Proc. Fla. State Hart. Soc. 99:122-127. 1986.
MECHANICAL AND PHYSICAL PROPERTIES FOR POSTHARVEST HANDLING
OF FLORIDA CITRUS
William M. Miller
University of Florida, IFAS
Citrus Research and Education Center
700 Experiment Station Road
Lake Alfred, FL 33850
Additional index words, freeze-damage, coefficient of fric
tion, surface roughness.
Abstract. During a two-season study, data were collected on
the following physical properties of Florida citrus: dimensional
size, mass, surface roughness, and volume. Coefficient of fric
tion values for citrus varieties and various handling surfaces
were also determined. Mechanical properties of the fruit in
compression and puncture loading were measured. These
studies were conducted during 2 yr when freezes (> 4 hr at
<2°C) occurred. Therefore, the effects of freeze damage on
these physical and mechanical properties were also mea
sured.
Although the materials handling techniques are wellestablished for citrus (9), physical properties data are lack
ing for the design of systems with optimal handling
capacities that minimize fruit damage. Any quality degra
dations from injuries such as decay may be more prevalent
in future systems utilizing mechanical harvesting (8). Sur
face injuries allow decay fungi to enter the fruit (3) and
abrasive injuries, specifically oleocellosis, are common (15).
Certain physical properties of citrus are also indicators
of quality. One example is fruit density and its direct re
lationship to the severity of freeze damage (14). Another
fruit quality attribute is turgidity which is important in re
sultant deformation from overfilled cartons and which
may be altered by post-harvest treatments such as irradia
tion (1).
An extensive survey of physical properties data for
fruits and vegetables was compiled by Mohsenin (12). Peel
strength properties were analyzed for three citrus varieties
by Churchill et al. (6). Viscoelastic properties were re
ported for creep recovery tests by Sarig and Nahir (13).
Gyasi et al. (10) developed a procedure to determine Poisson's ratio for citrus fruit flesh and rind. Gaffney and
Baird (7) measured properties relevant to heat transfer for
citrus such as rind thickness and moisture content. Chen
and Squire (5) determined coefficient of friction for
oranges on aluminum, masonite, and plexiglas surfaces.
They did not find a relationship between the abrasive in
jury level and applied frictional force.
The objective of this study was to measure and report
on pertinent materials handling properties; dimensional
size, mass, surface roughness, mechanical strength (com
pression and puncture), and coefficient of friction for Flor
ida citrus varieties. This research was conducted over 2
seasons in Florida which included severe freezes. Hence,
Florida Agricultural Experiment Station Journal Series No. 7686.
SI units are used throughout this manuscript; note that IN = 0.225
lbfand lkPa= 0.145 psi.
122
fruit density and mechanical property changes were also
monitored.
Materials and Methods
Following the nomenclature of Mohsenin (12), a, b, and
c dimensions of individual fruit were measured. A toploading balance, 0.1 g resolution, was utilized to determine
the mass m while fruit volume VOL-m was established by
water displacement. Subsequent calculated properties
from these measurements were sphericity, S = (abc)1/3/a
density, p = m/V and a calculated volume, VOL-c = it
abc/6.
Surface roughness of citrus peel was estimated from a
2.5 cm x 1.0 cm circumferential peel section mounted on
a motorized table driven horizontally (11). Displacement
(maximum, minimum, and average) was determined from
10 equally spaced readings of displacement along the 2.5
cm peel section. Fruit diameter, typically (a + b)/2, at the
equator was also measured. Normalized maximum rough
ness and a root mean square roughness were computed.
Compressive and puncture testing followed the proce
dures of ASAE (2) and Churchill et al. (6) using an Instron
universal test instrument with a 5kN load cell. Crosshead
and chart speed were 200 mm/min. The fruit was de
formed between two parallel plates for compressive tests.
For puncture tests, the fruit was positioned on a hard cork
cylindrical support, 11 cm O.D., 6 cm I.D., having a 45°, 1
cm, interior beveled edge to minimize bottom deflection
and rotation of the fruit.
For flat-plate contact, maximum force, the stress index,
and elastic modulus were calculated with a Poisson's ratio
of 0.33 (10) and formulae from ASAE (2). The force re
quired to compress the whole fruit to 0.75 of its original
diameter was also noted. In the case for puncture, a
maximum force was obtained while a modulus of elasticity
and an average stress were calculated.
A sliding friction table was designed and built to
evaluate fruit on 5 surfaces: galvanized sheet metal, unpainted plywood, Teflon, polyvinyl chloride, and UHMW
polyethylene. Fruit were prevented from rotating via a topmounted screen plate with a 1 cm nail inserted into each
fruit. A horizontally mounted load cell with a 90 N adapter
was used to measure the frictional force. Duplicate tests
were conducted for each surface.
All tests were conducted with citrus fruit that had been
hand harvested and washed on a pilot packingline. Except
for frictional tests, the fruit were randomly selected from
an unsized, non-waxed lot. In the case of friction, fruit of
the same dimensional size range were selected to facilitate
placement of the screen plate. Most fruit samples were
obtained from the Lake Alfred CREC groves. However,
both in 1983-84 and 1984-85 seasons, late season, non-fro
zen samples were obtained from commercial groves in the
southern Indian River citrus growing area of Florida after
freezes occurred in the Lake Alfred area. In testing a spe
cific variety, 40 fruit were measured for their dimensional
characteristic while 20 fruit were tested for mechanical
Proc. Fla. State Hort. Soc. 99: 1986.
compression and puncture properties. Varieties evaluated
for both seasons were: 'Dancy' tangerine, 'Hamlin' orange,
'Marsh' grapefruit, 'Pineapple' orange and 'Valencia'
760
orange.
600
Results and Discussion
A summary of the dimensional and mass data has been
compiled in Tables 1 and 2. The calculated volumes corre
lated highly (R2 > 0.98) with measured volume from dis
placement for both seasons but calculated values were less
in all cases (Fig. 1). This was also noted in data from
Mohsenin (12). For citrus, the measured volume vs. calcu
lated volume linear regression yielded a slope of 1.08, in
tercept of 4.6, while the Mohsenin compilation had a 1.16
slope with a 4.6 intercept. Sphericity values were lowest for
'Dancy' tangerines, 0.86 to 0.90, while 'Valencia' oranges
were nearly spherical, 0.98 to 0.99.
'Valencia' orange with no freeze damage had the high
est density, averaging 0.96 and 0.98 for the 1983-84 and
1984-85 seasons, respectively. Density of 'Marsh' grape
fruit averaged 0.85 and 0.80 for the 1983-84 and 1984-85
non freeze-damaged samples. The reduced density by de
siccation of fruit after freeze damage was evident for the
1983-84 'Hamlin' tests (Table 1) and the 1984-85 'Marsh'
grapefruit tests (Table 2). Similar trends for density were
reported by Carter and Barros (4) who studied juice yield
after freezes of 'Valencia' oranges. In general, such freeze
damage occurs at temperatures < -2°C for duration > 4
hr. This condition occurred during both the 1983-84 and
1984-85 seasons. In 1983-84, 8 hr < -2°C (-4.4°C
minimum) were experienced and in 1984-85, 18 hr <
-2°C (-5.6°C minimum) were encountered.
In Table 3, surface roughness estimates were computed
based on the maximum-minimum reading and a calculated
RMS value over a 2.5 cm peel section. RMS values repre
sent the deviation from the average dimensional displace
ment. All values were normalized based on the fruit diame-
460
Q
UJ
CC
300
4.60 + 1.08x
CO
<
R2= 0.906
160
160
300
450
600
750
CALCULATED VOLUME, cm3
Fig. 1. Relationship of measured volume by displacement technique
vs. calculated volume based on geometric mean diameter for Florida cit
rus varieties.
ter, thereby representing surface roughness. Considerable
variation was found among samples of a given variety relat
ing to such surface blemishes as windscar. The roughness
values of the various varieties calculated by either a
maximum-minimum or RMS basis were differentiated into
two sets by Duncan's multiple range test.
A coefficient of friction, fx, was determined for citrus
varieties on 5 fixed surfaces with the fruit undergoing a
sliding friction. A significant difference was found among
Table 1. Dimensional and mass data summary (mean and range), 1983-84 season.
Dimension,
Variety
cm
b
a
c
Mass, g
Cal.
volume cm3
Measured
volume cm3
Sphericity
Density p
(m)
(Vol-c)
(Vol-m)
(S)
g/cm3
0.858
0.922
0.771-0.941
0.844-0.979
6.75
6.05-7.85
6.68
5.95-7.85
5.36
4.63-6.10
137.1
101.7-207.7
127.9
93.1-195.2
149.2
109.0-226.5
9.57
8.20-11.00
9.45
8.33
7.98-10.94
7.35-9.50
385.6
253.0-527.0
399.8
251.8-592.3
456.6
296.0-661.0
0.916
0.846
0.869-0.961
Pin. orangey
23Jan.1984
7.26
6.35-8.42
0.797-0.898
7.19
6.30-8.36
6.94
5.75-7.77
175.8
124.1-240.0
191.5
127.8-286.4
209.2
140.0-315.0
0.979
0.900-0.998
0.843
Val. orange**
6 Mar. 1984
3 Apr. 1984
7.14
6.48-7.95
7.03
6.42-7.80
6.89
191.9
6.10-7.70
149.0-252.3
Hamlin orangex
7 Nov. 1983
27Jan.1984Z
6.62
5.75-7.65
6.57
5.70-7.65
6.43
5.45-7.45
106.0-227.5
Hamlin orangey
6 Feb. 1984
6.93
6.86
6.62
136.6
5.95-8.05
5.85-7.95
5.60-7.70
Hamlin orangey
13 Feb. 1984
7.09
7.03
6.25-8.20
6.79
5.85-7.85
142.9
6.25-8.30
Hamlin orangey
5 Mar. 1984
7.23
6.35-8.45
7.10
6.28-8.15
6.85
130.5
Dancy tangerine
12 Dec. 1983
Marsh g'fruit7
27Jan.1984
6.05-8.00
152.0
93.8-183.3
98.9-197.6
81.5-185.6
0.760-0.910
182.2
134.9-248.4
199.4
0.988
153.0-267.0
0.964
0.952-0.998
0.892-1.005
148.8
95.2-226.8
162.2
114.0-243.0
0.984
0.921-1.000
0.938
0.885-0.994
167.3
102.1-258.0
185.3
113.0-283.0
0.974
0.903-0.997
0.746
0.577-0.834
179.1
124.5-279.7
197.8
134.0-305.0
0.976
0.935-0.998
0.736
0.572-0.874
186.2
126.3-288.5
201.8
126.0-296.0
0.976
0.949-0.995
0.655
0.426-0.841
xTwo sample sets were analyzed.
yFreeze-damaged; 25-26 December 1983.
zFrom Indian River area.
Proc. Fla. State Hort. Soc. 99: 1986.
123
Table 2. Dimensional and mass data summary (mean and range), 1983-84
Dimension, cm
a
Variety
b
season.
Cal.
Measured
Mass,•g
volume cm3
volume cm3
Sphericity
Density p
(m)
(Vol-c)
(Vol-m)
(S)
g/cm3
178.9
117.0-256.0
0.902
0.878-0.928
0.884
0.974
0.941-0.992
0.932
c
Dancy tangerine
3 Dec. 1984
7.38
6.50-8.45
7.28
6.35-8.18
5.48
4.69-6.33
157.3
155.8
109.5-208.2
103.6-228.0
Hamlin orange
5 Nov. 1984
7.72
7.21
229.7
170.7-308.9
225.2
160.9-301.1
246.6
6.92-8.52
7.66
6.87-8.52
7.05
6.38-7.92
6.86
203.9
6.05-7.76
190.6
145.8-264.6
181.4
14Jan.1985
7.10
6.40-7.95
132.1-255.8
152.0-274.0
Val. orange"
14 Feb. 1985
7.03
6.21-7.88
6.99
6.86
6.02-7.70
194.2
133.4-252.1
177.9
119.6-247.2
Marsh g'fruity
8 Oct. 1984
10 Dec. 1984
10.06
7.88-11.12
9.94
7.88-11.06
9.14
405.0
203.1-508.8
482.6
Marsh g'fruit*
38 Feb. 1985
10.51
9.30-11.47
10.39
9.03-11.46
419.0
531.5
280.3-550.4
360.4-690.4
Pin. orange
6.11-7.78
6.37-8.20
7.09-9.98
9.22
8.02-10.78
230.5-627.9
180.0-328.0
0.763-0.957
0.908-0.961
0.987
0.960-0.999
0.904-0.966
197.9
0.990
0.984
133.0-264.0
0.967-0.999
0.8886-1.084
510.0
253.0-655.0
0.964
0.798
0.939-0.995
0.726-0.969
600.1
400.0-769.0
0.953
0.917-0.986
0.697
0.622-0.762
0.935
"Freeze-damaged; 21-22 January 1985.
yTwo sample sets were analyzed.
7From Indian River area.
Table 3. Combined surace roughness (e/d) values for various citrus vari
eties (mean and range), 1983-84 and 1984-85 season.
Variety
Dancy tangerine
Marsh grapefruit
Max.-min., cm
RMS, cm
x
x
Range
Range
0.0046 bz
0.0024-0.0071
0.0021 a
0.0009-0.0043
0.00127 b
0.00070-0.00229
0.00060 a
Hamlin orange
0.0028 a
0.00034-0.00187
0.00083 ab
0.0003-0.0072
0.00012-0.00241
Pineapple orange
0.0036 ab
0.0009-0.0053
0.00117 ab
0.00029-0.00185
Valencia orange
0.0031 ab
0.0008-0.0055
0.00085 ab
0.00052-0.00202
zMeans with same letters within columns do not differ significantly at 5%
level for Duncan's multiple range test.
both the surface tested and the citrus varieties (Table 4).
As expected, Teflon exhibited the minimal frictional resis
tance yielding an average jjl of 0.21 for all varieties. The
mean coefficient of friction for 'Dancy' tangerines was
higher than other varieties and may be related to surface
roughness (Table 3). The lower jjl value for Teflon would
merit its use as a surface laminate on shears and in automa
tic place packing and film wrapping equipment where fruit
lodging occurs.
Mechanical properties related to compression and
puncture are summarized in Tables 5 and 6. Maximum
force levels for both compression and puncture were
varied considerably among varieties and after freeze dam
age. Maximum force levels for either compression or
puncture tests were greatest for 'Marsh' grapefruit and at
minimum levels for 'Dancy' tangerines. This behavior
would be expected because of both the thin skin and dis
tinctly segmented structure for tangerines. Also, peel
thickness as a percent of radius is greater for grapefruit
Table 4. Coefficient of friction (u,) for citrus varieties on various surfaces,
non-rolling condition.2
Surface
Variety
Unpainted
plywood
UHMW-
Sheet
Mean
PVC
metal
Teflon
PE
0.22
0.23
0.20
0.36
0.45 a
0.38
0.39 a
0.33
0.37 a
0.19
0.23
0.42
0.36
0.36 a
0.21a
0.37 b
Dancy tangerine
Marsh grapefruit
Hamlin orange
Pineapple orange
0.42
0.41
0.45
0.59
0.40
Valencia orange
0.36
0.43
0.38
0.67
0.39
0.43
0.38
0.43
Mean
0.41 btf
0.48 c
0.46 be
0.53
0.46
0.35 a
ZF = 45.1 for surfaces (1% level sign.), F = 3.3 for variety (5% level sign.).
yMeans with same letters within columns do not differ significantly at 5%
level for Duncan's multiple range test.
Significant differences (5% level) for the stress index of
compression, average stress from puncture and the
maximum force in compression were observed. Differ
ences between the 2 seasons for mechanical properties of
the same variety were not significant at a 5% level for non
freeze-damaged samples. A linear correlation coefficient
matrix between various properties estimated was compiled
in Table 7. Note that maximum compressive force did not
correlate highly with other mechanical properties. Hence,
maximum compressive force should not be used as an indi
cator of fruit turgidity.
Relationships of the compression and puncture proper
ties to freeze damage were investigated for the 'Hamlin'
orange data of 1983-84. The parameters of average stress
index and elastic modulus (Fig. 2 and 3) exhibited a
marked decline after the freeze. Also, the maximum
puncture force vs. time declined but the maximum com
pressive force vs. time after freeze damage was unchanged
(Fig. 2b). The maximum compressive force may relate to
peel strength while the parameters normalized for size and
deformation accounted for internal structural integrity.
than for oranges or tangerines (7).
The R2 values for a linear curve fit between maximum
compressive force and density, compressive stress index
and density, and compressive-elastic modulus and density
were 0.01, 0.93**, and 0.99**, respectively. Corresponding
calculated from either the compression or puncture test.
values for puncture force v$. density, puncture average
Exclusive of freeze damaged fruit, there were highly
significant differences (1% level) among varieties for
maximum puncture force and the modulus of elasticity
124
Proc. Fla. State Hort. Soc. 99: 1986.
Table 5. Compression and puncture properties (mean and range), of Florida citrus, 1983-84 season.
Puncture
Compression
0 25
Variety
Max. force,
N
N
Stress index,
kPa
Max. force,
E,kPa
N
1146.3
610.7-1956.9
22.1
16-34
1394.4
1110.2-1813.9
65.8
58-78
205.5
181.3-243.8
573.4-948.0
39.4
25-60
123.3
78.1-187.5
461.6
2292.6
74.2
231.7
1017.0-3662.9
44-105
136.9-326.6
881.3
519.0-1145.5
2273.9
1720.3-3077.2
60.0
36-129
187.5
844.4
112.5-403.1
568.8-1198.9
913.4
635.9-1265.6
36.2
22-52
113.1
67.2-162.5
453.1
293.7
174.6-406.9
860.2
327.9-1106.3
31.3
18-51
286.8
216.3-408.5
831.9
593.6-1283.8
32.8
172.5
125-198
311.6
105-196
Marsh g'fruity
27Jan.1984
409.3
672.4
427.8
315-585
525-845
368.2-529.1
Pin. orangex
23Jan. 1984
236.8
180-365
442.7
270-552
388.7
301.1-518.1
1197.8
360.6
120-480
437.8
293-738
601.8
308.2-895.1
303.4
46-450
365.4
172-542
591.0
436.5-761.6
152.5
362.7
315.2
103-190
305-520
226.2-426.4
160.8
108-220
345.1
250-522
145.8
367.9
193.4-466.7
862.1-1693.4
3 Apr. 1984
27Jan.1984y
Hamlin orangex
6 Feb. 1984
Hamlin orange34
13 Feb. 1984
Hamlin orange34
5 Mar. 1984
80-202
248-515
E,kPa
348.4
228.8-653.4
148.5
Hamlin orangew
7 Nov. 1983
kPaxlO
68.9
50.0-106.3
Dancy tangerine
12 Dec. 1983
Valencia orangeyw
6 Mar. 1984
Avg stress,
18-52
726.2
338.6-624.4
276.8-725.2
97.8
393.9
56.3-160.9
256.0-521.4
103.4
56.2-162.5
384.4
160.0-556.0
wTwo sample sets were analyzed.
xFreeze-damaged; 25-26 December 1983.
yFrom Indian River area.
zForce at deformation = 0.25 (R! + R2).
Table 6. Compression and puncture properties (mean and range) of Florida citrus, 1984-85 season.
Puncture
Compression
Variety
Fo.25*
N
Max. force,
Avg stress,
Max. force,
N
Stress index,
kPa
E,kPa
N
kPaxlO
186.3
109-322
287.3
194.0-400.4
1009.4
706.2-1383.5
20.2
11-28
62.6
32.8-85.9
E,kPa
232.7
119.4-355.5
Dancy tangerine
3 Dec. 1984
134.4
Hamlin orange
5 Nov. 1984
384.3
539.1
378-680
561.2
447.4-698.9
1915.2
1514.5-2318.4
77.3
60-107
241.4
868.5
318-460
187.5-334.4
694.2-1135.5
Pin. orange
329.3
379.2
550.3
67.1
209.6
769.9
14Jan.1985
220-428
272-455
446.6-672.8
2095.8
1711.5-2661.4
46-88
145.3-276.6
643.0-913.4
Valencia orangey
14 Feb. 1985
363.1
303-435
412.7
579.7
417.4-741.4
2213.1
65.8
205.5
1437.5-3492.4
44-110
137.5-343.7
810.3
595.9-1133.2
Marsh g'fruitx
8 Oct. 1984
10 Dec. 1984
434.8
340-510
491.1
358.9-588.2
1360.2
1026.5-1832.0
72.8
228.2
179.7-293.8
733.2
584.0-1074.4
Marsh g'fruitw
18 Feb. 1985
208.4
1154.6
1314.6
835.5-1865.6
143.7
109.4-207.8
361.0
930-1360
467.7
296.5-628.2
46.0
118-275
88-185
335-550
1036.7
655-1630
58-94
35-67
276.5-445.6
wFreeze-damaged; 21-22 January 1985.
xTwo sample sets were analyzed.
yFrom Indian River area.
zForce at deformation = 0.25 (R! + R2).
stress vs. density, and puncture elastic modulus vs. density
were 0.83*, 0.82*, and 0.92**.
Summary
A Jack of materials handling data for fresh citrus led to
a study of pertinent physical properties. For various citrus
varieties grown in Florida, dimensional size, mass, surface
roughness, coefficient of friction, and mechanical proper
ties measurements were made throughout two seasons. Ex
perimental techniques were developed to determine sur
face roughness and coefficient of friction.
The reduction in density known to occur in freeze dam
aged 'Hamlin' oranges was highly correlated with mechanProc. Fla. State Hort. Soc. 99: 1986.
ical properties other than maximum compressive force.
Significant differences were found among varieties in their
surface roughness which may account for susceptibility to
abrasive injury and subsequent decay. For minimal frictional resistance, Teflon exhibited the lowest coefficient of
friction while other plastics were not significantly different
from unpainted plywood or sheet metal surfaces.
Maximum compressive force did not correlate with other
mechanical properties and should not be used as an indica
tion of fruit turgidity. Five mechanical parameters: compressive-stress
index,
compressive
elastic
modulus,
puncture force, puncture stress, and puncture elastic mod
ulus, exhibited a significant correlation with density of
freeze-damaged 'Hamlin' oranges.
125
Table 7. Matrix of linear correlation coefficients (R) between various mechanical properties for citrus varieties (including freeze-damaged samples).
Property
Puncture
Compression
Stress
Avg stress
index
r0.25
Compression
0.45
Fo.25
1
rmax
0.81**z
0.31
1
Stress index
0.95**
0.44
0.90**
0.95**
0.89**
0.03
0.95
0.44
0.89**
0.16
0.90**
1
0.79**
0.78**
0.87**
0.70**
E
Puncture
Avg stress
1.00**
0.94**
1
0.94**
1
E
7**denotes significance at 1% level.
400
z
80
300
£
b
,J
200
u.
100
□
UNDAMAGED
■
FREEZE-DAMAGED
0
50
(1 OCT.)
z
60
FREEZE
40
D UNDAMAGED
20
TIME. DAYS
100
■ FREEZE-DAMAGED
150
50
0
500
1
375
1000
100
TIME, DAYS
OCT.
x
2
250
750
u.
125
|
3000
O
2000
2
500
■ FREEZE-DAMAGED
0
4000
FREEZE
□ UNDAMAGED
50
(1 OCT.)
150
TIME, DAYS
D UNDAMAGED
250
■ FREEZE-DAMAGED
0
i
4000
FREEZE -
UNDAMAGED
1000
3000
FREEZE-DAMAGED
(1 OCT.)
50
TIME, DAYS
OCT.
TIME, DAYS
<00
150
2000
FREEZE-
D UNDAMAGED
1000
1000
■ FREEZE-DAMAGED
750
0
1
500
■ FREEZE-DAMAGED
0
(1 OCT.)
50
100
TIME,DAYS
Fig. 3. Puncture parameters (x ± SD) as function of time: (a)
maximum force, (b) modulus of elasticity, and (c) average stress for 'Ham
D UNDAMAGED
250
OCT.
150
TIME,
DAYS
Fig 2. Compressive parameters (x ± SD) as function of time: (a) force
at 0.25 (a + b), (b) maximum force, (c) modulus of elasticity, and (d) stress
index for 'Hamlin' oranges, 1983-84 season.
lin' oranges, 1983-84 season.
6. Churchill, D. B., H. R. Sumner, and J. D. Whitney. 1980. Peel
strength properties of three orange varieties. Trans. ASAE
23(1):173-176.
7. Gaffney, J. J. and C. D. Baird. 1980. Physical and thermal properties
of Florida Valencia oranges and Marsh grapefruit as related to heat
transfer. ASAE Paper No. 80-6011. St. Joseph, MI.
Literature Cited
1. Ahmed, E. M., F. G. Martin, and R. C. Fluck. 1973.
Damaging
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ASAE Standard 5368.1. ASAE Standards 1984. St. Joseph, MI.
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126
8. Gaffney, J. J., W. M. Miller, and G. E. Coppock. 1976. Citrus fruit
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