Influence Of Harvest Time

Postharvest Biology and Technology 37 (2005) 93–100

Influence of harvest time and storage temperature on characteristics of inulin from Jerusalem artichoke (Helianthus tuberosus L.) tubers
Wanpen Saengthongpinit 1 , Tanaboon Sajjaanantakul ∗
Department of Food Science and Technology, Faculty of Agro-Industry, Kasetsart University, Chatuchak, Bangkok 10900, Thailand Received 24 August 2004;accepted 1 March 2005

Abstract Jerusalem artichoke (Helianthus tuberosus L.) tubers were harvested 16, 18 and 20 weeks after planting at Kanchanaburi Research Station, Kasetsart University, Thailand. Tuber maturity contributed to changes in inulin characteristics. A decrease in the more polymerised fractions (degree of polymerisation, DP > 10) with an increase in fructose and sucrosecomposition was observed for late-harvested (20 weeks) tubers. The inulin DP distribution profile from tubers, stored at 2 and 5 ◦ C, significantly changed with increased storage time and temperature. Sucrose and DP 3–10 fractions increased while DP > 10 decreased, particularly after 4–6 weeks of storage. Changes in inulin composition were reflected by formation of a second fructan series, as revealed byHPAEC-PAD chromatograms. These peaks corresponded to inulo-n-ose fructan where inulo-tri-ose (3 ) and inulotetra-ose (4 ) were predominantly found after 2 weeks of tuber storage at 2 and 5 ◦ C. Inulo-n-ose (5 ) up to DP 17 increased as a percentage with longer storage time. Tubers in frozen storage of tubers at −18 ◦ C maintained their DP distribution profiles. © 2005 Elsevier B.V. All rightsreserved.
Keywords: Jerusalem artichoke; Inulin; Harvest time; Storage temperature; Inulo-n-ose; HPAEC-PAD

1. Introduction Jerusalem artichoke (Helianthus tuberosus L.) is a native plant of North America and is one of the primary sources for inulin in higher plants. Inulin is a
Corresponding author. Tel.: +66 2 5625022; fax: +66 2 5625021. E-mail addresses: wanpensaeng@hotmail.com (W.Saengthongpinit), tanaboon.s@ku.ac.th (T. Sajjaanantakul). 1 Present address: Department of Food Science and Technology, Faculty of Agricultural Technology, Rajabhat Phetchaburi University, Petchaburi 76000, Thailand. 0925-5214/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2005.03.004
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polydisperse fructan which has a degree of polymerisation (DP) 2–60 or higher.The fructosyl units are linked by (2 → 1) linkages with the end glucose residue (Hoebregs, 1997; Coussement, 1999). Jerusalem artichoke tubers are difficult to store outside the soil because of the rapid onset of rotting. Therefore, the crop must be harvested according to the daily capacity of processing facilities (Frese, 1993). Early-harvested tubers contain a greater amount of highlypolymerised sugar fractions, which offer more industrial value than late-harvested tubers or those after storage

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W. Saengthongpinit, T. Sajjaanantakul / Postharvest Biology and Technology 37 (2005) 93–100

(Schorr-Galindo and Guiraud, 1997). Degradation of inulin to sucrose and fructo-oligosaccharides is highest after cold shock. Storage of Jerusalem artichoke tubers at low temperature (4 ◦ C)for 34 days also increases the fructo-oligosaccharide content (Kang et al., 1993). Pinpong (1997) found that the optimum harvesting stage of Jerusalem artichokes in Thailand was between 18–20 weeks after planting. Weight of fresh tubers increased rapidly over 12–18 weeks. After 20 weeks, loss of weight and firmness, and reduction in specific gravity and carbohydrates of tubers occurred rapidly.The structure of inulin depends upon many factors, such as the plant source from which it is extracted, the climate and growing conditions, the harvesting maturity and the storage time after harvest (De Leenheer and Hoebregs, 1994; Coussement, 1999). The objectives of this study were to assess the influence of harvest time and storage temperature on carbohydrate composition and changes in inulin...