Kimchi Samples Research Articles

PCR-DGGE analysis of population dynamics of lactic acid bacteria in kimchi by addition of bacteriocins.

The effects of two crude bacteriocins (DF01 and K10) on lactic acid bacteria (LAB) communities and pH during kimchi fermentation were analyzed by polymerase chain reactiondenaturing gradient gel electrophoresis (PCR-DGGE). Crude LAB bacteriocins, prepared by ammonium sulfate precipitation, were added at 5 AU/mL, and kimchi was incubated at 20°C for 7 days. The pH and titratable acidity of the kimchies were determined daily, and the amplified 16S rRNA products were analyzed by PCR-DGGE. The common and main LAB were Weissella spp., Leuconostoc spp., and Lactobacillus spp. from both control and bacteriocin-treated samples. Among them, W. koreensis, W. confusa, and Lb. sakei were the predominant microorganisms throughout the fermentation period. Some obligate and facultatively heterofermentative LAB were detected from the bacteriocin-treated samples. The pH of the kimchi samples treated with each bacteriocin was higher (ca. 0.8 unit) than that of the control at day 4 and 5.

Evaluation of functional properties of lactobacilli isolated from Korean white kimchi

Kimchi, probably Korea's most famous traditional fermented food, is well known for its beneficial properties. Among several hundred different types of kimchi in Korea, white (baek) kimchi is prepared without chilli and is widely appreciated also by non-Koreans because of its unique mild flavour. In an approach to identify the bacteriological basis for proposed health benefits, we isolated 11 Lactobacillus strains from six samples of white kimchi, and investigated their safety and functional features. These strains represented the species Lactobacillus brevis, Lactobacillus plantarum and Lactobacillus sakei that dominated the populations within a range of 3 × 106 to 4 × 108 CFU/mL. Following safety assessment based on antibiotic resistance and biogenic amine production, 7 different strains were selected for further studies including evaluation of their adaptation to cabbage juice and resistance to phenol. Growth in and adaptation to the cabbage juice was favourably influenced by addition of 2% salt. Final selection was based on in vitro passage of simulated stomach duodenum conditions (SSDP model). The strains L. plantarum HAC01 and L. sakei HAC10 were administered to a diet-induced obese (DIO) mouse model receiving a high-fat (HF) diet to assess their functionality in-vivo. Animal groups receiving the viable strains showed significantly lower body weight and total weight gain during 8 weeks compared to the high-fat control group. This study provides preliminary information on the use of in-vitro and in-vivo features for safety and functionality evaluation of Lactobacillus strains from white kimchi. These “first-level” criteria for strain selection may serve as model, thereby facilitating potentially new probiotic developments.

Autoinducer-2 properties of kimchi are associated with lactic acid bacteria involved in its fermentation

Bacteria use the cell density-dependent quorum signalling system to regulate particular gene expressions. In food microbiology, signalling is well known for its relation to (foodborne) pathogenicity, food spoilage, and biofilm formation. Quorum quenching and inhibition are thus being considered as a feasible approach in food preservation and safety. In the case of the luxS-mediated universal quorum sensing using autoinducer-2 (AI-2), however, it could be a different issue. Several studies have reported a luxS AI-2 synthase homologue in numerous bacteria, comprising both pathogens and beneficial strains. A recent study has shown the AI-2 signal to restore the balance of the major phyla of the gut microbiota in antibiotic-induced dysbiosis. We measured the AI-2 activity of the lactic fermented food, kimchi, and found different AI-2 signalling intensities. In order to trace the origin of the signal production, we obtained 229 lactic acid bacterial isolates from the kimchi samples, and detected the AI-2 properties of each isolate using a modified AI-2 bioluminescence assay. Our results showed isolates of dominant species of the genera Lactobacillus, Weissella and Leuconostoc which either produced or inhibited the AI-2 signal. No isolate of the dominant species Lactobacillus sakei (75 isolates) and Lactobacillus curvatus (28 isolates) showed AI-2 producing activity, while AI-2 inhibition could not be detected for any of the 31 Lactobacillus plantarum isolates. These results suggest the AI-2 activity of kimchi to result from the interaction of the associated microbial food cultures (MFCs) during fermentation. Thus far, only sparse information is available on AI-2 signalling interaction in fermented food, however, we suggest that fermented food may be a supplier of AI-2 signalling molecules via typical MFCs.

Cross‐Cultural Comparison of Consumer Acceptability of Kimchi with Different Degree of Fermentation

AbstractStrong flavor developed during fermentation can affect foreign consumer's liking of kimchi (fermented vegetables with seasonings). This study was conducted to compare the cross‐cultural preference of American versus Korean consumers for kimchi fermented to different degrees. Kimchi samples fermented to different degrees (pH 5.9, LFK; pH 4.2, MFK; and pH 3.9, HFK) were presented to American (n = 111) and Korean consumers (n = 101). The degree of liking and attribute intensities were assessed using the 9‐point hedonic scale and Just‐about‐Right scale. Consumer demographics and kimchi consumption habits were also collected. American consumers significantly preferred MFK and HFK to LFK, whereas Korean consumers did not show any significant preference among the samples. American consumers reported that the sourness and spiciness of LFK were not intense enough. The frequency of kimchi consumption by American consumers was positively associated with their preference for more fermented kimchi, while the level of fermentation of the daily consumed kimchi was well associated with Korean consumers’ preference for kimchi.Practical ApplicationsIt is challenging for food industries to launch fermented ethnic food products, such as fermented soy products and vegetables, in foreign markets because acceptability for products with different degree of fermentation may differ across culture and also based on previous experience. The present study investigated how foreign consumers accept one such food, kimchi, at different fermentation levels, particularly in relation to their previous experiences. Results of the present study can help researchers and marketers to establish more effective strategies for developing ethnic foods targeting foreign markets by providing the optimal level of fermentation accepted by foreign consumers and consumer profile. In addition, our findings on the relationship between previous exposures and liking aid in understanding potential mechanisms underlying acquisition of liking for ethnic food by foreign consumers.

Effect of Low Salt Concentrations on Microbial Changes During Kimchi Fermentation Monitored by PCR-DGGE and Their Sensory Acceptance.

Various salt concentrations (1.0%, 1.3%, 1.6%, 1.9%, and 2.1% labeled as sample A, B, C, D, and E, respectively) were investigated for microbial diversity, identification of Lactic Acid Bacteria (LAB) in salted kimchi cabbage, prepared under laboratory conditions. These samples were stored at 4°C for 5 weeks in proper aluminum-metalized pouch packaging with calcium hydroxide gas absorber. A culture-independent method known as polymerase chain reaction - denaturing gradient gel electrophoresis was carried out to identify LAB distributions among various salt concentration samples that had identified 2 Weissella (W. confusa and W. soli), 1 Lactobacillus (Lb. sakei), and 3 Leuconostoc (Lc. mesenteroides, Lc. lactis, and Lc. gelidum) in the overall kimchi samples. The pH, titratable acidity, viable cell counts, and coliform counts were not affected by salt variations. In order to assess sensory acceptance, the conducted sensory evaluation using a 9-point hedonic scale had revealed that samples with 1.3% salt concentration (lower than the manufacturer's regular salt concentration) was more preferred, indicating that the use of 1.3% salt concentration was acceptable in normal kimchi fermentation for its quality and safety. Despite similarities in pH, titratable acidity, viable cell counts, coliform counts, and LAB distributions among the various salt concentrations of kimchi samples, the sample with 1.3% salt concentration was shown to be the most preferred, indicating that this salt concentration was suitable in kimchi production in order to reduce salt intake through kimchi consumptions.

Purification, characterization and mode of action of plantaricin K25 produced by Lactobacillus plantarum

The aim of this study was to elucidate the mode of action of a novel bacteriocin with low molecular weight that was isolated, purified and characterised from Lactobacillus plantarum K25 and found propagating in kimchi samples. This antimicrobial peptide, named plantaricin K25 was recovered from the producer cells by using adsorption-desorption method and purified by high-performance liquid chromatography. It exhibited a broad spectrum of inhibitory activity against both Gram-positive and Gram-negative bacteria. Plantaricin K25 retained bioactivity when exposed to high temperature (121 °C) and remained stable at pH values ranging from 2 to 8. This peptide was partially inactivated by proteinase and pronase and fully degraded by peptidase and trypsin. It remained active after being treated with lipase, amylase, catalase and certain detergents. Based on Tris-Tricine SDS-PAGE of purified bacteriocin, the molecular weight was estimated at 2 kDa. MALDI-TOF mass spectrophotometry showed that the precise molecular weight of the peptide was 1772 Da. Plantaricin K25 showed to be a pore-forming bacteriocin capable of permeabilising the cytoplasmic membrane of targeted bacterial cells. When viewed under SEM and TEM, cell membranes of Bacillus cereus appeared to collapse and disrupt after exposure to the bacteriocin. Plantaricin K25 inhibited the growth of B. cereus cultivated in mul-kimchi with reduction of viable cell counts compared to the control sample. Genome sequencing using Illumina MiSeq showed absence of virulence genes in strain K25 indicating its basic biosafety property. These results suggest that plantaricin K25 can be a suitable alternative to other preservatives used to improve the shelf life of many perishable food products.

The Quality Properties of Rapidly Fermented Mukeun (Long-Term Fermented) Kimchi with Different Salinity and Fermented Temperature

We conducted a study on mukeun (long-term fermented) kimchi ripened over one year in an attempt to develop an alternative salt and improve the quality of low-salt kimchi. However, few studies have focused on mukeun kimchi that has been fermented for a short time in different salinity conditions. Therefore, the aim of this study was to investigate the physicochemical characteristics that occur during the fermentation of mukeun kimchi samples produced with different conditions of salinity and fermentation temperature. Kimchi samples were produced at 3 different salinity levels: 1.6%, 2.4%, and 3.2%. Previous studies revealed that the optimum fermentation time at pH 4.1 was 128 hours at and 417 hours at ; furthermore, the samples were stored for 12 weeks under the condition of after fermentation. Total cell increased on week 0 of storage and decreased according to the storage period. Total cell was the highest at 3.2% salinity and had a high value at temperature during the storage period. Based on the physiochemical results, mukeun kimchi at a salinity of 3.2% can be fermented for a short time, and low-salt kimchi at a salinity of 1.6% and fermented at , is similar to mukeun kimchi at 2.4% salinity.

Source Tracking and Succession of Kimchi Lactic Acid Bacteria during Fermentation.

This study aimed at evaluating raw materials as potential lactic acid bacteria (LAB) sources for kimchi fermentation and investigating LAB successions during fermentation. The bacterial abundances and communities of five different sets of raw materials were investigated using plate-counting and pyrosequencing. LAB were found to be highly abundant in all garlic samples, suggesting that garlic may be a major LAB source for kimchi fermentation. LAB were observed in three and two out of five ginger and leek samples, respectively, indicating that they can also be potential important LAB sources. LAB were identified in only one cabbage sample with low abundance, suggesting that cabbage may not be an important LAB source. Bacterial successions during fermentation in the five kimchi samples were investigated by community analysis using pyrosequencing. LAB communities in initial kimchi were similar to the combined LAB communities of individual raw materials, suggesting that kimchi LAB were derived from their raw materials. LAB community analyses showed that species in the genera Leuconostoc, Lactobacillus, and Weissella were key players in kimchi fermentation, but their successions during fermentation varied with the species, indicating that members of the key genera may have different acid tolerance or growth competitiveness depending on their respective species.

Diversity and community analysis of fermenting bacteria isolated from eight major Korean fermented foods using arbitrary-primed PCR and 16S rRNA gene sequencing

Korean fermented foods are known to be beneficial for human health. Bacterial community studies have been conducted to figure out what roles the bacteria used to ferment these foods play in food fermentation. The metagenomic approach identifies both culturable and unculturable bacterial compositions, but this technique is limited in its ability to accurately determine the bacterial species from short 16S rRNA PCR products. In this study, we revisited the culture-dependent method using a relatively large number of bacterial isolates in an attempt to overcome the problem of bacterial identification, accepting that the unculturable bacterial population in each fermented food would be undetectable. Eight Korean fermented foods including kimchi, jeotgal, and meju were collected, and 1589 fermenting bacterial strains were randomly isolated. Bacteria were grouped by banding pattern using arbitrary-primed (AP) PCR prior to bacterial identification and sorted into 219 groups; 351 strains were not grouped because there was no identical AP-PCR band pattern. 16S rRNA sequence analysis identified the bacterial compositions of the fermented foods. As dominant genera, Lactobacillus and Leuconostoc strains were detected in four kimchi samples, Staphylococcus in three jeotgal samples, and Enterococcus and Bacillus in the meju sample. Interestingly, S. Equorum was most dominant in saeu-jeotgal, indicating that it is halophilic and may enhance the fermentation flavor. Further comparative analysis of this study with previous metagenomic results revealed that bacterial communities in fermented foods are highly similar at the genus level but often differ at the species level. This bacterial community study is useful for understanding the roles and functional properties of fermenting bacteria in the fermentation process of Korean fermented foods.

Three gastroenteritis outbreaks in South Korea caused by the consumption of kimchi tainted by norovirus GI.4.

In April 2013, outbreaks of acute gastroenteritis were reported at three schools in Jeonju, South Korea. Epidemiological investigations were performed to characterize the outbreaks and implement appropriate control measures. Retrospective cohort studies were performed at these schools. Stool and environmental samples were collected for bacterial and viral assessment. A food supplier of the schools, food company X, was inspected, and samples of cabbage kimchi and groundwater were tested for norovirus by real-time reverse-transcriptase polymerase chain reaction. The relatedness of the detected norovirus strains was evaluated by phylogenetic analysis. Of the 3347 questionnaires distributed, 631 (attack rate: 18.9%) met the case definition. Among the consumed food items, kimchi products (i.e., cabbage and fresh kimchi) were significantly associated with illness. The kimchi products were supplied by food company X. Among stool samples from 95 students and 34 food handlers at the 3 schools, 39 (41.1%) and 14 (41.2%) samples, respectively, were positive for norovirus. The samples of groundwater and cabbage kimchi at food company X were positive for norovirus. The predominant genotype of norovirus detected in the patient, groundwater, and cabbage kimchi samples, GI.4, shared high nucleotide identity. Kimchi products tainted with norovirus GI.4 from contaminated groundwater were linked to the acute gastroenteritis outbreaks. Therefore, kimchi manufacturers in South Korea should apply chlorine disinfection when using groundwater. Moreover, more stringent sanitation requirements and strict regulations for food companies are recommended.

An irreversible ripeness indicator to monitor the CO2 concentration in the headspace of packaged kimchi during storage

An irreversible chitosan-based indicator has been developed to monitor the kimchi quality corresponding to the partial pressure of CO2 gas in the packaging headspace. For this, 0.3% (w/v) solutions of chitosan and the Coomassie Brilliant Blue dye (BB) were mixed at volume ratios of 10:1, 10:2, and 10:5 to yield BB-incorporated chitosan-based CO2 indicators. A greater CO2 accumulation was observed for kimchi samples stored at 25°C than those stored at 15°C. Acidity measurements indicated optimal consumer satisfaction at 1 and 3 days (when the transparency measurements for the developed indicators were approximately 20%) for kimchi samples stored at 15 and 25°C, respectively. A Pearson correlation analysis revealed that the indicator transparency correlated well with several parameters used to indicate the kimchi quality.

김치 발효 및 저장조건에 따른 배추김치의 위암세포 성장 억제 효과

배추김치 제조 후 익힘 시간 및 김치 냉장고 저장 기간에 따른 김치의 위 암세포 증식 억제 효능 변화를 측정해 본 결과, 저장 30일 김치 시료 기준으로 익힘 과정을 거치지 않은 S0h 시료에 비하여 46시간의 익힘 과정을 거친 S46h 시료의 효능이 가장 우수하였고, 이어서 S47h, S48h 시료의 효능이 우수하였다. 그리고 S0h 경우는 상대적으로 암세포 증식 억제 효능이 가장 약하였다. 이는 적정 발효에 따른 발효 대사산물, 그리고 유산균 속 및 종 변화에 기인한 결과로 판단되며, 항암 효능 보유물질로 알려진 GABA의 농도와도 연관이 있을 수 있음을 제안해 주고 있다. 김치는 다양한 재료 유래의 기능성 물질, 대사산물 및 유산균을 보유하고 있는 발효식품이다. 따라서 본 연구는 김치제조 후 최적의 숙성 시간과 저장 기간을 선택하면 항암 기능성이 증진된 김치를 섭취할 수 있는 것을 제안해 주고 있다. In this study, we investigated cancer cell growth inhibitory effects of kimchi extracts obtained from cabbage kimchi. Kimchi extracts (S46h, S47h, S48h) were obtained from the samples fermented at <TEX>$15^{\circ}C$</TEX> for 46 h, 47 h, and 48 h during the first 10 days, which were subsequently stored at <TEX>$-1.4^{\circ}C$</TEX> in kimchi refrigerator (hereinafter DV kimchi extracts). The samples showed a higher anti-proliferative effect against AGS (human, gastric adenocarcinoma) cell lines compared to control kimchi extract (S0h) obtained from sample stored at <TEX>$-1.4^{\circ}C$</TEX> without fermentation. The DV kimchi contained higher levels of <TEX>${\gamma}$</TEX>-aminobutyric acid (GABA) and ornithine compared to the control kimchi extract. Among the DV kimchi extracts, the S46h sample showed a higher anti-proliferative effect against the cancer cell growth and contained higher amount of GABA than the other kimchi samples. These results suggest that the consumption of DV kimchi can be more beneficial, as it is rich in GABA and ornithine. Therefore, it could be helpful in retarding the proliferation of cancer cells compared to the control kimchi.

Pichia kudriavzevii is the major yeast involved in film-formation, off-odor production, and texture-softening in over-ripened Kimchi

Yeasts were isolated from over-ripened kimchi and identified. Isolates were identified as Pichia kudriavzevii, Kazachstania servazii, Kazachstania exigua, Kazachstania bulderi, and Rhodotorula mucilaginosa. Among the isolates, P. kudriavzevii GY1 and K. bulderi HY2 were separately inoculated into kimchi and incubated at 10°C for 21 days. After incubation, HY2 kimchi showed less offodors, whereas GY1 kimchi showed strong off- and moldyodors in the sensory evaluation. P. kudriavzevii GY1 showed significantly higher polygalacturonase activity than K. bulderi HY2. Volatile compounds in kimchi samples were analyzed by HSPM-GC. Peak areas of obnoxiousodor compounds, including methanethiol, were 6.61, 9.46, and 20.87% for control kimchi, HY2 kimchi, and GY1 kimchi, respectively. Therefore, P. kudriavzevii was mainly responsible for kimchi spoilage, including off-odors and texture softening. Moreover, K. bulderi was associated with kimchi deterioration at cell counts up to 8.0–9.0 log CFU/mL, even though its effects were not as strong as those of P. kudriavzevii.

매운맛 등급화 고춧가루로 제조한 배추김치의 이화학적 관능적 특성

This study investigated the spicy hot flavor related quality characteristics of baechu (Kimchi cabbage) Kimchi prepared using hot pepper powder in various capsaicin levels during 8 weeks of storage. The pHs in the Kimchi samples were in the optimum range of the pH 4.2-4.5 due to the relatively low storage temperature of <TEX>$2^{\circ}C$</TEX> during the entire storage periods. The L, a and b values of cap-150 sample group were significantly higher compared to those in the other samples at 8 weeks of storage. Grading hotness of the Kimchi was significantly clearly separated when varied levels of hotness for the hot pepper powder were used at 2-4 weeks of storage (p<0.001). Sensory spicy hotness of the cap-40 showed significantly the lowest with values of 4.57-4.38 representing mild hot:, that of cap-85 was medium hot with values of 5.81-6.00; and finally, that of cap-150 showed the values of 6.86-7.14, representing strong hot flavor at 2-4 weeks of storage (p<0.001). The grading of spicy hotness in the Kimchi increased by about one level at the optimal edible periods due to the leaching out of capsaicin from the hot pepper powder for those storage periods. Thus, the increased hotness of the Kimchi in the optimal edible periods should be considered when the desired hotness of the hot pepper is chosen for the Kimchi preparation. The hotness decreased as the organic acids were generated during ripening by the 8th weeks of storage.

배추김치 저장조건에 따른 발효특성 및 오르니틴 함량 변화

Abstract Changes in fermentation properties and ornithine levels of Baechu Kimchi by storage conditions were investigated. After making and fermenting Kimchi at 15℃ for 32 hr (S1), 36 hr (S2), 40 hr (S3), 44 hr (S4), and 48 hr (S5) during the first 10 days of storage. The Kimchi samples are subsequently stored in the 1℃ Kimchi refrigerator for up to 60 days. Changes in the pH values and lactic acid contents of S4 and S5 samples are slightly bigger than the S1, S2 and S3 samples which have no significance differences. According to lactic acid bacteria (LAB) number, all samples show the largest augmentation according to the number of Lactobacilli during the first 20 days of storage. After 20 days of storage, the S4 and S5 samples show larger accumulations of LAB than S1, S2 and S3 samples. The Weissella genus is predominated at the 40 day of storage in the S5 sample. Ornithine levels are increased up to 170 ㎎ per 100 g during the storage period of 40~50 days in the S5 sample. However, the increase of ornithine levels in S1, S2 and S3 samples is smaller than those of the S4 and S5 samples. These results indicate that the conditions of Kimchi fermentation, which is 48 hr at 15℃ before storage, is proved to be the most superior for ornithine levels within the Kimchi refrigerator. Key words: Kimchi, fermentation, storage, ornithine levels, Weissella genus

Isolation and characterization of a proteinaceous antifungal compound from Lactobacillus plantarum YML007 and its application as a food preservative

Korean kimchi is known for its myriad of lactic acid bacteria (LAB) with diverse bioactive compounds. This study was undertaken to isolate an efficient antifungal LAB strain among the isolated kimchi LABs. One thousand and four hundred LABs isolated from different kimchi samples were initially screened against Aspergillus niger. The strain exhibiting the highest antifungal activity was identified as Lactobacillus plantarum YML007 by 16S rRNA sequencing and biochemical assays using API 50 CHL kit. Lact.plantarum YML007 was further screened against Aspergillus oryzae, Aspergillus flavus, Fusarium oxysporum and other pathogenic bacteria. The morphological changes during the inhibition were assessed by scanning electron microscopy. Preliminary studies on the antifungal compound demonstrated its proteinaceous nature with a molecular weight of 1256·617Da, analysed by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF). The biopreservative activity of Lact.plantarum YML007 was evaluated using dried soybeans. Spores of A.niger were observed in the negative control after 15days of incubation. However, fungal growth was not observed in the soybeans treated with fivefold concentrated cell-free supernatant of Lact.plantarum YML007. The broad activity of Lact.plantarum YML007 against various food spoilage moulds and bacteria suggests its scope as a food preservative. After screening 1400 kimchi bacterial isolates, strain Lactobacillus plantarum YML007 was selected with strong antifungal activity against various foodborne pathogens. From the preliminary studies, it was found that the bioactive compound is a low molecular weight novel protein of 1256·617Da. Biopreservative potential of Lact.plantarum YML007 was demonstrated on soybean grains, and the results point out YML007 as a potent biopreservative having broad antimicrobial activity against various foodborne pathogens.

Metatranscriptomic analysis of lactic acid bacterial gene expression during kimchi fermentation

Barcode-based 16S rRNA gene pyrosequencing showed that the kimchi microbiome was dominated by six lactic acid bacteria (LAB), Leuconostoc (Lc.) mesenteroides, Lactobacillus (Lb.) sakei, Weissella (W.) koreensis, Lc. gelidum, Lc. carnosum, and Lc. gasicomitatum. Therefore, we used completed genome sequences of representatives of these bacteria to investigate metatranscriptomic gene-expression profiles during kimchi fermentation. Total mRNA was extracted from kimchi samples taken at five time points during a 29day-fermentation. Nearly all (97.7%) of the metagenome sequences that were recruited on all LAB genomes of GenBank mapped onto the six LAB strains; this high coverage rate indicated that this approach for assessing processes carried out by the kimchi microbiome was valid. Expressed mRNA sequences (as cDNA) were determined using Illumina GA IIx. Assignment of mRNA sequences to metabolic genes using MG-RAST revealed the prevalence of carbohydrate metabolism and lactic acid fermentation. The mRNA sequencing reads were mapped onto genomes of the six LAB strains, which showed that Lc. mesenteroides was most active during the early-stage fermentation, whereas gene expression by Lb. sakei and W. koreensis was high during later stages. However, gene expression by Lb. sakei decreased rapidly at 25days of fermentation, which was possibly caused by bacteriophage infection of the Lactobacillus species. Many genes related to carbohydrate transport and hydrolysis and lactate fermentation were actively expressed, which indicated typical heterolactic acid fermentation. Mannitol dehydrogenase-encoding genes (mdh) were identified from all Leuconostoc species and especially Lc. mesenteroides, which harbored three copies (two copies on chromosome and one copy on plasmid) of mdh with different expression patterns. These results contribute to knowledge of the active populations and gene expression in the LAB community responsible for an important fermentation process.

Comparison of Bacterial Community Changes in Fermenting Kimchi at Two Different Temperatures Using a Denaturing Gradient Gel Electrophoresis Analysis

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technique followed by sequencing of the 16S rDNA fragments eluted from the bands of interest on denaturing gradient gels was used to monitor changes in the bacterial microflora of two commercial kimchi, salted cabbage, and ingredient mix samples during 30 days of fermentation at 4°C and 10°C. Leuconostoc (Lc.) was the dominant lactic acid bacteria (LAB) over Lactobacillus (Lb.) species at 4°C. Weissella confusa was detected in the ingredient mix and also in kimchi samples throughout fermentation in both samples at 4°C and 10°C. Lc. gelidum was detected as the dominant LAB at 4°C in both samples. The temperature affected the LAB profile of kimchi by varing the pH, which was primarily caused by the temperature-dependent competition among different LAB species in kimchi. At 4°C, the sample variations in pH and titratable acidity were more conspicuous owing to the delayed growth of LAB. Temperature affected only initial decreases in pH and initial increases in viable cell counts, but affected both the initial increases and final values of titratable acidity. The initial microflora in the kimchi sample was probably determined by the microflora of the ingredient mix, not by that of the salted cabbage. The microbial distributions in the samples used in this study resembled across the different kimchi samples and the different fermentation temperatures as the numbers of LAB increased and titratable acidity decreased.

Development of a Lexicon for Commercially Available Cabbage (Baechu) Kimchi

AbstractCommercially available cabbage (baechu) kimchi is growing in popularity outside Korea in part because of globalization and a growing interest in specialty foods. Within Korea, commercially available kimchi is important because many households do not have time to prepare traditional kimchi at home. Despite this fact, little work has been published characterizing the sensory attributes of this popular fermented food. The objectives of this study were to (1) develop an initial sensory lexicon for popular commercially available cabbage (baechu) kimchi, including specific flavor references, in order to allow researchers to measure and compare sensory characteristics, and (2) to use the lexicon to determine if it described differences in a range of commercially available wedge (pogi) and sliced (mat) fresh and fermented baechu kimchi available in Korea. A lexicon with 15 flavors and two key texture terms was developed by a descriptive panel to characterize baechu kimchi samples and is presented here in both English and Korean to enhance use. Age (fresh or fermented) and manufacturer had a tremendous influence on the sensory characteristics of the commercial kimchi samples. Areas for future research include examining sensory properties of kimchi made from products other than cabbage, conducting consumer research to relate acceptability of baechu kimchi products with descriptive scores, and comparing homemade and commercially produced kimchi products.Practical ApplicationsThe development of this lexicon is the first of its kind for kimchi and can help sensory scientists better understand this unique product and will help manufacturers differentiate their products from competitors and improve existing products on the market. Sensory scientists will also be able to use this information to standardize the sensory attributes of baechu kimchi and provide a common platform on which to evaluate these products.

Isolation and Identification of γ-Aminobutyric acid (GABA)-producing lactic acid bacteria from Kimchi

Presumptive lactic acid bacteria (LAB) were isolated from 20 kimchi samples (total of 230 isolates) and screened for their capacity to synthesize γ-aminobutyric acid (GABA). Only 68 isolates (ca. 30%) showed this activity and were identified by a polyphasic approach consisting of morphological characteristics, catalase and biochemical tests, and species-specific polymerase chain reaction and 16S rRNA gene sequence analyses. Five species were found, including Lactobacillus plantarum (55 isolates), Lactobacillus brevis (six), Leuconostoc mesenteroides (four), Leuconostoc lactis (one), and Weissella viridescens (two). The 68 GABA-producing LAB isolates were isolated from only 11 among 20 kimchi samples indicating that they were not evenly distributed. This is the first report on the isolation of two species of Leuconostoc (Le. mesenteroides and Le. lactis) and one species of Weissella (Ws. viridescens) from kimchi with the capacity to synthesize GABA under in vitro conditions. Additionally, in previous screening results, Le. lactis and Ws. viridescens with the capacity to synthesize GABA isolated and identified from fermented food source were not observed.