Vol. 70, Nr. 9, 2005—JOURNAL OF FOOD SCIENCE C523Published on Web 11/15/2005

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Quality of Whole Lobster (Homarus americanus)Treated with Sodium TripolyphosphateBefore Cooking and Frozen StorageBBBBBETHETHETHETHETH L. C L. C L. C L. C L. CALDERALDERALDERALDERALDER, A, A, A, A, ALFREDLFREDLFREDLFREDLFRED A. B A. B A. B A. B A. BUSHWUSHWUSHWUSHWUSHWAAAAAYYYYY, R, R, R, R, ROBEROBEROBEROBEROBERTTTTT C. B C. B C. B C. B C. BAAAAAYERYERYERYERYER, K, K, K, K, KAAAAATHERINETHERINETHERINETHERINETHERINE A. D A. D A. D A. D A. DAAAAAVISVISVISVISVIS-D-D-D-D-DENTICIENTICIENTICIENTICIENTICI, , , , , ANDANDANDANDAND M M M M MARARARARARYYYYY E E E E ELLENLLENLLENLLENLLEN C C C C CAMIREAMIREAMIREAMIREAMIRE

ABSTRAABSTRAABSTRAABSTRAABSTRACTCTCTCTCT: : : : : The objectivThe objectivThe objectivThe objectivThe objective of this study was to detere of this study was to detere of this study was to detere of this study was to detere of this study was to determine the effects of prmine the effects of prmine the effects of prmine the effects of prmine the effects of pre-re-re-re-re-rigor trigor trigor trigor trigor treatment of lobster muscle witheatment of lobster muscle witheatment of lobster muscle witheatment of lobster muscle witheatment of lobster muscle withsodium tripolyphosphate (STP) before cooking, cryogenic freezing, and frozen storage. STP concentrations of 0.1%sodium tripolyphosphate (STP) before cooking, cryogenic freezing, and frozen storage. STP concentrations of 0.1%sodium tripolyphosphate (STP) before cooking, cryogenic freezing, and frozen storage. STP concentrations of 0.1%sodium tripolyphosphate (STP) before cooking, cryogenic freezing, and frozen storage. STP concentrations of 0.1%sodium tripolyphosphate (STP) before cooking, cryogenic freezing, and frozen storage. STP concentrations of 0.1%and 0.3% were prepared in 0.9% saline solution and injected into lobster before processing. Controls were injectedand 0.3% were prepared in 0.9% saline solution and injected into lobster before processing. Controls were injectedand 0.3% were prepared in 0.9% saline solution and injected into lobster before processing. Controls were injectedand 0.3% were prepared in 0.9% saline solution and injected into lobster before processing. Controls were injectedand 0.3% were prepared in 0.9% saline solution and injected into lobster before processing. Controls were injectedwith 0.9% saline solution. Lobsters were then steam-cooked, cryogenically frozen, and stored at –15 °C. Chemicalwith 0.9% saline solution. Lobsters were then steam-cooked, cryogenically frozen, and stored at –15 °C. Chemicalwith 0.9% saline solution. Lobsters were then steam-cooked, cryogenically frozen, and stored at –15 °C. Chemicalwith 0.9% saline solution. Lobsters were then steam-cooked, cryogenically frozen, and stored at –15 °C. Chemicalwith 0.9% saline solution. Lobsters were then steam-cooked, cryogenically frozen, and stored at –15 °C. Chemicaland textural analyses were conducted on reheated samples at storage months 0, 2, 4, and 6, and sensory analysesand textural analyses were conducted on reheated samples at storage months 0, 2, 4, and 6, and sensory analysesand textural analyses were conducted on reheated samples at storage months 0, 2, 4, and 6, and sensory analysesand textural analyses were conducted on reheated samples at storage months 0, 2, 4, and 6, and sensory analysesand textural analyses were conducted on reheated samples at storage months 0, 2, 4, and 6, and sensory analyseswere conducted at months 2 and 6. Cook loss results showed the 0.3% STP-treated lobsters had a 5% significantly (were conducted at months 2 and 6. Cook loss results showed the 0.3% STP-treated lobsters had a 5% significantly (were conducted at months 2 and 6. Cook loss results showed the 0.3% STP-treated lobsters had a 5% significantly (were conducted at months 2 and 6. Cook loss results showed the 0.3% STP-treated lobsters had a 5% significantly (were conducted at months 2 and 6. Cook loss results showed the 0.3% STP-treated lobsters had a 5% significantly (PPPPP����� 0.05) lo 0.05) lo 0.05) lo 0.05) lo 0.05) lowwwwwer cook loss than the 0.1% STP and contrer cook loss than the 0.1% STP and contrer cook loss than the 0.1% STP and contrer cook loss than the 0.1% STP and contrer cook loss than the 0.1% STP and control samplesol samplesol samplesol samplesol samples. . . . . Yield rYield rYield rYield rYield results results results results results revevevevevealed that STPealed that STPealed that STPealed that STPealed that STP-tr-tr-tr-tr-treated tails had aeated tails had aeated tails had aeated tails had aeated tails had a0.7% to 0.8% significantly (0.7% to 0.8% significantly (0.7% to 0.8% significantly (0.7% to 0.8% significantly (0.7% to 0.8% significantly (PPPPP ����� 0.05) higher meat yield than contr 0.05) higher meat yield than contr 0.05) higher meat yield than contr 0.05) higher meat yield than contr 0.05) higher meat yield than control samplesol samplesol samplesol samplesol samples. . . . . TTTTTotal moisturotal moisturotal moisturotal moisturotal moisture re re re re results shoesults shoesults shoesults shoesults showwwwwed thated thated thated thated thatSTP-treated lobster tail and claw meat had higher total moisture levels compared with control samples at month 6.STP-treated lobster tail and claw meat had higher total moisture levels compared with control samples at month 6.STP-treated lobster tail and claw meat had higher total moisture levels compared with control samples at month 6.STP-treated lobster tail and claw meat had higher total moisture levels compared with control samples at month 6.STP-treated lobster tail and claw meat had higher total moisture levels compared with control samples at month 6.Sensory results revealed that panelists rated both 0.1% and 0.3% STP-treated lobster tails significantly (Sensory results revealed that panelists rated both 0.1% and 0.3% STP-treated lobster tails significantly (Sensory results revealed that panelists rated both 0.1% and 0.3% STP-treated lobster tails significantly (Sensory results revealed that panelists rated both 0.1% and 0.3% STP-treated lobster tails significantly (Sensory results revealed that panelists rated both 0.1% and 0.3% STP-treated lobster tails significantly (PPPPP ����� 0.01) 0.01) 0.01) 0.01) 0.01)higher for flavor and texture, and significantly (higher for flavor and texture, and significantly (higher for flavor and texture, and significantly (higher for flavor and texture, and significantly (higher for flavor and texture, and significantly (PPPPP ����� 0.001) higher for overall acceptability than control samples at 0.001) higher for overall acceptability than control samples at 0.001) higher for overall acceptability than control samples at 0.001) higher for overall acceptability than control samples at 0.001) higher for overall acceptability than control samples atmonth 6. The results indicated that STP added at low concentrations may extend the shelf life of whole cookedmonth 6. The results indicated that STP added at low concentrations may extend the shelf life of whole cookedmonth 6. The results indicated that STP added at low concentrations may extend the shelf life of whole cookedmonth 6. The results indicated that STP added at low concentrations may extend the shelf life of whole cookedmonth 6. The results indicated that STP added at low concentrations may extend the shelf life of whole cookedcrcrcrcrcryyyyyogenically frogenically frogenically frogenically frogenically frooooozzzzzen lobsteren lobsteren lobsteren lobsteren lobster, decr, decr, decr, decr, decrease lipid oease lipid oease lipid oease lipid oease lipid oxidation oxidation oxidation oxidation oxidation ovvvvver frer frer frer frer frooooozzzzzen storen storen storen storen storage timeage timeage timeage timeage time, maintain textur, maintain textur, maintain textur, maintain textur, maintain textureeeee, color, color, color, color, color, and flav, and flav, and flav, and flav, and flavorororororattributes, increase yield, and decrease drip loss.attributes, increase yield, and decrease drip loss.attributes, increase yield, and decrease drip loss.attributes, increase yield, and decrease drip loss.attributes, increase yield, and decrease drip loss.

KKKKKeyworeyworeyworeyworeywords: lobsterds: lobsterds: lobsterds: lobsterds: lobster, , , , , HHHHHomarus americanusomarus americanusomarus americanusomarus americanusomarus americanus, sodium tr, sodium tr, sodium tr, sodium tr, sodium tripolyphosphateipolyphosphateipolyphosphateipolyphosphateipolyphosphate, cr, cr, cr, cr, cryyyyyogenic frogenic frogenic frogenic frogenic freeeeeeeeeezing, qualityzing, qualityzing, qualityzing, qualityzing, quality

Introduction

Frozen storage of cooked, whole lobsters is known to result intoughening of meat, development of off-flavors, and difficul-

ty of meat separation from the shell (Getchell and Highlands 1957).Work and others (1997) recently demonstrated that cryogenicallyfreezing lobsters before frozen storage could retain high-qualitytexture and flavor attributes of whole lobster. The excellent texturalqualities of both hard- and soft-shell lobsters were attributed tothe fast rate of freezing.

Fast freezing rates are recognized to retain quality attributes ofmuscle foods due to smaller ice crystal formation during the freez-ing process, which are less detrimental to muscle proteins com-pared with slower freezing rates (Foegeding and others 1996). How-ever, food quality is also dependent on frozen storagetemperatures. Ablett and Gould (1992) found that over 12 wk offrozen storage, freezing rate was not as crucial as storage tempera-ture in affecting membrane integrity of cod muscle tissue. Theyobserved collapsed sarcoplasmic membranes in cod samples storedat –12 °C, evidence of intracellular ice crystal formation regardlessof freezing technique, whereas cod samples stored at –35 °C hadvery little signs of condensation damage.

Long-term frozen storage can lead to undesirable sensory chang-es in seafood and loss of water-holding capacity (Getchell andHighlands 1957; Krivchenia and Fennema 1988; Chang and Regen-stein 1997). Henry and others (1995) showed benefits of adding

carbohydrate cryoprotectants and sodium tripolyphosphate toprecooked blue crab meat before cryogenic freezing in comparisonwith heat-pasteurized crab meat. Others have shown that the useof polyphosphates can enhance frozen-storage stability of cod andDungeness crab meat (Woyewoda and Bligh 1986; Crapo and Craw-ford 1991), reduce thaw drip in canned lobster meat (Rippen andothers 1996), and increase water-holding capacity of pre- and post-rigor lobster muscle (Regenstein and Stamm 1979).

Most recently, a patented method was designed for injection offood-grade additives into live seafood before processing to en-hance quality throughout frozen storage (Bayer and others 1999).The objective of this study was to determine the effects of pre-rigortreatment of lobster muscle with sodium tripolyphosphate beforecooking, cryogenic freezing, and frozen storage.

Materials and Methods

Lobster processingLobster processingLobster processingLobster processingLobster processingSoft-shell lobsters (Homarus americanus) ranging in weights

from 0.5 kg to 0.7 kg were provided by D.B. Rice Fisheries (BunkersHarbor, Maine, U.S.A.) in August 2001. Fifty-eight lobsters per treat-ment were injected with 5 mL of 0.9% saline (control), 0.1% sodiumtripolyphosphate (STP) in 0.9% saline or 0.3% STP (sodium tripoly-phosphate; FMC, Philadelphia, Pa., U.S.A.) in 0.9% saline and heldfor 10 min before processing at Cranberry Point Seafood Process-ing Facility (Gouldsboro, Maine, U.S.A.). Lobsters were injected intothe ventral side of the tail near the carapace (Bayer and others1999). Lobsters were cooked for 16 min in a continuous steam cook-er at 100 °C (CTX Steam Cooker, model nr VSWDM3546; LaitramMachinery, New Orleans, La., U.S.A.) for 15 to 20 min before individ-ually weighing and cryogenically freezing for 15 min with liquid ni-

MS 20040749 Submitted 11/14/04, Revised 3/4/05, Accepted 6/7/05. AuthorsCalder, Bushway, Davis-Dentici, and Camire are with Dept. of Food Sci-ence and Human Nutrition, Univ. of Maine, 5735 Hitchner Hall, Orono, ME04469. Author Bayer is with Dept. of Animal and Veterinary Sciences, Univ.of Maine, Rogers Hall, Orono, Maine. Direct inquiries to author Calder (E-mail: beth.calder@umit.maine.edu).

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trogen at temperatures between –55 °C to –57 °C using a 30-footfreezing tunnel (Modular Tunnel Freezer, model nr KFT36-10M;BOC Gases, Murray Hill, N.J., U.S.A.). Frozen lobsters were placedinto covered storage totes for transport to the Univ. of Maine’s Dept.of Food Science and Human Nutrition where they were held at –15 °C frozen storage until needed for analyses. Lobster tail and clawmeat quality attributes were determined after 0, 2, 4, and 6 mo ofstorage.

Chemical analysesChemical analysesChemical analysesChemical analysesChemical analysesChemical analyses were performed on lobster samples at

months 0, 2, 4, and 6. Lobsters were thawed at 4 °C for 24 h andsteamed for 20 min in a stainless-steel colander over 1.9 L of boil-ing water in a 7.7-L stainless-steel cooking pot, covered with tin-foil. Tail and claw meat samples were removed by hand, lightlyrinsed with potable water, and homogenized using a hand-pow-ered food processor (Culinare RocketChef; Best Direct, Pacoima,Calif., U.S.A.). Homogenized claw and tail meat samples were an-alyzed in duplicate for lipid oxidation, salt-soluble protein, andmoisture content.

Determination of lipid oxidationDetermination of lipid oxidationDetermination of lipid oxidationDetermination of lipid oxidationDetermination of lipid oxidationThiobarbituric acid (TBA) test results were performed according

to a modified method of Tarladgis and others (1960) and Rhee andWatts (1966) to determine thiobarbituric acid-reactive substances(TBARS) reported as �g malonaldehyde/g of tail or claw meat overtime. During TBA testing, the lowest detected amount of malonal-dehyde was 0.2 �g/g.

Determination of proteinDetermination of proteinDetermination of proteinDetermination of proteinDetermination of proteinTen grams of lobster muscle were homogenized with 90 mL of

5% saline solution for 30 s, and the homogenate was centrifuged at12000 × g for 20 min at 4 °C. Salt-soluble protein concentration wasmeasured by the Lowry procedure (Lowry and others 1951) to de-termine mg/g salt-soluble protein content in claw and tail samplesover time.

Determination of moistureDetermination of moistureDetermination of moistureDetermination of moistureDetermination of moistureLobster claw and tail meat were analyzed for total moisture us-

ing the standard AOAC procedure (1998).

Determination of cook loss and yieldDetermination of cook loss and yieldDetermination of cook loss and yieldDetermination of cook loss and yieldDetermination of cook loss and yieldCook loss, the percentage of weight (moisture) loss resulting

from the initial cook step of each lobster before freezing, was calcu-lated as:

% Cook loss: initial (raw) wt (g) – cooked wt (g) × 100initial (raw) wt (g)

Meat yield was based upon the percentage of lobster tail meatremoved from each cooked lobster:

% Yield (based on cooked weight):cooked tail wt (removed from shell) (g) × 100

whole cooked wt (g)

TTTTTexturexturexturexturexture analysise analysise analysise analysise analysisTail meat firmness was assessed to determine shear force need-

ed to penetrate through tail meat samples. A metal shear cell wascustom-designed with a beveled edge for an Instron (model nr4466 with a Series IX Automated Materials Testing System 7.5; In-stron, Inc., Canton, Mass., U.S.A.) to mimic the human bite. Sam-

ples for texture analysis were thawed and steamed in the samemanner as samples for chemical and sensory analyses. After re-heating, tails were cut in half as duplicates per lobster, and lengthand width (mm) were measured for each tail section using Mitu-toyo Digimatic calipers (model nr CD-6”BS; Mitutoyo Corp., Ka-wasaki, Japan). Lobster tail placement was perpendicular to theblade edge to cut across muscle fibers. The Instron scale load was0.5 kN, crosshead speed 500 mm/min, platen separation 50.1 mm,and sample rate 20.0 points/s. Maximum displacement (peak load)was measured in mm/cm, and force (load) was measured in kN perpound. The peak load or breaking point of the sample was calculat-ed in kN/mm.

Colorimetric analysisColorimetric analysisColorimetric analysisColorimetric analysisColorimetric analysisColorimetric analysis was performed on tail meat to coincide with

sensory analysis at months 2 and 6 using a Hunter LabScan II(Hunter Associates Laboratory, Reston, Va., U.S.A.). Standard back-ground and calibration tiles were used: white tile (CIE illuminantD65 10 ° observer, 1971) and black tile (no company specification).An optical aperture of 3 cm was used. L, a, and b values were re-corded as averages of 3 readings per sample, and chroma and huevalues were calculated.

Sensory analysisSensory analysisSensory analysisSensory analysisSensory analysisAn affective sensory test was conducted to determine consumer

acceptability of frozen lobster upon reheating at months 2 and 6.The lobsters were removed from frozen storage and placed at re-frigerated temperatures (4 °C) for 24 h before evaluation. Lobsterswere steamed for approximately 20 min. Tail meat was removedfrom the shell, lightly rinsed to remove tomale, dried, and weighed.Lobster claws were not evaluated during sensory testing. The tailmeat was cut vertically in half and then cut into 6 horizontal propor-tionate sections. Each panelist received 1 tail section per treat-ment on small plates labeled with 3-digit randomized codes pre-sented in random order. Butter (sweet cream, unsalted butter;Hannaford, Scarborough, Maine, U.S.A.) was provided. Thirty pan-elists (older than age 18 years) were recruited for this study fromthe Univ. of Maine community. Volunteers were allowed to partic-ipate after signing an informed consent form. Panelists were seatedin booths with fluorescent lighting at the Consumer Testing Centerlocated at the Univ. of Maine Dept. of Food Science and HumanNutrition. Sensory panelists evaluated sample attributes of exteriorand interior meat color, flavor, texture, and overall acceptabilityusing a 9-point hedonic scale (1 = dislike extremely to 9 = like ex-tremely). Data from the computerized sensory ballots were collect-ed by the SIMS 2000 program for Windows.

Statistical analysesStatistical analysesStatistical analysesStatistical analysesStatistical analysesChemical and physical data were analyzed using Systat version

9.0 (Systat Software, Inc. 1998). One-way analysis of variance (ANO-VA) was used to detect statistical differences (P � 0.05) among STPand control treatments at a specific frozen storage month. Signifi-cant differences (P � 0.05) between means were analyzed using theTukey HSD post hoc test. A multi-way ANOVA was used to evaluatedifferences of the potential effects of treatment over frozen storagetime, and the Tukey HSD Multiple Comparisons were used to de-termine significant differences (P � 0.05) of treatment meansacross time. Lobster tail and claw data were analyzed separately.Pearson correlation matrix analyses were performed on chemical,physical, and sensory data using Systat version 9.0.

Sensory data on lobster tails were analyzed using SAS 6.12 (SASInst. 1989) (P � 0.05) with Duncan’s long-range multiple post hoctest.

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Results and Discussion

TBARSTBARSTBARSTBARSTBARSTBARS ANOVA results for lobster tail and claw meat suggest an

increasing trend of malonaldehyde concentration for all treatmentsover frozen storage time as illustrated by Figure 1. At month 6, con-trol tail TBARS levels were higher than STP-treated tails, and 0.1%STP-treated claws were significantly (P � 0.05) lower in malonalde-hyde concentration than both control and 0.3% STP-treated clawmeat. Overall, tail and claw meat malonaldehyde concentrationsremained low and did not exceed 2.0 �g/g.

Multi-way ANOVA analyses detected significant effects of timeand treatment/month interactions on TBARS levels in lobster tailand claw meat. TBARS values for all 3 treatments significantly (P �0.05) increased over storage time for both tail and claw samples.

Higher TBARS values indicated an increased probability of off-flavor and odor formation. However, malonaldehyde concentra-tions never surpassed 2.0 �g/g, indicating that sensory panelistswould probably not be able to detect any off-flavors or odors atthese low concentrations. Worth noting, the 0.1% STP treated clawand tail meat had the lowest malonaldehyde concentration atmonth 6 compared with the other 2 treatments. At month 6, TBARSresults corresponded well to sensory results. Pearson correlationmatrix results indicated a strong negative relationship betweenTBARS values and panelists’ ratings of overall acceptability (r = –0.90) and flavor (r = –0.87) of lobster tails at month 6. STP-treatedlobster tails had lower TBARS values than control samples, andsensory panelists rated STP-treated tails significantly (P � 0.01)higher for flavor and significantly (P � 0.001) higher for overall ac-ceptability than control lobster tails.

Dyer and Horne (1953) studied yellow discoloration changes infrozen lobster claw meat, which also occurred in lobster claws in thisstudy at month 4. They attributed the changes in pigment color tofat oxidation. They hypothesized that peroxides oxidized the redlobster pigment (astacene) to form a yellow pigment. Peroxide val-ues were not obtained in this study, but malonaldehyde concentra-tions were low (�0.7 �g/g), an indication that astacene may be high-ly susceptible to oxidation in lobster claw meat.

Salt-soluble proteinSalt-soluble proteinSalt-soluble proteinSalt-soluble proteinSalt-soluble proteinSalt-soluble protein concentrations in lobster claw and tail meat

varied considerably across frozen storage time as shown by LowryANOVA results in Figure 2. Significant (P � 0.05) differences among

treatments were detected at months 0, 2, and 4 in tail meat. Atmonths 2 and 4, control lobster tails were lower in salt soluble pro-tein levels than the STP-treated samples. Control and 0.3% STP-treated lobster claw meat had consistently higher salt-soluble pro-tein levels than 0.1% STP-treated claw meat throughout storagetime. However, salt-soluble protein differences in claw meat werenot found to be significant among treatments.

Multi-way ANOVA results indicated significant treatment,month, and treatment/month interaction effects on salt-solubleprotein levels in lobster tail meat. Lobster tail meat treated withSTP had significantly (P � 0.05) higher Lowry values at months 2and 4, than storage months 0 and 6. For claw meat, all 3 treatmentshad significantly (P � 0.05) higher Lowry values at months 2 and 4than at months 0 and 6.

Pearson correlation matrix results indicated a strong positiverelationship between Lowry values and panelists’ ratings for tex-ture (r = 0.99) and overall acceptability (r = 1.00) of tail meat atmonth 2. Sensory ratings revealed that panelists did not detect anysignificant texture differences in lobster tail meat. However, atmonth 6, sensory panelists rated STP-treated lobster tails signifi-cantly (P � 0.01) higher for more desirable texture, even though nosignificant differences were noted for salt-soluble protein levelsacross treatments. Therefore, our sensory results at month 6 did notcorrespond well with the hypothesis that lower salt-soluble proteinlevels are an indication of tougher seafood texture.

TTTTTotal moisturotal moisturotal moisturotal moisturotal moistureeeeeMoisture one-way ANOVA results indicated that total moisture

levels in lobster tail and claw meat samples varied significantly (P� 0.05) at month 2. The 0.3% STP-treated tail and claw meat had sig-nificantly higher moisture levels than the other 2 treatments. Atmonth 6, lobster tails treated with STP had higher total moisturelevels than control samples, and the STP-treated claws had signif-icantly (P � 0.05) higher moisture levels than the control. Moisturedata at month 4 were eliminated due to loss of sample. Lobster tailmoisture data are shown in Figure 3.

Moisture multi-way ANOVA results indicated no significant ef-fects of treatment, time, or treatment/month interactions on mois-ture levels in lobster tail or claw meat.

Moisture results indicated that STP-treated lobster maintainedtotal moisture levels in tail and claw meat for 6 mo of frozen storage.However, control lobster claw and tail meat appeared to lose 3% to4% moisture between storage months 2 and 6. Rebach and others

Figure 1—Thiobarbituric acid-reactive substances (TBARS)means of lobster tail and claw meat over frozen storagetime. Significance P � 0.05. Means are an average ofduplicate samples based on homogenate of 8 tails and 16claws. Means within evaluation period not sharing a com-mon letter are significantly different.

Figure 2—Salt-soluble protein means of lobster tail and clawmeat over frozen storage time. Significance P � 0.05.Means are an average of duplicate samples based on ho-mogenate of 8 tails and 16 claws. Means within evalua-tion period not sharing a common letter are significantlydifferent.

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Quality of lobster treated with STP . . .

(1990) noted detrimental quality changes in frozen Jonah crabsoccurred first in leg meat compared with body meat. In this study,the yellowing of claw meat observed at month 4 of frozen storagemay also correspond to the decrease in moisture levels in controllobster claws after month 2. Pearson correlation matrix results forlobster suggest a strong positive relationship between moisturelevels and panelists’ ratings of flavor (r = 0.92), texture (r = 0.89),and overall acceptability (r = 0.94) at month 6.

Cook loss and yieldCook loss and yieldCook loss and yieldCook loss and yieldCook loss and yieldWeight data were collected to determine whether STP treat-

ments had any influence on decreasing cook loss and increasingtail yield. Weight measurements included initial (precooked) andwhole cooked lobster weight before freezing, and the weight ofcooked tail meat removed from the shell upon thawing and reheat-ing lobster before conducting analyses.

Cook loss results revealed significant (P � 0.05) differences be-tween 0.3%-STP treated lobsters and the other 2 treatments. The0.3% STP-treated lobsters had a 5% lower cook loss than the 0.1%STP and control samples, as illustrated by Figure 4. The 0.3% and0.1% STP-treated lobsters had a significantly (P � 0.05) higher tailmeat yield, based on whole cooked lobster weight. STP-treated tailshad a 0.7% to 0.8% higher meat yield than control samples, as shownin Figure 5.

The results indicated that injecting 0.3% STP into lobster signif-icantly decreased cook loss by 5%, and STP treatments significantly

(P � 0.05) increased tail meat yield. The cook loss and yield find-ings are similar to the results found by Froning and Sackett (1985)when they injected turkey breast muscle with salt and varioustypes of phosphates. The presence of salt and phosphates signif-icantly reduced expressible moisture and cook loss, but did notsignificantly affect shear values.

TTTTTexturexturexturexturextureeeeeTexture analysis was conducted to determine a correlation be-

tween sensory and physical tail texture data over storage time. Peakforce was measured to determine the force needed to shear tailmeat samples.

Texture ANOVA results revealed significant (P � 0.05) differenc-es in peak force at month 0 (((((Figure 6). Control samples had a signif-icantly higher maximum displacement mean than 0.1% and 0.3%STP-treated tails. No significant differences were detected at stor-age months 2, 4, and 6. Some tail samples did not remain intact uponre-steaming, and the tail muscle appeared disintegrated in theshell. These lobster meat samples were not feasible for textureanalyses. Therefore, unequal sample sizes were a problem for con-ducting texture analyses due to “mushy” tail meat sample ob-served across treatments.

Significant (P � 0.05) differences in peak force were detected atmonth 0 only. Control tail meat had a significantly higher peak forcethan STP-injected lobster, an indication that control tails had atougher or chewier texture at month 0 than STP-treated tails. Pear-

Figure 3—Mean percentage of total moisture in lobster tailand claw meat over frozen storage time. Significance P� 0.05. Means are an average of duplicate samples basedon homogenate of 8 tails and 16 claws. Means within evalu-ation period not sharing a common letter are significantlydifferent.

Figure 4—Mean percentage of lobster tail meat cook lossafter initial cooking. Significance P � 0.05. Each value isthe mean of 57 lobster tails taken from random periodsof frozen storage. Means within evaluation period not shar-ing a common letter are significantly different.

Figure 6—Mean peak force of lobster tail results at month0. Significance P � 0.05. Means are an average of 14 tailsfor control, 18 tails for 0.1% STP, and 18 tails for 0.3%STP. Means within evaluation period not sharing a com-mon letter are significantly different.

Figure 5—Mean percentage of lobster tail meat yield basedon whole cooked weight. Significance P � 0.05. Each valueis the mean of 57 lobster tails taken from random periodsof frozen storage. Means within evaluation period not shar-ing a common letter are significantly different.

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son correlation matrix results indicated a moderately strong nega-tive relationship between texture values and panelists’ ratings fortexture (r = –0.83) and overall acceptability (r = –0.82) at month 2.

Random occurrences of mushy tail texture were observed acrosstreatments upon reheating samples before conducting analyses. Itis worth noting that STP-treated lobster tails had a slightly lowerincidence of mushy tail meat throughout frozen storage, but thedifferences in the mean lobster tail samples used for Instron testingwere not significantly (P � 0.05) different. Mushiness in lobstermeat has also been reported with fresh cooked soft shell lobstersfrom personal communications with the Maine Lobster PromotionBoard. This textural problem has been noted in previous cryogeniclobster testing at the Univ. of Maine, but the cause is not known.

Mushy texture in crustacean muscle has been mostly attributedto the release of proteolytic enzymes from the hepatopancreascausing muscle degradation (Marshall and others 1987; Slatteryand others 1989; Kim and others 1996). These enzymes are heat-labile and are often inactivated at temperatures above 65 °C incrayfish (Kim and others 1996) and at internal temperatures at80 °C in blue swimmer crab (Slattery and others 1989). An inhousetest was recently conducted at the Univ. of Maine to determine in-ternal temperatures of lobster (weight range of approximately 0.45to 0.57 kg) during steam cooking. Lobster body cavity and tail tem-peratures were monitored and recorded during the steam cookprocess. Internal lobster temperatures reached above 80 °C after 6to 8 min for tail and 8 to 10 min for body sections during steam cook-ing in a commercial steamer (Steamcub, model nr 1 SCE; ClevelandRange, Inc, Cleveland, Ohio, U.S.A.).

In this study, handling and storage stresses on the soft-shell lob-sters 24 h before processing may have caused the release of pro-teolytic enzymes from the hepatopancreas into the surroundingmuscle of the lobster tail. Enzymatic activity may have contribut-ed to muscle deterioration until initial cooking at temperatures at100 °C for 16 min, which would then subsequently inactivate theseenzymes before freezing lobsters.

Parasitic infections are also known to cause mushy texture inseafood, but are uncommon among lobsters of the Homarus spe-cies. Physiological factors may also contribute to mushy texture inpost-molt lobsters. Research suggests that stage of molt may alsoaffect the meat texture in crustaceans (Slattery and others 1989;Mizuta and others 2001). Mizuta and others (2001) discovered thatpost-molt snow crabs had higher water and lower protein content,along with disintegrated sections of muscle tissue. Histological

characteristics suggested structural weakening of muscle fibers dueto physiological changes during the molt process. Similar decreasesin protein concentration possibly occur in soft-shell lobsters. Futurework could investigate the injection of antifreeze proteins to post-molt lobsters before processing. The additional proteins may in-crease lobster protein concentrations, while providing cryoprotec-tive benefits and possibly extending lobster quality during frozenstorage. Results appear promising that antifreeze proteins, whenadded to meat before freezing, reduce the size of ice crystal forma-tion at low concentrations, and also inhibit ice recrystallization(Payne and others 1993).

SensorySensorySensorySensorySensorySensory results revealed no significant (P � 0.05) differences

between treatments at month 2. However, panelists rated STP-treated lobster higher in overall acceptability, flavor, texture, andinterior/exterior meat color than control samples. Panelists rated alltreatment attributes between ratings of 6 to 7. Significant treat-ment differences were revealed at month 6, as illustrated in Figure7. Sensory panelists rated both 0.1% and 0.3% STP-treated lobstertails significantly (P � 0.01) higher for flavor and texture, and sig-nificantly (P � 0.001) higher in overall acceptability than controlsamples. The 0.3% STP-treated tails were also rated significantly (P� 0.05) higher than control samples for interior and exterior meatcolor. These results indicate that STP-treated lobster maintainedquality and sensory attributes in lobster over 6 mo of frozen storage.

ColorColorColorColorColorColorimetric analyses were conducted on tail meat samples in

conjunction with sensory testing to compare possible relationshipsbetween measures of L, a, and b values to panelists’ ratings ofmeat color among treatments. No significant (P � 0.05) differenceswere determined at month 2; however, ANOVA colorimetric resultsrevealed significant (P � 0.05) differences at month 6. Lobster tailstreated with 0.1% STP had a significantly higher a value or more redcolor than the other 2 treatments, but had a significantly lower huethan control and 0.3% STP samples. Lobster tails treated with 0.3%STP had a significantly lower b value (measure of yellowness-blue-ness) than 0.1% STP-treated lobster tails. The 0.3% STP-treated tailmeat samples also had significantly lower color saturation (chromavalue) than the 0.1% STP treatment. Colorimetric results for month6 are presented in Figure 8.

These significant (P � 0.05) differences in color appeared ac-

Figure 7—Mean sensory ratings of lobster tails at month6. Significance P � 0.05 for interior and exterior meatcolor, P � 0.01 for flavor and texture, and P � 0.001 foroverall acceptability attributes. Each value is the meanscore of 30 panelists. Means within evaluation period notsharing a common letter are significantly different.

Figure 8—Color attribute means of lobster tail results atmonth 6. Significance P � 0.05. Means are an average ofduplicate samples of lobster tail meat reheated the samed as sensory testing. Means within evaluation period notsharing a common letter are significantly different.

C528 JOURNAL OF FOOD SCIENCE—Vol. 70, Nr. 9, 2005 URLs and E-mail addresses are active links at www.ift.org

C: Food Chemistry & Toxicology

Quality of lobster treated with STP . . .

ceptable and not noticeable to sensory panelists. STP-treated lob-ster tails were rated higher for interior and exterior meat color thancontrol samples. Pearson correlation matrix results indicated a mod-erate negative relationship between b values and sensory panel-ists’ ratings for exterior meat color (r = –0.75) and between hue andpanelists’ ratings for overall acceptability (r = –0.70) at month 6.

Conclusions

The results indicate that STP added at low concentrations mayextend the shelf life of whole cooked cryogenically frozen lob-

sters, maintaining a high-quality product throughout 6 mo of fro-zen storage. STP injection, before processing, may decrease lipidoxidation over frozen storage time, increase yield, decrease cookloss, and extend more desirable texture, color, and flavor attributesin frozen lobster products. Results suggest that the effects of STPon lobster quality attributes appear more advantageous during thelatter storage months, an indication that seafood processors maybenefit from this technology if they intend to hold frozen productfor 6 mo.

AcknowledgmentsMaine Agricultural and Forest Experiment Station External Publi-cation nr 2810. We thank Dana Rice for providing lobsters for thisstudy and Cranberry Point Seafood Co. for allowing us the use oftheir processing equipment and facility. Thanks are also extendedto Icebrand Foods Co. for their donation of lobsters and use ofequipment for preliminary studies.

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