Low temperature and freezing pretreatment for konjac glucomannan powder to improve gel strength

Konjac glucomannan (KGM) gel has attracted widespread interest in the field of food. However, the low texture properties of gel limit its further application. In this study, the effect of KGM powder under different processing times (8 h, 12 h, 24 h and 48 h) and temperatures (4 °C, -18 °C, -80 °C) on the texture properties of gels were investigated. According to result of texture profile analysis (TPA) and puncture test, the gel prepared by pretreatment showed good texture characteristics. The gel prepared by freezing KGM powder at -18 °C for 8 h has the best gel strength in the sample, which is 1.6 times that of native KGM. The molecular weight of KGM decreased significantly after pretreatment (from 12.30 × 105 Da to 0.29 × 105 Da). In addition, low temperature and freezing treatment can influence the rheological behavior and regulate water composite in gel. According to experimental result, it can be attributed to that low temperature and the growth of ice crystal can make structures denser, promote KGM molecular chain entangled and increase the number of hydrogen bond. This study provides a convenient and effective method for improving the gel properties.