Subingredients and Natural Preservative Plants

a. Subingredients. Kimchi subingredients were examined for their ability to inhibit the growth of microorganisms. An increased garlic concentration (0-6%) in the preparation decreased the number of aerobic bacteria but increased LAB levels at 2 days (early stage fermentation) at 21 °C (44). A recipe of 2 percent garlic content in kimchi decreased the amount of aerobic bacteria significantly (50- to 1000-fold) compared to a kimchi recipe of 1% garlic. Cho and Jhon (45) also reported that 21 aerobic bacteria isolated from kimchi had inhibited growth in the presence of garlic extract. The isolated bacteria were 11 Bacillus sp., 2 Staphylococcus sp., 1 Micrococcus sp., 1 Flavobacterium sp., 2 Enterobacteriaceae and 4 Vibrionaceae. The 21 aerobic bacteria could not grow in the nutrient broth with a 4.5% garlic concentration at 30°C for 24 hours. Only one strain survived when the garlic concentration was 2.8%. Nine out of the 21 strains could survive in the 1% garlic concentration. Kim et al. (46) reported that garlic extract also significantly suppressed the growth of E. coli in tryptic soy broth (TBS). Based on the data, these investigators concluded that garlic is a major condiment having the ability to eliminate unnecessary microorganisms of aerobic bacteria and E. coli in kimchi.

Lee and Kim (47) reported that red pepper, garlic, and ginger (the main subingredients of kimchi) also inhibited growth of the LAB at only the early stage of fermentation (2 days at 25°C), but thereafter the overall growth rate was the same or accelerated compared to the control.

On the other hand, sucrose, MSG, fresh oyster, and salt-fermented anchovy and shrimp increased the fermentation rate (48). MSG reduced kimchi the fermentation period, by the stimulatory growth of the LAB, but the pH changes were similar to the control (49). The addition of MSG to kimchi showed growth stimulation of LAB with a buffering action and a constant pH level. But MSG affected the stability of ascorbic acid, thiamine, and h-carotene. The MSG addition enhanced the flavor because of glutamic acid, which reduced the sour taste.

b. Natural Preservatives. To develop a natural preservative that would extend the shelf life of kimchi, Moon et al. (50) screened 102 edible plants, 21 antimicrobial agents, and other related compounds for kimchi fermentation. Baical skullcap and Assam indigo from 42 oriental medicinal plants were shown to be effective for maintaining the fresh state of kimchi. Thirty-two herbs and spices, including peppermint, cinnamon, lemon balm, clove, hops, rosemary, sage, horseradish, and thyme showed high antimicrobial activity against the kimchi-fermenting microorganisms. Pine needles, persimmons, and oak leaves showed a significant bactericidal effect among the 28 fruits, vegetables, and related plants tested. Nisin and caffeic acid effectively slowed kimchi fermentation, making them good natural preservatives in extending the shelf life of kimchi. However, sensory evaluation is another important factor to consider for the selection of preservatives. Kim and Park (51) studied antimicrobial activities among 15 kinds of vegetables used as kimchi ingredients. Leek extracts showed particularly strong antimicrobial activities against Ped. cerevisiae and Lac. plantarum, known to be a major microorganism for the acidification of kimchi during fermentation.

Saps from pine needles are reported to suppress fermentation (52), as the pine needles extend by almost double the time needed to reach a pH 4.3. The total viable number and the Lactobacillus cell number decreased when pine needle extract was added to kimchi, regardless of fermentation temperatures.

The addition of green tea in kimchi extended its shelf life by lowering the titratable acidity, lactic acid, and acetic acid contents (53). We studied the increased preservative and antimutagenic effects of green tea leaves added to baechu kimchi (green tea added kimchi, GK) (54). The fermentation period for the GKs was extended compared to the control kimchi (CK). Although the initial pH and acidity between GKs and CK were similar, the time for the kimchis to reach optimally ripened status (pH 4.3) was different. CK took 6 days, while GK2 and GK4 took 10 and 14 days at 10°C, respectively (Fig. 6). Accordingly, the growth of Leuconostoc sp. and Lactobacillus sp. in the GKs was considerably delayed. As shown in Fig. 7, the growth of Leuconostoc sp. was greatly retarded, yet the levels are still

Fermentation time (days) Fermentation time (days)

Figure 6 Changes in pH and acidity of control kimchi (CK) and green-tea-leaves added kimchis (GK) during fermentation at 10°C. GK2: 2% green-tea-leaves-added; GK4: 4% green-tea-leaves-added. (From Ref. 54.)

0 2 4 6 8 10 12 14 o 2 4 6 8 10 12 14 Fermentation time (days) Fermentation time (days)

Figure 7 Changes in the numbers of Leuconostoc sp. and Lactobacillus sp. of control kimchi (CK) and green-tea-leaves-added kimchi (GK) during fermentation at 10°C. GK2: 2% green-tea-leaves-added; GK4: 4% green-tea-leaves-added. (From Ref. 54.)

0 2 4 6 8 10 12 14 o 2 4 6 8 10 12 14 Fermentation time (days) Fermentation time (days)

Figure 7 Changes in the numbers of Leuconostoc sp. and Lactobacillus sp. of control kimchi (CK) and green-tea-leaves-added kimchi (GK) during fermentation at 10°C. GK2: 2% green-tea-leaves-added; GK4: 4% green-tea-leaves-added. (From Ref. 54.)

high compared to the control. However, the population of Lactobacillus decreased with the addition of green tea, indicating that Leuconostoc sp. was dominated to Lactobacillus, giving a better taste to the kimchi.

The addition of ginseng (2%) to the kimchi boosted both its shelf life and its quality. Ginseng-added kimchi showed a more favorable tissue texture, improved overall acceptability, and retarded the rancidity of the kimchi (55,56).

The effects of low temperature heating and the addition of mustard oil on pH and total acidity of kimchi during storage at 15°C were studied (57). Mustard oil showed antimicrobial acitivity for Lac. plantarum, Lac. brevis, Leu. mesenteroides, and Ped. cervisiae. The addition of 200 ppm mustard oil, 0.1% mustard powder, and 0.01% H2O2 to kimchi reduced the fermentation rate. Low temperature heating (50 °C) of salted cabbages and the addition of 200 ppm mustard oil and 0.01% H2O2 to seasonings extended the time to reach the optimum ripening of the kimchi, about 2.5 times compared to the control. A combination of preheating at a low temperature (50 °C for 35 minutes) with addition of mustard oil and H2O2 to the seasoning and postheating at low temperature (65°C for 20 minutes) slowed the kimchi fermentation speed about 5 times, compared to the control.

Chitosan and oligochitosan decreased the fermentation rate. The pH was not lowered, and total acidity was lower, in the chitosan-added kimchi (58). The numbers of total viable cells, Leuconostoc sp. and Lac. plantarum, were lower in the chitosan-added kimchi than in the control. The sour and stale flavor of the kimchi was reduced by the chitosan addition. Our laboratories found that when the chitosan oligosaccharide is added (1%), the growth of LAB can greatly be inhibited, without a decrease of pH. The increase in total acidity was greatly retarded (more than twice) during fermentation at 15°C. More importantly, the taste of the final product received a high mark by the sensory evaluation test.

Chinese pepper also showed an antimicrobial property to extend the shelf life of kimchi. It is worth noting that experiments show that peppers have antimutagnic/anticancer activities in tests in vitro and in vivo (59). Choi et al. (60) studied the inhibitory effect of nisin (a bacteriocin produced by Strep. lactis) on kimchi fermentation at 15°C. The addition of 100 IU/g of nisin delayed fermentation by pH, total acidity, and LAB counts.

Bamboo leaves extract exhibited strong antimicrobial activity against Brettanomyces custersii, Klebsiella oxytoca, and Pichia membranaefaciens, which are responsible for softening the kimchi texture (61). The antimicrobial activity of bamboo leaves extract was better than 0.5% and 1.0% sorbic acid, and was stronger at pH 5 than at pH 7. The addition of bamboo leaves to radish-based dongchimi is an old tradition in prolonging the shelf life and improving the taste of kimchi (62).

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