Quality Responses of Sweet Pepper Varieties Under Irrigation and Fertilization Regimes

Abstract

Red sweet peppers are economically important since they are widely farmed and consumed worldwide. As a high-value crop, it has a significant impact on the horticulture economy. This study aimed to improve the quality of sweet pepper fruits (total polyphenols; chlorophyll A and B; lycopene, β-carotene, tannins, ABTS, DPPH, protein and 15N) using three hybrids—Kornelya F1, Kaptur F1 and Napoca F1—four fertilization methods (chemical, organic, biologic and unfertilized), and two irrigation regimes (5200 and 7800 m³·ha⁻¹, respectively). The results revealed substantial similarities between organic and conventional management practices. From a genetic point of view, ‘Kornelya’ cultivar reacted well with most compounds with antioxidant effects. This study revealed that peppers react positively when subjected to hydric and nutrient stress, with the fruits having the highest values for total polyphenols, chlorophyll A and B, lycopene, ABTS, and DPPH. Following the interactions between factors, ‘Kornelya’ reacted positively to organic and unfertilized methods with an irrigation regime of 5200 m³·ha⁻¹.

1. Introduction

Sweet pepper is a popular vegetable around of the world for nutritional compounds [1]. The species (Capsicum annuum L. ssp. annuum) is a Capsicum genus from the Solanaceae family, one a largest vegetable crops, used fresh or dried for culinary and processing [2,3]. Peppers have high nutritional value because of their antioxidant properties as well as other traits, such as flavor, color, and texture [4,5,6]. In most cases, secondary metabolites from pepper fruits are influenced by biotic and abiotic conditions [7,8]. This is why several vegetable fruits are highly valued not only for their nutritional value but also for their health benefits. The World Health Organization recommends a daily consumption of at least 400 g of vegetables and fruits [9]. Current agricultural practices prioritize yield over ecosystem sustainability and food production [10]. Reasons for this include rising consumer demand for healthier products and existing policies on sustainable food production, which prioritize organic farming approaches over chemical-intensive conventional cultivation [11].

China is the world’s largest producer of peppers, accounting for 38 million tons [12]. In recent years, Romania has consistently produced more than 135,000 tons each year. This constancy implies that Romania’s pepper-growing business is resilient, most likely due to factors such as favorable climatic conditions, technological advancements, and market demand. These characteristics support Romania’s position as a major player at the European market, with promising prospects for growth and sustainability [1,12], including crop production, which require less maintenance and are less prone to disease and pests than other crops from the Solanaceae family [13].

Consistently, horticultural research looking to understand the impact of irrigation regimes and growing techniques on the quantity and quality attributes of Solanaceum varieties has involved management and production practices, with the goal of identifying the critical parameters of fruit quality [14]. The quality of sweet pepper fruits is determined by the presence of polyphenol, lycopene, β-carotene, ascorbic acid, tocopherols, antioxidant activity [15,16,17,18], or amino acids [19], contents that differ by variety, nutrients, or irrigation etc. Pepper fruits’ compounds are beneficial for human health and are effective against cardiovascular disease, cancer, diabetes, neurological illnesses, and cataracts [7,20]. Phytochemicals are a class of physiologically active, non-nutritive substances found in many vegetables for fruits that have antioxidant activity and other health advantages [21]. Many studies have reported strong associations between the consumption of carotenoids and lycopene and a lower risk of cancer and coronary and cardiovascular diseases [7]. The positive effects of carotenoids are assumed to be due to their activity as antioxidants [22]. Tannins represent a wide group of compounds that can be found in fruits and vegetables. Tannins are also known as pro-anthocyanins that possess beneficial properties, such as antioxidant, antiaging, anticancer, anti-inflammatory, and anti-atherosclerotic effects, and protect the heart and blood vessels [23]. Given the rising demand from consumers for healthy products and existing policies promoting sustainable farming systems, organic cultivation is a viable alternative to traditional farming practices [24,25]. The consumption of these compounds has health benefits because of their antioxidant properties, offering high protection of cells from oxidative damage [26].

The effect of technological factors is directly reflected in the quality of the sweet pepper harvest. Pepper varieties differ in many morphological characteristics and their content of biologically active substances [1,27]. This direct link between yield and health has piqued the interest of plant breeders, who are focusing their research on genotypes with a high quality level [28]. As a result, it is critical to investigate the changes in different genotypes during maturity in various geographical areas to identify the optimum genotypes and techniques for achieving health advantages [1,28].

Fertilizers play an important role in improving the soil, environment, fruit quality, physiological growth, and photosynthesis of plants, the nutritional quality of fruits, and the contents of chlorophyll and total flavonoids [10]. Many studies from the literature highlight the special influence of fertilizing elements on the quality of pepper fruits [10,15]. The application of manure fertilizers has resulted in a good percentage of antioxidant activity (ABTS, DPPH) and phenols such as resveratrol, meta-coumaric acid, ortho-coumaric acid, clorogenic acid, caffeic acid, myricetin, rutin, luteolin-7-O-glucoside, and quercitin-3-O-rhamnoside [29], a type of phenolic compound; ascorbic acid, capsaicinoids, and carotenoids are among the chemicals that help against oxidative stress. In general, using an organic farming system is considered beneficial to the soil, the environment, and humans as a result of not using pesticides that are harmful to humans and the environment and thus obtaining safer fruits [30]. Fertilization is a vital aspect of agricultural productivity and can be classified into three types: chemical, biological, and organic. Chemical fertilizers are widely utilized in agriculture because their use generate high yield [31,32]. Alternatives, such as organic and biological fertilizers, are gaining popularity among producers and consumers because of their environmental friendliness. In this context, organic fertilizers including manure, algae, and biological fertilizers including microorganisms improve the quantity and quality of production [33]. In the last decade, much research has especially focused on the beneficial effect of biological fertilizers on the quality of the harvest. These fertilizers are thought to be more environmentally friendly than chemical fertilizers, which are overused and detrimental to the environment [34]. In the context of climate changes, drought, and salinization, irrigation systems focus on creating techniques that minimize water consumption or encourage the efficient use of water. The development of drip irrigation for greenhouses has significantly decreased the amount of water used for the irrigation of horticultural crops [33,34]. Vegetable crops have shown variations in the composition of specific nutritional components as irrigation regimes change in response to water availability [33,35]. Recent studies have shown that optimal irrigation determines the qualitative improvement of Solanaceae fruits in correlation with genotypes, growth conditions, and nutrition [33,36].

Compared to the previous research, our study focuses on the individual and combined effect of new cultivars compared to a domestic cultivar, three different nutrition methods (organic, biological and chemical) compared to an untreated version, and two irrigation regimes to improve the quality of long pepper fruits (ABTS, DPPH, total polyphenols; A and B chlorophyll; lycopene; and β-carotene, tannins, δ¹⁵N and protein).

2. Materials and Methods

2.1. Experimental Site

This study was conducted using three factors: 3 varieties, 4 fertilization regimes, and 2 irrigation regimes with three replications (n = 3). The experiment was carried out in a greenhouse via a split-plot design at the “V. Adamachi” Farm of Iasi University of Life Sciences (47°19′25″ N, 27°54′99″ E, 150 m altitude) during 2021–2022. Each experimental plot was represented by 12 plants for repetition, with 90 cm between rows and 35 cm between plants per row, with a total harvested area of 272 m² (Photos from experimental greenhouse are presented in Figure S1). The soil is characterized as a loam-clay chernozem with a pH of 7.20; an electrical conductivity (EC) of 482 µS·cm⁻¹, CaCO₃ of 0.42%, organic matter (OM) of 2.83%, C/N of 5.87, N total of 2.8 g·kg⁻¹, and P of 34 mg·kg⁻¹ were used for the experiment [36]. The experiment was conducted on a long cycle pepper crop from April to October (26 weeks). In rotation, the pepper crop followed after a cucumber crop that had no common diseases and pests, and the rotation system does not determine soil fatigue.

Description of red long sweet pepper (Capsicum annuum L. conv. annuum) cultivars, their market properties, cultivation requirements, and producers are presented in Table S1 in the Supplementary Materials.

Moreover, three different fertilization methods were used: chemical, organic, and biological, compared with an unfertilized version. Chemical fertilizers were applied to the soil at a dose of 800 kg ha⁻¹. Chemical nutrition used a complex of 400 kg·ha⁻¹ Nutrispore^® N:P:K -20:20:20, applied during the soil preparation, and 400 kg·ha⁻¹ Nutrispore^® N:P:K -8:24:24 (Agrofert, Ltd., Bucharest, Romania), applied two times during the vegetation period, when the first fruit reached 1 cm, with the last dose being administered when the fruit from the third level reached 1 cm. Organic fertilizer, represented by Orgevit^® (GVAMarcom Ltd., Galati, Romania), was applied in a dose of 2500 kg ha⁻¹. The organic manure was applied three times as follows: 50% of the total applied during soil preparation, 25% when the first fruit reached 1 cm, and the last dose (25%) when the fruit from the third level reached 1 cm. Biological fertilization with a Micoseed MB^® (Agrofert, Ltd., Bucharest, Romania), dose of 60 kg·ha⁻¹ was applied to the soil and during the vegetation period a 1.5 l·ha⁻¹ dose of Nutryaction^® (Agrofert, Ltd., Bucharest, Romania) was applied three times. The biological fertilizer was based on microorganisms and contains the following arbuscular mycorrhizal fungal spores: Claroideoglomus etunicatum, Funneliformis mosseae, Glomus aggregatum, and Rhizophagus intraradices. In addition, the product is complexed with fungi and bacteria belonging to the genera Trichoderma, Streptomyces, Bacillus, and Pseudomonas.

Two distinct irrigation regimes (IR) were implemented. Water was distributed using the farm’s drip irrigation system over the 26-week period, applying 200 m³·ha⁻¹ in variant 1 (IR1) and 300 m³·ha⁻¹ in variant 2 (IR2), resulting in a total doses of 5200 m³·ha⁻¹ (IR1) and 7800 m³·ha⁻¹ (IR2), respectively.

2.2. Materials and Sample Preparation

From each of the 24 variants, 10 fruits were collected when they reached physiological maturity (809 BBCH scale). The samples were chopped into small 1 cm pieces, homogenized, and freeze-dried using an ECO EVO freeze-dryer (Tred Technology S.R.L., Ripalimosani, Italy). The dried samples were powdered and stored at −80 °C until analysis [37]. Each statistic represents the mean of three replicates (n = 3). The flowchart of the sweet peppers analyzed is presented in Figure S2.

2.3. Chemicals and Materials Used in the Experiment

HPLC-grade methanol, formic acid, hydrochloric acid, acetone, hexane, and water were acquired from Panreac (Barcelona, Spain). Sodium carbonate, Folin–Ciocalteu reagent, gallic acid, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6 sulfonic acid) diammonium salt (ABTS), potassium persulfate, (+)-catechin, and vanillin were obtained from Sigma-Aldrich (Steinheim, Germany).

2.4. Hydrophilic Extraction

Hydrophilic extraction was performed using a solution of deionized water and methanol (20:80, v/v) containing 1% formic acid. A total of 0.2 g of freeze-dried material was extracted with 1 mL of extraction solvent after being sonicated in an ultrasonic bath for 10 min and centrifuged at 15,000 rpm for 15 min. The supernatant was collected, and the pellet was extracted again via the same technique. The samples were transferred to vials and kept at −80 °C until analysis. This extraction was tested for antioxidant activity, total phenolic compounds, and total condensed tannins. The total polyphenol content (TPC) was assessed via the Folin–Ciocalteu reagent in accordance with Slinkard and Singleton’s method. First, 10 μL of hydrophilic extract was combined with 175 μL of distilled water, followed by 12 μL of Folin–Ciocalteu reagent. After 3 min, 30 μL of 20% aqueous sodium carbonate solution was added. The samples were allowed to rest for 1 h before being read at 765 nm with a spectrophotometer and compared to a range of known quantities of similarly produced gallic acid standards. The results are presented as milligrams of gallic acid equivalents per 100 g of fresh weight (mg GAE·100 g⁻¹ f.w.) [37].

2.5. Antioxidant Activity

The antioxidant activity was determined via two distinct tests, ABTS and DPPH, with a Synergy HTX multimode microplate reader (Biotek Instruments, Winooski, VT, USA). The ABTS free radical scavenging activity of the phenolic extract was tested via the previously disclosed procedures of Biotek Instruments [37]. The antioxidant activity data are presented as mmol Trolox equivalents per 100 g dry weight (mmol TE 100 g⁻¹ d.w.). The DPPH method was adapted to a microplate reader [38]. Antioxidant activity was measured as mmol of Trolox equivalents per 100 g dry weight (mmol TE 100 g⁻¹ d.w.).

2.6. Analysis of Condensed Tannins

The evaluation of condensed tannins was performed via the method described by Deepa et al., 2007 [35] with minor changes. Briefly, hydrophilic extracts were mixed with a methanol vanillin solution (4% w/v) and concentrated hydrochloric acid for 20 min in the dark at room temperature. The absorbance was measured at 500 nm. The results are presented as milligram equivalents per 100 g of dry weight (mg TE·100 g⁻¹ d.w.).

2.7. Pigment Extraction and Analysis

We isolated lipophilic pigments following the protocol outlined by Nagata and Yamashita. In summary, 1 mL of a solvent mixture including hexane and acetone (4:6, v:v) was used to extract 0.2 g of freeze-dried material in the dark. The sample was then centrifuged for 15 min at 15,000 rpm. Using the same procedure, the pellet was again removed from the supernatant. Prior to analysis, the samples were placed in vials and stored at −80 °C [39].

The absorbance of the pigment extract was determined at 453, 505, 645, and 663 nm via a Synergy HTX multimode microplate reader (Biotek Instruments, Winooski, VT, USA). Nagata and Yamashita provided formulae for estimating chlorophyll A, chlorophyll B, β-carotene, and lycopene concentrations [39].

2.8. Protein Content Analysis

Protein content was determined by elemental analysis following the protocol performed by Muñoz-Redondo et al., 2023 [40]. About 6.5 g of dried pulp was weighed into tin capsules (3.3 × 5 mm, IVA Analysentechnik e. K., Dusseldorf, Germany). The determination of % N values was performed using a Flash EA elemental analyzer with TCD detector. A nitrogen to protein conversion factor of 6.25 was used to determine protein for each gram of material.

2.9. Determination of δ¹⁵N via EA-IRMS

All the peppers were sampled at the mature stage and homogenized by grinding and milling before analysis. The powdered materials were transferred into 2 mL Eppendorf tubes and kept at −18 °C until analysis. A total of 4 mg of freeze-dried sweet pepper was weighed into tin capsules (3.3 × 5 mm, IVA Analysentechnik e. K., Dusseldorf, Germany) to determine the δ¹⁵N values. ISODAT software (version 3.0 from Thermo Scientific, Bremen, Germany) was used to acquire and process the signals collected by the IRMS devices. The nitrogen isotope ratios are represented relative to the international standard ratio and marked in delta notation, but milliurity (mUr) can also be used to comply with the International System of Units (SI), according to the formula published in Brand [40]. The instrument was calibrated with the following international reference standards: IAEA N1 (ammonium sulfate, δ¹⁵N = 0.43‰), IAEA NO₃ (potassium nitrate, δ¹⁵N value of −4.70‰), and IAEA N₂ (potassium nitrate, δ¹⁵N value of 20.30‰). To control and assure the quality of the results, working standards were inserted into each sequence, which was evaluated every ten samples. The analytical uncertainty was 0.3‰.

2.10. Statistical Analysis

Univariate statistical analyses were carried out to identify differences between samples via Statistix v. 9.0 software. The data were subjected to analysis of variance (ANOVA), followed by a comparison of means via Tukey’s test.

To comprehensively analyze pepper fruit quality under different fertilization and irrigation systems, principal component analysis (PCA) was applied to simplify the complex quality data sets. The PCA provided valuable information on genotype responses, allowing us to compare fruit nutritional outcomes effectively. In addition, Pearson correlation analysis was used to gain a deeper understanding of the relationships between different traits and to explore how these traits collectively respond to different fertilization and irrigation strategies, thus facilitating a comprehensive understanding of the grading of the factors used.

3. Results

3.1. Influence of Variety on Sweet Pepper Quality

ABTS and DPPH tests revealed differences in antioxidant activity among sweet pepper types (p ≤ 0.05). ‘Kornelya’ has the highest values of ABTS and DPPH, followed by ‘Napoca’ and ‘Kaptur’. Even if there are differences in antioxidant capacity between varieties, ABTS does not show any significance in terms of the results obtained. ‘Kornelya’ presented higher levels of polyphenol, chlorophyll A and B, lycopene, and β-carotene than the other varieties. In terms of ¹⁵N content, the differences between cultivars are not significant. The protein content was also greater in the case of ‘Kornelya’, with 27% difference to ‘Napoca’. The data in Table 1 show that there were significant differences in tannin content among the three varieties used. Similar results were also obtained in other studies on horticultural species in protected areas [19,36].

3.2. Influence of Fertilizers on Sweet Pepper Quality

Significant differences (p ≤ 0.05) in antioxidant activity, chlorophyll levels, and other biochemical indicators were detected between the fertilization types. Compared with chemical fertilization, biological fertilization, organic fertilization, and the unfertilized version resulted in higher ABTS and DPPH levels. Similarly, compared with the other fertilization methods, the control resulted in greater levels of chlorophyll A and B. These findings indicate that control and organic fertilization improved the antioxidant capacity and chlorophyll content of sweet peppers. Similar results were also obtained with peppers or strawberries grown in greenhouses, but the values were different [41,42].

This study confirmed data from previous studies [40,43], which demonstrated that vegetables grown under chemical fertilization tend to have lower δ¹⁵N values. In our case, the mean value for δ¹⁵N of the samples was lower (6.6) than the values found for the biological, control and organic fertilization treatments (7.5, 7.5, and 7.4, respectively), where no fertilizers from chemical synthesis were used. IRMS is a powerful technique for organic vegetable traceability. The results obtained for protein content were not significant, regardless of the fertilization regime applied to the long pepper crop.

3.3. Influence of Irrigation on Sweet Pepper Quality

Irrigation regimes have a considerable effect on sweet pepper quality. Drip irrigation with 5200 and 7800 m³·ha⁻¹ highlights changes in antioxidant activity, phytochemical composition, and pigment concentration. The rational application of irrigation led to increased antioxidant activity and chlorophyll, β-carotene, and lycopene contents in peppers, demonstrating a positive relationship between water availability and quality. The data in Table 1 show that more water favors the primary compounds resulting from photosynthesis, particularly the N compounds, whereas a lower amount favors the secondary metabolism compounds (polyphenols, chlorophyll A and B, lycopene). Similar results have been obtained for other Solanaceae species, such as tomatoes [43,44].

3.4. Interaction Effect of Variety and Fertilization on Sweet Pepper Quality

The effects of pepper and fertilization methods resulted in significant changes in the antioxidant activity, pigment level, and tannin content (Table 2). Chemical, organic, and biological fertilization caused differences in all three types of varieties. Specifically, in the variants without fertilization and biological application, higher values of such indicator are noted in the plants’ fruits. The untreated version increased the antioxidant activity and pigment richness of the ‘Kornelya’ variety more than the organic version did.

In contrast, ‘Kaptur’ presented a lower tannin level regardless of the fertilization type. These findings imply that the interplay between variety and fertilization method has a substantial effect on the quality features of sweet peppers.

The interaction between variety and fertilization type significantly influenced the antioxidant activity and chlorophyll content of sweet peppers (p ≤ 0.05). For example, ‘Kornelya’ treated with organic fertilization and an irrigation regime of 5200 m³·ha⁻¹ presented the highest antioxidant activity and chlorophyll levels compared with those of the other combinations. In contrast, ‘Kaptur’ treated with chemical fertilizer presented antioxidative activity and a lower chlorophyll concentration. In the case of protein content, the values between the variants are low, and in the case of ¹⁵N, the differences obtained between cultivar and fertilization combination are insignificant. Similar results were obtained for tomatoes by other authors [14,45].

3.5. Interaction Effect of Variety and Irrigation on Sweet Pepper Quality

Data on the influence of cultivar and irrigation on long pepper fruit quality are presented in Table 3. The antioxidant activity determined by ABTS differed among the cultivar types and irrigation regimes. ‘Kornelya’ under 7800 m³·ha⁻¹ presented the highest value at 1.10 mg TE·100 g⁻¹ d.w. The pigment content also varied with ‘Kornelya’ and the highest values were recorded when the plants were irrigated with a lower amount of water at 5200 m³·ha⁻¹. However, the tannin concentration did not exhibit a consistent pattern among the genotypes under the different amounts of irrigation. These findings highlight the need to address both variety and irrigation level in pepper production to increase fruit quality. This is what research indicates. The data obtained are in line with other studies carried out in the past, which supports the findings of our previous study [46]. Satisfactory results were also obtained in the context of lower water use, suggesting that ‘Kornelya’ responds very well to lower irrigation conditions.

3.6. Interaction Effect of Fertilization and Irrigation on Sweet Pepper Quality

The effects of the interaction between fertilization and irrigation on several quality parameters in long peppers are presented in Table 4. For most of the compounds determined, fruit quality differs according to nutrients and irrigation, except for protein, for which the values obtained are not significant. The data in the tables highlight that higher values for chlorophyll and lycopene pigments are obtained in the untreated samples and those irrigated with a lower amount of water. β-Carotene is mainly produced by chemical fertilization when more water is used, and a relatively high tannin concentration is obtained in the presence of chemical fertilization and relatively low amounts of water. In general, chemical fertilization results in lower amounts of 15 N in the fruit than organic fertilization does, which stimulates greater amounts of protein.

3.7. Interaction Effect of Variety, Fertilization, and Irrigation on Sweet Pepper Quality

The effects of the interaction between genotype, fertilization, and irrigation on several quality parameters in pepper fruits are presented in Figure 1. For all analyzed parameters, cultivar, fertilization, and irrigation factors significantly improved fruit quality in regard to the levels of antioxidant compounds and pigments. The 15N values ranged from 6.2 in ‘Kornelya’ chemically fertilized and irrigated with the lowest irrigation standard (IR1), to 8.2 in the same cultivar in the control version irrigated with 7800 mc/ha. High values are found especially in the case of the organic fertilized variants with a higher irrigation regime, in this case 8.1.

In general, chemical fertilization results in lower amounts of 15 N in the fruit than organic fertilization does, which stimulates greater amounts of protein. It can also be seen from Figure 1 that protein assimilation is also a cultivar characteristic; ‘Kornelya’ has a higher protein content than ‘Kaptur’ and ‘Napoca’.

Regarding TPC, it can be noted that the content varies significantly according to the interaction between all three factors, from 3.8 mg GAE·100 g ⁻¹ d.w. in the case of ‘Kaptur’ fertilized biologically and irrigated with 5200 mc/ha, to 5.9 mg GAE·100 g ⁻¹ d.w. in the case of the Kornelya variety chemically fertilized and irrigated with 7800 mc/ha. It can be seen that TPC has higher values in the case of ‘Kornelya’, regardless of fertilization but with higher values of irrigation regime.

The antioxidant capacity analyzed by ABTS varies in lower limits, from 0.86 mg TE·100 g ⁻¹ d.w. in the case of ‘Napoca’ cultivar fertilized organically and irrigated with 7800 mc/ha and ‘Kaptur’ cultivar fertilized chemically and irrigated with IR2, to 1.22 mg TE·100 g ⁻¹ d.w. in ‘Kornelya’ in the control version and irrigated with 7800 mc/ha. This can be attributed either to the better nutrient stress adaptation of ‘Kornelya’ cultivar or better exploration of soil macro and microelement remnants from the previous crop.

Additionally, in the case of DPPH, the values of this parameter were higher and statistically determined values were found in ‘Kornelya’, irrespective of fertilization.

The data in the tables highlight that higher values for chlorophyll and lycopene pigments are obtained in the untreated samples and those irrigated with a lower amount of water in the ‘Kornelya’ cultivar; β-Carotene is mainly produced by chemical fertilization when more water is used for the same cultivar and a relatively high tannin concentration is obtained in the presence of chemical fertilization and relatively higher amounts of water.

4. Discussion

The current study investigated the effects of interactions among long pepper cultivars, irrigation regimes, and fertilization methods on the quality attributes of fruits. In the current context of restrictive technologies to protect the environment and obtain food-safe products, sustainable farming systems demand more restrictions regarding the use of chemical inputs. Significant information on how to increase pepper quality was obtained through extensive tests that includ antioxidant activity, chlorophyll levels, pigment concentrations, and other compounds with an essential role in human nutrition.

The comparison of three types of cultivars demonstrated the significance of genetic factors affecting sweet pepper quality. ‘Kornelya’ outperformed the other varieties in terms of the DPPH antioxidant levels, as well as pigments levels. These findings are consistent with prior research showing genetic diversity in phytochemical composition among different long pepper cultivars [35]. The fact that the highest values for the main pigments are present in ‘Kornelya’ fruits suggests that it is possible to obtain high-quality fruits, regardless of fertilization and irrigation. The ‘Napoca’ variety also produces nutrient-rich fruits, compare to ‘Kaptur’. The data presented in other works show that ‘Kaptur’ results in high yields [43], but its quality suffers mainly. The selection of a cultivar adapted to crops in protected areas guarantees that high-quality fruit can be obtained by choosing the best genotype. Data highlight the positive correlation between pigment content and antioxidant activity. Variations in antioxidant activity and chlorophyll levels could be due to genetic differences across types. This is what research indicates. The quality of fruits is affected by several factors, including their variety [41].

The results of a principal component analysis (PCA) further illustrate these relationships by visualizing the variance among the cultivars and treatments. The PCA biplot of the entire data set (Figure S3) highlights a strong positive correlation between antioxidant activity (ABTS and DPPH) and total phenolic content (TPC), particularly associated with ‘Napoca’-related samples. In contrast, ‘Kornelya’-related samples are aligned with higher levels of chlorophyll (A and B), lycopene, and β-carotene, reinforcing their superior pigment content. Meanwhile, ‘Kaptur’-related samples cluster toward the center of the biplot, indicating weaker associations with most quality-related variables.

The PCA biplots for individual cultivars (‘Napoca F1’, ‘Kaptur F1’, and ‘Kornelya F1’) further emphasize these distinctions (Figure S4). In ‘Napoca F1’, “Chemical × IR2” and “Organic × IR2” correlate with high TPC and antioxidant activity, while “Biologic × IR1” aligns with chlorophyll traits. For ‘Kornelya F1’, “Control × IR1” is linked to high chlorophyll, lycopene, and protein levels, while “Organic × IR2” and “Chemical × IR2” are associated with antioxidant activity and tannins. β-carotene and 15N are enhanced by “Organic × IR1” and “Biologic × IR2”. In ‘Kaptur F1’, “Control × IR2” clusters with chlorophyll traits, while “Chemical × IR2” and “Organic × IR1” align with β-carotene. Across all three cultivars, the PCA biplots demonstrate clear separations between treatments, illustrating how different management strategies concerning fertilization and irrigation regimes affect the biochemical parameters.

The choice of fertilization method had a significant effect on sweet pepper quality. Compared with organic or biological fertilization, chemical nutrition improves antioxidant activity. This may be due to the higher solubility of nutrients from synthetic fertilizers. These findings support previous research demonstrating the benefits of conventional fertilizers in improving plant physiological growth, nutritional quality, and antioxidant content [47]. The increased antioxidant capacity reported in chemically fertilized peppers suggests a possible mechanism by which conventional farming practices lead to improved nutritional quality and health benefits in agricultural goods. The increased level of nutritive compounds in the untreated variant can also be explained by the fact that the species benefit resiliently from nutrients from previous crops but also in response to nutrient-related antistress factors. In particular, the growth mechanisms of biological species and plants, particularly those subjected to stress, are accelerated as natural impulses [43,48]. Although chemical fertilization accelerates the total pigment content with repercussions on the antioxidant capacity, biological and organic fertilization is one of the most viable nutritive methods to obtain quality products (Figures S7 and S8).

The irrigation regime significantly influences pepper quality characteristics. In particular, the application of less irrigation improved the water application rate, resulting in increased antioxidant activity, phytochemical composition, and pigment concentration, and higher correlation between the main PCA (Figures S5 and S6). The positive relationship between irrigation intensity and quality features emphasizes the importance of water availability in promoting optimal plant physiological processes and nutrient uptake. Water is the main means of nutrient circulation in plants and the deposition of reserve substances in fruits. With the exception of chlorophyll and lycopene, the other compounds studied show small relative differences between the two watering standards, which means that even under slightly lower humidity conditions, the cultivars accumulate important antioxidant compounds [46,49], showing the benefits to increasing water efficiency and fruit quality [49].

Furthermore, the interaction impacts of variety, fertilization, and irrigation regime demonstrated the complexity of factors affecting the quality of pepper fruits. Specific combinations had synergistic benefits, increasing the antioxidant activity and chlorophyll concentration (Figure S9). This emphasizes the need to consider several agronomic parameters when developing optimal growing practices.

The data regarding the main analyzed compounds determined by the interaction between cultivar and fertilization show that they are positively influenced, especially in ‘Kornelya’, regardless of the type of fertilization, high values being obtained also in the non-fertilized version. Furthermore, a question can be raised: If the plants have not been fertilized, how is it that the main bioactive components are present in higher quantity? The answer can be justified physiologically because under stress conditions, plant metabolism changes in the sense that generative activity is more intense than vegetative activity, PCAs being directed to fruits (Figure S3). This may also be due to the fact that the plants have been grown on an undrained soil with a higher clay content, which has the ability to retain a higher amount of macro- and microelements, with a nutritive role, on the surface of the particle.

Data on the increase in pigment content in fruits under nutrient stress have also been presented by Brezeanu et al., 2022 [1]. The data increased 31.2% in the case of TPC and 20.2% in the case of ABTS, compared with chemically fertilized ‘Kaptur’. Additionally, in the case of the interaction between cultivar and lower fertilization regime, an increasing trend in antioxidant content was observed, mainly due to optimal water consumption, which indicates good adaptation of endemic cultivars. Greater differences are observed for chlorophyll and carotenoid pigments, the same being true for the control variant, which was irrigated with less water. With the exception of 15N, all PCA increased in ‘Kornelya’ under both irrigation regimes. Under the influence of fertilization and irrigation, the PCA are distributed unevenly, which is why specific technological measures can be taken to improve the quality of pepper fruits. The results obtained in the present study regarding the interaction effect on pepper fruit quality are the same as those reported for pepper [1,43] or tomato fruits [36,48].

Overall, the findings of this study have important implications for sustainable agricultural strategies aimed at increasing sweet pepper quality while reducing environmental effects. The use of ecologically friendly approaches, such as organic and biological fertilization and precision irrigation, appears to be a promising path for increasing crop nutritional content and antioxidant capacity. By explaining the complicated relationship between agricultural practices and sweet pepper quality, this study helps establish sustainable production strategies that benefit both human health and the environment.

These findings highlight the potential of sustainable agriculture to increase both human health and environmental sustainability.

The data from Supplementary Materials also highlight a positive correlation in the pepper fruit of PCA. Lower water stress and lack of fertilization for all varieties led to the accumulation of higher contents of antioxidant compounds, which means that even in the context of organic agriculture and climate change, local long pepper varieties are a viable solution from a nutraceutical point of view.

5. Conclusions

The study of the qualitative features of long pepper varieties grown under various irrigation regimes and fertilization systems has shed light on the intricate interplay between technological factors.

Varieties, irrigation, and fertilization measures strongly influence the nutraceutical quality of long peppers. Our study confirmed that ‘Kornelya’ reached in contents of total chlorophyll and carotenoid pigments, TPC, and antioxidant activity.

In the organic and untreated variants, there were notable positive effects on antioxidant activity and pigment contents. With the exception of TPC and protein, where chemical fertilization increased the content, organic and biological fertilization ensured the production of nutraceutical-rich fruits, even with a reduced but constant irrigation regime.

Additionally, when pepper plants are subjected to hydric and nutrient stress, they can accumulate greater amounts of antioxidant compounds through physiological mechanisms. This study revealed that under the influence of abiotic stress factors, such as irrigation and fertilization, sweet peppers have the ability to accumulate high amounts of antioxidant compounds in fruits. Finally, our study highlights the need for further research on the efficiency of different doses of organic and biological fertilizers to determine their impact on improving pepper fruit quality and production sustainability.

Author Contributions

Conceptualization, V.S., S.M.A.E. and J.M.M.-R.; methodology, V.S., J.L.O.-D., J.C.M. and J.M.M.-R.; software, V.S., G.-C.T., A.C. and S.M.A.E.; validation, V.S., J.L.O.-D., J.C.M. and J.M.M.-R.; formal analysis, S.M.A.E. and F.N.; investigation, V.S., G.-C.T., A.C., S.M.A.E. and F.N.; resources, V.S., J.L.O.-D., J.C.M. and J.M.M.-R.; data curation, V.S. and J.M.M.-R.; writing—original draft preparation, V.S.; writing—review and editing, V.S., G.-C.T. and J.M.M.-R.; visualization, V.S., G.-C.T., A.C., S.M.A.E. and F.N.; bibliography, S.M.A.E., G.-C.T., A.C. and F.N.; supervision, V.S., J.L.O.-D., J.C.M. and J.M.M.-R. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Acknowledgments

Thanks to Mihaela Rosca for her pertinent comments and statistical support.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figure and Tables

Figure 1. Influence of cultivar, fertilizer, and irrigation regime interaction on long sweet pepper quality. Chem—chemical; Bio—biologic; Org—organic; Ctrl—control; IR1—5200 m3·ha−1; IR2—7800 m3·ha−1. Within each column, a—higher value for each parameter. Values associated with different letters are significantly different according to Tukey’s test.

Figure 1. Influence of cultivar, fertilizer, and irrigation regime interaction on long sweet pepper quality. Chem—chemical; Bio—biologic; Org—organic; Ctrl—control; IR1—5200 m3·ha−1; IR2—7800 m3·ha−1. Within each column, a—higher value for each parameter. Values associated with different letters are significantly different according to Tukey’s test.

Table 1

Influence of the experimental treatments on long sweet pepper quality.

Variable	δ15N	Protein (%)	TPC (mg GAE·100 g−1 d.w.)	ABTS (mg TE·100 g−1 d.w.)	DPPH (mg TE·100 g−1 d.w.)	Chlorophyll A (mg·100 g−1 d.w.)	Chlorophyll B (mg·100 g−1 d.w.)	Lycopene (mg·100 g−1 d.w.)	β-Carotene (mg·100 g−1 d.w.)	Tannins (mg CE·100 g−1 d.w.)
Variety effects:
Kaptur F1	7.3	9.5 b	4.7 b	0.98	1.19 b	0.82 c	0.96 b	0.64 b	0.56 b	0.29 b
Kornelya F1	7.2	11.5 a	5.4 a	1.04	1.30 a	1.35 a	1.43 a	1.10 a	0.76 a	0.37 a
Napoca F1	7.3	9.0 b	5.2 a	0.99	1.27 a	1.04 b	0.76 c	0.55 c	0.51 c	0.28 b
p-value	ns	***	***	ns	***	***	***	***	***	***
Fertilization effects:
Chemical	6.6 b	10.1	5.3 a	1.03	1.24 ab	0.81 c	0.84 b	0.74 b	0.83 a	0.33 a
Biological	7.5 a	9.8	4.8 b	0.96	1.22 b	1.23 b	0.93 b	0.70 bc	0.51 c	0.27 b
Organic	7.4 a	10.0	4.9 b	0.98	1.24 ab	0.79 c	0.83 b	0.63 c	0.73 b	0.32 a
Control	7.5 a	10.2	5.3 a	1.04	1.32 a	1.43 a	1.59 a	0.98 a	0.37 d	0.32 a
p-value	***	ns	***	ns	*	***	***	***	***	***
Irrigation regimes:
IR1	7.2 b	9.5 b	5.0 b	0.99	1.29 a	1.27 a	1.18 a	0.84 a	0.56 b	0.31
IR2	7.4 a	10.5 a	5.2 a	1.01	1.22 b	0.86 b	0.92 b	0.69 b	0.66 a	0.31
p-value	***	***	*	ns	**	***	***	***	***	ns

IR1—5200 m³·ha⁻¹; IR2—7800 m³·ha⁻¹. The data in the table are the average values for each variable. Within each column: ns—no statistically significant difference according to Tukey’s test at p > 0.05 and a—higher value for each parameter. *—significant difference; values associated with different letters are significantly different according to Tukey’s test at p = (0.01–0.05). **—very significant difference; values associated with different letters are very significantly different according to Tukey’s test at p = (0.001–0.01). ***—extremely significant difference; values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.

Table 2

Influence of cultivar and fertilization regime on long sweet pepper quality.

Variable	δ15N	Protein (%)	TPC (mg GAE·100 g−1 d.w.)	ABTS (mg TE·100 g−1 d.w.)	DPPH (mg TE·100 g−1 d.w.)	Chlorophyll A (mg·100 g−1 d.w.)	Chlorophyll B (mg·100 g−1 d.w.)	Lycopene (mg·100 g−1 d.w.)	β-Carotene (mg·100 g−1 d.w.)	Tannins (mg CE·100 g−1 d.w.)
Kaptur F1 × Chemical	6.6	9.3 de	4.8 cd	0.94 b	1.16 bc	0.82 e	0.97 bc	0.75 cde	0.75 c	0.29 bc
Kaptur F1 × Biologic	7.5	9.4 de	4.4 d	1.01 ab	1.24 abc	0.79 e	0.89 bc	0.57 fg	0.41 g	0.29 bc
Kaptur F1 × Organic	7.5	9.5 de	4.5 d	0.97 ab	1.15 bc	0.56 f	0.73 c	0.52 g	0.68 cd	0.30 bc
Kaptur F1 × Control	7.5	10.0 bcde	5.0 bcd	1.01 ab	1.21 bc	1.10 cd	1.26 b	0.71 def	0.42 g	0.27 c
Kornelya F1 × Chemical	6.6	11.3 abc	5.8 a	1.13 a	1.27 abc	0.82 e	0.87 bc	0.95 b	1.17 a	0.39 a
Kornelya F1 × Biologic	7.6	11.5 ab	5.2 abc	0.91 b	1.29 abc	1.32 c	1.08 bc	0.92 bc	0.70 cd	0.32 b
Kornelya F1 × Organic	7.3	11.1 abcd	4.9 bcd	1.04 ab	1.32 ab	0.93 de	0.98 bc	0.81 bcd	0.96 b	0.38 a
Kornelya F1 × Control	7.4	12.2 a	5.6 a	1.09 ab	1.33 ab	2.33 a	2.79 a	1.71 a	0.22 h	0.39 a
Napoca F1 × Chemical	6.6	9.8 cde	5.3 abc	1.01 ab	1.28 abc	0.79 e	0.68 c	0.51 g	0.58 de	0.31 bc
Napoca F1 × Biologic	7.5	8.5 e	4.8 cd	0.96 ab	1.12 c	1.59 b	0.83 c	0.61 efg	0.43 fg	0.21 d
Napoca F1 × Organic	7.5	9.6 cde	5.4 ab	0.94 b	1.26 abc	0.90 de	0.79 c	0.55 fg	0.55 ef	0.28 bc
Napoca F1 × Control	7.6	8.3 e	5.4 abc	1.03 ab	1.41 a	0.86 e	0.73 c	0.51 g	0.47 efg	0.30 bc
p-value	ns	*	**	*	**	***	***	***	***	***

The data in the table are the average values for each combination of variety and fertilizer. Within each column, ns—no statistically significant difference according to Tukey’s test at p > 0.05 and a—higher value for each parameter. *—significant difference; values associated with different letters are significantly different according to Tukey’s test at p = (0.01–0.05). **—very significant difference; values associated with different letters are very significantly different according to Tukey’s test at p = (0.001–0.01). ***—extremely significant difference; values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.

Table 3

Influence of cultivar and irrigation regime on long sweet pepper quality.

Variable	δ15N	Protein (%)	TPC (mg GAE·100 g−1 d.w.)	ABTS (mg TE·100 g−1 d.w.)	DPPH (mg TE·100 g−1 d.w.)	Chlorophyll A (mg·100 g−1 d.w.)	Chlorophyll B (mg·100 g−1 d.w.)	Lycopene (mg·100 g−1 d.w.)	β-Carotene (mg·100 g−1 d.w.)	Tannins (mg CE·100 g−1 d.w.)
Kaptur F1 × IR1	7.2 bc	9.0	4.7	1.01 ab	1.22	0.87 d	0.93 bc	0.63 c	0.49 d	0.29 b
Kaptur F1 × IR2	7.3 ab	10.1	4.7	0.96 b	1.16	0.76 d	0.99 bc	0.65 c	0.64 c	0.28 b
Kornelya F1 × IR1	6.9 c	11.3	5.2	0.99 ab	1.32	1.66 a	1.84 a	1.43 a	0.95 a	0.37 a
Kornelya F1 × IR2	7.6 a	11.8	5.5	1.10 a	1.29	1.03 c	1.03 b	0.77 b	0.57 c	0.37 a
Napoca F1 × IR1	7.4 ab	8.3	5.2	0.98 b	1.34	1.27 b	0.77 c	0.45 d	0.24 e	0.26 b
Napoca F1 × IR2	7.2 b	9.8	5.3	0.99 ab	1.20	0.80 d	0.75 c	0.64 c	0.78 b	0.29 b
p-value	***	ns	ns	*	ns	***	***	***	***	*

IR1—5200 m³·ha⁻¹; IR2—7800 m³·ha⁻¹. The data in the table are the average values for each combination of variety and irrigation. Within each column, ns—no statistically significant difference according to Tukey’s test at p > 0.05 and a—higher value for each parameter. *—significant difference; values associated with different letters are significantly different according to Tukey’s test at p = (0.01–0.05). ***—extremely significant difference; values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.

Table 4

Influence of nutrient system and irrigation regime on long sweet pepper quality.

Variable	δ15N	Protein (%)	TPC (mg GAE·100 g−1 d.w.)	ABTS (mg TE·100 g−1 d.w.)	DPPH (mg TE·100 g−1 d.w.)	Chlorophyll A (mg·100 g−1 d.w.)	Chlorophyll B (mg·100 g−1 d.w.)	Lycopene (mg·100 g−1 d.w.)	β-Carotene (mg·100 g−1 d.w.)	Tannins (mg CE·100 g−1 d.w.)
Chemical F1 × IR1	6.5 e	9.9	5.5 a	1.05	1.31 abc	0.96 cd	0.91 bc	0.72 bcd	0.64 c	0.37 a
Chemical × IR2	6.8 de	10.3	5.1 abc	1.01	1.17 c	0.66 f	0.77 c	0.76 bc	1.03 a	0.29 cde
Biologic × IR1	7.3 bc	9.1	4.6 cd	0.94	1.24 abc	1.53 b	0.97 bc	0.77 b	0.59 c	0.26 e
Biologic F1 × IR2	7.7 ab	10.5	5.0 bc	0.98	1.19 abc	0.93 cd	0.90 bc	0.63 cd	0.43 d	0.29 de
Organic × IR1	7.7 ab	9.4	4.5 d	0.99	1.31 ab	0.75 ef	0.82 c	0.66 bcd	0.87 b	0.32 bcd
Organic × IR2	7.2 cd	10.7	5.4 ab	0.98	1.18 bc	0.84 de	0.84 c	0.60 d	0.59 c	0.32 bc
Control × IR1	7.1 cd	9.7	5.4 ab	0.99	1.31 ab	1.83 a	2.01 a	1.19 a	0.14 e	0.29 cde
Control × IR2	7.9 a	10.6	5.3 ab	1.10	1.32 a	1.03 c	1.18 b	0.77 b	0.60 c	0.35 ab
p-value	***	ns	***	ns	*	***	***	***	***	***

IR1—5200 m³·ha⁻¹; IR2—7800 m³·ha⁻¹. The data in the table are the average values for each combination of fertilizer and irrigation. Within each column, ns—no statistically significant difference according to Tukey’s test at p > 0.05 and a—higher value for each parameter. *—significant difference; values associated with different letters are significantly different according to Tukey’s test at p = (0.01–0.05). ***—extremely significant difference; values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae11020128/s1, Figure S1: Photos from sweet pepper field. Figure S2: Sweet pepper flowchart analysis. Figures S3–S9: PCS and person correlation. Table S1: Cultivar description. Table S2: F and p-value for all analyses.

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