Effect of blanching pretreatment and microwave-vacuum drying on drying kinetics and physicochemical properties of purple
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ORIGINAL ARTICLE
Effect of blanching pretreatment and microwave-vacuum drying on drying kinetics and physicochemical properties of purplefleshed sweet potato Sigit Uji Marzuki1,3 • Yudi Pranoto2 • Tabkrich Khumsap1 • Loc Thai Nguyen1
Revised: 18 August 2020 / Accepted: 9 September 2020 Ó Association of Food Scientists & Technologists (India) 2020
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 9 10-7–4.05 9 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, Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13197-020-04789-5) contains supplementary material, which is available to authorized users. & Loc Thai Nguyen [email protected] 1
Department of Food, Agriculture and Bioresources, School of Environment, Resources and Development, Asian Institute of Technology, 58 Moo 9, Km. 42, Paholyothin Highway, Klong Luang, Pathumthani 12120, Thailand
2
Faculty of Agricultural Technology, Universitas Gadjah Mada, Jl. Flora No. 1, Bulaksumur, Yogyakarta 55281, Indonesia
3
Indonesian Agency for Agricultural Research and Development (IAARD), Ministry of Agriculture, Jakarta 12540, Indonesia
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 microwavevacuum dried samples. Keywords Blanching pretreatment Drying kinetics Microwave-vacuum drying Power level Quality
Introduction Purple-fleshed sweet potato (Ipomoea batatas L.) (PFSP) contains high levels of anthocyanins (7.5 mg/g), polyphenols (74.6 mg/g) and dietary fiber (15.8%) (Lim et al. 2013). Anthocyanins can be used as food colorant and was found to exhibit strong radical scavenging activity, antimutagenic activity, to reduce high blood pressure, and to prevent colorectal cancer (Lim et al. 2013). Therefore, PFSP can be considered as a potential ingredient for functional foods with promising health benefits. PFSP is usually abundant during peak seasons, from late October through December. Due to its high water content (* 64%), PFSP tuber is
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