Investigating the effect of freezing operating conditions on microstructure of frozen minced beef using an innovative X-ray micro-computed tomography method

The freezing rate determines the ice crystal size distribution and morphology. Ice crystal characteristics may have a direct impact on the microstructure of food products, providing irreversible cell and tissue damages resulting in quality losses. In this paper, an innovative method was used for imaging and quantifying ice crystals directly in frozen samples of minced beef by X-ray micro-computed tomography. The results were compared to those obtained by X-ray micro-computed tomography on freeze-dried samples. The effects of the integral cooling rate on ice crystal characteristics were studied for various mechanical and cryogenic freezing operating conditions. It was pointed out that crystals become 2.5 times smaller when the freezing temperature goes down from −30 °C to −100 °C. These crystals are also more numerous with a narrower distribution. Fluorescence optical microscopy and electron scanning microscopy were also used to do qualitative analysis. These results confirmed the effect of the freezing temperature on ice crystal sizes. •Frozen beef microstructure was quantified by X-ray micro-computed tomography.•Freeze-dried samples were analyzed using SEM and fluorescence microscopy.•Imaging frozen sample could give more reliable results than imaging freeze-dried ones.•Freezing rates affected ice crystal sizes and numbers.•Due to food thermal resistance, bigger crystals were observed at the center of the product.