Kimchi Fermentation-Driven Detoxification of Flaxseed: Impact on Physicochemical Quality and Antioxidant Potential

Abstract

Flaxseed (Linum usitatissimum L.) is a rich source of α-linolenic acid (ALA) and lignans but contains toxic cyanogenic glycosides (CGs) that limit its application in foods. This study investigated the efficacy of a specialized Lactobacillaceae consortium in detoxifying flaxseed and the subsequent effects of adding this cyanogenic glycoside-depleted flaxseed (CGDF) to a kimchi matrix. Ground flaxseed and CGDF were added to the kimchi seasoning mixture at concentrations of 0.5%, 1.0%, and 2.0% (w/w) and fermented at 4 °C for 8 weeks. Analytical results confirmed that the fermentation process reduced linustatin and neolinustatin to undetectable levels (<500 mg/kg) and reduced total hydrogen cyanide (HCN) to below the Japanese regulatory limit of 10 mg/kg established under the Food Sanitation Act. During fermentation, CGDF-supplemented groups exhibited a delayed decrease in pH and higher retention of free sugars and vitamin C compared to the control and raw flaxseed groups. Notably, the 2.0% CGDF group maintained high oxidative stability of ALA, which we attribute to a putative antioxidant protection mechanism driven by the bioconversion of lignan glycosides into bioactive aglycones. These findings suggest that incorporating biologically detoxified flaxseed into kimchi creates a functional food system that ensures safety while enhancing nutritional stability. Overall, this work provides foundational evidence for developing safe, nutritionally enhanced functional foods within the One Health framework, integrating food safety, microbial ecology, and improved bioactive compound availability.

1. Introduction

The global functional food market has witnessed a surge in the utilization of flaxseed (Linum usitatissimum L.) as a premium health-promoting substrate [1,2]. The global flaxseed market was valued at approximately USD 860 million in 2024 and is projected to reach USD 1989 million by 2030, with Asia-Pacific and North America leading growth [3]. Flaxseed is uniquely positioned as a vital terrestrial alternative to marine-based omega-3 sources, containing a high concentration of α-linolenic acid (ALA) in its lipid fraction, which constitutes approximately 37% to 45% of the total seed weight [4,5,6,7,8]. Beyond its lipid profile, flaxseed provides a robust matrix of high-quality vegetable proteins and dietary fiber, which accounts for nearly 28% of its composition [6]. Regular consumption of flaxseed has been linked to reduced risks of atherosclerosis, hypertension, and various cancers, primarily due to its bioactive lignans, such as secoisolariciresinol diglucoside (SDG) [9]. Flaxseed is also a source of potentially toxic cyanogenic glycosides (CGs), which serve as the plant’s intrinsic chemical defense mechanism [6]. However, the commercial integration of flaxseed and other plants containing CGs is restricted in several markets due to food safety regulations. For example, Japan enforces strict limits on hydrogen cyanide (HCN) content in imported flaxseed products under the Food Sanitation Act, setting a maximum allowable concentration of 10 mg HCN per kg for processed foods [10]. The primary CGs in flaxseed—linustatin, neolinustatin, and linamarin—liberate toxic HCN upon enzymatic hydrolysis by β-glucosidase and hydroxynitrile lyase [5]. HCN is a potent respiratory inhibitor that can induce severe neurological, cardiovascular, and endocrine dysfunctions in both humans and animals [5,11]. Consequently, international markets such as Japan and South Korea maintain stringent regulatory thresholds for CG concentration in imported flaxseed, necessitating advanced detoxification before human consumption [3].

Traditional abiotic detoxification strategies, including high-heat treatments and chemical solvent extractions, often involve significant “nutritional trade-offs” [12]. For instance, microwave roasting can reduce HCN potential by up to 83.3%, but it simultaneously degrades heat-labile ALA and essential amino acids while promoting undesirable lipid oxidation [13]. Similarly, chemical extractions using methanol or ethanol can be effective but may leave toxic residues and cause the loss of beneficial polar compounds, such as lignans [13]. In contrast, biological bioprocessing using lactic acid bacteria (LAB) offers a superior alternative by efficiently depleting CGs while preserving the substrate’s primary nutritional integrity [14].

Kimchi, the iconic Korean fermented vegetable dish, represents a complex and dynamic reservoir for diverse LAB genera, including Leuconostoc, Lactobacillus (now including Lactiplantibacillus), and Weissella [15,16]. These indigenous microorganisms possess an extensive portfolio of glycosyl hydrolases, particularly β-glucosidase, which are critical for the bioconversion of plant-derived glycosides into bioactive aglycones [17,18]. Metatranscriptomic analyses of kimchi fermentation confirm that carbohydrate-transport and hydrolysis genes are among the most actively expressed during maturation [18,19,20,21]. Specifically, the activity of kimchi-derived LAB has been shown to neutralize toxic CGs, significantly improve the bioavailability of bioactive SDG, and enhance the overall quality of the fermented matrix [17,22]. Beyond detoxifying CGs, kimchi fermentation may broadly hydrolyze plant-derived glycosides, as evidenced by the conversion of lignan diglucoside into bioactive aglycones in this study. This suggests that β-glucosidase activity in kimchi’s microbial community could represent a general mechanism for enhancing bioavailability of glycoside-bound phytochemicals during fermentation.

This study aims to develop a novel functional kimchi [18] fortified with CG-depleted flaxseed (CGDF). Building on our previous research, which established a 72 h fermentation protocol using a specific Lactobacillaceae consortium to reduce HCN to undetectable levels, we incorporated this detoxified substrate into a standardized kimchi matrix. We hypothesize that the enzyme-mediated fermentation will not only ensure toxicological safety but also is consistent with an antioxidant protection effect that protects the unstable ALA from oxidation during storage. This approach aligns with the “One Health” framework by integrating plant chemical safety, microbial ecology, and human metabolic well-being into a unified, sustainable food innovation [23].

2. Materials and Methods

2.1. Materials

The whole flaxseed used in this study was the CDC Sorrel variety obtained from Prairie Tide Diversified Inc. (Saskatoon, SK, Canada), characterized by its high lignan content. The kimchi used in this experiment was made using Napa cabbage purchased from a local farm (Yeongdong, Chungcheongbuk, Republic of Korea) in April 2025, while the remaining ingredients for the kimchi seasoning were purchased from Nonghyup Hanaro Mart (Seoul, Republic of Korea). Methylene chloride (DCM), methanol (MeOH), and N,N-dimethylformamide (DMF; ultrapure, GC, ≥99.5%) were purchased from Fisher Scientific International Inc. (Fair Lawn, NJ, USA). Deionized reversed osmosis (RO) water (resistivity > 18.2 MΩ∙cm at 25 °C) was prepared by a Milli-Q RO system from Millipore (Bedford, MA, USA). Solvents of analytical reagent grade, deuterium oxide (D₂O; 99.9 atom% D) and dimethyl sulfoxide (DMSO) were obtained from Sigma-Aldrich (St. Louis, MO, USA).

2.2. Preparation of Ground Flaxseed and CGDF

To remove CGs, a specialized fermentation process was conducted using a defined Lactobacillaceae consortium previously isolated and characterized in our laboratory [4,24]. This consortium is predominantly composed of L. plantarum, Limosilactobacillus fermentum, and Lentilactobacillus spp., all of which possess β-glucosidase activity. Importantly, whole-genome shotgun sequencing data previously generated for this consortium [24] include Distributed Accelerated Method for Protein Sequence Alignment with k-mer-based Optimized Network-guided Database Searching (DIAMOND)-annotated functional assignments against the National Center for Biotechnology Information (NCBI) non-redundant protein database, enabling interrogation of glycosyl hydrolase gene families (GH1/GH3) associated with β-glucosidase activity. These metagenomic resources provide a robust foundation supporting the presence of β-glucosidase-encoding genes within the consortium, consistent with its observed ability to hydrolyze CGs. One kilogram of flaxseed was fermented anaerobically at 30 °C for 72 h. Following fermentation, the hull gum was separated via a dehulling process using a Robot Coupe C80 automatic sieve (Robot Coupe, Vincennes, France). The final dehulled flaxseed product was dried overnight at 60 °C to produce CGDF, during which CGs were removed at or below detection limits. To maximize the bioavailability of essential fatty acids and lignans, both raw flaxseed and CGDF were finely ground using a coffee grinder prior to integration into the kimchi matrix [25].

2.3. Physical Pretreatment: Grinding for Bioavailability Enhancement

Flaxseed (Figure 1A,C) was ground using a disk mill to maximize the bioavailability of its functional components, including lignans (SDG) and ALA, and to ensure uniform quality during kimchi production. As shown in the microscopic analysis (100× magnification) in Figure 1, whole flaxseed (A and C) retains its hard outer shell, potentially limiting component leaching during fermentation. In contrast, ground flaxseed (B) and ground CGDF (D) have dramatically increased surface area, creating a structure that facilitates interaction with LAB enzymes and organic acids within the kimchi seasoning mixture. Flaxseed comminution is a critical prerequisite for efficient enzymatic detoxification. Whole flaxseed encapsulates its bioactive and toxic compounds within a robust hull, which physically restricts microbial access. The grinding process markedly increases the specific surface area, allowing the Lactobacillaceae (specifically Lactiplantibacillus spp.) consortium to penetrate the seed matrix deeply [4]. This physical alteration facilitates a ‘lock-and-key’ interaction, enabling extracellular β-glucosidases to effectively access the sequestered substrate sites of both CGs and lignan diglucoside, thereby accelerating the bioconversion process during subsequent fermentation stages.

2.4. Standardized Kimchi Formulation

The kimchi production process was based on the standard recipe of the Rural Development Administration of the Republic of Korea, with a total batch weight of 3000 g (

Table 1. Composition and formulation of kimchi enriched with ground flaxseed and CGDF.

Ingredients	Ratio (%)	Control (g)	Flax 0.5 (g)	Flax 1.0 (g)	Flax 2.0 (g)	CGDF 0.5 (g)	CGDF 1.0 (g)	CGDF 2.0 (g)
Salted Napa cabbage	69.0	2070	2070	2070	2070	2070	2070	2070
Coarse red pepper powder	0.8	24	24	24	24	24	24	24
Fine red pepper powder	0.8	24	24	24	24	24	24	24
Garlic	2.5	75	75	75	75	75	75	75
Ginger	0.6	18	18	18	18	18	18	18
Salted shrimp	2.5	75	75	75	75	75	75	75
Anchovy sauce	1.8	54	54	54	54	54	54	54
Sugar	1.8	54	54	54	54	54	54	54
Radish	8.0	240	240	240	240	240	240	240
Green onion	0.8	24	24	24	24	24	24	24
Starch powder	0.4	12	12	12	12	12	12	12
Onion	11.0	330	330	330	330	330	330	330
Total Mix (Sub-total)	100	3000	3000	3000	3000	3000	3000	3000
Ground flaxseed a			4.65	9.30	18.60
Ground CGDF a						4.65	9.30	18.60

^a Added ingredients: The percentages of ground flaxseed and CGDF (0.5, 1.0, and 2.0%) were calculated based on the weight of the seasoning mixture (930 g), not the total kimchi weight.

). Salted Napa cabbage accounted for 69% (2070 g) of the total weight, while the seasoning mixture comprised the remaining 31% (930 g). The experimental groups were divided into: (1) a control group (no flaxseed); (2) Ground flaxseed groups (added at 0.5%, 1.0%, and 2.0% of the seasoning weight); and (3) Ground CGDF groups (added at 0.5%, 1.0%, and 2.0% of the seasoning weight). The experimental groups were supplemented with ground CGDF at 0.5%, 1.0%, and 2.0% (w/w) relative to the seasoning paste weight. The specific amounts added were 4.65 g, 9.30 g, and 18.60 g, respectively, per 930 g of seasoning mixture, not the final product weight. All ingredients were thoroughly mixed before being applied to the salted cabbage leaves. The samples were packaged in plastic containers (diameter, 11.5 cm; height, 8.3 cm) and pre-fermented at room temperature for 12 h and subsequently matured at 4 °C for 0, 2, 4, and 6 weeks.

2.5. Analytical Procedures

To monitor the acidification kinetics during the 6-week maturation period, 100 g of kimchi from each experimental group was collected and homogenized using a high-speed hand blender (Model 4191, Braun GmbH, Kronberg, Germany). The homogenate was filtered through four layers of sterile cheesecloth to obtain the kimchi juice. The pH was measured at room temperature using an automatic pH meter (Orion Star A211, Thermo Fisher Scientific, Waltham, MA, USA) according to AOAC Official Method 981.12 [26].

2.6. NMR-Based Metabolomic Analysis

Proton nuclear magnetic resonance (¹H-NMR) spectroscopy (600 MHz, Bruker Avance III HD, Mississauga, ON, Canada) was employed to quantify temporal changes in water-soluble metabolites during the 6-week fermentation period. The NMR spectra were analyzed using the TopSpin™ 3.8 software (Bruker BioSpin GmbH, Billerica, MA, USA). Kimchi samples (control, flaxseed 0.5–2.0, CGDF 0.5–2.0) were collected at weeks 0, 2, 4, and 6. For metabolite extraction, 1 g of lyophilized kimchi powder was homogenized with 10 mL of 0.1 M phosphate-buffered D₂O (pH 7.0) containing 0.01% trimethylsilylpropanoic acid (TSP) as an internal standard for chemical shift (0.00 ppm) and quantification. The linustatin and neolinustatin contents in flaxseed and kimchi samples were quantified by comparison with the internal standard DMF.

The CG compounds were quantified by integrating ¹H-NMR resonance signals corresponding to the methyl group of the cyanohydrin moiety (around 1.5 ppm) and the methylene group adjacent to the glycosidic linkage (around 0.9 ppm). The concentrations of major water-soluble molecules—including organic acids (total acidity), sugars (sucrose, glucose, fructose), vitamin C, and phenolic compounds (total polyphenolics and flavonoids)—were determined by integrating ¹H-NMR resonance signals unique to each metabolite: lactic acid (1.33 ppm, CH₃), acetic acid (2.08 ppm, CH₃), sucrose (5.40 ppm, anomeric H), glucose (5.23 ppm, anomeric H), fructose (4.03 ppm, CH), vitamin C (4.50 ppm, CH), and aromatic protons of phenolic compounds (6.20–7.80 ppm).

All values were normalized to mg/100 g dry weight (DW) to ensure comparability across groups, regardless of moisture variation.

2.7. Statistical Analysis

All experiments were performed in triplicate (n = 3). Data were analyzed using the Statistical Package for the Social Sciences (SPSS) software (version 18.0, SPSS Inc., Chicago, IL, USA). Data were presented as mean ± standard deviation (SD). The differences between means were assessed using a one-way analysis of variance (ANOVA), followed by Duncan’s multiple range test for multiple comparisons to ensure statistical rigor. A p-value p < 0.05 was considered statistically significant.

3. Results and Discussion

3.1. Detoxification Efficiency of Lactobacillaceae Fermentation

The fermentation process successfully detoxified the flaxseed substrate. ¹H-NMR analysis revealed distinct resonance peaks characteristic of CGs at 1.5 ppm and 0.9 ppm in the untreated flaxseed extract (Figure 2). The raw flaxseed initially contained high concentrations of diglucoside, specifically linustatin (2414 ± 24 mg/kg) and neolinustatin (3300 ± 30 mg/kg), with a total HCN of 371 ± 25 mg/kg (

Table 2. Changes in CG content and detoxification efficiency.

Target Compound	Untreated Flax (Control) a	Fermented Flax (CGDF) b	Reduction Status
Linustatin (mg/kg)	2414 ± 24	ND (<500) c	Depleted
Neolinustatin (mg/kg)	3300 ± 30	ND (<500) c	Depleted
Total HCN (mg/kg)	371 ± 25	<10	>97.3% Removed

Data are expressed as mean ± standard deviation (n = 3). Linustatin and neolinustatin contents were determined by comparing to the DMF internal standard [25]. ^a Untreated CDC Sorrel variety. ^b CGDF: Flaxseed processed via 72 h fermentation and degumming. ^c ND: Not detected within the limit of detection (LOD).

). However, as Lactobacillaceae consortium fermentation proceeded, the area of these resonances decreased sharply. After 72 h of fermentation and the degumming process, even in a scaled-up 1 kg sample, ¹H-NMR analysis showed that resonance signals corresponding to CGs (linustatin and neolinustatin) were reduced to levels below 10 mg/kg HCN potential, indicating near-complete removal of cyanogenic precursors. This degree of detoxification meets international food safety standards, which require CGs to be sufficiently minimized to prevent harmful cyanide release during consumption.

In scaling this process from bench-scale (35 g) to industrial-scale (1 kg and beyond), several factors become critical: the material-to-liquid ratio, the initial inoculum density, and maintaining anaerobic conditions. While this study successfully demonstrated the detoxification of CGs in a 1 kg batch, further industrial-scale validation (ton-scale) is required to ensure consistent heat transfer and microbial stability. Additionally, starter culture stability tests during repeated subculturing are essential for commercial implementation to ensure that β-glucosidase activity remains consistent without genetic drift.

3.2. Scientific Validation of the Kimchi Matrix

The kimchi mixture ratios presented in Table 1 were designed to be highly suitable for quantitatively analyzing the effects of flaxseed, a functional ingredient, while maintaining the traditional fermentation environment of kimchi. The total seasoning mixture, excluding cabbage, is calculated to be 930 g out of the total mixture ratio of 100% (3000 g). The flaxseed (flax and CGDF) addition levels of 4.65 g, 9.30 g, and 18.6 g in this study correspond to 0.5%, 1.0%, and 2.0% of the total seasoning amount, respectively. The outer hull of flaxseed contains insoluble mucilage components, including flax gum. Adding whole flaxseed (Figure 1A,C) may abnormally increase the viscosity of kimchi broth or impair texture. The grinding process (Figure 1B,D) overcomes these physical limitations and provides an optimal environment in which the SDG (lignans) in flaxseed can directly react with organic acids and LAB enzymes (β-glucosidase) in the kimchi fermentation liquid. This increased the antioxidant activity and vitamin C preservation effects observed in the CGDF group by solubilizing insoluble polymers present in ground flaxseed, rather than merely an additive effect.

This experimental design ensures precise evaluation of dose-dependent effects of flaxseed and CGDF within a traditional kimchi matrix, allowing clear interpretation of ingredient interactions on fermentation dynamics and nutrient stability. Specifically, the experiment can demonstrate proportional correlations between dosage and changes in pH, acidity, and vitamin C concentration during maturation.

3.3. Physicochemical and Functional Quality of CGDF-Kimchi

The maturation of kimchi over 6 weeks exhibited distinct fermentation profiles between the control and the flaxseed-fortified groups (Figure 3). The total acidity of all groups increased progressively, peaking at Week 6. Notably, the CGDF 0.5% group exhibited the highest total acidity by the end of the fermentation period, suggesting that the lower concentration of fermented flaxseed provided an optimal environment for LAB metabolic activity without over-inhibiting the microbial population. This aligns with findings by Moon and Lee [27], who reported that oil-rich seed powders can modulate acidification kinetics in fermented vegetables through antimicrobial interactions.

The dynamics of free sugars revealed a significant metabolic shift. Sucrose was rapidly hydrolyzed across all groups, serving as the primary carbon source for LAB. Paradoxically, the CGDF 0.5% group maintained significantly higher fructose and glucose concentrations at Week 6 than the control (p < 0.05). Similarly, vitamin C retention was superior in the CGDF groups (particularly 0.5% and 1.0%) relative to the Control. We attribute this nutrient retention to an “Antioxidant Shield” effect. The metabolic profile obtained via ¹H-NMR suggests that CGDF may modulate the fermentation environment, potentially influencing the microbial succession. High concentrations of lignans and flavonoids released from the CGDF matrix likely function as direct radical scavengers, quenching reactive oxygen species (ROS) generated during fermentation and thereby sparing labile nutrients such as ascorbic acid and monomeric sugars from oxidative degradation. Consequently, CGDF functions not merely as an additive but as a bioactive stabilizer, extending the optimal ripening window while maintaining nutritional density. This reflects the model proposed by Park et al. [15], where antioxidant enrichment mitigates the oxidative stress associated with rapid fermentation, and aligns with recent observations by Jung et al. [28], regarding metabolic regulation in kimchi.

Conversely, concentrations exceeding 2.0% were observed to induce excessive viscosity and strong herbal notes, potentially limiting consumer acceptability despite high antioxidant levels [29]. Therefore, the 0.5–1.0% concentration range is suggested as the optimal inclusion level for balancing functional efficacy with sensory quality.

3.4. Antioxidant Enhancement via Bioconversion

Functional evaluation showed a substantial increase in bioactive compounds over time. Total polyphenolic and flavonoid contents in CGDF-supplemented kimchi reached their maximum concentrations at Week 6, significantly surpassing those of the control (Figure 3). Specifically, the CGDF 2.0 group showed the highest absolute phenolic content, correlating with the higher baseline of SDG provided by the dosage. This increase is attributed to the putative bioconversion of lignan glycosides. The ¹H-NMR signals in the aromatic region (6.20–7.80 ppm) support the deglycosylation of SDG into bioactive aglycones (e.g., secoisolariciresinol, SECO), a process driven by the β-glucosidase activity of the kimchi microbial community (e.g., Lactiplantibacillus, Leuconostoc, and Weissella spp.). This observation is consistent with the mechanisms described by Michlmayr and Kneifel [19] and Renchinkhand et al. [30], who established that LAB-derived β-glucosidases play a critical role in activating plant glycosides during fermentation. This enzymatic activation transforms the inert storage forms of phytochemicals into potent radical scavengers, underpinning the antioxidant enhancement observed in Section 3.3. Although individual polyphenols possess varying antioxidant potencies, a strong positive correlation was observed between the total phenolic content and the functional quality of the kimchi.

3.5. Confirmation of CG Absence via Kimchi Fermentation

The fermentation process successfully detoxified the flaxseed substrate. ¹H-NMR analysis of untreated flaxseed identified distinct resonance peaks characteristic of linustatin and neolinustatin (1.5 ppm and 0.9 ppm) (Figure 2). Following the 72 h Lactobacillaceae consortium fermentation, these signals were eliminated. Quantitative analysis confirmed that total hydrogen cyanide (HCN) potential was reduced to concentrations equivalent to less than 10 mg/kg (Table 2). This degree of detoxification satisfies strict international food safety standards, including the regulations enforced by the Ministry of Health, Labour and Welfare in Japan [10]. The complete elimination of CGs is attributed to the robust β-glucosidase activity of the specific starter culture (e.g., L. plantarum and Leuconostoc mesenteroides), which selectively cleaves the glycosidic bonds of cyanogenic precursors [14,19,30].

Unlike the preceding study by Wu et al. [31], which used ground flaxseed powder, this study demonstrates academic originality by directly fermenting whole flaxseed, thereby minimizing oil and lignan losses. Regarding the analytical scope, the stability of the fatty acid profile during this specific fermentation process has been previously validated [4], justifying the focus on ALA retention in this study. This aligns with the findings of Son et al. [17], indicating that the enzymatic activity of kimchi LAB effectively hydrolyzes plant glycosides while the acidic environment facilitates the volatilization of HCN (Figure 4).

While ¹H NMR provided robust data on lignan bioconversion and metabolite flux, the lack of specific microbial enumeration and direct radical scavenging assays (e.g., DPPH, ABTS) represents a limitation of the present study. However, it is important to note that whole-genome shotgun sequencing of this consortium was previously performed by Tse et al. [24], generating a DIAMOND-annotated metagenomic dataset capable of resolving functional genes, such as glycosyl hydrolase families (GH1/GH3) associated with β-glucosidase activity. Although these genomic resources were not re-interrogated here, they provide a valuable foundation for future work aimed at linking fermentation-derived metabolite profiles with specific microbial taxa and enzyme systems. Consequently, future research should integrate industrial-scale validation with in vivo bioavailability assessments and targeted microbial and functional gene profiling to fully characterize ecosystem dynamics and the enzymatic drivers of CG hydrolysis.

3.6. The Functional Role During the Fermentation of Complete CG Removal

The simultaneous elimination of toxic CGs and the increase in bioactive lignans suggest a dual functional role for the LAB-derived enzymes (Figure 5). The microbial β-glucosidase activity, crucial for detoxifying linustatin, concurrently hydrolyzes the glycosidic bonds of SDG [32]. This simultaneous hydrolytic mechanism transforms the inert glycosides into bioactive aglycones, mirroring the metabolic activation that typically occurs in the human gut, but achieving it ex vivo during fermentation [33].

Based on these observations, we propose a “Matrix-Embedded Antioxidant” hypothesis to explain the physical stability of the CGDF-kimchi (Section 3.3). Unlike liquid oil additives, which often accelerate lipid oxidation in acidic kimchi brines due to direct exposure, the cellular matrix of ground CGDF provides physical encapsulation. This structural integrity, combined with the continuous release of antioxidant aglycones, creates a stable ‘lignan-protein-lipid matrix’ that buffers lipid droplets against acid hydrolysis and intercepts oxidation chain reactions. This combined enzymatic and physical mechanism offers a plausible explanation for the extended optimal ripening window and enhanced oxidative stability observed in the CGDF group.

3.7. Broader Implications for Plant-Based Fermented Foods

The successful application of this bioprocess highlights kimchi fermentation as a versatile platform for activating other glycoside-rich botanicals (e.g., ginseng saponins, soy isoflavones) [30]. By converting plant defence compounds into bioavailable nutrients, this approach aligns with the “One Health” framework, bridging plant chemistry, microbial biotechnology, and human health [34].

4. Conclusions

In conclusion, this study demonstrates that 72 h Lactobacillaceae-mediated fermentation is a viable strategy to resolve the nutritional trade-off of flaxseed. This process achieved complete detoxification (HCN < 10 mg/kg) while significantly preserving ALA and concentrating lignans. When incorporated into Napa cabbage kimchi, particularly at 0.5–1.0% concentrations, the resulting CGDF afforded a distinct antioxidant protection effect. Contrary to the typical acceleration of acidification observed with nutrient enrichment, the CGDF matrix paradoxically extended the optimal ripening window by mitigating oxidative stress, thereby preserving labile nutrients such as vitamin C and glucose. A critical mechanistic observation is that kimchi fermentation facilitates the simultaneous hydrolysis of both toxic CGs and lignan diglucoside, effectively transforming plant defense compounds into bioavailable nutrients. These findings lay the foundation for next-generation functional foods within the “One Health” framework. However, as direct radical scavenging assays (e.g., DPPH, ABTS) were not included in this study, the antioxidant potential was inferred primarily from metabolite profiles. Consequently, future research should focus on validating these findings through direct antioxidant kinetics, industrial-scale validation, in vivo bioavailability assessments, and targeted multi-omics approaches to fully characterize the breadth of this enzymatic activity.