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DIGESTION OF FOOD
GROUP 6 - DAD
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OBJECTIVES
1. TO BE ABLE TO SHOW THE
DIGESTION OF A CARBOHYDRATE
BY SALIVA AND PANCREATIC
JUICE.
2. TO SHOW THE EFFECT OF THE
GASTRIC AND PANCREATIC
PROTEASES ON PROTEINS.
3. TO SHOW THE EFFECT OF
PANCREATIC ENZYMES ON FAT.
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DISCUSSION
The process of digestion involves a series of
hydrolytic process. The changes on the food intakes
are due to the catalytic activity of the various
enzymes in the saliva, in the gastric and pancreatic
juices.
Dietary carbohydrates include starch, sucrose,
lactose and indigestible fiber. These carbohydrates
are digested into simpler forms mostly glucose but
galactose and fructose maybe are produced. The
principal sites of dietary carbohydrate digestion are
the mouth and intestinal lumen. This digestion is
rapid and involves several enzymes.
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DISCUSSION
Proteins are digested into amino acids which are
absorbed through the intestinal epithelial cells
and enter the blood. Protein digestion is due to
digestive proteases usually produced and
secreted in its inactive forms. The process begins
in the stomach up to the small intestines.
The major dietary is triacylglycerol which is
obtained from the fat stores of the plants and
animals in the food supply. These are water
insoluble must be emulsified by bile salts and
digested in the small intestine to fatty acids.
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CARBOHYDRATE DIGESTION
MATERIALS

Cooked Starch
+  Lugol’s Iodine solution

Litmus paper

Benedict’s solution

Na2CO3
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1.
1. Put a drop of cooked
starch mixture on a water
glass and add a drop of
Lugol’s
iodine
solution.
Observe and record results.
2.
2. Collect 10ml of saliva in a
test tube & filter it into
another test tube. Test
filtered saliva with red and
blue litmus paper. Observe
and record results.
PROCEDURE
ACTION OF SALIVA ON STARCH
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3. To 10ml of filtered saliva in a
test tube adds 5ml of cooked starch
solution. Immerse the tube
containing the mixture in a beaker of
H2O, keeping the H2O warm at 37°C40°C for about 30 minutes. At 5
minute intervals, remove a drop of
mixture and place it on a watch glass
and test with iodine solution.
4. Transfer remaining cooked
starch and saliva mixture in a test and
add 4ml of Benedict’s solution. Heat
the tube gently to boling.
PROCEDURE
ACTION OF SALIVA ON STARCH
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RESULTS
Lugol’s Iodine Benedict’s Test
Test
COOKED
STARCH
The concentrated
starch in the middle
became dark purple
while the fluids
became yellow green
COOKED
STARCH +
SALIVA
YELLOW
The concentrated
starch and fluid
became baby blue
BLUE
+ Materials
•
Commercial Pepsin
•Concentrated
HCl
•NaOH
•CuSO4
•O.5%
solution
Na2CO3
PROTEIN DIGESTION
ACTION OF THE GASTRIC PROTEASE ON
PROTEIN
+ PROTEIN DIGESTION
(Action of Gastric Protease on Protein)
1. Label 3 test tubes into A, B, C. Then fill half of each tube with
warm H2O
2. Into each tube put a small amount of grated white of hard
boiled egg.
3. To the first tube, add a pinch of commercial pepsin and 2
drops of concentrated HCl.
4. To the second test tube, add only a pinch of pepsin, add
nothing to the H2O-egg-white mixture in the third tube.
5. Place these tubes in a warm H2O bath kept at body
temperature for at least 1 hour.
6. Filter the contents of each tube and test the filtrate with NaOh
and CuSO4 solution. Observe and record the results.
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RESULTS
TEST TUBE
BIURET TEST
A
Lavender in
color, clear
B
Blue in color,
small amt. of
precipitate
C
Sky blue in color,
w/ greater
precipitate
A
B
C
RESULTS
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A
B
C
+ POST LABORATORY QUESTIONS
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What are the enzymes used in
carbohyrdate digestion? Lipid
digestion? Protein digestion?
 Carbohydrate Digestion : Amylase, Pepsin
 Lipid Digestion : Lipase, Pancreatic Proteases
(Pancreatin)
 Protein Digestion : Trypsin, Pepsin, Pancreatic
Proteases
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What are the similarities and
differences of these enzymes?
They are alike in the way that these enzymes break down
macromolecules into their builiding blocks. They are found in the
digestive tract of both humans and animals where they aid in the
digestion of food.
However they differ in function and are classified by their substrates.
Proteases and peptidases split proteins into amino acids,
Lipases split fat into three fatty acids and glycerol,
Carbohydrases split carbohydrates such as starch into sugars,
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What are the factors that would
bring about carbohydrate
digestion? Lipid digestion? Protein
digestion?
 CARBOHYDRATE DIGESTION : Salivary
amylase, Pepsin, Lactase
 LIPID DIGESTION : Bile acids, Pancreatic
Lipase
 PROTEIN DIGESTION : Trypsin, Pancreatic
Proteases
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Trace the pathway of carbohydrate
digestion, lipid digestion and
protein digestion.
CARBOHYDRATE DIGESTION :
Mouth breaks down polysaccharides through amylase.
The stomach, however, because of its high acid content
stops the process and is continued in the duodenum
(small intestine). The pH changes dramatically from a
strong acid to an alkaline content. The pancreas secrete a
bicarbonate to neutralize while in the duodenum thus
finishes the breaking down of chyme to simple sugars.
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LIPID DIGESTION:
Triglycerides and other dietary facts are relatively
unaffected by conditions in the stomach and enter
the duodenum in the form of large lipid drops. Bile
salts emulsify them into tiny droplets the pancreatic
lipase could attack. The enzymes breaks the
triglycerides apart and lipids released interact with
bile salts to form the small complexes called
micelles. When a micelle contacts the intestinal
epithelium , the enclosed lipids diffuse across the
cell membrane and enter the cytoplasm. The
intestinal cells use the arriving lipids to
manufacture new triglycerides that are then coated
with proteins.
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PROTEIN DIGESTION :
In the mouth, initial physical breakdown of protein
begins. The stomach continues physical breakdown
and begins chemical breakdown by secreting
pepsinogenic which is converted into an enzyme
called pepsin. Pepsin breaks down protein into
amino acids. The food is then moved to the
duodenum. It works with the pancreas to complete
the physical and chemical breakdown of protein
into single amino acid molecules with the help of
trypsin. The small intestine absorbs the amino acid
molecule allowing them to pass into the
bloodstream.
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What tests are used to the
completeness of carbohydrate
digestion? Lipid digestion? Protein
digestion?
 CARBOHYDRATE DIGESTION : Iodine test,
Benedict’s test, Barfoed’s test, Seliwanoff’s test, Bials
test
 LIPID DIGESTION : Sudan red test, Grease spot
test
 PROTEIN DIGESTION : Biuret’s test
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What are the factors affecting
carbohydrate digestion? Lipid
digestion? Protein digestion?
 CARBOHYDRATE DIGESTION : Botanical source of
carbo., main classes and subclasses of carbo.,
physical and chemical structure, calcium, cooking
and addition to formulated food
LIPID DIGESTION : Insolubility in water
PROTEIN DIGESTION : Concentration of enzyme,
amount of protein food needed, acidity of food, time,
presence of any digestive inhibitors
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THANK YOU.