Temperature control for microwave vacuum drying of raspberries

Abstract

In order to optimize the microwave vacuum drying of raspberries, the temperature variation of different constant power microwave vacuum conditions was investigated. The conventional microwave vacuum drying (MVD) and the three different steady temperature control scheme was selected. A microwave intermittent vacuum drying scheme (MIVD), microwave vacuum drying power curves control scheme (MVD-T), and microwave vacuum drying power curves with intermittent control scheme (MIVD-T) were developed and conducted. As shown, temperatures under control schemes were all kept at more moderate ranges compared to constant power, where MIVD-T showed less fluctuation by adopting power curve changing with time as input variable. It was found that temperature control schemes could improve the appearance, as MVD-T and MIVD-T both reduced carbonization on the exterior and interior of raspberries. For antioxidant properties, there were differences between different schemes, in which MIVD-T could maintain more total monomeric anthocyanin (TMA) compounds and keep other antioxidant compounds similar to other drying methods. Control schemes such as MIVD, MVD-T, and MIVD-T were effective in obtaining more steady temperature materials than conventional microwave vacuum drying and were beneficial for drying quality.

Keywords:

• Raspberries
• microwave vacuum drying
• power control
• temperature control
• antioxidant properties

Acknowledgments

This research was supported by Science and Technology Project of Jiangsu Province – Modern Agriculture (BE2022319), Special Fund for Basic Scientific Research and Business Expenses of Central Public Welfare Scientific Research Institutes (S202006-02) and Youth Fund of Natural Science Foundation of Jiangsu Province (BK2022204).

Author contributions

QG: writing-original draft; data curation. FW: methodology, validation. JW: methodology; data curation. JW: investigation, writing—original draft, data curation. FS: conceptualization, investigation. GJ: validation, software. WS: funding acquisition; methodology. CS: supervision; writing-reviewing and editing; project administration.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.