The e�ect of ionic strength, polyphosphates type, pH, cookingtemperature and preblending on the functional properties of normal

and pale, soft, exudative (PSE) pork

Peter J. Torley a,b, Bruce R. D'Arcy a, Graham R. Trout c,*aDepartment of Food Science and Technology, University of Queensland, Gatton College, Queensland 4345, Australia

bFood Science Australia, PO Box 3312, Tingalpa, Queensland 4173, AustraliacFood Science and Nutrition Program, School of Biomolecular and Biomedical Science, Gri�th University, Logan Campus, Queensland 4111, Australia

Received 10 March 1999; received in revised form 20 December 1999; accepted 23 December 1999

Abstract

Compared to processed meat product made from normal pork, products made from pale soft exudative (PSE) pork have higher

cook loss (CL) and weaker texture. In this study interactions between a range of processing conditions (ionic strength, polyphosphateaddition, polyphosphate chain length, pH, cooking temperature and time between preparation and cooking), and their e�ect on thetexture [shear stress (SS), true shear strain (TSS)] and CL of gels made from normal and PSE pork were examined. Of the processing

conditions studied, ionic strength, polyphosphate addition and polyphosphate chain length a�ected the functional properties of normaland PSE pork di�erently. Generally, the functional properties of normal pork were superior to PSE pork, with no combination ofconditions making all the functional properties of PSE pork equal to those of normal pork under the same conditions. The combi-nation of conditions that was most e�ective in reducing the di�erence between normal and PSE pork was high ionic strength in the

presence of added polyphosphate. Under these conditions there was no signi®cant di�erence in CL between normal and PSE pork,although the texture (SS and TSS) of the PSE pork samples was still inferior. # 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Water-holding capacity; Texture; Polyphosphate chain length; Fibre optic probe; Salt

1. Introduction

Pale, soft, exudative (PSE) muscle is a quality defectthat is commonly found in pork (Trout, Myler, Cassell,Dyson & Reiser, 1991). Rapid post-mortem glycolysis,slow carcase chilling rates, or a combination of boththese conditions can result in muscle having a hightemperature (538�C) and low muscle pH (<6.0), whichfavours denaturation of muscle proteins particularlymyosin (O�er, 1991). Denaturation of myosin is importantsince this protein has a major role in determining thefunctional properties, such as textural strength and cookloss, of the meat products after cooking (O�er et al., 1989).The functional properties of PSE pork and normal

pork have been compared in a range of processed meat

products, including ham (Honkavaara, 1988; Kau�-man, Wachholz, Henderson & Lochner, 1978; Kemp,Fox & Moody, 1974), bacon (Taylor, Dant & French,1973), dried sausage (Townsend, Davis, Lyon &Mescher, 1980), and ®nely comminuted sausage (Hon-kavaara, 1990). The functional properties of processedmeat products made from PSE pork are poorer thanthose made from normal pork; this may be due to dif-ferences in the biochemical and physical properties. Inparticular, myosin in PSE pork di�ers from myosin innormal pork in that it tends to have a smaller head size(O�er et al., 1989), smaller inter®lament spacing(Lahucky, Marinova, Astruc, Vignon & Monin, 1996),lower ATPase activity (Penny, 1969), decreasedenthalpy of denaturation (Honikel & Kim, 1986; Sta-bursvik, Fretheim & Froystein, 1984), and lower solu-bility (Sung, Ito & Fukazawa, 1976). These di�erencesin myosin properties may cause the optimal conditionsfor processing PSE pork to di�er from those requiredfor processing normal pork.

0309-1740/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

PI I : S0309-1740(00 )00004-8

Meat Science 55 (2000) 451±462

www.elsevier.com/locate/meatsci

* Corresponding author. Tel.: +61-7-3382-1378; fax: +61-7-3382-

1034.

E-mail address: g.trout@mailbox.gu.edu.au (G.R. Trout).

Processing conditions have a complex e�ect on thefunctional properties of meat. For example, ionicstrength, pH, pyrophosphate (PPi) addition and cook-ing temperature interact to a�ect the cook loss frombeef homogenates (Trout & Schmidt, 1984, 1986b,1987). While beef and normal pork could be expected torespond in a similar manner to variations in processingconditions, PSE pork may respond di�erently.The hypothesis tested in this study is that appropriate

combinations of processing conditions will improve thefunctional properties of PSE pork so as to be similar tothose of normal pork. As indicated above, the bio-chemical properties of myosin in PSE and normal porkmuscle are signi®cantly di�erent. These di�erences inbiochemical properties a�ect solubility of the myosinand ultimately the functional properties of cooked pro-ducts made from PSE pork. To date, there has be nostudy that has simultaneously examined the e�ect ofdi�erent processing conditions on the functional prop-erties of PSE pork. This present study contains twoexperiments that examine the e�ect of di�erent proces-sing properties on the functional properties of normaland PSE pork. The ®rst experiment examines the e�ectof holding time before cooking and polyphosphateaddition on the functional properties of normal andPSE pork. The second experiment examines the e�ect ofcombinations of ionic conditions (ionic strength, PPiaddition and pH) and cooking temperature on thefunctional properties of PSE and normal pork.

2. Materials and methods

2.1. Experimental design

2.1.1. Experiment 1The objective of Experiment 1 was to examine the

e�ect of pork quality (normal and PSE pork), polypho-sphate type/NaCl mixtures of equal ionic strength [nopolyphosphate (NaCl only), pyrophosphate + NaCl(PPi) and tripolyphosphate + NaCl (TPP)], and timebetween preparation and cooking (1, 2, 4, 8 and 24 h)on functional properties of pork homogenates as asses-sed by texture measurements [shear stress (SS), trueshear strain (TSS)] and cook loss (CL). The formula-tions of the polyphosphate treatments are given in Table 1.The raw pH of all treatments was adjusted to a targetpH of 6.00 using HCl or NaOH; the average measuredpH of all treatments was 6.04. The experiment wasreplicated twice using a split-plot design.

2.1.2. Experiment 2The objective in Experiment 2 was to determine if

combinations of processing conditions studied canreduce the di�erence in functional properties betweennormal and PSE pork. The study examined the e�ect of

meat quality (normal and PSE pork), raw product pH(5.9 and 6.4), TPP concentration (0 and 0.37% TPP),total ionic strength (0.25, 0.30, 0.35 and 0.41) and ®nalcooking temperature (60.0, 66.7, 73.3 and 80.0�C).Functional properties of the pork homogenates wereassessed by texture measurements [shear stress (SS), trueshear strain (TSS)] and cook loss (CL). The completeexperiment (i.e. a total of 128 treatment combinations)was replicated twice; four sub-samples were cooked ateach of the four cooking temperatures. Because of thescope of the study, a partially balanced, incomplete,block design was used (Cochran & Cox, 1957) with ablock size of eight, so that a manageable number ofeight treatments were performed on 1 day. The for-mulations of the polyphosphate treatments are given inTable 2. The pH of the raw homogenates was adjusted

Table 1

The rate of addition of NaCl, pyrophosphate (PPi) and tripolypho-

sphate (TPP) and ionic strength of treatments used in Experiment 1

Polyphosphate treatment Ionic species

added

Addition

rate (%)aIonic

strengthb

No polyphosphate NaCl 1.89 0.25

PPi NaCl 1.28 0.17

PPi 0.35 0.08

TPP NaCl 1.28 0.17

TPP 0.37 0.08

a All treatments contain 30% added water. The water, NaCl and

polyphosphate addition rates are expressed as a percentage of the

weight of meat.b The ionic strengths of the PPi and TPP were calculated using the

published dissociation constants of Trout and Schmidt (1986a).

Table 2

The rate of addition of NaCl, tripolyphosphate (TPP) and ionic

strength of treatments used in Experiment 2

TPP concentration Ionic

strength

Ionic species

added

Concentration

(%)a,b

0% TPP 0.25 NaCl 1.89

0.30 NaCl 2.31

0.35 NaCl 2.73

0.41 NaCl 3.15

0.37% TPP 0.25 NaCl 1.28

TPP 0.37

0.30 NaCl 1.70

TPP 0.37

0.35 NaCl 2.12

TPP 0.37

0.41 NaCl 2.54

TPP 0.37

a All treatments contain 30% added water. The water, NaCl and

polyphosphate addition rates are expressed as a percentage of the

weight of meat.b The ionic strengths of the PPi and TPP were calculated using the

published dissociation constants of Trout and Schmidt (1986a).

452 P.J. Torley et al. /Meat Science 55 (2000) 451±462

to the target pH levels of 5.90 and 6.40 using dilute HClor NaOH; the mean measured pH values of the two pHtreatments was 5.87 and 6.43, respectively.

2.2. Meat collection and preparation

The meat for these studies was obtained approxi-mately 24 h post-mortem from commercially slaugh-tered 6- to 9-month old pigs with a carcase weight of 60to 90 kg. Legs were selected on the basis of ®bre opticprobe (FOP) readings (Pro Electro Optics Ltd, Barnsley,UK) and ultimate pH of the semimembranosus and thebiceps femoris muscles. Legs were classi®ed as PSE if thesemimembranosus and biceps femoris muscles had FOPvalues greater than 65 and ultimate pH values less than5.9. Normal legs had FOP values of less than 45 andultimate pH values less than 5.9 (S.V. Myler, 1992, pers.comm.).The legs were immediately transported back to the

laboratory and derinded, boned and closely trimmed toremove as much fat and connective tissue as possible.Normal and PSE meat were kept separate, with themeat from legs of each quality type pooled. The musclesused for this work were the M. semimembranosus, M.biceps femoris, M. gluteus medius, M. gluteus accessoriusand the light portion of the M. semitendinosus. Thetrimmed meat was minced three times through a com-bination of a kidney plate, double sided knife, 12 mmhole plate, double sided knife and 6 mm-hole plate. Themeat was stored overnight at 0�C.

2.3. Sample preparation

2.3.1. Experiment 1In Experiment 1, the minced meat was mixed with

water, containing HCl (BDH Chemicals) or NaOH(Sigma Chemicals), and NaCl (BDH Chemicals) andPPi (Na4P2O7, Sigma Chemicals) or TPP (Na5P3O10,Sigma Chemicals). The meat was mixed in a mixer(Kenwood Chef, Kenwood Ltd, Havant, UK) at theminimum speed for 60 s while the non-meat ingre-dients were added. The homogenate was then mixed fortwo periods of 60 s at the maximum speed. The bowlwas scraped down between each of the three mixingperiods. The meat homogenate was degassed in avacuum packaging machine, and sealed in a poly-ethylene bag.To ®ll the homogenate into tubes, one corner was cut

o� the pouch containing the meat homogenate. Thepouch was placed into a 12 l sausage stu�er with the cuto� corner placed in front of the ®lling nozzle. The meathomogenate was then ®lled into 12 polycarbonatecooking tubes (240 to 250 mm long, 19 mm internaldiameter) which were coated with a spray-on oil (Pureand Simple, Samuel Taylor, NSW, Australia) to preventmeat adhering to the tubes. The tubes were then

vacuum-sealed in polyethylene bags. The tubes werestored at 0�C until required for cooking.

2.3.2. Experiment 2The methods used in Experiment 2 were the same as

used in Experiment 1, except for two modi®cations.Firstly, the NaCl and TPP were dissolved in the mixtureof water and 0.5 M HCl or NaOH prior to their addi-tion to the meat. Secondly, the meat was mixed onminimum speed for 30 s, then mixed at maximum speedfor two periods of 60 s.

2.4. Cooking conditions

The samples were cooked in a waterbath [W28, GrantInstruments (Cambridge) Ltd, Barrington, UK]. Thecooking tubes were placed in a specially manufacturedcooking rack, capable of holding a total of 24 tubes thatensured that water could ¯ow around all tubes.Temperature measurements were made with thermo-couples located on the long axis of the cooking tubescontaining the meat homogenate; this data indicatedthat all tubes were heated at the same rate. The sampleswere placed in the water bath that was initially set 20�Clower than the target temperature. Immediately afterthe samples were placed in the water bath, the tem-perature setting of the water bath was adjusted to the®nal temperature. This resulted in a heating rate ofabout 0.9�C/min. Three cooking tubes from eachhomogenate preparation were heated at each tempera-ture. The total cooking time was 45 min. The order ofthe cooking temperatures was randomised from batch-to-batch so that there was no interaction between thetime between preparation and cooking and cookingtemperature.After cooking, the samples were immediately cooled

in an ice and water mixture for 45 min. Following thecook loss determinations, the cooled samples were storedovernight at 3�C until required for torsion testing.In Experiment 1, the initial water temperature was

52.5�C, and the ®nal cooking temperature was 72.5�C.In Experiment 2, four cooking regimes were used. Theinitial and ®nal cooking temperatures were respectively:40 and 60�C; 46.7 and 66.7�C; 53.3 and 73.3�C; and 60and 80�C. The probability of signi®cant di�erencesbetween treatments was calculated using the least sig-ni®cant di�erence (LSD) test.

2.5. Cook loss measurements

Percentage cook loss (CL) was measured by deter-mining weight loss from the meat homogenate duringcooking. The weight of homogenate ®lled into eachcooking tube was measured. Immediately after thesamples were cooked and cooled, the meat gels wereremoved from their cooking tube, patted dry with a

P.J. Torley et al. /Meat Science 55 (2000) 451±462 453

paper towel, and weighed. CL was determined on threetubes for each treatment at each cooking temperature.

2.6. Textural measurements

The shear stress (SS) and true shear strain (TSS)values of the meat gels were measured with a torsiontester (Gel Consultants Inc., Raleigh, NC) using themethod of Hamann (1983). The method used is descri-bed brie¯y below.The meat gels were allowed to equilibrate to room

temperature (approximately 25�C) before testing. Themeat gels were cut into 29 mm long cylinders. A poly-styrene disk was glued to each end of the meat gelcylinder using cyanoacrylate glue (Loctite 406, LoctiteAustralia Pty Ltd, NSW, Australia). The samples werethen shaped into a dumbbell with a minimum diameterof 10 mm using a purpose-designed grinder. The dumb-bells were then twisted (2.5 revolutions/min) to failure,using a computer-controlled viscometer (5XHBTDV,Brook®eld Engineering Laboratories Inc., MA, USA,modi®ed by Gel Consultants Inc.). A program suppliedby Gel Consultants Inc. was used to record the SS andTSS at failure.

2.7. pH measurement

Meat homogenate (2 g) was homogenised with demi-neralised water (20 g). The sample was equilibratedovernight at 2�C and warmed to room temperature(about 25�C) before the pH was measured using a cali-brated pH meter (HI 9025C Hanna Instruments, Singa-pore) and a glass combination pH electrode (Model No476530, Corning Glass Works, Corning, New York).

2.8. Data analysis

The data were analysed by analysis of variance (AOV)using the mixed procedure and the generalised linearmodel (GLM) procedure in SAS for Windows (version6.08, SAS Institute Inc., Cary, NC). When main e�ectsor interactions were signi®cant (P<0.05), signi®cantdi�erences between treatment means were calculatedusing the least signi®cant di�erence (LSD) test.

2.8.1. Experiment 1In an initial analysis, measured pH was included as a

covariate in the AOV of all three variables Ð SS, TSSand CL. However, these analyses showed that the pHhad no signi®cant e�ect (P>0.05) on the AOV of SSand CL as a covariate and hence was only included as acovariate in the AOV of TSS.

2.8.2. Experiment 2In an initial analysis, measured pH, storage time or

the interaction between measured pH and storage time

were used as covariates in the AOV of SS, TSS, and CL.These analyses showed that none of the covariates had asigni®cant e�ect on (P>0.05) AOV of SS and TSS andwere not included in these analyses. Measured pH had asigni®cant e�ect (P=0.0003) on CL and was included asa covariate in the AOV of CL.

3. Results

3.1. Experiment 1

The processing conditions had similar e�ects on TSSand CL, which was di�erent from the e�ect on SS. WithTSS and CL, meat quality and polyphosphate type hadno signi®cant e�ect (P>0.05) on either property aseither a main e�ect or as an interaction. Whereas, withSS, there was a signi®cant interaction (P=0.0055)between meat quality (normal and PSE pork) andpolyphosphate type (Fig. 1). In contrast, the timebetween preparation and cooking had a signi®cante�ect on all three measures of functional properties(P40.0001) but there was no interaction between timefrom preparation to cooking and any of the other vari-ables studied (Table 3).The SS of gels made from normal and PSE pork

responded di�erently to the addition of polyphosphates(Fig. 1). With normal pork, both polyphosphates (PPi andTPP) signi®cantly increased the SS of the gels (P<0.05)compared to the treatment with no polyphosphate at the

Fig. 1. The e�ect of no polyphosphate [NaCl only, NaCl ionic

strength (IS)=0.25], pyrophosphate (PPi; NaCl IS=0.17, PPi

IS=0.08) and tripolyphosphate (TPP; NaCl IS=0.17, TPP IS=0.08)

addition on the shear stress of normal and pale, soft, exudative (PSE)

pork (Experiment 1). a±d Values with the same letter are not sig-

ni®cantly di�erent at the 5% level. Values are averaged across holding

time before cooking (1, 2, 4, 8 and 24 h). Average pH is 6.04. Legend:

solid bars, normal pork; cross-hatched bars, PSE pork.

454 P.J. Torley et al. /Meat Science 55 (2000) 451±462

same ionic strength. Of the polyphosphates, PPi pro-duced the largest increase in SS, with TPP producing anincrease that was intermediate between that producedby PPi and the treatment with no polyphosphates.With PSE pork, both polyphosphate treatments pro-duced similar and signi®cant increases (P<0.05) in theSS of the gels compared to treatment with no poly-phosphates, but the increase in SS was much smallerthan that produced by the polyphosphates with normalpork.As indicated previously, the time between preparation

and cooking had a signi®cant e�ect on all three mea-sures of functional properties (P40.0001) but there wasno interaction between time and any of the other vari-ables studied (Table 3). With increasing time betweenpreparation and cooking, there was a progressiveincrease in SS and TSS, and corresponding decrease inCL (Table 3). CL decreased rapidly (P<0.0020)between 1 h and 2 h holding times and then decreasedslowly over the remaining 22 h. Both SS and TSSincreased (P<0.05) slowly but signi®cantly over the 24h period.

3.2. Experiment 2

The three di�erent measures of functionality SS, TSSand CL responded di�erently to changes in processingconditions. Because of these di�erences, each functionalproperty will be discussed individually in terms of itshighest order signi®cant interaction. The signi®canthigh order interactions will be grouped under subhead-ings involving meat quality interactions, ionic conditioninteractions, and cooking temperature interactions.

3.2.1. Meat quality ± TPP interaction3.2.1.1. Shear stress and true shear strain. The e�ect ofTPP addition on the textural parameters, SS and TSS,depended (P<0.05) on meat quality type (Fig. 2). Whenaveraged over meat quality type, TPP additionincreased (P<0.05) the SS of the gels by 22 kPa (from25 to 47 kPa); however, the increase in SS (Fig. 2A) was

much larger (P<0.05) for the normal pork, 24 kPa(from 32 to 56 kPA) than for PSE pork, 19kPa (from 19to 38 kPA). TPP addition produced a similar e�ect onTSS (Fig. 2B) as on SS. TPP increased TSS by 0.33(from 1.30 to 1.63) for normal pork gels and 0.26 (from1.10 to 1.36) for PSE pork gels. The overall e�ect ofaddition of TPP to PSE pork was that it increased thetextural properties (SS and TSS) to the same level asthat produced with normal pork without TPP.

3.2.1.2. Cook loss. There was no e�ect of meat qualityor TPP on CL as a main e�ect or as an interaction(P>0.05).

Table 3

The e�ect of time between preperation and cooking on the mean shear

stress, true shear strain and cook loss of pork homogenatesa

Time (h) Shear stress (kPa) True shear strain Cook loss (%)

1 30.9a 1.182a 20.8a

2 31.2a 1.193ab 19.3b

4 32.6ab 1.204ab 18.9b

8 33.7b 1.219b 18.7bc

24 37.1c 1.290c 17.9c

a Values within the same column with the same letter are not sig-

ni®cantly di�erent (P<0.05). Values are averaged across meat quality

(normal and PSE pork) and polyphosphate addtition (NaCl only, PPi

and TPP). Total added ionic strength is 0.25, average pH is 6.04.

Fig. 2. The e�ect of tripolyphosphate (TPP) addition to normal and

pale, soft, exudative (PSE) pork on the (A) shear stress and (B) true

shear strain (Experiment 2). a±d Values with the same letter are not

signi®cantly di�erent at the 5% level. Values are averaged across total

added ionic strength (0.25, 0.30, 0.35 and 0.41), pH (5.9 and 6.4) and

cooking temperature (60, 66.7, 73.3 and 80�C). Legend: solid bars,

normal pork; cross-hatched bars, PSE pork.

P.J. Torley et al. /Meat Science 55 (2000) 451±462 455

3.2.2. Meat quality ± ionic strength ± TPP interactionsMeat quality, ionic strength and TPP had di�erent

e�ects on the functional properties of the pork gels. TheSS was in¯uenced by an interaction between meat qual-ity and ionic strength (P=0.0150); TSS was not in¯u-enced by an interaction between any of these threetreatments (P>0.05); and CL was in¯uenced by aninteraction between all three treatment variables(P=0.0026). The signi®cant interactions will be descri-bed below.

3.2.2.1. Shear stress. With SS, the meat quality andionic strength interaction resulted because gels fromPSE and normal pork responded di�erently to increasesin ionic strength (Fig. 3). For normal pork, the SS of thegels increased signi®cantly (P<0.05) with each incre-mental increase in ionic strength between 0.25 and 0.45.For PSE pork, SS increased (P>0.05) with the initialincrease in ionic strength (0.25 to 0.30) but then essentiallyplateaued. The SS of PSE pork gels did not increase(P>0.05) between ionic strengths of 0.30 and 0.35 orbetween 0.35 and 0.41 although there was a small sig-ni®cant increase (P>0.05) in SS between 0.30 and 0.41.

3.2.2.2. Cook loss. With CL, the three-way interactionbetween meat quality, TPP addition and ionic strengthoccurred because the normal and PSE pork respondeddi�erently to increasing ionic strength in the presenceand absence of TPP (Fig. 4). For PSE pork with 0%TPP,CL decreased from 17 to 12% when the ionic strengthincreased from 0.25 to 0.30 and then plateaued and didnot decrease further as the ionic strength increased from

0.30 to 0.41. With PSE pork with 0.37% TPP, the CLdecreased progressively from 17 to 5% as the ionicstrength increased from 0.25 to 0.41. With normal porkwith 0% TPP, CL decreased progressively with increas-ing ionic strength in an identical trend as for the PSEwith 0.37% TPP. With normal pork that contained0.37% TPP, CL was lower initially (12%) and decreasedsigni®cantly between ionic strengths of 0.25 and 0.35when it reached a minimum value of 5% and did notdecrease further with an increase in ionic strength to0.41.The results show that normal pork with 0.37% TPP

produces minimum CL at an ionic strength of 0.35,normal pork with 0% TPP and PSE pork with 0.37%TPP produces minimum CL at an ionic strength of 0.41,and that the CL cannot be decreased below 12% in PSEpork that contains no 0% TPP, even when the ionicstrength is increased to 0.41.

3.2.3. Ionic strength ± pH ± TPP interactionThere was a signi®cant interaction between the ionic

strength, pH and TPP addition for SS (P=0.0119), TSS(P=0.0222) and CL (P=0.0018). The pattern ofresponse to variation in the ionic conditions di�eredbetween the three functional properties (Fig. 5).

3.2.3.1. Shear stress. With SS, the three-way interactionoccurred because the di�erent pH±TPP treatmentsresponded di�erently to increasing ionic strength (Fig. 5A).Both pH treatments that contained TPP had higher SSvalues initially and the SS increased progressively withincreasing ionic strength to a maximum value at an

Fig. 3. The e�ect of ionic strength on the shear stress of normal and

PSE pork (Experiment 2). The LSD (P<0.05) for shear stress is 3.30

kPa. Values are averaged over pH (5.9 and 6.4), TPP concentration (0

and 0.37%) and cooking temperature (60, 66.7, 73.3 and 80�C).Legend: &, PSE pork; ~, normal pork.

Fig. 4. The e�ect of tripolyphosphate (TPP) and ionic strength and

pH on cook loss from normal and PSE pork (Experiment 2). The LSD

(P<0.05) for cook loss is 1.8%. Values are averaged over pH (5.90

and 6.4) and cooking temperature (60, 66.7, 73.3 and 80�C) Legend:&, PSE pork with 0% TPP; +, PSE pork with 0.37% TPP; *, nor-

mal pork with 0% TPP; ^, normal pork with 0.37% TPP; PSE pork,

broken line; normal pork, solid line.

456 P.J. Torley et al. /Meat Science 55 (2000) 451±462

ionic strength of 0.35. In the case of the two pH treat-ments that contained 0% TPP, the SS did not changewith increasing ionic strength when the ionic strengthincreased from 0.25 to 0.35 and then produced a smallincrease in SS between 0.35 and 0.41.

3.2.3.2. True shear strain. In general, increasing ionicstrength increased TSS. However, the e�ect of ionicstrength was strongly a�ected by the addition of TPPand the pH of the treatment (Fig. 5B). The greatest andmost consistent increase in TSS with increasing ionicstrength was for the 0% TPP, pH 5.9 treatments; thistreatment showed a consistent and signi®cant(P40.0001 in all cases) increase in TSS with eachincremental increase in ionic strength. For the other pHand TPP treatment combinations, there was a muchsmaller increase in TSS with increasing ionic strength.The reason for the smaller response for the high pHtreatment and the treatments with TPP was that TSSwas close to the maximum obtainable value even at lowionic strength and increasing the ionic strength couldnot increase the TSS further.

3.2.3.3. Cook loss. Generally CL decreased withincreasing ionic strength irrespective of pH and TPPaddition, though the pattern of the decrease in CL dif-fered depending on the treatment (Fig. 5C). In both the0% TPP and 0.37% TPP, pH 5.9 treatments, there wasa signi®cant decrease (P40.0001) in CL with anincrease in ionic strength from 0.25 to 0.41. The increasein ionic strength produced a 13.7% decrease with 0%TPP treatments and a 9.4% decrease in CL with the0.37% TPP treatment.The e�ect of ionic strength on CL was smaller with

the pH 6.4 treatments than with the pH 5.9 treatments.With the pH 6.4, 0% TPP treatment, there was a non-signi®cant 1.5% decrease in CL (P>0.05) with anincrease in ionic strength from 0.25 to 0.41 and with thepH 6.4, 0.37% TPP treatments a signi®cant 4.3%decrease (P<0.05) in CL.

3.2.4. Cooking temperature and cooking temperatureinteractions3.2.4.1. Shear strain and true shear stress. Cookingtemperature had a signi®cant e�ect on SS (P40.0001)and TSS (P=0.0004) but there was no interactionbetween cooking temperature and any of the othertreatments (P>0.5) (data not shown). Over the tem-perature range investigated, SS increased with increas-ing cooking temperature from 32 kPa at 60�C to 40 kPaat 73.3�C but plateaued and did not increase sig-ni®cantly above 73.3�C. In contrast to SS, TSSdecreased rapidly (from 1.6 to 1.2) with increasingcooking temperature between 60 and 73.3�C initiallyand then increased slowly as is it approached anasymptote at 1.1 at 80�C.

Fig. 5. The e�ect of tripolyphosphate (TPP) addition, ionic strength

and pH on pork (A) shear stress, (B) true shear strain and (C) cook

loss (Experiment 2). The LSD (P<0.05) for shear stress is 4.9 kPa;

true shear strain is 0.11; and cook loss is 3.5%. Values are averaged

over meat quality (normal and PSE pork) and cooking temperature

(60, 66.7, 73.3 and 80�C). Legend:&, pH 5.9 with 0% TPP;+, pH 5.9

with 0.37% TPP; *, pH 6.4 with 0% TPP; ^, pH 6.4 with 0.37%

TPP; pH 5.9, broken line; pH 6.4, solid line.

P.J. Torley et al. /Meat Science 55 (2000) 451±462 457

3.2.4.2. Cook loss. CL was signi®cantly a�ected byinteractions between cooking temperature and pH(P40.0001), cooking temperature and TPP addition(P=0.0216), and cooking temperature and ionicstrength (P=0.0002) (Figs. 5, 6 and 7). In all cases, CLincreased with increasing cooking temperature, fromabout 4% at 60�C, to as high as 20% at 80�C. The e�ectof high pH, high ionic strength and the presence of TPPwas to reduce the rate at which CL decrease withincreasing temperature.

The di�erence in CL between the pH 5.9 and 6.5treatments increased with increasing cooking tempera-ture (Fig. 6). At the lowest cooking temperature of60�C, the CL of the pH 5.90 was 4.0% higher (P<0.05)than that of the pH 6.4 treatment (2.0 versus 6.0%). At80�C, this di�erence in CL (P<0.05) was 11% (11.0versus 22.0%).The di�erence in CL between the 0% TPP and 0.37%

TPP treatments increased with increasing cooking tem-perature (Fig. 7). At the lowest cooking temperature of60�C, the CL of the 0% TPP treatment was 1.1% higher(P<0.05) than that of the 0.37% TPP treatment (3.9versus 5.0%). At 80�C, this di�erence in CL (P<0.05)was 3.3% (14.0 versus 17.3%).The e�ect of cooking temperature on CLwas dependent

on the ionic strength of the treatment (Fig. 8). As theionic strength increased, the e�ect of temperature on CLdecreased. At the lowest ionic strength (0.25) increasingthe temperature from 60 to 80�C increased cooking lossfrom 7 to 22% whereas at the highest ionic strength(0.41) the corresponding increase was from 2 to 11%.

4. Discussion

4.1. Meat quality, ionic strength, TPP addition andcooking temperature

4.1.1. Meat quality interactions with ionic strength andTPP additionThe e�ect of variation in ionic strength or polypho-

sphate addition on the functional properties of normal

Fig. 7. The e�ect of cooking temperature and TPP on cook loss

(Experiment 2). The LSD (P<0.05) for cook loss is 1.2%. Values are

averaged over pH (5.9 and 6.4), ionic strength (0.25, 0.30, 0.35 and

0.41) and meat quality (normal and PSE). Legend: &, 0% TPP; ~,

0.37% TPP.

Fig. 6. The e�ect of cooking temperature and pH on cook loss

(Experiment 2). The LSD (P<0.05) for cook loss is 1.2%. Values are

averaged over TPP concentration (0.0 and 0.37%), ionic strength

(0.25, 0.30, 0.35 and 0.41) and meat quality (normal and PSE).

Legend: &, pH 5.9; ~, pH 6.4.

Fig. 8. The e�ect of cooking temperature and ionic strength on the

cook loss (Experiment 2). The LSD (P<0.05) for cook loss is 1.6%.

Values are averaged across tripolyphosphate (TPP) addition (0 and

0.37% TPP), pH (5.9 and 6.4) and meat quality (normal and PSE

pork). Legend: &, 0.25 ionic strength; +, 0.30 ionic strength; *, 0.35

ionic strength; ^, 0.41 ionic strength.

458 P.J. Torley et al. /Meat Science 55 (2000) 451±462

and PSE pork di�ered depending on the measure offunctional properties that was used. Overall, the addi-tion of polyphosphates or an increase in the ionicstrength improved the functional properties of bothnormal and PSE pork. However, the functional proper-ties of PSE pork generally showed a smaller response toboth addition of polyphosphate and increasing ionicstrength (Figs. 1, 2, 3 and 4). The improvement in thefunctional properties of normal pork produced byincreasing ionic strength (Trout & Schmidt, 1986b,1987) and the addition of polyphosphates (Bendall,1954; Trout & Schmidt, 1986b, 1987) was similar to thatpreviously reported.The fact that PPi and TPP had di�erent e�ects on SS,

TSS and CL and also had di�erent e�ects on normaland PSE pork has not previously been reported. Thediscussion below outlines some of these di�erences andgives some insight into why they occur.One of the important observations in this study was

that at the same ionic strength and pH, PPi and TPPproduced a greater reduction in CL than the sametreatment without polyphosphate with both normal andPSE pork. Although previously Van Hoof (1975) hasshown that PPi and TPP has a greater e�ect on WHCthan a similar concentration of salt, they could not ®ndthe reason for the di�erence since the polyphosphateswere added directly to the products without adjustingthe ionic strength or pH. Hence in the study by VanHoof (1975) the greater e�ectiveness of the two poly-phosphates was due to the combined e�ects of di�er-ences in ionic strength, pH and type of polyphosphate.Results of our current study show that both PPi andTPP have some property, independent of their ability toincrease ionic strength and pH, which can increase theWHC of both normal and PSE pork. Moreover, PPican more e�ectively increase WHC than TPP. The abil-ity of this intrinsic property of polyphosphates toincrease WHC has been previously shown to occur withbeef muscle (Trout and Schmidt, 1986a).In contrast to the results obtained with CL, PPi had a

greater e�ect than TPP on SS of normal pork but noton PSE pork (Fig. 1). This e�ect appears to haveoccurred because both PPi and TPP produced verysmall increases in SS with PSE pork (10 kPa) comparedto the treatment without polyphosphate. And becauseof the small increase in SS, any di�erence in e�ective-ness of the polyphosphates was not detectable. Withnormal pork both polyphosphates produced largeincreases in SS (17 to 27 kPa), hence the greater e�ec-tiveness of PPi was easily observed.The question arises why, in this study, did the poly-

phosphate treatments at high ionic strength (in bothExperiments 1 and 2) have similar e�ects on CL ofnormal and PSE pork but di�erent e�ects on SS? Thatis, why did the polyphosphates at high ionic strengthinduce minimum CL (i.e. maximum functionality) with

PSE pork gels, comparable to that of normal pork, butdid not have a similar e�ect on SS.One possible explanation for this e�ect is that within

limits CL is independent of the concentration of func-tional muscle protein in the product whereas SS (ameasure of gel strength) is dependent on the concentra-tion of these proteins (Foegeding, 1990; Smith, 1987;Park, Lanier & Pilkington, 1993; Park, Lanier & Green,1988).Unpublished research carried out in our laboratories

provides evidence to support this concept. Our researchcompared the extraction of protein from the myo®brilA-band, and myo®brillar swelling using a light micro-scopy technique similar to that used by O�er and Tri-nick (1983). Myo®brils were prepared from normal andPSE pork muscle (M. semimembranous), and individualmyo®brils were observed under the microscope whilethey were sequentially incubated with a range of con-centrations of NaCl and pyrophosphate (O�er & Tri-nick). We observed that less protein was extracted fromthe A-band of myo®brils made from PSE muscle, thanfrom normal muscle. And interestingly, a large percen-tage of myo®brils from PSE muscle (up to 50%depending on the extent of PSE) did not swell comparedto myo®brils from non-PSE muscle where all myo®brilsswelled approximately equally. The reason for this dif-ference in response is that the myosin heads in themyo®brils of PSE muscle are partially denatured (Hon-ikel & Kim, 1986; Izumi, Ito & Fukawaza, 1977; O�eret al., 1989; Penny, 1967a, 1967b; Stabursvik et al.,1984; Sung et al., 1976) which prevents the actomyosinbeing split by the polyphosphates (Izumi et al.) andlimits myo®brillar swelling.In this study it appears that the di�erent e�ects of

polyphosphate on PSE pork on CL and SS is becausethe polyphosphates mainly a�ect the non-denaturedmuscle proteins. Addition of the polyphosphates at highionic strength cause the non-denatured myo®brils in thePSE muscle to swell, solubilise and produce a threedimensional protein network that can e�ectively bind allthe water in the gel and retain it after heating. Althoughin the normal pork muscle, there is more non-denaturedmuscle proteins to swell and bind the water, this is oflittle bene®t since all the water in the gels can be e�ec-tively bound by the much smaller amount of protein inPSE pork. In contrast, with SS the strength of the heatedgel is dependent on the amount of un-denatured muscleprotein available to form the protein network structureprior to heating (Foegeding, 1990; Park et al., 1988,1993; Smith, 1987). Hence the lower un-denatured pro-tein concentration in the PSE gel results in a weaker gel.The di�erent e�ects of ionic conditions on CL and SS

are most likely related to the amount of water added tothe homogenates. If a higher concentration of water hadbeen added to the product, it is quite conceivable thatthe result obtained would have been di�erent. With the

P.J. Torley et al. /Meat Science 55 (2000) 451±462 459

greater amount of added water, the smaller amount offunctional protein in the PSE muscle may not have beenable to bind all the water and minimize CL. Hence, theamount of water added to the homogenates, in e�ect,determines if the ionic conditions can minimize CL inPSE pork (i.e. make it comparable to CL of normalpork). Moreover, at higher water addition rates, it maynot be possible to minimize CL by optimising ionicconditions, as occurred in this study, since the amountof functional protein available to bind the water maybecome the limiting factor.These results indicate that changing the ionic condi-

tions in PSE pork can only improve the functionality ofthe non-denatured muscle proteins and does not appearto be able to re-nature the denatured muscle proteins andmake them functional. As a result, PSE pork respondsless to changes in ionic conditions than normal pork.

4.1.2. Ionic conditions and the functional properties ofporkIn Experiment 2, there was an interaction between

ionic strength, pH and TPP addition for SS, TSS andCL (Fig. 5). The nature of this interaction was di�erentfor each of the measures of functional properties. Thedi�erences in response of the three measures of func-tional properties indicated that each measured di�erentaspects of muscle protein quality as has been previouslyreported (Foegeding, 1990; Park et al., 1988, 1993;Smith, 1987). In previous studies with beef it has beenshown that ionic strength, polyphosphate addition andpH all a�ect the functional properties of products madefrom beef (Trout & Schmidt, 1986b, 1987). While theresults produced in the present study di�ered in detailfrom these studies on beef, some general similaritieswere observed.

4.1.2.1. Ionic strength. With pork in this study and beefin earlier studies (Trout & Schmidt, 1986b, 1987), it hasbeen shown that an increase in the ionic strengthincreases gel strength and decreases CL. These func-tional properties, however, do not change linearly withincreasing ionic strength. At low ionic strength and inthe absence of polyphosphates functional propertiesincrease essentially linearly with increasing ionicstrength (Trout & Schmidt, 1987); whereas at high ionicstrength in the presence of TPP, the functional proper-ties of both beef and pork gels changed little withincreasing ionic strength (beef: Trout & Schmidt, 1986b,1987; pork: Fig. 5A and B).In the present study on pork, there was no large

increase in functional properties with increasing ionicstrength (Fig. 5C). This general lack of e�ect was prob-ably because the ionic strength range used in this studywas not wide enough to show the same large increase inbeef functional properties as seen in the earlier studies(Trout & Schmidt, 1987). The reason for this is that at

high ionic strength, the functional properties areapproaching a maximum value so that increasing ionicstrength can only produce minimal increases in func-tionality.

4.1.2.2. pH. As a generalization, in this study increasingpH of the raw homogenates from 5.9 to 6.4 increased allthree measures of functional properties as has beenpreviously reported (Trout & Schmidt, 1986b, 1987).Although trends produced by increasing pH depend onthe technique used to measure functional properties(Fig. 5; Trout & Schmidt, 1986b, 1987). Studies on beefhave shown a similar tendency for functional propertiesto increase with increasing pH (over the range pH 5.5 to6.35) (Trout & Schmidt, 1986b).

4.1.2.3. Polyphosphate type. In both Experiments 1 and2, addition of PPi and TPP produced a synergistic e�ecton functional properties. The e�ect of the polypho-sphates on functionality is described as synergistic inthis study since both polyphosphates produced muchlarger increases in functionality than the treatment ofthe same ionic strength and pH but without polypho-sphates. Similar synergistic e�ects of polyphosphateshave been previously observed in a number of studies(Bendall, 1954; Hellendoorn, 1962; Trout & Schmidt,1986b, 1987). An explanation for the synergistic e�ectof polyphosphates on functionality has also been pro-posed (O�er & Knight, 1988; Trout & Schmidt, 1986c,1987).

4.1.3. Cooking temperature and the functionalpropertiesCooking temperature had a signi®cant e�ect on func-

tional properties. SS and CL (Fig. 5) increased, and TSSdecreased with increasing cooking temperature. Thechanges in texture and WHC observed with increasingtemperature were consistent with the changes reportedfor beef products (Trout & Schmidt, 1987).

4.1.3.1. Cook loss. In the present study, CL was a�ectedby signi®cant ®rst order interactions between cookingtemperature, and ionic strength, pH, and TPP. Theseinteractions with cooking temperature were such thathigh ionic strength, high pH and the presence of TPPreduced the increase in CL that occurred with increasingcooking temperature. This trend is similar to that pre-viously observed with beef homogenates; however, inthe earlier study the interaction with cooking tempera-ture and the other processing variables was more com-plex (Trout & Schmidt, 1987).The molecular basis for the e�ect of cooking tem-

perature on functional properties and the interactionsbetween ionic strength, polyphosphate type and pH andcooking temperature on functional properties has beendescribed previously (Trout & Schmidt, 1987).

460 P.J. Torley et al. /Meat Science 55 (2000) 451±462

4.1.3.2. Shear stress and true shear strain. Cookingtemperature had a signi®cant e�ect on SS and TSS as amain e�ect (P<0.05) but there was no signi®cant inter-action (P>0.05) with any of the other variables. It isnot readily apparent why these interactions did notoccur in our study with pork as they had in earlier stu-dies with beef (Trout & Schmidt, 1987), although pre-paration, testing and species di�erences may havecaused the di�erence.In conclusion, the results in this study show that with

cooking temperature it is necessary to ®nd a compro-mise between textural characteristics (SS and TSS) andCL. As the cooking temperature increases, the SS, TSSand CL change at di�erent rates. The present resultsindicate that a cooking temperature of between 66.7 and73.3�C o�ered the best compromise between textural andyield characteristics.

4.2. Time between preparation and cooking and thefunctional properties of pork

One of the important results in Experiment 1, was thatincreasing time between preparation and cooking sig-ni®cantly (P<0.05) increased SS and TSS, and decreasedCL (Table 3). The method used in the present study issimilar to that used commercially for the preblending ofmeat where preblending improves the functional prop-erties of salted meat by allowing greater protein solubili-sation (Hand, Mandigo & Calkins, 1992).Most studies on preblending have focused on the

production of salted meat as a raw material, which isthen incorporated later into a processed meat product.Therefore, these studies have examined the e�ect ofholding preblended meat over longer time periods thanthat used in the present study (Abu-Bakar, Reagan,Wynne & Carpenter, 1982; Hand et al., 1992; Ockerman& Leon Crespo, 1982; Reagan, Pirkle, Campion & Car-penter, 1981). Relatively little data have been collectedabout the changes that occur in the functional proper-ties of meat during the ®rst 24 h after salt addition.Unlike in earlier studies, this study shows a consistent

improvement in all three measures of protein function-ality with increased holding time. Earlier studies onpreblending measured the e�ect of holding for up to 24h, and found that preblending had a positive, negativeor no e�ect on functional properties depending on thetype and frequency of measurements that were made(Hand, Hollingsworth, Calkins & Mandigo, 1987; Ock-erman & Leon Crespo, 1982; Hand et al., 1992). Addi-tionally, these previous studies showed that extending theholding time of preblended meat past 24 h did notappear to have any further bene®cial e�ect on functionalproperties and may have a negative e�ect on functionalproperties (Hand et al., 1992; Ockerman & Leon Crespo).The consistent improvement in functional properties

over the 24 h holding period between preparation and

cooking, found in the present study, may be due to thedi�erent approaches used to carry out the studies. Theimportant feature of this study was that the homo-genates were prepared and ®lled into the tubes and heldin the tubes and not mixed prior to heating. In previousstudies, the ground meat is pre-blended with salt, heldfor varying lengths of time, processed, ®lled into con-tainers and then cooked immediately (Hand et al., 1987,1992; Ockerman & Leon Crespo, 1982).The di�erence in results between this and previous

studies is related to di�erent approaches used in thestudies. In the present study where the raw productswere stored after they had been prepared, more muscleproteins were progressively solubilized over time toproduce a stronger more structured swollen proteinnetwork (Trout & Schmidt, 1987). The resulting proteinnetwork that developed over time could bind morewater and produce a stronger gel when heated than thatformed initially. In the previous studies on pre-blendingdescribed above, if such a swollen protein networkstructure was produced during preblending and storageit would be destroyed by the mixing that occurred dur-ing subequent processing. Hence the bene®ts of pre-blending as seen in this study would be lost.Results in the present study are supported by those of

Torley and Lanier (1992). These researchers found thatif pre-blended beef (stored at 25�C for 3 h) is re-mixedand ®lled out into cooking tubes just prior to cooking, ithas lower SS and TSS than samples cooked immediatelyafter preparation, or held at 25�C for 3 h and cookedwithout re-mixing (Torley & Lanier). The small bene-®cial e�ect of pre-blending shown in previous studiesmay have been simply due to improved protein solubi-lisation without the bene®ts of time necessary to pro-duce the ordered network structure in the ®nal productrequired for increased functional properties.The results from Experiment 1 and those obtained in

the earlier study by Torley and Lanier (1992) suggestthat the full bene®ts of pre-blending may not always beobtained commercially. This is because in commercialpractice products prepared from pre-blended materialare normally processed just prior to cooking, whichdisturbs any structure that has developed during sto-rage. To obtain the bene®ts of pre-blending processorswould have to store the prepared product for 12 to 24 hbefore cooking. This may not be commercially possiblebecause of practical considerations such as the unavail-ability of chiller space to store the product for the lengthof time necessary to obtain the bene®cial e�ects ofpre-blending.

5. Conclusions

There was no combination of conditions under whichPSE pork had functional properties that were the equal,

P.J. Torley et al. /Meat Science 55 (2000) 451±462 461

or superior, to those of normal pork under the sameconditions. Processing PSE pork at high ionic strengthsin the presence of added polyphosphates appeared to bethe best conditions for maximum functionality. Thiscombination of conditions gave the lowest cook loss forPSE pork, though the texture was still inferior.Ionic strength, pH and addition of polyphosphates

had much smaller e�ects on the functional properties ofPSE pork than normal pork. We hypothesised that thereason for this smaller e�ect on functional propertieswas that with PSE pork there was less undenaturedmuscle proteins for the salts to interact with to increasefunctional properties. This di�erence between normaland PSE pork was greater with textural properties (SSand TSS) than with CL because CL appeared to be lesse�ected by the smaller amount of functional protein inthe PSE pork.

Acknowledgements

The authors wish to acknowledge the ®nancial sup-port of the Pig Research and Development Corporationin the form of a post-graduate scholarship to P.J.T. Theauthors would like to thank Joe Cassell, Sue Dyson andDavid Reiser for their technical assistance on this project.

References

Abu-Bakar, A., Reagan, J. O., Wynne, R. L., & Carpenter, J. A.

(1982). Journal of Food Science, 47, 374±379, 385.

Bendall, J. R. (1954). Journal of the Science of Food and Agriculture, 5,

468±475.

Cochran, W. G., & Cox, G. M. (1957). Experimental designs. New

York: John Wiley and Sons Inc.

Foegeding, E. A. (1990). Journal of Food Science, 55, 932±936, 941.

Hamann, D. D.(1983) Structural failure in solid foods. In M. Peleg, &

E. B. Bagley, Physical properties of foods (pp. 351±383). Westport:

AVI Publishing Company Inc.

Hand, L. W., Hollingsworth, C. A., Calkins, C. R., & Mandigo, R. W.

(1987). Journal of Food Science, 52, 1149±1151.

Hand, L. W., Mandigo, R. W., & Calkins, C. R. (1992). Meat Science,

31, 13±24.

Hellendoorn, E. W. (1962). Food Technology, 16, 119±124.

Honkavaara, M. (1988). Meat Science, 24, 201±207.

Honkavaara, M. (1990). Fleischwirtschaft International, 2, 20±22.

Honikel, K. O., & Kim, C. J. (1986). Fleischwirtschaft, 66, 349±353.

Izumi, K., Ito, T., & Fukazawa, T. (1977). Journal of Food Science, 42,

113±116.

Kau�man, R. G., Wachholz, D., Henderson, D., & Lochner, J. V.

(1978). Journal of Animal Science, 46, 1236±1240.

Kemp, J. D., Fox, J. D., & Moody, W. G. (1974). Journal of Food

Science, 39, 972±976.

Lahucky, R., Marinova, P., Astruc, T., Vignon, X., & Monin, G.

(1996). In Proceedings of the International Congress of Meat Science

and Technology, 42, 50±51.

Ockerman, H. W., & Leon Crespo, F. (1982). Journal of Food Science,

47, 849±851, 857.

O�er, G. (1991). Meat Science, 30, 157±184.

O�er, G., & Knight, P. (1988). The structural basis of water-holding in

meat. Part 1: general principles and water uptake in meat proces-

sing. In R. Lawrie, Developments in Meat Science Ð Volume 4 (pp.

63±171). London: Elsevier Applied Science.

O�er, G., Knight, P., Jeacocke, R., Almond, R., Cousins, T., Elsey, J.,

Parsons, N., Sharp, A., Starr, R., & Purslow, P. (1989). Food

Microstructure, 8, 151±170.

O�er, G., & Trinick, J. (1983). Meat Science, 8, 245±281.

Park, J. W., Lanier, T. C., & Green, D. P. (1988). Journal of Food

Science, 53, 1±3.

Park, J. W., Lanier, T. C., & Pilkington, D. H. (1993). Journal of Food

Science, 58, 467±472.

Penny, I. F. (1967a). Journal of Food Technology, 2, 325±338.

Penny, I. F. (1967b). The Biochemical Journal, 104, 609±615.

Penny, I. F. (1969). Journal of Food Technology, 4, 269±273.

Reagan, J. O., Pirkle, S. L., Campion, D. R., & Carpenter, J. A.

(1981). Journal of Food Science, 46, 838±849.

Smith, D. M. (1987). Journal of Food Science, 52, 22±27.

Stabursvik, E., Fretheim, K., & Froystein, T. (1984). Journal of the

Science of Food and Agriculture, 35, 240±244.

Sung, S. K., Ito, T., & Fukazawa, T. (1976). Journal of Food Science,

41, 102±107.

Taylor, A. A., Dant, S. J., & French, J. W. L. (1973). Journal of Food

Technology, 8, 167±174.

Torley, P. J., & Lanier, T. C. (1992). Setting ability of salted beef/

pollock surimi mixtures. In E. G. Bligh, Seafood science and tech-

nology (pp. 305±316). Osney Mead, Oxford: Fishing News Books.

Townsend, W. E., Davis, C. E., Lyon, C. E., & Mescher, S. E. (1980).

Journal of Food Science, 45, 622±626.

Trout, G.R., Myler, S.V., Cassell, J.F., Dyson, S. & Reiser, P.D.

(1991) An evaluation of the quality of Australian pork. In Manip-

ulating pig production III (pp. 70). Australian Pig Science Associa-

tion, Attwood.

Trout, G. R., & Schmidt, G. R. (1984). Journal of Food Science, 49,

687±694.

Trout, G. R., & Schmidt, G. R. (1986a). Journal of Agriculture and

Food Chemistry, 34, 41±45.

Trout, G. R., & Schmidt, G. R. (1986b). Journal of Food Science, 51,

1416±1423.

Trout, G. R., & Schmidt, G. R. (1986c). Non-protein Additives. In A.

M. Pearson, Advances in Meat Science. Westport Ct: AVI Publish-

ing Co. (Chapter 8).

Trout, G. R., & Schmidt, G. R. (1978). Meat Science, 20, 129±147.

Van Hoof, J. (1975). In Proceedings of the European meat research

workers meeting (vol. 21) (pp. 35-37).

462 P.J. Torley et al. /Meat Science 55 (2000) 451±462