E:FoodEngineering&PhysicalProperties

JFS E: Food Engineering and Physical Properties

Effect of a Gelatin Coatingon the Shelf Life of FreshMeatM.N. ANTONIEWSKI, S.A. BARRINGER, C.L. KNIPE, AND H.N. ZERBY

ABSTRACT: The end of shelf life for freshmeat is determined by unacceptable aroma, appearance, and color, whichappear before unacceptablemicrobial counts. Addition of a bovine gelatin coating to freshmeatmay extend its shelflife. This studyutilized a 20%bovine gelatin solution thatwas spray-coatedontobeef tenderloins, pork loins, salmonfillets, and chicken breasts which were packaged in an 80%O2 and 20%CO2 modified atmosphere and stored underfluorescent light at 4 C for 2 wk. All of the gelatin-coated fresh meat products showed a reduction in purge. Thegelatin reduced purge by acting as a barrier to water loss. There was a reduction in color deterioration for gelatin-coated beef, a slight reduction of color deterioration for gelatin-coated pork, andno reduction in color deteriorationfor salmon and chicken. The gelatin coat reduced color deterioration by acting as a barrier to oxygen, but also hada negative effect on color due to its own color deterioration. No change in lipid oxidation was seen with any of thegelatin-coated meat products. The gelatin coat was not an effective barrier for lipid oxidation at refrigeration tem-peratures. Sensory analysis of beef tenderloins confirmed that color deterioration was reduced, and flavor was notaffected by the application of a gelatin coat. The gelatin coat was equally effective during light and dark storage. Itwasmore effective on vacuum packaged products than onmodified atmosphere packaged products.

Keywords: coating, freshmeat, gelatin, modified atmosphere packaging, shelf life

Introduction

Consumer demand in the food industry is for fresh products.The demand is a cause of concern for food companies sincefresh foods have a short shelf life. Specifically for fresh meat prod-ucts, microbial counts for a product in modified atmosphere pack-aging (MAP) are consistently within an acceptable level after 3 wkof storage (Pietrasik and others 2006). However, since the color ofmeat starts to deteriorate after 12 d of storage in MAP, while micro-bial counts are not at spoilage levels, the shelf life of meat in MAPdoes not exceed 2 wk (Gill and Jones 1994). Hence, if the deteriora-tion of color of fresh meat products can be slowed, an opportunityarises that will reduce the waste of fresh meat products, includingbeef, pork, poultry, and fish. The meat industry would benefit fi-nancially from such an opportunity.

The characteristics that lead to consumer rejection of freshmeatproducts include appearance and aroma deterioration. A deterio-ration of appearance encompasses purge, which accumulates onthe bottom of a meat tray, and loss in fresh meat color, whichis associated with oxygenated myoglobin (Gennadios and others1997; Mead 2004). The shift from fresh meat color is evident whenoxymyoglobin (red) is oxidized to metmyoglobin (brown). Aromadeterioration is most often associated with rancidity volatiles thatare a result of lipid oxidation (Gennadios and others 1997). If purge,myoglobin oxidation, and lipid oxidation can be slowed in freshmeat products, their shelf life would be extended. One proposalthat the meat industry could utilize to extend the shelf life of freshmeat products is to apply a coating to the meat. The coating wouldact as a barrier to water and oxygen, thereby reducing purge, colordeterioration, and aroma deterioration (Krochta and De Mulder-Johnson 1997). Specifically, gelatin has been proposed for use as

MS 20070250 Submitted 4/6/2007, Accepted 5/19/2007. Authors are withDept. of Food Science & Technology and Dept. of Animal Science, The OhioState Univ., Columbus, OH 43210, U.S.A. Direct inquiries to author Bar-ringer (E-mail: barringer.11@osu.edu).

a coating on meat products (Mendis and others 2005). The gelatinmatrix is thought to act as a barrier to water and oxygen; hence,water loss and myoglobin and lipid oxidation would be slowedand shelf life would be extended (Krochta and De Mulder-Johnson1997).

Gelatin has previously been used to study its effect on the exten-sion of shelf life of various meat products. Reduction in purge re-sulted from the application of a gelatin coating to pork and poultryproducts (Keil 1961; Whitman and others 1971; Moorjani and oth-ers 1978; Marggrander and Hofmann 1997). Concerning color de-terioration, it was found that beef, pork, poultry, and fish productsshowed a reduction in color deterioration when a gelatin coat wasapplied (Klose and others 1952; Keil and others 1960; Whitman andothers 1971; Villegas and others 1999; Lopez-Caballero and others2004). Lipid oxidation,which correlates to aromadeterioration, wasreduced when a gelatin coat was applied to pork, poultry, and fishproducts (Klose and others 1952; Marggrander and Hofmann 1997;Villegas and others 1999; Ou and others 2001). However, these stud-ies dipped themeat in gelatin solutions or used a gelatinwrap. Theydid not look at spraying the gelatin onto the meat, which shouldproduce less cross-contamination and be easier to perform in aproduction environment.

With a growing consumer interest in fresh products, and a foodmanufacturer interest in shelf-life extension, it is important to ex-amine ways in which both interests can be met. This study demon-strates how spraying of a gelatin coating onto fresh beef, pork, poul-try, and fish aids in the extension of shelf life of these productsunder commercial modified atmosphere storage conditions in thelight.

Materials and Methods

Gelatin solution preparationBovine gelatin (lot nr 31083105, Flavex Protein Ingredients, The

Arnhem Group, Cranford, N.J., U.S.A.) was added to deionized

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water at approximately 70 C to allow for the gelatin powder todissolve into solution. A 20% (g gelatin/g hot water) solution wasmade.

CoatingWhole beef tenderloins (Giant Eagle Inc., Columbus, Ohio,

U.S.A.), whole pork loins (Giant Eagle Inc.), 24 individual chickenbreasts (Giant Eagle Inc.), or 4 whole salmon fillets (Giant EagleInc.) were obtained per run. Each beef and pork loin (20 8 cm)was cut with a slicer (Model 1612, Hobart, Troy, Ohio, U.S.A.) in thelaboratory in order to obtain 24, 1.5-cm-thick slices. The chickenwas purchased in pieces and used as is. Each of the 4 salmonfillets was cut into 6 equal pieces so that 24 samples could beobtained. Half (12) of the samples were used for uncoated con-trols, and the other half (12) of the samples were coated withthe gelatin solution. A slotted approach was used for the separa-tion of uncoated controls and coated variables for the beef andpork samples. Every other slice of loin and fillet was assigned toone of the 2 groups. The initial mass of all of the samples wasrecorded.

For coated samples, 1 freshly cut slice or piece of meat wasplaced onto a conveyor belt that ran 10.12 m/min. The slice wascoated with an airless hand gun with no nozzle (Model A4B, Nord-son Corp., Westlake, Ohio, U.S.A.) that was positioned 30 cm di-rectly vertical to where the meat passed on the conveyor belt. Themeat was manually flipped in order to coat both sides of the sam-ples with gelatin solution. Themeat was coatedwith approximately0.02 g gelatin/g meat. After application of the gelatin, the sampleswere allowed to sit for approximately 20 min in order to allow thegelatin to cool and set.

PackagingThe samples were stored under commercial modified atmo-

sphere storage conditions. Control and gelatin-coated meat sam-ples were placed into a tray (Cryovac 2.0 C5978 tray, SealedAir Corp., Saddle Brook, N.J., U.S.A.) and sealed with oxygen-impermeable film (Cryovac LID1050 film, Sealed Air Corp.) usinga packaging machine (Model T200, Multivac Inc., Kansas City, Mo.,U.S.A.). The packaging machine pulled a vacuum in the tray to 0.6kPa, flushed with a 20% CO2/80% O2 gas mixture (OSU Gas Cylin-der Warehouse, Columbus, Ohio, U.S.A.) to 98 kPa, and sealed thepackage at 140 C. The trayswere labeledwith sample numbers thatcorresponded to individual storage time.

StorageAll meat samples were stored in a 4 C cooler under fluores-

cent lights (Model IC9232 with 32 W T lamps, Cooper Industries,Inc., Peachtree City, Ga., U.S.A.) for 1, 7, or 14 d. The fluorescentlights were hung above the meat so that an intensity of 1050 luxwas achieved. Eight of the samples were removed from the coolerfor analysis after 1 d of storage, eight at 7 d of storage, and eightafter 14 d of storage. Throughout the 2 wk of storage, the sampleswere randomly repositioned under the fluorescent lights so that auniform exposure could be achieved.

Vacuum and dark storageFor vacuum packaging, meat samples were placed into a tray

(Cryovac 2.0 C5978 tray, Sealed Air Corp.), and inserted into a vac-uum pouch (12 18, 3 mil STD barrier Prime Source VacuumPouch, Prime Source Packaging Ltd., Spring, Tex., U.S.A.). The vac-uum environment was applied with a machine (Ultravac Model

UV2100-D, Koch Equipment LLC, Kansas City, Mo., U.S.A.). Thesamples stored in the dark were wrapped in aluminum foil.

PurgeAfter 1, 7, or 14 d of storage, the meat samples were withdrawn

from their packages. The mass of the exudate in the tray was ob-tained by blotting the trays with a paper towel. The mass of the ex-udate was used along with the initial mass of themeat prior to stor-age to determine the percent of weight loss as purge during storage.The formula for the calculation of weight loss due to purge is as fol-lows:

Weight loss (%) = mass of exudate (g)initialmass of loin (g)

100

ColorThemeat samples weremeasured immediately after being taken

out of their packages. The samples were not allowed to bloom in or-der to simulate retail conditions. AMinolta Colorimeter (Model CR-300, Minolta Corp., Ramsey, N.J., U.S.A.) was used to gather L, a,and b values. The samples were measured 5 times, straight acrossthe surface of the meat that was exposed to the fluorescent light.The average L, a, and b values of the samples stored for 1 d wereused along with the average L, a, and b values of the samplesstored for 7 and 14 d in order to calculate E with the formula asfollows:

E =(L L )2 + (a a)2 + (b b)2

where L, a, and b denote values at 1 d of storage time, and L, a,and b denote values at either 7 or 14 d of storage time.

Lipid oxidationThe thiobarbituric acid reactive substances (TBARS) assay was

used to determine the amount of lipid oxidation in the meat sam-ples (Pfalzgraff and others 1995a). A 0.5-cm-thick slice, with thevisible fat removed with a knife, was obtained from the surface ofthe meat that was exposed to the light. For the samples that werecoated in gelatin, the gelatin coat was removed prior to lipid ox-idation analysis by scraping the gelatin off with a knife. The slicewas cut into small pieces to decrease variability and make blend-ing easier, and from the small pieces, three 10.0-g portions of thetissue were analyzed for lipid oxidation. Each 10.0-g portion wasblended using a homogenizer (T25 Basic S1, Jane & Kunkel GmbH& Co., Staufen, Germany) in a 50-mL capsule with 20 mL 10%trichloroacteic acid (Product A322-500, Fisher Scientific Intl., FairLawn, N.J., U.S.A.) for 90 s. The capsule was centrifuged (CentricModel 225, Fisher Scientific Intl.) at 7280 g for 10 min. The super-natant was filtered (Whatman nr 1, The Whatman Group, Brent-ford,Middlesex, U.K.). Twomilliliters of the filtrate weremixedwith2 mL of TBA (2-thiobarbituric acid, Sigma-Aldrich Co., St. Louis,Mo., U.S.A.) reagent (300-mg 2-thiobarbituric acid/100 mL deion-izedH2O), and heated for 20min in a boiling water bath. After cool-ing to ambient temperature, the absorbance was read at 531 nm.The TBARS were reported as malondialdehyde (MDA) equivalents(nmol MDA/mL) using a standard curve with malondialdehyde bis(dimethyl acetal) (ZeptoMetrix Corp., Buffalo, N.Y., U.S.A.) standardat concentrations of 3.125, 6.25, 9.375, 12.5, and 25 nmolMDA/mL.

SensoryBeef samples stored 1, 7, and 14 d were analyzed by 50 peo-

ple per day for sensory testing. There were 22 to 26 males and 24

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to 28 females per day. The panelists were first presented with 2visual samples1 control and 1 gelatin-coated sampleto deter-mine which raw sample they preferred for overall appearance andlevel of redness and freshness. The panelists were then presentedwith 2 aroma samples to determine which raw sample they pre-ferred for overall odor. The panelists were then given 2 cooked sam-ples to determine which cooked samples they preferred for overallappearance, aroma, preference, flavor, and tenderness. The cookedsamples were cooked for 2min on double-sided grills (George Fore-man contact grill GRP99, Salton Inc., Lake Forest, Ill., U.S.A.) so thatboth sides of the sample were exposed to the heat for the sameamount of time. The grill was set at 190.6 C. Each of the 2 sampleswas assigned a different 3-digit random number in order to makethe control and the gelatin-coated samples undistinguishable fromone another.

Gelatin analysisThe color and lipid oxidation of the gelatin without meat was

measured at days 1, 7, and 14. A 20% bovine gelatin solution waspoured into 12 packaging trays to a depth of 1.5 cm. The gelatinsat for 20 min to allow gelling to occur. The gelatin samples werepackaged, stored, and analyzed (four at each day) for color and lipidoxidation.

Statistical analysisMINITAB Release 14.0 (Minitab Inc., State College, Pa., U.S.A.)

was used for statistical analysis to determine differences at the 5%level between treatments over storage time using 2-way analysis ofvariance (ANOVA). If a significant difference was observed, Tukeysmethod was used for posthoc analysis. Compusense Five (Version4.6, Compusense Inc., Guelph, Ontario, Canada) computer soft-ware was used to collect and analyze the sensory data.

Results and Discussion

PurgeAddition of a gelatin coat significantly reduced purge for beef

tenderloin, pork loin, salmon fillets, and chicken breast in com-parison to their respective controls (Figure 1). Purge significantlyincreased as storage time increased for all of the samples, includ-ing beef, pork, salmon, and chicken (Figure 1). A reduction in purgedue to the application of a gelatin coat on meat samples has beenobserved in previous studies. Marggrander and Hofmann (1997)found that gelatin-coated pork bellies lost 1% less water than con-trols. Whitman and others (1971) observed that pork livers coated

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Figure 1 --- Purge of control and gelatin-coated (gelatin)meat products, where * indicates a significant dif-ference between species-specific control and gelatin-coated samples

with a solution of gelatin displayed a reduction in purge. Keil (1961)found that dry sausages dipped into a solution containing gelatinhad a relatively small weight loss at the end of holding time. Finally,Moorjani and others (1978) observed that smoked poultry piecesthat were coated with a film made of gelatin had 51.0% to 57.4%moisture retention after cooking, while controls had 42.0% to 50.0%moisture retention.

The gelatin coating acts as a barrier to water and reduces exu-dates that result from water loss in fresh meat products. Gelatin isable to act as a barrier to water because of its surface activity (Finchand Jobling 1977). Substances that have high surface tension repelwater; hence, the gelatin coat traps the purge from the meat prod-uct and inhibits it from accumulating in the bottom of the meatpackage. Braudo and others (1967) found that the contact angle ofwater on the surface of a 15% gelatin solution was 123 3 , whichis high for a hydrophilic substrate. Diffusion of water into gelatindecreases with increasing concentration (Finch and Jobling 1977).Since the gelatin solution used in this experimentwas at a high con-centration, even if water penetrated the surface of the gelatin, dif-fusion of water through the coating would be limited.

Color and sensory appearanceColor deterioration is measured by the total color change and

changes in lightness and redness of the meat sample. Total colorchange increased for all of the fresh meat samples as storage timeincreased (Figure 2). Therefore, gelatin-coated samples that displaya smaller total color change than their controls would have an ex-tension in shelf life. Addition of a gelatin coat to beef, pork, andsalmon lowered the total color change in comparison to controls(Figure 2). Addition of a gelatin coat to chicken breasts increasedthe total color change in comparison to the control chicken (Figure2). It is important to note that differences in total color change can-not be stated as being statistically different because the averages ofL, a, and b values were used to calculate total color change.

For all of the freshmeat samples, as storage time increased therewas a significant increase in L, indicating that the samples becamelighter (Figure 3), and a significant decrease in a, indicating thatthe samples became less red (Figure 4). Therefore, a coating thatcan maintain darker and redder meat samples indicates an exten-sion in shelf life, and samples preferred by consumers.

Addition of a gelatin coat significantly reduced L val-ues (darker) and significantly increased a values (redder)of coated beef tenderloins in comparison to beef controls(Figure 3 and 4). This was confirmed by the sensory analysis(Table 1). The panelists said that the gelatin-coated beef wassignificantly redder than the control at days 1, 7, and 14. The abilityof a gelatin coat to reduce color deterioration in beef has been

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Figure 2 --- Total color change of control and gelatin-coated (gelatin) meat products

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observed before. Keil and others (1960) found that beef loins andsausages brushed with a solution of gelatin had a color that wasvisually equal to their respective color prior to storage.

For pork loins, addition of a gelatin coat had no significant ef-fect on L and a values (Figure 3 and 4). Gelatin-coated pork hadthe same level of lightness and redness as control pork. In previ-ous studies, gelatin did protect against color degradation. Villegasand others (1999) found that ham and bacon pieces dipped intoa gelatin solution had higher Hunter a values in comparison tocontrols, and the color preservation effect increased with increas-ing gelatin concentration. In another study, Whitman and others(1971) observed that pork chops coated with a solution containinggelatin displayed visual color preservation.

For salmon fillets and chicken breasts, addition of a gelatin coatsignificantly increased L values and significantly decreased a val-ues in comparison to their respective controls (Figure 3 and 4).Gelatin-coated salmon and chicken were significantly lighter andless red than control salmon and chicken. Previous studies foundthat gelatin improved the color. Klose and others (1952) observed

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Figure 3 --- Lightness of control and gelatin-coated(gelatin) meat products, where * indicates a significantdifference between species-specific control and gelatin-coated samples

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Figure 4 ---Redness of control and gelatin-coated (gelatin)meat products, where * indicates a significant differencebetween species-specific control and gelatin-coatedsamples

Table 1 --- Sensory results of control and gelatin-coated beef

Characteristic: Better appearance Redder Fresher Better odor Better overall Better flavor More tenderState: Raw Cooked Raw Raw Raw Cooked Cooked Cooked CookedDay 1 Control NSD Gelatin Control Control NSD NSD NSD NSDDay 7 NSD NSD Gelatin Gelatin NSD NSD NSD NSD NSDDay 14 NSD NSD Gelatin NSD Control NSD NSD NSD NSDNSD = no significant difference found between control and gelatin-coated beef.

that light-meat turkey steaks that were judged visually showedslightly but significantly better appearance than the controls. Addi-tionally, Lopez-Caballero and others (2004) found that cod fillet fishpatties coated with gelatin had lower final Hunter L values thancontrols, indicating color preservation.

The gelatin coat on fresh meat products reduces color deterio-ration by acting as a barrier to oxygen. When oxymyoglobin (red)is oxidized tometmyoglobin (brown), consumers reject meat prod-ucts. Oxygen is a promoter of oxidation, so if the presence of oxygencan be eliminated or reduced, the color of fresh meat products canbemaintained. Gelatin forms hydrogen bonds, and because of this,it is a good O2 barrier film (Krochta and de Mulder-Johnson 1997).Additionally, Lopez-Caballero and others (2004) stated that gelatincoatings were convenient barriers to O2 because of their stability atcold temperatures. Whitman and others (1971) found that a coat-ing of 10% to 50% gelatin and 50% to 90% of a polyhydric alcoholpermitted limited access of oxygen to meat.

The effectiveness of a gelatin coat at reducing color deteriorationin freshmeat products varied between different species. The differ-ent level of effectiveness of the gelatin was due to varying levels ofmyoglobin in the different meat products and the color changes inthe gelatin itself over time. A gelatin coat significantly reduced colorloss for beef tenderloin, had little or no effect on pork loins, had aslight but significant negative effect on salmon fillets, and had a sig-nificantly negative effect on chicken breasts. Beef has more myo-globin than pork, fish, or poultry (Aberle and others 2001); thus,the gelatin coat was most effective in preventing beef color loss.The typical colors of meat products include bright, cherry red beef,grayish pink pork, gray-white to dark red fish, and gray-white todull red chicken (Aberle and others 2001). However, the gelatin it-self changed color during storage. L value significantly increasedand a value significantly decreased as storage time increased, in-dicating that the gelatin became significantly lighter and less red(Figure 5). Species that have less myoglobin in their meat (chicken< salmon< pork) were negatively affected by the change in color ofthe gelatin which, in some cases, was greater than the color preser-vation of myoglobin.

Lipid oxidation and sensory aroma and flavorAddition of a gelatin coat produced no significant difference be-

tween TBARS values for coated beef, pork, salmon, and chickenand their respective controls (Figure 6). The TBARS values for beefand pork loins, salmon fillets and chicken breasts significantly in-creased with an increase in storage time, indicating that lipid oxi-dation for all samples increased with storage time (Figure 6). Sen-sory panelists preferred the smell of the raw control after 1 and 14d of storage, and found no significant difference between the smellof the raw control and gelatin-coated sample after 7 d of storage(Table 1). Additionally, the panelists found no significant differencebetween the smell and flavor of the cooked control and gelatin-coated samples at 1, 7, and 14 d of storage (Table 1). Therefore, thegelatin is not a barrier to rancidity volatiles.

A gelatin coat on fresh meat products should reduce lipid oxi-dation because the hydrogen bonds in gelatin act as a barrier to

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oxygen (Krochta and de Mulder-Johnson 1997). In this study, ap-plication of a gelatin coat was enough of an oxygen barrier to re-duce color deterioration in some meat products but not enoughof a barrier to reduce lipid oxidation. The inability of the gelatincoat to reduce lipid oxidation may be due to a temperature effect.Previous studies have found that a gelatin coat reduced lipid oxi-dation in frozen meat products. Marggrander and Hofmann (1997)found that pork bellies spray-coated with gelatin and stored frozenfor 6, 12, and 18 mo had lower TBARS values than controls. Villegasand others (1999) observed that ham and bacon pieces dipped intogelatin, and stored frozen for 7 mo, showed significantly lower lipidoxidation than controls. Finally, Klose and others (1952) found thatturkey steaks coated with a gelatin coat and stored at 12 C for6 mo had some protection from peroxide and rancidity. However,no effect on lipid oxidation is observed in the literature when thegelatin is held at refrigeration temperatures. For example, Lopez-Caballero and others (2004) observed the cod fillet patties coatedwith gelatin and stored at 2 C for 15 d displayed discoloration pre-vention but did not have an antioxidant effect. Additionally, Ou andothers (2002) found that tilapia fillets with a gelatin coat that arestored in the refrigerator showed no difference in volatile base ni-

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Figure 5 --- Lightness (L) and redness (a) of gelatin aloneduring storage

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trogen (a quality indicator) from controls, and were significantlydifferent from fresh fillets in sensory testing.

SensoryThe panelists found no significant differences between

the gelatin and control beef samples once they were cooked(Table 1). There were no significant differences in appearance,odor, flavor, or tenderness. The gelatin did not contribute itsown flavor to the cooked sample since it melts during cooking.However, during cooking, the gelatin gave off an aroma that wasnot the same as the control samples. In the raw samples, somedifferences were seen. On day 1, the control samples had signif-icantly better appearance, odor, and freshness while the gelatinsamples were significantly redder. On day 7, the gelatin sampleswere significantly redder and fresher, and there was no differencein appearance or odor. On day 14, the gelatin samples were stillsignificantly redder, and there was no difference in appearance,freshness, or odor.

Storage under vacuum or in the darkBeef tenderloins were also stored in the dark and in vacuum

packaging to determine if this changed the effectiveness of thegelatin coating. The total amount of purge and reduction in purgedue to the gelatin coating were not affected by storing in the lightcompared with in the dark, as would be expected (Figure 7). How-ever, vacuum packaging causes more purge than modified atmo-sphere packaging because the vacuum pulls water out of the my-ofibrils (Pietrasik and others 2006). In this study, vacuum storagesignificantly increased the amount of purge for the control sam-ples, but did not significantly change the amount of purge for thegelatin samples (Figure 7). Therefore, the purge reduction with agelatin coating is greater in vacuum storage than modified atmo-sphere storage.

Both light and oxygen encourage oxidation of myoglobin (Liuand others 1995; Lee and others 2001), but oxygen had a muchlarger effect on the color change than light. Gelatin produced a verysimilar improvement in L or a value whether stored in the lightor dark in MAP (Figure 8 and 9). However, in vacuum storage, thecontrol color changed very little while the gelatin-coated samplesbecame significantly darker and redder, which is more desirable tothe consumer. Pietrasik and others (2006) found that beef samplesstored in vacuumpackaging significantly decreased in redness withincreasing storage time. Thus the gelatin coating was equally effec-tive in preventing color change in the light and the dark, and im-proved the color during vacuum storage. The TBARS values werenot significantly different between the gelatin-coated samples andthe controls for any of the storage conditions.

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Figure 7 --- Purge of control and gelatin-coated (gelatin)meat products stored under modified atmosphere or vac-uum packaging and in the light and in the dark

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Conclusion

The spray application of a bovine gelatin coat to beef tender-loins, pork loins, salmon fillets, and chicken breasts helped toextend the shelf life of the products stored at 4 C in a modified at-mosphere of 80% O2 and 20% CO2 exposed to the fluorescent lightdue to purge reduction for all products and color preservation forbeef. The gelatin coat, when applied to fresh meat products at theonset of storage, could be beneficial to the meat industry becauseconsumer acceptability of the product would be prolonged, andless waste would result.

The significant reduction in purge that was observed when agelatin coat is applied to fresh meat products could have manybenefits. Diapers, or pads, that are normally at the bottom offresh meat trays, which absorb purge so it is less likely to be seenby the consumer, might be eliminated. Additionally, purge har-bors microbial growth. Hence, a gelatin coat could limit the viableenvironment for microbiological organisms and increase productsafety.

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Figure 8 --- Lightness of control and gelatin-coated(gelatin) meat products, stored under modified atmo-sphere or vacuum packaging and in the light and in thedark

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Figure 9 ---Redness of control and gelatin-coated (gelatin)meat products, stored under modified atmosphere or vac-uum packaging and in the light and in the dark

The sensory panelists found no significant difference betweenthe flavor, aroma, and overall preference of the cooked controls andgelatin-coated samples, but therewere somedifferences among theraw samples. The effectiveness of gelatin to act as a barrier to oxy-gen may be lower at refrigeration temperatures than at frozen tem-peratures; therefore, no reduction in lipid oxidation was observedfor the refrigerated gelatin-coated samples in this study.

AcknowledgmentsThis project was supported by the USDA Cooperative State Re-search, Education and Extension Service, special grant nr 2005-34328-16024, and The Arnhem Group.

ReferencesAberle ED, Forrest JC, Gerrard DE, Mills EW. 2001. Principles of meat science. 4th ed.Dubuque, Iowa: Kendall/Hunt. p 42, 113, 251.

Braudo EE, Tolstoguzov VB, Slonimskii GL. 1967. O CMAHIBAEMOCTI CTUDHEJIPLEHOKELATIHI. Vysokolom Soedin Ser B 9(11):796.

Finch CA, Jobling A. 1977. The physical properties of gelatin. In: Ward AG, Courts A,editors. The science and technology of gelatin. London, U.K.: Academic Press. p24994.

Gennadios A, Hanna MA, Kurth LB. 1997. Application of edible coatings on meats,poultry, and seafoods: a review. LWT-Food Sci Technol 30(4):33750.

Gill CO, Jones T. 1994. The display life of retail-packaged beef steaks after their storagein master packs under various atmospheres. Meat Sci 38(3):38596.

Keil HL, inventor; Armour & Co., assignee. 1961 Feb 14. Coating foods and composi-tion therefor. U.S. patent 2,971,849.

Keil HL, Hills C, Hagen RF, Flaws RW, inventors; Armour &Co., assignee. 1960 Sept 20.Coating composition,method of applying same to a food, and coated food product.U.S. patent 2,953,462.

Klose AA, Mecchi EP, Hanson HL. 1952. Use of antioxidants in the frozen storage ofturkeys. Food Technol 6(9):30811.

Krochta JM, De Mulder-Johnson C. 1997. Edible and biodegradable polymer films:challenges and opportunities. Food Technol 51(2):6174.

Lee SK, Kim YS, Kim JY, Song YH. 2001. Effect of muscle pH and display condi-tions on surface color in Hanwoo (Korean Native Cattle) beef. Asian Austral J Anim14(3):36571.

Liu Q, Lanari MC, Schaefer DM. 1995. A review of dietary vitamin E supplementationfor improvement of beef quality. J Anim Sci 73(10):313140.

Lopez-Caballero ME, Gomez-Guillen MC, Perez-Mateos M, Montero P. 2004. Achitosan-gelatin blend as a coating for fish patties. Food Hydrocolloids 19(2):30311.

Marggrander K, Hofmann K. 1997. Reduction of freezer burn and loss on dryingduring long term storage of pork with gelatin spray solution. Fleischwirtschaft77(1):1920.

Mead GM. 2004. Keeping poultry meat fresh. Food Sci Technol 19(1):201.Mendis E, Rajapakse N, Kim S. 2005. Antioxidant properties of a radical-scavengingpeptide purified from enzymatically prepared fish skin gelatin hydrolysate. J AgricFood Chem 53(3):5817.

Moorjani MN, Raja KCM, Puttarajappa P, Khabade VS, Mhendraker NS, Ma-hadevaswany M. 1978. Studies on curing and smoking poultry meat. Indian J PoultSci 13:527.

Ou CY, Tsay SF, Lai CH, Weng YM. 2001. Using gelatin-based antimicrobial ediblecoating to prolong shelf-life of tilapia fillets. J Food Qual 25(3):21322.

Pfalzgraf A, Frigg M, Steinhart H. 1995. -tocopherol contents and lipid oxidation inpork muscle and adipose tissue during storage. J Agric Food Chem 43(5):133942.

Pietrasik Z, Dhanda JS, Shand PJ, Pegg RB. 2006. Influence of injection, packaging, andstorage conditions on the quality of beef and bison steaks. J Food Sci 71(2):1108.

Villegas R, OConnor TP, Kerry JP, Buckley DJ. 1999. Effect of gelatin dip on the oxida-tive and colour stability of cooked ham and bacon pieces during frozen storage. IntJ Food Sci Technol 34(4):3859.

Whitman GR, Weston, Rosenthal H, inventors; General Foods Corp., assignee. 1971July 19. Process of coating food. U.S. patent 3,556,814.

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