Effects of low‐temperature blanching on tissue firmness and cell wall strengthening during sweet potato flour processing

Summary Free starch rate has been one of the most important criterions to evaluate the quality of sweet potato flour. Low‐temperature blanching ( LTB ) of sweet potatoes before steam cooking has shown significant increase in tissue firmness and cell wall strengthening. This research indicated that pectin methylesterase ( PME ) activity decreased by 87.8% after 30 min of blanching in water at 60 °C, while polygalacturonase ( PG ) and β‐amylase activity decreased 69.4% and 7.44%, respectively, under the same condition. Both PME and β‐amylase played important roles in tissue firmness. Further studies of tissue firmness and methyl esterification showed that the combination of LTB and Ca 2+ could increase the activity of PME and significantly enhance the pectin gel hardness to strengthen the cell walls and decrease free starch rate from 12.83% to 7.28%.