Question

An experiment to confirm that ripe tomatoes contain ascorbic acid

Answer 1

Answer:

EXPERIMENTAL PROCEDURE AND RESUI,TS

Two sets of tests were made to measure the extent of variability in the

ascorbic acid content of field tomatoes and to test various techniques of

extraction. In both sets the fruits were very carefully selected for uni-

formity of ripeness, color, size and firmness aird wiped with a damp cloth.

The freshly harvested fruit was cut in half, longitudinally, with a sharp

knife. A segment of the proper size was quickly cut from one half. When

a composite sample from several fruit was being prepared, the segments

were quickly assembled on the weighing pan and then plunged at once into

oxalic acid and blended. A duplicate composite sample of segments was

then prepared from the opposite half of each fruit. For tesrinf individual

fruits^a iO-gmm segment'*as cut from one half and blendedivith oxalic

acid. This-was rep"eated with a duplicate segment from the opposite half.

The procedure described under "A{aterials and Methods" for as,corbic

acid extraction requires a 50-gram sample in 150 milliliters of oxalic acid.

This concentration ratio precl-udes the possibility of extracting ten or even

five normal-sized whole fruit together in oxalic acid. A practical routine

procedure demands some compronrise to overcorne the problem of individual

variability. The method of cornpositing a number of segments is one such

compromise. A second method was tested in which a number of fr-uit were

blended for 15 seconds without oxalic acid. An aliouot of the resultant

slurry was immediately weighed into oxalic acid to give the correct con-

centration and the analvsis completed as before. This procedure was found

to be adequate only if the ope'ration was completed iir 30 seconds or less.

The data from all these tests (Table 1) give ample evidence of the variability

of ascorbic acid leveis both 'within and between individual fruits. The

results also support the validity of the technique of extracting in oxalic acid

duplicate 50-gram composite samples made up of 5-gram segments from

each half of each of ten fruits. Adequate compensation for the variability

factor is not obtained by using only five fruits. 'The method of macerating

fruit without oxalic a.id, altlio.rgh it probably leads to a smaller sarnpHnf

errot, involves too qreat a risk of loss of ascorbic acid to be accepted as a

standard routine prdcedure.

Ontogenetic Variation of Ascorbic Acid in Greenhouse Tomatoes

With the methods outlined above, a study was initiated to determine

the levels of ascorbic acid in greenhouse tomatoes during the growth and

development of the plant. Fruit from a spring crop of the F, hybrid,

llichigan-Ohio, planted in January and receiving all the normal cultural and

ferrilizer treatments, was used for this purpose. In practice this crop is

allowed to grow for about 6 months, producing 12 or more clusters of fiuit.

In this experiment samples were collected for ascorbic acid assay as

soon as the small green fruit began to appear on the first cluster. Successive

samples r.l'ere taken at varying intervals as the fruir grew in size, developed,

matured and ripened. This procedure vras followed with each cluster and

conrinued for it/, monrhs.