Pectin degradation and the firmness of the canned sweet potatoes

From a culinary standpoint, firmness is one of the most important attributes of thermally processed sweet potatoes; nevertheless, the consistent production of a canned sweet potato that would hold its shape while being prepared for the table is a problem confronting the sweet potato processors. Although considerable research has been conducted on variables generally associated with the firmness of cooked fruits and vegetables, the firmness of canned sweet potatoes is an attribute which is not fully understood.

This study was undertaken in an attempt to improve the firmness of canned sweet potatoes. The following four major studies were conducted:

1. Effect of four thermal processing treatments on the firmness of the canned product,

2. The relationship between changes in the AIS content during thermal processing and the firmness of the canned product,

3. The relationship between changes in the pectic materials during thermal processing and the firmness of the canned product, and

4. The relationship between the diameter and the firmness of the canned product.

The firmness of the raw and canned sweet potatoes was rated objectively using the ASCO Firmness Meter and subjectively by taste panel evaluation. The changes in the AIS and in the pectic substances were determined chemically. The results of the pectin analysis were expressed as percentage AGA of the dry AIS. Under the conditions of this study, several conclusions were indicated:

1. The possibility of favorably influencing the firmness of canned sweet potatoes by thermal processing treatments designed to effect low degrees of cooking was indicated.

2. Thermal processing effected a marked decrease in the AIS content. The two high processing temperature treatments had a greater solubilizing effect on the AIS, regardless of processing time, than the two low processing temperature treatments. There was no relationship between the AIS changes and the firmness of the canned product.

3. Thermal processing effected a marked decrease on the pectic substances. The two low heat penetration ratio treatments effected a lower degree of depolymerization on the total pec tin than the two high heat penetration ratio treatments. The changes in the pectic substances were not significantly related to the firmness of the canned product.

4. Storage time was found to be a significant factor in the objective evaluation of firmness and in the chemical analysis for the AIS and pectin content of the canned sweet potatoes.