of watermelon (Sugar Baby, Crimson Sweet and Charleston Gray). To study the stability, two pasteurization scales (85 ̊C/15min and 95 ̊C/15min) and one sterilization scale (105 ̊C/15min) were applied to the different nectars produced. The results obtained showed that the Sugar Baby variety is richer in lycopene (24.39 mg∙kg) with a higher pH (5.80). In addition, the study showed, for the Sugar Baby variety, an increase of lycopene with the addition of sugar and the heat treatment (a maximum of 42.83 mg∙kg for SbF12T105). On the other hand, for the Crimson Sweet and Charleston varieties, the highest rate of lycopene, except the heat-treated ones, are those formulated at 12  ̊B (10.46 mg∙kg for CrF12T105 and 18.40 mg∙kg for ChF12T105). Without any health consequences, the formulation combined with heat treatment would preserve the lycopene content of watermelon nectars.


Introduction
Watermelon (Citrullus lanatus) is a plant of the Cucurbitaceae family. The fruit is a particular berry, spherical in shape, more or less oblong [1]. Its flesh which can be red, yellow, greenish or white generally weighs between 4 to 16 kg however there is watermelon with bigger weight (120 kg) [1]. Several bioactive compounds have been determined and the beneficial effects demonstrated by in vivo and in vitro studies [2]. Watermelon is also very rich in phenolic compounds, which are mainly derivatives of hydroxycinnamic acid and lycopene which gives watermelon its characteristic flesh red color and powerful antioxidant activity [3] [4]. The main pigment that causes red flesh color in watermelon is lycopene, which is considered one of the most important natural carotenoids in fruits [5].
It has the highest rate of oxygen quenching singlet of all carotenoids tested from biological systems [6]. Lycopene has been a research focus in many areas, including health care products, cosmetics, and nutrition, and has been shown to serve physiological functions in the human body [5] [7] [8]. Watermelon juice is produced commercially with heat treatment which can cause different types of changes such as coloring, flavor or other attributes, but, nevertheless, non-heat treatments are used [9] [10] [11]. Thus, the objective of this work is to study the impact of heat treatment and the addition of sugar during formulation on the lycopene concentration of watermelon nectars.

Plant Material
For the study, three varieties of watermelon grown in Senegal have been used.

Formulation
Separately, the three (3) varieties of watermelon (Sugar Baby (Sb), Crimson Sweet (Cr) and Charleston Gray (Ch)) were cut into pieces and the red pulps collected. To obtain raw nectar (SbF 0 T 0 for Sugar Baby, CrF 0 T 0 for Crimson Sweet and ChF 0 T 0 for Charleston Gray), the pulp was ground using an electric juice blender (LOKI type LBL 201-C). Two formulations, at 12 ˚Brix (F12) and

Codification of Samples
The coding of the samples was carried out at three levels (Depending on the variety V, the formulation made F and the heat treatment applied T

Analytical Methods
For the study, different analyzes were carried out. The soluble solids content (brix), which is expressed in g•100 g −1 of product, was determined using a digital refractometer ATAGO PAL-α. The pH was determined using an analog pH meter (HANNA HI 223) with an accuracy of 0.05 at 25˚C (Standards NF V76-122).
To determine the color component (L* a* b) of the nectars, a colorimeter (CM-5, Konica Minolta Sensing Americas Inc., US) was used. The different color components allow us to define the product according to the three-dimensional space with L* indicating the lightness or luminance which varies from black to white; a* which corresponds to the green-red antagonist couple and b* corresponding to the blue-yellow antagonist couple. The lycopene content was determined by using the method described by Benakmoum et al. [12]. For this, centrifugation of the extract with an Hexane/Acetone/Ethanol (50/50/1) mixture is made at 5000 rpm for 15 minutes. The organic phase obtained was recovered with hexane, before carrying out a measurement of the absorbance at 472 nm using a UV spectrophotometer (Shumadzu UVmini-1240).

Statistical Analyzes
The results of the various analyses carried out were subject to statistical processing.

Results and Discussions
The physicochemical and biochemical properties of the raw nectars are given in Table 1. The results of the study of correlations between the various parameters of the raw products are presented in Table 2 and lycopene content's results by

Characterization of Watermelons
The characterization results of the three varieties of watermelon are given in Table 1. This table shows overall significant differences between watermelons.
In terms of pH, there are no significant differences between the varieties Crimson Sweet (5.20) and Charleston Gray (5.21). These values are higher than the pH of watermelon with seeds, from the eastern USA, obtained by Perkins [13].
But differences are noted with the Sugar Baby variety (5.80) which is less acidic and quite similar to ripe watermelon without seeds observed by Perkins [13]. However, significant differences are noted, for the soluble solids content

Statistical Analyzes
Comparison between the physicochemical and biochemical parameters (Table   1)  The correlations (Table 2) between other analytical parameters shows overall

Study of the Evolution of Lycopene Concentration
The lycopene content in raw products and those formulated and having undergone a heat treatment, is determined and the various results are represented by Figure   2 and Figure 3. These figures represent the evolution of lycopene concentration based on sample characteristics (variety, formulation and heat treatment).  concentrations obtained are much lower than those observed by Choudhary [20] on different watermelon genotypes in India including Sugar Baby (53.6 mg•kg −1 ).
Indeed, studies carried out on tomatoes have shown that lycopene is stored in globular or tubular form, in the form of crystalloids whether or not surrounded by membranes, or dissolved in plastoglobules, lipid droplets enclosing carotenoids and tocopherols [21] [22]. A decrease of the initial lycopene concentration is also noted for pasteurized raw watermelon at 85˚C/15 min (23.23 mg•kg −1 for SbF 12 T 85 ). This could be explained, by the rigidity of the chromoplast envelope which resists the heating applied or by the degradation of lycopene in solution.
Concerning the Charleston Gray variety (Ch), an increase according to the heat treatment is noted only for the raw products (F 0 ) and those at 12 ˚B (F 12 ). The concentration increase is lower than those obtained with Sugar Baby. This low increase could be explained by the initial low lycopene concentration in the raw  In short, it appears that, for the Sugar Baby variety, the addition of sugar but also the heat treatment temperature promotes the increase in the lycopene content. Conversely, for the Crimson Sweet and Charleston Gray varieties, the addition of sugar combined with the heat treatment reduces the lycopene concentration in the nectars. Apart from the raw nectars of Crimson Sweet and Charleston Grey, those formulated at 12 ˚B show the best increases in lycopene concentration.

Conclusion
This study allows us to observe that the Sugar Baby variety is much richer in lycopene than the Crimson Sweet and Charleston Gray varieties. On the other hand, there is not a general tendency which emerges on the impact of the heat treatment and the formulation on the nectars of all the varieties studied. Nevertheless, it emerges that for all the watermelons, a formulation at 12 ˚B combined with high heat treatment (high pasteurization or sterilization) would allow to have a significant increase in lycopene.

Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this paper.