Ultrasound in Pigmented Rice Processing: A Versatile Approach for Anthocyanin Retention and Extraction: A Review

Pigmented rice contains anthocyanins and other bioactive phenolic compounds; however, its processing is challenged by the relatively low starch digestibility of some pigmented varieties, prolonged drying times, anthocyanin degradation, and inefficient pigment recovery. This review evaluates ultrasound as a complementary technology for addressing these challenges, focusing on three major applications: starch modification, ultrasound-assisted drying, and anthocyanin extraction. Specifically, ultrasound-induced physical effects can disrupt starch-granule organization, alter molecular order, and thereby modulate starch functionality and digestibility. When combined with enzymatic or hydrothermal treatments, ultrasound may further accelerate structural modification, although the resulting effects depend on the treatment conditions and the specific rice matrix. In drying applications, ultrasound enhances heat and mass transfer and shortens processing time, thereby limiting prolonged thermal exposure. Similarly, in extraction, ultrasound-assisted methods promote solvent penetration, matrix disruption, and pigment diffusion, collectively improving the recovery of anthocyanins and other bioactive compounds from rice grains and milling byproducts. Nevertheless, these effects are strongly influenced by ultrasound frequency, power, treatment duration, temperature, reactor configuration, and solvent system, and excessive treatment may in turn promote pigment degradation. Overall, ultrasound represents a parameter-dependent complementary approach for improving processing efficiency, anthocyanin recovery, and the functional quality of pigmented-rice products, though direct evidence for anthocyanin preservation during ultrasound-assisted rice processing remains comparatively limited.