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. 2021 Aug;58(8):2884-2895.
doi: 10.1007/s13197-020-04789-5. Epub 2020 Sep 22.

Effect of blanching pretreatment and microwave-vacuum drying on drying kinetics and physicochemical properties of purple-fleshed sweet potato

Sigit Uji Marzuki  1   2 , Yudi Pranoto  3 , Tabkrich Khumsap  1 , Loc Thai Nguyen  1
Affiliations

Effect of blanching pretreatment and microwave-vacuum drying on drying kinetics and physicochemical properties of purple-fleshed sweet potato

Sigit Uji Marzuki et al. J Food Sci Technol. 2021 Aug.

Abstract

In this study, drying kinetics and quality of purple-fleshed sweet potato (PFSP) subjected to microwave-vacuum drying were investigated. The effects of hot water and steam blanching pretreatment on physicochemical characteristics of the dried products were also considered. The samples were dehydrated in a custom-made microwave-vacuum system at different power levels including 450, 600 and 850 W. Hot air drying at 70 °C was also conducted for comparison. The results showed that drying time of PFSP under microwave-vacuum conditions ranged from 6 to 12 min, significantly reduced as compared to that of hot air drying (600 min). The improvement of drying rate was also evidenced by increased effective moisture diffusivity (2.22 × 10-7-4.05 × 10-7 m2/s) of the samples. Drying kinetics of PFSP was best fitted by Page and logarithmic model with R2 ranging from 0.991 to 0.998, and RMSE from 0.016 to 0.030. PFSP dried under microwave-vacuum condition had lower water absorption index and swelling capacity than hot air drying. Color, antioxidant activity and total phenolic content of dried PFSP were also improved under microwave-vacuum drying. The effects of blanching pretreatment on quality of dried PFSP were more dominant in hot air than microwave-vacuum dried samples.

Keywords: Blanching pretreatment; Drying kinetics; Microwave-vacuum drying; Power level; Quality.

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Conflict of interest statement

Conflict of interestThe authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
Drying curve of purple-fleshed sweet potato by microwave-vacuum method at different power levels. Inset: Drying curve by hot air method at 70 °C
Fig. 2
Fig. 2
Physicochemical properties of purple-fleshed sweet potato. a DPPH free radical scavenging activity, b total phenolic content and, c anthocyanin content. HAD: Hot air drying at 70 °C; MVD 450 W: Microwave-vacuum drying at 450 W; MVD 600 W: Microwave-vacuum drying at 600 W; MVD 850 W: Microwave- vacuum drying at 450 W. UT Untreated, SB steam blanched, HWB hot water blanched. Small letters (a–c) indicate significant difference among drying methods (p < 0.05); Uppercase letters (A–B) indicate significant difference among blanching pretreatment (p < 0.05)
Fig. 3
Fig. 3
Microstructure of different purple-fleshed sweet potato samples subjected to different pretreatment and drying methods. a Untreated, hot air dying, b untreated, microwave vacuum drying, c steam blanched, microwave vacuum drying, d hot water blanched, microwave-vacuum drying
See this image and copyright information in PMC

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