Enzymes in Fruit Investigation Write-up
Problem and Hypothesis:
This investigation was carried out in order to identify which fruits have proteolytic enzymes, the
enzymes that digest collagen in gelatine. Fruits like papaya and closely related to papaya, such as
babaco, contain more proteolytic enzymes. Furthermore, pineapple was also hypothesized to contain
large quantities of proteolytic enzymes because of the existence of bromelain. Additionally, the
effectiveness of local ‘wonder’ fruits was tested. It was hypothesized that noni and borojó, believed to
have magical healing properties, would have more proteolytic enzymes and thus digest the collagen
more fully. In order to test this hypothesis, a small strip of photographic film was placed in a fixed
volume of each fruit’s juice with the gelatine and collagen-containing side facing downward, and left
for approximately 30 minutes, and then compared to an undigested strip of film. Thus, the
independent variable was the fruit juice, while the dependent variable was the transparency of colour
change observed in the strip of film.
Experimental Design:
1. The fruit to be tested were chosen. Pineapple, babaco, honeydew melon, guanabana, papaya,
borojó and noni (both of which are local fruits believed to have ‘magical’ properties). Juice
was extracted by tightly squeezing large chunks of the fruit. The juice obtained was then
strained to eliminate pulp and seeds.
2. The ridges and holes on the sides of photographic film were cut off. The film was then cut
into 3x2 cm rectangles. Enough rectangles were cut out so that one could go in each of the
fruit juices; in this experiment seven rectangles were used.
3. 20ml of each juice was placed in petri dishes. It was evenly spread over the entire surface area
of the dish’s bottom side.
4. The photographic film was placed with the gelatine side facing down. In order to maximise
the surface area in contact with the juice, the film was flattened by folding it and reversing the
curve. Immediately after placing the film in the petri dish the lid was placed.
5. The petri dishes were transferred into a cupboard, and the doors were closed. The film was left
in the juice for 30 minutes. In this way, the samples were kept in the dark and at room
temperature.
6. After 30 minutes had passed, the film was removed from the juice and thoroughly rinsed to
remove any traces of juice that might continue digesting the collagen.
7. In order to evaluate how much
collagen had been digested by the
enzymes, the film was placed on
an overhead projector’s box, on
the Fresnel lens (point 5 on the
diagram). The samples of film
used in the experiment were
compared to an undigested strip
of film of the same size.
Data Recorded:
The scale used to measure the change in the transparency of the photographic film is from 0 to 4, in
which 0 displays an opacity matching that of an undigested piece of film’s and where 4 displays
complete transparency or colour change.
Data Table:
Fruit used
Babaco
Pineapple
Honeydew melon
Guanabana
Papaya
Borojó
Noni
Transparency value (0-4)
3
2
2
1
0
1
1
Conclusion and Evaluation:
Babaco, a close relative of papaya, displayed the most digestive capabilities, fully supporting
part of the hypothesis. Pineapple also partially supported the hypothesis, as its digestive capabilities
were among the most noticeable, but given its reputation and the information known about pineapple
and the bromelain it contains the result was expected to be higher. The results suggest that papaya, a
fruit predicted to be the best digestive fruit, and the local ‘magical’ fruits, contain little to no
proteolytic enzymes as they hardly digested the gelatine in the film. The results for these fruits
(papaya, borojó, noni, guanábana) cannot be considered firm evidence for or against the hypothesis as
their reliability and validity is questionable.
The photographic film was left in the papaya juice for at least 10 minutes less than the 30
minutes decided on in the experiment. The noni and borojó samples were left for even less time.
Thus, the proteolytic enzymes would not have had enough time, or the same amount of time, to digest
the collagen as they did in the pineapple, babaco and honeydew melon samples.
Another factor detracting from the reliability of certain results was the environment in which
they were kept as the film was soaked in the juice. While the babaco, pineapple and melon samples
were kept in relatively stable conditions (exact values and fluctuations were not recorded or taken
into account, another factor to be taken into account): the light was blocked out, temperature was kept
at or around room temperature and the samples were not moved at all until the time span ended, The
other samples were kept under aluminium foil. In this case, the light intensity would have remained
constant. Temperature, however, is likely to have fluctuated given aluminium foil’s heat conducting
property. The samples may have also been moved during the time span as the foil was adjusted.
In the cases of noni and borojó, the photographic film was dipped into the pulp rather than the
juice. In addition to this, rather than just putting the gelatine side in contact with the fruit, the whole
strip was dipped vertically into the pulp.
Concentration also played an important part in the validity of the results. The volume of
water, and thus the concentration of the proteolytic enzymes for the juices were unknown. Because of
this, the photographic film strips were soaked in juices with very different and unknown
concentrations of enzymes, making it impossible to make a proper and fair comparison between the
juices.
Taking into account all of these shortcomings and unfair conditions, it is safe to say that the
results obtained cannot be used to support or disprove the hypothesis of this investigation.