Study of the Release Kinetics of Capsaicin Extracted from Charapita Chili (Capsicum frutescens) from an O/W Emulsion Made with Sacha Inchi Oil (Plukenetia volubilis) and Encapsulated in Calcium Alginate Beads ^†

Abstract

Capsaicin has multiple applications such as analgesic for muscle pain, anti-inflammatory, anticancer, antidepressant, and others. It is a lipophilic compound that produces irritation, therefore, for its application, it is necessary to encapsulate it in emulsions or biopolymers. The objective of this work was to prepare a direct O/W emulsion containing capsaicin extracted from Charapita chili (Capsicum frutescens) with Sacha Inchi (Plukenetia volubilis) oil as the oil phase and encapsulated in calcium alginate beads, intending to increase the useful life of the capsaicin. Capsaicin was extracted from Charapita chili powder using ethanol, then the extract was dried for 40 min at 55 °C. To obtain the emulsion, the dry extract was dissolved in 100 mL of Sacha Inchi oil and mixed with sodium alginate by stirring at 14,000 rpm. Then, the emulsion was combined with sodium alginate by stirring at 14,000 rpm. This mixture was dripped onto 200 mL of a 0.2 M solution of calcium chloride, obtaining beads of a spherical shape. The experimental kinetic data are described with the Korsmeyer–Peppas model, where the maximum release was reached at 180 min, the value of the constant n was 0.7857, and the rate constant K was 2.95. As the constant n < 0.85, the release process was due to the diffusion and swelling of the beads. The emulsion obtained could be used to develop pharmaceutical products; moreover, the encapsulated emulsion in calcium alginate could be used in the formulation of functional foods to take advantage of the capsaicin from Charapita chili and the functional properties of the Sacha Inchi oil.

1. Introduction

There is a great variety of chili peppers in Peru, which have been cultivated by our ancestral cultures and have made Peruvian cuisine famous [1]. However, the scientific study of our chili peppers is still incipient. Among these chili peppers is the Charapita chili (Capsicum frutescens), which is characterized as a small yellow fruit that is very aromatic and spicy. It is grown in the Peruvian Amazon, in the areas of Loreto, San Martin, and Ucayali.

Currently, the extraction of capsaicin from chili fruits is carried out using Soxhlet extraction equipment, in which methanol, ethanol, acetone, etc., are used as solvents [2]. In addition, to carry out the extraction, ultrasound, microwave, and supercritical fluid techniques are used. Capsaicin molecules (8-methyl-N-vanillyl-trans-6-nanenamide) are hydrophobic vanilloide compounds that give spicy foods their pungent quality. It is a secondary metabolite found in the composition of different varieties of chili peppers with high therapeutic and nutritional potential because they contain a wide range of bioactive compounds, such as capsaicinoids, carotenoids, polyphenols, flavonoids, vitamins, and minerals [3].

Regarding therapeutic applications, Muwen et al. [4] carried out a review on capsaicin as an analgesic in chronic pain caused by osteoarthritis and rheumatoid arthritis. Capsaicin has anti-inflammatory characteristics, which are widely used in gels, creams, and ointments. As an anticancer compound, Willian et al. [5] highlighted that capsaicin exhibits potent anticancer effect on several types of human cancer, including gastric cancer, breast cancer, lung cancer, prostate cancer, etc.

The direct oral administration of capsaicin causes adverse effects in our body because it produces irritation in the oral cavity and stomach, which leads to the emergence of stomatitis and gastric ulcers [6]. In addition, capsaicin has low solubility in water, a short half-life, and cytotoxicity at high concentrations. Due to these disadvantages, administration systems are being developed that are based on different encapsulation techniques, such as emulsions, liposomes, micelles, nanoparticles, etc. The encapsulation of active ingredients in micro- and nanoemulsions are widely used to improve the oral availability of hydrophobic ingredients and are prepared by using high speed and pressure homogenizers [7].

The objective of this research was to study the encapsulation of capsaicin emulsion obtained from the Charapita chili.

2. Materials and Methods

2.1. Collection and Processing

The Charapita chili was purchased at the market of the fishing terminal Villa Maria del Triunfo in Lima, Peru. One kilogram of the fruit was cut into halves and placed in trays of a food dryer (IKE, Foshan City, Guangdong, China) for 4 h at 50 °C. The dried sample was then ground with a stainless-steel blade mill to obtain the chili powder.

2.2. Capsaicin Extraction Process

The method proposed by Hoyos [2] was carried out with some modifications. First, 6 g of the powdered material was placed in a filter paper bag, which was then introduced into the Soxhlet apparatus. For the extraction of capsaicin, 100 mL of absolute ethanol was used. The extraction of capsaicin was carried out for 6 h, maintaining the temperature of the heating blanket at 50 °C. The extract was dried in a Rotavapor equipment (D-Lab, Beijing, China) for 40 min at 55 °C. All extractions were performed in triplicate.

2.3. Emulsion Preparation Process

The emulsion preparation was performed according to the method proposed by Chan [8]. First, 0.1 g of dry extract was dissolved in 100 mL of Sacha Inchi oil, which had been bought from a local market in Lima city, Peru, by constant stirring at 500 rpm. Then, 10 mL of capsaicin solution was mixed with 40 mL of sodium alginate solution (1.6%) and the mixture was placed in homogenization equipment (VELP, Usmate Velate, Italy) at 14,000 rpm for 3 min to obtain a stable microemulsion.

2.4. Emulsion Encapsulation Process

The microemulsion was combined with 40 mL of sodium alginate by stirring at 14,000 rpm, and then this mixture, with the help of a peristaltic pump, was dripped onto a 200 mL solution of calcium chloride (0.2 M) with constant stirring at 250 rpm for 30 min to obtain beads of a spherical shape. To remove excess calcium chlorine, the beads were washed with distilled water and then dried in a food dryer (IKE, Guangdong, China) at 40 °C for 30 min, as shown in Figure 1.

2.5. Capsaicin Release Kinetics

The process began with 5 g of beads in 300 mL of absolute ethanol, and the mixture was kept under constant agitation at 300 rpm throughout the course of the kinetics. To follow the kinetics of the capsaicin release process, 5 mL aliquots were taken at different time intervals. To determine the concentration of capsaicin in each aliquot, the spectrophotometric method (Thermo Fisher Scientific, Waltham, MA, USA) was used, measuring the absorbance at the wavelength λ = 281 nm. The release kinetics of capsaicin corresponded to concentration versus time and was obtained based on the calibration curve, as shown in Figure 2.

3. Results and Discussion

A stable direct O/W emulsion of capsaicin was obtained, in which the emulsifying agent was the biopolymer sodium alginate. When the concentration of the biopolymer is in excess, the emulsion can be directly encapsulated through a cross-linking reaction with calcium ions, Ca²⁺, resulting in homogeneous and resistant spherical beads. Figure 2 shows the concentration of capsaicin released as a function of time. From this result, it can be deduced that the maximum capsaicin is reached after 180 min.

Emulsions are used to transport substances with nutritive and active principles [4,5]. Chan [8] used palm oil to obtain a direct O/W emulsion and employed calcium alginate beads in its encapsulation. In this research, a stable direct O/W emulsion carrying capsaicin was obtained, and a sodium alginate biopolymer was used as an emulsifying agent instead of calcium alginate. In addition, the same method was used but with Sacha Inchi (Plukenetia volubilis) oil and capsaicin. The encapsulated emulsion increased the slow release of capsaicin with the objective of increasing its stability for future application in the food and pharmaceutical industry.

The release kinetics are described by the Korsmeyer–Peppas model [9], whose linear form is expressed through Equation (1), where the constant n indicates the release mechanism, K is the velocity constant, and the relation $C_t/C_{\inf }$ represents the fraction of capsaicin released. The results of the analysis of the experimental data based on Equation (1) using the least squares statistical method is as shown in Figure 3.

$$\ln \left({\displaystyle \frac{C_t}{C_{\inf }}}\right)=\ln K+n\cdot \ln t$$

(1)

According to the value obtained for the mean square deviation R² = 0.9954, it is deduced that the kinetic data are adequately described by the Korsmeyer–Peppas model. Furthermore, the value of n = 0.7892 $(n\le 0.85)$ indicates that the release mechanism of capsaicin from the internal part of the beads corresponds to the diffusion and swelling of the beads.

4. Conclusions

Capsaicin was extracted from Charapita chili using absolute ethanol as the solvent. A direct O/W microemulsion containing capsaicin was prepared using sodium alginate as an emulsifier agent. The emulsion was encapsulated in alginate beads due to excess sodium alginate. The release kinetics of capsaicin from the calcium alginate beads in the ethyl alcohol medium determined that the maximum release was reached at 180 min. The kinetic data were adequately described with the Korsmeyer–Peppas model, and the value of the constant n = 0.7857 indicated that the release mechanism of capsaicin from the beads corresponded to the mechanisms of diffusion and swelling of the beads. It is necessary to continue the applications of capsaicin emulsions in the pharmaceutical and food industry.