Irradiation of Food and Packaging - American Chemical Society

Chapter 19

Physical Evaluation of High-Dose Irradiated Multilayer Pouches

Downloaded by PURDUE UNIV on August 22, 2016 | http://pubs.acs.org Publication Date: January 2, 2004 | doi: 10.1021/bk-2004-0875.ch019

Vicki

A . L o v e r i d g e a n d L a u r e n E. Milch

Department of Defense Combat Feeding Program, U.S. A r m y Soldier, Biological and Chemical Command ( S B C C O M ) , Natick, MA 01760-5018

High-dose irradiated shelf-stable entrees, prepared by the U.S. Army Soldier Systems Command-Natick for N A S A , have a formal F D A approval which includes a waiver for packaging material. The total entree process includes filling, vacuum evacuation/sealing, insertion into paperboard cartons, dry ice freezing and shipping, irradiation, thawing and return shipment. In order to minimize package failure five candidate pouches were evaluated including the current "Quad" pouch used for Meal, Ready to Eat (MRE) entrees. Testing included seal strength, leak tests, drop and vibration tests, frozen pouch abuse and internal pressure resistance. Significant losses in seal strength were found in four pouches. Separate evaluation eliminated the freezing step as contributing to seal strength reduction. Internal pressure resistance, a M R E requirement, indicated no sample failures. If pouches have sufficient seal strength initially then seal strength reduction appears to be of minor concern.

© 2004 American Chemical Society

Komolprasert and Morehouse; Irradiation of Food and Packaging ACS Symposium Series; American Chemical Society: Washington, DC, 2004.

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Introduction Food and Drug Administration (FDA) approval of packaging for foods to be irradiated has typically been addressed after approvals have been obtained for the food products themselves. In the case of fresh and frozen poultry, commercialization was delayed in part because the typical packaging for wholesale and retail poultry had advanced technically beyond the F D A approvals issued many years ago. Packaging suitable for high-dose irradiated foods was delineated in the 1970's by Natick Soldier Center scientists (/). Five laminate systems were developed, investigated and data gathered in anticipation of an F D A petition for high-dose foods. These structures, however, are considered obsolete in the industry where every year new materials and processes create new packaging fdms. A pouch for a high-dose irradiated food still requires somewhat of a miracle material. The product is vacuum-sealed, frozen to dry ice temperatures to minimize flavor changes, rough handling while frozen, irradiated, thawed, and rough handling again while being shipped or assembled into meals. In addition, even if a pouch employed the film structures outlined historically, separate approvals would be required for different additives or adhesives used to laminate the layers of the material. Irradiated entrees prepared for N A S A have formal F D A approval (March 1995) with a waiver for packaging material. Entrees are irradiated to a minimum dose of 44 kGy. Preparing irradiated entrees for N A S A highlighted problems with packaging that was intended for retorting in that a high rate of package failure occurred. Failures typically occurred due to flex cracking at the edge of the vacuum packed product. These failures often were hard to find since the entrees had very little fluid or sauce. One hundred percent inspection was required which involved opening the paperboard carton, inspecting each surface then reinserting into the cartons and reseating the cartons. In order to minimize package failure for N A S A production and gather data on a variety of pouches currently available, Natick initiated investigations on five candidate pouches. The pouches included a new Quad pouch developed for the M R E (Polyester/Nylon/Aluminum Foil/Polypropylene), a foreign commercial pouch (Nylon/Aluminum Foil/polyester/linear low density polyethylene), and three generations (#3, #4 and #5) of test pouches that coextruded the inner layers to avoid adhesive use (Figures 1-5). Since the pouches were either commercial products or proprietary research and development pouches, additional information on adhesives was not available. Testing included visual inspections, tensile strength testing, Meade leak tests, drop and vibration tests, frozen pouch abuse testing and burst strength.



External side

Internal side PET- polyethylene terephthalate (polyester) Figure 1. Quad Retort Laminate.

External side

Internal side PET- polyethylene terephthalate (polyester) Figure 2. South African Laminate (General Natick structure circa 1975).



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Figure 3. Coextruded Laminates #3.

Figure 4. Coextruded Laminates #4.



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PET- polyethylene terephthalate (polyester) Figure 5. Coextruded Laminate #5 (2001).

Evaluations Twelve samples of pre and post-processed (minimum 44 kGy dose) pouches were inspected for each evaluation. Visual inspection indicated that the M R E Quad pouch had very few defects, the foreign commercial pouch contained surface bubbles (air trapped between laminates) and bottom and closure seal wrinkles. The first two generations of coextruded pouch had grainy surfaces, #3 had side seal delaminations, and #4 had tear notch wrinkles and side seal wrinkles. Tensile strength testing of the manufacture's seals ( A S T M F88-94 (2)) indicated that most pouches lost seal strength after processing. The Quad pouch lost 25% (A -3.83 lbf) of its original seal strength, the foreign commercial pouch gained 6.3% (A +0.73 lbf), the coextruded #3 lost 7% (A -0.93 lbO, the coextruded #4 lost 19%(A -1.99 lbf), and the #5 lost 28% (A -4.17 lbf) in Natick evaluations. The manufacturer of the coextruded pouches conducted alternate tensile strength testing and found a 31% seal strength loss in the #4 pouch after processing. Overall the foreign commercial pouch had the strongest after processing seal strengths (excluding closure seal) with the coextruded #3, coextruded #5, the Quad, and the coextruded #4 following in that order. The general effect of polypropylene tending to lose crosslinks (Quad pouch) and polyethylene (foreign commercial and coextruded samples #3 and #4) gaining crosslinks (3) is supported by the results of the seal strength testing and the



310 films' sealant layers. The gaining of seal strength by the foreign commercial and the lower deltas and percent losses of #3 and #4 pouches reflect this. The #5 pouch with a polyethylene sealant layer lost seal strength in similar fashion to the Quad's polypropylene however its initial seal strength was higher than all other samples. Post irradiation samples of the Quad pouch, the foreign commercial pouch and the coextruded #3 sample were initially leak tested via the Meade test (submersion in water under vacuum at 26 psi). A l l samples except for one sub lot of the foreign commercial pouch (closure seal only) passed this inspection. The Quad pouch and the foreign commercial pouch were subjected to drop/vibration testing while assembled into typical M R E cases. One case per prototype was evaluated. The Quad pouch was packed in the M R E entree paperboard carton. The foreign commercial pouch was packed into a padded mailing envelope because of its larger size and our interest in potentially using the package in a field evaluation. The shipping case was subjected to drop and vibration tests in accordance with A S T M standards at room temperature. Following the drop/vibration test the pouches were first visually inspected and then subjected to the Meade test to inspect for leakage. A l l of the Quad pouches passed while eight of the twelve foreign commercial pouches failed the Meade test at the closure seal. Testing also included immediate container abuse testing in which pouches were packed in either the paperboard carton (Quad and coextruded pouches) or the padded envelopes (for the foreign commercial pouch). This test consists of a drop down a slide at a height determined by the weight of the product (Figure 6).

Figure 6. Immediate Container Abuse Test Apparatus


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Pouches were dropped at room temperature, examined visually then frozen to 16°F and dropped, visually examined and then Meade tested. A l l samples of the Quad pouch passed, four of twelve foreign commercial pouches failed the final Meade test. Fewer samples of the coextruded pouches were evaluated, one of five #3 pouches failed the Meade test and both of the #4 pouches tested failed the Meade test after immediate container abuse. A burst strength test used for evaluating the M R E retort pouch seals was also employed to evaluate the post-processed pouches. The test consists of subjecting the pouch to 20 psig of internal pressure held constant for 30 seconds. A l l samples passed this M R E retort pouch requirement. Seal Strength-Process Effect Breakdown It was unclear what step in the processing contributes to the loss of seal strength. The Quad pouch was selected to further investigate the loss of seal strength since that was the pouch chosen to package product processed under the overall program. Evaluations were conducted on samples drawn sequentially from the lot of pouch material used for all previous evaluations. First, 24 units of previously processed turkey slices were vacuum packaged and alternate samples were frozen to -20°F for a minimum of 48 hours prior to testing. No significant difference in bottom seal tensile strengths were found and a significant increase in tensile seal strengths were noted in the side seals after freezing (Table I ) .

Table I. High Dose Packaging Tensile Strength Testing-Quad Pouch Load at Peak (lbf) Total Process

Freezing

Irradiation

Pre

Post

Not Frozen

Frozen

Pre

Post

Side Seal

14.49

10.66*

13.39

13.73*

12.51

12.50

Bottom Seal

14.04

11.03*

11.50

11.75

13.66

10.86*

* Significant (P

Irradiation of Food and Packaging - American Chemical Society

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