Lab 03: Determination of the content of reducing sugar using Benedict’s test
2007 Al-Bio
Lab 3: What has happened to the banana? Problem:
Why yellow bananas are sweeter than green bananas? Hypothesis:
Yellow bananas are sweeter than green bananas because some starch is converted into reducing sugar during riening! Aim:
"o rove the hyothesis by comaring the amount of reducing sugar and starch in bananas of different degree of rieness! Principle: Etraction o! chemicals !rom bananas
"o grind u the tissue# so as to destroy the cell membrane and release chemicals inside for quantitative analyses of reducing sugar with with Benedict’s solution and starch with iodine solution! "odine test
$ince a blue%blac& colouration is formed when adding iodine solution into starch# the intensity of blue%blac& colour can be used to determine the 'uantity of starch in the samle bananas! The higher the colour intensity indicates a higher concentration of starch in the samle! Benedict#s test
Boiling the mi(ture of reducing sugars and Benedict’s solution gives bric& red reciitate! )n 'uantitative test of Benedict’s solution solution is in excess# the amount of ppt. formed is proportional to the amount of reducing sugar# if Benedict’s
in the samle! reducing sugar in *re%e(erimental trials will be carried out to determine the volume ratio of banana e(tracts to Benedict’s solutions! + greenish or blue colour of the resultant solution after heat will be an accetable ratio for the e(eriment! "his ensure comlete reaction of reducing sugar with e(cess Benedict’s solution! $ariables:
"he independent variable is the the degree of ripeness of bananas , i!e! colour of bananas"n Benedict#s test # the dependent variable is the amount of reducing sugar in bananas ,according to the hyothesis# the amount of reducing sugar deends on the degree of rieness of bananas- !
"his can be measured as the amount of brick-
in the test! red precipitate formed in "n iodine test# the dependent variable is the amount of starch in bananas! "his can be measured as the intensity of blue-black colour resulted in the test!
+lso there are some control variables should be &et as constant throughout the e(eriment! "hey are the mass *age ./
Lab 03: Determination of the content of reducing sugar using Benedict’s test
2007 Al-Bio
of food samples , volume of water for extraction , the volume ratio of extracts to Benedict’s solution, temperature of water bath , heating duration , the volume ratio of extracts to iodine solution1! Epected res%lt trend of larger amount of bric&%red reciitate and lower intensity of blue%blac& colour is found in banana
with a higher degree of rieness! ,i!e! an ascending amount of reducing sugar and a descending amount of starch will be found from green banana to greenish yellow banana and than yellow banana!Ass%mptions:
.!
the only reducing agent for reciitate formation in the e(eriment is reducing sugar in the solutions
2! all sweet taste of the yellow banana comes from reducing sugar ,e!g! not from sucrose3! o genetic variation among the banana samles will cause different in the testing biochemical change! 4! all chemical changes stoed during e(traction and the whole e(eriment 5! the reaction of reducing sugar and starch are comleted during tests! List o! apparat%s ---Proced%res
.!
2&' o! each !ood samples were weighted with electronic balance!
2!
samles (ere minced with &nife and then be 'ro%nd !or &min) (ith 2& cm 3 o! *0o+ (ater in mortar searately! ,to revent contamination# all aaratus were cleaned thoroughly with water before dealing with different food samles! 6ot water was used to dissolove the starch for easy e(traction-
3!
4!
Boiling tubes were labeled as follow: Boliling tube label
.
2
3
7ontent
filtered green
filtered greenish yellow
filtered yellow
raw banana e(tract
half%rie banana e(tract
rie banana e(tract
e(tracts were filtered through 2 layers o! m%slin cloth into the above three labeled boiling tubes .# 2 and 3 resectively
5!
+fter re%e(erimental trials# the ratio of banana e(tracts to Benedict’s solutions was decided! By use of measuring cylinder and iettes# the filtered e(tracts# water# Benedict’s solution and iodine solution were transferred into the following labeled test tubes resectively! ,*iette should be erect and be read at the same level as eyes to revent reading error,est t%bes !or Benedict#s test and controls o! Benedict#s test
"est tube label
B.
B2
B3
samle
green raw
greenish yellow
yellow rie il
banana
half%rie banana banana
*age 2/
B4
Lab 03: Determination of the content of reducing sugar using Benedict’s test
volume of Benedict’s
2007 Al-Bio
.0
.0
.0
.0
5
5
5
0
0
0
0
5
/&
/&
/&
/&
solution cm3. volume of samle e(tract cm3. volume of water cm3.
"otal volume of content cm3.
8 "est tube B4 was the control to show no contamination in water and reagent and the formation of reciitate is due to the reaction between chemicals in e(tracts and the Benedict’s solution! ,est t%bes !or "odine test and controls o! "odine test
"est tube label
).
)2
)3
samle
green raw
greenish yellow
yellow rie il
banana
half%rie banana banana
.
.
.
.
5
5
5
0
0
0
0
5
*
*
*
*
volume of )odine
)4
solution cm3. volume of samle e(tract cm3. volume of water cm3.
"otal volume of content cm3. 8
"est tubes )4 was the control to show no contamination in water and iodine solution and the colour change of iodine solution is due to the resence of starch in e(tracts!
*age 3/
Lab 03: Determination of the content of reducing sugar using Benedict’s test
2007 Al-Bio
!
9ecord the initial obserations o! Benedict#s test and the colo%r chan'es o! iodine test)
!
the test tubes for Benedict’s test ,B.%B3- and control of Benedict’s test ,B4- were boiled in (ater bath !or & mins! ,water bath for even heating; 5mins! was re'uired as sufficient time for comletely reaction of
reducing sugar or Benedict’s solution; safety glass was used to rotect the eyes form Bunsen’s flame and the sitting out of mi(ture from test tube during heating
the test tubes were removed from water bath and were allowed to stand !or 20 mins in test tube rac&! ,to allow sedimentation of all reciitates-
=!
"he amount of bric&%red reciitate was meas%red as the hei'ht o! the precipitate deposited at the bottom of the test tubes with a ruler!
1es%lts: ,able /: bserations and amo%nt o! precipitate o! sample etracts be!ore and a!ter heatin' in Benedict#s test
"est tube label
B.
B2
B3
B4
content
green raw
greenish
yellow
water and
banana
yellow half%
rie
Benedict’s
and
rie banana
banana
solution
Benedict’s and
and
solution
Benedict’s
Benedict’s
solution
solution
)nitial
blue
blue solution
blue
blue
observation
solution
with no red
solution
solution
,before heating-
with no
reciitate
with no
with no
red
red
red
reciitate
reciitate reciitate
>bservation
greenish
greenish
greenish
blue
after heating
solution
solution with
solution
solution
with red
red reciitate
with red
with no
reciitate
red
reciitate
reciitate 6eight of reciitate at
0!2
0!4
.!0
bottom of test tube after 20 mins! ,cm-
*age 4/
0!0
Lab 03: Determination of the content of reducing sugar using Benedict’s test
2007 Al-Bio
,able 2: ,he inal obseration o! sample etracts in "odine test
"est tube label
).
)2
)3
)4
samle
green raw
greenish
yellow
il
banana
yellow half%
rie
rie banana
banana
)ntensity of dar& blue color
no dar& high
medium
low
blue colour obtained
8 )odine solution is originally brown in colour!
*age 5/
Lab 03: Determination of the content of reducing sugar using Benedict’s test
2007 Al-Bio
4isc%ssion 1es%lt interpretation
rom result table .# the greenish colour of the mixtures in tubes B1, B2 and B3 shows that Benedict’s solution was in excess and complete reaction of reducing sugar in these tubes occurred ! +ccording to the rincile# the amount of reducing sugar roortional to the height of reciitate formed! When comaring the height of reciitate in tubes B.# B2 and B3# it is found that yellow rie banana ,B3- contains the greatest amount of reducing sugar ,6eight of reciitate @ .!0 cm-# greenish yellow half%rie banana ,B2contains lesser amount of reducing sugar ,6eight of reciitate @ 0!4 cm- and the green raw banana contains the least amount of reducing sugar ,6eight of reciitate @ 0!2 cm-! That means the amount of reducing sugar increase with the degree of ripeness of banana.
rom result table 2# the intensity of dar& blue colour decreases from tube ). ,high intensity- to tube )2 ,medium intensity- and then tube )3 ,low intensity-! +s the intensity increases with the amount of starch in samles# thus the amount of starch is highest in green raw banana ,).-# lesser in greenish yellow half%rie banana ,)2- and the least in yellow rie banana That means the amount of starch decrease with the increase in the degree of ripeness of banana. The decrease in starch content and increase of reducing sugar as banana get ripening support the hypothesis of the experiment . Yellow bananas are sweeter than green bananas because some starch is converted into
reducing sugar during riening thers
%
other significant discussion (e.g. abnormalities, limitation, sources of error, wrong assumption, any new assumption, improvement suggestion, suggestion of following experiment for further investigationetc.!
+oncl%sion The hypothesis is supported by the experiment. The conversion of starch into reducing sugar during ripening cause a sweeter taste in yellow banana than green banana.
*age /
