**2.1 Mesquite gum purification**

*Nanoemulsions - Properties, Fabrications and Applications*

(*Citrus paradise*) belongs to the Citrus genus, a class of flowering plants in the family Rutaceae [22]. The active constituents exist in this kind of citrus essential oil, such as limonene, a-pinene, b-pinene and a-terpinolene [22, 23]. Its seed and peel extract (essential oil) has shown the antibacterial and antifungal property [24]. Persian lemon (*citrus latifolia tanaka)* is composed of citric, malic and formic acids, as well from pectin, hesperidin, and essential oils as D-limonene (**Figure 4**) and phellandrene, which are the volatile liquid fractions responsible for the characteristic smell of lemon. These compounds can be extracted by distillation, and are commonly employed in the cosmetic, pharmaceutical and

*Main constituents of mesquite gum (from left to right): L-arabinose, D-galactose, 4-O-Methyl-D-glucuronic* 

As part of a nano-emulsion, D-limonene has been used as the oil phase of different O/W nano-emulsions. For instance, in the work of Li and Chiang, who have successfully formed D-limonene O/W nano-emulsions phase by an ultrasonic method, using Span 85 and Tween 20 as surfactants [26]. Another example is the work of Donsì et al. [27], who achieved D-limonene nano-emulsions formation through a high pressure homogenizer, using a wide type of emulsifiers. The latter authors have explored the antibacterial properties of these systems by testing against *Escherichia coli* and *lactobacillus delbrueckii*, demonstrating D-limonene nano-emulsion capacity to control and eliminate microbial organisms [27, 28]. As these studies, there are some other investigations about D-limonene nano-emulsions, but none of such studies explores the formulation with a natural

**48**

food industry [25].

*D-limonene chemical structure.*

**Figure 3.**

**Figure 4.**

*acid and L-rhamnose.*

emulsifier as mesquite gum.

Mesquite gum was extracted from mesquite pearls obtained from a local candy store at Sonora (Sonora, México). The purification process of the mesquite gum begins with the selection of the cleanest pearls by visual inspection as indicated by literature [17]; afterwards the pearls were ground in a ceramic mortar until a powder was obtained. Then a 20% (wt) solution of this powder was prepared, which was filtered (in order to eliminate impurities like dust and pieces of wood), details of the process can be found in literature [12].

Afterwards, several drying processes were experimented, specifically oven and lyophilization. The drying process by oven was discarded since it was very slow, and in addition, the gum obtained was of a brown tone, indicating a possible degradation of the gum or caramelization. Regarding the lyophilization method, several strategies were tested. First, it was tested with a lyophilized sample at 20%, and a gum with a "sponge" texture was obtained, later this "sponge" gum was re-lyophilized in order to obtain a denser version. Therefore, it was decided to test lyophilized 40% mesquite gum solutions in a controlled manner, this last process was selected to be used for the production of gum for the nano-emulsions of this research.

#### **2.2 Infrared spectrum analysis (FT-IR) of the gums**

To carry out this analysis, the Thermo Nicolet 6700 FT-IR spectrophotometer with its attenuated total reflectance accessory (Thermo Scientific) was used, using solid samples (powders).

**Figure 5** shows the FT-IR spectra of the different gums characterized in this research, which are largely comparable with the FT-IR spectrum of Arabic gum (GA) reported in the literature [17, 18]. Therefore, it follows that the different mesquite gums produced (oven dried procedure, dense lyophilized and controlled Lyophilized) essentially have the same chemical composition in terms of sugars, amino acids and proteins. Absorbance of the ▬OH and ▬CH groups are observed at 3375 and 2932 cm<sup>−</sup><sup>1</sup> (similar to that reported in the literature [17]), and a band centered between 1650 and 1600 cm<sup>−</sup><sup>1</sup> that can be assigned to the primary amides. There is a smaller band around 1500 cm<sup>−</sup><sup>1</sup> that is assigned to the secondary or substituted amides. The bands of the primary and secondary amides are characteristic of the presence of peptide bonds and confirm the presence of the protein [17], There is also a band at 1400 cm<sup>−</sup><sup>1</sup> that can be attributed to a carboxylic group. The bands that are around 1000 and 900 cm<sup>−</sup><sup>1</sup> can be attributed to the glycosidic acetal groups of pyranose, according to the literature [17].

### **2.3 Concentration of aldehydes of citric essential oils**

The citrus essential oils used during this research were a generous donation from the FRUTECH company. The determination is made by the hydroxylamine hydrochloride method (ISO 1279: 1973). A Titroline Alpha plus automatic titrator from SI Analytics was used to obtain the aldehyde concentration of the citrus oils of pink grapefruit and Persian lemon. Four grams of oil are weighed in a beaker, 50 mL of hydroxylamine hydrochloride solution are added, stirring for 1 minute at 300 rpm, and then it was allowed to rest for 30 minutes. Subsequently, a titration

**Figure 5.** *IR spectra of the different gums.*

with methanolic KOH is performed and the amount of mL used is recorded to reach a pH of 3. In order to determine the concentration of aldehydes, the following mathematical formula is used:

%*carbonyl compounds* = (*<sup>a</sup>* <sup>×</sup> *<sup>N</sup> meq* <sup>×</sup> 100)⁄*<sup>P</sup>*

```
where
```
a = Volume of the potassium hydroxide solution used in the neutralization of the sample in mL.

N = Normality of the potassium hydroxide solution.

P = Weight of the sample, in grams.

meq = Milliequivalent corresponding to the carbonyl compound in which the result is expressed.

Aldehydes are a family of organic compounds (R▬CHO), which are indicative of the quality of essential oils, the higher the concentration of aldehydes, the higher the oil quality [29]. The released HCl is evaluated, which is related to the content of carbonyl groups in the sample and it can be calculated in grams of the aldehyde. The results are shown in **Table 1**, these are within the expected ranges (For Persian lemon is 3.5–7.5 and 0.8 1.5% for pink grapefruit) according to literature [28].


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**Figure 6.**

**essential oils**

*Development of Nano-Emulsions of Essential Citrus Oil Stabilized with Mesquite Gum*

It can be seen that Persian Lemon oil has a concentration of aldehydes 3 times greater than pink grapefruit oil, which is why it was a determining factor for the selection of Persian lemon oil as an oil phase. It should be noted that aldehydes are the components with the highest added value since they provide most of the odor, taste and therapeutic qualities, and are therefore the most important components. In addition, some authors attribute the antibacterial activity to aldehydes, although there is controversy in this aspect since other authors give this property to terpenes [30–32].

*Chromatographic profile of the sample analyzed: (A) Persian lemon oil and (B) pink grapefruit oil.*

The analysis was carried out in a gas chromatograph model 7890ª coupled to a Mass Spectrometer (Agilent Technologies). For the analysis 2 μL of each oil sample is injected, the column HP-5MS (Agilent Technologies) is responsible for passing or retaining each compound of citrus essential oils and uses Helium as a carrier gas at a temperature of 280°C and the Wiley library is used as a database for the identification of each component. This analysis allows the separation and identification of the components of the essential oils. Terpenes have a lower retention time than aldehydes, so this method is used to corroborate the concentration of aldehydes. As observed in the chromatograms (**Figure 6**) D-limonene is the signal with more abundance in the citrus essential oils used in this research and is a component widely used in microbial inhibition in the food, pharmaceutical and cosmetic industry [33, 34]. The mechanism of the antibacterial function of essential oils is still not detailed, according to the literature [35]. As mentioned earlier there is a controversy regarding antibacterial activity and the relationship with aldehydes and terpenes. As we can see in **Figure 6**, Persian lemon oil has a higher concentration of aldehydes.

**2.4 Volatile profile by gas chromatography of citric essential oils**

**3. Methodology for the formulation of nano-emulsions of citrus** 

A reproducible process for the formulation of nano-emulsions of essential citrus oils is described. The initial process of preparing the nano-emulsions consists

*DOI: http://dx.doi.org/10.5772/intechopen.84157*

**Table 1.** *Concentration of Aldehydes.*

*Development of Nano-Emulsions of Essential Citrus Oil Stabilized with Mesquite Gum DOI: http://dx.doi.org/10.5772/intechopen.84157*

**Figure 6.** *Chromatographic profile of the sample analyzed: (A) Persian lemon oil and (B) pink grapefruit oil.*

It can be seen that Persian Lemon oil has a concentration of aldehydes 3 times greater than pink grapefruit oil, which is why it was a determining factor for the selection of Persian lemon oil as an oil phase. It should be noted that aldehydes are the components with the highest added value since they provide most of the odor, taste and therapeutic qualities, and are therefore the most important components. In addition, some authors attribute the antibacterial activity to aldehydes, although there is controversy in this aspect since other authors give this property to terpenes [30–32].

#### **2.4 Volatile profile by gas chromatography of citric essential oils**

The analysis was carried out in a gas chromatograph model 7890ª coupled to a Mass Spectrometer (Agilent Technologies). For the analysis 2 μL of each oil sample is injected, the column HP-5MS (Agilent Technologies) is responsible for passing or retaining each compound of citrus essential oils and uses Helium as a carrier gas at a temperature of 280°C and the Wiley library is used as a database for the identification of each component. This analysis allows the separation and identification of the components of the essential oils. Terpenes have a lower retention time than aldehydes, so this method is used to corroborate the concentration of aldehydes.

As observed in the chromatograms (**Figure 6**) D-limonene is the signal with more abundance in the citrus essential oils used in this research and is a component widely used in microbial inhibition in the food, pharmaceutical and cosmetic industry [33, 34].

The mechanism of the antibacterial function of essential oils is still not detailed, according to the literature [35]. As mentioned earlier there is a controversy regarding antibacterial activity and the relationship with aldehydes and terpenes. As we can see in **Figure 6**, Persian lemon oil has a higher concentration of aldehydes.
