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Proc. Fla. State Hart. Soc. 111:251-255. 1998.
WAX MICROEMULSION FORMULATIONS USED AS FRUIT COATINGS
Robert D. Hagenmaier
U.S. Citrus and Subtropical Products Laboratory
USDA, ARS, SAA
P.O. Box 1909
Winter Haven, FL 33883-1909
e-mail: RHagenmr@concentric.net
Additional index words. Edible coatings, 'Hamlin' oranges,
'Sunburst' tangerines.
Abstract. Wax microemulsions were made with three emulsifi-
cation techniques. Formulations are presented for making an-
ionic microemulsions with carnauba wax, candelilla wax,
oxidized polyethylene, beeswax, paraffin, montan wax and var
ious hydrocarbon waxes, and also for making nonionic micro
emulsions with squalene, hydrocarbon waxes and rice bran
wax. Citrus fruit were coated with various mixtures of a wax
emulsion and rosin. Those coatings with higher percentage
wax had lower internal CO2 and higher O2.
In recent years we have evaluated the performance of var
ious wax microemulsions as food and fruit coatings (Hagen
maier and Baker, 1993, 1994a, 194b, 1996, 1997). In the
course of those studies, more than 600 microemulsions were
made in our laboratory, in attempts to develop better coat
ings. In our published studies <10% of the microemulsions
were used, as there was insufficient time to thoroughly evalu
ate all of those made. Here now is a summary of all formula
tions, not just the 10% included in our publications.
Why were so many different formulations made? First, in
the course of work on coatings it became evident that the per
formance of any particular wax as a coating depended consid
erably on the quality of the emulsions and also the presence
of minor ingredients in the formula. Thus, a conclusion
about the potential as edible coating of any given wax would
seem to require the testing of a number of different formula
tions. Secondly, in order to make progress in developing wax
coatings, it was considered necessary to know the composi
tion of any coatings used. In early work, the wax microemul
sions evaluated in our laboratory were samples received from
suppliers whose formulations were proprietary information.
We found that much trial and error was involved in arriving
at suitable formulations, which resulted in many trials. In gen
eral, little information on wax microemulsion formulations
was found in the literature (Bennett, 1975), especially formu
lations whose ingredients were restricted to those approved
for use in foods.
The purpose here is to make available the techniques and
ingredients used in our laboratory to make wax microemul
sions, in order to make it easier for others to make and test
these, particularly for use as food and fruit coatings.
South Atlantic Area, Agricultural Research Service, U.S. Department of
Agriculture. Mention of a trademark or proprietary product is for identifica
tion only and does not imply a guarantee or warranty of the product by the
U.S. Department of Agriculture. The U.S. Department of Agriculture prohib
its discrimination in all its programs and activities on the basis of race, color,
national origin, gender, religion, age, disability, political beliefs, sexual ori
entation, and marital or family status.
Materials and Methods
Polyethylene waxes E10 and E20 were from Eastman
Chemical (Kingsport, TN); AC629, AC680, AC673 and AC316
were from Allied Signal Inc. (Morristown, NJ); and PED121
was from Clariant Corp. (Charlotte, NC). FDA approval for
polyethylene wax (oxidized polyethylene) is given in 21 CFR
172.260 (FDA, 1995). The candelilla wax (21 CFR 184.1976)
was bleached (No. 75 from Strahl & Pitsch Inc., W. Babylon,
NY, type cbw2 from Berial, S. A., Mexico D. F., or No. 7808
from Botanical Wax, Arlington Heights, IL) or unbleached
'filtrada' from Berial, S. A. The beeswax (21 CFR 184.1973)
was from Koster Keunen Inc. (Sayville, NY). The rice bran
wax (21 CFR 172.890) was from Strahl & Pitsch or Koster Ke
unen Inc. Yellow No. 3 and No. 1 carnauba wax (21 CFR
184.1978) were from Strahl & Pitsch Inc. The petroleum wax
(21 CFR 172.88 and 178.3710) with 61°C m.p., was Parvan
4450 from Exxon (Houston, TX). The paraffin wax (CFR
178.3710) type 126, also with 61°C m.p., was from Koster Ke
unen Inc. Rosin modified maleic wood resin (21 CFR
172.210) was type 807Afrom Resinall Corp. (Stamford, CT).
Hydrogenated wood rosin (21 CFR 172.210) was Foral AX
from Hercules Inc., (Wilmington, DE). The montan wax (21
CFR 172.210) was type KPS from Clariant Corp. Hydrocarbon
waxes Polywax 500 (21 CFR 172.888) and Be Squarel95 (21
CFR 172.886) were from Petrolite Corp. (Tulsa, OK). The
oleic acid (21 CFR 172.860) was Emersol 6321, from Henkel
Corp. (Cincinnati, OH). The myristic acid was Hystrene 9014
from Witco Corp. (Memphis, TN) and Emery 655 from Hen
kel Corp. Mineral oil (21 CFR 172.878z) was from Squibb 8c
Sons (Princeton, NJ) and petrolatum jelly (21 CFR 172.880)
was from Albertson's (Boise, ID). The surfactants were sorbi-
tan monostearate (21 CFR 172.842), Capmul S from Abitec
Corp. (Janesville, WI) or Durtan 60 from Durkee Industrial
Foods (Cleveland, OH). Glycerol mono/di-oleate (21
CFR182.4505,GRAS) was GMO-Kfrom Abitec Corp. Polysor-
bate 60 (21 CFR 172.836) was Capmul POE-S from Abitec
Corp. or Tween 60Kfrom ICI Surfactants (Wilmington, DE)
Microemulsions were made by three methods. For the wa
ter-to-wax method, the wax and other ingredients (less the
water) were heated 10-20°C above the melting point of the
wax, hot water (95-100°) slowly added with stirring, and the
mixture cooled to 50°C in a water bath, with stirring. For the
wax-to-water method the same molten wax mixture was
poured into the vortex of hot water being rapidly stirred in a
beaker, and the mixture cooled in the same manner. For the
pressure method, which is similar to the water-to-wax method,
the unmelted wax, together with part of water (the initial wa
ter) was placed in a 2-liter pressure cell (Parr Instrument Co.,
Moline, IL), heated to approximately 10-30°C above the melt
ing point of the wax, hot water forced into the cell with a
pump (Haskel Inc., Burbank, CA) and the emulsion cooled
to 50°C. For all three methods the total amount of water in
corporated was that required to make an emulsion contain
ing 60-80% water.
The quality of the emulsions was evaluated by appearance
and performance. Appearance was primarily evaluated by
measurement of turbidity with the Ratio/XR turbidimeter
Proc. Fla. StateHort. Soc. Ill: 1998. 251
(Hach Co., Loveland, CO). This measures turbidity over the
range 0-2000 nephelometric turbidity units (NTU). In addi
tion, the amount of cream that separated by gravity was ob
served after storage at about 25°C for at least one week.
For measurement of gloss, the emulsions were dried on
polystyrene weigh boats (0.5 g on an area of 25 cm2) or ap
plied to apples or citrus (0.3 ml per fruit). Gloss was evaluated
by panel or by measurement of gloss units (G.U.) with a re
flectance meter (micro-TRI-gloss, BYK Gardner Inc., Silver
Spring, MD). Tendency of coatings to 'fracture' was deter
mined subjectively after hitting and rubbing together two
pieces of fruit, then wiping the contact surfaces with a black
cloth, and rating the amount of coating found on the cloth
(1.0 = none; 2.0 = minimal; 3.0 = significant but acceptable;
4.0 = heavy and unacceptable; and 5.0 = virtually all coating
removed).
The coatings applied to citrus fruit consisted of mixtures
of a wax microemulsion made of various mixtures of a wax
emulsion and a wood rosin solution. The wax microemulsion
contained 7.6% carnauba No. 3, 8.2% E20, 0.8% Foral AX
and 4.5% morpholine and the balance water. The rosin solu
tion contained 16.4% Resinall 807A, 4.6% oleic acid, 8.8%
morpholine and the balance water. The five coatings used
consisted of 0, 5, 15, 30 and 100% of the rosin solution and
the balance wax microemulsion. The coated fruit were stored
7 days at 21°C. Internal gases and air flux were measured (10
fruit per treatment). Air flux is the amount of air passing
through the peel at an applied pressure of 0.08 atmosphere
(Hagenmaier and Baker, 1993).
Samples of internal gases for internal O2 and CO2 analyses
(ten fruit per treatment) were withdrawn by syringe from
fruit submerged in water for the occasion. The CO2 concen
trations were measured with a Hewlett Packard 5890 gas chro-
matograph fitted with a GSQ column (30 m x 0.53 mm i.d.
from J&W, Folsom, CA) and a thermal conductivity detector.
The O2 concentration of the same samples was measured with
a Model 507 analyzer (Inpack, Wilmington, MA). Standard
gas mixtures were used for calibration.
Statistix 4.1 (Analytical Software, Tallahassee, FL) was
used for computation of statistical parameters. Error bars on
the graphs show standard errors when these are not covered
by the symbols.
Results and Discussion
Experience has shown that a necessary condition for hav
ing a good wax coating is that the wax be prepared as a micro
emulsion, so that when the water evaporates the emulsion will
have a smooth surface. This means that the wax emulsion has
wax globules of sufficiently small size (<0.2 |im diameter) that
it appears transparent to translucent, and not milky white
(Prince, 1977). For present purposes it was considered the
wax was successfully emulsified if the wax globule size was suf
ficiently small that turbidity <1500 NTU and the cream
formed by gravity separation made up <7% of the volume.
These criteria may have been too strict, as some microemul-
sions with turbidity >2000 NTU, especially those made with
high-melting polyethylene, had no cream formation and may
have been suitable for use as coatings.
Out of >600 attempts to prepare suitable anionic wax mi-
croemulsions, >200 were made that met these criteria.
Table 1 summarizes the formulations of the anionic micro-
emulsions. All of these emulsions were made with ingredients
acceptable by the Code of Federal Regulations for use in food
and/or fruit coatings. The ingredients for all of these coat
ings consist only of water, wax, fatty acids and a base (morpho
line or ammonia, sometimes supplemented with KOH).
The ranges indicated for various ingredients in Table 1
mean only that good emulsions were made in our laboratory
within that range. Sometimes our only attempts were within
that range, and sometimes poor emulsions were made with in
gredients outside that range. Table 1 shows only the successes
and not the many failures.
Carnauba wax emulsions. The type of carnauba wax used
was Yellow No. 3 for most of our carnauba wax formulations.
Those made in the pressure cell generally had lower turbidity
and cream than those made in beakers by water-to-wax or
wax-to-water methods, and the same was true for other waxes
as well. This is generally well known (Burns and Straus, 1965).
However, pressure vessels are expensive and not always avail
able. The water-to-wax method was used extensively for mor-
pholine-based carnauba wax emulsions, and these were
generally very easy to make. As a demonstration, a good qual
ity carnauba wax microemulsion (turbidity = 530 NTU) was
made with a stirring rod being the only mixing equipment
(data not shown). Carnauba emulsions made by the wax-to-
water method, by contrast, generally were quite turbid, ex
cept when Foral AX was added before emulsification (5% was
sufficient, data not shown). However, addition of this ingredi
ent seems to be approved only for waxes used as citrus coat
ings (21 CFR 172.210).
Compared with morpholine, those emulsions made with
aqueous ammonia as an ingredient are of more general ac
ceptability with foods because this ingredient is GRAS (21
CFR 184.1139). Morpholine, by contrast, is approved as an in
gredient only for those formulations used as a fruit coating
(21 CFR 172.235). Ammonia could not be used for making
carnauba wax emulsions by the water-to-wax method because
this boiled off too quickly, as the relatively high melting point
of this wax (85°) requires that the emulsification temperature
be somewhat high. For ammonia-based emulsions made in
the pressure cell, best results were obtained by heating the
mixture of wax, initial water, fatty acids and ammonia to
120°C, followed by addition of enough hot water to attain
about 25% total solids. A small amount of KOH was added
when making some carnauba wax emulsions, because some
observations, not statistically significant, suggested this im
proved gloss of the coatings (data not shown).
Combinations of carnauba and candelilla waxes. Mixtures of
candelilla wax and carnauba wax with >45% candelilla had
sufficiently low melting point to make it possible to make
emulsions in an open beaker by the water-to-wax method
without having the ammonia flash off (Table 1). The tech
nique was to add the ammonia (by syringe) under the surface,
to an agitated 95°C mixture of wax and 10% water (under a
hood), then adding the remainder of the hot water. The pres
sure cell would be much preferred for ammonia-based emul
sions, however. With morpholine rather than ammonia as the
base, microemulsions with various ratios of combinations of
carnauba and candelilla waxes were made over a fairly wide
range of conditions.
Candelilla wax. Emulsion quality was quite dependent on
the grade and lot no., more so than other waxes. Type S&P 75
was used for most work. With one batch, many morpholine-
based emulsions with turbidities as low as 315-500 NTU were
made with 8-10 g oleic acid/100 g wax, using the water-to-wax
252 Proc. Fla. StateHort. Soc. Ill: 1998.
Table 1. Components of anionic wax microemulsions with turbidity <1500 NTU (g/100 g wax) and less than 10% cream layer "'•.
Type wax
C3W
C1W
75% C3W, 25% RBW
50% C3W, 50% CnW
20-50% C3W, bal CnW
CnW
60-80% AC316, balance CnW
50-80% AC673, balance CnW
50-90% AC673, AC680 or E20,
balance CnW
AC629orE10
AC680 or E20
AC673
50% E20, 50% PtW
88% CnW, 12% PfnW
50-67% BW, bal. CnW
50% BW, 50% C3W
40-60% C3W, balance W20
nr ACfi7^
MW
82% AC680,18% PfnW
Fatty acids
Oleic
14-20
6-20
12-15
20
25
7-8
7-11
8-15
5-15
0-12
18-20
14-25
18-28
0-20
0-13
0-28
18-20
0-18
12
0-11
11-12
18-31
12-15
13
(g/100) gwax
Total
14-20
8-24*
20?
20
25
20?
20
8-20"
12-24X
6-16X
23-25?
19-25?
18-28
12-20
18-20?
12-28?
18-20
18
15?
22X
22-24
18-31
12-15
17?
Emulsification
technique
WWX
PC(70-110)
WWX
wwx
wwx
WWXorPC(50)
WXW or WWX
WWX
WWX or PC (48-100)
WWX
PC (50-150)
PC (50-100)
WXW
WXW
PC(50)
WXW
WXW or PC(160)
WXW
PC (50)
WWXorPC(50)
WWX
WXW
WXW
WXW
Morpholine,
NH3, KOH
(moles/100 gwax)
0.10-0.20 mor. + <0.01 KOH
0.14-0.26 NH,, + 0.01 KOH
0.14-0.21 NH3
0.23 mor.
0.17 mor.
0.25 NHS
0.15 mor.
0.07-0.18 mor.
0.21-0.26 NH,
0.08 mor. + (U3NH,
0.3 NH,+ 0-0.14 mor.
0.32 NH3
0.17-0.23 mor.
0.11-0.20 mor.
0.26 NH3
0.17-0.21 mor.
0.22 mor.
0.20 mor.
0.21 NH3 +0.03 mor.
0.25 NH3
0.18 mor.
0.17-0.22 mor.
0.18 mor.
0.17 mor.
pH
9.1-9.3
9.2-10.6
9.2-9.6
8.8
NV
9.5-10.1
8.7-9.0
8.6-9.1
9.2-10.1
8.7-9.2
9.6-10.1
9.8-10.0
8.6-9.0
8.7-8.9
9.5-9.9
8.5-8.8
9.3
8.9-9.1
9.3
9.4
8.7
8.5-8.9
8.8
8.9
Lowest turb.
(NTU)
400
325
423
462
NV
280
230
175
166
339
482
58
178
330
233
204
577
857
540
351
1250
200
480
660
Abbreviations for table: C3W = Carnauba wax No. 3, C1W = Carnauba wax No. 1, CnW = Candelilla wax, BW = beeswax, RBW = rice bran wax, PfnW = paraf
fin wax, PtW = petroleum wax or BeSquare, MW = montan wax, WWX = water-to-wax, WXW = wax-to-water, PC(50) = pressure cell with initial water of 50 g/
100 g wax, Mor = morpholine, turb. = turbidity, NTU = nephelometric turbidity units.
^Balance myristic acid, i.e., the only two fatty acids are oleic and myristic.
"Balance myristic or palmitic acid.
method. With a second batch, and also with types cbw2 or fil-
trada, a minimum of 10 g oleic acid was required to make
emulsions with turbidities of 700-1000. Emulsions with both
batches are included in Table 1.
Ammonia-based candelilla emulsions were made by two
methods. Those made with the water-to-wax method typically
had turbidities of about 1000 NTU. Those made in the pres
sure cell had somewhat lower turbidities (typically about 300
NTU) when made with either of the two batches of S&P can
delilla wax just mentioned. The least turbid (175 NTU) was
candelilla microemulsion containing 6 g oleic acid and 6 g
palmitic acid per 100 gwax (Table 1). In general, good emul
sions were made in the pressure cell by heating the wax mix
ture to 100-130°C before addition of the balance of the water
to achieve about 25% total solids.
For both carnauba and also the candelilla wax emulsions
the lowest turbidity was achieved with different combinations
of fatty acids depending on whether ammonia or morpholine
was used (Table 1). With morpholine and no ammonia, the
least turbid emulsions were made with oleic acid without sup
plementation with myristic or palmitic acid. With ammonia
and no morpholine, some saturated fatty acid was required;
the least turbid emulsions were made with about 16% fatty ac
id, consisting of about half oleic and half myristic or palmitic
acid. Candelilla and carnauba wax coatings in general had
higher gloss if the microemulsions were rapidly cooled. For
example, candelilla wax coatings on polystyrene had mean
gloss at 20° of 31 NTU when made from microemulsions that
had been cooled from 70 to 40°C in about 2 min, compared
to 6 NTU for those cooled in about 20 min (data not shown).
Red Delicious apples coated with carnauba or candelilla wax
had higher gloss when coated with carnauba or candelilla wax
emulsions that were rapidly cooled (data not shown).
Oxidized Polyethylene. The higher-density polyethylene wax
es tended to make coatings with higher gloss than low-density
polyethylene (data not shown). Unfortunately, the higher-
density polyethylenes tend to be more difficult to emulsify,
partly because of the higher softening points. Types AC629,
E10, AC680 and E20 were rather easy to emulsify by the wax-
to-water or pressure cell method (Table 1). Good emulsions
were made with various combinations of oleic, stearic, palmit
ic, myristic and lauric acids, although those made with only
lauric acid tended to be somewhat turbid. The more dense
polyethylenes (types AC 673 and AC 316) were more difficult
to emulsify. Fruit coatings made from the higher-melting
polyethylene types tended to fracture, especially AC316,
which the manufacturer considered too hard to recommend
as a fruit coating (data not shown).
Polyethylene wax-candelilla wax mixtures. Addition of 55 g
candelilla wax per 100 g AC316 was sufficient to prevent frac
ture of the coating without marked decrease in gloss. With
AC673, only 35 g candelilla/100 g polyethylene wax was suffi
cient (data not shown). Addition of shellac improved gloss
and flexibility of AC673-candelilla coatings but not AC316-
candelilla coatings. With AC316 (softening point 140°C)
good emulsions were made with the pressure cell at 146-
179°C, and with AC673 (softening point 115°C) at cell tem
peratures of 143-162°C. Exceptionally low-turbidity AC673-
candelilla wax microemulsions (turbidity < 70 NTU) were
made at pressure cell temperature of 161-162°C (Table 1).
These appeared completely clear, like solutions. At higher
cell temperatures, some charred deposits were found on the
Proc. Fla. StateHort. Soc. Ill: 1998. 253
interior walls of the pressure cell and emulsion turbidity was
higher.
Polyethylene wax was also useful for forming co-emulsions
with other difficult-to-emulsify waxes. Note, for example, the
emulsions that contain petroleum wax and paraffin wax (Ta
ble 1). For the formulations whose wax component consisted
of 50% polyethylene wax and 50% petroleum wax, emulsions
with virtually the same turbidity were made with either oleic
acid or stearic acid as the only fatty acid.
Beeswax. Beeswax emulsions with low turbidity could only
be made by mixing the beeswax with other waxes (Table 1).
Beeswax emulsions were difficult to make by the water-to-wax
method because the viscosity was very high before inversion.
Formulations with more than 50% beeswax had 20-30%
cream and very high turbidity. Beeswax coatings tended to
have low gloss.
Montan wax. Montan wax microemulsions (Table 1) tend
ed to have low gloss when dried as coatings (data not shown).
It is important that any coating spread well on surfaces.
The polyethylene, candelilla wax, paraffin and beeswax for
mulations tended to bead up on surfaces, whereas those con
taining carnauba and montan wax had better spread. Spread
was generally better with higher solids content. Spread was
also generally improved with addition of a leveling agent,
such as shellac or protein (Hagenmaier and Baker, 1997).
In addition to the formulations just discussed, hundreds
more were formed by mixing separate microemulsions. In all
cases where anionic emulsions of low turbidity were mixed,
the resulting emulsions had turbidity intermediate between
those being mixed, and no evidence of incompatibility was ev
ident. However, formulations made by mixing separate emul
sions might have different properties than those made by
mixing waxes before emulsification. Wax may not rapidly dif
fuse from one globule to another.
Nonionic emulsions. (Table 2) Nonionic microemulsions
were made with nonionic emulsifiers rather than fatty acids
and base. Except for squalene, the ingredients used for the
nonionic emulsions are also accepted by FDA for foods. The
nonionic emulsions tended to be somewhat more turbid than
the anionic emulsions, except for the squalene emulsion which
had a turbidity of only 446 NTU (data not shown). In retro
spect, it would seem that insufficient amounts of emulsifiers
may have been used in many of these formulations. The values
shown for hydrophile-lipophile balance (HLB) are weight-av
erage values based on the following values for individual surfac
tants: 14.9 for polysorbate 60, 4.7 for sorbitan monostearate
and 3.4 for glycerol monooleate (Petrowski, 1976).
The squalene emulsion seems to have potential as a vehi
cle for applying squalene to prevent chilling injury. Squalene
Table 2. Nonionic emulsions made by the water-to-wax method.
Wax or Lipid Emulsifiers (g/100 g wax) HLBZ
Squalene
Parvan 4450
Mineral oil, petrolatum
or rice bran wax: lOOg
Polywax 500
polysorbate 60: 47-67 g
oleic monoglyceride: 12-24 g
sorbitan monostearate: 0-7 g 11.2-11.9
polysorbate 60: 13 g ., «
sorbitan monostearate: 7 g
polysorbate 60: 19 g
sorbitan monostearate: llg
polysorbate 60: 26 g
sorbitan monostearate: 9 g
11.2
12.3
applied as a 10% hexane solution was used to establish its ef
fectiveness for this use (McDonald et al., 1993). Use of an
aqueous emulsion would seem more acceptable than the hex
ane solution, providing it is still effective.
Anionic emulsions with rice bran wax had somewhat high
turbidity when mixed with 3 parts by weight carnauba wax
and emulsified with 22 g oleic acid 0.17 moles morpholine
per 100 g wax.
Wax coating formulations are often mixtures of wax mi-
croemulsion and other ingredients added to improve gloss or
spread. An example would be citrus coatings made from mix
tures of wood rosin and wax microemulsion. Oranges and
tangerines with such coatings tended to have higher internal
CO2 as rosin percentage increased (Fig. 1). Flux was virtually
the same for all coated fruit, both oranges and tangerines,
0.4-0.7 ml/min, and the dependence of internal O2 or CO2 on
flux was not significant (data not shown). Interior gases were,
however, significantly dependent, p < 0.001, on rosin content.
Thus it seems that internal gas differences were determined
more by the permeance of the coatings than differences in
the tendency of different coatings to block diffusion through
pores. It is generally well known that coatings high in rosin es
ter tend to increase internal CO2 and lower internal O2
(Hagenmaier and Baker, 1994).
Sunburst tangerines: uncoated fruit
had 9.1 % O2and 7.8% CO2
(X -o-r--< i i \ r r — i 9
20 40 60 80
% rosin (balance wax)
100
Figure la. Interior gas compositions with coatings made with different ra
tios of wood rosin to wax.
3 Hamlin oranges: uncoated fruit
had 18.6% O2 and 2.8% CO2
20 40 60 80
% rosin (balance wax)
100
'Hydrophile-lipophile balance.
Figure lb. Interior gas compositions with coatings made with different ra
tios of wood rosin to wax.
254 Proc. Fla. State Hort. Soc. Ill: 1998.
Compared to 'Hamlin oranges, the internal O2 of coated
'Sunburst' tangerines was much lower and the internal CO2
higher (Fig. 1), indicating that gas permeance was much
higher for the oranges. As mentioned, the air flux was virtual
ly the same for both types of fruit. Therefore, the reason for
the difference is the difference in the gas permeance, rather
than any difference in open pores through which gas diffused
(Hagenmaier and Baker, 1993).
In summary, formulations were presented for making wax
microemulsions. Coatings made from a mixture of wax micro-
emulsion and rosin had lower permeance to CO2 and O2 with
increasing amounts of wood rosin.
Literature Cited
Bennett, H. 1965. 'Industrial Waxes' Volumes 1 and 2, Chemical Pub. Co,
Inc. NY. 1975
Burns, F. G. and I. Y. Straus. 1965. Chemical Specialties Mfrs. Assoc, Proc. of
Annual Meeting, 52:226-7.
FDA, Code of Federal Regulations (CFA), Food and Drug Administration, Ti
tle 21. 1995. Note: this is also the source for all other CFR regulations cited in the text.
Hagenmaier, R. D. and R. A. Baker. 1993. Reduction in gas exchange of cit
rus fruit by wax coatings. J. Agr. Food Chem. 41 (2):283-287.
Hagenmaier, R. D. and R. A. Baker. 1994a. Wax microemulsions and emul
sions as citrus coatings. J. Agr. Food Chem. 42(4):899-902.
Hagenmaier, R. D. and R. A. Baker.. 1994. Internal gases, ethanol content
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Proc. Fla. State Hort. Soc. 111:255-257. 1998.
PROGRESS ON BLOSSOM END CLEARING IN GRAPEFRUIT
Ed Echeverria, Jacqueline Burns, and William Miller
University of Florida, Citrus Research and Education Center
700 Experiment Station Road
Lake Alfred, FL 33850
Additional index words. Postharvest.
Abstract. Blossom-end clearing (BEC) in grapefruit is a disorder
that typically appears as a water-soaked area on the blossom-
end of fruit. Previously we have shown that BEC (1) can be
completely eliminated by proper postharvest handling, (2) can
be reduced by overnight storage of harvested fruit at 75°F, 95%
RH before handling through the packingline, and (3) can be re
duced by reducing fruit impact forces on the packingline. In
this study we used controlled impact studies to demonstrate
that BEC could be induced more readily in field-harvested fruit,
where pulp temperatures were high. Reducing pulp tempera
tures by overnight storage at 70 F, 95% RH markedly reduced
the appearance of BEC. The incidence of BEC steadily in
creased throughout the harvesting season from late January
to June, and we could not demonstrate a peak of BEC appear
ance during bloom time. Withholding irrigation 24 hours before
harvest did not affect the occurrence of BEC. Symptoms of
BEC can appear in less than 5 minutes after fruit impact. The
severity of symptoms may be associated with the amount of al
bedo available to absorb juice released on fruit impact.
Florida Agricultural Experiment Station Journal Series No. N-01677. This
project was supported by a grant from the Florida Department of Citrus.
Introduction and Review of Literature
Previous studies have indicated that Blossom End Clear
ing (BEC) in grapefruit is markedly influenced by tempera
ture, fruit turgidity, and fruit impact forces (Echeverria and
Burns, 1994). Studies conducted in a commercial packing
house setting as well as under controlled conditions demon
strated that elevated pulp temperature and reduced relative
humidity increased the appearance of BEC. High fruit impact
forces during handling, such as those that may occur in areas
of the packingline (e.g., the fruit dump site), increase the ap
pearance of BEC in fruit lots packed later in the season when
outside temperatures are high. In addition, it was observed
that BEC appeared more frequently in fruit in which the cen
tral spongy core had disappeared. As fruit mature and age,
the disappearance of the spongy core occurs naturally and
creates a hollow central core that may weaken the segment
juncture. A significant fruit impact can rupture the segment
juncture and enclosed juice vesicles, permitting the released
juice to travel through the open central core and to the peel
unobstructed. A wet or 'clear' area appears on the peel usual
ly located on, but not limited to, the blossom end of the fruit.
Under natural conditions, temperature and fruit turgidity
may play a larger role in BEC development as temperature
and humidity increase and fruit age during the harvest sea
son. The aim of this project was to investigate the interrela
tionship between fruit age, temperature, fruit turgidity and
the incidence of BEC. We harvested fruit throughout the sea
son and induced BEC under various temperature regimes.
We attempted to alter fruit turgidity by altering the irrigation
strategy immediately before harvest. Commercial packers
Proc. Fla. State Hort. Soc. Ill: 1998. 255
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