Pre-harvest Curing: Effects on Skin Adhesion, Chemical Composition and Shelf-life of Sweetpotato Roots under Tropical Conditions

ABSTRACT

Excoriation (skinning injury) is a serious post-harvest problem for sweetpotato roots. In industrialized countries, sweetpotatoes are exposed to post-harvest curing to facilitate skin toughening and wound healing. However, in developing regions, such a practice is barely undertaken. Pre-harvest curing (PHC), where sweetpotatoes are subjected to defoliation before harvest, is a potential alternative to post-harvest curing. A field trial was conducted in southern Ethiopia. Roots underwent PHC treatment for 3, 7, 10, and 14 days, with 0 days as a control sample. Skin adhesion and chemical composition (ash, crude fibre, crude protein, dry matter, and starch) of the parenchyma and the periderm were measured. Storage testing at ambient conditions for 30 days was conducted.

Skin adhesion among all the treatments was significantly increased. The maximum skin adhesion was observed after 14 days (358.92 mN.m); however after 7 days of PHC, no significant change occurred. Root dry matter and ash content remained unaffected by the treatments. An increase in periderm crude fibre was observed for treatment samples, indicating lignification. Parenchyma crude protein concentration demonstrated a sudden drop in value from the control to 3 days of PHC (5.19 to 2.32%). For successive durations, crude protein started to increase from 3 days, demonstrating an active protein metabolism. Starch, the most important constituent affecting palatability and processing of sweetpotato, was not affected by PHC. Roots subjected to PHC for 10 and 14 days presented a potential for enhancing shelf life by having a significantly lower weight loss after 30 days of storage.

KEYWORDS:

• pre-harvest curing
• skin-adhesion
• sweetpotato
• weight loss

Acknowledgements

This work was sponsored by German Academic Exchange Services (DAAD), RELOAD project funded by the German Federal Ministry of Education and Research within the framework of the GlobE Initiative (grant no. 031A247A-D) and Project RE4Food.

The authors thank the Ethiopian Institute of Agriculture Research (EIAR), Addis Ababa and Hawasa University, Hawasa for the collaborative partnership. AP would like to thank Mr Fanta Urage and Mr Desta Danial for their support at the field trial location.