Effectiveness of modified atmosphere packaging in preserving a ...

Packaging Technologyand Scienceis growing as a result of lifestyle changes and consumers’increased demand for convenience foods.To maintain their high quality, they are usuallydistributed under chilled conditions. Extendingour understanding of the effects of MAP on storagestability should be helpful in designing storageconditions and extending the shelf lives of thiscategory of foods.MATERIALS AND METHODSPreparation of braised green pepperswith dry anchoviesAs a typical combination ready-to-eat product,braised green peppers with dry anchovies wereselected for this study based on its central positionin Korean side dish products. 6 The braised greenpeppers with dry anchovies were processed followingthe typical traditional preparation procedure.First, 25 g of soy sauce, 30 g of sugar and175 ml of tap water were combined in a previouslyheated kettle, and were heated with mixing for30 s. Corn syrup (50 ml) was added to the mixture,which was heated for another 30 s. Dry anchovies(150 g) that had been heated in a frying pan for1 min were added to the braised mixture, and then200 g of green peppers from which the pedicleparts had been removed was added. The wholemixture was braised with continuous mixing for4 min and cooled under ambient conditions, producingabout 500 g of final product. Large quantitiesof this formulation in 22 batches were prepared,mixed thoroughly for homogeneity, and then usedfor the storage test.Packaging and storage of the productTo evaluate the primary quality index, the preparedproduct was divided into 80 g portions,placed on a polystyrene tray (18 × 13 × 2.5 cm), andstretch-wrapped in air with 12 mm thick linear lowdensitypolyethylene (LLDPE) film (Clean Wrap,Busan, Korea), which had an oxygen permeance of616 ml/h/m 2 /atm at 10°C. The product was storedat 10°C for 14 days, and a headspace gas compositionclose to atmospheric air was maintained. In thestorage test under gas-flushed conditions, theK-E. LEE ET AL.products (80 g portions) were placed on a polypropylenetray (11 × 7.3 × 3.5 cm) and were packagedwith a multilayered 12 mm nylon/polyethylene/nylon/ethylene vinyl alcohol (EVOH)/nylon/polyethylene/LLDPE gas barrier film (18 × 13 cm)(T6035B, oxygen permeance less than 5 ml/day/m 2 /atm at 23°C according to the manufacturer’sinformation, Sealed Air, Duncan, SC, USA). Thefinal free volume was equal to 150 ml. The followingmodified atmospheres supplied from premixedcylinders were tested: 30% CO 2 /70% N 2 ,60% CO 2 /40% N 2 , and 100% CO 2 . In the storagetest of MAP, air-filled control and vacuum packageswere also prepared for comparative purposes.All packaged products were stored at constanttemperatures (5, 10, 15 or 20°C), and quality assessmentswere conducted periodically. Most of thestorage tests were carried out at 10°C, which is theusual temperature limit proposed for storingchilled foods to ensure their safety. 7–9 Storage testsat higher temperatures also simulated abusivestorage conditions to examine the effects of temperatureas an impediment to preservation.Quality analysesTriplicate samples of each treatment were used toassess the quality attributes of the stored products.Aerobic bacterial and yeast/mould growth,expressed in colony-forming units (CFU) per gram,were quantified as the major indices of microbialquality. Samples (25 g) of the green peppers or dryanchovies were aseptically transferred into sterilestomacher bags, to which 75 ml of sterile 0.5%peptone water was then added. 10 The sampleswere then homogenized in a stomacher (Lab-Blender, TMC International, Seoul, Korea) for4 min. Aliquots of 1 ml were plated directly or as10-fold dilutions in 0.5% peptone water onto platecount agar (PCA, Difco Laboratories, Detroit, MI,USA) for total aerobic bacterial counts, or onto pHadjusted(to pH 3.5 with 10% tartaric acid) potatodextrose agar (PDA, Difco Laboratories) for yeast/mould counts. The colonies on the PCA platesincubated for 72 h at 30°C were counted as totalaerobic bacterial counts, and were expressed inCFU per gram. The PDA plates were incubated for5 days at 25°C, after which the yeast/mould countswere recorded.Copyright © 2008 John Wiley & Sons, Ltd. 418 Packag. Technol. Sci. 2008; 21: 417–423DOI: 10.1002/pts

Packaging Technologyand Sciencecific growth rate (1/day), N max = maximum celldensity in CFU/g, and A is defined as( )−µ maxttlagµmax1 ⎛ e + 1 e −1⎞A= t+ ⋅ln⎜t µµ ⎝ 1+ 1 ( e −1⎟ , with tlag maxmax)lag =⎠lag time.The microbial growth kinetic parameters (logN o ,logN max , m max and t lag ), determined using theMicroFit programme (Institute of Food Research,Norwich, UK), can be used to analyse the effectsof storage or packaging variables on the microbialstability of the food. 16–18log(CFU/g)98765432100 5 10 15 20 25 30Time (day)Figure 2. Effect of different MAPs on the growth ofaerobic bacteria on the green peppers of the braised sidedish product stored at 10°C. , Air control; , vacuum;, 30% CO 2 and 70% N 2 ; , 60% CO 2 and 40% N 2 ;and , 100% CO 2 . The solid lines are fi tted to Equation1, except for the condition of 100% CO 2 .MAP versus air packagingK-E. LEE ET AL.The effects of MAP on the quality of the productwere also investigated, and the main results of thestorage at 10°C are presented. MAP with ≥30%CO 2 significantly retarded bacterial growth onthe product (Figure 2). Packaging with 100% CO 2resulted in negligible growth of aerobic bacteriaafter 36 days of storage at 10°C. Compared withair packaging, vacuum packaging gave a slightlyextended lag time (Table 1). The effect of 30% CO 2and 70% N 2 was mainly confined to a lowermaximum specific growth rate, whereas 60% CO 2and 40% N 2 produced both an extended lag timeand a reduced growth rate. The effectiveness ofCO 2 in inhibiting microbial growth is well known,and high CO 2 concentrations are widely used inMAP to maintain the quality and extend the shelflife of meat, fish, dairy and fresh pasta products,which are susceptible to bacterial spoilage. 1,19,20Although MAP conditions of 100% CO 2 bestinhibited bacterial growth on the product, theseconditions are often avoided in the packaging ofchilled prepared foods because of package collapseand tissue discolouration by the dissolution of CO 2into aqueous and fatty foods. The product used inthis study, braised green peppers with dry anchovies,also underwent a slight visible discolourationduring packaging with 100% CO 2 , which caused asensory colour score slightly below that of theother packaging processes (hedonic colour scores,without statistical significance in difference at a =0.05, for the green peppers of 7.7 with air, 7.9 witha vacuum, 8.4 with 30% CO 2 /70% N 2 , 9.5 with 60%Table 1. Microbial growth parameters for the prepared foodproduct under different packaging conditionsMicrobial growth parameters(Equation 1)PackagingN o N max m max t lagR 2Air control 1.35 8.09 2.23 3.55 0.980Vacuum 1.27 6.92 2.10 4.01 0.97230% CO 2 /70% N 2 1.34 6.33 0.66 3.82 0.99360% CO 2 /40% N 2 1.58 6.08 0.80 5.70 0.986Copyright © 2008 John Wiley & Sons, Ltd. 420 Packag. Technol. Sci. 2008; 21: 417–423DOI: 10.1002/pts

EFFECTIVENESS OF MAP FOR A PREPARED FOODCO 2 /40% N 2 , and 7.4 with 100% CO 2 ). Consideringall these factors, we used MAP with 60% CO 2 /40%N 2 in the subsequent studies to examine the temperatureeffect on MAP and air packaging. Thisgas composition is the most commonly used atmospherefor the MAP of fish, fresh pasta, pre-cookedmeat and combination products to inhibit microbialspoilage and oxidative deterioration. 1,2,4,5,12The effect of storage temperature on microbiologicalevolution is given in Figure 3 for stretchwrapair packaging and MAP with 60% CO 2 /40%N 2 . It was confirmed that this high CO 2 MAPextends the lag time and reduces the growth rateof aerobic bacteria. MAP did not allow an increasein the aerobic bacterial count for 58 days at 5°C.The temperature effect on microbial spoilagewas analysed by investigating the parameters ofthe aerobic bacterial growth curves (Equation 1) atdifferent temperatures. The increase in the lag timeand the decrease in the growth rate with decreasedtemperature could be described according to alog(CFU/g)108642015 o C10 o C5 o CStretch-wrapped air packaging0 10 20 30 40 50 60Time (day)Packaging Technologyand Sciencesquare root model, in Equations 2 and 3, respectively(Figure 4):{ }1 t = b ⋅ T −Tlag lag lag, min (2){ }µ max = µ ⋅ − µ minb T T , (3)where T is temperature (°C), b lag and b m are theslope parameters, and T lag,min and T m,min are thehypothetical minimum temperatures correspondingto the extrapolation onto the x-axis of nogrowth. 21 Because lag time (t lag ) in Equation 2becomes infinite at T lag,min , and maximum specificgrowth rate (m max ) in Equation 3 is zero at T m,min ,bacterial growth is not allowed below any of thehypothetical minimum temperatures (T lag,min orT m,min ).MAP with 60% CO 2 and 40% N 2 mainly acts toincrease the hypothetical minimum temperatures(T lag,min and T m,min ) in the temperature dependenceof the lag time and growth rate, rather than influencingthe slope parameters (b lag and b m ) in Equations2 and 3 (Table 2).Shelf life extension by MAPEquations 2 and 3 can be used to estimate the evolutionof bacterial spoilage and the shelf life of thebraised ready-to-eat product under different temperatureconditions. Generally, an aerobic bacterialcount of 10 5 –10 7 CFU/g is used as the critical10820 o C10 o CMAP with 60% CO 2 and 40%1.81.5µ max2.52.0log (CFU/g)64215 o C5 o Ct lag -1/21.20.90.60.3t lag1.51.00.5m max 1/200 10 20 30 40 50 60Time (day)Figure 3. Growth of aerobic bacteria on the greenpeppers of the braised side dish product at differentstorage temperatures for stretch-wrap air packaging andMAP at 60% CO 2 and 40% N 2 . The solid lines are fi ttedto Equation 1, except for MAP at 5°C.00.00 5 10 15 20 25Temperature ( o C)Figure 4. Temperature dependence of lag time andmaximum specifi c growth rate. , t lag for stretch-wrap airpackaging; , t lag for MAP with 60% CO 2 /40% N 2 ; ,m max for stretch-wrap air packaging; and , m max for MAPwith 60% CO 2 /40% N 2 .Copyright © 2008 John Wiley & Sons, Ltd. 421 Packag. Technol. Sci. 2008; 21: 417–423DOI: 10.1002/pts

Packaging Technologyand ScienceK-E. LEE ET AL.Table 2. Square root model parameters used to describe the temperature dependence ofaerobic bacterial growth on the green peppers in braised green peppers with dry anchoviesParameters inEquation 2 Equation 3Packagingb lag T lag,min R 2 b m T m,min R 2Stretch-wrap air packaging 0.0429 −0.10 0.993 0.0592 −20.54 0.807MAP (60% CO 2 and 40% N 2 ) 0.0486 4.24 0.998 0.0446 −17.11 0.865limit for microbial food quality. 12,22,23 In this study,a strict condition of 10 5 CFU/g was used to estimatethe conservative shelf life of the product. Asan estimate of shelf life (t s ), the time for the bacterialcount to increase from an initial microbialcount of 10 1.4 CFU/g (N o ) to the critical limit of10 5 CFU/g (N c ) was calculated according to1 ⎛ Ncts= tlag+⎝⎜ ⎞lnµ No⎠⎟(4)maxIn Equation 4, the shelf life consists of the lagtime (t lag ) and the exponential growth phase period1 ⎛( ln N c ⎞µ max⎝⎜No⎠⎟ ), which assumes implicitly that thequality limit is met in the exponential phase: thelag time was calculated by substituting b lag andT lag,min values of Table 2 into Equation 2, and theexponential growth phase period was obtained byadopting m max given by inputting b m and T m,minvalues of Table 2 into Equation 3. Some typicalshelf life estimates at different temperatures were24.5 days at 5°C, 7.9 days at 10°C, and 4.3 days at15°C for stretch-wrap air packaging; and 18.4 daysat 10°C and 7.7 days at 15°C for MAP with 60%CO 2 and 40% N 2 . The shelf life was extended 2.3times by MAP relative to that achieved with airpackaging at 10°C, and was a little less at the highertemperature of 15°C. Because there was no growthat 5°C after 58 days (Figure 3), the shelf life extensionat that low temperature was greater, suggestingthe greater effectiveness of MAP in extendingshelf life at lower temperatures. The greater preservativeeffect of high CO 2 at lower temperatureshas also been reported by Corbo et al. for chillstoredfish fillets. 23 Thus, chilled temperatureand MAP are commonly combined for betterpreservation of perishable foods. 4,5This study examined the extension of shelf lifeby MAP based on the growth of aerobic bacteria,which was used as the primary quality index forstretch-wrap air packaging. MAP may change thepattern of food spoilage, and thus other spoilageorganisms, such as anaerobic microorganisms,may outcompete the aerobic bacteria, thus changingthe primary quality index used to determineshelf life. A further extensive study of the relationshipbetween the packaging atmosphere and thedominant spoilage organisms is required to ensurethe accuracy of shelf life determinations underMAP conditions. In particular, the storage and distributionof MAP products at abusive temperaturesare usually not recommended and should beexamined carefully with respect to food safety ifapplied in practice. The heating step in food preparationand its relatively low water activity, around0.90, would prevent the proliferation of manypathogenic and spoilage organisms in chilledstorage. 1 Hygienic control of the processing conditionsis still emphasized to ensure the safety andquality of the product. The results of this study arelimited by the assumption that the shelf lives ofchilled foods are predominantly determined bythe total aerobic bacterial growth. 11,12,23CONCLUSIONThe effectiveness of MAP with a 60% CO 2 /40% N 2gas mixture in extending the shelf life of a preparedready-to-eat side dish was higher at lowerCopyright © 2008 John Wiley & Sons, Ltd. 422 Packag. Technol. Sci. 2008; 21: 417–423DOI: 10.1002/pts

EFFECTIVENESS OF MAP FOR A PREPARED FOODtemperatures. The mathematical modelling analysisof the MAP effect on microbial growth retardationshowed that the MAP conditions of 60%CO 2 /40% N 2 raised the hypothetical minimumtemperature in the description of the temperaturedependence of lag time and growth rate.ACKNOWLEDGEMENTThis work was supported by a research grant from theMinistry of Agriculture and Forestry, Korea.REFERENCES1. Farber JM. Microbiological aspects of modifiedatmospherepackaging technology – a review. J.Food Prot. 1991; 54: 58–70.2. Day BPF. Guidelines for the Good Manufacturing andHandling of Modified Atmosphere Packed Food Products.The Campden Food and Drink Research Association:Chipping Campden, UK, 1992; 26–70.3. Sanguandeekul R, Siripatrawan U, Narakaew V.Changes in the quality of abalone (Haliotis asininaLinnaeus) packaged under atmospheric air, vacuumand modified atmosphere. Packag. Technol. Sci. 2008;21: 159–164.4. Goulas AE. Combined effect of chill storage andmodified atmosphere packaging on mussels (Mytilusgalloprovincialis) preservation. Packag. Technol. Sci.2008; DOI: 10.1002/pts.791.5. Rosnes JT, Kleiberg GH, Sivertsvik M, Lunestad BT,Lorentzen G. Effect of modified atmosphere packagingand superchilled storage on the shelf-life offarmed ready-to-cook spotted wolf-fish (Anarhichasminor). Packag. Technol. Sci. 2006; 19: 325–333.6. Lyu ES, Lee DS, Chung SK. A survey of Koreanhousewives’ perception on the commercial Koreanbasic side dishes in Busan area. J. Korean Soc. FoodSci. Nutr. 2006; 35: 440–447.7. Walker SJ. Chilled food microbiology. In ChilledFoods: A Comprehensive Guide, Dennis C, Stringer M(eds). Ellis Horwood: New York, 1992; 165–195.8. Betts GD. Critical factors affecting the safety of minimallyprocessed chilled foods. In Sous Vide andCook-Chill Processing for the Food Industry, Ghazala S(ed.). Aspen Publishers: Gaithersburg, MD, 1998;131–164.9. Martens T. Harmonization of safety criteria for minimallyprocessed foods. In Inventory Report FAIRPackaging Technologyand ScienceCT96–1020. Alma Sous Vide Competence Centre:Leuven, Belgium, 1998.10. Swanson KMJ, Busta FF, Peterson EH, Johnson MG.Colony count methods. In Compendium of Methodsfor the Microbiological Examination of Foods, VanserzantC, Splittstoesser DF (eds). American PublicHealth Association: Washington, D.C., 1992; 75–95.11. Ahmad S, Srivastava PK. Quality and shelf life evaluationof fermented sausages of buffalo meat withdifferent levels of heart and fat. Meat Sci. 2007; 75:603–609.12. Patsias A, Chouliara I, Badeka A, Savvaidis IN,Kontominas MG. Shelf-life of a chilled precookedchicken product stored in air and under modifiedatmospheres: microbiological, chemical, sensoryattributes. Food Microbiol. 2006; 23: 423–429.13. Blixt Y, Borch E. Comparison of shelf life of vacuum-packedpork and beef. Meat Sci. 2002; 60: 371–378.14. Corbo MR, Del Nobile MA, Sinigaglia M. A novelapproach for calculating shelf life of minimally processedvegetables. Int. J. Food Microbiol. 2006; 106:69–73.15. Baranyi J, Roberts TA. A dynamic approach to predictingbacterial growth in food. Int. J. Food Microbiol.1994; 23: 277–294.16. Kim G-T, Ko Y-D, Lee DS. Shelf life determinationof Korean seasoned side dishes. Food Sci. Technol.Int. 2003; 9: 257–263.17. McDonald K, Sun DW. Predictive food microbiologyfor the meat industry: a review. Int. J. FoodMicrobiol. 1999; 52: 1–27.18. Lopez S, Prieto M, Dijkstra J, Dhanoa MS, France J.Statistical evaluation of mathematical models formicrobial growth. Int. J. Food Microbiol. 2004; 96:289–300.19. Stiles ME. Scientific principles of controlled/modifiedatmosphere packaging. In Modified AtmospherePackaging of Food, Ooraikul B, Stiles ME (eds). EllisHorwood; New York, 1991; 18–25.20. Parry RT. Introduction. In Principles and Applicationsof Modified Atmosphere Packaging of Foods, Parry RT(ed.). Blackie Academic & Professional: London,1993; 1–18.21. McMeekin TA, Olley JN, Ross T, Ratkowsky DA.Predicted Microbiology. Research Studies Press:Somerset, UK, 1993; 87–113.22. Shapton DA, Shapton NF. Principles of Practices forthe Safe Processing of Foods. Butterworth-Heinemann:Oxford, UK, 1994; 388–441.23. Corbo MR, Altieri C, Bevilacqua A et al. Estimatingpackaging atmosphere–temperature effects on theshelf life of cod fillets. Eur. Food Res. Technol. 2005;220: 509–513.Copyright © 2008 John Wiley & Sons, Ltd. 423 Packag. Technol. Sci. 2008; 21: 417–423DOI: 10.1002/pts