Continuous tubular microwave heating of particulate foods at high temperatures

ABSTRACT

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.

KEYWORDS:

• Microwave in-flow heating
• continuous process
• tubular heating
• pumpable foods
• particulate foods
• microwave-assisted HTST system
• high-concentration large particulates
• preservation
• high-temperature short-time (HTST)
• heat rapidness

Acknowledgment

This work was partly sponsored by the Swedish Board of Agriculture and by a group of companies. The authors would like to direct their warmest thanks to Erik Baderstedt, Emma Bragd, Niklas Lorén, Haris Hondo, Camilla Öhgren and Erik Kaunisto at RISE Agrifood and Bioscience, Katarina Larsson at Chalmers University of Technology, Ingegerd Sjöholm at LTH, and to the company participants Lena Nilsson and Carola Edsman, Arla Foods, Ewa Rytterstig, Domstein Foods, Annika Ternevi, Emelie Elmlund and Caroline Jonsson, Santa Maria, and Leif Gustavsson, Binar Elektronik.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was partly financed by the Swedish Board of Agriculture [grant number Dnr 3.2.18-200/14].

Notes on contributors

Birgitta Wäppling Raaholt

Birgitta Wäppling Raaholt holds a PhD degree in electromagnetics and applications of microwave processing from Chalmers University of Technology, Gothenburg, Sweden since 2015, a degree of Licentiate of Engineering in electromagnetics and microwave engineering from Chalmers University of Technology since 2000, and a MSc degree in engineering physics from Chalmers University of Technology, Gothenburg, Sweden since 1992. Her main research interests are advanced, resource efficient food processing technologies for preparation, preservation and manufacturing, electromagnetic processing, process modelling and optimization of achieved product quality and process efficiency. Her current research interests also involve measurement technology and sustainable food production systems.

Lars Hamberg

Lars Hamberg received his PhD degree in food science from Chalmers University of Technology, Gothenburg, Sweden, in 2003, and a MSc degree in chemical engineering with applied physics in 1998 from Chalmers University of Technology. His current research interests include food processing and preservation, flow processing of foods, as well as food process efficiency in production and sustainable food production systems.

Sven Isaksson

Sven Isaksson holds a Lic. Eng. degree in electromagnetics and microwave engineering from Chalmers University of Technology since 2002, and a MSc degree in electrical engineering with physics since 1997. Since many years his primary research interests are modelling, design and optimization of microwave heating processes, and microwave measurement techniques. Other research interests involve food processing technologies, sustainable food production systems and technological solutions enabling digitalization in the food industry.