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The effect of oyster shell powder on the extension of the shelf-life of Kimchi
Food Control 17 (2006) 695–699 www.elsevier.com/locate/foodcont
The effect of oyster shell powder on the extension of the shelf-life of Kimchi Yang Mun Choi a, Jong Hyun Whang b, Jin Man Kim c, Hyung Joo Suh b
d,*
a Department of Food Service and Industry, Shinsung College, Chungnam 343-860, Republic of Korea Department of Kimchi and Food Science, Chongju National College of Science and Technology, Jeungpyeong 368-701, Republic of Korea c Department of Food Science and Biotechnology of Animal Resources, Konkuk University, Seoul 143-701, Republic of Korea d Department of Food and Nutrition, College of Health Sciences, Korea University, 1 Jeongneung-dong, Sungbuk-ku, Seoul 136-703, Republic of Korea
Received 13 November 2004; received in revised form 5 April 2005; accepted 11 April 2005
Abstract The effect of shell powder addition (0%, 0.05%, 0.1% and 0.5%) on the pH, titratable acidity, lactic acid contents, microbial counts, and sensory evaluation of Kimchi was studied for prolonging its shelf-life. With the addition of shell powder with 0.5%, the changing rates of pH, the acidity and the lactic acid contents were retarded, resulting in the slowest change and the highest final pH. The sourness, crispness and overall evaluation of 0.5% shell powder-treated Kimchi were remarkably improved. And, the bitterness of 0.5% shell powder-treated Kimchi was also lower than the control. The addition of shell powder with 0.5% enhanced the shelf-life and the quality of Kimchi for preservation and consumption. 2005 Elsevier Ltd. All rights reserved. Keywords: Shell powder; Kimchi; Shelf-life; Sensory evaluation
1. Introduction Kimchi is a traditional fermented vegetable food in Korea and known to be the product fermented mainly by the lactic acid bacteria. The major raw material (oriental cabbage or radish) is salted after pre-brining, blended with various spices (red pepper, garlic, green onion, ginger, etc.) and other minor ingredients (seasonings, salted seafoods, fruits and vegetables, cereals, fish and meats, etc.), and then fermented. Kimchi has a characteristic sour, sweet, and carbonated taste. It differs considerably in this respect from sauerkraut and pickle that are popular fermented-vegetable products in the West (Cheigh & Park, 1994; Lee, 1996). *
Corresponding author. Tel.: +82 2 940 2853; fax: +82 2 941 7825. E-mail address: [email protected] (H.J. Suh).
0956-7135/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2005.04.005
Kimchi is a natural lactic acid-fermented food, which can be acidified due to over-production of lactic acid by lactic acid bacteria, and enzymes during distribution. Several studies have been conducted to extend the shelf-life of Kimchi through heat treatment (Kang, Ku, Lee, & Kim, 1991), radiation (Song et al., 2004), antiseptic (Park & Woo, 1988) and antimicrobial agents (Ahn, 1988; Moon, Byun, Kim, & Han, 1995), herb medicine (Jung, Chung, & Park, 2002; Lee, Cho, Choi, & Kim, 1998) and pH adjuster (Lee & Kim, 2003; Park, Park, Cheong, & Lee, 2002). However, the processes described above are not enough to make better commercial Kimchi without temperature control. During the process of preventing or delaying the acidification of Kimchi, natural flavor and freshness of Kimchi should be preserved and lactic acid bacteria should also be kept alive at the same time, thus suggesting the use of natural neutralizer.
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Y.M. Choi et al. / Food Control 17 (2006) 695–699
At present, in shell-harvesting districts, large amounts of shells are piled up near the seaside, which creates several serious problems such as the emission of offensive odors and soil pollution from heavy metals contained in the viscera. The main component of shell is CaCO3, and by heat treatment, CaCO3 in the shell is converted to CaO, which exhibits antibacterial activity. In fact, there were reports that shell powder heated to over 700 C exhibited a bactericidal activity (Sawai, Shiga, & Kojima, 2001; Shiga, Sawai, & Kojima, 1999). Therefore, the use of this material in food processing is expected not only to prolong the shelf-life of foodstuffs, but also to be a source of minerals. The objective of this study was to investigate the effect of oyster shell powder as a neutralizer on the fermentation and quality of Kimchi in order to extend the shelf-life of Kimchi.
2. Materials and methods 2.1. Materials To prepare Kimchi, Chinese cabbage (Brassica campestris var. peknensis), radish, onion, minced ginger and garlic, and scallion were purchased at a local food market in Seoul, Korea and stored in a refrigerator at 5 C. White sugar, liquefied fish sauce, hot pepper, salt, and mono-sodium glutamate (MSG) from a local food company were stored at room temperature wrapped with aluminum foil. Oyster shell powder was purchased from Sunin Co. (Seoul, Korea). Oyster shell was composed of 93% crude ash containing 60% of calcium. And, oyster shell contained other minerals as follows: magnesium 476 mg/100 g, iron 53 mg/100 g, phosphorus 21 mg/100 g, potassium 7 mg/100 g, and sodium 2 mg/ 100 g. 2.2. Kimchi preparation Kimchi was prepared based on the following compositions (weight compositions): Chinese cabbage 79.1%, radish 8.3%, hot pepper 2.9%, onion 2.8%, liquefied fish sauce 2.6%, scallion 2.1%, white sugar 0.9%, minced garlic 0.8% and ginger 0.4%, and MSG 0.1%. Cleaned and trimmed Chinese cabbage was cut into pieces (3 · 4 cm), and immersed twice in 20% NaCl solution (w/v) for 3 h. After removing some residual salt with tap water, the Chinese cabbage was drained at room temperature for 1 h. Sliced radish, and minced ginger and garlic were put into a metal bowl. After mixing gently, onion and green onion, liquefied fish sauce, sugar, and MSG were added and blended gently. Finally, 0.05%, 0.1% and 0.5% calcium of oyster shell against the weight of salted Chinese cabbage were added to the condiment and spreaded on the Chinese cabbage for Kimchi preparation.
Prepared Kimchi was packed in 2000 mL of plastic vessels without headspace and stored for 14 days at 10 C. 2.3. Measurement of pH and titratable acidity The cabbage tissue and Kimchi juice were homogenized together by using Polytron homogenizer (RT1200C, Switzerland), and centrifuged at 3000 · g for 20 min. pH and titratable acidity of the supernatant were determined by pH meter and pH-metric method, respectively (Sistrunk & Kozup, 1982). Total acidity was calculated as a percentage of lactic acid. 2.4. Microbial analysis The above supernatant was diluted with 0.1% peptone water. Plate count agar (Difco, St. Louis, USA) was used for the determination of total viable counts, and MRS agar (Difco, St. Louis, USA) was used of lactic acid bacteria. All plates were triplicated, incubated at 37 C for 48 h, and viable cell numbers were determined as colony forming units (cfu) per mL (Oh, Choi, & Kim, 1998). 2.5. Sensory evaluation Sensory evaluation on the sourness, bitterness, overall taste and crispness were carried out in triplicates by the panels using a five-point hedonic scale method (Herbert & Joel, 1993). The sour and bitter tastes were evaluated as very low (1 point), low (2 point), medium (3 point), strong (4 point), and very strong (5 point). The crispness and overall taste were evaluated as very poor (1 point), poor (2 point), moderate (3 point), good (4 point) and very good (5 point). The results of sensory evaluation were expressed as the means ± standard deviation (SD) of 10 panelists. Significance was verified by performing DuncanÕs multiple range test using the SPSS software package.
3. Results and discussion 3.1. pH, titratable acidity and lactic acid content Figs. 1 and 2 show the changes in the pH and titratable acidity of Kimchi during fermentation. The addition of oyster shell powder resulted in producing a higher pH than the control. The higher amount of the shell powder was added, the higher the pH was maintained. The final pH of the control was 4.27, but the addition of shell powder resulted in pH 4.28 (0.05% of shell powder), 4.37 (0.1%), and 5.05 (0.5%). Titratable acidities of the test groups increased as the fermentation time increased. On the 15th day of fermentation, the acidity of the control was 1.14%. The addition of 0.05%, 0.1% and 0.5%
Y.M. Choi et al. / Food Control 17 (2006) 695–699 0.7
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Fig. 1. Changes in pH of Kimchi added with shell powder during fermentation at 10 C.
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Fig. 2. Changes in titratable acidity of Kimchi added with shell powder during fermentation at 10 C.
shell powder resulted in 1.19%, 1.18%, and 0.59% of acidity, respectively. These results are consistent with those of Park et al. (2002) and Kim, Kim, Park, Kim, and Youn (1999) in that the addition of calcium powder or calcium lactate to Kimchi increased the pH. This could be explained by the fact that the shell powder reacted with lactic acid produced by the fermentation of Kimchi, producing calcium lactate which can act as a buffer and a soluble calcium fortifier. In general, Kimchi had the best taste when pH was about 4.2 and the total acidity reached the level of 0.7% (Mheen & Kwon, 1984). However, when the pH of Kimchi drops below 4.0, homofermentative Lactobacillus plantarum strains, which generally proliferate in the late stage of Kimchi fermentation, reportedly play an important role in its over-fermentation (Mheen & Kwon, 1984). The addition of 0.5% shell powder resulted in the final pH of 5.05 and the acidity of 0.59% on the 15th day of fermentation. The results showed that the shell powder neutralized
Fig. 3. Changes in lactic acid contents of Kimchi added with shell powder during fermentation at 10 C.
the lactic acid which was produced during Kimchi fermentation. The free lactic acid contents of Kimchi added with shell powder (0.1% and 0.5%) were lower than that of the control on the 15th day of fermentation (Fig. 3). However, free lactic acid contents of Kimchi added with low amount of shell powder (0.05% and 0.1%) were found to be in similar to that of the control. This result shows that the rate of lactic acid production in the control Kimchi is remarkably higher than that of Kimchi added with 0.5% of shell powder. The production rate of lactic acid has a close relationship with the distribution of lactic acid bacteria in Kimchi. Some important species thought to be responsible for Kimchi fermentation are Leuconostoc (Lc.) mesenteroides, Lc. pseudomesenteroides and Lc. lactis, as well as lactobacilli including Lactobacillus (Lb.) brevis and Lb. plantarum. Lc. mesenteroides was reported to predominate in the early stages of fermentation and to be responsible for the initial anaerobic state of Kimchi; as the pH gradually falls to 4.0, Lb. plantarum becomes predominant (Kim, Kim, & Kim, 1994; Lee, Ko, & Ha, 1992; Mheen & Kwon, 1984; Potts & Fleming, 1982). 3.2. Total microbes and lactic acid bacteria Fig. 4 shows the number of total microbes and lactic acid bacteria during the fermentation of Kimchi added with shell powder from 0.05% to 0.5%. Total number of the microbes increased rapidly up to the 5th day of fermentation. Up to 10th day of fermentation, there was no significant difference (p > 0.05) among the control and the test groups added with shell powder of 0.05% and 0.1%. However, the addition of 0.5% shell powder showed a significant (p < 0.05) inhibitory effect on the microbial growth. The changes of the number of lactic acid bacteria also showed a same tendency as
Y.M. Choi et al. / Food Control 17 (2006) 695–699 11
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Fig. 4. Changes in total microbes and lactic acid bacteria of Kimchi added with shell powder during fermentation at 10 C.
that of the total microbes. Cho and Rhee (1991) reported that the numbers of lactic acid bacteria increased as the pH decreased, which is in agreement with our results. The ratio of lactic acid bacteria to total microbes during the fermentation was higher in the treated group than in the control, and the higher ratio resulted in the higher quality of Kimchi with more hygienic Kimchi. Lee, Park, and Choi (1999) suggested that the ratio of lactic acid bacteria to total microbes would be as follows: in the beginning of the fermentation, total microbes would increase because of the growth of aerobic and non-aerobic bacteria. As fermentation proceeds, organic acid would be created and acid-durable non-aerobic germs would increase. Thereby, the number of lactic acid bacteria would increase and consequently the ratio of lactic acid bacteria would increase during later stages of Kimchi fermentation, which is consistent with the result of this experiment. 3.3. Sensory evaluation Shell powder treatments (0%, 0.05%, 0.1% and 0.5% against salted Chinese cabbage) were investigated for the extension of shelf-life of Kimchi, and, for that purpose, the sensory test was carried out to differentiate non-treated from treated Kimchi with shell powder after 15 days of fermentation (Table 1). The sour taste of Kimchi treated with 0.5% shell powder was lower than that of the control. However, there were not significant differences (p > 0.05) among the control, 0.05%, and 0.1% of shell powder treatments. The bitter taste of Kimchi treated with 0.5% shell powder was lower than that of the control without significant difference (p > 0.05). Kimchi is known to exert bitter taste when it is over-fermented (Jang et al., 1991). The over-fermentation of Kimchi could be delayed with the addition of 0.5% shell powder. Since the bitter taste is noticed when Kimchi is over-fermented, it can be inferred that this might be caused by various microbes. The increased addition of shell powder resulted in the increase of crispness. The crispness of Kimchi is closely
Table 1 Sensory evaluation of Kimchi treated with different concentrations of shell powder after 15 days of fermentation Treatment
Attributes Sour
Control Shell powder 0.05% Shell powder 0.1% Shell powder 0.5%
Bitter a
4.2 ± 0.5 4.1 ± 0.4a 4.1 ± 0.3a 3.5 ± 0.2b
Crispness Overall taste b
2.2 ± 0.2 2.3 ± 0.3b 2.1 ± 0.2b 1.8 ± 0.4b
2.0 ± 0.2b 2.3 ± 0.3b 2.5 ± 0.2b 3.2 ± 0.2a
2.3 ± 0.2b 2.2 ± 0.2b 2.9 ± 0.2b 3.7 ± 0.2a
Values are means of 10 panels, different superscripts indicate significant differences at p < 0.05.
related with the hardness of tissue (Park, Kim, & Kim, 1996a), which is related to the cell wall polysaccharides such as pectin (Saldana & Meyer, 1981). Calcium combines with pectin and increases the hardness of tissue (Buescher, Hudson, & Adams, 1979), thus raising the crispness of Kimchi. In terms of evaluation of overall taste, the control Kimchi was rated lower than that with addition of shell powder. There was significant a difference (p < 0.05) between the control and Kimchi added with 0.5% of shell powder. The addition of shell powder has been known to change the sourness and crispness of Kimchi, resulting in producing large influence on the overall taste (Park, Kim, & Kim, 1996b). Thus, it can be concluded that shell powder plays an important role in the enhancement of shelf-life and the quality of Kimchi not only by neutralizing acids but also by raising the content of calcium that is easy to absorb. Especially, 0.5% addition of shell powder resulted in the prolonging the shelf-life and better quality of Kimchi for preservation and consumption.
References Ahn, S. J. (1988). The effect of salt and food preservatives on the growth of lactic acid bacteria isolated from Kimchi. Korean Journal of Society of Food Science, 4, 39–50. Buescher, R. W., Hudson, J. M., & Adams, J. R. (1979). Inhibition of polygalacturonase softening of cucumber pickles by calcium chloride. Journal of Food Science, 44, 1786–1789.
Y.M. Choi et al. / Food Control 17 (2006) 695–699 Cheigh, H. S., & Park, K. Y. (1994). Biochemical, microbiological and nutritional aspects of Kimchi (Korean fermented vegetable products). Critical Reviews in Food Science and Nutrition, 34, 175–203. Cho, Y., & Rhee, H. S. (1991). Effect of lactic acid bacteria and temperature on Kimchi fermentation (II). Korean Journal of Society of Food Science, 7, 89–95. Herbert, A., & Joel, L. S. (1993). Sensory evaluation practices. New York, USA: Academic Press. Jang, K. S., Kim, M. J., Oh, Y. A., Kim, I. D., No, H. K., & Kim, S. D. (1991). Effects of various sub-ingredients on sensory quality of Korean cabbage Kimchi. Journal of Korean Society of Food Nutrition, 20, 233–240. Jung, H. O., Chung, D. O., & Park, I. D. (2002). A study on sensory characteristics of herb onion Kimchi differing in herb content. Korean Journal of Culinary Research, 8, 259–265. Kang, K. O., Ku, K. H., Lee, H. J., & Kim, W. J. (1991). Effect of enzyme and inorganic acid salts addition and heat treatment on Kimchi fermentation. Korean Journal of Food Science and Technology, 23, 183–187. Kim, D. G., Kim, B. K., & Kim, I. D. (1994). Effect of reducing sugar content in Chinese cabbage on Kimchi fermentation. Korean Journal of Society of Food Science, 23, 73–77. Kim, S. D., Kim, I. D., Park, I. K., Kim, M. H., & Youn, K. S. (1999). Effects of calcium lactate and acetate on the fermentation of Kimchi. Korean Journal of Postharvest Science and Technology, 6, 333–338. Lee, C. H. (1996). Lactic acid fermented foods and their benefits in Asia. Foods and Biotechnology, 5, 187–197. Lee, C. W., Ko, C. Y., & Ha, D. M. (1992). Microfloral changes of the lactic acid bacteria during Kimchi fermentation and identification of the isolates. Korean Journal of Applied Microbiology and Biotechnology, 20, 102–109. Lee, M. Y., & Kim, S. D. (2003). Calcium lactate treatment after salting of Chinese cabbage improves firmness and shelf-life of Kimchi. Journal of Food Science and Nutrtion, 8, 270–277. Lee, S. H., Cho, O. K., Choi, W. J., & Kim, S. D. (1998). The effects of mixed medicinal herb extracts with antimicrobial activity on the shelf-life of Kimchi. Korean Journal of Food Science and Technology, 30, 1404–1408. Lee, S. H., Park, N. Y., & Choi, W. J. (1999). Changes of the lactic acid bacteria and selective inhibitory substances against homo and hetero lactic acid bacteria isolated from Kimchi. Korean Journal of Applied Microbiology and Biotechnology, 27, 410–414.
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Mheen, T. L., & Kwon, T. W. (1984). Effect of temperature and salt concentration on Kimchi fermentation. Korean Journal of Society of Food Science and Nutrition, 16, 443–450. Moon, K. D., Byun, J. A., Kim, S. J., & Han, D. S. (1995). Screening of natural preservatives to inhibit Kimchi fermentation. Korean Journal of Food Science and Technology, 27, 257–263. Oh, Y. A., Choi, K. H., & Kim, S. D. (1998). Changes in enzyme activities and population of lactic acid bacteria during the Kimchi fermentation supplemented with water extract of pine needle. Journal of Korean Society of Food Science and Nutrition, 27, 244–251. Park, I. K., Kim, S. H., & Kim, S. D. (1996a). Effect of initial temperature of salt solution during salting on the fermentation of Kimchi. Journal of Korean Society of Food Science and Nutrition, 25, 747–753. Park, I. K., Kim, S. H., & Kim, S. D. (1996b). Effect of organic acids addition during salting on the fermentation of Kimchi. Korean Journal of East Asian Society of Dietary Life, 6, 195–204. Park, K. J., & Woo, S. J. (1988). Effect of Na-acetate, Na-malate and K-sorbate on the pH acidity and sourness during Kimchi fermentation. Korean Journal of Food Science and Technology, 20, 40–44. Park, W. P., Park, K. D., Cheong, Y. J., & Lee, I. S. (2002). Effect of calcium powder addition on the quality characteristics of Kimchi. Journal of Korean Society of Food Science and Nutrition, 31, 428–432. Potts, E. A., & Fleming, H. P. (1982). Prevention of mold-induced softening in air-purged, brined cucumbers by acidification. Journal of Food Science, 47, 1723–1727. Saldana, G., & Meyer, R. (1981). Effects of added calcium on texture and quality of canned Jalapeon Peppers. Journal of Food Science, 46, 1518–1521. Sawai, J., Shiga, H., & Kojima, H. (2001). Kinetic analysis of the bacterial action of heated scallop-shell powder. International Journal of Food Microbiology, 71, 211–218. Shiga, H., Sawai, J., & Kojima, H. (1999). Utilization of heated shell powder in biocontrol. Transactions of Materials Research Society of Japan, 24, 557–560. Sistrunk, W. A., & Kozup, J. (1982). Influence of processing methodology on quality of cucumber pickles. Journal of Food Science, 47, 949–953. Song, H. P., Kim, D. H., Yook, H. S., Kim, K. S., Kwon, J. H., & Byun, M. W. (2004). Application of gamma irradiation for aging control and improvement of shelf-life of Kimchi, Korean salted and fermented vegetables. Radiation Physics and Chemistry, 71, 57–60.
The effect of oyster shell powder on the extension of the shelf-life of Kimchi Yang Mun Choi a, Jong Hyun Whang b, Jin Man Kim c, Hyung Joo Suh b
d,*
a Department of Food Service and Industry, Shinsung College, Chungnam 343-860, Republic of Korea Department of Kimchi and Food Science, Chongju National College of Science and Technology, Jeungpyeong 368-701, Republic of Korea c Department of Food Science and Biotechnology of Animal Resources, Konkuk University, Seoul 143-701, Republic of Korea d Department of Food and Nutrition, College of Health Sciences, Korea University, 1 Jeongneung-dong, Sungbuk-ku, Seoul 136-703, Republic of Korea
Received 13 November 2004; received in revised form 5 April 2005; accepted 11 April 2005
Abstract The effect of shell powder addition (0%, 0.05%, 0.1% and 0.5%) on the pH, titratable acidity, lactic acid contents, microbial counts, and sensory evaluation of Kimchi was studied for prolonging its shelf-life. With the addition of shell powder with 0.5%, the changing rates of pH, the acidity and the lactic acid contents were retarded, resulting in the slowest change and the highest final pH. The sourness, crispness and overall evaluation of 0.5% shell powder-treated Kimchi were remarkably improved. And, the bitterness of 0.5% shell powder-treated Kimchi was also lower than the control. The addition of shell powder with 0.5% enhanced the shelf-life and the quality of Kimchi for preservation and consumption. 2005 Elsevier Ltd. All rights reserved. Keywords: Shell powder; Kimchi; Shelf-life; Sensory evaluation
1. Introduction Kimchi is a traditional fermented vegetable food in Korea and known to be the product fermented mainly by the lactic acid bacteria. The major raw material (oriental cabbage or radish) is salted after pre-brining, blended with various spices (red pepper, garlic, green onion, ginger, etc.) and other minor ingredients (seasonings, salted seafoods, fruits and vegetables, cereals, fish and meats, etc.), and then fermented. Kimchi has a characteristic sour, sweet, and carbonated taste. It differs considerably in this respect from sauerkraut and pickle that are popular fermented-vegetable products in the West (Cheigh & Park, 1994; Lee, 1996). *
Corresponding author. Tel.: +82 2 940 2853; fax: +82 2 941 7825. E-mail address: [email protected] (H.J. Suh).
0956-7135/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2005.04.005
Kimchi is a natural lactic acid-fermented food, which can be acidified due to over-production of lactic acid by lactic acid bacteria, and enzymes during distribution. Several studies have been conducted to extend the shelf-life of Kimchi through heat treatment (Kang, Ku, Lee, & Kim, 1991), radiation (Song et al., 2004), antiseptic (Park & Woo, 1988) and antimicrobial agents (Ahn, 1988; Moon, Byun, Kim, & Han, 1995), herb medicine (Jung, Chung, & Park, 2002; Lee, Cho, Choi, & Kim, 1998) and pH adjuster (Lee & Kim, 2003; Park, Park, Cheong, & Lee, 2002). However, the processes described above are not enough to make better commercial Kimchi without temperature control. During the process of preventing or delaying the acidification of Kimchi, natural flavor and freshness of Kimchi should be preserved and lactic acid bacteria should also be kept alive at the same time, thus suggesting the use of natural neutralizer.
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Y.M. Choi et al. / Food Control 17 (2006) 695–699
At present, in shell-harvesting districts, large amounts of shells are piled up near the seaside, which creates several serious problems such as the emission of offensive odors and soil pollution from heavy metals contained in the viscera. The main component of shell is CaCO3, and by heat treatment, CaCO3 in the shell is converted to CaO, which exhibits antibacterial activity. In fact, there were reports that shell powder heated to over 700 C exhibited a bactericidal activity (Sawai, Shiga, & Kojima, 2001; Shiga, Sawai, & Kojima, 1999). Therefore, the use of this material in food processing is expected not only to prolong the shelf-life of foodstuffs, but also to be a source of minerals. The objective of this study was to investigate the effect of oyster shell powder as a neutralizer on the fermentation and quality of Kimchi in order to extend the shelf-life of Kimchi.
2. Materials and methods 2.1. Materials To prepare Kimchi, Chinese cabbage (Brassica campestris var. peknensis), radish, onion, minced ginger and garlic, and scallion were purchased at a local food market in Seoul, Korea and stored in a refrigerator at 5 C. White sugar, liquefied fish sauce, hot pepper, salt, and mono-sodium glutamate (MSG) from a local food company were stored at room temperature wrapped with aluminum foil. Oyster shell powder was purchased from Sunin Co. (Seoul, Korea). Oyster shell was composed of 93% crude ash containing 60% of calcium. And, oyster shell contained other minerals as follows: magnesium 476 mg/100 g, iron 53 mg/100 g, phosphorus 21 mg/100 g, potassium 7 mg/100 g, and sodium 2 mg/ 100 g. 2.2. Kimchi preparation Kimchi was prepared based on the following compositions (weight compositions): Chinese cabbage 79.1%, radish 8.3%, hot pepper 2.9%, onion 2.8%, liquefied fish sauce 2.6%, scallion 2.1%, white sugar 0.9%, minced garlic 0.8% and ginger 0.4%, and MSG 0.1%. Cleaned and trimmed Chinese cabbage was cut into pieces (3 · 4 cm), and immersed twice in 20% NaCl solution (w/v) for 3 h. After removing some residual salt with tap water, the Chinese cabbage was drained at room temperature for 1 h. Sliced radish, and minced ginger and garlic were put into a metal bowl. After mixing gently, onion and green onion, liquefied fish sauce, sugar, and MSG were added and blended gently. Finally, 0.05%, 0.1% and 0.5% calcium of oyster shell against the weight of salted Chinese cabbage were added to the condiment and spreaded on the Chinese cabbage for Kimchi preparation.
Prepared Kimchi was packed in 2000 mL of plastic vessels without headspace and stored for 14 days at 10 C. 2.3. Measurement of pH and titratable acidity The cabbage tissue and Kimchi juice were homogenized together by using Polytron homogenizer (RT1200C, Switzerland), and centrifuged at 3000 · g for 20 min. pH and titratable acidity of the supernatant were determined by pH meter and pH-metric method, respectively (Sistrunk & Kozup, 1982). Total acidity was calculated as a percentage of lactic acid. 2.4. Microbial analysis The above supernatant was diluted with 0.1% peptone water. Plate count agar (Difco, St. Louis, USA) was used for the determination of total viable counts, and MRS agar (Difco, St. Louis, USA) was used of lactic acid bacteria. All plates were triplicated, incubated at 37 C for 48 h, and viable cell numbers were determined as colony forming units (cfu) per mL (Oh, Choi, & Kim, 1998). 2.5. Sensory evaluation Sensory evaluation on the sourness, bitterness, overall taste and crispness were carried out in triplicates by the panels using a five-point hedonic scale method (Herbert & Joel, 1993). The sour and bitter tastes were evaluated as very low (1 point), low (2 point), medium (3 point), strong (4 point), and very strong (5 point). The crispness and overall taste were evaluated as very poor (1 point), poor (2 point), moderate (3 point), good (4 point) and very good (5 point). The results of sensory evaluation were expressed as the means ± standard deviation (SD) of 10 panelists. Significance was verified by performing DuncanÕs multiple range test using the SPSS software package.
3. Results and discussion 3.1. pH, titratable acidity and lactic acid content Figs. 1 and 2 show the changes in the pH and titratable acidity of Kimchi during fermentation. The addition of oyster shell powder resulted in producing a higher pH than the control. The higher amount of the shell powder was added, the higher the pH was maintained. The final pH of the control was 4.27, but the addition of shell powder resulted in pH 4.28 (0.05% of shell powder), 4.37 (0.1%), and 5.05 (0.5%). Titratable acidities of the test groups increased as the fermentation time increased. On the 15th day of fermentation, the acidity of the control was 1.14%. The addition of 0.05%, 0.1% and 0.5%
Y.M. Choi et al. / Food Control 17 (2006) 695–699 0.7
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Fig. 1. Changes in pH of Kimchi added with shell powder during fermentation at 10 C.
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Fermentation time (day)
Fig. 2. Changes in titratable acidity of Kimchi added with shell powder during fermentation at 10 C.
shell powder resulted in 1.19%, 1.18%, and 0.59% of acidity, respectively. These results are consistent with those of Park et al. (2002) and Kim, Kim, Park, Kim, and Youn (1999) in that the addition of calcium powder or calcium lactate to Kimchi increased the pH. This could be explained by the fact that the shell powder reacted with lactic acid produced by the fermentation of Kimchi, producing calcium lactate which can act as a buffer and a soluble calcium fortifier. In general, Kimchi had the best taste when pH was about 4.2 and the total acidity reached the level of 0.7% (Mheen & Kwon, 1984). However, when the pH of Kimchi drops below 4.0, homofermentative Lactobacillus plantarum strains, which generally proliferate in the late stage of Kimchi fermentation, reportedly play an important role in its over-fermentation (Mheen & Kwon, 1984). The addition of 0.5% shell powder resulted in the final pH of 5.05 and the acidity of 0.59% on the 15th day of fermentation. The results showed that the shell powder neutralized
Fig. 3. Changes in lactic acid contents of Kimchi added with shell powder during fermentation at 10 C.
the lactic acid which was produced during Kimchi fermentation. The free lactic acid contents of Kimchi added with shell powder (0.1% and 0.5%) were lower than that of the control on the 15th day of fermentation (Fig. 3). However, free lactic acid contents of Kimchi added with low amount of shell powder (0.05% and 0.1%) were found to be in similar to that of the control. This result shows that the rate of lactic acid production in the control Kimchi is remarkably higher than that of Kimchi added with 0.5% of shell powder. The production rate of lactic acid has a close relationship with the distribution of lactic acid bacteria in Kimchi. Some important species thought to be responsible for Kimchi fermentation are Leuconostoc (Lc.) mesenteroides, Lc. pseudomesenteroides and Lc. lactis, as well as lactobacilli including Lactobacillus (Lb.) brevis and Lb. plantarum. Lc. mesenteroides was reported to predominate in the early stages of fermentation and to be responsible for the initial anaerobic state of Kimchi; as the pH gradually falls to 4.0, Lb. plantarum becomes predominant (Kim, Kim, & Kim, 1994; Lee, Ko, & Ha, 1992; Mheen & Kwon, 1984; Potts & Fleming, 1982). 3.2. Total microbes and lactic acid bacteria Fig. 4 shows the number of total microbes and lactic acid bacteria during the fermentation of Kimchi added with shell powder from 0.05% to 0.5%. Total number of the microbes increased rapidly up to the 5th day of fermentation. Up to 10th day of fermentation, there was no significant difference (p > 0.05) among the control and the test groups added with shell powder of 0.05% and 0.1%. However, the addition of 0.5% shell powder showed a significant (p < 0.05) inhibitory effect on the microbial growth. The changes of the number of lactic acid bacteria also showed a same tendency as
Y.M. Choi et al. / Food Control 17 (2006) 695–699 11
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9 8 7 6 5
0.0% 0.05% 0.1% 0.5%
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Lactic acid bacteria (log CFU/ml)
Total microbial number (log CFU/ml)
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6
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4
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Fig. 4. Changes in total microbes and lactic acid bacteria of Kimchi added with shell powder during fermentation at 10 C.
that of the total microbes. Cho and Rhee (1991) reported that the numbers of lactic acid bacteria increased as the pH decreased, which is in agreement with our results. The ratio of lactic acid bacteria to total microbes during the fermentation was higher in the treated group than in the control, and the higher ratio resulted in the higher quality of Kimchi with more hygienic Kimchi. Lee, Park, and Choi (1999) suggested that the ratio of lactic acid bacteria to total microbes would be as follows: in the beginning of the fermentation, total microbes would increase because of the growth of aerobic and non-aerobic bacteria. As fermentation proceeds, organic acid would be created and acid-durable non-aerobic germs would increase. Thereby, the number of lactic acid bacteria would increase and consequently the ratio of lactic acid bacteria would increase during later stages of Kimchi fermentation, which is consistent with the result of this experiment. 3.3. Sensory evaluation Shell powder treatments (0%, 0.05%, 0.1% and 0.5% against salted Chinese cabbage) were investigated for the extension of shelf-life of Kimchi, and, for that purpose, the sensory test was carried out to differentiate non-treated from treated Kimchi with shell powder after 15 days of fermentation (Table 1). The sour taste of Kimchi treated with 0.5% shell powder was lower than that of the control. However, there were not significant differences (p > 0.05) among the control, 0.05%, and 0.1% of shell powder treatments. The bitter taste of Kimchi treated with 0.5% shell powder was lower than that of the control without significant difference (p > 0.05). Kimchi is known to exert bitter taste when it is over-fermented (Jang et al., 1991). The over-fermentation of Kimchi could be delayed with the addition of 0.5% shell powder. Since the bitter taste is noticed when Kimchi is over-fermented, it can be inferred that this might be caused by various microbes. The increased addition of shell powder resulted in the increase of crispness. The crispness of Kimchi is closely
Table 1 Sensory evaluation of Kimchi treated with different concentrations of shell powder after 15 days of fermentation Treatment
Attributes Sour
Control Shell powder 0.05% Shell powder 0.1% Shell powder 0.5%
Bitter a
4.2 ± 0.5 4.1 ± 0.4a 4.1 ± 0.3a 3.5 ± 0.2b
Crispness Overall taste b
2.2 ± 0.2 2.3 ± 0.3b 2.1 ± 0.2b 1.8 ± 0.4b
2.0 ± 0.2b 2.3 ± 0.3b 2.5 ± 0.2b 3.2 ± 0.2a
2.3 ± 0.2b 2.2 ± 0.2b 2.9 ± 0.2b 3.7 ± 0.2a
Values are means of 10 panels, different superscripts indicate significant differences at p < 0.05.
related with the hardness of tissue (Park, Kim, & Kim, 1996a), which is related to the cell wall polysaccharides such as pectin (Saldana & Meyer, 1981). Calcium combines with pectin and increases the hardness of tissue (Buescher, Hudson, & Adams, 1979), thus raising the crispness of Kimchi. In terms of evaluation of overall taste, the control Kimchi was rated lower than that with addition of shell powder. There was significant a difference (p < 0.05) between the control and Kimchi added with 0.5% of shell powder. The addition of shell powder has been known to change the sourness and crispness of Kimchi, resulting in producing large influence on the overall taste (Park, Kim, & Kim, 1996b). Thus, it can be concluded that shell powder plays an important role in the enhancement of shelf-life and the quality of Kimchi not only by neutralizing acids but also by raising the content of calcium that is easy to absorb. Especially, 0.5% addition of shell powder resulted in the prolonging the shelf-life and better quality of Kimchi for preservation and consumption.
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