JOURNAL OF MICROBIOLOGY & BIOLOGY EDUCATION, December 2014, p. 297-298 DOI: http://dx.doi.org/10.1128/jmbe.v15i2.695
Tips & Tools
Kimchi: Spicy Science for the Undergraduate Microbiology Laboratory †
1Department
Virginia A. Young1* and Adam M. Kiefer2 of Biology, Mercer University, Macon, GA 31207, 2Department of Chemistry, Mercer University, Macon, GA 31207
INTRODUCTION Historically, fermented foods were made using naturally occurring microorganisms, and these processes continue today. One example is kimchi, a traditional Korean fermented cabbage dish. We were inspired to create a kimchi laboratory exercise after reading Sandor Katz’s The Art of Fermentation; the text is a valuable resource for fermentation recipes and for discussions on the impact of fermentation on human development (4). Herein we report a laboratory project based around the preparation of kimchi, where students are introduced to the concept of fermentation using endogenous microbes.
PROCEDURE For three semesters (6 sections, ~20 students per section), we incorporated an applied microbiology laboratory exercise using the cheese, yogurt, and buttermilk recipes outlined by Drake and McKillip (2) into our majors microbiology course. The procedures for making cheese, yogurt, and buttermilk are straightforward and provide an introduction to fermentation via inoculation. Vegetable fermentation, as occurs in the preparation of sauerkraut and kimchi, uses a brining step to enrich the medium for naturally occurring lactic acid bacteria (LAB). This exercise provides an opportunity for students to contrast the process of enrichment for vegetable fermentations with the inoculated fermentations of milk to make cheese, yogurt, and buttermilk in which known strains of microorganisms were added to milk. Pre-lab worksheet and hypothesis formulation Prior to the lab, students were given a worksheet (Appendix 1) to explore their opinions on consuming fermented foods and their understanding of fermentation processes. Specifically, the students were asked to hypothesize where *Corresponding author. Mailing address: Department of Biology, 1400 Coleman Avenue, Macon, GA 31207. Phone: 478-301-2577. Fax: 478-301-2067. E-mail: [email protected]. †Supplemental materials available at http://jmbe.asm.org
the LAB originated in the kimchi process and to design experiments to test their hypotheses. Groups decided to swab, culture, and Gram stain different kimchi ingredients, such as the flour, the raw cabbage, and the brined cabbage (Appendix 2). Kimchi preparation Students worked in groups of three or four to prepare kimchi in a classroom separate from the microbiology laboratory. Kimchi recipes vary widely, depending on vegetables available, regional preferences, and individual preference. The recipe we used is provided in Appendix 2 and can be modified easily. An overview of the experimental protocol as carried out during a two-hour laboratory period is as follows. The instructor rinsed, chopped, and pre-brined the Napa cabbage for two hours prior to the lab period. During the laboratory period, students made kimchi paste, prepared the other vegetables (carrots, radishes, etc.) and rinsed the cabbage after it had brined for two and a half hours. Students then mixed the rinsed cabbage with the kimchi paste and vegetable mixture. The kimchi was packed into food-safe jars such that all vegetables were fully submerged in the liquid. Lids were tightened and jars were left at room temperature for two to three days prior to refrigeration. Students tasted the kimchi two weeks later. Post-lab worksheet and hypothesis testing Throughout the kimchi preparation, students tested their hypotheses regarding the source of the LAB in the kimchi fermentation process. Sterilized equipment was used to sample the kimchi; samples were then taken to the lab. The recipe was completed prior to students moving to the microbiology lab to perform Gram stains and isolation streaks on their samples from various stages of the kimchi preparation. At this point, students completed additional questions (Appendix 1) regarding the fermentation process. One question asked the students to predict the changes that occur in the kimchi as the fermentation progressed over days and weeks; again, students designed simple experiments to test these hypotheses, focusing their efforts on changes in
©2014 Author(s). Published by the American Society for Microbiology. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial-NoDerivatives 4.0 International license (https://creativecommons.org/licenses/by-nc-nd/4.0/ and https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode), which grants the public the nonexclusive right to copy, distribute, or display the published work.
Volume 15, Number 2
Journal of Microbiology & Biology Education Downloaded from www.asmscience.org by IP: 80.82.77.83 On: Thu, 10 Aug 2017 07:00:45
297
YOUNG and KIEFER: UNDERGRADUATE KIMCHI LAB
pH and relative levels of fermenting species of LAB. Since these experiments were more advanced, students were instructed to find scientific literature to support their predictions. Prior to the experiment, a relevant paper by Di Cagno et al. (1) was discussed in lecture and introduced students to relevant peer-reviewed sources. Students were encouraged to apply their knowledge of microbial metabolic pathways to defend their predictions about pH levels and succession of LAB species throughout the fermentation. Additionally, students measured the pH of the kimchi fermentation over time, and their results confirmed reports from the scientific literature. Another post-lab question prompted students to synthesize their understanding of metabolic processes and the intrinsic factors influencing microbial growth on food. Students were asked why the kimchi is safe to eat even though it sits at room temperature for a few days. Class discussion of this concept included the historical importance of fermentation as a means of food preservation prior to refrigeration; this discussion also facilitated the exploration of different cultures and other fermented foods (4).
ASSESSMENT Students were graded on their participation in the group process of preparing kimchi, their individual completion of the worksheet, their hypothesis and experimental design, and their laboratory skills (Gram stains, culturing on selective and differential media, etc.) in completing their experiments. Our students’ results confirmed that the LAB occur on the cabbage and are enriched through the brining process. This exercise connects food safety to microbial metabolism due to the production of acids by the LAB; as a result of fermentation, the pH of the kimchi decreases and inhibits the growth of other microorganisms (6). This connection helped our students understand why refrigeration is not the only answer to keeping foods safe from potentially harmful microorganisms.
CONCLUSION This exercise meets several ASM curriculum guidelines (5), such as how to control microbial growth, how
298
to enrich for specific microorganisms, and the ability of humans to utilize and harness microorganisms. Furthermore, this exercise builds laboratory skills, such as the formulation and testing of hypotheses and the isolation of the LAB from vegetable matter. By pairing kimchi preparation with a yogurt-making lab, students are exposed to different types of fermentation (inoculated vs. endemic, vegetable vs. milk, etc.) and the use of microorganisms in food preservation. This activity could be adapted to a non-majors science course by modifying or excluding the hypothesis testing.
SUPPLEMENTAL MATERIALS Appendix 1: Pre- and post-lab questions Appendix 2: Kimchi instructions
ACKNOWLEDGMENTS The authors declare that there are no conflicts of interest.
REFERENCES 1. Di Cagno, R ., R . Coda, M. De Angelis, and M. Gobbetti. 2013. Exploitation of vegetables and fruits through lactic acid fermentation. Food Microbiol. 33(1):1–10. 2. Drake, M. A., and J. McKillip. 2000. Fermentation microbiology: making cheese, yogurt, and buttermilk as a lab exercise. Am. Biol. Teach. 62:65–67. 3. Jung, J. Y., S. H. Lee, H. J. Lee, H. Seo, W. Park, and C. O. Jeon. 2012. Effects of Leuconostoc mesenteroides starter cultures on microbial communities and metabolites during kimchi fermentation. Int. J. Food Microbiol. 153:378–387. 4. Katz, S. E. 2012. The art of fermentation: an in-depth exploration of essential concepts and processes from around the world. Chelsea Green Publishing, White River Junction, VT. 5. Merkel, S. 2012. The development of curricular guidelines for introductory microbiology that focus on understanding. J. Microbiol. Biol. Educ. 13:32–38. 6. Scott, R., and W. C. Sullivan. 2008. Ecology of fermented foods. Human Ecol. Rev. 15:25–31.
Journal of Microbiology & Biology Education Downloaded from www.asmscience.org by IP: 80.82.77.83 On: Thu, 10 Aug 2017 07:00:45
Volume 15, Number 2
Tips & Tools
Kimchi: Spicy Science for the Undergraduate Microbiology Laboratory †
1Department
Virginia A. Young1* and Adam M. Kiefer2 of Biology, Mercer University, Macon, GA 31207, 2Department of Chemistry, Mercer University, Macon, GA 31207
INTRODUCTION Historically, fermented foods were made using naturally occurring microorganisms, and these processes continue today. One example is kimchi, a traditional Korean fermented cabbage dish. We were inspired to create a kimchi laboratory exercise after reading Sandor Katz’s The Art of Fermentation; the text is a valuable resource for fermentation recipes and for discussions on the impact of fermentation on human development (4). Herein we report a laboratory project based around the preparation of kimchi, where students are introduced to the concept of fermentation using endogenous microbes.
PROCEDURE For three semesters (6 sections, ~20 students per section), we incorporated an applied microbiology laboratory exercise using the cheese, yogurt, and buttermilk recipes outlined by Drake and McKillip (2) into our majors microbiology course. The procedures for making cheese, yogurt, and buttermilk are straightforward and provide an introduction to fermentation via inoculation. Vegetable fermentation, as occurs in the preparation of sauerkraut and kimchi, uses a brining step to enrich the medium for naturally occurring lactic acid bacteria (LAB). This exercise provides an opportunity for students to contrast the process of enrichment for vegetable fermentations with the inoculated fermentations of milk to make cheese, yogurt, and buttermilk in which known strains of microorganisms were added to milk. Pre-lab worksheet and hypothesis formulation Prior to the lab, students were given a worksheet (Appendix 1) to explore their opinions on consuming fermented foods and their understanding of fermentation processes. Specifically, the students were asked to hypothesize where *Corresponding author. Mailing address: Department of Biology, 1400 Coleman Avenue, Macon, GA 31207. Phone: 478-301-2577. Fax: 478-301-2067. E-mail: [email protected]. †Supplemental materials available at http://jmbe.asm.org
the LAB originated in the kimchi process and to design experiments to test their hypotheses. Groups decided to swab, culture, and Gram stain different kimchi ingredients, such as the flour, the raw cabbage, and the brined cabbage (Appendix 2). Kimchi preparation Students worked in groups of three or four to prepare kimchi in a classroom separate from the microbiology laboratory. Kimchi recipes vary widely, depending on vegetables available, regional preferences, and individual preference. The recipe we used is provided in Appendix 2 and can be modified easily. An overview of the experimental protocol as carried out during a two-hour laboratory period is as follows. The instructor rinsed, chopped, and pre-brined the Napa cabbage for two hours prior to the lab period. During the laboratory period, students made kimchi paste, prepared the other vegetables (carrots, radishes, etc.) and rinsed the cabbage after it had brined for two and a half hours. Students then mixed the rinsed cabbage with the kimchi paste and vegetable mixture. The kimchi was packed into food-safe jars such that all vegetables were fully submerged in the liquid. Lids were tightened and jars were left at room temperature for two to three days prior to refrigeration. Students tasted the kimchi two weeks later. Post-lab worksheet and hypothesis testing Throughout the kimchi preparation, students tested their hypotheses regarding the source of the LAB in the kimchi fermentation process. Sterilized equipment was used to sample the kimchi; samples were then taken to the lab. The recipe was completed prior to students moving to the microbiology lab to perform Gram stains and isolation streaks on their samples from various stages of the kimchi preparation. At this point, students completed additional questions (Appendix 1) regarding the fermentation process. One question asked the students to predict the changes that occur in the kimchi as the fermentation progressed over days and weeks; again, students designed simple experiments to test these hypotheses, focusing their efforts on changes in
©2014 Author(s). Published by the American Society for Microbiology. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial-NoDerivatives 4.0 International license (https://creativecommons.org/licenses/by-nc-nd/4.0/ and https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode), which grants the public the nonexclusive right to copy, distribute, or display the published work.
Volume 15, Number 2
Journal of Microbiology & Biology Education Downloaded from www.asmscience.org by IP: 80.82.77.83 On: Thu, 10 Aug 2017 07:00:45
297
YOUNG and KIEFER: UNDERGRADUATE KIMCHI LAB
pH and relative levels of fermenting species of LAB. Since these experiments were more advanced, students were instructed to find scientific literature to support their predictions. Prior to the experiment, a relevant paper by Di Cagno et al. (1) was discussed in lecture and introduced students to relevant peer-reviewed sources. Students were encouraged to apply their knowledge of microbial metabolic pathways to defend their predictions about pH levels and succession of LAB species throughout the fermentation. Additionally, students measured the pH of the kimchi fermentation over time, and their results confirmed reports from the scientific literature. Another post-lab question prompted students to synthesize their understanding of metabolic processes and the intrinsic factors influencing microbial growth on food. Students were asked why the kimchi is safe to eat even though it sits at room temperature for a few days. Class discussion of this concept included the historical importance of fermentation as a means of food preservation prior to refrigeration; this discussion also facilitated the exploration of different cultures and other fermented foods (4).
ASSESSMENT Students were graded on their participation in the group process of preparing kimchi, their individual completion of the worksheet, their hypothesis and experimental design, and their laboratory skills (Gram stains, culturing on selective and differential media, etc.) in completing their experiments. Our students’ results confirmed that the LAB occur on the cabbage and are enriched through the brining process. This exercise connects food safety to microbial metabolism due to the production of acids by the LAB; as a result of fermentation, the pH of the kimchi decreases and inhibits the growth of other microorganisms (6). This connection helped our students understand why refrigeration is not the only answer to keeping foods safe from potentially harmful microorganisms.
CONCLUSION This exercise meets several ASM curriculum guidelines (5), such as how to control microbial growth, how
298
to enrich for specific microorganisms, and the ability of humans to utilize and harness microorganisms. Furthermore, this exercise builds laboratory skills, such as the formulation and testing of hypotheses and the isolation of the LAB from vegetable matter. By pairing kimchi preparation with a yogurt-making lab, students are exposed to different types of fermentation (inoculated vs. endemic, vegetable vs. milk, etc.) and the use of microorganisms in food preservation. This activity could be adapted to a non-majors science course by modifying or excluding the hypothesis testing.
SUPPLEMENTAL MATERIALS Appendix 1: Pre- and post-lab questions Appendix 2: Kimchi instructions
ACKNOWLEDGMENTS The authors declare that there are no conflicts of interest.
REFERENCES 1. Di Cagno, R ., R . Coda, M. De Angelis, and M. Gobbetti. 2013. Exploitation of vegetables and fruits through lactic acid fermentation. Food Microbiol. 33(1):1–10. 2. Drake, M. A., and J. McKillip. 2000. Fermentation microbiology: making cheese, yogurt, and buttermilk as a lab exercise. Am. Biol. Teach. 62:65–67. 3. Jung, J. Y., S. H. Lee, H. J. Lee, H. Seo, W. Park, and C. O. Jeon. 2012. Effects of Leuconostoc mesenteroides starter cultures on microbial communities and metabolites during kimchi fermentation. Int. J. Food Microbiol. 153:378–387. 4. Katz, S. E. 2012. The art of fermentation: an in-depth exploration of essential concepts and processes from around the world. Chelsea Green Publishing, White River Junction, VT. 5. Merkel, S. 2012. The development of curricular guidelines for introductory microbiology that focus on understanding. J. Microbiol. Biol. Educ. 13:32–38. 6. Scott, R., and W. C. Sullivan. 2008. Ecology of fermented foods. Human Ecol. Rev. 15:25–31.
Journal of Microbiology & Biology Education Downloaded from www.asmscience.org by IP: 80.82.77.83 On: Thu, 10 Aug 2017 07:00:45
Volume 15, Number 2
