Kyu Hang Kyung

Antimicrobial activity of sulfur compounds derived from cabbage.

Selected sulfur compounds found in cabbage and its fermentation product, sauerkraut, were tested for minimum inhibitory concentration (MIC) against growth of 15 species of bacteria and 4 species of yeasts. S-Methyl-L-cysteine sulfoxide, sinigrin, and dimethyl sulfide at 500 ppm were not inhibitory to any of the bacteria and yeasts tested. Dimethyl disulfide at 500 ppm retarded some, but did not prevent growth of any of the test microorganisms. Dimethyl trisulfide had an MIC to bacteria of 200 ppm and to yeast of 20 ppm. Methyl methanethiosulfinate had an MIC between 50 and 200 ppm for all bacteria, and between 6 and 10 ppm for all yeasts tested. Methyl methanethiosulfonate had an MIC between 20 and 100 ppm for bacteria and between 50 and 500 ppm for yeasts. Allyl isothiocyanate had an MIC between 50 and 500 ppm for bacteria and between 1 and 4 ppm for yeasts. Methyl methanethiosulfinate was 10 to 100 times more inhibitory against Listeria monocytogenes at pH values of 5, 6, and 7 and was much less influenced by pH than was sodium benzoate.

Antimicrobial properties of allium species.

The antimicrobial activity of Allium species has long been recognized, with allicin, other thiosulfinates, and their transformation products having antimicrobial activity. Alliums are inhibitory against all tested microorganisms such as bacteria, fungi, viruses, and parasites. Alliums inhibit multi-drug-resistant microorganisms and often work synergistically with common antimicrobials. Allium-derived antimicrobial compounds inhibit microorganisms by reacting with the sulfhydryl (SH) groups of cellular proteins. It used to be thought that allicin reacts only with cysteine and not with non-SH amino acids, but evidence has accumulated that allicin and other thiosulfinates also react with non-SH amino acids.

Microbial ecology of watery kimchi.

The biochemistry and microbial ecology of 2 similar types of watery (mul) kimchi, containing sliced and unsliced radish and vegetables (nabak and dongchimi, respectively), were investigated. Samples from kimchi were fermented at 4, 10, and 20 °C were analyzed by plating on differential and selective media, high-performance liquid chromatography, and high-throughput DNA sequencing of 16S rDNA. Nabak kimchi showed similar trends as dongchimi, with increasing lactic and acetic acids and decreasing pH for each temperature, but differences in microbiota were apparent. Interestingly, bacteria from the Proteobacterium phylum, including Enterobacteriaceae, decreased more rapidly during fermentation at 4 °C in nabak cabbage fermentations compared with dongchimi. Although changes for Proteobacterium and Enterobacteriaceae populations were similar during fermentation at 10 and 20 °C, the homolactic stage of fermentation did not develop for the 4 and 10 °C samples of both nabak and dongchimi during the experiment. These data show the differences in biochemistry and microbial ecology that can result from preparation method and fermentation conditions of the kimchi, which may impact safety (Enterobacteriaceae populations may include pathogenic bacteria) and quality (homolactic fermentation can be undesirable, if too much acid is produced) of the product. In addition, the data also illustrate the need for improved methods for identifying and differentiating closely related lactic acid bacteria species using high-throughput sequencing methods.

Green pigmentation characteristics of amino compounds with thiosulfinates obtained from garlic (Allium sativum L.)

Pigmentation of various amino compounds with garlic thiosulfinates was investigated. Aminocarbonyl compounds including aldehydes, amino acids, peptides, and proteins formed compound-specific characteristic pigments with thiosulfinates, regardless of their origin. An intact amino group was essential, and the replacement of an amino group’s hydrogen atom made them unable to form pigment. Water-soluble proteins exhibited relatively intense green pigmentation, whereas water-insoluble ones showed negligible pigmentation. Taurine, a natural amino compound, which has a sulfonate group in place of the carboxyl group of an amino acid, also participated in pigment formation with thiosulfinates. Other sulfonates with an amino group, including aminosulfonic acid and ptoluenesulfonamide, did not form pigment. This is the first time that the pigmentation of proteins, amino aldehydes, ammonia and taurine with thiosulfinates has been reported.

Factors influencing the stability of garlic thiosulfinates

Despite a potent antimicrobial activity, garlic (Allium sativum L.) has not been used as a commercial food preservative because of instability of the antimicrobial activity, among other reasons. Factors influencing the stability of thiosulfinates in garlic were investigated to improve understanding of the antimicrobial activity of garlic in food preservation. As temperature, pH, the garlic concentration, and the liquid oil content increased, the stability of thiosulfinates decreased. Thiosulfinates were more unstable as the degree of unsaturation of fatty acids was increased. Solid fatty acid did not affect the stability of thiosulfinates. Other major food components, such as free amino acids, proteins, and carbohydrates did not influence the stability of thiosulfinates. Garlic can be used as a natural preservative for food items with low pH values and with low oil contents stored at low temperatures.

Isolation and Purification of Garlic Specific Organic Compounds

Garlic specific organic compounds were separated and purified using a recycling preparative high-performance liquid chromatography (HPLC) from blanched garlic cloves. Identification of the compounds involved comparing the previously reported HPLC retention times as well as other identification methods including 1 H- and 13 C-nuclear magnetic resonance and liquid chromatography-mass spectrometry. The yields of garlic specific organic compounds were 12.2, 42.5, 1.6, 1.2, and 4.8% on wet weight basis of garlic for alliin(S-allyl-L-cysteine sulfoxide), isoalliin(S-1-propenyl-L-cysteine sulfoxide), γ-glutamyl-S-allylcysteine, γ-glutamyl-S-1-propenylcysteine and γ-glutamyl-phenylalanine, respectively. All the compounds, except for γ-glutamylphenylalanine, contained sulfur.

3-(Allyltrisulfanyl)-2-Aminopropanoic Acid, a Novel Nonvolatile Water-Soluble Antimicrobial Sulfur Compound in Heated Garlic

A nonvolatile and slightly water-soluble antimicrobial sulfur compound newly isolated from heated garlic extract was characterized. The compound was generated most when heated at 120°C for 30 minutes and completely disappeared after 90 minutes of heating. It has a molecular mass of 225 daltons with an elemental ratio of C₆H₁₁N₁O₂S₃, and the interpretation of ¹H- and ¹³C-nuclear magnetic resonance and Fourier transform-infrared data showed that the compound was CH₂=CH-CH₂-S-S-S-CH₂-CH(NH₂)COOH, 3-(allyltrisulfanyl)-2-aminopropanoic acid, a derivative of cysteine, presumably derived from alliin (S-allyl-L-cysteine sulfoxide). This novel compound has comparatively potent anti-yeast activity and rather weak antibacterial activity, similar to other antimicrobial compounds in garlic.

Green pigmentation and pH change of homogenized garlic

AbstractpH of greening garlic was stable below 6.25 during storage at 30°C for 12 h. pH of non-greening garlic increased for 2 h and stayed above 6.28. Garlic homogenate concentrations influenced absorbance at 590 nm (blue) and pH. Blue pigment formation was proportional to garlic concentrations up to 30% with a pH drop. Absorbance at 590 nm and pH decreased at a slow rate as the garlic concentration increased. Absorbance values at 440 nm (yellow) increased in proportion to concentrations of garlic in direct relationship with changes in pH. An inverse relationship between blue pigment formation and pH decline was observed.

Cysteine reacts to form blue-green pigments with thiosulfinates obtained from garlic (Allium sativum L.).

Cysteine was found to form pigments with garlic thiosulfinates in this investigation, in contrast to previous reports. Pigments were formed only when the molar concentration ratios of cysteine to total thiosulfinates were smaller than 2:1. Cysteine does not form pigments with thiosulfinates in the same manner as other pigment-forming amino compounds because it has a sulfhydryl (SH) group. A colour reaction of cysteine with thiosulfinates is proposed where colourless disulphide-type S-alk(en)yl mercaptocysteines (SAMCs) are formed first by the SH-involved reaction between cysteine and thiosulfinates, and then SAMCs react with residual thiosulfinates to form pigments. When the cysteine to total thiosulfinate molar concentration ratio was 2:1 or greater, total thiosulfinates were consumed to form SAMCs without leaving any thiosulfinates remaining available for the following colour reactions.