Ultrasound-assisted cellulase pretreatment and cooking with enzymatic hydrolysates enhance the freeze-thaw stability of brown rice

Brown rice (BR) is rich in nutrients and becoming a good source for convenience rice development. However, the bran layer of BR and freeze-thawing in food supply chains affects the rice texture and limits the palatability. This study aims to apply the preprocessing method of ultrasound-assisted cellulase (UAC) that has been demonstrated to improve the textural attributes of BR, and further make use of the enzymatic hydrolysates for rice cooking, to stabilize the texture against freeze-thawing. BR with cellulase pretreatment and addition of the enzymatic hy-drolysates during cooking exhibited stable hardness and stickiness over five freeze-thaw cycles as compared to the rice cooked with water or the diluted hydrolysates. As observed by scanning electron microscopy and low -field nuclear magnetic resonance, BR cooked with the hydrolysates displayed more homogenous microstructure and the reduced water mobility against freeze-thawing, revealing that sugar and proteins in the hydrolysates contributed to promote the water holding capacity of cooked rice. Moreover, BR cooked with the hydrolysates exhibit noted advantages in fiber (0.23 g/kg) and proteins (0.19 g/kg) content. The combination of UAC pre-treatment and cooking with the enzymatic hydrolysates provides a promising processing method for convenience brown rice with improved freeze-thaw stability and nutritional quality.