Artículo científico

 

Physicochemical and antioxidant properties of jalapeño pepper (Capsicum annuum var. annuum) during storage

 

Propiedades fisicoquímicas y antioxidantes del chile jalapeño (Capsicum annuum var. annuum) durante almacenamiento

 

Liliana G. Mendoza-Sánchez¹; María R. Mendoza-López²; Oscar García-Barradas², Ebner Azuara-Nieto¹; Luz A. Pascual-Pineda²; Maribel Jiménez-Fernández^1*

 

¹ Instituto de Ciencias Básicas.

² Unidad de Servicios de Apoyo en Resolución Analítica, Universidad Veracruzana. Av. Dr. Luis Castelazo s/n, Col. Industrial-Ánimas, Xalapa, Veracruz, C.P. 91000, MÉXICO. Corro-e: maribjimenez@uv.mx, tel: (228) 841 89 00 (*Autor para correspondencia).

 

Received: June 18, 2015.
Accepted: November 13, 2015.

 

Abstract

Jalapeño pepper is consumed both green (unripe) and red (ripe), so it is important to evaluate the components present in both states. The aim of this study was to evaluate the effect of storage time (30 days) at room temperature (25 °C) on the physicochemical, antioxidant and textural parameters of Capsicum annuum var. annuum. During this period, there was a significant increase (P ≤ 0.05) in the soluble solids content, acidity, and reducing sugars, whereas moisture, ash, and pH decreased. The firmness of the pericarp varied from 5.17 N to 2.88 N. The capsaicin in green state was lower than that found for the red state. Some antioxidant compounds showed a significant increase (P ≤ 0.05) from day 15 of storage. The radical scavenging of DPPH was higher (58.35 %) in the red state of maturity in comparison with the green state of maturity (19.42 %). Some properties analyzed in Jalapeño pepper showed significant changes (P ≤ 0.05) between day 15 and 20 of storage, coinciding with the color change from green to red. Jalapeño pepper at the red stage is a good source of antioxidants including ascorbic acid, carotenoids and polyphenols.

Keywords: maturation, fruit, postharvest, chili.

 

Resumen

El chile jalapeño se consume en estado verde (inmaduro) y rojo (maduro); por lo que es importante evaluar los componentes presentes en ambos. El objetivo de este estudio fue determinar el efecto del tiempo de almacenamiento (30 días) a temperatura ambiente (25 °C), sobre los cambios fisicoquímicos, antioxidantes y los parámetros texturales de Capsicum annuum var. annuum. Durante este periodo, se produjo un aumento significativo (P ≤ 0.05) en el contenido de sólidos solubles, acidez y azúcares reductores; mientras que la humedad, las cenizas y el pH, disminuyeron. La firmeza del pericarpio varió de 5.17 a 2.88 N. La capsaicina en estado verde fue menor que la encontrada en estado rojo. Algunos de los compuestos antioxidantes mostraron incremento significativo (P ≤ 0.05) a partir del día 15 de almacenamiento. La captura de radical DPPH fue mayor (58.35 %) en el estado rojo, en comparación con el estado verde de madurez (19.42 %). Algunas de las propiedades analizadas mostraron cambios significativos entre los días 15 y 20 de almacenamiento, coincidiendo con el cambio de color de verde a rojo. El chile jalapeño en estado rojo es una buena fuente de antioxidantes, incluyendo ácido ascórbico, carotenoides y polifenoles.

Palabras clave: maduración, fruto, postcosecha, chile.

 

INTRODUCTION

The pepper (Capsicum) is one of the most important crops for human consumption, because it is a good source of different phytochemicals, including vitamins A and C, phenolic compounds, flavonoids and carotenoids, among others (Chuah et al., 2008; Topuz & Ozdemir, 2007). It is mainly consumed fresh, but it is also consumed after being put through a drying process in the form of sauces, powders, and pickles (Salinas, Liévano, Ulín-Montejo, Mercado, & Petit, 2010). The main peppers are jalapeño, serrano, habanero, ancho, mulato, pasilla, and piquin. Peppers are eaten unripe in a green state but eventually they vary in color from green to red. This last color is the result of the accumulation of different carotenoids in the chromoplasts during ripening. The predominant red pigments are capsanthin and capsorubin, and orange and yellow pigments are lutein, β-carotene (provitamin A), zeaxanthin, violaxanthin, and antheraxanthin (Paran, Ben-Chaim, Kang, & Jahn, 2007).

Phytochemical changes occur during the ripening period and the resultant effect on their antioxidant activity affects consumption and processing (Howard, Talcott, Brenes, & Villalon, 2000). There are studies that show the effect of ripening on the antioxidant properties of Capsicum annuum, Capsicum frutenscens and Capsicum chínense. Conforti, Statti, and Menichini (2007) studied the antioxidant activity of immature green and red peppers of C. annuum L. var. Acuminatum. They found that the concentration of antioxidant compounds increased as the peppers reached maturity. The influence of the ripening of C. chinese on the content of phenols, flavonoids, carotenoids, and capsaicinoids has also been reported, where a different composition between the two stages of ripening can be observed (Menichini et al., 2009).

Despite its wide acceptance in various regional markets and its marketing potential, there is little information about the jalapeño pepper (Capsicum annuum var. annuum) in terms of its antioxidant activity and the physicochemical changes associated with the ripening process under controlled conditions, to support the establishment of the most suitable post-harvest handling. The study of the ripening process of this fruit is of great importance to generate information about its properties under controlled environmental conditions. Knowledge of the changes occurring during maturation holds great significance from both a dietary and nutritional point of view. It is therefore imperative to study the changes in the content of antioxidants at different maturity stages. The aim of this study was to evaluate the effect of storage time at 25 °C (RH = 68 %) in the jalapeño pepper (C. annuum var. annuum) in the green and red stage of maturity on the physicochemical, antioxidant, and textural properties of the fruit.

 

MATERIALS AND METHODS

Collection and sample preparation

Ten kilograms of the fruits of Capsicum annuum var. annuum were collected during October and November 2012 in a local farm near Jalapa Veracruz, located at latitude 19° 55' 42", longitude -96° 42' 03" and an elevation of 870 m. Fruits were harvested 110 days after planting when they reached the maximum size and a bright green homogeneous color. The fruits harvested were washed with water to remove dust and impurities, and were drained of excess water for 2 hours at room temperature. Afterwards, the samples were divided into six batches of 50 fruits (for analysis in each time: day 0, 5, 10, 15, 20, 25 and 30 day) and stored at 25 °C and 68 % RH, and their physicochemical, antioxidant, and textual characteristics were determined every five days for 30 days.

 

Evaluation of the physicochemical properties

The moisture, ash, reducing sugars, °Brix, titratable acidity, pH, total carotenoids and vitamin C were analyzed by the method described by the Official Methods of Analysis (AOAC, 1995). The a_w of each sample was obtained using an Aqualab (Decagon Devices, model series 3, US). Analysis of the color of the jalapeño pepper was determined using a colorimeter (ColorFlex V1-72, Hunter Lab, US). Through the direct reading of the pericarp of three peppers at each sampling, L*, a*, b*, Chroma, and hue angle (°Hue) were evaluated. The browning index and the total color change (ΔE) were determined. In order to quantify total polyphenols, the method described by Singleton, Orthofer, and Lamuela (1999) was used. The calibration curve was performed in a gallic acid standard solution at concentrations of 0.2, 0.6, 1.0, 1.4, and 1.6 mg·mL ^-1 (R² = 0.980). The separation identification and quantification of capsaicin and capsaicinoids were performed by the method used by Manirakiza, Covaci, and Schepens, (2003).

Texture analysis was conducted using the texture analyzer TA-XT-2i (Stable Micro Systems, UK) with a load cell of 5 kg. The data were processed using Texture Expert Exceed Software, version 1.00 (UK). A penetration test was performed with a needle probe of 2 mm, a pretest speed of 1 mm·s^-1, a test speed of 0.5 mm·s^-1, and a post-test speed of 0.3 mm·s^-1. The test was performed using the middle of the fruit, cut into 3 x 3 cm squares; the puncture was made at a distance of 8 mm in order to obtain the value in Newtons of the strength required to break the shell and obtain the maximum force for the fruit at 8 mm from the pulp.

 

Evaluation of antioxidant activity

To evaluate antioxidant activity, the extract proposed by Oboh, Raddatz, and Henle (2009) was used, with 1 g of pepper homogenized in 10 mL of distilled water. To determine reducing power, the method of Yen and Gen (1995) was used. The absorbance was read at 700 nm. The reducing power was reported as the absorbance of each sample. Radical scavenging activity of free radicals by 2,2-diphenyl-1-picrylhydrazyl (DPPH) was determined following the methodology described by Lyana-Pathirana, Shahidi, and Alassalvar (2006). The β-carotene bleaching assay was determined through the β-carotene test by Oboh et al. (2009). The absorbance of the samples and control was measured at 470 nm using a spectrometer (Perkin-Elmer Lambda 40 UV/Vis, US) against a target consisting of a β-carotene-free emulsion.

 

Fatty acid and volatile compound determination

The profile of fatty acids present in the jalapeño pepper was determined in the oil extracted by the Soxhlet method as described by the AOAC (1995). Fatty acids were determined by converting the oil into methyl esters through the addition of BF₃, in accordance with the methods of López, Castellote, and López (2001). The technique used to determine volatile compounds in different states of jalapeño pepper was Headspace/gas Chromatography/mass spectrometry (GC/MC). In order to obtain the volatile compounds, 8.5 g of chili were placed into 50-mL vials, which were sealed with a polytetrafluoroethylene (PTFE)/Si cap. The Headspace was programmed at a temperature of 100 °C and an equilibrium time of 0.50 min. The injection was performed at an initial temperature of 250 °C with splitless injection, using an Agilent brand equipment, =model 122-5062 column DB-(5 %-phenyl)-methylpolysiloxane (length 60 m, diameter of 250 μm x 0.25 μm, maximum temperature 325 °C), initial flow 1.0 mL·min^-1, initial oven temperature 40 °C, and a maximum temperature of 280 °C.

 

Statistical analysis

The experimental unit corresponded to 50 randomly-selected fruits for each time of analysis. All analyzes were done in triplicate (n = 3). Data analysis was performed using the program Statistical Analysis System (2004), the analysis of variance (ANOVA) and the Tukey test (P ≤ 0.05). The experimental data are presented as the mean and standard deviation (SD).

 

RESULTS AND DISCUSSION

Physicochemical properties during jalapeño ripening

Table 1 shows the values of the physicochemical properties determined in jalapeño pepper (C. annuum var. annuum) analyzed every five days during 30 days of storage, in which it can be observed that the percentage of moisture content, ash, pH and water activity decreased according to the storage time. This can be attributed to an increase in metabolic reactions and the concentration of organic acids involved in the Krebs cycle during fruit ripening. Organic acids constitute the energy reserves, and are part of the metabolic reactions involved in the synthesis of pigments, enzymes, and other materials, as well as the degradation of pectin and cellulose, which is essential for the maturation process. Similarly to these properties, carbohydrates showed a significant increase (P ≤ 0.05) until day 15, which may be because most fruits accumulate starch during their early stages of development, and simpler sugars (°Brix) arise during ripening as a result of the activity of the enzymes α-amylase, β-amylase, and starch phosphorylase (Kays, 1997). The analysis of variance revealed that the moisture content, ash and carbohydrates had significant changes (P ≤ 0.05) between day 10 and 15 of storage, and other properties between day 15 and 20. It was also noted that all properties except ash showed no significant differences (P ≤ 0.05) between day 20 and 25 of storage.

On the other hand, color is one of the most important parameters for selecting most foodstuffs. Jalapeño pepper is consumed both unripe (green) and ripe (red), so it is important to evaluate the color in both states. Table 1 shows that there was a significant increase (P ≤ 0.05) in the parameters a* and b* between day 15 and 20 of storage, reflected visually as a change in the color from green to red, which is a feature corresponding to the beginning of maturation. The hue angle value also reflects the different states of maturation. The external appearance from day 0 until day 25 of storage under controlled conditions at 25 °C presented a total color change of 34.38 units, indicating a major change in the coloration. The stored samples showed no significant difference in total color change between day 5 and 15 (green pepper) and between day 20 and 30 of storage (red pepper). Their attractive red color is due to the presence of carotenoids, which have been reported to act as free radical scavengers (Deepa, Kaur, Goerge, Singh, & Kappor, 2007).

Capsaicin and dihydrocapsaicin contents were 91.29 mg·mL ^-1 and 76.16 mg·mL ^-1 in green pepper (day 0), respectively. These values were lower than those recorded for red pepper (day 30), containing 1,525.68 g·mL^-1 of capsaicin and 2,372.50 g·mL^-1 of dihydrocapsaicin. Studies have proved that capsaicinoid content is higher when green peppers mature, although the capsaicinoid content trends downward during senescence (Alvarez-Parrilla, de la Rosa, Amarowicz, & Shahidi, 2011).

The data on texture obtained by the penetration test for pepper in different ripeness states show that the fracture strength of the outer waxy layer of the pericarp decreased from an initial value of 1.57 N to 1.11 N, while the maximum force of the pulp decreased from 5.17 N to 2.88 N on day 30. These changes in texture may be due to the loss of water due to breathability and enzymatic changes or because the greater the loss of water, the greater the degradation of the pectin enzyme and the lower the force required to penetrate.

 

Component concentration during storage

Table 2 shows the concentration of some components (total carotenoids, vitamin C and polyphenol content) and the antioxidant activity (reducing power, DPPH radical scavenging activity and antioxidant activity as oxidation of β-carotene/linoleic) in the jalapeño pepper during storage. It is known that carotenoids provide in part the color of maturity (Paran et al., 2007). The total carotenoids content at the green maturity stage (day 0) was 1,754.90 ± 27.29 mg·100 g^-1 of fresh weight and at the red maturity stage (day 30), the total carotenoids content was 1,180.2 ± 10.91 mg·100 g^-1 of fresh weight; these values were higher than those reported by Menichini et al. (2009), who found 62.7 ± 5.5 to 362 ± 23.1 mg·100 g^-1 for mature peppers of the variety Lamuyo. Similar to the other components, total carotenoids presented two trends. From day 15 to day 30, there was a slight loss of total carotenes, probably due to the disappearance of chlorophyll and lutein during early maturation or the inhibition of their biosynthesis as a result of the transformation of chloroplasts into chromoplasts, reducing their functionality and blocking photosynthesis (Mínguez-Mosquera, & Hornero-Méndez, 1994). Subsequently, by day 15, there was a significant increase (P ≤ 0.05) to over double the value of day 0, until a concentration of 3,450 mg·100 g^-1 of fresh weight was reached, which decreased during storage until a concentration of 1,180 mg·100 g^-1 on day 30. This may be due to metabolic processes that give rise to the conversion of existing pigments and synthesis of new carotenoids (Roura, Moreira, Capriste, & del Valle, 2001).

Peppers are among the vegetables with the highest ascorbic acid content (Vanderslice, Higgs, Hayes, & Block, 1990; Marín, Ferreres, Tómas-Barberán, & Gil, 2004). In this study, a significant difference (P ≤ 0.05) in the ascorbic acid content of pepper was found during the 30-day ripening period. The ascorbic acid content varied from 95.1 mg·100 g^-1 on day 0 to 149.5 mg·100 g^-1 on day 25. These concentrations of ascorbic acid in green peppers are within the 46.6 to 243 mg·100 g^-1 range reported by several authors (Gibbs & O'Garro, 2004), which could indicate that there is a considerable variation in the levels of vitamin C among cultivars. This study found a significant increase (P ≤ 0.05) in ascorbic acid on day 15 compared with the content on day 0, 5 and 10, for which the content of vitamin C was significantly equal (P ≤ 0.05). Martínez, López, González-Raurich, and Bernardo (2005) found an increase of about 50 % in the ascorbic acid content of red pepper when studying the effect of the storage of C. annuum L., which can be attributed to the metabolism of carbohydrates, as there is an accumulation of sugars in mature fruits.

The jalapeño pepper is well known for being an excellent source of phenolic compounds, capsaicinoids, and ascorbic acid (Chuah et al., 2008; Topuz & Ozdemir, 2007). Phenolic content varied significantly (P ≤ 0.05) during the 30-day ripening period. The initial polyphenol value was 504.6 mg gallic acid·100 g^-1 of fresh weight, whereas on day 30, it was 349.8 mg gallic acid·100 g^-1 of fresh weight. Ripeness is one of the main factors that determine the content of phenolic compounds in fruits and vegetables. In this study, the jalapeño pepper had a lower polyphenol content on day 30 compared with day 0, which coincides the results of Marín et al. (2004), who reported high phenolic content for immature green chili, while the content in red immature and mature pepper was reduced by about four to five times. This is consistent with other authors who found that the polyphenol content decreased with the increase in fruit ripening, as determined by studying methanolic extracts of C. annuum var. acuminatum (Conforti et al., 2007). Previous studies have shown that the phenolic compound profile of pepper is related to its maturity stage and color, with the total flavonoid content decreasing during ripening and the amount of other phenolic compounds increasing (Zhuang, Chen, Sun, & Cao, 2012).

The antioxidant activity was evaluated using different techniques (Table 2). Reducing power measures the ability to donate an electron of an antioxidant. It was calculated by the intensity of the resulting blue-green solution, which absorbs at 700 nm (Balasundram, Sundram, & Samman, 2006). Therefore, an increase in absorbance is indicative of a high reducing power in the green pepper samples. Reducing power decreased during storage time and it showed a linear relationship (R² = 0.905) with the polyphenols content, indicating that polyphenols present in jalapeño pepper act as a reducing agent by reducing ferric ion (Fe³⁺) to ferrous ion (Fe²⁺) in this test. On the other hand, the percentage of inhibition of DPPH radical was determined in the aqueous extracts during the 30 days of storage of jalapeño pepper. Radical inhibition in the immature green state (day 0) was 19.42 %, while for the red state of maturity it was 58.35 %. These results agree with those of Matsufuji, Nakamura, Chino, and Takeda (1998), who conducted a study of differences in the antioxidant capacity between different colorations of the pericarp in Bell pepper (C. annuum L.) and found that the major inhibition of the radical was in the pericarp of red bell pepper (about 90 %) and the lowest capacity detected was found in green bell pepper (about 10 %). Red pepper extract showed a higher antioxidant capacity than green. The antioxidant capacity of red pepper has been attributed to its high levels of carotenoids, capsanthin and esters, including palmitic, myristic, and lauric, which also carry high antioxidant power (Cervantes-Paz et al., 2012). It can also be attributed to the synergistic action between the compounds and the presence of capsanthins and cryptoxanthin, mainly due to the system of conjugated double bonds capable of capturing free radicals (Young & Lowe, 2001).

For the measurement of oxidation of β-carotene, hexane extracts were made at a concentration of 1 g·mL^-1, in triplicate, from day 0 to day 30. It demonstrated that the addition of pepper extract from different storage days inhibited the oxidation of linoleic acid. The antioxidant activity of green jalapeño pepper (day 0) was 16.24 %, increasing to 60.79 % by day 10. Pepper extract showed greater antioxidant power on day 25 of storage (74.11 ± 0.14 %), probably due to the presence of capsaicin and hydrocapsaicin, which are absent in the other stages of maturation, and the increase in vitamin E content, as has also been reported by (Conforti et al., 2007).

 

Fatty acid and volatile compound profile

At the green maturity stage (day 0), 11 fatty acids were identified: dodecanioc acid, pentadecanoic acid, 9-hexadecenoic acid, hexadecanoic acid, heptadecanoic acid, 9,12-octadecadienoic acid, 9-octadecenoic acid, 9,12,15-octadecatrienoic acid, octadecanoic acid, eicosanoic acid, and docosanoic acid. Table 3 shows that 54.98 % of the fatty acids present in the fruit pericap were saturated, 5.15 % monounsaturated, and 39.87 % polyunsaturated. It is noteworthy that those found in a higher proportion were palmitic acid, linoleic acid (Ω6), and linolenic acid (Ω3). The high content of polyunsaturated fatty acids in Capsicum, particularly the essential fatty acids linoleic and linolenic, has been previously reported in other studies (Bekker, Ulchenko, & Glushenkova, 2002). Tetradecanoic acid was present only in the red state but not in the green state, and pentadecanoic acid, heptadecanoic acid and 9,12,15-octadecatrienoic acid were not detected at the red maturity stage. With respect to green pepper, there was a decrease in hexadecanoic and octadecanoic acids, and an increase in most of the fatty acids present, especially dodecanoic acid, with a sixfold increase by proportion, and 9-hexadecanoic acid, which increased fourfold by proportion. The acids found in a greater proportion in the sample for day 30 were palmitic acid and linoleic acid (Ω6). The percentage of saturated acids in red pepper pericap in the ripe state was 56.06 %, whereas 10.98 % was monounsaturated and 32.91 % was polyunsaturated.

There are significant changes (P ≤ 0.05) in capsaicinoids and aromatic compounds during the maturation process (Mazida, Salleh, & Osman, 2005). Furthermore, the presence of about 64 aromatic compounds has been reported in another variety of pepper (Luning, de Rijk, Wichers, & Roozen, 1994). Table 4 shows that during maturation under controlled conditions, eight compounds were formed. The percentage of ethyl alcohol, acetone, dimethyl sulfide, acetaldehyde, 3-methoxy-1-propene, hexane, pentanal, and toluene present in fresh jalapeño pepper (C. annuum var. annuum) is based on the 30 days of storage. Depending on the level of maturity, either unripe (green) or ripe (red), the aroma was different due to the difference in volatile compounds. One of these compounds, dimethyl sulfide, was present in greater quantity during the 30 days of maturation compared to other volatile compounds present. No significant differences (P ≤ 0.5) were found in the first 10 days, but thereafter a slight decrease occurred. Dimethyl sulfide is a compound formed by the hydrolysis of its precursor S-methylmethionine, which is a common amino acid present in plants (Sawamura, Shimoda, & Osajima, 1978). On the other hand, acetaldehyde was present only until day 30. It is produced by the biochemical reactions resulting from respiration in the fruit. With respect to acetone, it presents a greater proportion from day 15 on, and its presence may be due to the degradation of sugars and carotenes during the ripening process (Podd & Van Staden, 1998).

 

CONCLUSIONS

Some physicochemical properties of C. annuum var. annuum changed between 15 to 20 days of storage. The color of the pepper samples changed from green to bright red. Total carotenoids, capsaisin and vitamin C content increased during the first 15 days of storage, and the best antioxidant properties were found when the sample changed from green to bright red. In red pepper important functional fatty acids were found. The presence of volatile compounds depended on the state of maturation. The study suggests the nutritional benefit of consuming Jalapeño pepper in the red state because of enhanced functional properties.

 

ACKNOWLEDGEMENTS

The authors acknowledge the support provided by Food Development and Research Laboratory (L-IDEA) project 124229 and Mexico's National Science and Technology Council (CONACyT), which awarded the scholarship required to conduct this research within the Master in Food Science program at the University of Veracruz.

 

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