Retardation of browning and softening of thermally processed pears packed in retortable pouches
Creators: name: Maldonado Ugaz, José Antonio
Publisher: name: No Publisher Supplied
Year: 2010

description: 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 (they are packed in flexible pouches), and provide important nutrients. The most common MRE wet pack fruit rations are pears, pineapples and mixed fruits in syrup, apple sauce, and apple pieces in spiced sauce. 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 these, especially pears in syrup, turn brown and mushy during storage before the required shelf life, and get rejected by the soldiers. Preliminar experiments had suggested that the oxygen left in the headspace of these pouches after vacuum packaging had a significant role in the browning, and that softening was due to canned Bartlett pears being used instead of fresh pears as starting material and being reprocessed into MRE rations. 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. The MRE pear rations were made using canned Bartlett pears and fresh D’Anjou pears, which have a longer harvesting season and shelf life. Accelerated storage studies were carried out at 48.8ºC for 45 days as requested by the U.S. Army Natick Soldier Research, Development and Engineering Center,  and samples were withdrawn periodically to measure headspace volume and composition, color, ascorbic acid concentration and hardness of the pears. Some of the samples produced were sent to the U.S. Army Natick Soldier Research, Development and Engineering Center for sensory evaluation by a trained panel. The control formulation showed a significant consumption of oxygen in the headspace, degradation of ascorbic acid in the product during thermal processing and during storage, and formation of carbon dioxide during storage. Based on these findings we think that browning is mainly due to ascorbic acid degradation; other browning mechanisms were ruled out as the main cause for browning. Minimizing the residual headspace to almost zero 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, a preferred solution from the manufacturer’s point of view since it wouldn’t increase production time, 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. The results from this study will allow the manufacturers of wet pack fruit MRE rations to improve the stability of their product without doing major capital investments or significantly increasing costs.