Potential role of cell wall pectin polysaccharides, water state, and cellular structure on twice increase-decrease texture changes during kohlrabi pickling process

Pickled kohlrabi is a traditional and favored vegetable product in China. During pickling, the hardness, springiness, and chewiness of kohlrabi all experienced a typical change with twice increase-decrease trend. However, little is known about its mechanism. In this study, in situ analysis including immunofluorescence, low field nuclear magnetic, and transmission electron microscopy were used to explore the effects of cell wall pectin, water state, and cellular structure on kohlrabi texture changes during pickling. Results revealed that at the early stage, due to the rapid loss of water after three times salting, the cells shrank and the interstitial space reduced, resulting in the first increase on kohlrabi texture. Subsequently, the dehydration-rehydration caused by the first brine processing resulted in the first decrease on kohlrabi texture. Then under the action of PME enzyme, more low-esterified pectin was produced, and chelate-soluble pectin with more branched structure was further formed, leading to another elevation of the sample texture. As the pickling continued, under the combined action of PG and PME, the molecular weight of pectin was decreased and the rigidity of the cell tissue was destroyed, caused kohlrabi texture continued to decline. These researches could provide important information and guidance for better maintaining the texture of pickled vegetables during processing.

Automated summary

This study used in situ analysis methods such as immunofluorescence, low field nuclear magnetic, and transmission electron microscopy to explore the effects of cell wall pectin, water state, and cellular structure on the texture changes of pickled kohlrabi. The research found that the texture initially increased due to water loss, then decreased due to dehydration-rehydration, and subsequently increased again due to the production of more low-esterified pectin. However, continued pickling caused the texture to decline due to the decrease in pectin molecular weight and the destruction of cell tissue rigidity.