Impact of Storage on Bioactive and Toxic Compounds in Jicama (Pachyrhizus erosus) Tubers: Effects on Thyroid Cancer and Inflammatory Responses

Abstract

Background

Jicama (Pachyrhizus erosus) tubers contain isoflavones and phenolic acids with potential chemopreventive and anti-inflammatory effects. This study analyzed bioactive and toxic compounds in fresh jicama tuber (flesh and peel) and assessed changes during freezing for 3 and 4 months. Antioxidant, cytotoxic, and anti-inflammatory effects were evaluated on human thyroid cancer (FTC133, 8505 C, TPC1), and normal cells (Nthy-ori 3 − 1), and RAW 264.7 macrophages.

Methods

High-performance liquid chromatography (HPLC) identified active compounds. Antioxidant activity was tested using FRAP and DPPH assays. Cytotoxicity was evaluated using the MTT assay, while anti-inflammatory effects were measured via TNF-α, IL-6 (ELISA), and nitric oxide levels (Griess assay).

Results

Fresh peel contained the highest levels of isoflavones (mg/100 g dry weight) - biochanin A; 52.5, daidzein; 23.0, genistein; 2.6) and phenolic acids (chlorogenic; 61.7, isochlorogenic acids; 95.8), which declined significantly after freezing. No rotenone was detected. Peel extracts exhibited the strongest cytotoxicity against thyroid cancer cells, particularly FTC133, showing dose-dependent inhibition of cell viability. However, they also exhibited cytotoxicity against normal thyroid cells, highlighting potential risks. Flesh extracts showed weaker cytotoxic effects but demonstrated slightly stronger anti-inflammatory activity than peel extracts. Both extracts effectively reduced TNF-α, IL-6, and nitric oxide levels in RAW 264.7 macrophages. Storage time during freezing had no significant impact on anti-inflammatory activity or cytotoxic potency, but it significantly reduced antioxidant activity.

Conclusion

Jicama peel is richer in bioactive compounds than the flesh and exhibits strong cytotoxic effects on thyroid cancer cells, although it also affects normal cells. Freezing reduces phytonutrient content and antioxidant potential but does not alter anti-inflammatory efficacy.

Introduction

Pachyrhizus erosus (L.) Urb., commonly known as jicama, is a climbing plant of the Fabaceae family, cultivated for its edible tuber. It is unique example of Fabaceae vegetables, as in the majority of these plants, the seeds and/or the sprouts, but not tuber, are eaten as the significant element of human diet [1–3]. This crop is mostly known in Latin America and Asia, for its versatility in both culinary and medicinal applications, while in other regions, especially in Europe, this vegetable is poorly recognized or even completely unknown. Jicama tubers are notable for their rich composition of carbohydrates and fibers, including starch, sucrose, pectins, cellulose, xyloglucans, inulin, fructooligosaccharides, fructose, and glucose; proteins, fats, vitamins, and minerals, offering multiple health benefits as a functional food. Inulin is found in concentrations up to 13.4%, making jicama a valuable prebiotic source for industrial applications [4–7]. Jicama tubers contain low but varied profile of proteins, the content of which decreases as the plant matures. The tubers are especially rich in aspartic acid, providing a unique amino acid profile, including essential ones like histidine, lysine, and leucine compared to other root vegetables [4, 7]. Though generally low in fats, jicama tubers contain beneficial fatty acids, specifically comprising palmitic, stearic, oleic, and linoleic acids. Jicama is rich in several vitamins, with a particularly high amount of vitamin C, it also contains significant levels of choline as well as smaller amounts of vitamins E, and different vitamins B. Key minerals in jicama tubers include potassium, calcium, magnesium, phosphorus [7].

Phytochemical studies on the leaves, tubers, and seeds of jicama have led to the identification of over 50 bioactive compounds across various chemical classes, with the predominance of flavonoids and isoflavones (genistein, daidzein), triterpenoids (kaikasaponin III, phaseoside IV), organic acids, and volatile organic compounds [1, 8, 9]. These compounds contribute to the plant’s functional and therapeutic properties, making jicama a potential source of bioactive ingredients for health applications [1]. Moreover, this plant contains rotenone, a natural insecticidal compound that renders parts of the plant toxic if not properly processed [10]. It is considered harmful due to its potent neurotoxic effects. Chronic exposure to rotenone has been linked to the development of Parkinson’s disease-like symptoms in experimental models, primarily through inhibition of mitochondrial complex I and induction of oxidative stress. Due to these serious health concerns, the presence of rotenone in food matrices requires careful monitoring to ensure consumer safety [11].

Traditional uses of jicama include remedies for skin conditions and as an anti-parasitic agent [8]. Some studies have shown that the isoflavones in jicama tubers exhibit estrogen-like effects. Experiments with mice demonstrated that administration of the tuber led to the increased endometrial proliferation and growth in uterine and ovarian tissues, suggesting an estrogenic effect. A study using an ethanol extract of tubers in rats also showed enhanced endometrial and ovarian follicle development, particularly in animals with induced hypoestrogenic conditions [12]. Estrogens have been shown to stimulate the proliferation of thyroid cells in vitro, indicating that they may contribute to thyroid gland growth under certain conditions. Moreover, estrogen itself can promote the growth of human thyroid cancer cells and their proliferation through either ER-dependent or ER-independent pathways [13, 14]. Whether isoflavones may inhibit the growth of human thyroid cancer and/or goiter remains to be explored [15]. It is known that legume vegetables may have influence on thyroid function. Although jicama belongs to the legume family and contains isoflavonoid compounds, their structure and concentration differ from those predominant in soy (e.g., genistein, daidzein). Current evidence does not clearly establish whether jicama-derived isoflavones exert comparable effects on thyroid hormone metabolism, particularly in the context of iodine deficiency and this aspect needs further study.

The tubers are primarily consumed raw or cooked, with preparation methods varying globally. Fresh tubers are commonly served with lime and chili or added to salads and soups. These culinary uses reflect the plant’s global economic value and jicama’s nutritional composition makes it a valuable dietary option, rich in essential nutrients and bioactive compounds with prebiotic, antioxidant, anti-inflammatory and chemopreventive properties, enhancing its potential as a functional food.

This study aims to comprehensively analyze the distribution of isoflavones, phenolic acids, and rotenone in the skin and flesh of fresh jicama tubers, addressing the limited research on the bioactive profile of this crop. Furthermore, the study evaluates the changes in these compounds during storage, a largely underexplored area in terms of their preventive potential. In addition, the research investigates the chemopreventive effect, including cytotoxic, anti-inflammatory, and antioxidant activity, directed to thyroid cancer cell lines to provide an understanding of jicama’s functional potential.

Materials and Methods

Material

Jicama tubers (Pachyrhizus erosus) were obtained from Juárez local market in northern Mexico in April 2023. Half of the tubers were peeled, and the water content was measured in both the peel and flesh. The remaining tubers were frozen at -20 °C for periods of 3 and 4 months. After these storage periods, the tubers were peeled again, and water content was re-measured in the peel and flesh. Subsequently, extraction of the skin (S) and flesh (F) (both fresh (F) and after 3 and 4 months of freezing (FR)) was conducted using a Soxhlet apparatus for 3 h, as described previously [16]. The part of the resulting methanolic extracts were stored in freezer before the HPLC analysis and evaluation of the antioxidant activity, while the rest were evaporated, using Rotavapor^® R-300 system coupled with recirculating chiller system F-305 (Buchi, Switzerland) for cellular studies. The obtained dry extracts were dissolved in DMSO.

Qualitative and Quantitative Analysis of Active Compounds

Isoflavones and phenolic compounds analysis.

The quantification of isoflavones and phenolic acids followed an established procedure [17], utilizing a Dionex HPLC system equipped with a PDA 100 UV-VIS detector and a Hypersil Gold C-18 column (5 μm, 250 × 4.6 mm, Thermo EC). The analysis was conducted in gradient mode with two solvents: a 1% aqueous solution of formic acid (solvent A) and acetonitrile (solvent B), with 5–60% solvent B over 60 min, and flow rate of 1 mL/min. Detection was monitored at wavelengths of 254 and 285 nm. Identification of individual isoflavones and phenolic acids in jicama peels and fleshes methanolic extracts was based on the comparisons of the retention times and UV spectra with authentic reference standards, which included biochanin A, daidzein, formononetin, genistein, glycitein, and ononin, and different phenolic acids: p-coumaric acid, cinnamic acid, gallic acid, ferulic acid, vanillic acid, chlorogenic acid, sinapic acid, protocatechuic acid, gentisic acid, syringic acid, caffeic acid. Standards for HPLC analysis were purchased from Fluka Chemie. The concentration of each isoflavone and phenolic acid was calculated from the peak areas in relation to standard calibration curves, generated using reference standards in the range of 0.06–1.00 mg/mL. Each sample was analyzed in triplicate, and results were expressed as mean values in mg/100 g of dry weight of tubers.

Rotenone Analysis

The presence of rotenone was analyzed in the extracts, prepared as described in the section Material, by means of HPLC, using the same liquid chromatograph described above, with analytical conditions described previously [18]. Briefly, the analysis was performed in the isocratic mode, with water and acetonitrile (1:1) as mobile phase, at detection wavelength 290 nm. Standard rotenone was used to identify the presence of the compound in the extracts, with calibration curve prepared within the range of 0.06 to 1.00 mg/mL, and the limit of detection 0.02 mg/mL. Time of analysis was 20 min, and the retention time for the standard rotenone was 14.1 min.

Determination of the Antioxidant Activity

Total antioxidant capacities were determined using two complementary tests: DPPH (1,1-Diphenyl-2-picrylhydrazyl), and FRAP (Ferric-Reducing/Antioxidant Power), as previously described in details [19]. DPPH solution (3.9 mL, 25 mg/L) in methanol was mixed with the tested extracts (0.1 mL). The reaction was monitored at 515 nm until the absorbance was stable. The results were expressed as µM Trolox/100 g dw [19]. FRAP assay measures the ability to reduce ferric-tripyridyltriazine (Fe³⁺-TPTZ) to a ferrous form (Fe²⁺), which absorbs light at 593 nm. The reducing ability of the sample was expressed in ferrous ion equivalents (micromol of Fe²⁺ per 100 g of plant dry weight) within the standard incubation period of 15 min after reagent addition [19]. All analyses were performed in three replicates using 48-well plates and automatic reader (Synergy-2, BioTek Instruments Inc., Winooski, VT, USA), with syringe rapid dispensers.

Cytotoxic Activity

Human thyroid cancer (FTC133, TPC1, 8505 C) and normal epithelial (Nthy-ori 3–1) cells, used in the study, were grown grown at conditions previously described [20]. The examined extracts were diluted in the culture media from freshly made stock solution in DMSO (10 mg/mL) to the working concentrations (from 0 to 100 µg/mL). Cell viability was determined by MTT assay, as described previously [20]. Briefly, cells were seeded onto 96-well plates (1.5 × 10⁴ cells/well) and cultured for 24 h. Then, different concentrations of the tested extracts of jicama was added and the cells were incubated for 48 h, following the determination of cell viability. Doxorubicin was used as a reference standard. The absorbance was measured at 490 nm using a Biotek Synergy microplate reader (BioTek Instruments Inc., Winooski, VT, USA). All analyses were performed in triplicate, the results are expressed as % of cell viability (mean ± SD).

In Vitro Inflammation Model

For the anti-inflammatory assays, RAW 264.7 murine macrophages were seeded in 96-well plates at a density of 1.5 × 10⁵ cells per well. The cells were pre-treated with jicama tuber extracts at concentrations of 50 and 100 µg/mL for 1 h, after which 10 ng/mL of lipopolysaccharide (LPS) was added to induce an inflammatory response, following the protocol by Paśko et al. [20]. Dexamethasone (0.5 µg/mL) served as a positive control. Incubation continued for an additional 24 h, and the cell culture supernatants were collected for subsequent analysis.

Determination of Nitric Oxide Levels

Nitric oxide levels in the cell culture supernatants were measured using the Griess Reagent Kit from Promega Corporation (Madison, WI, USA), following the manufacturer’s protocol. Measurements were taken in triplicate using a Biotek Synergy microplate reader (BioTek Instruments Inc., Winooski, VT, USA) and expressed as a percentage relative to the LPS-treated control.

Analysis of TNF-α and IL-6

Levels of TNF-α and IL-6 cytokines in the cell culture supernatants were determined using Human ELISA kits from Bioassay Technology Laboratory (Shanghai, China), according to the kit instructions. Each measurement was conducted in triplicate, using a BioTek Instruments microplate reader (Winooski, VT, USA), and results were presented as a percentage relative to the LPS control group.

Statistical Analysis

All experiments were conducted in triplicate, with results reported as mean values ± standard deviation (SD). Statistical significance between groups was evaluated using a one-way analysis of variance (ANOVA), followed by Tukey’s post hoc test. Differences were considered statistically significant at p-values ≤ 0.05. These analyses were performed using STATISTICA software v. 13.3 (TIBCO Software Inc., Palo Alto, CA, USA).

Results

Active Compounds in Jicama Tubers

Biochanin A, followed by daidzein, was the predominant isoflavone found in the examined samples, while genistein was determined only in small amounts (Table 1). Interestingly, the compounds were detected in all peels’ samples, but not in the flesh samples, with the exception of fresh flesh which contained only small amounts of daidzein. Freezing process significantly reduced the content of the isoflavones, as twofold decrease was noted after 3 months of freezing, in comparison to fresh samples. Moreover, additional one month of freezing resulted in significant decrease in biochanin A in the skin, down to 15.6 mg/100 g dw.

Table 1.

The concentration of active compounds and antioxidant capacity of fresh (F) and frozen (FR) Jicama skin (S) and flesh (F)

	SF	FF	SFR(3 M)	FFR(3 M)	SFR(4 M)	FFR(4 M)
Isoflavones mg/100 g dw ± SD n = 3
Daidzein	23.0 ± 2.0abc	2.2 ± 1.0ad	8.8 ± 0.0bd	Nd	7.1 ± 1.1cd	Nd
Genistein	2.6 ± 0.6a	Nd	1.2 ± 0.5a	Nd	Nd	Nd
Biochanin A	52.5 ± 6.2ab	Nd	25.9 ± 5.7a	Nd	15.6 ± 2.5b	Nd
Phenolic acids mg/100 g dw ± SD n = 3
Chlorogenic acid	61.7 ± 5.1abcde	70.3 ± 1.4afghi	46.2 ± 3.5bfjkl	28.5 ± 1.5cgjm	34.4 ± 1.5dhkmo	16.1 ± 1.3eilno
Caffeic acid	Nd	44.2 ± 3.7	Nd	Nd	Nd	Nd
Isochlorogenic acid	95.8 ± 3.8	Nd	Nd	Nd	Nd	Nd
Antioxidant activity
FRAP [µM Fe2+/100 g dw]	2229 ± 68 abcde	110.9 ± 4 afghi	1764 ± 27 bfjkl	90.1 ± 9 cgjm	846 ± 16 dhkmo	84.1 ± 11 eilno
DPPH TEACo [µM/100 g dw	883 ± 61abcde	41.4 ± 12afghi	575 ± 61bfjkl	15.6 ± 4.8cgjm	210.7 ± 32dhkmn	15.5 ± 7.1eiln

SF– fresh skin; FF– fresh flesh; SFR– frozen skin; FFR– frozen flesh; 3 M, 4 M– frozen for 3 or 4 months. Within each row, values with the same asterisk do not differ significantly (p < 0.05)

Chlorogenic acid was detected in all examined samples. In fresh samples, flesh has a slightly higher content of chlorogenic acid (70.3 mg/100 g dw) compared to skin (61.7 mg/100 g dw). Freezing for 3 months reduced the amount of the compound in both skin and flesh, with almost twofold decrease to 28.5 mg/100 g dw observed in the flesh. After 4 months of freezing, further decrease was observed, with skin containing 34.4 mg/100 g dw and flesh 16.1 mg/100 g dw. Caffeic acid was only detected in fresh flesh (44.2 mg/100 g dw), while isochlorogenic acid in fresh skin (95.8 mg/100 g dw), and its content was quite high.

Hopefully, we did not detect rotenone in evaluated jicama tubers (fleshes and peels) which indicate that these vegetables are safe for eaters in this aspect,

In summary, the diverse range of bioactive compounds in jicama, such as isoflavones, and phenolic acids, reflects its potential as a source of health-promoting compounds. The concentrations of these compounds, as indicated in Table 1, provide an insight into jicama’s phytochemical richness and applications in both medicinal and agricultural contexts but also give some hints about storage process.

Antioxidant Activity

The antioxidant capacity of jicama samples of various storage conditions was evaluated using FRAP and DPPH assays. The fresh skin demonstrated the highest antioxidant capacity among all samples, as indicated by its superior FRAP value. This result highlights the skin as the richest source of antioxidants in fresh jicama. In contrast, the flesh consistently showed significantly lower antioxidant capacity. For frozen samples, notable declines in antioxidant activity were observed. The FRAP value for the skin decreased significantly after three months of freezing and dropped further after four months to 846 µM Fe²⁺/100 g DW. This indicates that prolonged freezing continues to degrade the antioxidant capacity of the skin without recovery. The flesh, however, exhibited greater stability. Although the FRAP value of frozen flesh was slightly but significantly lower, compared to fresh flesh, there was no substantial change between three and four months of freezing, suggesting that the freezing duration had less impact on the flesh’s antioxidant ability.

DPPH assay results were similar to those from the FRAP analysis. Fresh skin exhibited the highest radical scavenging activity, confirming its superior antioxidant potential. Fresh flesh showed lower DPPH activity, consistent with the lower FRAP values. Among frozen samples, both the skin and flesh experienced reduced DPPH activity compared to fresh samples. However, while the antioxidant activity of the skin continued to decline significantly with prolonged freezing, the flesh exhibited no significant difference between three and four months of freezing, further highlighting its relative stability.

In conclusion, freezing diminishes the antioxidant capacity of both jicama skin and flesh. The reduction is more pronounced in the skin, while the flesh remains relatively stable, with only slight decreases. These findings suggest that storage conditions, especially freezing, have a significant negative impact on antioxidant activity, particularly in the skin.

Cytotoxic Activity

Among the thyroid cell lines tested (Fig. 1), thyroid papillary cancer TPC1 cells were most vulnerable to the examined extracts, and the strongest effect was noted for skin extracts, when compared to flesh. The impact of skin extracts on viability of TPC1 cells was stable (about 65%), in terms of the influence of storage conditions. In case of flesh extract there was a clear decrease in cytotoxicity along with the freezing; viability rose from 68.4% (fresh) to 89.3% after four months of freezing, indicating that frozen flesh extract is less cytotoxic to TPC1 cells over time. There was some variability in the influence of skin extracts on thyroid follicular cancer FTC133 cells; viability increased from 67.7% (fresh) to 81.5% after three months, then decreased to 71.8% after four months. This suggests that while the cytotoxic effect may fluctuate, it remains generally moderate for FTC133 cells in contrast to flesh extracts, which shown very low cytotoxicity toward the cells. What was expected, skin extracts were not active towards 8505 C anaplastic thyroid cancer cells, which is recognized as rather resistant to chemotherapeutic agents. Viability ranged from 75.6% (fresh skin) to 79.8% (after four months), indicating moderate cytotoxicity, while for the flesh it was even higher (82.8% for fresh flesh, and 88.8% after four months), indicating no effect.

Fig. 1.

Cytotoxic effect of fresh and frozen (for 3 and 4 months) skin and flesh extracts (100 µg/ml) on normal and thyroid cancer cells. An asterisk (*) indicates a significant difference between cancer cell lines and normal cell lines. An open circle (○) denotes a significant difference between the same frozen and fresh extracts for each respective cell line

The viability of non-cancerous Nthy-ori 3 − 1 cells was somewhat affected by the skin extract, with viability increasing slightly from 69.6% (fresh) to 78.9% after four months of freezing, indicating a slight decrease in cytotoxicity with freezing. In case of flesh extract (FF, FFR3, FFR4) cell viability remained high at 100% in all conditions, suggesting that the flesh extract had no cytotoxic effect on normal thyroid cells, even with prolonged freezing.

To sum up, flesh extract showed no cytotoxic effects on non-cancerous thyroid cells, while the effect for the skin extracts was more pronounced. However, what should be highlighted, the effect of skin extracts was significantly weaker when compared to the one observed towards TPC1 cancer cells. Flesh extract, especially in frozen conditions, demonstrated low cytotoxicity to all tested cell lines, including cancer cells, with the cytotoxic effect decreasing over time in frozen samples. These results suggest that jicama skin extract has a moderate cytotoxic effect on both cancerous and non-cancerous thyroid cells, while flesh extract is minimally cytotoxic, particularly when frozen, indicating that it may be safer or less aggressive in applications where cell viability is important. This could have implications for the potential use of jicama in chemoprevention target.

Anti-inflammatory Activity

Skin extracts appear to have a more consistent and potent anti-inflammatory effect, particularly on NO and IL-6, across all freezing durations and concentrations (Fig. 2). This could be due to a higher concentration of bioactive compounds in the skin. Flesh extracts demonstrated moderate anti-inflammatory effects, but their efficacy, especially for TNF-alpha and IL-6, seems to decline with prolonged freezing. After freezing (both 3 and 4 months), there was a slight reduction in the anti-inflammatory activity of both skin and flesh extracts, though the impact was more pronounced in flesh samples. These findings suggest that the skin of jicama tubers could be a more effective source of anti-inflammatory compounds compared to the flesh, and that freezing storage might slightly reduce their efficacy over time, particularly for flesh extracts. This could become an interesting suggestion for future studies and applications aiming to optimize storage and processing methods to retain the anti-inflammatory properties of jicama extracts.

Fig. 2.

The effect of fresh and frozen (for 3 and 4 months) skin and flesh extracts on: tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and nitric oxide (NO) release in LPS-stimulated RAW 264.7 macrophages. RAW cells were pre-treated with 50 and 100 µg/mL of extracts for 1 h, afterwards cells were incubated with (10 ng/mL) or without LPS (untreated) for the next 24 h. Dexamethasone (DEX) was used as a reference. Values are presented as the mean ± SD (standard deviation) of three independent experiments in triplicate

Impact of Freezing

The result of our study sheds some new light on the impact of freezing on the bioactive compounds and biological activities of jicama tubers, emphasizing the nutritional and functional differences between the skin and flesh. Fresh jicama skin contains higher amount of isoflavones (daidzein, genistein, and biochanin A) and certain phenolic acids, such as chlorogenic and isochlorogenic acid, compared to the flesh. However, freezing significantly reduces these compounds, with daidzein and genistein disappearing entirely from the flesh after just three months. Biochanin A, although present in the skin after freezing, also diminishes over time. Interestingly, while freezing reduces the concentration of bioactive compounds, the jicama skin still retains some beneficial properties over time, including a moderate cytotoxic effect against cancer cells and potent anti-inflammatory activity. This cytotoxic effect on cancer cells is especially notable, as it suggests potential applications of jicama skin extracts in cancer research. The flesh, on the other hand, shows minimal cytotoxicity toward both normal and cancer cells, suggesting it may be safer for applications where preserving cell viability is crucial.

Discussion

These findings suggest that fresh jicama skin is a richer source of isoflavones and certain phenolic acids compared to flesh. Freezing diminishes the content of these bioactive compounds, with some disappearing entirely after prolonged storage. Thus, fresh jicama, especially the skin, might be more beneficial for bioactive compound intake. Information about isoflavones found until now in jicama is scarce. In jicama tuber genistein (1655.30 µg/g fw) and daidzein (1104.54 µg/g fw) were detected, formononetin (65.13 µg/g fw) and wigetin (2.9 µg/g fw) were noted in the leaves, while neotenin (41 µg/g fw) and dehydroneotenin (4 µg/g fw) in the seeds [1, 21, 22]. Thus, our study is the first to demonstrate the presence of biochanin A in jicama tuber, determined in quite high amount. It is also worth to underline that the examined jicama tuber peels can be a good source of isoflavones, with their sum of almost 80 mg/100 mg.

Several phenolic acids were described in jicama, particularly in the leaves, where they contribute to antioxidant properties. These included gentisic acid (69.03 µg/g dw), p-coumaric acid (612.83 µg/g dw), p-hydroxybenzoic acid (161.63 µg/g dw), and salicylic acid (58.83 µg/g dw). In jicama tuber, only the presence of caffeic and ferulic acids were reported [1, 22]. Our results indicate the presence of chlorogenic and isochlorogenic acids in jicama tuber for the first time.

The presence of rotenone in plant or food samples is a nutritional limitation because it restricts their potential use as a food source despite sometimes high content of beneficial nutrients. Rotenone is a naturally occurring compound found in various parts of jicama, particularly concentrated in the seeds, where it functions as a phytoalexin, protecting the plant against pathogens. Although rotenone has pesticidal properties that benefit the plant, it poses significant health concerns for humans due to its toxicity. This toxicity has limited the use of jicama seeds in human nutrition, despite their high nutritional value and the oil they yield [1]. Additionally, the seeds, stems, and leaves contain rotenoids, which are biogenetically related to isoflavones and key rotenoids isolated from jicama are: rotenone, hydroxyrotenone, dolineone, hydroxydolineone, pachyrhizon, hydroxypachyrhizon. The highest concentrations of rotenone are present in the seed coats, making seed consumption potentially harmful unless rotenone is effectively degraded. However, achieving this degradation for safe consumption typically requires specific treatments [10].

Overall, Pachyrhizus erosus demonstrates interesting antioxidant properties, although these can be significantly affected by storage conditions. Efforts to optimize preservation methods, should be estimated especially that freezing may not help maintain or even decrease the antioxidant capacity of jicama. Other authors also emphasized the antioxidant properties of Pachyrhizus erosus. Ethanolic extracts of jicama tubers showed potent antioxidant activities, with ethyl acetate fractions achieving an IC₅₀ value of 531.77 µg/mL in ABTS radical scavenging assays [23]. Water and 70% ethanol extracts of the tuber also demonstrated strong DPPH and ABTS radical scavenging abilities, attributed to their polyphenol and flavonoid content [24]. Similarly, dichloromethane and ethanol extracts are rich in phenolic and flavonoid compounds, which contribute to jicama’s high antioxidant potential [25]. Storage and processing methods can influence these properties. A study by Aji & Wikandari [26] revealed that fermentation using Lactobacillus plantarum enhanced the antioxidant potential of jicama extracts. This enhancement is likely due to the release of bound phenolic compounds during fermentation.

The consistently higher antioxidant activity of jicama obtained by the FRAP assay compared to the DPPH assay for all studied extracts can be attributed to the fundamental differences in their mechanisms of action and sensitivity to various antioxidant compounds. FRAP primarily detects antioxidants that act through single electron transfer mechanisms and is particularly sensitive to compounds such as phenolics, flavonoids, and vitamin C, which can be found in jicama roots. Moreover, FRAP measures the total reducing capacity of a sample and does not discriminate between antioxidant types– so any molecule capable of electron donation will contribute to a higher overall value. DPPH assay, on the other hand, measures the ability to scavenge free radicals by donating hydrogen atoms or electrons. It is more selective and less responsive to certain types of antioxidants, especially those that are hydrophilic or larger in size, and is affected by steric hindrance around the radical site. DPPH works best for small, lipophilic antioxidants and is performed in organic solvents, which can limit the reactivity of polar compounds [27].

Our study seems to be the first to indicate possible cytotoxic potential of jicama tubers against thyroid normal and cancer cells. Skin extracts were not active towards anaplastic thyroid cancer cells, which is recognized as rather resistant to chemotherapeutic agents [28]. Although preliminary findings suggest that jicama may offer chemopreventive benefits, the absence of direct studies on its impact on thyroid function warrants further investigation [29].

According to the Global Cancer Statistics 2020 [30], the incidence of thyroid cancer varies geographically, with notably higher rates observed in North America and parts of Europe compared to South America. Nevertheless, certain Latin American countries, report relatively elevated incidence rates compared to neighboring regions. These epidemiological trends highlight the growing global and regional public health importance of thyroid cancer and support the exploration of culturally appropriate preventive strategies, such as the use of traditional foods like jicama.

Until now studies on jicama have demonstrated the cytotoxic activity of compounds extracted from seeds. It has been shown that rotenone presented in seeds exhibits cytotoxic effects against several cancer cell lines, including human breast cancer cells (MCF-7; IC₅₀ 20 nM) and lung cancer cells (A-549; IC₅₀ 25 nM). Experiments also involved murine cancer cell lines, such as nasopharyngeal carcinoma KB cells and lymphocytic leukemia P-388 cells, where both rotenone and 12α-hydroxyrotenone displayed strong cytotoxic activity [31]. We didn’t found rotenone in evaluated tubers which means that for observed cytotoxic potential, especially of skin other active compounds are responsible.

Research on the effects of jicama tuber extract on inflammation is limited. Two studies provided insights into the potential impact of jicama fiber extracts on immune and inflammatory responses. In one study, fiber extract from jicama was shown to stimulate phagocytic activity in J774.1 macrophage cells, as evidenced by a significant increase in the production of TNF-α and IL-6 in both J774.1 cells and mouse peritoneal macrophages. Additionally, the extract enhanced gene expression levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Oral administration of the fiber extract also increased the phagocytic activity of peritoneal macrophages in BALB/c mice [32]. In a separate study, the fiber extract from jicama promoted the production of immunoglobulin M (IgM) in the human hybridoma cell line HB4C5. Furthermore, in mouse primary splenocytes, the extract stimulated the production of IgM, IgG, and IgA in a dose-dependent manner, along with increased production of interleukins IL-5 and IL-10 [33].

Until now studies have investigated optimal storage conditions for jicama tubers, particularly focusing on temperature’s impact on shelf life, decay, and discoloration. Research indicates that the ideal storage temperature for freshly harvested jicama tubers is approximately 12.5–13 °C. At this temperature, tubers remained in good condition for over four weeks. Lower temperatures, such as 0 °C, accelerated decay, with visible spoilage occurring within just one week. Consequently, temperatures above 13 °C are recommended for prolonging tuber quality [34]. Storing tubers in soil was identified as an effective method for maintaining freshness, while freezing was also viable. Whole, unpeeled tubers can be frozen for up to 12 months, whereas peeled and cut tubers are best stored frozen for up to nine months [34]. As it was highlighted before, freezing of jicama tubers is easy but not optimal for the nutritional value. Dehydration is another effective approach for extending jicama’s shelf life. The recommended process involves peeling, slicing or cubing the tuber, and drying it at 52 °C for 8–12 h in a food dehydrator. Dried jicama stored in airtight containers can last up to one year at room temperature and up to five years if kept in the freezer [34, 35]. Recent evidence strongly supports that freezing causes a decrease in antioxidant activity in root vegetables, primarily due to ice-crystal damage and subsequent oxidative degradation of key compounds. Structural disruption releases antioxidants but makes them vulnerable to enzymatic oxidation (e.g., polyphenol oxidase action) and chemical oxidation. This results in lower measured antioxidant capacity (by assays like DPPH, ABTS, ORAC) in frozen-stored roots versus their fresh counterparts. Studies on carrots, turnips, and other roots consistently report declines in total phenolics and antioxidant power after freezing or during frozen storage [36–38].

Current studies rarely address the distribution of key bioactive compounds, such as isoflavones, phenolic acids, and rotenone, between the skin and flesh of jicama. Understanding this distribution is critical for maximizing the utilization of the tuber, including often-discarded skin, in nutritional and therapeutic applications. The assessment of antioxidant, cytotoxic, and anti-inflammatory properties of jicama extracts addresses a significant gap in understanding their broader health impacts, which could inform both dietary recommendations and potential functional food applications.

Conclusions

Our findings confirm that jicama tubers do not contain detectable levels of rotenone in the skin or flesh, indicating that these parts are safe for consumption. This absence of rotenone, a known toxin, alleviates some concerns regarding the use of jicama tubers in human nutrition, although its presence in the seeds still restricts their use as a food source.

Our study is the first to document the effects of freezing on the key bioactive compounds and biological activities in jicama tubers, highlighting that jicama skin retains more nutritional and functional value than the flesh, even after freezing. This insight could inform future storage and processing strategies, suggesting that optimally jicama should be consumed fresh, particularly if targeting bioactive compound intake. The study also opens doors for potential applications of jicama extracts, particularly from the skin, rich in isoflavones, in fields such as chemoprevention and anti-inflammatory treatments. By addressing these underexplored areas, this study contributes valuable knowledge to the field of food science and nutrition, emphasizing the importance of storage and compound distribution in enhancing the health-promoting potential of jicama.

Author Contributions

Conceptualization: PP, ED, AG, OPL, SG. Data curation; PP, MM, AC. Formal analysis; PP, AG, AC, MM. Funding acquisition: PP, ED, SG. Investigation: PP, AG, MM, ED, AC. Methodology: AG, OPL, SG. Project administration; PP and SG. Resources: PP, ED, OPL. Software: PP, AC, MM. Supervision; ED, OPL, SG. Validation; AG, PP, SG. Visualization: PP. Writing - original draft; PP, AG, SG, and Writing - review & editing ED, OPL, SG.

Funding

The research has been supported by a grant from the Priority Research Area qLIFE under the Strategic Programme Excellence Initiative at Jagiellonian University and N42/DBS/000435, N42/DBS/000283. The publication was created with the use of equipment, the purchase of which has been supported by a grant from the Priority Research Area qLIFE under the Strategic Programme Excellence Initiative at Jagiellonian University (No. 06/IDUB/2019/94).

Data Availability

The raw data supporting the conclusions of this article will be made available by the authors on request.

Declarations

Ethics Approval

Not applicable.

Competing Interests

One of the authors of the submitted paper, Prof. Paredes-López, is the Editor-in-Chief of the journal Plant Foods for Human Nutrition, and our group has been collaborating with him for 30 years.