A pilot-scale process for continuous in-flow microwave processing of particulate pumpable foods, designed and implemented at RISE Agrifood and Bioscience, was evaluated for heat treatment of a particulate, viscous model food at high-temperature conditions at 2450 MHz. The microwave system has three consecutive cavities, one excited by the TM020 microwave mode that heats primarily in the centre of the tube, and two cavities fed by TM120 modes that heat primarily in the tube periphery. In this paper, combined TM020 and TM120 tubular microwave heating is evaluated as an alternative to high-temperature short-time (HTST) processing for a high-concentrated particulate model product. Rapidness in heating of the product was evaluated after tubular microwave heating for different time-temperature conditions, corresponding to the required microbiological inactivation for a model product intended for storage at ambient conditions. Moreover, the effects on product quality of the microwave heated model soup were investigated in terms of texture, piece integrity and colour. Microstructural analysis was used to gain an understanding of the effects of heating at a microscopic scale. It was found that the microwave-assisted HTST system results in large process flexibility. Additionally, it offers advantages in product quality in terms of piece integrity and texture.