Effect of prefreezing on surface color and structural and textural properties of kiwifruit after microwave-vacuum drying with temperature control by microwave power manipulation

• Published in: Food Science and Technology Research Vol. 29; no. 6; pp. 453 - 463
• Main Authors: Ando, Yasumasa, Okada, Takeyuki
• Format: Journal Article
• Language: English
• Published: Tsukuba Japanese Society for Food Science and Technology 01.01.2023; Japan Science and Technology Agency
• Subjects: Actinidia; Color; Discoloration; Drying; Freeze drying; Kiwifruit; Microwave-vacuum drying; Prefreezing; Temperature control; Texture; Thawing; Thin walls; Vacuum; Vacuum drying; Vapor pressure; X-ray CT
• ISSN: 1344-6606; 1881-3984
• DOI: 10.3136/fstr.FSTR-D-23-00100

The present study describes the effects of prefreezing on drying rate, surface color, internal structure, and textural properties of kiwifruit treated with microwave-vacuum drying (MVD) under controlled-temperature conditions at 20, 30, and 40 °C. The prefreezing was effective in reducing the drying time in the MVD process under properly controlled temperature conditions. The MVD samples without prefreezing had the same level of low a* value (high greenness) as the freeze-dried sample, but the prefrozen-MVD samples showed a slight browning due to discoloration during thawing in an atmospheric pressure environment. The prefreezing suppressed sample shrinkage during the MVD process and allowed the formation of a porous structure with many large voids with thin walls. Thanks to this structure, the prefrozen-MVD samples showed textural characteristics similar to the freeze-dried sample, but the porous structure was not formed in the MVD at 20 °C, indicating that a high microwave power is required to generate a high enough vapor pressure to form the porous structure.