Effect of Konjac Glucomannan with Different Oxidizing Degrees on the Quality of Set-type Yoghurt

The food concept of "healthy low-fat" has attracted significant public attention in recent years. Oxidized konjac glucomannan (OKGM) was introduced as a fat replacer to address the issue of low gel strength in low-fat yoghurt. The effects of different oxidation degrees of OKGM on the quality of yoghurt were investigated by analyzing the physicochemical properties, texture, rheological properties and microstructure of yoghurt. The research demonstrated that yoghurt containing high oxidation degrees of OKGM (OK-60, OK-90, OK-120) increased the hardness from 375.90 g to 436.67 g and the water holding capacity from 28.03% to 31.89% compared to yoghurt without added OKGM. In addition, it improved the rheological properties of yoghurt including apparent viscosity and viscoelasticity. The results of scanning electron microscopy and confocal laser microscopy revealed that high oxidation degrees of OKGM reduced integral pores in yoghurt, promoted casein micelles aggregation, and increased average particle size from 88.27 nm to 125.33 nm. In contrast, natural konjac glucomannan (KGM) and lower levels of OKGM oxidation (OK-30) reduced texture, apparent viscosity, and viscoelasticity of the yoghurt, disrupted yoghurt gel structure and compromised its stability. The results of sensory evaluation showed that high oxidation levels improved the glossiness, uniformity, and overall taste of yoghurt, providing a theoretical basis for the development of high-quality, low-fat, and healthy yoghurt products.