Retardation of browning and softening of thermally processed pears packed in retortable pouches.

摘要

Wet pack fruit rations have been included in the U.S. Army Meals Ready-to-Eat (MRE) program menus since 1992, when they replaced freeze-dried fruits. These rations, designed for soldiers in the field, have high acceptability, are very convenient to carry, and provide important nutrients. The required shelf life for MRE wet pack fruit rations is 36 months at 26.7ºC or 6 months at 37.7ºC. However many of the wet pack fruits, especially pears in syrup, turn brown and mushy during storage before the required shelf life, and get rejected by the soldiers.;Preliminary experiments had suggested that the oxygen left in the headspace of the pouches after vacuum packaging had a significant role in the browning, and that softening was due to canned pears being used instead of fresh pears as starting material. Therefore, our objective was to develop strategies to slow down the browning of MRE pears by reducing the available oxygen, and to find a year-long available fresh pear that could be used as starting material to avoid double processing.;Accelerated storage studies were carried out at 48.8ºC for 45 days, and samples were withdrawn periodically to measure headspace volume and composition, color, ascorbic acid concentration and hardness of the pears. Sensory evaluation by a trained panel was done at the U.S. Army Natick Soldier Research, Development and Engineering Center.;The control formulation showed a significant consumption of oxygen in the headspace, degradation of ascorbic acid in the product, and formation of carbon dioxide during storage. Based on these findings we think that browning is mainly due to ascorbic acid degradation. Minimizing the residual headspace by pulling vacuum for a longer time during packing and doing agitated retorting reduced ascorbic acid degradation by approximately 87% after thermal processing and decreased browning by approximately 34% after 30 days of storage. Oxygen scavenger films were also used to reduce the oxygen in the headspace, but the results were inconsistent. Using fresh D'Anjou pears instead of canned Bartlett pears was enough to increase the hardness of the MRE rations to acceptable levels according to the sensory analysis.