Effects of freezing rate and terminal freezing temperature on frozen croissant dough

Abstract

Freezing process has an adverse effect on bread obtained from frozen dough. Croissant is one of the representative breads produced by freezing process to improve the productivity and reduce laboring cost. In this study, the quality of croissant was evaluated by various combinations of freezing rate and terminal freezing temperature (Tt). Firstly, the croissant dough was frozen with 0.72 to 3.56°C/min as the freezing rate, while Tt was set to -20, -40, and -55°C, respectively. In DSC thermogram, the peak was the broadest at the fastest freezing conditions indicating that ice crystals were evenly distributed during phase transition in the dough. Additionally, SEM images showed that the microstructure was kept intact at the fastest freezing rate. However, the yeast viability was higher at slow freezing rates. Moreover, the minor peak in the thermogram of yeast indicated that ice crystals were grown within cell and cell membrane. Intracellular ice crystals negatively influenced on both cell membrane and cytoplasm. Therefore, the yeast viability was decreased by the reduction of Tt. During storage, the bread qualities such as specific volume and firmness were deteriorated as increasing storage time. The poor quality was caused by damaging gluten network and yeast viability because of changes of ice crystal redistribution during storage periods. The obtained results showed that the dough frozen at 1.84°C/min to -20°C was the best freezing method to produce the fresh quality of croissant from frozen dough. Further work should be required to graft this freezing process onto other types of bread, which might provide better and improved process for the frozen bakery industry.

Keywords: frozen dough

freezing rate, terminal freezing temperature, ice crystal, yeast viability, croissant Student number: 2013-23272