A Test for Evaluation of the Serum Separation Potential ofTomato Ketchup NIKOLAOS G. STOFOROS and DAVID S. REID ABSTRACT MATERIALS & METHODS The tendency of tomato ketchup to separate into a structural solids Ketchup sample preparation phase and a serum phase was measuredby placing a small amount of A typical homogenizedcommercial ketchup (McCormick and Com- ketchup on a wire screen mounted at the bottom of a plexiglass tube. pany Inc., Hunt Valley, MD) was used. The effect of storage tem- The screen retained structural solids along with “bound” serum while perature on serum separationwas then studied using nonhomogenizcd “unbound” serum drained through and collected in a holder tube ketchup samples prepared from 32” Brix concentrate tomato paste. below the screen. Rate and degree of separation were particularly The paste was obtained from tomatoes of the UC 204 variety using applicable to study separation potential of single serving ketchup conventional “Hot Break” or “Cold Break” procedures. Batches of pouches. Although reducing storage temperature decreasedinitial rate 200-1OOOgketchup were prepared using the method described by of serum separation, final amount of serum loss was independent of Marsh et al. (1979a). Details of the procedure, starting from raw temperature. tomatoes and ending with ketchup, are reported elsewhere (Stoforos, 1984). INTRODUCTION AMONG THE PROPERTIESof ketchupthat determineits Serum separation test gradeis the tendencyof the productto retainthe liquid portion For serum separation measurements, a “screen tube” was con- in suspension(Anon, 1953).Phaseseparationin tomatoket- structed by the Food Science and Technology Department shop. A chupis particularlyapparent in someindividualservingpouches stainless steel screen (60 mesh/inch, wire size 0.190 mm, openings but testsprovidelittle informationconcerningserumseparation 0.234 mm) was mounted at one end of a 2.54 cm outside diameter potentialof ketchup.Factorsdeterminingthe qualityof tomato pIexiglass tube as shown in Fig. 1. A 50 mL polypropylene centrifuge productsin termsof consistencyhavebeenidentified.How- tube (Nalgene #3110-9500) was used to hold the screen tube. ever, “thin” or “thick” ketchupsmay haveeithera high or At the beginning of each test, the weights of holder tube, and the screen tube and holder tube combined were measured (~0.1 mg). low degreeof serumseparation(Davis et al., 1954; Twigg, The combined tubes were placed into a test tube rack and, using a 1959;Marshet al., 1979b;Shomeret al., 1983).In the blotter plastic pipet, S-5.5 g ketchup samples were carefully applied on the test a ketchupsampleis appliedto a filter paperand the dis- screen. Care was taken to not force the sample through the screen and tanceof serumflow on the paper,measuredafter an appro- to ensure that the sample was forming an even, slightly domed shape priatetime, is usedasanindicatorof separation potential(Nelson on the screen without extending up the sidewalls of the screen tube. et al., 1957).Twigg (1959),comparingthe blotter test with the rate of filtration test (filtration undervacuumof diluted sample,McCollahet al., 1950)selectedthe blotter as more appropriatefor serumseparation measurements.However,Palma (1983)showedthe resultsobtainedusingthe blotter testwere dependenton the rate of evaporationof water from the filter paper,thatis, uponthe humiditysurrounding theblotter.Also, he found no relationshipbetweenserumflow on the blotter and separationof ketchupin individualservingpouches.An- other serumseparationindicatoris a new type of Bostwick consistometer which measuresdistancebetweenthe point of colorlessliquid and the red body in a given period of time (Gould, 1983).Resultsfrom a gravity sedimentation test (Ro- binsonet al., 1956; Smit and Nortje, 1958)were also corre- lated with tendencyof serumfor separation(Shomeret al., 1983).Serumseparationin tomatojuice was also measured by Caradecet al. (1985)by monitoringthe amountof serum drainedthrougha 60”cone-shaped 42 meshscreen. However,in singleportionketchuppacks,individualpouches can have very different degreesof separation,even though filled from the same,presumablyuniform, sub-batchof ket- chup. Thus study of only the bulk propertiesof ketchupis clearlynot sufficientto understand serumseparation in pouches. The effect of variousparameters on serumseparationcannot be studiedunlessreliablequantitativemeasurements can be obtained.The purposeof this studywas to developa reliable test indicativeof the serumseparationpotentialof ketchupin individualservingpouches. The authors are affiliated with the Dept. of Food Science & Technology, Univ. of California, Davis, CA 95616. Fig. 1 -Schematic diagram of the screen tube. 1626-JOURNAL OF FOOD SCIENCE-Volume 55, No. 6, 1990 depen- layer. headspaceduring sealing.987 are presented in F ig. approaching nitrocellulose-coated. (l).l/A canbe shownto represent same soluble solids content as the ketchup samples.andA (hour)and to ensure that no weight loss occurred during the experiment.58*0.10 0.64 betweenthis test and the serum separationpotential was tested. The asymptotictrendof the percent 8.the material used for the pouches was composed of nonheat-sealable. 2 andTable1. As can At intervals. The pouches ied.0302 0. that for ketchup preparation (Stoforos. To prevent evaporation. 6.0344 0.An additional of ketchup had different degreesof serum separation. No. W ith a cor- off. which the serumflows. During s -o. of the experiment. The percentserumloss after 932.40t0.42 parts (by weight) water or the artificial strum previously described. The percentserum loss (SL) was calculated from From the aboveexpression. The orientation of the pouchesduring stor- age affected both the air bubble position and the slope of the ketchup surface which was in contact with the air bubble.A regression equa- a Average of three replicates f one standard deviation tion foundto adequately predictpercentserumlossas a func- tion of time. A gravity sedimentation test was also performed and correlation 820 -a.1471 0. the initial rateof separation (l/A) decreased. the tubes with the ketchup sample were placed B (dimensionless) aree m p iricalconstants. 1627 .0372 0. we found that l/B bottom.as the sampleweight increased. 3 0A30 Gravity sedimentation test I z Ketchup We.Theresultsof percentserumlossversustim e 5. Weighing intervals of 1.0189 FSL In order to investigate the separationof serum as it occurs in the pouches.5hours)increased. II I.0267 0. 11.09 0.was No attempts to change the shape of the sample were made. tak- in a desiccator containing about 3. depending on reasonm ightbe the changeof samplegeometrythat hasbeen size and position of the bubble resulting from the air incorporation as observedfor large samples(~8 grams). The weight of the SL = t A+Bt (1) combined tubeswith the ketchup samplewas obtainedat the beginning and the end of each test in order to determine the sample weight and wheret represents the elapsedtim e in hours. In case of unevenly delivered sample. arepresented in Table1. be seenfrom F ig. Sodium benzoate the initial rate of serumloss. and 48 loss(coefficientA.983 serumloss versustim e curveswas also observedin all sub- 11. 17.42eO. as used by McCormick and Company. Each point represents the average of three replicates while each bar indicates one standard deviation. 1984). of dimensions similar to commercial with a correlationcoefficientR* = 0. 24.0282 0. the screen tube was replaced in its holder and was foundto describethe inverseof the initial rateof serum returned to the desiccator. I.1984)]. 1 QQO-JOURNAL OF FOOD SCIENCE.989thefollowinglinearrelationship After each weighing.0495 (2) when two consecutivemeasurements were the same. in all cases.5 cm “artificial” serum in the ing the lim it as tim e approaches infinity.17 0. the screentube was carefully separatedfrom the holder tube.40 rimless culture tubes covered with parafilm.0600 0. Ketchup A weight (g)' (hr) B R2 Differentweightsof homogenized commercialketchupsam- 2. polyethylene. 2. amountof serumloss(at 932.22 the gravity sedimentation test.988.6166 0. This was prob- SL = Serum weight ably dueto the fact that the averagedistancethe serumhasto x 100 Ketchup weight flow beforeseparation was furtherfor largersamplesize. one part ketchup was diluted with six -v.5.ght (g. medium density. Z-Effect of ketchup sample weight on serum separation. were made.957 sequentexperiments on serumseparation[about80 different 17. Inc. the test was redone. 2. relationcoefficientR* = 0. the P/L ratio versus time was calculatedby measuringthe solids precipiate 0'.09 0.cellophanewhich was adhesively laminated on a lim iting valueof 5 3 %for theparticularketchupsamplestud- one side to 2.2625 0.64-cO. Theincreaseof serumlosswith increasing sampleweight were fabricated so that the polyethylene was the heat sealable inner maybe dueto the fact that a certainamountof serum. By differentiating Eq. The test was considered complete A = 0. the combined tubeswere removed from the desiccator. but with high fructose (1) with respectto tim e andtakingthe lim it of the resulting corn sweetener(42” Be) substituted for tomato paste to result in the expression astim e goesto zero.2% basedon the addedwater) was added as a preservative. the preliminaryexperiments. (1) for the experiments with Preliminaryexperiments were performedto determinethe different ketchup sample weight preferred samplemassto be usedduringserumseparation tests. Table1) asa functionof thesampleweight hr and 1. The 1:7 dilution was 0 used to obtain acceleratedseparation. with sampleweightthroughthe following expression 1 Ketchup pouches . 4.58 The samples were allowed to settle at least 1 month in 18x50 mm -D.5hours(FSL) correlated Each test was performed in triplicate. since at lower dilutions many TIME (hours) homogenizedketchup samplesshow little separationin the time scale Fig.0487& + 0. The artificial serum was preparedusing the same method as represents the final percent serum loss. ones (flat outside dimensions 4 x 7.5 cm). = 0.22kO. for (0. The flat stock Equation(3) indicatesthat as sampleweightincreased. I II I 100 200 300 400 500 600 700 800 900 1000 height (P) and the total height (L) of the sample.964 experimental conditions(Stoforos.FromEq. The coefficientsA and B. During this time. 4 wk provided sufficient data to generatea smooth curve (SW in grams) for the ketchup samplesstudied. 10 -o.0 mil clean. Serum separation 40 was affected by these factors. Poucheswere cold filled with 9-log ketchup. the sampleweightaffected the condensedmoisture on the exterior of the holder tube was wiped both the rateandthe final amountof serumloss.0370SW . and the dentonly on the crosssectionalareaof the surfacethrough top sealed using a bartype heat-sealer. Other ketchup formulations may re- quire variations of this schedule. transparentpouches. allowing for a headspacevolume. I.from cylindricalto Volume 55.3416 0.8.39 0. 2. is held by the porousbed which is Preliminary data indicated pouchesfilled from the same sub-batch createdby the structuralsolidsof the ketchup.0. and the weight of the holder tube with accumulatedserum was measured. I. II I. RESULTS & DISCUSSION Determining optimum sample mass Table 1 -Coefficients associated with Eq.2.989 plesweretested. __. The functionof the screenusedin our testwas Hot Break 3.6 ‘C separation of ketchupin pouchescanbe seenfrom Fig.~.B. 1990 .significantdifferenceswere observed was a factorthat shouldbe standardized duringthe serumsep.----. .0926 0. we could seean analogouseffect of Fig.it is clearthat the sampleweight perforations. 3. where there was no void space. wherethe ketchupair interfacewas held in horizontalposition.~. (1) are presentedin Table 2. therewas someserumon the top right side of pouch A Table Z-Coefficients associated with Eq.6 0.0623 0..we observedthat loweringstoragetem- performed. ----4--O tion in the rangeof 1 to 3% for most subsequent experiments z : .from Fig.0246 0. and -0.-.2105 0._.0314 0.the separationtest was per- for venting(Fig. 23.the screentubedid not havethe flat portion temperature on serumseparation.0242 1. that naturalserumseparation Cold Break 23.Thoseresultswill be serumseparation.-..6 0..(2) minimizethetime requiredto reach the final separation. Thebottomrightsideof pouches B and D showedsmall air bubblesalmostfilled with serum. the entirescreentubewas formedat threedifferenttemperatures. H.in order to better distinguishbetweendif.0321 0.3 ‘C Single serving pouches (I . -0./ -o.3. 4-Effect of temperature on serum separation.. This -m. 3.The resultsare per./. Cold Break -0. During developmentof the test.1984).~I as shown.I +p~ -e. peratureslowed serumseparation.However. For both hot and cold 7628-JOURNAL OF FOOD SCIENCE-Volume 55.. -0. -____. (1) for the experiments study. severalexperimentswere In ketchuppouches.-__------ __.and (3) conservematerial..the S-g sample weight was selectedas the standardsampleweight for the Effect of storage temperature proposedserumseparationtest.3 0. 50 of 5 replicates)was found.. No. that this effect was samplewould start to flow was not the samefor all the sam- also dependent on the screentube dimensions. In theseexperiments.. 4. andin a third.-.-: -. = Cold slopeof the ketchupsurfacewhich is in contactwith the air Break.-. (Stoforos. on hot breakand cold breakketchupsamples.3 ‘C 5 . no serumwas observedon top.~.991 We could alsoconcludethat the developedtest simulatedthis Hot Break 23..The “filtration” of the Hot Break -0.-.comparinghomoge- arationtests.Note.-- A 30 / :.000 for ketchupin poucheswasdueto drainageof theserumthrough Cold Break 3. The correspondingcoefficientsassociated as the percentof one standarddeviationon the averagevalue with Eq.9 ‘C +’ 3. In pouch E.998 the solidsmatrix ratherthanto the settlingof insolublesolids. 20 i ‘q -e.996 phenomenon. There were samplesthat did not flow through4 mm* From the abovediscussion. reportedlater. Sample . The chosenscreensizewas the one with maximumopenings able to hold every ketchupsamplestudied(Stoforos.~. (C.. = Hot Break) bubble. betweenvarious samples(for example.PouchC illustrated ing the effect of storage temperature the role of the air bubbleas a serum-holdingshell.1984).1211 0.B.9. ples. 6. Wishing to (1) maximizethe amountof final nizedwith nonhomogenized ketchups).6”).0164 0.. SERUM SEPN POTENTIAL OF TOMATO KETCHUP.6 ‘0 photographwas taken 1 month after the poucheshad been filled with homogenized commercialketchupsamplesandstored 0 ~.2371 0.6.0245 0. wherethe ketchupwas slightly mounded. --.a variationof 20 to 50% (expressed presentedin Fig.0249 0. 23.9 0.In pouchB. the test was performedoutsidethe desic.3.3 0. In another.In one. l). Fig.‘0 4.(23. The final form of the test.9 0.no 0 50 100150200 250 300350400 450 500550600 serumseparation wasobserved.A shrinkageof the ketchupresultedin an increasein The minimum size of perforationsthroughwhich the whole the exposedsurfaceof the sample. 3. as it is 1 describedin the Materialsand MethodsSectiongave a varia- 40 ?+=+.-. conical./~. lh4) B R2 It canbe inferred.-. . placedinsidethe holdertube and coveredwith a plasticstop. 3-Effect of air bubble size and position on serum separation of ketchup in pouches.941 only to supportthe ketchupsample. ferentketchupsamples. How- ever. .9 ‘C The importanceof air bubble size and position on serum s i .962 serumwas donethroughthe insolublesolids of the ketchup. TIME (hours) From pouchesA and B. . 0 IP l .To examinethe effect of cator.~. and resultsin a layer of serumabovethe product.. Table 2) ments of tomato puree. 1969.which is probably due to the settlingof the solidsmatrix. Ransford. Instituto Technologlco de Ti- independentof storagetemperature.J. 764-E. With a correlationcoefficientR* = 1. B. Colleee Park.000.. Pres. Lindner. B. T. Mexico. 1984).S. MD.60 3.29x 103!T. W. juana. Effect of continuous steam injection of tomato juice on film deposition during Thoughthe initial rate of serumseparationdecreasedas tem.the final amount 1 . foros. Personal communication. I.. Nielsen. RT. 6.999 was cessors.86x lo4 exp(.1984 processing For the cold break sample. AVl Publishing Co. P.A. Food Technol. Food Proc.B.E. of serumlosswas independent of temperature. is made to McCormick and Company Inc. % avis.. G. E. R.The ketchupsam- ple was supportedby a screen. D. A. Twigg. R.J. 1957. Food Technol. 1983. S..J. Yield and uality of catsup reduced to a standard solids and consistency level. 10: 109.ailResearch Organization. Consistency and-Serum Separation of Catsup. 1979a. J.andthat the serum Grateful acknowledgement sumort of this work. Univ. 3: 195. Kimball. acc&ed S/3/90.A. 50: 1493. 9 nfluence of hand pi ng practices.L.30 3. 1950. and Vetter.2. 12: 356. Factors influenc- ing the uahty of tomato paste. Ms received 7)18/89. 5-Arrhenius plot showing effect of temperature on initial rate of serum separation. L.K. Inc. No. J.. .. Food Sci. Factors influenmng the degree of settling m tomato juice. Pres. Leonard.Dept.L.this testquantifiedboth rateandfinal amount of serumloss.. CT. Univ. and Buhlert.isdueto liquid drainage. 11: 406.. 1953. Anonymous. MS. and Gould.In contrastto previ- ouslyusedtests.. ada. SUMMARY A TEST simulatingserum separationof tomato ketchupin individualservingpoucheswas developed. Pectic changes during processing. Serum Separation of Tomato Ketchu Dept. eliminatingthe needfor prolongedexperiments. DC.N. of Ma&and.W. Progress Report to California League of Food Pro- an R*=0. 1990-JOURNAL OF FOOD SCIENCE-1629 . Davis.L. Ph. or artificial serum)and eitherthe serumseparationtest or the Stoforos.50 3.. Gould. ” the serumseparationof ketchupin bottles. Food Proc... Univ.65 3.40 3. Nelson. J. G. 1983. G.. McGill.. of Agriculture.. M. United States Standards for Grades of Tomato Catsu 4th issue. No. % .This confirmsthat serumsepa- rationin pouches..I..~. the effect of storagetemperatureon serumseparation was studied.B. J.45 3.55 3.K. 3: 189. CA.R. 1983.. D. Heil.R. Shomer. of California.P. Steinberg. 1958. 1985. effective August 31 U. N. Processing. 1956.and the serumdrainedthrough the insolublesolidsmatrix in a mechanismsimilar to that oc- curring in naturalseparationin pouches.the initial rate of serumloss (l/A.. for Tabsbeingthe absolutetemperature (K) and l/A in hour-‘.J. Observations on the consistency of sedimentationtest (performedon samplesdilutedwith water tomato aste. Tomato products: A new serum separation measurement. Marsh. of Food Science & Technology. Buhlert. 1954. 2nd ed. Method of determining the amount of tomato solids required. peraturedecreased. Robinson. Food Technol. J. - l/A = 1. R. followedthe ArrheniusEquation(Fig.. Tomato Production.. J.B. W. 5).B.I.. 4: 339.C.R. McColloch. and Vasiliver. Davis.) (4) Marsh.93x lOlo exp(-5... Food Technol.L. and Vilas. B.R. Volume 55. J.A. II. J. de Weese.. Agricu P - tural Marketin son.L. Gravity sedimentation test Institute of Technology and Storage of A E. J.The gravity sedimentation test bettersimulated dissertation. Yield hot breaksampleswere describedby and quality of catsup produced to a standard solids and consistency level. and Hand. W.80x 103/T& (5) Food TeeR nol.the Arrheniusexpressionwith tomato variety trials. The mechanism which enables the cell wall to retain homogeneous ap earance of tomato juice. revised 3/8/90. T No correlationwas foundbetweenresultsusingthe gravity Smit. break temperature and cultivar. By meansof the test..~. 1984.Althoughreducingstoragetem- peraturedecreased initial rate of separation. A saturation-likemodel correlatedserumloss with time.. serumseparationas it occurredin pouchesof ketchup(Sto.. Westport. Marvland. S.the resultsfor the Marsh. Consistency measure- break samples. Moyer. C.70 1 /Tabs ( 1 /KM 1000 REFERENCES Fig. Wolcott. CA. the final amountof serumlosswas almost Palma. for financial separationtest is a more appropriatetest. 8: 330.. 1979b. subse uent concentration. J. I.G.. R. and Merson.A. and Nortje.B..~.E. thesis. of California.. II. 3.D. M. and Quality Evaluation.35 3. 1985. and Bearens.. l/A = 1. Leonard.
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