7/23/2019 Tangler t Pai Bul 1987

1/5

Rheological Properties of Tomato Concentrates as

Affected by Particle Size and Methods of Concentration

T. TANGLERTPAIBUL (nee SORNSRIVICHAI) and M. A. RAO

ABSTRACT

Shear ate-shear tressdata were obtainedon tomato concentrates

made rom juices that were produced sing inisher screen penings

(FSO): 0.020, 0.027, 0.033, and 0.045 in. In general, he apparent

viscosity of the concentrates t a shear ate of 100 set- increased

with increasen FSO. However,concentrates ade rom uice using

a 0.027 in FSO had the highest apparent iscosity. Magnitudes f

yield stressof concentratesncreasedn direct proportion o FSO.

Apparent iscosities f concentrates adeby evaporatingomatouice

were ower han hoseobtained itherby evaporatinghe serumor by

reverseosmosis oncentration f the serum.

INTRODUCTION

THERE IS a considerable volume of literature in which the

viscosity or consistency characteristics or other physical prop-

erties of tomato juice and concentrates have been related to

processsingconditions (Kertesz and Loconti, 1944; McColloch

et al., 1950; Davis et al., 1954; Whittenberger and Nutting,

1957, 19.58;Kopelmann and Mannheim, 1964; Mannheim and

Kopelmann, 1964). In most cases, however, the viscosities or

consistencies reported were the results of single-point mea-

surements; hat is, a single viscosity or consistometer ime was

given for each sample. Few studies have taken the non-New-

tonian nature of tomato concentrates nto consideration.

The Bostwick consistometer values of tomat o concentrates

are related to the insoluble soli ds by an exponential relationship

(Marsh et al., 1977) that become very small (

7/23/2019 Tangler t Pai Bul 1987

2/5

EFFECT OF PROCESSING ON TOMATO VISCOSITY. .

evaporated tomato serum, and (3) from serum that was con-

centrated by reverse osmosis.

MATERIALS & METHODS

Preparation of tomato juice

One hundred sixty kilograms of fresh tomatoes, cultivar FM6203,

were hand-picked from commercial fields in Erie county, Ne w York,

stored in a 21.1C room overnight and processed in the Experiment

Stations pilot plant. The tomatoes were sorted, washed, and crushed

in a hammer mill (W.J. Fitzpatrick Co., Chicago, IL) and the ma-

cerate was heated immediately in a steam-jacketed kettle to 98C. The

time interval between crushing the tomatoes and for the macerate to

reach 98C was approximately 1-2 min. The macerate was held at

98C for 4 min and 5 set as calculated using a z-value of 8.33C

(Nelson and TressleT, 1980), and using t, of 45 set at 103.9C (Bim-

baum et al., 1977). The macerate was transferred to a finisher (fab-

ricated in the Dept. of Food Science & Technology) that was operated

at 1000 pm and with various screen openings (FSO): 0.020, 0.027,

0.033, and 0.045 in. (or 0.508, 0.686, 0.838, and 1.143 mm, re-

spectively). Juice from the finisher was boiled in a steam-jacketed

kettle and hot-filled into No. 303 cans. The cans were sealed, rolled

for 3 min, and spin cooled in cold water. They were stored in a

- 3.9C room until experimentation. Seventy-six cans of tomato juice

from 0.033 in. screen and two cans each of the juice from 0.027 and

0.045 in. screens were produced.

Preparation of tomato concentrates by evaporation of juice (JE)

Lots of juice fr om the finisher equipped with different FSO were

transferred to a steam-jacketed vacuum kettle described in detail by

Saravacos and Moyer (1967). The kettle was operated at 132.4 kPa

(26-27 in. vacuum). The concentrates from 0.033 in screen were

taken out periodically at the approximate total solids (T.S.) of 10, 15,

20, 25, and 28%; in addition, a sample with the highest concentration

of about 30% T.S. was obtained. Other concentrates, f rom 0.020,

0.027, and 0.045 in. screens, were taken when the concentrations

were about 30% T.S. The tomato concentrates were canned and

stored as described for the juice.

Preparation of tomato concentrates by evaporation of serum

(SE)

Canned tomato juice from 0.033 in. screen described earlier was

centrifuged at 11,700 X g at 20C for 45 min (Sorvall RC-5, Ivan

Sorvall, Inc., Norwalk, CT), and the volume of serum was measured

and transferred to a beaker. The pulp was scraped from the centrifuge

tubes and transferred into a plastic bottle and stored in a refrigerator.

The serum was concentrated in a steam-jacketed kettle to various

Brix. When the concentrated serum was cooled to room temperature,

it was proportionally combined with the separated pulp to obtain con-

centrates (150 mL) of 10, 12, 14, 16, 18, 22, and 28 Brix.

A 25 Brix serum concentrate was prepared to study the effect of

heat applied to serum on the rheological properties of the reconstituted

concentrates. It was diluted with distilled water to obtain serum sam-

ples at 22, 20, 18, 16, 14, 12, and IO Brix. The diluted serum

samples were proportionally combined with the separated pulp to ob-

tain 100 mL samples of concentrates. All SE concentrates were al-

lowed to rehydrate overnight in the refrigerator. The portions of the

concentrates that were not used on the next day were stored at -3.9C.

Preparation of tomato concentrates by reverse osmosis

concentration of serum (SRO)

Serum and puip were separated from canned tomato juice in the

manner described for SE concentrates. Instead of evaporation, reverse

osmosis was used to concentrate the serum using a cellulose acetate

membranetype S-97 CAB) (Osmonics, nc., Minnetonka,MN) in a

batch type reverse osmosis unit with a volumetric capacity of 200 mL

at 63.1 MPa (900 psig) (Abcor Inc., Cambridge, MA). Continuous

agitation of the serum above the membrane surface was provided by

means of a magnetic stirrer. The concentrated serum was collected

periodically at various Brix and then proportionally combined with

the separated pulp. The SRO concentrates were allowed to rehydrate

in the refrigerator overnight before use in experiments. Portions of

the concentrates that were not used in the experiment on the next day

were stored at - 3.9C.

Natural tomato soluble solids determination

An A0 AB BE Refractometer (American Optical Corp., Buffalo,

NY) was used to determine the natural tomato soluble solids (NTSS)

in Brix. In the case of a very concentrated samples, only its serum

portion was used for NTSS determination because the presence of the

pulp in large amounts obscured the reading.

Total solids determination

A sample was weighed in an aluminum pan and dried in a vacuum

oven (Central Scientific Co., Chicago, IL) operated at 2l.lC (70F),

64.9 kPa (28 in. vacuum) for 48 hr. The dry sample was cooled in a

desiccator for at least 2 hr before its weight was measured.

Determination of particle size distribution

The wet sieving technique proposed by Kimball and Kertesz (1952)

was employed to determined weighted average diameter of particles

in tomato juice and concentrate samples. A set of five U.S.A. Sian-

dard sieve series (Newark Wire Cloth Co., Newark, NJ) with 20, 40,

60, and 100, and 140 mesh openings were used. For the particles

retained on the sieve with the largest openings, the average effective

particle size (diameter) was assumed to be 50% over the diameter of

the openings. For particles which passed through one sieve but not

the next one, an average effective particle diameter half way between

the diameters of the openings of the two sieves was assumed. All

experiments were replicated and the weighted average diameters of

the particles were calculated.

Rheological measurements

Flow properties of the concentrates were determined with a con-

centric cylinder viscometer (Haake RV2, Haake Inc., Saddle Brook,

NJ) as described earlier (Vitali and Rao, 1984) at five temperatures:

lo, 25, 40, 55, and 70C for the concentrates processed from FSO

of 0.045, and 0.033, and 0.027 in. For concentrates fr om 0.020 in.

screen, whose rheological behavior was determined first, the temper-

atures employed were 5, 15, 25, 35, and 45C. Yield stress of

samples was determined using the relaxation technique described by

Van Wazer et al. (1963).

RESULTS & DISCUSSION

Rheological properties of tomato concentrates and tomato

juice

Flow curves consisting of log shear ate (y ) against og shear

stress (7) of tomato concentrates rom the three different con-

centration processes and from the four different screen sizes,

as well as concentrated serum, showed power-law behavior.

T = Ky

(1)

Linear regression analysis was performed on the data resulting

in values of slopes (n), intercepts (K), and correlation coeffi-

cients. The correlation coefficients were in the range 0.97 to

1.00. The flow behavior index n of the tomato concentrates

was found to vary from 0.266 to 0.444. With values of n being

less than 1, tomato concentrates are shear thinning fluids. The

flow behavior index showed no definite trends with concen-

tration, temperature, or methods of concentration in accord-

ance with the findings by Harper and El Sahrigi (1965) and

Rao et al. (1981). Using magnitudes of K and n, apparent

viscosities of the concentrates were calculated from the rela-

tionship:

~)a,100 K (loo)- (2)

Effect of temperature. The effect of temperature on the

apparent viscosity of the concentrates at 100 set- was de-

scribed well by the Arrhenius relationship:

WOO = v= exp WRT) (3)

Magnitudes of the activation energy (E,) of the concentrates

ranged from 2.0 to 3.0 kcallmole and were within the range

of values reported by others (Harper and El Sahrigi, 1965; Rao

et al., 1981).

142-JOURNAL OF FOOD SCIENCE- Volume 52, No. 1, 1987

7/23/2019 Tangler t Pai Bul 1987

3/5

Effect of concentration. The relationships between appar-

ent viscosity and concentration were of the power type. The

exponents did not vary much with either screen sizes or tem-

peratures (Table 1). At 25X, for all screen sizes the exponent

of the power relationship was 2.24 with a correlation coeffi-

cient of 0.954; this magnitude is in the range of values: 2.5

and 2.0 reported by Rao et al. (1981) and Harper and El Sabrigi

(1965), respectively.

Effect of screen size

Shear rate-shear stress data of a 20% T.S., JE concentrate

are shown in Fig. 1. From the data, it can be ascertained hat

in general smaller FSO (theoretically smaller particle size dis-

tribution) yielded lower apparent viscosities. However, the

concentrates from 0.027 in. screen had the highest apparent

viscosity among the four screen sizes. Similar results were

obtained for tomato uice (Somsrivichai, 1986). It is interesting

to note that particle size distributions of samples from 0.027

in. and 0.045 in. screens were similar to each other on one

hand (Fig. 2) and those using 0.020 in and 0.033 in. were

similar to each other on the other hand (Fig. 3).

The observed influence of screen size may be explained in

that small screens reduce the size of the particles. However,

at the same time t hey remove some of the large particles from

the finished products resulting in t omato concentrateswith nar-

row particle size distribution and a small amount of large par-

ticles. Based on theories of suspension heology (Jinescu, 1974),

small suspendedparticles may give high viscosity due to their

greater surface area. Large particles contribute to high viscos-

ity also. Therefore, small screen sizes can affect the gross

viscosity of tomato concentrates n two opposite manners: one

is enhancing gross viscosity due to l arge surface area of small

particles and the other one is diminishing the gross viscosity

due to the exclusion of large particles. Screen size of 0.020 in

may produce tomato concentrates with too small particle size

distribution and very small amount of large particles resulting

in small magnitude of viscosity while 0.027 in. screen may

produce small particles as well as allow some of the large

particles to be in the tomato concentrates. t may be that using

0.027 in. screen resulted in tomato uice and concentrateswith

appropriate particle sizes which yielded the highest viscosity.

Effect of methods of concentration

Effect of methods of concentration on qloo of tomato con-

centrates with 16% T.S. from three different processes: uice-

evaporation, serum-evaporation, and serum-reverse osmosis,

can be seen n Fig. 4. At low concentrations, apparent viscos-

ities of SRO and SE concentrates were not significantly dif-

ferent At higher concentrations, concentrates from serum-

evaporation were exposed to heat for longer periods of time,

therefore, their apparent viscosities were less than that of con-

centrates rom serum-reverseosmosis. Nevertheless, both SRO

and SE concentrates showed higher apparent viscosities than

that of JE concentrates at the same concentrations.

From data in Fig. 4 it appears that concentrating tomato

serum by means of evaporation or reverse osmosis does not

have significant effect on apparent viscosity of reconstituted

concentrates with unheated pulp. When heat is applied to the

whole tomato uice, both serum and pulp are subjected o heat.

Structure of pulp may be affected by heat. Particle sizes or

volume of the pulp may be reduced during the heat treatment.

Moreover, concentrating tomato juice and tomato serum by

heating to the same Brix requires different heating time be-

cause tomato juice has lower heat transfer coefficient than the

serum (Kopelman and Mannheim, 1964).

Kopelman and Mannheim (1964) found that SE concentrates

had much lower viscosity than JE concentrates. They con-

cluded that lower consistency in SE may be attributed to the

centrifugation during serum separation (which was not speci-

fied in their publication) which led to crushing of the cells and

the disruption of the solid suspension structure of the juice.

However, their tomato concentrates were made by cold break

method (60C). Pectic enzymes may still have been active in

the concentrates resulting in subsequent oss of consistency.

Effect of heat in concentration step. It has been known

for a number of years hat when tomato concentratesare diluted

to lower concentration, the diluted products have lower vis-

cosity than if they are concentrated straight from the juice. In

the present study, this effect was first observed for a JE con-

centrate. Figure 5 contains the apparent viscosities of two 16%

T.S. JE tomato concentrates: one prepared by straight concen-

tration of juice and the other by dilution of a concentrate with

41% total solids. It is clearly seen hat the straight concentrate

had higher apparent viscosity than the diluted concentrate.

Figure 6 shows that SE tomato concentrates prepared from

dilution also have lower apparent viscosity than the straight

concentrates. In this case, only the serum experienced heat.

Structure of the pulp should be the same n both concentrates,

diluted and straight, only the nature of the serum was different.

Heat alters the structure of pectic substancesby means of hy-

drolysis. Colloidal properties of serum may be altered by heat

resulting in l ower apparent viscosity of reconstituted tomato

concentrates with unheated pulp. In this respect, Caradec and

Nelson, (1985) reported that viscosity of tomato juice serum

decreasedwith heat treatment. The observation of Caradec and

Nelson (1985) is i n agreement with the present results in that

heat treatment reduces the viscosity of serum and juice.

Marsh et al. (1977) found that pulp lost bound water as a

result of the physical forces that developed as concentration

progressed and the loss altered their ability to i nfluence con-

sistency. Therefore, water removal by means of evaporation

may irreversibly affect the rheological properties of the final

products.

Labuza (1977) suggested that the apparent loss of consis-

tency or viscosity was most likely due to the failure of the

macromolecular polymeric substances, comprising the water

insoluble solids, to resorb to their maximum extent. Pectic

substancesand other long-chair carbohydrate polymers can be

hydrolyzed by heat (Kertesz, 1951) resulting in smaller mol-

ecules. Colloidal properties exhibited by pectic substancesare

changed. Cell wall materials become less rigid and smaller in

size when heat is applied.

Yield stresses of tomato concentrates

Yield stressesof tomato concentrates rom juice evaporation

process using four FSO were determined over the concentra-

Table l-Slope of the plot in (q,& versus In (total solids) of tomato concent rates from different processes

Screen

Temperature (C)

size

Process

(in.) 5 10 15 25 35

40 45 55 70

Juice evaporation

0.020 2.29 - 2.63 2.64 2.82

- 2.85 - -

Juice evaporation

0.027 - 2.55 - 2.46 -

2.50 - 2.64 2.82

Juice evaporation

0.033 - 2.86 - 2.94 -

2.91 3.08 2.97

Juice evaporation

0.045 - 2.77 - 2.80 -

2.77 q 2.84

3.16

Serum evaporation

0.033 - - - 2.36 -

- - - -

Serum reverse osmosis

0.033 - - - 2.82 -

- - - -

alq~ is apparent viscosity at a shear rate of 100 x-1.

Volume 52, ho. 1, 1987-JOURNAL OF FOOD SCIENCE-143

7/23/2019 Tangler t Pai Bul 1987

4/5

EFFECT OF PROCESSING ON TOMATO VISCOSITY. .

JE Concentrates, 20 XT.S., 25 C

* 0.020 in. screen

0.027

.5 0

A

0.033

c

E

\

z

5 -

c

3

4.5 -

t

41 ) I I I

4 4.5

5 5.5 6

6.5 7

Ln (f. xc-)

Fig. l-Shear rate ( -shear stress (T) data at 25 C of 20% juice

evaporated (JE) concentrates that were made using tomato juices

from different finisher screens.

Tomato Juice Solids

8 high value= 160 ,,

8

0 Screen ize

1.143mm

0

High or Low Value

2

p 60

,a

1C 40

20

40

SiefL Size

100

Fig. 2-Volume of pulp retained on sieves for juice samples

from finisher screens of 0.027 in. (0.686 mm) and 0.045 in. (1.143

mm).

tion range 9 to 14%. These concentrations were selected in

order that t he most sensitive torque measuring head (50 g-cm)

of the viscometer could be used. Their magnitudes, shown in

Fig. 7, depend on total solids of the concentrates as well as

on FSO. Regression analysis of concentration versus In of yield

stress resulted in quadratic equations as found earlier by (Rao

et al., 1981). The use of l arger finisher screens resulted in

concentrates with higher yield stress. Also, as total solids of

the concentrates increased, the magnitude of yield stress in-

creased.

When values of yield stress are determined for a fluid, an-

other flow model containing the yield stress erm, such as that

of Herschel-Bulkley (Eq. 4), must be employed to fit the vis-

cometric data.

T = TOH + KH 9

(4)

In Eq. (4), 7 is the shear stress, i, is the shear rate, r0H is the

yield stress, KH is the consistency index, and nH is the Bow

behavior index.

It should be pointed out that magnitudes of rheoiogical param-

eters obtained from this analysis in which yield stress was

included will be somewhat different f rom t he analysis based

Tomato Juice Solids

0 ScreenSize 0.508mm

a

80

E

60

8

+- - High or Low Value

0 ScreenSize 0.838mm

8 - High or Low Value

SiZCeSize

100

1

Fig. 3-Volume of pulp retained on sieves for juice samples

from finisher screens of 0.020 in. (0.508 mm) and 0.033 in. (0.838

mm).

0.2

z-

E

-0.3

\

m

z

* SE Concentrate, 16.62 XT.S.

0 JE Concentrate. 15.98 2T.S.

-1.3

0.0028

0.00305 0.0033 0.00355 0.0038

l/T (K)

Fig. 4-Apparent viscosity at 100 set- (q,& as a function of

temperature of 16% concentrates made by evaporation of juice,

evaporation of serum, and reverse osmosis concentration of

serum.

-0.2

Q Diluted Concentrate

0 Straight Concentrate

P

q

::

0.0028

0.0029 0.003

0.0031 0.0032

0.0033

0.0034

l/T (K)

Fig. &Apparent viscosity at 700 set- (q,& as a function of

temperature of straight and diluted, 15% total solids, juice evap-

orated concentrates, from 0.033 in. screen.

on the simple power law model (Eq. 1). However, apparent

viscosities will be the same in both analyses, only the flow

144-JOURNAL OF FOOD SCIENCE-Volume 52, No. 1, 7987

7/23/2019 Tangler t Pai Bul 1987

5/5

2.2 2.45

2.7

2.95

3.2

Ln (Concentration. 2T.S.)

Fig. (T-Plot of In concentration (% total solids) versus In appar-

ent viscosity (Pa.s) at 25 C of serum evaporated straight and

diluted concentrates from 0.033 in. screen.

4

I

* 0.020 in. screen

3.5 -

0 0.027

n 0.033

3 - 0.045- 0

E

\

z

_ 2.5 -

L

:

2 -

1.5 -

1

I

I

I

I

9

10 11

12 13 14

Concentration (5T.S.)

Fig. 7-Yield stress (NlmZ) of juice evaporated (JE) tomato con-

centrates from different finisher screens as a function of con-

centration (% total solids).

behavior index, n, and the consistency ndex, K, will be dif-

ferent.

REFERENCES

Birnba um, D.G., Leonard, S., Heil, J.R., Buhlert, J.E., Wolcott, T.K., and

Ansar, A. 1977. Microbial activity in heated and unheated tomato serum

concentrates. J. Food Proc. Preserv. 1: 103.

Caradee, P.L. and Nelson, P.E. 1985. Effect of temperature on the serum

viscosity of tomato juice. J. Food sci. 50: 1497.

Casson,N. 1959. A flow equation for pigment-oil sus ensions of the print-

ing ink type. In Rheology of Disperse Systems,

EC. Mill (Ed.), p. 82.

Pergamon Press, New York.

Charm, S.E. 1962. The nature of role of fluid consistency in food engi-

neermg applications. Adv. Food Res. 11: 356.

Davis, R.B., DeWeese,D., and Gould, W.A. 1954. Consistency measure-

ments of tomato puree. Food Technol. 8: 330.

Dzuy, N.Q. and Boger, D.V. 1983. Yield stress measurement for concen-

trated suspensions. . Rheologgy 27(4): 321.

Hand, D.B., Moyer, J.C., Ransford, J.R., Hening, J.C. and Whittenberger,

R.T. 1955. Effect of processing onditions on the viscosity of tomato uices.

Food Technol. 9: 228.

Harper, J.C. and El Sahrigi, A.F. 1965. Viscometric behavior of tomato

concentrates. J. Food Sci. 30: 470.

Herschel, W.H. and Bulkley, R. 1926. Measurement of consistency as ap-

plied to rubber-benzenesolutions. Proc. Am. Sot. Test. Mater. 26(H): 621.

Jinescu, V.V. 1974. The rheology of suspensions. nt. Chem. Eng. 14(3):

397.

Kattan, A.A., Ogle, W.L., and Kramer, A. 1956. Effect of processvariables

on quality of canned tomato juice. Proc. Am. Sot. Hort. Sci. 68: 470.

Kertesz, Z.I. 1951. The Pectic Substances. nterscience Publishers, Inc.,

New York.

Kertesz, Z.I. and Loconti, J.D. 1944. Factors determinin the consistency

of commercial canned tomato juice. NYSAES Tech. Bu

K

. 272.

Kimball, L.B. and Kertesz, Z.I. 1952. Practical determination of size dis-

tribution of suspended particles in macerated tomato products. Food

Technol. 6: 68.

Kopelman, I.J. and Mannheim, H.C. 1964. Evaluation of two methods of

tomato juice concentration. I. Heat-transfer coefficients. Food Technol.

18: 907.

Labuza, T.P. 1977. The pro

B

erties of water in relationship to water binding

in foods: Review. J. Foo Proc. Preserv. 1: 167.

Luh, B.S., Dempsey, W.H., and Leonard, S. 1954. Consistency of pastes

;a:, puree from Pearson and San Marzano Tomatoes. Food Technol. 8:

Luh, B.S., Leonard, S.J., and Phaff, H.J. 1956. Hydrolysis of pectic mate-

rials and oligouronides by tomato polygalacturonase. Food Res. 21: 448.

Mannheim, H.C. and Ko elman, I.J. 1964. Evaluation of two methods of

juice concentration. II. K roduct evaluation. Food Technol. 18: 911.

Marsh, G.L., Buhlert, J., and Leonard, S. 1977. Effect of degree of concen-

tration and of heat treatment on consistency of tomato pastes after di-

lution. J. Food Proc. Preserv. 1: 340.

McColloch, R.J., Nielson, B.W., and Beavens, E.A. 1950. Factors influenc-

ing the uality of tomato paste. II. Pectic changes during processing.

Food Tee nol. 4: 339.

Mizrahi, S. and Berk, Z. 1972. Flow behavior of concentrated orange uice:

Mathematical treatment. J. Text. Studies 3: 69.

Nelson, P.E. and Tressler, D.K. 1986. Tomato uice and tomato uice blends.

In Fruit and Vegetable Juice Processing Technology, Ch. 12, 3 rd ed.,

AVI Publishing Company, Westport, CT.

Rao, M.A., Bourne, M.C., and Cooley, H.J. 1981. Flow properties of t omato

concentrates. J. Text. Studies 12: 521.

Rao, M.A. and Cooley, H.J. 1983. Applicability of flow models with yield

for tomato concentrates. J. Food Proc. Eng. 6: 159.

Robinson, W.B., Kimball, L.B., Ransford, J.R., Moyer, J.C., and Hand, D.B.

1956. Factors influencmg the degree of settling m tomato juice. Fo od

Technol. 10: 109.

Saravacos,G.D. and Moyer, J.C. 1967. Heating rates of fruit products in

an agitated kettle. Food Technol. 21: 372.

Smit, C.J.B. and Nortje, B.K. 1958. Observation on the consistency of to-

mato paste. Food Technol. 12: 356.

Sornsrivichai, T. 1986. A study on rheological properties of tomato con-

centrates as affected by concentration methods, processing conditions

and pulp content. Ph.D. thesis, Cornell Univ., Ithaca, NY.

Surak, J.G., Matthhews, R.F., Wang. V., Padua, H.A., and Hamilton, R.M.

1979. Particle size distribution of commercial tomato juices, Proc. Fla.

Stats Hort. Sot. 92: 159.

Tanford, C. 1961. Physical Chemistry of Macromolecules. John Wiley,

New York.

Van Wazer, J.R., Lyons, J.W., Kim, K.Y., and Colwell, R.E. 1963. Vis-

cosity and Flow Measurement. A Laboratory Handbook of Rheology.

Interscience Pub., New York.

Vitali, A.A. and Rao, M.A. 1984. Flow

orange uice: Serum viscosity and e p

roperties of low-pul

ect of pulp content. B

concentrated

Food Sci. 49:

676.

Whittenberger , R.T. and Nutting, G.C. 1957. Effect of tomat o cell struc-

tures on consistency of tomato juice. Food Technol. 11: 19.

Whittenberger, R.T. and Nutting, G.C. 1958. High viscosity of cell wall

suspensionsprepared from t omato juice. Food Technol. 12: 420.

Ms. received 4118186;evised 8/22/86; accepted8/22/86.

Oneof us (TS)was he recipient f a scholarshiprom he AnandhaMahidolFoun-

dation, Bangkok, hailand.

his work also was supported by funds from the

Hatch

act.

Based on a paper presented at the 46th Annual Meeting of the Institute of Food

Technologists, June 15-18, Dallas, TX.

Volume 52, No. 1, 1987-JOURNAL OF FOOD SCIENCE-145