agronomy Article Influence of Soil Composition on the Profile and Content of Polyphenols in Habanero Peppers (Capsicum chinense Jacq.) Julio Oney-Montalvo 1, Alberto Uc-Varguez 1, Emmanuel Ramírez-Rivera 1,2 , Manuel Ramírez-Sucre 1 and Ingrid Rodríguez-Buenfil 1,* 1 Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco A.C. Sede Sureste, Tablaje Catastral 31264 Km. 5.5 Carretera Sierra Papacal-Chuburna Puerto, Parque Científico Tecnológico de Yucatán, Mérida 97302, Mexico; [email protected] (J.O.-M.); [email protected] (A.U.-V.); [email protected] (E.R.-R.); [email protected] (M.R.-S.) 2 Tecnológico Nacional de Mexico/Tecnológico Superior de Zongolica, Departamento de Innovación Agrícola Sustentable Km. 4 Carretera S/N, Tepetlitlanapa, Zongolica 95005, Mexico * Correspondence: [email protected]; Tel.: +52-3333455200 (ext. 4011) Received: 10 July 2020; Accepted: 18 August 2020; Published: 21 August 2020 Abstract: Capsicum chinense Jacq. obtained the designation of origin in 2010 due to the unique organoleptic properties given by the characteristics of soils in the Peninsula of Yucatán. So, the aim of this work was to investigate the effect of soil composition on the profile and concentration of polyphenols, antioxidant activity, and its relationship with the degree of maturity in habanero pepper (Capsicum chinense Jacq.). Pepper plants were grown in three soils named according to the Maya classification as: K’ankab lu’um (red soil); Box lu’um (black soil); and Chich lu’um (brown soil). The crops were cultivated in four different dates. The peppers were analyzed for antioxidant activity, profile and content of polyphenols. The results indicated that peppers grown in black soil had the highest concentration of total polyphenols (122.78 12.60 mg of gallic ± acid 100 g 1), catechin (61.64 7.55 mg 100 g 1) and antioxidant activity by DPPH (86.51 0.82%). − ± − ± Physicochemical characterization indicated that black soil has the highest concentration of organic matter (10.93 0.23%), nitrogen (52.01 7.05 mg kg 1), manganese (5.24 0.45 mg kg 1) and electric ± ± − ± − conductivity (2.32 0.16 d Sm 1) compared to the other soils evaluated. These results demonstrate ± − that the physicochemical composition of soils could be related to the biosynthesis of polyphenols in the habanero pepper. Keywords: polyphenols; soil; maturity; antioxidant activity; habanero pepper 1. Introduction Habanero pepper (Capsicum chinense Jacq.) is considered the main fruit species in the Yucatan Peninsula in Mexico, this pepper is internationally recognized for having a superior quality than those grown in other parts of the world due to its longer shelf life and high pungency [1]. These characteristics allowed to obtain the designation of origin in 2010 (Chile habanero de la península de Yucatán) by the “Mexican Institute of Industrial Property” (IMPI) and positioned it as a socio-economic reference in the region [2]. The soil and the climatic characteristics of the Yucatan Peninsula are considered factors that give properties to the habanero pepper grown in this region as flavor and color, which differentiates it from other peppers. Traditionally, pepper plants grown in the Yucatan Peninsula are cultivated in three main soils, named according to the Mayan classification as: (1) K’ankab lu’um (red soil); (2) Box lu’um (black soil); or (3) Chich lu’um (brown soil) [3]. These soils are characterized for having a different Agronomy 2020, 10, 1234; doi:10.3390/agronomy10091234 www.mdpi.com/journal/agronomy Agronomy 2020, 10, 1234 2 of 14 chemical and physical composition. The red color in the soil seems to be related to the formation of hematite produced by the oxidation of iron, whereas the black color could be associated with the high content of organic material. The red soil is characterized for being a rocky soil with a lower organic matter content compared to other soils in the area (black and brown soils), and with the ability to retain less moisture than the Box lu’um (black soil), which is characterized by being in the upper zones of the micro relief, making it higher in moisture retention, in addition to have high contents of organic matter and assimilable phosphorus. The Chich lu’um (brown soil) is characterized by being a gravel soil of reddish brown to black colors, in addition to have the ability to retain more moisture [3]. Phenolic compounds are considered one of the most important groups of secondary metabolites distributed all over the plants; these compounds have been widely studied in recent years due to different pharmacological effects, highlighting their antioxidant and anti-inflammatory activity [4]. Despite habanero pepper (Capsicum chinense Jacq.) having been mainly studied for its high content of capsaicinoids, which classifies it as one of the hottest peppers in the world [5], in literature are also found works studying the profile and content of polyphenols of habanero peppers [6]. In other work, Campos et al. [7] have shown habanero pepper as an important source of polyphenols, recommending its consumption and proposing the use of habanero pepper extracts to increase nutritional value. In peppers, profile and content of polyphenols are mainly related to plant genotype [8], but the degree of maturity and soil composition may play an important role [9,10]. Soils are a complicated physical, chemical and biological system that strongly influences the growth, development and quality of plants, affecting the synthesis and accumulation of secondary metabolites [11]. A clear example is the work done by Meckelmann et al. [12], who demonstrated that Peruvian peppers cultivars grown in different geographical location (subjected to different soils, temperatures, irrigations and 1 altitudes) showed different content of total polyphenols (27.7 mg of gallic acid g− in Chiclayo and 1 13.4 mg of gallic acid g− in Piura). On the other hand, a study has shown a significant effect of the degree of maturity in the concentration of metabolites in habanero pepper, reporting changes in the 1 1 concentration of polyphenols (782 5.8 mg 100 g− in immature peppers and 759 2.3 mg 100 g− in ± 1 ± mature peppers) and the antioxidant activity (97.1 0.97 µg mL− in immature peppers and 287 1 ± ± 2.57 µg mL− in mature peppers) [13]. Another example of this effect is shown in the work carried out by Howard et al. [14], who determined a higher concentration of total polyphenols, total flavonoids, luteolin and quercetin in mature habanero peppers. Accordingly, this work aimed to estimate the effect of soil composition on the profile and concentration of polyphenols, antioxidant activity, and its relationship with the degree of maturity in the habanero pepper. 2. Materials and Methods 2.1. Plant Growth Conditions The crops of habanero peppers (Capsicum chinense Jacq. ‘Jaguar’) were cultivated in four different dates of the year, 3 March 2017 (Crop 1), 2 May 2017 (Crop 2), 18 September 2017 (Crop 3) and 14 March 2018 (Crop 4), habanero pepper plants had an average growing cycle of 8 months, the date of harvest was selected based on the availability of peppers (>100) grown in the three soils and with the two degrees of maturity. The crops were harvested at 142 post-transplant day (PTD). The plants were developed in a greenhouse in Sierra Papacal, Yucatán in Mexico (CIATEJ, Sede Sureste). The greenhouse had a north-south orientation, a ridge height of 7.0 m, with a triple-layer plastic cover (25% shade), and lateral walls of high-density plastic anti-trips screens. The crops were composed by 300 polyethylene bags, filled with 12 kg of soil each (100 polyethylene bags with red soil, 100 with brown soil and 100 with black soil). Habanero plants were planted after 48 days from germination. Data Loggers were placed along the greenhouse to monitored temperature and relative humidity in the crops. Agronomy 2020, 10, 1234 3 of 14 Water from a local well was used for irrigation. Electric conductivity of the water oscillated from 2.8 to 3.4 mS. For fertilization, the methodology of Martínez-Estévez et al. [15] was used, which is recommended for habanero pepper cultivated in the soils of Yucatan. The fertilizer used after 10 post-transplant days (PTD) was the Triple 18 Ultrasol® (SQM, Santiago de Chile, Chile), that is a commercial fertilizer with a formula of 18N-18P-18K% (nitrogen-phosphorus-potassium); it was applied with the irrigation twice a week (12 g dissolved in 20 L of water). The micronutrients were applied spraying the commercial product Bayfolan® Forte (Bayer CropScience, Edo. de Mexico, Mexico) (24 mL diluted in 16 L of water) superficially on the leaves once a week. After 20 post-transplant days and before floral initiation, a growth regulator containing gibberellin, cytokinin, and auxin (Biozyme® TF, Arysta LifeScience, Guatemala, Guatemala) was applied (16 mL diluted in 16 L of water) once a week. Irrigation was applied sporadically (about twice a week) during the first 15 days after the transplant; subsequently, the irrigation frequency was maintained at 2 L per polyethylene bag, every third day. 2.2. Physicochemical Characterization of the Soil The physicochemical characterization of the soils was performed using the methods described below, analyzing three samples from each of the soils studied for each determination. 2.2.1. PH Measurement For pH measured, 10 g of soil were weighed, then mixed with 10 mL of distilled water for 5 s and left to suspend for 30 min [16]. Finally, the pH of the soils was performed by a pH-meter Thermo Scientific Orion Star A211. 2.2.2. Determination of the Percentage of Organic Matter The percentage of organic matter was determined by the Walkley and Black method [17].