Abstract: This work aims to study the regulatory mechanism of calcium fortification on the texture of kelp pickle during the shelf-life period in order to provide theoretical support for improving its texture quality using exogenous calcium. The effects of fermentation acidity and sodium/calcium ratio on the texture of kelp pickle during its shelf life at 4 ℃ were studied, and the evolution of water distribution and the structure of calcium ion bridge was analyzed. The results showed the hardness of kelp pickle decreased with increasing fermentation acidity, but its changes were effectively slowed down by exogenous calcium lactate. The rate of hardness preservation of kelp pickle with a sodium/calcium of 1.5:1 increased by 92.8% compared with the control group. The results of scanning electron microscopy (SEM) and low-frequency nuclear magnetic resonance (NMR) spectroscopy showed calcium lactate alleviated the morphological damage of kelp tissues caused by acid produced during fermentation, and inhibited the transition of bound water to free water during the shelf-life period. The proportion of free water in kelp pickle with a sodium/calcium ratio of 2:1 increased by only 10.29 percentage points after six months of storage. The results of X-ray photoelectron spectroscopy (XPS) showed that the mechanism by which calcium lactate enhanced the texture of kelp pickle during its shelf-life might be related to the formation of a stable calcium ion bridge at a sodium/calcium ratio of 2:1 or 1.5:1.

Key words: kelp; microbial fermentation; calcium lactate; texture properties; calcium bridge structure