Amylase is an enzyme capable of breaking a starch polysaccharide into monosaccharide’s.

Lugol’s solution (contains iodine) can be used to detect the presence of starch. A positive test is dark blue.

Benedicts solution (contains Cu++) can be used to detect the presence of monosaccharide’s. The Cu++ reacts with the aldehyde group and forms Cuprous oxide. Cuprous oxide precipitates out of solution as a green to brownish red color.

Starch & amylase

Starch only

Lugol’s Lugol’sBenedict’s Benedict’s

+ or - ?+ or - ? + or - ? + or - ?

Incubate at 37C for at least 30 minutes Page 463 - 464

                                                                                                                                                                                                   

                                                                                                                                                                                                   

                                                                                                                                                                                                   

pH?

Lipase is an enzyme that can digest lipids (triglycerides). The digestion of triglycerides results in the release of fatty acids, which causes a decrease in pH. Remember that pH decreases as a solution becomes more acidic.

Phenol red is red at pH > 7 and is yellow at pH < 7.

We can use the color of phenol red as an indicator of pH – thus lipid digestion. We can add bicarbonate to milk to increase pH so when phenol red is added it is pinkish.

Milk + lipase + bile color change?

Milk + lipase + water color change?

Milk + boiled lipase + water color change?

Milk + bile + water color change?

Milk + water color change?

Which one will change the fastest? Will temperature affect the rate of change?

Page 466

Proteins are polymers of amino acid monomerss

                                                                                                                                                                                                   

The enzyme pepsin breaks down proteins (polymer) into amino acids (monomers). This enzyme works best in a low pH environment.

Biurets solution turns pink in the presence of amino acids, so it can be used to test for protein digestion (I’ll do this as a demonstration).

Ninhydride is purple in the presence of protein. The more ‘intense’ the color – the more protein present.

Pepsin + serum + ninhydride color?

Pepsin + albumin + ninhydride color?

Pepsin + water + ninhydride color?