Hamin Hwang

4-19-2005

extra credit report

Kimchee and Fermentation

Introduction

            Each country has its own unique food item that is special and has been providing local community with rich nutrition and various flavors.  Such food item in Korea is called Kimchee.  It was not well-known to the world until the Olympic Games in 1988.  This was the first time when numerous people were exposed to such interesting flavors of Kimchee—spicy, fermented bok choy or Chinese cabbage product.  By fermentation, Koreans were able to preserve much nutritional values of the cabbage, improve and develop layers of different flavors, and significantly increases shelf life of the product.  Moreover, Kimchee fermentation has been providing Koreans with rich source of vitamin C and B throughout the history.  One popular misconception is that Kimchee fermentation is only for preserving bok choy.  However, it is used to preserve over 100 different food items, such as onions, garlic, and radish as well as fish, clam, oysters, squid, and various other marine food sources in coastal areas.

            Fermentation process is based on a few different microorganisms, such as Weissella spp, Leuconostoc spp, and Lactobacillus spp (Lee et al., 2002 andLim et al., 1989  Leuconostoc mesenteriodes is predominating in the early stages as it provides anaerobic conditions at pH of the Kimchee is around 7.0-8.0.  Following the this stage, lactobacillus spp play a major role in fermentation.  Lactobacillus spp are anaerobes that produce lactic acid from simple sugars, such as mono or disaccharides.  The primary means of preservation comes from low pH and salt tolerance that inhibits growth of non-halophilic microorganisms. (Shin et al., 1996).  As anaerobic condition is achieved, Lactobacillus plantarum becomes predominant and pH will go down to 3.5 from the production of lactic acid (Mheen and Kwon 1984).  However, if stored for too long or not under optimal storage conditions, Kimchee will over acidify, becoming too sour for enjoyable consumption.

Method and Procedure

Preparation of Cabbage

  1. in 20 L of water, put 500 grams of salt to make brine solution
  2. clean and cut 2 head of bok choy so that it becomes 8 pieces
  3. submerge bok choy into the brine solution for 8 hours
  4. rinse bok choy with fresh water and cut it to many small pieces

Preparation of Sugar

1.      mix 100 gram of powdered rice with 200mL of water and bring to boil slowly

2.      add 45 grams of salt into the viscous liquid (powdered rice + water)

Preparation of spices

1.      blend 4 cloves of garlic, 8 chilli pepper, 2 small onion, 2 ginger, 2 oyster

Mixing & fermentation

1.      add bok choy, viscous liquid (powdered rice + water + salt) with blend of spices

2.      Place into a glass jar with open top.  Put shrink wrap on the top with rubber bands to seal, instead of using original metal/plastic lid.

Data

Ph of Kimchee over period of 20 days

Day

pH

1

7.3

3

7

7

5.5

10

4.5

17

4.3

20

4.1

 

Conditions: Room Temperature of 76 degrees F

Results and Discussion

            For the first three days, little pH change is observed, this is due to Leuconostoc mesenteriodes that is changing substrate to anaerobic condition, but not producing lactic acids (Mheen and Kwon 1984).  In addition, microbes are not large in number; therefore, more time is necessary for rapid growth of the microbial community.  As expected, pH of the Kimchee drops from 7 to 4.5 within the next 7 days.  This must be when Lactobacillus spp. is at the log phase of growth.  At around 10th day, Lactobacillus spp reach the stationary phase, and pH is at 4.3.

            As Kimchee is acidifying at rapid rate, sourness from lactic acid can be detected when ingested.  This sour taste increases dramatically as level pH decrease from day 10 to day 20.


Works Cited

Lee et al., 2002 J.S. Lee, K.C. Lee, J.S. Ahn, T.I. Mheen, Y.R. Pyun and Y.H. Park, Weissella koreensis sp. nov., isolated from kimchi, Int. J. Syst. Evol. Microbiol. 52 (2002), pp. 1257–1261.

 

Lim et al., 1989 C.R. Lim, H.K. Park and H.U. Han, Reevalution of isolation and identification of gram-positive bacteria in kimchi, Korean J. Microbiol. 27 (1989), pp. 404–413 (in Korean).

Mheen and Kwon, 1984 T.I.

 

Mheen and T.W. Kwon, Effect of temperature and salt concentration on kimchi fermentation, Korean J. Food Sci. Technol. 16 (1984), pp. 443–450.

 

Shin et al., 1996 D.H. Shin, M.S. Kim, J.S. Han, D.K. Lim and W.S. Bak, Changes of chemical composition and microflora in commercial kimchi, Korean J. Food. Sci. Technol. 28 (1996), pp. 137–145 (in Korean).