23/24 (7) Biology HL IA (N21) – Kimchi Fermentation

1.0 Introduction

1.1 Research Question:

What is the effect of increasing salinity (5.0%, 10.0%, 15.0%, 20.0%, 25.0%) of brine on the rate of lactic acid fermentation of Kkakdugi Kimchi (of Raphanus sativus var. Longipinnatus) as measured by the change of pH through a digital pH probe after 3 days of fermentation at 25oC?

1.2 Introduction:

Kimchi is a Korean traditional fermented vegetable which is emblematic to the Korean culture and is becoming globally renowned for its unique taste and health benefits. Like many other Korean families, my family takes part in the annual ‘Kimjang’ festival which is a communal Kimchi making activity that prepares families to sustain the long cold winter with sufficient Kimchi. However, due to COVID-19 restrictions in 2020, gathering for this annual season was impossible. Luckily, by Kimjang season, Queensland restrictions allowed minimal outdoor access which allowed my family to proceed with Kimjang. But unfortunately for family who lived in Melbourne outdoor access was strictly prohibited. For this reason, our family transported a 30kg proportion of Kimchi in a large esky (cooling box) so that the rate of fermentation could be slowed. However, the large cooling box became an inconvenience as the postage fee would escalate and the rate of fermentation became more rapid as the cooling packs started to melt. Therefore, at the time of arrival, the Kimchi had arrived at an over fermented stage which produced an undesired taste of aged, sour Kimchi. This led me to investigate another factor in which the rate of fermentation could be manipulated, salinity of brine.

1.3 Background Information:

Before the fermentation process, the traditional Kimchi making procedure comprises of a brining step which creates a hypertonic environment allowing bacteria and radish cells to be plasmolysed (Henney, Taylor and Boon, 2010). The difference in solute concentration allows spontaneous net movement of water molecules through the permeable phospholipid bilayer, specifically from an area of low solute concentration to an area of high solute concentration, illustrated in figure 1. As the solute concentration gets higher, more water is drawn out of the cell in attempt to reach an isotonic or equilibrium state. In foods, this allows for longer preservation and easier penetration of seasonings as the osmotic pressure increases

. Furthermore, for bacteria that cannot tolerate high salt concentrations become dehydrated and are disadvantaged to the hypertonic environment, unlike

Lactobacillales (Lactic Acid Bacteria/ LAB) which favour the environment and begin to metabolise glucose into lactic acid (Wilfred Desrosier, 2018). This then lowers the pH and further inhibits the growth of non-desired microorganisms such as Salmonella typhimurium, Shigella sonnei and Escherichia coli (Kang and Han, 2005)…