Some factors affecting the quality of citrus fruits

Material Information

Some factors affecting the quality of citrus fruits
Series Title:
Citrus Station mimeo report
Sites, J. W
Citrus Experiment Station (Lake Alfred, Fla.)
Place of Publication:
Lake Alfred FL
Florida Citrus Experiment Station
Publication Date:
Physical Description:
6 leaves : ; 28 cm.


Subjects / Keywords:
Citrus fruits -- Quality -- Florida ( lcsh )
Station Lake ( local )
Juices ( jstor )
Grapes ( jstor )
Orange fruits ( jstor )
government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )


General Note:
Caption title.
Statement of Responsibility:
J.W. Sites.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
74149681 ( OCLC )


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Some Factors Affecting the Quality
of Citrus Fruits

J. W. Sites

This discussion of factors affecting fruit quality is an attempt to present
in a general way the importance of certain factors known to affect citrus fruit
quality and the magnitude of the differences which they may bring about. Obvi-
ously only certain factors can be discussed and these not in detail but it is
hoped to convey a general impression of their scope and importance.
Varietal Differences.- Rather wide differences in juice quality may be
accounted for solely as varietal differences. Adequate comparisons may only be
made where rootstock, soil, fertilization, weather conditions and other factors
are comparable. Table 1 presents a simple comparison of five of the major
varieties grown in Florida when fruit was harvested at approximate peaks of
quality and grown under comparable conditions. It is to be observed that the
Hamlin orange, although frequently considered an inferior orange ranks high as a
source of vitamin C. The inferiority of Marsh seedless grapefruit as compared
to Duncan is evident in all respects except percentage of juice by weight.
Table 1

Comparison of five major citrus varieties at optimum periods
of juice quality grown on rough lemon rootstock
under comparable cultural conditions

S Soluble Mgs. Vit. C
Variety Size solids % Acid Ratio % Juice-wt. per 100 mls.

Hamlin (216) 11.68 0.92 12.65 47.04 65.7
(Dec. 22, 1952)

Pineapple (216) 12.70 1.13 11.28 45.24 68.1
(Jan. 13, 1953)

Valencia (200) 12.32 0.87 14.16 52.97 45
(May 22, 1953)

Duncan (70) 9.80 1.50 6.55 41.08 ( 37.6
(Jan. 31, 1952)
Marsh (80) 8.31 1.23 6.79 48.72 :i2.1
(Jan. 31, 1952) J

Fertilization.- Most pronounced differences in fruit quality as affected
by fertilization practices occur when acute deficiencies of nutritional elements
are present. Table 2 presents data of a single season for comparison, showing
effects on juice characteristics where a range of nitrogen, phosphorus, potas-
sium and supplemental elements (magnesium, manganese, copper and zinc) are

Citrus Station Mimeo Report 54-7. Florida Citrus Experiment Station,
lake Alfred, Florida. 472-10/6/53 J~


Effect of varying amounts of nutrient elements supplied in the fertilizer
mixture upon juice characteristics of fruit produced.

Juice by Soluble Titratable Ratio mgs. vit. C
Treatments weight solids acid solids/acid 100 mis/juice

"Supplemental elements" Pineapple Oranges
4-6-8 (40% organic) 49.63 9.22 0.94 9.96 56.3
4-6-8-3-1-1/2 (40% organic) 49.76 10.70 1.14 9.50 66.5
Seasonal average values, Block X fertilizer experiment, 1953.
"Nitrogen" Hamlin Oranges
2-6-8-4-1-1/2 44.16 10.61 .99 11.05 60.0
4-6-8-4-1-1/2* 45.08 10.97 1.02 ll.04 60.4
Seasonal average values, Block XI nitrogen source experiment, 1953.
"Phosphorus" Pineapple Oranges
4-0-8-4-1-1/2 42.92 12.59 1.23 10.38 73.5
4-6-8-4-1-1/2 44.47 12.12 1.04 11.85 68.4
4-18-8-4-1-1/2 45.57 11.80 1.04 11.64 61.8
Seasonal average values, Block XIII phosphorus experiment, 1953.
"Potassium" Valencia Oranges
4-6-0-4-1-1/2 53.03 11.90 0.86 14.63 40.8
4-6-8-4-1-1/2 53.24 12.42 1.09 12.07 50.8
4-6-16-4-1-1/2 52.55 12.48 1.08 12.35 51.1
Seasonal average values, Block XVII potash experiment, 1953.

Average values of trees supplied with sodium nitrate and ammonium sulfate.

Citrus Station Mimeo Report 54-7. Florida Citrus Experiment Station,
Lake Alfred, Florida. 472a-10/6/53 JWS.

Pest Control.- Insect and disease pests and their control present a major
problem to the citrus grower and may drastically affect the quality of the fruit
produced. The effect on quality may result directly from the pest or indirectly
from the control measure used. The use of oil in the control of scale insects
is a good example of the latter. Although oil is quite satisfactory as a control
for scale it is harmful to the tree and reduces the internal quality of the fruit
produced. Table 3 presents data showing the marked decrease in soluble solids,
titratable acid and vitamin C content which resulted when oil sprays were used
for scale control as compared to parathion. Parathion is equally as satisfactory
as oil as a scalicide and has no harmful effect on fruit quality.
Table 3

Effect of oil and parathion sprays on the juice
characteristics of Pineapple oranges1

SMgs. vit. C
Spray Date of % Soluble % Titratable Ratio % Juice per 100 mls.
material application solids acid by weight juice

Parathion July 15 11.66** 1.18 9.97 49.48 63.8**
Oil July 15 10.93 1.14 9.73 49.23 57.4

Parathion August 15 11.62** 1.21* 9.76 46.06 61.0**
Oil August 15 10.46 1.14 9.28 49.16 51.1

1 Seasonal average values from samples collected from November through January.
Work done in cooperation with W. L. Thompson, Entomologist.
Differences significant at the 5% level.
** 1% o "

Lead Arsenate Sprays for Grapefruit.- It seems evident that consumer accept-
ance of Florida grown grapefruit, sold fresh or in cans, leaves something to be
desired. How else can we account for the poor return to growers of grapefruit
during the past two years when Florida supplied approximately 85% of all the
grapefruit produced in the United States. The production of grapefruit with a
lower acid content (juice with a higher ratio and a sweeter taste) would be a
step in the right direction. This may be accomplished to a certain extent by a
more judicial use of lead arsenate. Widespread use of lower concentrations of
lead arsenate sprays would go far toward improving quality of Florida grapefruit.
Data in Table 4 presents results of varying poundages of lead arsenate on the
acid content of Marsh grapefruit. It is evident that the light application of
.4 pounds of lead arsenate per 100 gallons has had a pronounced effect on reducing
the acid content and at this concentration the toxicity is also reduced. Improve-
ment of grapefruit quality however must be a combined effort. Increasing yields
at the processing plant by extracting juice from grapefruit peels has certainly
increased the naringin content of the juice and has done much to make the product
bitter and less palatable.

Citrus Station Mimeo Report 54-7. Florida Citrus Experiment Station,
Lake Alfred, Florida. 472b-10/6/53 JWN

Table 4

Effect of varying amount of lead arsenate upon the titratable
acid content of Marsh grapefruit'

Treatment Year
Treatment1950-51 1951-52 1952-53

0 lbs. Lead Arsenate 1.51 1.37 1.46

0.4 Ibs. Lead Arsenate 1.47 1.29 1.37

1 1/4 lbs. Lead Arsenate 1.40 1.21 1.29

Data supplied by Dr. E.
Lake Alfred, Florida.

J. Deszyck, Citrus Experiment Station,

Irrigation.- Research in irrigation practices has demonstrated that the
internal quality of the fruit may often be affected. Trees grown under conditions
of continuous abundant soil moisture tend to produce fruit high in juice, low in
soluble solids and low in acid content. The use of irrigation during prolonged
drouth periods to protect trees and crop is highly recommended but if used indis-
criminately will result in increased production costs and poorer quality fruit.

Table 5
Juice constituents of oranges and grapefruit as affected by applications
of irrigation in March, May and-November of 1949

Percent gs. vit. C Volume of Gms. of
Treatment Brix Ratio per 100 mls. juice per soluble solids
juice fruit mis. per fruit
Hamlin Oranges
Irrigated 8.63 0.86 10.44** 51.5 74* 6.56
Non-irrigated 9.05** 0.98 9.58 57.5** 70 6.52
Pineapple Oranges
Irrigated 9.48 .90 11.36 60.4 83 8.15
SNon-irrigated 10.85** .98** 11.44 66.0** 84 9.55**
Valencia Oranges
Irrigated 10.65 0.83 13.56* 59.5 105 11.61
Non-irrigated 11.59** 0.96** 12.71 53.7** 104 12.63**
Duncan Grapefruit
Irrigated 8,17 1.32 6.36** 41.5 244 20.59*
Non-irrigated 8.62** 1.46** 6.16 45.0** 212 18.88
Marsh Grapefruit
Irrigated 7.31 1.28 5.84 35.2 211 15.86
Non-irrigated 8.17** 1.43** 5.95 41.1"* 190 16.01

John W., Herman J. Reitz and E. J. Deszyck.
ch with Florida citrus. Fla. Sta. Hort. Soc.
Lcantly different at the 5% level.
Sn n" 1% it

Some results
Proc. 1951.

of irrigation

Citrus Station Mimeo Report 54-7. Florida Citrus Experiment Station,
Lake Alfred, Florida. 472c-10/6/53 JWS

1 Sites,
* Signifj
** I

Position of Fruit on the Tree.- The position of the fruit on the trees and
the consequent effect of position on juice characteristics merits some considera-
tion in any discussion of fruit quality. In general the internal quality of the
fruit increases beginning at the bottom of the tree and continuing toward the
top and beginning at the inside and continuing toward the outside. The possible
usefulness of this information as a guide to spot-picking or selecting fruit for
fancy juice packs is presented in Table 6.

Table 6

The effect of spot-picking certain portions of the
soluble solids in the juice of the fruit

tree upon the average

Percerit of total Average percent
Section of tree not included fruit included soluble solids of
fruit included

- 100.0 10.24

Inside 82.1 10.57

Top inside 92.3 10.26

Canopy 67.6 10.34

Inside and top inside 74.4 10.64

Inside, top inside and canopy 41.9 11.12

Fruit Size.- Although many people are in a general way familiar with the
fact that juice characteristics vary in relation to fruit size the importance of
this factor is often not sufficiently appreciated. Table 7 presents the dif-
ferences in juice composition of a large lot of Valencia oranges from trees all
receiving the same cultural treatment, randomly sampled after sizing in the
packinghouse. It is apparent from these data that fruit size is of considerable
importance, especially to the fruit processor.

Weather Conditions.- Notwithstanding the effects on fruit quality previously
attributed to other factors weather conditions, over which we have no control also
determine to a large extent the quality of fruit which may be produced. Generally
speaking the quality of the fruit is inversely proportional to the total annual
rainfall. There are exceptions to this trend in certain years probably because
of unequal distribution of rainfall. Also it has not been established with
certainty whether these differences between seasons are due solely to soil mois-
ture or to other weather conditions associated with rain or combinations of both.

Citrus Station Mimeo Report 54-7. Florida Citrus Experiment Station,
Lake Alfred, Florida. 472d-10/6/53 JWS

Table 7

Effect of size of fruit on juice characteristics
of Valencia oranges1

% Juice Volume of Percent Vitamin C
Size by wt. juice per Brix acid Ratio mgs./100 ls.
fruit mls.

324 52.38 63 13.25 .71 18.66 44.6
288 54.60 71 12.85 .63 20.40 37.7

250 55.63 86 12.70 .61 20.82 35.6

216 53.33 95 11.90 .56 21.25 33.8

200 54.93 111 11.70 .57 20.53 34.0

176 49.42 113 10.95 .52 21.06 29.9

150 48.93 120 10.60 .52 20.38 29.1
126 46.24 118 9.90 .49 20.20 28.0

randomly selected fruit picked June 9, 1952.
W. Sites and E. J. Deszyck.

Unpublished data

Citrus Station Mimeo Report 54-7. Florida Citrus Experiment Station,
Lake Alfred, Florida. 472e-10/6/53 JUS