ammonia gas permeability of meat packaging materials

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Ammonia Gas Permeability of MeatPackaging MaterialsFaris Karim, Faraj Hijaz, Curtis L. Kastner, and J. Scott Smith

Abstract: Meat products are packaged in polymer films designed to protect the product from exterior contaminants suchas light, humidity, and harmful chemicals. Unfortunately, there is almost no data on ammonia permeability of packagingfilms. We investigated ammonia permeability of common meat packaging films: low-density polyethylene (LDPE; 2.2mil), multilayer polyolefin (MLP; 3 mil), and vacuum (V-PA/PE; 3 mil, 0.6 mil polyamide/2.4 mil polyethylene). Thefilms were fabricated into 10 × 5 cm pouches and filled with 50 mL deionized water. Pouches were placed in a plexiglassenclosure in a freezer and exposed to 50, 100, 250, or 500 ppm ammonia gas for 6, 12, 24, and 48 h at −17 ± 3 ◦Cand 21 ± 3 ◦C. At freezing temperatures, no ammonia residues were detected and no differences in pH were found inthe water. At room temperature, ammonia levels and pH of the water increased significantly (P < 0.05) with increasingexposure times and ammonia concentrations. Average ammonia levels in the water were 7.77 ppm for MLP, 5.94 ppm forLDPE, and 0.89 ppm for V-PA/PE at 500 ppm exposure for 48 h at 21 ± 3 ◦C. Average pH values were 8.64 for MLP,8.38 for LDPE, and 7.23 for V-PA/PE (unexposed ranged from 5.49 to 6.44) at 500 ppm exposure for 48 h. The resultsshowed that temperature influenced ammonia permeability. Meat packaging materials have low ammonia permeabilityand protect meat products exposed to ammonia leaks during frozen storage.

Keywords: ammonia, packaging, polyethylene, polyolefin

IntroductionAmmonia has important advantages as a refrigerant: high effi-

ciency in cooling and freezing food products (Holmstrom 1994),relatively low environmental impact (Ross 1994a), and low pro-duction costs (Arnold 1993), with no impact on the ozone layer.Ammonia is the refrigerant of choice for food products and therefrigeration backbone of the food industry (IIAR 2006).

The food industry uses refrigeration with ammonia to coolfruits, vegetables, poultry, fish, beverages, dairy products, milk, andmeat (Lorentzen 1988) and most fabrication facilities, slaughter-houses, and cold storage warehouses use ammonia as their refrig-erant (Ross 1994b; Sun 1998). Even though ammonia has manyadvantages as refrigerant, its toxicity remains the major disad-vantage. Furthermore, ammonia leaks will occur in refriger-ated/frozen food storage facilities because of typical equipmentfailures and operator error. Carelessness may be part of the prob-lem, but more often, equipment failures are the issue (Ostner1986).

In many cases, ammonia leaks have resulted in multimilliondollars losses (EPA 2001). The largest ammonia leak incident oc-curred in Florida in 1974 in a commercial cold storage warehouse(Goodfellow and others 1978). The total value of damaged prod-uct was $45000000, including 121 types of products in 150281cases and 939 lots. In February 1994, another ammonia leak oc-curred in Olympic Cold Storage in Washington. Total of 58 tonsof frozen seafood and vegetables worth around several hundred

MS 20100842 Submitted 7/26/2010, Accepted 11/4/2010. Authors are with FoodScience Inst., Dept. of Animal Sciences and Industry, 208 Call Hall, Kansas StateUniv., Manhattan, KS 66506, U.S.A. Direct inquiries to author Smith (E-mail:[email protected]).

thousand dollars were exposed to an ammonia spill. All contami-nated foods were condemned because of high levels of ammoniain the analyzed samples and a strong ammonia odor.

In addition to refrigeration and freezing, most perishable foodscurrently are packaged in plastic films to protect against externaland internal deteriorations. Package integrity and barrier charac-teristics are important, and their effectiveness at preserving andprotecting commercial sterilized food in sealed packages has beenwell investigated (Denny 1989; Harper and others 1995). Single-layer or multilayer polymer films made of variety of polymer ma-terials can sufficiently protect food (Jasse and others 1994).

One aspect of package protection is the degree of permeabilityto gases and vapors harmful to the quality and the safety of foodproducts. Packaging permeability is determined by the type ofpolymers. Several factors affect the properties of polymers to per-meability including crystallinity; polarity; chain-to-chain packingability; glass transition temperature; size, shape, and polarity of thepermeant; temperature; and pressure (Pascat 1986; Sperling 1992;Robertson 1993). Temperature and pressure also are important indetermining a polymer’s permeability to gases and vapors (Jasse andothers 1994). Permeant molecules permeate polymers through 4stages (Ashley 1985): (1) absorption onto the polymer surface, (2)solubilization in the polymer texture, (3) diffusion through thepolymer along a concentration gradient, and (4) desorption fromthe other polymer surface. Mannheim and Miltz (1987) concludedthat an increase in oxygen permeability due to flex cracking of thepolymer during transportation may adversely affect food shelf life.

Literatures offer almost no data regarding permeability of foodpackaging to ammonia gas. In addition, there is a lack of in-formation related to the level of protection that food packagingmaterials provide during exposure to ammonia gas. The objectiveof this research was to evaluate the permeability of 3 differentpackaging materials commonly used in the meat industry to low

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Ammonia permeability meat packaging. . .

concentrations of ammonia gas at different times in freezing androom temperatures.

Material and Methods

Experimental designThree different meat packaging materials (Table 8), low-density

polyethylene (LDPE; 2.2 mil), multilayer coextruded polyolefinwith high oxygen permeability (MLP; 3 mil), and vacuum(V-PA/PE; 3 mil, 0.06 mil polyamide/2.4 mil polyethylene), wereassigned randomly to various ammonia concentrations for differentexposure times at freezing and room temperatures (−17 ± 3 ◦Cand 21 ± 3 ◦C). Ammonia exposure concentrations were 0 (con-trol), 50, 100, 250, and 500 ppm, with exposure times of 0 (con-trol), 6, 12, 24, and 48 h. All experiments were replicated 3 times.The exposure chamber was a plexiglass box inserted inside a freezer(1.3 cuf; Haier America, N.Y., U.S.A.). The experiment was car-ried out in a fume hood with an air flow rate of 123 FPM (feetper minute) (Labconco Corp., Kansas City, Mo., U.S.A.).

Sample preparationPlastic films were fabricated into 10 × 5 cm pouches with a

Midwest Pacific impulse heat sealer (J. J. Elemer Corp., St. Louis,Mo., U.S.A.) and filled with 50 mL deionized water and sealed. Apinhole was made in 1 corner of the pouches before sealing themto remove any trapped air. Each pouch was approximately 2.3 cmthick. In the experiment performed under freezing conditions,pouches were placed inside an air-tight 1.7 L plastic container(Lock and Lock, Heritage Mint Ltd., Scottsdale, Ariz., U.S.A.)that was placed in a freezer for 4 to 6 h (−18 ◦C) until thepouches were frozen. Frozen pouches were assigned randomly tothe experiment treatments.

In the experiment conducted at room temperature, poucheswere fabricated, filled with deionized water, sealed, and assigneddirectly to the experimental treatments. All pouches were codedand placed in the treatment chamber. A total of 144 pouches wereassigned randomly to the treatments; there were 12 pouches ineach treatment and 4 replicates of each type and 1 pouch of eachtype was removed at 6, 12, 24, and 48 h for both temperaturetreatments. For the control group, a total of 12 pouches wereassigned to the same temperature and time condition as pouches

in the experimental treatment but were not exposed to ammoniagas; there was 1 control pouch for each replicate treatment.

Exposure chamberThe treatment chamber was a Plexiglas box measuring 38 ×

13.5 × 36 cm (width × depth × height; volume 18.5 L) and waspreviously described by Karim and others (2010). The exposurechamber was tested for leaks and proper seal by pressurizing withair, locking, and immersing in a water bath. No bubbles were ob-served coming from the chamber during this test. In addition, aToxiRae PGM-30 Photo-Ionization Detector (PID) (accuracy ±2 ppm or ± 10% of the reading; RAE Systems, Calif., U.S.A.) wasinserted into the chamber and locked the chamber. The detectorwas operated and calibrated according to the ToxiRae PGM-30instruction manual. A concentration of 50 ppm ammonia gas wasintroduced into the chamber from a calibrated 50 ppm (± 2%)ammonia gas cylinder. When the concentration of 50 ppm wasreached and detected, the ammonia gas supply was stopped, andthe chamber was locked. After 7 h, the detector was removed,readings were recorded, and the data were analyzed using ProRae-Suite software (RAE Systems). There was no depletion of ammo-nia concentration inside the chamber. These results indicated thechamber had no leaks.

Treatment pouches were inserted into the chamber through around front door (15 cm dia) and attached to stainless steel hookssuspended on 2 Plexiglas bars attached horizontally between theleft and the right sides of the box. On the back side of the chamber,2 L-shaped threaded fittings were mounted to serve as gas inletand outlet, one in the upper right and the other in the lowerleft. These allowed the ammonia gas to be distributed uniformlythroughout the chamber.

Exposure system designThe exposure system as illustrated in Karim and others (2010)

was designed to simulate realistic conditions of low-level of am-monia exposure and allowed for manual control of the ammoniaflow rate entering the chamber, and maintaining a desired level ofammonia concentration. The ammonia cylinder was connected toa 0 to 65 mm gas flow regulator inlet (Cole-Parmer InstrumentCo., Vernon Hills, Ill., U.S.A.), and the gas flow regulator outlet

Table 1–Ammonia exposure concentrations as measured with the MinRae 2000 at the end of each treatment.

Ammonia concentration (ppm)1

Time (h) 50 100 250 500

6 30 ± 1.15 76 ± 13.3 168 ± 12.1 372 ± 17.312 33 ± 1.15 71 ± 10.4 164 ± 19.6 444 ± 50.224 29 ± 1.15 61 ± 10.4 152 ± 2.31 368 ± 13.848 29 ± 1.15 54 ± 10.9 140 ± 2.89 350 ± 12.71Values are means ± standard error of 3 replicates.

Table 2–Water pH levels in multilayer polyolefin pouches exposed to 50, 100, 250, and 500 ppm ammonia for 6, 12, 24, and 48 hat room temperature.


Time (h) 50 100 250 500

Control (0) 5.52 ± 0.02Aa 5.52 ± 0.11Aa 5.77 ± 0.26Aa 5.93 ± 0.48Aa

6 5.99 ± 0.01ABa 6.04 ± 0.20ABa 6.32 ± 0.06ABab 6.97 ± 0.48ABb

12 6.17 ± 0.05ABa 6.35 ± 0.02BCab 6.64 ± 0.11ABb 7.19 ± 0.25ABc

24 6.40 ± 0.07BCa 6.63 ± 0.06Ca 7.26 ± 0.42BCab 7.85 ± 0.70BCb

48 7.12 ± 0.66Ca 7.43 ± 0.41Da 8.40 ± 0.85Ca 8.64 ± 0.60Ca

1Values are means ± standard deviation of 3 replicates.A to DMeans with different capitalized superscript letters within a column are significantly different at P < 0.05.a to cMeans with different superscript letters within a row are significantly different at P < 0.05.

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was fitted to a T-shaped plastic connector. The exposure cham-ber inlet and detector outlet were attached to this connector. Thechamber outlet was assembled with a T-shaped tube connectorhooked to a one-way plastic valve (TETRA Technologies Inc.,The Woodlands, Tex., U.S.A.), which was connected to a sec-ond identical gas flow regulator to monitor the ammonia exhaustflow rate. The valve served as a pressure release device to preventbreakage in the chamber if pressure levels became too high dur-ing flushing and to prevent ambient air from entering the chamberand diluting the ammonia concentration, especially under freezingconditions.

The other end of the T-shaped connector was attached to aglass heat exchanger to warm the ammonia gas before it reachedthe detector, especially in experiments performed under freezingtemperatures. Plastic tubing (TYGON S-50-HL, class VI, size0.46 × 0.16 cm) was used to combine the system parts together.

Operation procedureAmmonia gas cylinders with concentrations of 50, 100, 250,

500, and 1000 ppm (calibrated concentrations were 48.8, 90,238.7, 474, and 992.0 ppm; 2% with atmospheric gas used formakeup) were obtained from Linweld Inc., (Manhattan, Kans.,U.S.A.) and manufactured by Matheson Tri-Gas Inc. (Joliet, Ill.,U.S.A.). Two cylinders were used in each treatment. The 1000ppm ammonia concentration cylinder introduced ammonia at thedesired level to flush the chamber while maintaining a continuousexposure of the required ammonia concentration for the requiredtime with 50, 100, 250, and 500 ppm concentration cylinders.

A stainless steel, double-stage regulator (Air Products, BrownWelding, Salina, Kans., U.S.A.) was mounted on the low-concentration cylinder to control the flow rate pressure of am-monia gas into the gas flow regulator. The temperature inside thechamber was monitored with a SmartButton data logger (accuracy:± 1 ◦C from −30 to 45 ◦C; ACR Systems Inc., Surrey, BritishColumbia, Canada). The chamber was flushed with ammonia gasfrom the higher ammonia concentration cylinder (1000 ppm), anda reading was taken using the MiniRae 2000 self-sampling detec-

tor (accuracy 2 ppm or 10% of the reading from 0 to 2000 ppm;RAE Systems). The detector inlet port was connected to the glassheat exchanger end, and the detector outlet port was connectedto a tube going into the chamber inlet. To avoid ammonia lossfrom the chamber, the detector takes an ammonia gas sample fromthe chamber, detects the gas, and circulates the gas back into thechamber. The detector was operated and calibrated according tothe MiniRae 2000 instruction manual. After the desired concen-tration inside the chamber was reached, ammonia gas from thedesired concentration cylinder was applied by adjusting the gascylinder regulator to a pressure of 2.5 psi and the flow rate to85 mL/min. Ammonia exhaust flow rate was monitored by thesecond gas flow regulator (with its dial opened to the maximumto allow exhaust to flow freely). At the end of each experiment,the ammonia cylinder supply was turned off, and the ammoniaconcentration inside the chamber was measured with the MiniRae2000 detector (Table 1).

Indophenol assay ammonia measurementWe chose the indophenol to measure the ammonia levels in

the pouches water. The indophenol method offers many advan-tages including high sensitivity (up to 0.03 ppm), small sam-ple size (1 g with recovery of 94% to 113%) (Hijaz and others2007), easily prepared reagent, and short measuring time. Sodiumhypochlorite solution (10% to 15% available chlorine) and sodium

Table 5–Water ammonia levels in vacuum pouches exposed to50, 100, 250, and 500 ppm ammonia for 6, 12, 24, and 48 h atroom temperature.

Ammonia concentration (ppm)1,2

Time (h) 50 100 250 500

6 NDa NDa NDa NDa

12 NDa NDa NDa 0.23 ± 0.07abc

24 NDa NDa 0.14 ± 0.13ac 0.47 ± 0.15b

48 NDa NDa 0.34 ± 0.18bc 0.89 ± 0.20d

1Values are means ± standard deviation of 3 replicates.2At time 0 (control), ammonia levels were not detectable for all concentrations.a to dMeans with different superscript letters are significantly different at P < 0.05.

Table 3–Water pH levels in low density polyethylene pouches exposed to 50, 100, 250, and 500 ppm ammonia for 6, 12, 24, and 48h at room temperature.


Time (h) 50 100 250 500


6 5.93 ± 0.04ABa 5.99 ± 0.12Ba 6.15 ± 0.30ABa 6.99 ± 0.50ABb

12 6.17 ± 0.03ABa 6.28 ± 0.05BCa 6.66 ± 0.04ABb 7.22 ± 0.24ABc

24 6.42 ± 0.03BCa 6.62 ± 0.07Ca 7.11 ± 0.26BCab 7.85 ± 0.62Bb

48 7.09 ± 0.58Ca 7.30 ± 0.32Da 8.24 ± 0.87Ca 8.39 ± 0.75Ba


Table 4–Water pH levels in vacuum pouches exposed to 50, 100, 250, and 500 ppm ammonia for 6, 12, 24, and 48 h at roomtemperature.


Time (h) 50 100 250 500


6 5.84 ± 0.12ABa 5.76 ± 0.09Ba 5.94 ± 0.07ABa 6.20 ± 0.62ABb

12 5.92 ± 0.06ABa 5.92 ± 0.13BCa 6.15 ± 0.04ABb 6.33 ± 0.54ABc

24 6.04 ± 0.09BCa 6.22 ± 0.22Ca 6.28 ± 0.21BCab 6.65 ± 0.74Bb

48 6.24 ± 0.09Ca 6.32 ± 0.17Da 6.96 ± 0.47Ca 7.23 ± 1.27Ba


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nitroferricyanide (III) dihydrate were purchased from SigmaChemical Co. (St. Louis, Mo., U.S.A.). Phenol, sodium hydrox-ide, sodium phosphate dibasic dodecahydrate, and a GenesysTM

10 visible spectrophotometer were purchased from Fisher Scien-tific Co. (Pittsburgh, Pa., U.S.A.). The reagents were prepared andstored according to Broderick and Kang (1980).

The pouches exposed to ammonia at freezing temperatures weredefrosted overnight at 4 to 8 ◦C in a refrigerator, and 200 μL ofthe water from each pouch were transferred to glass test tubes.The water was mixed with 2.5 mL phenol reagent and 2 mLhypochlorite reagent. The test tubes were placed in a 95 ◦C waterbath for 5 min and allowed to stand at room temperature untilapproximately 25 ◦C. To construct the standard curve, solutionsof 0.05, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, and 10 ppm ammoniaas nitrogen were prepared from the commercial standard 1000ppm ammonium chloride (Thermo Electron Corp., Miami, Fla.,U.S.A.). The blank was prepared with 200 μL of distilled water.Finally, the 630 nm spectrum was used to scan the samples and thestandards in a Genesys 10 visible spectrophotometer. For pouchesexposed to ammonia at room temperature, 200 μL of the waterfrom each pouch were transferred directly to glass test tubes andthe procedure continued from there.

pH determinationWater pH was measured by inserting a pH meter probe in

the pouches (Denver Instruments UP-5 pH meter, single elec-trode, Denver Instrument, Denver, Colo., U.S.A.). The pH ofeach sample was measured twice after the water temperature sta-bilized between 20 and 25 ◦C. Frozen samples were defrosted atroom temperature before pH was determined.

Statistical analysisSAS (version 9.1, SAS Inst. Inc., Cary, NC., U.S.A., 2002) was

used for data analysis. The experimental design was a 4 × 4 × 3Factorial Complete Randomized Design and the control wherethe control was the experimental unit, which did not exposed tothe ammonia gas and being measured at time 0 h. PROC GLMwas used to determine significant differences among the inter-

actions between concentrations levels, times, and package type.And the Tukey adjustment to preserve the experiment-wise errorrate was 0.05. The method of comparison was pair-wise compar-ison including the control using Tukey adjustment for multiplecomparisons.

Results and Discussion

pHNo significant change in pH was observed among pouches ex-

posed to ammonia gas at freezing temperatures (−17 ± 3 ◦C).For pouches exposed to ammonia at room temperature (21 ± 3◦C), the overall model (time and concentration) showed signifi-cant increases in pH (P < 0.05) for all packaging types as exposuretime and as ammonia concentration increased (Table 2, 3, and 4).Post hoc analysis showed the main effects of exposure times andammonia concentrations were significant (P < 0.05), althoughtime and concentration showed significant interaction (P < 0.05).There was no significant interaction between package type andammonia concentration (P < 0.05), which indicates that pH in-creased independently of increasing ammonia concentration andpackage type. However, the interaction between time and pack-age type was significant (P < 0.05). The maximum differences inpH values from the control mean were 2.71 ± 0.8 for the MLP,2.45 ± 0.97 for LDPE, and 1.30 ± 1.04 for V-PA/PE when thepouches were exposed to 500 ppm for 48 h.

The alkalinity of ammonia generally increases water pH becauseammonium hydroxide forms. Ammonium hydroxide is a weakbase that is partly ionized in water to form ammonium (NH4

+)and hydroxyl (OH−) ions (the alkalinity property for the aqueoussolution of ammonia relates to hydroxide ions).

Table 2 lists pH values for water in MLP pouches. The wa-ter in MLP had a higher pH than water in all other packagingtypes. Statistical analysis showed significant increases in pH (P <

0.05) as exposure time and as ammonia concentration increased.However, the interaction between exposure time and ammoniaconcentration was not significant (P < 0.09). The pouch waterpH levels showed significant differences from the controls after 24h of ammonia exposure for all concentrations. Meanwhile, there

Table 6–Water ammonia levels in multilayer polyolefin pouches exposed to 50, 100, 250, and 500 ppm ammonia for 6, 12, 24, and48 h at room temperature.


Time (h) 50 100 250 500

6 NDa NDa 0.41 ± 0.15ab 0.80 ± 0.24abc

12 NDa 0.45 ± 0.06ab 0.93 ± 0.17bcd 1.78 ± 0.18de

24 0.37 ± 0.01ab 0.87 ± 0.05abc 1.95 ± 0.48e 4.20 ± 0.44f

48 0.73 ± 0.05abc 1.46 ± 0.06cde 3.98 ± 0.66f 7.77 ± 0.67g

1Values are means ± standard deviation of 3 replicates.2At time 0 (control), ammonia levels were not detectable for all concentrations.a to gMean with different superscript letters significantly different at P < 0.05.

Table 7–Water ammonia levels in low density polyethylene pouches exposed to 50, 100, 250, and 500 ppm ammonia for 6, 12, 24,and 48 h at room temperature.


Time (h) 50 100 250 500

6 NDa NDa 0.27 ± 0.24ab 0.67 ± 0.26bc

12 NDa 0.38 ± 0.04ab 0.73 ± 0.21bc 1.62 ± 0.30d

24 0.31 ± 0.03ab 0.70 ± 0.04bc 1.45 ± 0.31d 3.27 ± 0.12e

48 0.58 ± 0.03ab 1.19 ± 0.04cd 2.80 ± 0.49e 5.94 ± 0.16f

1Values are means ± standard deviation of 3 replicates.2At time 0 (control), ammonia level was not detectable for all concentrations.a to f Mean with different superscript letters significantly different at P < 0.05.


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were no significant differences in the pH from the controls for allconcentrations after 6 h of exposure time.

Water in the LDPE pouch had a similar profile to MLP(Table 3). The statistical analysis for pH related to exposure timeand ammonia exposure concentration showed significant results(P < 0.05), but their interaction was not significant (P < 0.46).In addition, the water pH showed significant difference from thecontrols for all exposure concentrations after 24 h of exposuretime.

The pH of water in V-PA/PE pouches increased significantly(P < 0.05) in the overall model as exposure time and ammoniaconcentration increased, but post hoc analysis showed no signif-icant interaction between exposure times and ammonia concen-trations (P < 0.98). The V-PA/PE pouches were less permeableto ammonia (Table 5); thus, the pH increase over time (P < 0.05)may be due to the effect of the V-PA/PE materials on pH. A con-trol test under the same exposure conditions (without ammoniagas) was conducted at room temperature to determine the ef-fect of vacuum packaging material on pH. Water in the V-PA/PEpouches was elevated by 0.2 pH unit from the control. In contrast,no significant effects were found in water from the MLP or LDPEpackages.

Ammonia levelsThere was no significant change in ammonia level among

pouches exposed to ammonia gas at freezing temperatures (−17 ±3 ◦C). For pouches exposed to ammonia at room temperature (21± 3 ◦C), the overall model showed significant increases in ammo-nia levels (P < 0.05) as exposure time and ammonia concentrationincreased. Post hoc analysis showed the main effects of exposuretime and ammonia concentration were statically significant (P <

0.05). Exposure time and ammonia concentration showed a sig-nificant interaction (P < 0.05), as did exposure time and packagetype (P < 0.05) and ammonia concentration and package type(P < 0.05).

Two methods for determining ammonia levels of less than 10ppm in the pouches were evaluated: the ion selective electrode(ISE) and the indophenol methods. Hijaz and others (2007) con-cluded that the ISE and indophenol methods are precise enoughto detect ammonia concentrations in meat water. However, theISE method is unstable and time consuming when used to mea-sure low levels of ammonia. The indophenol method gives moreprecise results when used to measure low levels of ammonia inruminal fluid (Broderick and Kang 1980). Therefore, we con-cluded the indophenol method was more suitable for our researchneeds.

Ammonia levels in water increased significantly (P < 0.05) withincreasing exposure time and ammonia concentration. The differ-ences in maximum ammonia migrations for the control were 7.77± 0.67 for MLP, 5.94 ± 0.16 for LDPE, and 0.89 ± 0.20 forV-PA/PE. Table 5, 6, and 7 show the ammonia levels in water forV-PA/PE (Table 5), MLP (Table 6), and LDPE (Table 7) respec-tively. Ammonia levels increased significantly (P < 0.05) in waterfor V-PA/PE, MLP, and LDPE with increasing ammonia concen-

tration and exposure time. In addition, the interaction betweenexposure time and ammonia concentration was significant (P <

0.05) for all types of packaging materials.Table 8 shows water vapor and oxygen transmission rates for

the MLP, LDPE, and V-PA/PE packaging materials. MLP is morepermeable to oxygen (5000 cc/m2/24 h/atm) and water vapor(9.3 g/m2/24 h/atm) than LDPE and V-PA/PE. It is also morepermeable to ammonia than LDPE and V-PA/PE. However, wetested the MLP under normal conditions without exposing itto a vacuum or heat, unlike the process described by Teixeiraand others (1986) that required vacuum sealing, a vacuum pack-aging machine, and inserting the vacuum package in hot water(88.7 ◦C) to shrink it.

LDPE had a slightly different permeability profile than MLP.Oxygen (3743 cc/m2/24 h/atm) and water vapor (8.3 g/m2/24h/atm) transmission rates were slightly lower for LDPE than forMLP. Although MLP film is thicker (3 mil) than LDPE (2.2 mil),MLP was more permeable to ammonia. The V-PA/PE was theleast permeable to ammonia which is in agreement with its oxygen(60 to 70 cc/m2/24 h/atm) and water vapor (6.3 g/m2/24 h/atm)transmission rates. This low permeability to ammonia could bedue to the film’s 2-layer properties, especially the polyamide layer,which is a good barrier to gases and aromatics (Mauer and Ozen2004).

No changes in water ammonia levels or pH values were observedwhen the pouches were exposed to ammonia gas at freezing tem-peratures (−17 ± 3 ◦C), possibly because of low diffusion rate atthe low temperature. All pouches were permeable to ammonia atroom temperature (21 ± 3 ◦C). Permeant temperature and pres-sure affect the permeability of food packaging to gases and vapors(Jasse and others 1994). Ammonia gas was supplied at a specifiedflow rate, so no changes in the permeability transmission rate weredue to pressure differences. Although ammonia has a high affinityto water, dissolving readily in water or any product containingwater, the saturation point for ammonia remained unknown inthis experiment because the reaction between ammonia and wa-ter in the pouches was continuous until the saturation point isreached.

ConclusionsAmmonia content and the pH levels of water in pouches ex-

posed to ammonia were highest for MLP and LDPE pouches.Both showed similar permeability profiles when exposed to am-monia at the same concentrations and exposure times, althoughMLP was slightly more permeable than LDPE. V-PA/PE was theleast permeable of the 3 materials tested. Oxygen permeabilityof the packaging materials was related to ammonia permeabilityrather than water vapor diffusion. Temperature affected the rateof permeability. All pouches were permeable to ammonia at roomtemperature but not at freezing temperature. Our results showthat the 3 types of meat packaging material used in this studyprotect meat from low levels of ammonia exposure, which may beencountered during frozen storage refrigerant leak.

Table 8–Physical properties of selected packaging materials used to evaluate ammonia permeability (provided by suppliers).

Packaging material Thickness (mil)A Oxygen transmission rate cc /m2/24 h/atm Water vapor transmission rate g/m2/24 h/atm

MLPB 3.0 5000 (23 ◦C/0% r.h.) 9.30 (37.7 ◦C/100% r.h.)LDPEC 2.2 3743 (23 ◦C/0% r.h.) 8.32 (37.5 ◦C/100% r.h.)V-PA/PED 3.0 60–70 (23 ◦C/75% r.h.) 6.30–10.2 (23 ◦C/85% r.h.)AOne mil = 0.001 inch or 0.025 mm.BMultilayerpolyolifene; Clow-density polyethylene; Dvacuum film.

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AcknowledgmentsThis research was supported in part by the Cooperative State

Research, Education, and Extension Service, United States Dept.of Agriculture, under agreement nr 93–34211-8362, and by theKansas Agricultural Experiment Station. Contribution nr 10–032-J from the Kansas Agricultural Experiment Station, Manhattan,Kans., U.S.A.

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