Quality Of Kimchi Research Articles

Promising ingredients used for kimchi fermentation: Effects of Cordyceps militaris fermentation products on the over-acidification and quality of kimchi

Promising ingredients used for kimchi fermentation: Effects of Cordyceps militaris fermentation products on the over-acidification and quality of kimchi

Effect of long-term supercooling preservation using a stepwise algorithm on the freshness of kimchi cabbage

Kimchi cabbage is a Korean traditional fermented vegetable that is rich in nutrients and probiotics. Temperature changes caused microbial growth adversely affect the quality of kimchi. Therefore, controlling the preservation temperature is important to prevent over-fermentation of kimchi. Supercooling has emerged as an alternative storage method; however, maintaining the supercooled state of food is challenging. In this study, a stepwise cooling algorithm for supercooling preservation was developed and applied. All samples were maintained in a supercooled state, and no ice nucleation was detected. Assessments of CO2 content, pH, and titratable acidity revealed that supercooled samples exhibited more delayed fermentation than refrigerated samples. However, moisture content and hardness of the unfrozen (refrigerated and supercooled) samples were not significantly different. Microbial analysis and community composition indicated that the supercooling treatment delayed kimchi fermentation by approximately three months. Conclusively, supercooling is effective for maintaining the freshness of kimchi cabbage during long-term storage. This study contributes to the optimization of kimchi preservation strategies, offering potential benefits for both consumers and producers in terms of product quality, shelf life, and food safety.

Effects of sequential combination of cryogenic immersion freezing and ultra-cold frozen storage on the quality of Korean white kimchi

This study aimed to assess the effects of three different freezing techniques — cold room freezing (CRF; −20 °C), air-blast freezing (ABF; −70 °C), and cryogenic immersion freezing (CIF; −70 °C) — on the microstructure and physicochemical properties of Korean white kimchi (KWK) during frozen storage at −20 °C and − 45 °C for 8 weeks. CIF-treated KWK exhibited a higher freezing rate and after ultra-cold (UC; −45 °C) frozen storage, it showed a greater number and smaller diameter and area of ice crystals than CRF- and ABF-treated KWK. Drip loss was reduced and CIE color changes were delayed in KWK under UC frozen storage. The pH, titratable acidity, and reducing sugar content of frozen KWK remained unaffected by the freezing method, storage temperature, or duration. Thus, CIF combined with UC frozen storage preserves the physicochemical quality of KWK with minimal histological damage during long-term storage. Industrial relevanceIn the kimchi industry, where the shelf life of commercial products is often constrained by successive fermentation under low-temperature storage and distribution conditions, introducing frozen kimchi is a promising solution to reduce waste of overripe kimchi in the supply chain. This study highlights the effectiveness of combining CIF and UC frozen storage methods to minimize the damage caused by freezing in kimchi. This innovative technology provides a practical means for streamlining freezing processes, saving operational time, and ensuring kimchi quality during long-term storage and distribution.

Metabolic shift during fermentation in kimchi according to capsaicinoid concentration

The cultivar of red pepper used in kimchi contributes to spiciness, red color, and fermentation characteristics. Capsaicinoids are the main components of red pepper. Therefore, understanding changes in metabolites during kimchi fermentation according to capsaicinoid concentration is necessary to control the quality of kimchi. The purpose of this study was to investigate the effect of capsaicinoids on metabolites during kimchi fermentation. To profile the effect of capsaicinoid concentrations on kimchi fermentation, five kimchi samples were prepared using different concentrations of capsaicinoids (4, 12, 30.7, 40.9, and 50.3 mg/kg) and stored at 4 °C for 28 days. During kimchi fermentation, pH, titratable acidity, capsaicinoid concentration, total viable and lactic acid bacteria, free sugars, amino acids, and microbial community were evaluated. Each result was statistically analyzed for changes in capsaicin concentration and fermentation time. The capsaicinoid concentration did not change during kimchi fermentation but the growth of lactic acid bacteria changed. According to the growth of lactic acid bacteria, free sugar, amino acids, and microbial community changed with the capsaicinoid concentration. Overall, the results of this study provide preliminary information on the use of red pepper and capsaicinoids in the kimchi industry.

Physicochemical Property Analyses of Deep‐Frozen Kimchi Cabbage during Long‐Term Storage

Temperature control is critical to prevent overfermentation during the storage, distribution, and export of kimchi. Studies to optimize the freezing conditions for kimchi are lacking. Thus, the present study aimed to evaluate the optimum freezing and storage temperature for kimchi during long‐term storage. Kimchi was frozen at −18°C, −40°C, and −80°C for 4 months, followed by thawing at 2°C until the core temperature reached 0°C. Thawing loss was maximum for samples frozen at −18°C, with increased cell membrane disruption, thus considerably decreasing the hardness. Compared to kimchi stored at −18°C, those frozen at −40°C and −80°C resisted the changes in pH, titratable acidity, reducing sugar content, antioxidant activity, and total phenol content. However, the total aerobic count and total lactic acid bacteria values of samples frozen at −18°C sharply decreased among treatments. Therefore, freezing at freezer temperature, particularly −80°C is ideal to maintain the kimchi quality for long‐term storage.

Effects of pulsed electric fields on controlling fermentation rate of brined Raphanus sativus

This study investigated the effects of pulsed electric fields (PEF) on the fermentation quality characteristics, morphology, and antioxidant activities of brined and fermented radish with different PEF strengths (1.5 kV/cm. 2.0 kV/cm). Electrical conductivity and Z-index showed that as the strength of PEF increased, the permeability of the cell membrane and the degree of disruption of the cell increased. The pretreatment with PEF accelerated the brining rate, thereby reducing the time required for brining by approximately PEF1.5 kV/cm (56.6%) and PEF2.0 kV/cm (70%) compared to Control. The growth rate of lactic acid bacteria viability was inhibited in the PEF group thus approximately 1–2 log CFU/ml lower than Control. The cellular structure maintenance of radish was improved in the PEF group than in the control group. Altogether, these findings suggest that PEF could effectively increase the storage period (2–5 days) for controlling the excessive growth of lactic acid bacteria which induce overripening during the fermentation of vegetables. Industrial relevanceA fermented food produced by lactic acid bacteria (LAB) is kimchi, a traditional Korean food that is consumed worldwide; however, excessive growth of LAB can reduce the quality of kimchi. PEF technology can be used to control LAB in kimchi to produce a superior product without the addition of antimicrobial agents.

Optimization of number of wireless temperature sensors using clustering algorithm for deep learning algorithm-based Kimchi quality prediction

The production and storage of kimchi in a factory require monitoring temperature and humidity to maintain optimal quality. Recently, smart packaging devices such as wireless sensors have been used, but their installation and maintenance are costly and require additional resources. In this study, kimchi is packaged in polyethylene packages and placed in plastic baskets. Thirty baskets are stacked in the middle of the storage room. Wireless sensors placed inside the baskets collect temperature data alongside the kimchi for 60 days. The data is sent to a server through communication unit using 4G network. Two clustering algorithms, Competitive Learning Neural Network (CLNN) and k-means, are used to determine the optimal number and location of sensors. Deep learning algorithms, specifically Long Short-Term Memory (LSTM), predict the acidity and ripeness grade of the kimchi. The study found that the optimal number of temperature sensor groups for CLNN was 6 for acidity and 4 for ripeness grade classification. Increasing the number of sensors improved the kimchi acidity prediction, and the accuracy of ripeness classification increased with the number of sensors. The location of the wireless sensors was determined based on the heights of the stacked plastic baskets using the CLNN + LSTM model. This work presents a process for optimizing sensor placement and evaluating kimchi quality during storage and fermentation using clustering and deep learning techniques to maintain optimal quality.

Effects of ingredient size on microbial communities and metabolites of radish kimchi

In this study, changes in physicochemical characteristics, microbial communities, and metabolites were investigated to identify the fermentation characteristics of radish kimchi according to the size of radish cubes used. The small-sized radish kimchi group showed the highest hardness value and glucose content in the early stages of fermentation. The relative abundance of major lactic acid bacteria, including Leuconostoc, Weissella, and Lactobacillus, was the highest in the small-sized radish kimchi group on day 5 of fermentation, which resulted in rapid production of lactic acid, thereby causing a decrease in pH and an increase in titratable acidity. The size of the radish in kimchi plays a pivotal role in determining various factors, most notably during the first 5 days of fermentation, leading to marked metabolic changes. A total of 17 metabolites, including glucose, sucrose, lactic acid, malic acid, citric acid, and GABA, exhibited significant differences in the small-size radish kimchi group. Interestingly, the sucrose content was higher in the large-sized radish group at the beginning of fermentation. This study revealed that ingredient size can selectively affect the growth of specific microorganisms in an environment where several microorganisms coexist, which could change the quality of radish kimchi.

Efficacy of Pectobacterium carotovorum subsp. carotovorum inactivation using ultraviolet C light-emitting diodes: Investigation of inactivation efficacy toward planktonic and biofilm cells on the stainless steel surfaces of cutting machines

The presence of Pectobacterium carotovorum subsp. carotovorum (P. carotovorum) in kimchi cabbage (Brassica rapa L. subsp. pekinensis) negatively influences kimchi quality. Accordingly, inactivation processes to effectively control spoilage caused by plant bacteria, including P. carotovorum, are crucial for extending the shelf life of kimchi. In this regard, ultraviolet C light-emitting diode (UVC-LED) technologies are increasingly attracting attention as non-thermal and non-contact sterilization technologies and are also considered as alternatives to chemical disinfectants. In this study, we investigated the efficacy of the inactivation of P. carotovorum planktonic and biofilm cells that cause cabbage soft rot disease using the UVC-LED treatment technology as a potential disinfection method for a safe kimchi manufacturing process. A biofilm was formed on the surface of a stainless-steel cutter knife using the recommended CDC biofilm reactor system and thereafter, exposed to a range of UVC-LED intensities. Our results indicated that P. carotovorum planktonic and biofilm cells to UVC-LED irradiation at 9.0 mJ/cm2 resulted in >5.0 and >2.0 log10 inactivation, respectively. Additionally, the P. carotovorum planktonic and biofilm cell inactivation kinetics fitted the non-linear reduction curve. The UVC-LED treatment was also found to be highly efficient in eliminating planktonic cells, showing consistency with the Weibull and Weibull tailing models for planktonic cells.

Effect of electron beam irradiation on sliced Korean cabbage (Brassica rapa L. ssp. pekinensis) kimchi: Kinetics of microbial inactivation and changes in physiochemical and microbial quality

Ensuring microbial safety and controlled kimchi fermentation without thermal sterilization is challenging owing to the background microbiota present in raw materials of kimchi. In this study, we investigated the effect of electron beam (EB) irradiation on naturally occurring microbiota and physicochemical characteristics of sliced Korean cabbage kimchi (KCK). In addition, the inactivation kinetics of natural microbes during EB irradiation were evaluated. The total aerobic bacteria (TAB) and total lactic acid bacteria (TLAB) counts in sliced KCK significantly decreased (p < 0.05) with an increase in EB irradiation. In particular, the total coliform (TC) count in unripened and optimally ripened kimchi was reduced to below the detection limit (1 log CFU/g) following 4 kGy EB irradiation. In contrast, no significant difference was observed in the physicochemical characteristics, viz., pH, titratable acidity, salinity, electrical conductivity, and reducing sugar content between the non-irradiated and irradiated slices of KCK. These results imply that EB irradiation effectively controlled microorganisms i.e., TC without adversely affecting the quality of kimchi. Furthermore, we determined that the Gompertz model was relatively more suitable for predicting the inactivation of TAB, TLAB, TC, or yeast and molds in sliced KCK than the linear model.

A Bibliometric Framework for Quantifying Research on Kimchi, A Staple Korean Dish

Kimchi is one of the fermented foods studied and discussed by researchers for many decades. Several perspectives have been considered while investigating the role of Kimchi. Thus, this demands a scientific review of this domain. This study is an honest attempt to map the scientific production of Kimchi. A descriptive, performance and bibliometric analysis were conducted to achieve the objective based on 924 documents recovered from the Scopus database. The results suggest a steady growth in the number of publications since 2016. The initial data shows that 160 journals have contributed 924 articles between 1979-2022. It is found that South Korea contributes nearly 94% (868 articles) of the total contribution, followed by the United States, China, and Japan. The institution-wise analysis (Figure 4) of the published articles based on the authors' affiliations suggests that most articles have been published by South Korean Institutes, followed by the United States. With 19 publications, the Journal of the Korean Society of Food Science and Nutrition has emerged as the most influential journal in Kimchi literature. The keyword analysis identifies nine themes. This analysis's findings reveal that the properties of Kimchi and the quality and sensory evaluation of kimchi were the most niche topics in this domain. Findings also revealed that the health benefits of Kimchi, the quality of Kimchi, and the bacteria involved in Kimchi fermentation were emerging themes in the Kimchi knowledge base. The findings of this study are helpful for future researchers in identifying the most influential authors, journals, and articles. Further, this study’s results also determine future research objectives in the Kimchi studies.

Fabrication of Gold Nanoparticles and Cinnamaldehyde-Functionalized Paper-Based Films and Their Antimicrobial Activities against White Film-Forming Yeasts.

During storage and fermentation of kimchi, white film-forming yeasts (WFY) are generated on the surface of kimchi under various conditions. These yeasts include Candida sake, Pichia kudriavzevii, Kazachstania servazzii, Debaryomyces hansenii, and Hanseniaspora uvarum. Because of the off-odor and texture-softening properties of WFY that degrade the quality of kimchi, a method to prevent WFY is required. In this study, cinnamaldehyde (CIN) and gold nanoparticles (AuNPs) with a large surface area were grafted on a paper surface, which was termed the "Paper_AuNPs_CIN" film. CIN is an antimicrobial agent that is approved for use in food applications. In the as-fabricated Paper_AuNPs_CIN film, antimicrobial CIN molecules were physically adsorbed to the surface of AuNPs and simultaneously chemically synthesized on the paper surface via the imine reaction. The Paper_AuNPs_CIN film exhibited greater antimicrobial activity against the three WFY strains than a Paper_CIN film (which contains only CIN molecules). Since more CIN molecules were adsorbed to the large surface area of the paper-reduced AuNPs, the Paper_AuNPs_CIN film exhibited a higher antimicrobial activity. Using AuNPs and CIN simultaneously to inhibit the growth of WFY is a novel approach that has not yet been reported. The morphology and elemental mapping of the functionalized films were examined via scanning electron microscopy and energy-dispersive spectroscopy, elemental composition was analyzed via inductively coupled plasma optical emission spectroscopy, and chemical bonding and optical properties were investigated via Fourier transform infrared spectroscopy and diffuse reflectance spectroscopy. Additionally, agar-well diffusion assays were used to determine the antimicrobial activity against three representative WFY strains: C. sake, P. kudriavzevii, and K. servazzii.

Rapid Quantitative Analysis of Metabolites in Kimchi Using LC-Q-Orbitrap MS.

Kimchi is a traditional Korean salted spontaneous lactic acid bacteria (LAB)-fermented food made using various vegetables. Organic acids, free sugars, and amino acids are key metabolites produced during LAB fermentation that determine the taste and quality of kimchi. However, each metabolite is typically analyzed using an independent analytical method, which is time-consuming and expensive. Therefore, in this study, we developed a method based on LC-Q-Orbitrap MS using which 20 types of representative fermented kimchi metabolites were selected and simultaneously analyzed within 10 min. The established method was validated, and its detection and quantification limits, linearity, precision, and accuracy were found to satisfy the Association of Official Agricultural Chemists (AOAC) validation guidelines. The 20 metabolites were simultaneously extracted from kimchi with different degrees of fermentation and quantitatively analyzed using LC-Q-Orbitrap MS. These results were analyzed using linear discriminant analysis and heat mapping, and the metabolites were grouped into early, middle, and late stages of fermentation. Malic acid (6.518-7.701 mMol) was only present in the initial stage of fermentation, and l-phenylalanine rapidly increased from the middle stage (2.180 mMol) to late stage (4.770 mMol). Lactic acid, which is representative of the sour taste of kimchi, was detected in the middle stage and increased rapidly up to 74.452 mMol in the late stage. In summary, in this study, 20 major kimchi metabolites were accurately analyzed within 10 min and grouped based on the degree of fermentation. Therefore, the method established in this study accurately and rapidly provides information on kimchi consumption and fermentation that could be highly valuable to the kimchi industry and kimchi consumers.

Metagenomic comparison of homemade and commercial kimchi prepared in Korea and the United States

It is well known that there is a myriad of factors that determine the kimchi microbial composition during fermentation, including but not limited to, salt concentrations, temperature, raw ingredients, and even manufacturing processes. Because different environments breed different species of microorganisms, the location of where raw ingredients were cultivated can also affect the kimchi microbiota. Previous studies have shown that there is a significant difference in microbial composition between kimchi from different countries, but none has been made between homemade kimchi. Seven samples of homemade kimchi from the US and South Korea (equally made under the same fermentation conditions) and commercial kimchi were used in the study. High differences in genera relative abundances between Korean and the US homemade kimchi could be concluded. The results also exhibited differences in microbial composition and diversity levels between Korean and the US commercial kimchi. This study provides further insight into understanding the complexity of how kimchi microbiome is developed by having the results support the idea that the environment where raw ingredients originate from affect the kimchi quality and taste.

Effect of ultraviolet-C light-emitting diode irradiation on inactivation of white colony-forming yeast in kimchi seasoning

The presence of white colony-forming yeasts (WCFYs) in raw materials negatively affects the quality of kimchi. Accordingly, disinfection processes to effectively control spoilage yeasts, including WCFYs, are crucial for extending the shelf life of kimchi. However, conventional disinfection procedures could result in undesirable changes in the nutritional attributes or sensory characteristics of the food. Therefore, in this study, we investigated whether ultraviolet-C light-emitting diode (UVC-LED) treatment combined with an impeller system could inactivate Candida sake and Kazachstania servazzii cells without causing significant variations in the physicochemical characteristics of kimchi seasoning. UVC-LED at 1680 mJ/cm2 combined with the impeller system at 70 and 140 rotations per min (rpm) reduced the number of C. sake cells in kimchi seasoning by 2.29 and 2.79 log10 CFU/g, respectively, whereas the reduction in the number of K. servazzii cells was observed to be < 2 log10 CFU/g. After UVC-LED irradiation up to 1680 mJ/cm2, the changes in titratable acidity, pH, viscosity, and volatile compounds of the kimchi seasoning remained mostly constant (p > 0.05). We observed that the efficacy of UVC-LED treatment increased as the impeller rotation speed increased. K. servazzii was more resistant to UVC-LED irradiation than C. sake. These experimental results demonstrate that UVC-LED treatment may be a practical alternative to the limited disinfection approaches for high-quality kimchi production.

Analysis of Cultivable Microbial Community during Kimchi Fermentation Using MALDI-TOF MS.

Kimchi, a traditional Korean fermented vegetable, has received considerable attention for its health-promoting effects. This study analyzes the cultivable microbial community in kimchi fermented at different temperatures using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to comprehensively understand the factors affecting the quality of kimchi. Of the 5204 strains isolated from kimchi, aligned with the in-house database, 4467 (85.8%) were correctly identified at the species level. The fermentation temperature affected the microbial community by varying the pH and acidity, which was mainly caused by temperature-dependent competition between the different lactic acid bacteria (LAB) species in kimchi. LAB, such as Levilactobacillus (Lb.) brevis and Lactiplantibacillus (Lpb.) plantarum associated with rancidity and tissue softening, proliferated faster at higher temperatures than at low temperature. In addition, LAB, such as Latilactobacillus (Lat.) sakei and Leuconostoc (Leu.) mesenteroides, which produce beneficial substances and flavor, were mainly distributed in kimchi fermented at 4 °C. This study shows as a novelty that MALDI-TOF MS is a robust and economically affordable method for investigating viable microbial communities in kimchi.

Free Amino Acid and Volatile Compound Profiles of Jeotgal Alternatives and Its Application to Kimchi.

Jeotgal containing abundant free amino acids plays an important role in the unique savory taste (umami) and flavor in kimchi. However, it is also responsible for the unpleasant fishy smell and high salt content of kimchi. Therefore, the present study aimed to identify alternative jeotgal sources and investigate the fermentation properties of jeotgal alternatives added to kimchi. The tomato hot-water extract (TH2) and dry-aged beef hot-water extract (DBH) were selected as jeotgal alternatives for kimchi preparation based on their glutamic acid contents. Characteristics of kimchi with TH2 alone (JA1) and TH2 and DBH in combination (1:1, JA2) were compared with kimchi prepared using commercially available anchovy fish sauce (CON). The pH of JA1 and JA2 was slightly decreased during fermentation, whereas the salinity was significantly lower than CON (p < 0.05). Notably, the most effective factor of the savory taste of kimchi, glutamic acid contents of JA1 and JA2 were significantly higher than that of CON (p < 0.05). In conclusion, JA1 showed slower fermentation with lower salinity and higher glutamic acid content than CON. Overall, this study showed that JA1 derived from TH2 could improve the taste and quality of kimchi by increasing glutamic acid content and decreasing the unpleasant flavor.

김치 유래 복합 종균 적용이 김치의 발효과정에 미치는 영향

In this study, we compared the changes in the quality of kimchi fermented with a complex starter and a single starter. Lactic acid bacteria strains isolated from kimchi were used as starters, and fermention was performed at 10°C for 26 days. The rate of reduction in lactic acid bacteria was low, the initial pH was maintained at a constant level, and the dominance rate of the starter was high at 83% on the 15th day of fermentation with the complex starter, compared to fermentation with the control and single starters. Regarding the CO2 and free sugar content, which are factors affecting product quality and are influenced by lactic acid bacteria fermentation, 1.4 and 1.5 times higher CO2 and mannitol production, respectively, were observed during fermentation of free sugars with the complex starter than in fermentation with the single starter. These results show that the use of a complex starter can improve the distribution quality of kimchi as it results in an extended shelf life and enhanced sensory quality.

Assessment of human norovirus inhibition in cabbage kimchi by electron beam irradiation using RT-qPCR combined with immunomagnetic separation.

Cabbage Kimchi, a traditional Korean fermented food, has occasionally been related to acute gastroenteritis caused by human norovirus (HuNoV). The present study examined the inhibitory effects of electron beam (e-beam) irradiation (1, 3, 5, 7, and 10 kGy) on HuNoV GII.4 in suspension or cabbage Kimchi using reverse transcription quantitative polymerase chain reaction combined with immunomagnetic separation (IMS/RT-qPCR). In addition, physicochemical and sensorial analyses were conducted to assess any change in the quality of cabbage Kimchi following e-beam irradiation. Following e-beam irradiation at 1 to 10 kGy, HuNoV significantly decreased to 0.28 to 2.08 log10 copy number/mL in suspension (P <0.05). HuNoV levels in cabbage Kimchi were also significantly reduced to 0.26 to 1.57 log10 copy number/mL following irradiation with 1 to 10 kGy (P <0.05) compared to positive control (6.0 log10 copy number/mL). The D-values for 1 log10 reduction (90% inhibition) of HuNoV in suspension and cabbage Kimchi were 4.94 and 6.96 kGy of e-beam, respectively. The pH and acidity in the irradiated cabbage Kimchi were 4.41 to 4.58 and 0.61% to 0.71%, respectively, indicating that e-beam did not affect the optimal pH or acidity. Although a slight increase of greenness was observed in the leaf portion of cabbage Kimchi irradiated with 7 to 10 kGy of e-beam, this color change was minimal and went undetected by panelists in the sensorial evaluation. The five properties of sensorial quality assessed were no different in the irradiated Kimchi sample compared with the control sample (nonirradiated cabbage Kimchi). Therefore, this study suggests that ≥6.96 kGy of e-beam could be applied in the cabbage Kimchi industry to obtain >90% of HuNoV without affecting the quality. PRACTICAL APPLICATION: As the most representative food in Korea, Kimchi needs the sanitation technology that can inhibit viral infection. Our findings suggest that e-beam irradiation can be used to reduce HuNoV effectively in Kimchi without changes in sensorial quality.

Improvement in the Quality of Kimchi by Fermentation with Leuconostoc mesenteroides ATCC 8293 as Starter Culture

Improvement in the Quality of Kimchi by Fermentation with Leuconostoc mesenteroides ATCC 8293 as Starter Culture