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  • Dairy Pipeline

    University of WisconsinExtension College of Agricultural and Life Sciences

    Wisconsin Center for Dairy Research

    A Technical Resource for Dairy Manufacturers Volume 18 Number 4 2006

    Getting the pink out

    W.L. Wendorff, Dept. of Food Science, UWMadison

    Extract of annatto seed, from the annattotree, supplies the yellow-orange color tocheese. These annatto-colored cheeses aresusceptible to pink discoloration when storedunder high intensity fluorescent lights in retail display cases. Manyquestions arise concerning pinking of annatto-colored cheeses,including: where does the pink color come from, what factors contributeto the potential for pink discoloration, and how can we control thepinking of annatto-colored cheeses?

    Origin of pink discolorationPrevious researchers (1,2,3,) have reported that high intensityfluorescent light affects color stability and causes lipid oxidation inannatto-colored cheeses. UW researchers (3) have reported that pinkdiscoloration can appear in cheddar and colby cheese after only 6-8hours of fluorescent light exposure. A rapid loss of the yellowcomponent of the annatto coloring the cheese produces this pink colorat the cheese surface. After an extended period under the lights the redcomponent of the annatto color is also lost, but at a slower rate. Thus apink color dominates before progressing to a bleached-out appearance.In a survey of Madison, Wisconsin supermarket dairy cases, we foundfluorescent light intensities ranging from 140 to 640 footcandles, withan average intensity of 300 footcandles. In our research studies (3), weheld cheeses under a light intensity of 250 footcandles and did find, insome cases, that pinking occurred within two days at that intensity.

    Barnicoat (4) reported that sulfhydrylcompounds present in aged cheddar cheesewere responsible for oxidation of the annattocolorant, which resulted in pink discoloration.On the other hand, Govindarajan and Morris(2) reported that the pink compound formedwas not the result of oxidation of norbixin fromannatto, but that hydrogen sulfide was involvedin the formation of a pink colored, micro-fineprecipitate of norbixin. In our studies (5), wedid not determine the specific chemicalreaction taking place to form the pink or redcompound but we did observe that formation ofthe pink discoloration from annatto colorantcoincides with the development of lipidoxidation in the affected cheese.

    Factors affecting pink discolorationWe have evaluated the effect of light type andintensity, storage temperature, exposure time,cheese composition, and age and source ofcolorant on stability of annatto colorants incheese. Following is a summary of the results.

    Light type and intensityCheeses stored under cool white fluorescentlighting showed a faster rate of pinking thansoft white lighting, although both types of lightdid induce pink discoloration. Increased lightintensity meant faster development of pinkcolor over the first 2 days of exposure, but it didnot differ after longer storage.

    Storage temperature and timeSamples stored at 47F had a faster rate ofpinking than those stored at 36F. However, no

    Controlling pink discoloration of cheese

    Controlling pink discoloration of cheese .................. 1

    Black spots in aged cheddar ......................................... 4

    Save money by separating for higher fat cream..... 6

    Curd clinic ........................................................................... 8

    News from CDR ............................................................. 10

    continued on page 2

  • 2

    Volume 18 Number 4 2006

    significant differences in color stability occurred between the twostorage temperatures when stored beyond 2 days.

    Cheese compositionCheese pH is a major factor affecting pink discoloration inannatto-colored cheeses. At pH 5.4, the red and yellowcomponents of annatto were reduced at a comparable rate andthe cheese developed a bleached appearance under fluorescentlighting. However, at pH 4.8 and 5.1, the yellow componentdecreased at a very rapid rate while the red component decreasedat a slower rate. The result was a very intense pink color. Full fatcheeses produced a more intense pink color than reduced fatcheeses during the first 7 days of storage.

    Source and age of colorantSome differences were observed in color stabilities of singlestrength annatto colorants produced from different sources ofannatto seeds. As with any biological crop, seasonal, geographic,and climatic conditions may all influence color stabilities ofannatto. Colorant manufacturers monitor and blend sources toproduce uniform colorants from available seeds. In our studies,older annatto colorants produce greater pink discoloration.

    Influence of packaging on pinkingWe evaluated packaging systems, packaging films and lightblocking agents to determine if any of these factors couldeliminate or reduce the pinking problem in annatto-coloredcheeses.

    Packaging systems and filmsAfter evaluating modified atmospheric packaging (MAP), wefound that films with higher oxygen transmission rates (OTR)produced pink discoloration in cheddar cheese before the cheesepackaged in films with lower OTRs. Discoloration was firstobserved around the cracks and slits on the surface of cheese andin the head space at the end of the packages, where oxygen was

    most likely available. Films with lower OTRshad less oxidized flavor after 7 days. However,after 2 days of storage under fluorescentlighting all cheeses had oxidized flavor.

    With comparable OTR in packaging films,vacuum packaged cheeses initially retainedthe yellow component of annatto better thanMAP cheeses. However, the reducedconditions present in vacuum packagedcheeses tended to produce a more intensepink color after 7 days. With vacuumpackaging, color stability of cheese samplesdisplayed under cool white and soft whitelight was not significantly different.

    continued from page 1

    Cheese pH is a majorfactor affecting pink

    discoloration inannatto-colored

    cheeses.

  • 3

    Volume 18 Number 4 2006

    Light blocking agentsTube guards with UV-blocking agent did not prevent light-induced pink discoloration. Perhaps near-visible wavelength lightcatalyzes pink discoloration. Transparent colored films (red,sunburst, and burnt-orange) did not retard pink discoloration,but the burnt-orange film did reduce lipid oxidation in vacuumpackaged cheeses stored for more than 7 days under fluorescentlight. Aluminum laminated film provided the greatest protectionagainst pink discoloration in vacuum packaged cheeses.

    Preventing pinking in annatto colored cheesesThe high intensity fluorescent lighting used in retail dairy casescan seriously affect the quality of dairy products. For example,oxidized flavors developing in fluid milk products has beenextensively documented. Now we know that high intensityfluorescent lighting can cause the loss of color components fromthe annatto colorant in cheese, producing a pink discoloration inthose cheeses. Along with the pink discoloration, anobjectionable oxidized flavor also develops. To reduce thepotential for pink discoloration in annatto-colored cheeses,cheesemakers should avoid using old colorants and selectappropriate packaging with a low oxygen transmission rate(OTR). Light blocking film, e.g., aluminum laminated film, willprovide good protection against potential pinking but at aslightly higher cost than transparent packaging films.

    At the retail display case, the intensity of fluorescent lightingshould be held to no more than 160-200 footcandles at theexposed surface of the cheese. Island display cases, withoverhead fluorescent lighting, are ideal for displaying coloredcheeses. In many horizontal display cases, we found fluorescentbulbs within 6 inches of the product emitting 640 footcandles onthe cheese surface. Not only did this drive the formation of pinkdiscoloration on the cheese, but the product temperature of 60-65F also contributed significantly to the breakdown of the bodyand texture and the development of off-flavors. In our studies, wefound about 2 to 5% of the top or front pieces of cheddar or colbycheeses in supermarket retail display cases showed pinkdiscoloration and the potential for oxidized flavor defects.Consumer rejection of the discolored cheese alone couldrepresent a loss of over $30 million per year to the dairy industry.

    In summary, cheese manufacturers can produce high qualityannatto-colored cheeses and package those in low OTR barrierfilms to extend shelf-life. But manufacturers must also work withtheir distributors, brokers and retailers to make sure theyunderstand the correct display lighting and handling proceduresfor cheeses so that the consumer is getting a quality product timeafter time.

    References1. Moir, G.M. 1933. Discoloration in New ZealandCheddar cheese. Muddy, bleached and pink defects.II. Biochemical investigations. J. Dairy Res. 4: 238-245.

    2. Govindarajan, S., and H.A. Morris. 1973. Pinkdiscoloration in Cheddar cheese. J. Food Sci. 38:675-678.

    3. Hong, C.M., W.L. Wendorff, and R.L. Bradley, Jr.1995. Factors affecting light-induced pinkdiscoloration of annatto-colored cheese. J. FoodSci. 60: 94-97.

    4. Barnicoat, C.R. 1950. Cheese discoloration:oxidation of bixin in annatto-coloured cheesepromoted by sulphhydryl compounds. J. Dairy Res.21: 209-213.

    5. Hong, C.M., W.L. Wendorff, and R.L. Bradley, Jr.1995. Effects of packaging and lighting on pinkdiscoloration and lipid oxidation of annatto-colored cheeses. J. Dairy Sci. 78: 1896-1902.

    At the retail display case,the intensity of fluorescentlighting should be held tono more than 160-200footcandle