Group Title: Citrus Station mimeo report - Florida Citrus Experiment Station ; CES 66-6
Title: A colorimetric method for furfural as an index of flavor deterioration in canned citrus juices during storage
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00072438/00001
 Material Information
Title: A colorimetric method for furfural as an index of flavor deterioration in canned citrus juices during storage
Series Title: Citrus Station mimeo report
Physical Description: 5 leaves : ill. ; 28 cm.
Language: English
Creator: Blair, J. S
Maraulja, M. D
Olsen, R. W
Citrus Experiment Station (Lake Alfred, Fla.)
Florida Citrus Commission
Publisher: Florida Citrus Commission :
Citrus Experiment Station
Place of Publication: Lake Alfred FL
Publication Date: 1965
 Subjects
Subject: Canned orange juice -- Quality -- Florida   ( lcsh )
Orange juice -- Flavor and odor -- Florida   ( lcsh )
Citrus juices -- Quality -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: J.S. Blair and M.D. Maraulja and R.W. Olsen.
General Note: Caption title.
 Record Information
Bibliographic ID: UF00072438
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 76758424

Full Text


11-n
Florida Citrus Commission and
Citrus Experiment Station CES 66-6
Lake Alfred, Florida 400-10/12/65-MDM



A Colorimetric Method for Furfural as an Index of Flavor Deterioration in
Canned Citrus Juices during Storage

J. S. Blair and M. D. Maraulja
Florida Citrus Commission
and
R. W. Olsen
Florida Citrus Experiment Station
Lake Alfred, Florida


An investigation was begun in 1964 and continued in 1965 to develop a quan-
titative method that would correlated with the degree of off-flavor found in
canned citrus juices after storage. This study was based on the postulation by
Blair2 that the development of the polymerized compound, thiofurfural, was
mainly responsible for the "skunky-like" malodor and some of the off-flavors
found in canned citrus juices after storage under usual commercial conditions.
He also reported that when such a juice was distilled, the thiofurfural depoly-
merized and furfural was qualitatively detectable in the distillate. The pur-
poses of this paper are to (1) describe a quantitative method for the determi-
nation of furfural in distillates from canned citrus juices and (2) discuss
results obtained, using this colorimetric method, to determine the effect of
temperature and time of storage on the flavor of canned orange and grapefruit
juices.


Processing and Storage of Canned Citrus Juices

Canned Hamlin orange, Valencia orange and grapefruit juices were processed
and packed in a commercial plant during the 1963-64 citrus season. A sufficient
quantity of No. 2 cans of each of these packs was obtained immediately after
packing for use in this investigation and stored at 40, 500, 600, 70 and 800F.
at the Citrus Experiment Station.


Analytical Procedures

Preparation of Reagents

Benzidine dihydrochloride solution. This reagent must be prepared as
needed and should be used immediately since it deteriorates rapidly upon exposure
to light and room temperature. Preparation consists of dissolving 3.35 grams of
benzidine dihydrochloride in a mixture of 325 ml. of reagent grade anhydrous
methanol and 60 ml. of distilled water. The compound will completely dissolve
in about 3 minutes using a magnetic stirring apparatus. The reagent may be
stored in the dark at 00F. or lower for up to 3 hours for re-use.

Previously employed by the Research Division of the American Can Company,
Barrington, Illinois; partially employed during 1963-64 by the Florida Citrus
Commission following his retirement.
2
Blair, J. S. Thiofurfural as an important factor in the development of
off-flavor in canned orange juice during storage. Citrus Station Mimeo Report
CES 65-4, October 6, 1964.










Sodium acetate solutions. Two grams of citric acid monohydrate and 1.0
gram of sodium acetate are dissolved in a solution containing 250 ml. of glacial
acetic acid, 120 ml. of 4.0 N sodium hydroxide, and 20 ml. of distilled water.
The pH will be 3.5. This solution is then transferred to a glass-stoppered
bottle, stored at room temperature, and used as needed for addition to samples.

A second sodium acetate solution, approximately 0.2 M, is prepared for use
in making up furfural stock solutions. This is done by dissolving 27.2 grams
of dry sodium acetate in 850 ml. distilled water. The pH is adjusted to 4.6 with
15 ml. glacial acetic acid and the volume brought to 1 liter with distilled
water.

Preparation of furfural standard solutions. One gram of furfural is
weighed and transferred to a 100 ml. volumetric flask and brought to volume with
approximately 0.2 M sodium acetate solution having a pH of 4.6. This results
in a stock solution of 10,000 parts per million. Before using this solution it
is allowed to stand, under nitrogen and in a closed outer container to exclude
light, at 320F. for four days. Apparently, this solution is unstable for a short
time and, therefore, necessitates the storage conditions indicated. Ten milli-
liters of this solution is removed and diluted to 100 ml. again with 0.2 M sodium
acetate solution to provide a second stock solution of 1,000 parts per million.
Five to eight milliliters of this solution is then transferred to each of a number
of small screw-cap vials from which the air is excluded by flooding with nitrogen
before capping tightly. Both stock solutions are treated in a similar manner and
stored at 320F. Exposure to room temperature, air, or light repeatedly for short
periods of time causes deterioration of these solutions. At any time when it is
desired to make a standard curve, a vial of the 1,000 ppm solution may be removed
from storage, a standard furfural solution prepared, and the remainder of the
stock solution discarded. A standard furfural solution of 100 ppm or 100 micro-
grams per milliliter is prepared by diluting one milliliter of the 1,000 ppm
solution to 10 ml. with distilled water. More dilute furfural standards are pre-
pared by taking aliquots of 0.5, 1.0, 1.5, 2.0, and 3.0 ml. of the 100 ppm
solution and diluting these to 25 ml. with distilled water in 50 ml. Nessler
tubes. The furfural content of these standards ranges from 50 to 300 micrograms
in 25 ml.

Sample preparation. One liter of the canned single-strength citrus juice
is taken for analysis. If refrigerated, the temperature of the juice should be
adjusted to room temperature. With the use of a pH meter and magnetic stirring
apparatus, the pH of the juice sample is then adjusted to 5.8 + 0.1 with 4 N
sodium hydroxide solution and then transferred to a two liter boiling flask.
After the addition of 2 or 3 drops of Dow Corning anti-foam solution, the sample
is brought to boiling as quickly as possible using a "Ful-Kontrol" electric
heater set at full heating capacity. The condensate is passed through a water-
cooled spiral condenser and the cool distillate then passed through a standard
Clevenger oil-trap to remove peel oil. Fifty milliliters of the distillate are
collected and divided into two 25 ml. portions for testing.

Color measurement. The 25 ml. samples of distillates, furfural standards,
or distilled water used as a reagent blank must be in 50 ml. test tubes or
Nessler tubes. To each sample, 9 ml. + 0.2 of sodium acetate solution, pH 3.5,

Florida Citrus Commission and
Florida Citrus Experiment Station,
Lake Alfred, Florida. 400-10/12/65-MDM








is added using an automatic pipette. The tubes are then capped with polyethy-.
lene stoppers and the contents mixed by inverting them several times. Freshly
prepared benzidine dihydrochloride reagent is then added, using a small graduated
cylinder and adding 19 ml. + 0.1 to each sample. The tubes are again capped,
inverted and then placed in the dark at room temperature for color development.
The magenta or purplish-red color is light-sensitive and subject to some fading
if its development occurs even in moderate light. The final sample pH will be
between 3.9 and 4.1. This is the optimum pH range for color development. Above
pH 4.2 and below 3.8, the development of color will be incomplete. After 25
minutes the color is measured using a Photovolt, Model 450, Nessler Tube Colori-
meter, a 530 millimicron filter, and a 20 mm. inside diameter Nessler tube that
is graduated at one centimeter intervals of inside length. Only one of these
tubes is used for color measurement in the colorimeter and should be fitted at
the top with a pour spout. An 8.0 cm. light path is used in all light trans-
mittance measurements. Sample light transmittance readings are converted to
micrograms of furfural by referring to the furfural calibration curve. The two
values, resulting from the analysis of the two 25 ml. portions of distillate
from each juice, are added together. The resulting value represents micrograms
of furfural per 50 ml. of distillate.

The differences in calibration curves when using benzidine dihydrochloride
from different sources are shown in Table 1.


Table 1
Effect of benzidine dihydrochloride from
different sources on color development in
the benzidine test

% Light transmittance
Furfural Baker Fischer
micorgrams reagent reagent
50 78.0 83.0
100 55.0 59.0
150 37.0 41.0
200 26.5 29.0
300 14.0 13.0



The curve must be calibrated whenever the source is changed. To convert from
micrograms per 50 ml. distillate to micrograms per liter of juice, the value
per 50 ml. of distillate is multiplied by the factor 4.16. This factor was de-
rived by the analysis of 8 samples of canned Valencia orange juice varying in
furfural content from 62 micrograms to 552 micrograms per 50 ml. of distillate.

Table 2
Furfural content of canned Valencia orange juice after storage
Time and Furfural micrograms
temperature one liter 50 ml. of Conversion
of storage of juice distillate factor
3 mo. at 600F. 234 62 3.77
3 mo. at 700F. 466 110 4.24
6 mo. at 600F. 794 186 4.27
6 mo. at 700F. 926 218 4.25
3 mo. at 800F. 1052 244 4.31
4 mo. at 800F. 1428 336 4.25
5 mo. at 800F. 1870 450 4.16
6 mo. at 800F. 2268 552 4.11


Average
Conversion factor from curve


4.17
4.16









Following the first 50 ml., 6-100 ml. fractions of distillate from each of the 8
samples were also taken for analysis and the furfural content of all fractions
of distillate were totalled for each sample. The amount found in the first 50
ml. of distillate from each of the 8 samples of juice, containing different
amounts of furfural, was plotted against the total micrograms of furfural per
liter of juice. The result was a straight line which showed that the total
micrograms of furfural per liter of juice is 4.16 times that found in the first
50 ml. of distillate.


Results and Discussion

Results relative to the furfural content in distillates from canned citrus
juices, which had been stored at 400, 500, 600, 700, and 800F. over a period of
seven or eight months, are shown in Tables 3, 4, 5, and 6. Average flavor
grades, based upon the evaluation of these products by a taste panel, are also
listed in these tables. Samples for analysis were taken from storage at monthly
intervals.

As would be expected, deterioration of flavor of the canned citrus juices
increased as both the time and temperature of storage increased. The rate of
deterioration of flavor was greatest in the juices stored at 80F. Thereafter,
as the storage temperature decreased there was a very gradual increase in flavor
quality. The rate of deterioration of flavor was more rapid with increasing
storage time than it was when the storage temperature increased. Generally, the
furfural in the distillates from the stored juices increased with both increas-
ing storage time and temperature. Most important is the fact that the rate of
flavor deterioration is also indicated by the furfural values. For example,
after storage for 5 months at 40, 500, 600, 700, and 800F., the furfural in the
distillates from the canned Hamlin orange juice (Table 3) were 120, 205, 230,
270, and 945 micrograms/liter. Data obtained (Tables 3, 4, 5) show that the
furfural values also increase with increasing time of storage. Considering the
data obtained from this investigation, a storage temperature of 600F. should be
satisfactory to prolong the storage life of commercially packed canned orange
juice and canned grapefruit juice.

The effect on the flavor stability during storage of canned juices made
from different varieties of oranges is evident from the data in Table 6. When
average furfural values of 296, 481, 751, and 2898 micrograms per liter for
canned grapefruit juice are compared with average flavor grades of 7, 6, 5, and
4, it is evident that as the flavor deterioratYonrHesre is an increase in the
average furfural values. This relationship is also the same for canned Hamlin
and Valencia juices. However, the amount of furfural in the distillates from
the three different canned juices, stored under the same conditions, varied con-
siderably. Furfural values for the canned grapefruit juice were the highest and
averaged approximately two and three times as much as those for the Valencia
juice and Hamlin juice, respectively. Nevertheless, the rate of deterioration
of flavor is greater in canned Hamlin juice than in canned Valencia juice, both
of which have less flavor stability than canned grapefruit juice. This is
apparently true because of the better flavor in Valencia orange juice immediately
after canning than that in canned Hamlin juice. Also, grapefruit juice after
canning retains its typical flavor for longer storage periods than canned orange
juices.

Florida Citrus Commission and
Florida Citrus Experiment Station,
Lake Alfred, Florida. 400-10/12/65 MDM









Table 3. Effect of storage temperature and time on the flavor and furfural value of commercial canned
Hamlin orange juice

Storage temperature
800F. 700F. 600F. 500F. 400F.


Furfural
ig/liter

275
420
585
705
945
1185
1515


Average
flavor
grade

7-Good
6-Fair
6-Fair
5-Fair
5-Fair
5-Fair
4-Poor


Furfural
jg/liter

210
225
255
340
270
375
465


Average
flavor
grade

7-Good
6-Fair
6-Fair
5-Fair
5-Fair
6-Fair
5-Fair


Average
Furfural flavor Furfural
jg/liter grade pg/liter

135 7-Good 80
165 6-Fair 130
210 7-Good 170
360 5-Fair 240
230 5-Fair 205
245 5-Fair 190
490 5-Fair 225


Average
flavor
grade

7-Good
6-Fair
6-Fair
6-Fair
6-Fair
6-Fair
5-Fair


Furfural
pg/liter

120
135
130
140
120
105
75


Table 4. Effect of storage temperature and time on the flavor and furfural value of commercial canned
Valencia orange juice
Storage temperature
800F. 700F. 600F. 500F. 400F.
Storage Average Average Average Average Average
time- flavor Furfural flavor Furfural flavor Furfural flavor Furfural flavor Furfural
months grade ig/liter grade xug/liter grade pg/liter grade pg/liter grade ig/liter
1 6-Fair 425 6-Fair 245 6-Fair 150 7-Good 105 7-Good -
2 5-Fair 765 6-Fair 360 7-Good 260 7-Good 120 8-Good 105
3 5-Fair 1052 5-Fair 466 6-Fair 260 7-Good 125 7-Go6d 70
4 4-Poor 1428 5-Fair 540 6-Fair 285 6-Fair 150 6-Fair 100
5 4-Poor 1870 5-Fair 680 5-Fair 345 6-Fair 165 6-Fair 105
6 4-Poor 2268 5-Fair 926 5-Fair 794 6-Fair 200 6-Fair 105
7 3-Poor 2760 4-Poor 805 5-Fair 495 5-Fair 210 6-Fair 135
8 3-Poor 3450 4-Poor 1380 4-Poor 645 5-Fair 255 6-Fair 135


Storage
time
months

1
2
3
4
5
6
7


Average
flavor
grade

6-Fair
5-Fair
4-Poor
4-Poor
4-Poor
5-Fair
3-Poor







Table 5
Effect of storage temperature and time on the flavor and furfural value of commercial canned
grapefruit juice
Storage temperature
800F. 700F. 600F. 500F. 400F.


Storage Average


flavor
grade
6-Fair
5-Fair
5-Fair
4-Poor
4-Poor
4-Poor
3-Poor


Furfural
pg/liter
810
1335
1515
2310
2870
3866
4725


Average
flavor
grade
6-Fair
6-Fair
5-Fair
5-Fair
5-Fair
5-Fair
5-Fair


Furfural
pg/liter
465
540
810
840
985
960
1380


Average
flavor
grade
7-Good
6-Fair
6-Fair
5-Fair
4-Poor
5-Fair
5-Fair


Furfural
pg/liter
375
420
625
630
720
855
745


Average
flavor
grade
7-Good
5-Fair
5-Fair
5-Fair
6-Fair
5-Fair
5-Fair


Furfural
pg/liter
290
395
390
465
430
380
510


Average
flavor
grade
7-Good
6-Fair
6-Fair
5-Fair
6-Fair
7-Good
5-Fair


Table 6
Comparison of minimum, maximum, and average furfural values with average flavor grades for
commercial canned citrus juices after storage for different times and temperatures
Flavor grade 7-Good 6-Fair 5-Fair 3,4-Poor
Fruit Furfural-micrograms/liter
variety Min. Max. Av. Min. Max. Av. Min. Max. Av. Min. Max. Av.
Hamlin 80 210 143 105 275 178 75 1185 354 465 1515 843
Valencia 70 260 131 100 425 201 210 1052 593 645 2268 1826

Grapefruit 235 375 296 290 810 481 270 1515 751 720 4725 2898


Florida Citrus Commission and
Florida Citrus Experiment Station,
Lake Alfred, Florida. 400-10/12/65 MDM


time-
months
1
2
3
4
5
6
7


Furfural
pg/liter
235
290
395
300
355
285
270










Examination of the data presented in Tables 3, 4, 5, and 6 will show that
some irregularities are apparent between furfural values and storage times and
temperatures. Thus, the furfural values for canned Hamlin orange juice decreased
from 340 to 270 micrograms/liter when the storage time at 70F. increased from
4 to 5 months (Table 3). Canned Hamlin orange and canned grapefruit juices
stored at 50 and 60F., showed the most erratic differences between furfural
values (Tables 3 and 5). The relationship between furfural values and changes
in flavor of canned Valencia orange juice was the most consistent (Table 4).

For all three packs of juices, results showed more uniform increases in
furfural values at the higher storage temperatures of 700 and 800F. at which
temperatures the furfural levels were the highest. There is ample literature
describing the use of benzidine or other reagents to detect high furfural con-
centrations. However, no information could be found concerning the determi-
nation of low furfural levels, such as those found in canned citrus juices
after storage.

Since data from this study seemed to indicate that, in general, the benzi-
dine test is less sensitive at the lower concentrations of furfural, and effort
was made to increase the sensitivity of this test by changing the composition of
the benzidine reagent. Results obtained are shown in Table 7


Table 7
Effect of reagent composition on color development in the benzidine test
3.35g. Benzidinel 5.00g. Benzidine 5.00g. Benzidine
Furfural- 36 mg. Citric acid 36 mg. Citric acid 86 mg. Citric acid
micrograms 9.0ml. Na Ac solution 9.0ml. Na Ac solution 9.0ml. Na Ac solution
% Light transmittance
50 78.0 80.5 66.0
100 55.0 52.0 37.0
150 37.0 33.0 21.0
200 26.5 19.5 13.0
300 14.0 9.0 -

Composition of reagent used in this investigation.


Increasing the benzidine dihydrochloride to 5.0 g. in 325 ml. of methanol-
water solution deepened the magenta color but caused more line curvature
(Figure 1). Color development increased further and a straighter curve resulted
when the citric acid in the sodium acetate buffer was also increased from 36 to
86 mg. This degree of success indicates the possibility of improvement in the
sensitivity of this method.

Acknowledgments

The authors wish to thank Cypress Gardens Citrus Products, Inc., Winter
Haven, Florida, for providing the three packs of canned juices which were used
in this investigation.

The assistance of the tast panel members, which made possible the monthly
flavor evaluations of the canned orange and grapefruit juices included in this
report, were appreciated very much. Members of the taste panel were R. W. Olsen,
Roger Patrick, E. C. Hill, M. H. Dougherty, R. W. Barron, S. K. Long, Louise
Cherry, P. J. Fellers, F. W. Wenzel, and M. D. Maraulja.





EFFECT


OF REAGENT


ON CALIBRATION


COMPOSITION
CURVE


BENZID I NE
0 3.35 G
a 5.00 G
0 5.00 G


CITRIC
ACID
36MG
36 MG
86MG


HNoAc 49L
SOLUTION
9.0 ML
9.0 ML 25
9.0ML


[)
150-
0
O
100. o


50 z


PERCENT LIGHT TRAHSMITTANCE


FIG. I




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs