Abstract
Total, soluble and insoluble oxalates were extracted and analyzed by high performance liquid chromatography (HPLC) following the preparation of kimchi using silver beet (Beta vulgaris var. cicla) stems and leaves. As silver beet contains high oxalate concentrations and consumption of high levels can cause the development of kidney stones in some people, the reduction of oxalate during preparation and fermentation of kimchi was investigated. The silver beet stems and leaves were soaked in a 10% brine solution for 11 h and then washed in cold tap water. The total, soluble and insoluble oxalate contents of the silver beet leaves were reduced by soaking in brine, from 4275.81 ± 165.48 mg/100 g to 3709.49 ± 216.51 mg/100 g fresh weight (FW). Fermenting the kimchi for 5 days at 19.3 ± 0.8 °C in 5 L ceramic jars with a water airtight seal resulted in a mean 38.50% reduction in total oxalate content and a mean 22.86% reduction in soluble oxalates. The total calcium content was essentially the same before and after the fermentation of the kimchi (mean 296.1 mg/100 g FW). The study showed that fermentation of kimchi significantly (p < 0.05) reduced the total oxalate concentration in the initial mix from 609.32 ± 15.69 to 374.71 ± 7.94 mg/100 g FW in the final mix which led to a 72.3% reduction in the amount of calcium bound to insoluble oxalate.
Highlights
Kimchi, a fermented traditional food has been made in Korea for several hundred years [1]
The beneficial effects of kimchi on human health may be derived from the nutrients in kimchi, such as vitamins, minerals and phytochemicals present, in the ingredients used to make the kimchi or the fermentation products produced by the lactic acid bacteria [4]
The mean pH of the initial kimchi mix was 5.06 ± 0.307 and this reached 4.34 ± 0.042 after 5 days fermentation at 19.3 ± 0.8 °C. This decrease in pH was due to the formation of lactic acid by the bacteria
Summary
A fermented traditional food has been made in Korea for several hundred years [1] It is a method of preserving food for use in the winter and it is gaining popularity as a functional food because of the phytochemicals formed during the fermentation process [2]. The main ingredient of traditional kimchi, Chinese cabbage, is cut and soaked in a 10% to 15% salt solution for several hours until the leaves and stems become soft. This study involved the measurement of the effect of soaking silver beet stems and leaves in brine and the effect of low pH and microbial fermentation on the oxalate content in silver beet during the production of traditional kimchi
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