110 FLORIDA STATE HORTICULTURAL SOCIETY

heavy bearing sorts there is at least one of

these factors favoring fruitfulness.

This, combined with the results of the pol

lination investigation, suggests the introduc

tion of greater numbers of bees into the grove

as a possible means of increasing the produc

tiveness of Had en by increasing the number

of functionally perfect flowers pollinated.

THE VITAMIN C CONTENT OF PSIDIUM GUAJAVA

GUY WADDINGTON and FRANKLIN M. CIST Rollins College, Winter Park, Fla.

During the past few years a limited num

ber of tropical fruits have been reported to

contain abnormally large quantities of ascorbic

acid, contrasting sharply with the great ma

jority of fruits which in general contain from

less than 10 mg. up to 60 mg. of ascorbic acid

per 100 g. of fruit The cashew-apple (Ana-

cardium occidental) and the myrobalan

(Phyllanthus emblica), by use of the indo

phenol method of analysis1, have revealed the

presence of as much as 350 and 479 mg.

of ascorbic acid per 100 g. of fruit

respectively; while the common guava

(Ptidium guajava) has been reported from

Hawaii2, India&, and S. Africa4 to contain ex

ceptionally high values of ascorbic acid, which

in the case of the S. African fruit runs up 450

mg, per 100 g. of fruit. A dried fruit product

from this same variety of guavas was prepared,

which showed a 3% ascorbic acid content.

These extremely high vitamin C values sug

gest several reasons for the further investiga

tion of this problem. Firstly, the accepted

methods of determining ascorbic acid by oxi

dation to dehydroascorbic with 2, 6 dichloro-

benzenoneindophenol or with iodine are not

completely specific. A bio-assay method can

be used to check results semi-quantitatively

but it seems desirable to find a completely in

dependent chemical method of analysis which

will remove all doubt as to the reality of these

high vitamin C values. Secondly, since con

siderable plantings of guavas exist in Florida,

precise information concerning the vitamin

content of this fruit will certainly be of in

terest and may be of use to the grower arid

processer. Thirdly, the urgent need at this

time of fruit concentrates of high vitamin C

potency suggests that the possibilities of this

fruit be investigated* To these ends experi

ments have been made on the ascorbic acid

content of the fleshy pericarp of a number of

varieties of Psidium guajava and preliminary

experiments have been carried out on the

preparation of a vitamin^rich concentrate

from this fruit.

Experimental Methods and Materials

Guavas were obtained from three Florida

districts, namely, Boynton, Bradenton and

Orlando, during the winter months.

Four methods of analysis were used in all.

Three of these, the indophenol, iodine and

iodate methods are basically the same, all

depending on the oxidation of ascorbic acid

to dehydroascorbic acid. The iodateB method,

which agrees very well with the indophenol

method, was used predominantly. The other

method, which depends on the formation of a

specific red color when the 2, 4 dinitrophenyl-

hydrazine osazone of dehydroascorbic acid is

treated with 85 per cent sulfuric acid at 5°C, is

independent of the other three methods and

should give convincing evidence of the pres

ence, or absence, of substances in the fruit

which might interfere with the above mention

ed oxidation methods of analysis.

For all analyses the fruit extract was pre

pared by taking a weighed sample of the fleshy

part of the guava (about 10 grams is satisfac

tory), immediately grinding this to a smooth

FLORIDA STATE HORTICULTURAL SOCIETY 111

paste with 2 per cent metaphosphoric acid

solution, and then transferring this to a 100

ml volumetric flask and diluting to the mark

with more of the 2 per cent metaphosphoric

acid solution. .

Fifty ml. aliquots of the extract may be tit

rated with standard solution of 2, 6 dicholoro-

benzenoneindophenol or with iodine according

to established procedures or the more recently

' developed iodate method^ may be used. . In

this last method, 2 ml. portions of 10 per cent

potassium iodide and starch indicator solution

are added to an aliquot part of the extract,

which is then titrated with 0.01 N potassium

iodate to the usual starch endpoint. A 0.1 N

stock solution of potassium iodate may be made

tip and diluted to 0.01 N as required.

The colorimetric method follows Roe and

Keuth'er'sS modification of the method of Roe

and Hall used to determine ascorbic acid in

urine. The procedure as applied to guavas is

as follows: Prepare a pure ascorbic acid solu

tion of 0.02 mg. per ml. and dilute the guava

extract to approximately this concentration.

Filter the fruit extract and pipette 2 ml. por

tions of the filtrate and of the standard ascorbic

acid solutions into 15 ml. centrifuge tubes. Add

to each tube 1 drop of 0.1 N potassium iodate,

followed by 4 ml. of a saturated solution of

2, 4 dinitrophenylhydrazine in 1 N hydrochloric

acid. Allow to stand in darkness for 15 to 24

hours and then centrifuge. Decant the super

natant liquid from the matted crystals and wash

with 5 mL of 10 per cent acetic acid. Centri

fuge and drain; then to the matted crystals add

ice cold 85 per cent sulfuric acid, finally trans

ferring the content of each tube to 25 ml.

volumetric flasks which are then filled to the

mark with' additional cold 85 per cent sulfuric

acid. Allow the flasks to stand in ice water

for 10 minutes and then compare their colors

in a colorimeter.

All drying of the fruit was carried out in an

Abderhalden pistol equipped with a calcium

chloride side chamber, evacuated by means of

a Hyvac pump and heated by the vapor of boil

ing acetone which gives a constant tempera

ture of 66 °C.

Before being placed in the vacuum chamber

the fruit was either macerated with a mini

mum quantity of 2 per cent metaphosphoric

acid solution or segments of the fruit were

blanched for 2 minutes in a nearly boiling solu

tion of 2 per cent acid or in very hot water as

suggested by Goldberg and Levy4.

Results

Analyses were carried out on as many varie

ties of guavas as could be obtained. These in

cluded large and small fruit, a variety of shapes,

flesh color ranging from white to deep salmon,

and maturity from very green to over ripe.

Averaging the results of ten analyses on

mature or nearly matured fruit, an average

value of 564 mg. ascorbic acid per 100 grams

of fruit was obtained. One variety with very

large white-fleshed fruit gave values of 37

mg. and 45 mg. of ascorbic acid per 100 g.

of fruit. Five others ranged from 430 to 500

mg. per 100 g. of fruit, averaging 465 m£.,

and a group of three ranged from 940 to 1160

mg., averaging 1077 mg. of accorbic acid per

100 g. of fruit.

No significant correlation could be discover

ed between ascorbic acid content and shape,

size or flesh color, although the varieties con

taining the greatest amounts were either small

or medium in size. Extensive investigations

of all known varieties will have to be made

in order to answer the question of varietal

dependance of ascorbic acid content. Any

possible use of guavas depending on vitamin

C content should of course be preceded by

careful choice of the best varieties.

It is to be noted that nearly ripe but still

very firm fruit contains as much or nearly as

much vitamin C as fully mature fruit. In

dividual values of 940 and 1130 mg. of ascor

bic acid per 100 g. of fruit were obtained on

firm,, somewhat under-ripe fruit. Over-ripe

fruit and hard green fruit showed lower values.

Blanching segments of guava flesh" in near

ly boiling water followed by drying in vacuo

at 56 °C gave aproduct containing extremely

large quantities of vitamin C. Individual ex

periments led to products containing respec

tively 4100, 4400, 3800 and 5240 mg. of

vitamin C per 100 g. of fruit, definitely ex

ceeding the 2000 mg. value reported for dried

hips (Rosa canina), one of the richest natural

sources of Vitamin C previously reported*. The

112 FLORIDA STATE HORTICULTURAL SOCIETY

first two analyses mentioned were from pink-

fleshed fruits and the latter from small pale-

fleshed fruits. Grinding fruit in a small quan

tity of 2 per cent metaphosphoric. acid solu

tion before drying led to a 50 per cent loss of

vitamin C. Blanching in nearly boiling 2 per

cent metaphosphoric acid gave no improve

ment over blanching in water.

Systematic study of the keeping qualities

of the dried product has hot been carried out

but incidental observations over a six weeks

period with no particular care being given to

methods of storage; indicated in most cases

less than 10 per cent loss of ascorbic acid con

tent.

As previously suggested, the possibility

should not be overlooked that these ascorbic

acid values, being so much greater than in

most fruits, are caused, in part at least, by

otiher reducing substances which are also

oxidizable by the three titratiori reagents,

potassium iodate, iodine and 2,6-dichloroben-

zenoneindophenol thus giving too large values.

Six separate samples of dried .guava and

one of fresh guava were analyzed fyoth by. tjie colorimejbric method and by the iodate method

giving results as shown in Table, I. Values

are in mg. ascorbic acid per 100 g. of ̂ ruit.

Sample

number 1 3 5 6

Colori-

metdc 4000 3620 3500 870 890 1080 427

Iodate 4000 3500 3750 910 920 1060 400

Samples 1—6 are dried guava, 7 being fresh

fruit. It is to he noted that agreement is

reasonably good and that deviations are

random*

This agreement by. the. two methods on

guava samples must mean either that the ascor

bic acid values are real or that the interfer

ing substance forms an insoluble derivative

with 2, 4 ilinitrophenyl hydrazine which reacts with 85 per cent ice. cold sulfuric within 10

minutes to give a red color which is identical

with that formed by . dehydroascorbic acid

under the -same circumstances^ This latter

contingency while hot ruled out, is regarded

as being highly improbable. : It is believed,

on this evidence that considerable confidence

may be felt in analytical values obtained dn

guava by the use of the 2,6 dichlorobenzen-

oneindophenor method or other accepted titra-

tion methods based on the oxidation of ascor

bic acid.

Summary

I. Analyses, of the fruits of psidium gua-

jaya grown ift Florida yielded an average, value

of .504 mg. of ascorbic, acid per 100 g, of

fruit. .

II. Varietal differences exist, the range of

ascorbic acid values: observed being from 37

to. 1J60 mg.: of ascorbic acid per 100 g. of

fruit. . : ; •.,/•<

IIIv, From* guava flesh dried edible con

centrates have been prepared containing as

high as 5.2 per cent ascorbic acid.. •*

•IV. A colorimetric method of analysis has

been applied to guavas and gives results in

good agreement*with the commonly used tit

ratiori methods.

Bibliography

1. A.W.iRi. Joachim arid D* G. Panditie-sekere—Agricultural j.. of Ceylon-—95, .137

(1940).. . . .

2. C. p. Miller, K. Bazore and R, C.

Robbins-UHawaii Exjp»$,' gtation^—Bulletin 77,

1936. " .' . .". ;■ ' . . •'"'.-.• ";■" 3. g,. Raganathan, Ind. J, Me.i Res.—23,

?39, (1935). ..." .

4. L. Goldberg and L. keyy, JScience 148, 287, (i94i).. . .. . ; . : .

. 5. JR. Bajlentine^ Ind. and $ng, Chem.

Anal. ^4.-13, 80, (J94X). ' . 6. J, H. Roe apd C. A. Keuthery Science

95, 77, (1942). . .

. 7. J. H.Roe and J.. M. Hall, Jour. £iol. Chem—12$, 329, (1939). . . ..

. 8. H. Lund,B/ Spur and I*. S, Fridericia,

Biochem. J,—2if 1,825, (1934). . . [ . Chemical Laboratory.., ,.

Rollins College • •.. *' Winter Park, Florida . .,

April 21,

Wolfe and Lynch—New Varieties of Mango for Florida

Fig. 1. Brooks Mango.

Fig. 2. Fascell Mango.

Wolfe and Lynch—New Varieties of Mango for Florida

Fig. 3. Springfels Mango.

1 1 1 1

i

m Wk.

JM

IS

us*

#*?<£

Fig. 4. Fragrance Mango.

Wolfe and Lynch—New Varieties of Mango for Florida

„„_,

Fig. 5. Simmonds Mango.

Fig. 6. Borsha Mango.

Lynch and Wolfe-Khaya Nyasica, A New Mahogany for

South Florida

Fig. 1. Khaya nyasica trees 12 years old growing among

Carribean pine saplings. Pine sapling in foreground

about 24 years old.