Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2003
Publication Date: 4/20/2003
Citation: Walter, Jr, W.M., Truong, V-D., Simunovic, N., McFeeters, R.F. 2003. Low-temperature blanching of sweetpotatoes to improve firmness retention: Effect on compositional and textural properties. Journal of Food Science. 68(4):1244-1247. Interpretive Summary: Sweetpotato processors in the United States are able to produce canned sweetpotatoes for only a few months each year. If this crop is processed after more than a short period of storage after harvest, it becomes soft and disintegrates. The severity of softening and disintegration increases as storage time before processing increases. Our research has shown that blanching cut sweetpotatoes in water at 62C for 30 to 45 min, followed by canning in 30% sucrose syrup, resulted in a firm product which did not disintegrate and was well liked by sensory panels. In order to better understand the mechanistic cause for this quality increase, we compared tissue firmness and the composition of selected tissue components. We found that changes in pectic substances may explain part of the effect, but unknown factors also play a role. This new process will permit processors to prepare a product of consistent firmness and wholeness, regardless of the post-harvest history of the season and, as a result, could extend the processing season. However, since firmness retention increases with blanching time and a too firm product is not desirable to consumers, processors wishing to adapt this technology will have to reconcile blanching time, product quality, and processing efficiency.
Technical Abstract: Low temperature blanching of sweetpotatoes (SP) prior to cooking has been shown to significantly increase firmness retention. However, no information is available concerning the effect of this process on the components of sweetpotatoes. The objective of this research was to evaluate the effect of blanching followed by cooking on SP firmness and on the quantities of selected compositional components as compared to conventionally cooked tissue. Cylinders made from Jewel SP were either cooked at 100C, or blanched at 62C and then cooked. Cylinder firmness, pectin methylesterase activity (PME), degree of pectin methylation (DPM), and the amounts of galacturonic acid (GA), and cell wall material (CWM) were measured. Firmness of SP cooked after blanching increased to 19.0 Newtons (N) for blanched (90 min), cooked tissue as compared to 3.5 N for unblanched. Blanched samples had a lower DPM than unblanched. PME activity decreased 82% after 20 min of blanching, while sample firmness continued to increase with blanching time, indicating that demethylation of pectins was not responsible for all of the observed firmness retention. The data indicate that mediation of firming due to pectin demethylation appears to explain part of the observed increased firmness retention caused by low temperature blanching, but unknown factors also play a role.