Experiment 07: Fruit juice and meat tenderizer
2007 Al-Bio Marking Scheme
Experiment 07: Fruit juice and meat tenderizer
Area B1 (max. 15 marks)
Aim: ( max. 1 )
- To study the meat tenderizing ability in the provided fruits (papaya, pineapple and kiwi fruit) in term of
protein digesting activity
and compare the activity in the fruits. Hence deduce the relative tenderizing effect of the provided fruits on
meat.
Principle: (max. 8)
A. Background of the aim
Given: meat can be tenderized by fruits. However the process of tenderisation is stopped after cooking and
the meat is no longer broken down
- Fruits may have protein digesting substances to break down proteins in meat. As the tenderizing
effect can be stopped after cooking, the protein digesting substances may be proteases which are
protein in nature and would be denatured by high temperature during cooking.
Given: People not used to working with these fruits find that if they handle the ripe fruit with their bare hands,
they can become very sore and reddened.
- The hands become very sore and reddened may due to the action of protease on the surface of the
hands.
Alternation:
Aim: ( max. 1 )
- To prove the hypothesis that the meat tenderizing effect in fruit juice is due to their protein digesting
property / the presence of protease in them.
Also to compare their meat tenderizing acivity in term of casein digesting activity / to investigate the
different in the activity of these fruit juice.
Hypothesis:
Hypothesize that meat tenderizer and fruits with different meat tenderizing ability are due to the presence
and different in activity of protease or protein digesting substance inside.
Principle: (max. 8)
A. Background of the aim
Given: meat can be tenderized by fruits. However the process of tenderisation is stopped after cooking
and the meat is no longer broken down
-
Fruits may have protein digesting substances to break down proteins in meat. As the
tenderizing effect can be stopped after cooking, the protein digesting substances may be
proteases which are protein in nature and would be denatured by high temperature during
cooking.
Given: People not used to working with these fruits find that if they handle the ripe fruit with their bare
hands, they can become very sore and reddened.
- The hands become very sore and reddened may due to the action of protease on the surface of
the hands.
Thus the above hypothesis is proposed.
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Experiment 07: Fruit juice and meat tenderizer
2007 Al-Bio Marking Scheme
B. Proteins are main components of meat’s muscle fibres
Milk agar contains milk protein (casein) which give the characteristic white colour to the agar
-
milk protein can be used to test the presence and efficiency of protease
breakdown of casein demonstrate breakdown of meat protein
C. Break down of milk protein in milk agar will cause the appearance of a clear zone
- clear zone around the fruit juice if a drop of the juice was applied to a well on a milk agar plate
- The diameter and clearance of the clear zone represent the efficiency of the action of the protease in the
juice on the milk agar and, hence, the activity of that protease / meat tenderizing substance
- The higher the activity of the protease (/ protein breaking ability) in a fruit, it may has a better meat
tenderizer functionally.
D. Extraction Process
- enzyme inside cells of fruits can be obtained by bursting the cells to get the extracted enzyme containing
juice.
E. Incubation
- increase protease activity for more obvious results
- faster diffusion rate of protease in agar
F. Assumption
- all protease in various type of fruit having the same diffusion rate in milk agar / the area of clear zone not
-
limited by diffusion rate of juice protease in agar
the effect of different in degree of maturation of fruit samples can be ignored.
Even distribution of enzyme in fruit,
Even distribution of casein in agar
Only protease in fruits digest casein in milk agar
Enzymatic activity on casein is similar to that on meat
(Part A to F : max. 5)
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Experiment 07: Fruit juice and meat tenderizer
2007 Al-Bio Marking Scheme
Dependent variable (½): measurable parameter that can indicate or represent the protein digesting activity
(e.g area or diameter of clear zone around juice containing wells)
Factors affecting dependent variable (control variables and independent variable):
Independent variable (½)
-
the different in protein digesting efficiency / different fruit juices
control variables (max. 1)
-
volume of juices in wells,
size and shape of wells on agar plate,
incubation temperature,
time for incubation
-
concentration of casein in agar (given)
composition and density of agar (given)
any dilution procedure about juice
degree of maturation of fruits (given)
Expected results: (max. 1)
No clear zone can be found around the control (water) and
different size of clear zone around the juice containing wells can be ranked
or
clear zone formed by various fruit juice can be seen and size of the zones is possible to be measured. We can
comment in the different in protein digestion effect and hence the meat tenderizing effect of different fruit
juices by comparing the size of clear zone.
List of apparatus and materials (0 or -½)
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Experiment 07: Fruit juice and meat tenderizer
2007 Al-Bio Marking Scheme
Procedures (max.6)
-in reported speech
Steps
(max. 3)
- Label and making wells on milk agar plate
- Extraction of fruit juice
- Adding juice and water into the labeled wells respectively
- Cover the plate
- Initial observation on the plate
- Place the plate into a incubator
- Final observation and measurement (Area or diameter of
clear zone and other observation)
Quantities and Units
Diameter / with the same straw
Volume ratios of water to juice
Temp., incubation period
Control (or explained in the procedures): (max. 1)
Water instead of juice to prove no contamination of the agar plate with protein digesting initially or during the
above procedures , hence, any occurrence of clear area is due to the effect of the juice on it
Precautions
(max. 2)
Steps
Explanation
- Deal with the agar lightly during making wells Agar is delicate, rude dealing have cause damage or
non-smooth edge of the wells
 difficulty in measuring diameter or area of irregular clear
zone
-
Label at bottom or sides of the plate instead of
the cover unless the relative position of the
cover and the plate is fixed with plastic tape
Displacement of the cover may lead to mismatching of the
labels and the wells
-
Wash apparatus every time after used if it is
reused
Prevent mixing / contamination of the juice with the juice
of other fruit which is prepared with the same apparatus
previously
-
The straw for well making must be kept as
vertical as possible
Avoid difference in surface area of the side wall of the well
due to oblique cutting
-
Prevent overflow of juice on surface of the agar As mixing of the juice may occur and making it hard to
/ detachment of agar from bottom of petri dish decide the clear area is due to the effect of either or both of
around the wells
the juices
/ digestion of milk protein from the top surface of agar
instead of from the edge of the wells making the diameter
of clear zone not reliable.
-
Evenly separated wells on plate
Prevent overlap of clear zones
-
Cover the plate before putting into incubator
Prevent evaporation of water in juice and agar.
-
Minimize the frequency and duration of
opening of incubator.
Prevent any significant fluctuation of temperature inside the
incubator that causing any significant error on the result
that cannot be ignored.
- others
Others
- technique descriptions
- good table presentation
- others
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Experiment 07: Fruit juice and meat tenderizer
2007 Al-Bio Marking Scheme
Area B2 (max. 6 marks)
-
Correct and proper title for all tables and graphs (if any) (max. 1)
-
Data table (and graph): (max. 4)
-- proper row heading with S.I. unit (if needed)
--- Well labels,
--- Sample / Well content,
--- Initial observation (any clear zone / colour of well)
--- Final observation (any clear zone / degree of clearness of clear zone …etc)
--- Diameter of clear zone / Area of clear zone
-- formula and calculation for area or dilution (if any)
-- complete table lines
-- tidy and well presented for easy reading
-
Records of other constants (max. 1)
-- volume of juice added
-- temp. of incubator
-- duration of incubation
-- size of wells …etc.
-
Others (max. 1)
e.g. bar chart presentation (Title, x-axis name, y-axis name, unit and scale)
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Experiment 07: Fruit juice and meat tenderizer
2007 Al-Bio Marking Scheme
Area B3 (max. 9 marks)
- data description and interpretation
(max. 5)
compare to expected results:
-- absence clear zone around water + clear zone around other juices
 clear zones around other wells are due to the presence of juice
-- clear zone around juices
 presence of protein digesting power
(i.e. hypothesis is proved: tenderizing power due to the presence of protease in fruits)
-- different in size of clear zone
Ranking of clear zone size  ranking of protease activity  ranking of meat tenderizing power
explanation:
--- may be higher conc. of protease ( same or different kind of protease in different fruits)
--- may be more efficient protease (i.e. different kind of protease)
∵ Both reasons have no evidence from the result and given information
∴ only reflect the rank of enzyme activity and meat tenderizing power
Suggestion of possible reasons for unexpected results:
-- larger size (but less transparent) clear zones : lemon juice > pineapple > kiwi fruit > papaya
== > higher digestion rate (efficience) but less effective digestion (products are longer peptide chains
instead of short chains or a.a.)
== > high diffusion rate and disperse enzymes (i.e. larger area but lower conc.)
== > lower pH value causing better pH condition for fast digestion / poor pH condition for poor
effectiveness of digestion / direct denaturation of milk protein by low pH.
-- more transparent (but smaller size) clear zones: papaya, kiwi fruit > pineapple > lemon juice
== > vice versa
∴ The choice of fruit as the better meat tenderizer depends on the size of meat and the time for
tenderizing.
∵ the above reasons cannot be proved in this experiment
∴ further experiment should be carried out, e.g.
-- addition of weak acids (e.g. citric acid) into one of the well without any juice to test for the
effect of low pH on the clearness of milk agar
-- …etc.
-
other significant discussion (max. 3)
(e.g. limitation, sources of error, any assumption rejected, improvement suggestion…etc.)
-
conclusion (max. 2)
The presence of protease / protein digesting activity causing the meat tenderizing power in the provide
fruits.
The descending order of meat tenderizing power among the provided fruits is : ___________________.
* with reference to the above guidelines, reports were marked by overall impression.
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