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

and gloss of citrus fruit coated with polyethylene wax, camauba wax, shel

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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