Lab Knowledge

Question 1

commercial TLC plates

Answer 1

• chemically inert silica (SiO2) is mixed with a binding agent, bound to a glass or plastic plate in a very thin layer and activated by heat to form a silica gel

Question 2

Explain how TLC works (4)

Answer 2

1. Lipids are spotted onto the plates and subsequently seperated by placing one edge of the TLC plate into a mixture of organic solvents and allowing this solvent to travel across the TLC plate
2. The solvent is less polar than the silica gel. Depending on the relative solubility of lipids in the solvent, they will migrate different distances up the TLC plate over time and be “resolved” from each other due to their different affinities for the mobile and stationary phases
3. Polar lipids have a stronger affinity for the silica gel whereas nonpolar lipids will have a stronger affinity for the mobile phase
4. Unsaturated bonds in lipids will react reversibily with iodine allowing detection of the lipids after TLC have been performed. The double bonds in unsaturated fatty acids are visualized in this manner

Question 3

Following the extraction and quantification of lipids from cows milk what arethe layers you get after centrifuge?

Answer 3

1. A white layer of denatured protein should be found between the aqueous and organic phases that contains denatured protein.
2. The top layer is water with water soluble carbohydrates, amino acids and small peptides.
3. The bottom layer of organic layer has CHCl3/MeOH and the lipids

Question 4

Beer is made in part from

Answer 4

fermented barley

Question 5

Starch can be converted to the diasccharide maltose by

Answer 5

barley seed enzyme a-amylase (malting)

Question 6

Brewing yeast added to the malted barley …

Answer 6

takes up maltose and converts it to glucose within the cell

Question 7

How is glucose produced to beer after adding yeast to malted barley…..

Answer 7

Gluycose is fermented to CO2 and alcohol forming beer.

Question 8

Carbohydrates remaining in beer after fermentation are a result of …. These carbohydrates are mainly comprised of……

Answer 8

• incomplete malting
• the disaccharide maltose

Question 9

Explain the DNS (dinitrosalicyclic acid) reaction (2)

process+ purpose

Answer 9

• One molecule of 2-hydroxy-3,5-dinitrobenzoic acid reacts with one molecule of reducing sugar under basic conditions and heat to produce a red compound and oxidized sugar. The red compund is measured spectrophotometrically at 540nm.
• determine the concenration of reducing sugar

Question 10

Folin-Lowry assay (3)

process+ purpose

Answer 10

• Determines the protein content in whole beer
• First step Biuret reaction: a pair of peptide bonds in adjacent polypeptide chains within a protein can complex with a copper ion (cu2+) to generate a “tetradentate-Cu+ complex.” This complex has a reddish blue colour and can be measured spectrophotometrically at 540 nm.
• To improve the sensitivity of protein detection 1000-fold the folin-ciocalteu reagent is added. The reagent has a bunch of metals and the transfer of electron from the tetradentate-Cu+ complex results in the oxidation of these metals producing an intense blue colour. The blue compounds can be assayed spectrophotometricallt at 750 nm

Question 11

Ninhydrin Assay (2)

process+ purpose

Answer 11

• Determines the amino acid content of beer
• Ninhydrin reacts with deprotonated primary amines such as a-amino acids to give an orange to dark red compound. This compound can be assayed spectrophotometrically at 570nm