lipids Flashcards
(25 cards)
What does the term lipid describe?
A set of macromolecules that are very poorly soluble in water and mostly hydrophobic
Lipids include triglycerides, waxes, phospholipids, and steroids.
What is the main biological function of lipids?
Storing energy
They are also used as precursors to hormones, for protection and lubrication, and as structural components of cell membranes.
What are triglycerides composed of?
Three fatty acids connected to a molecule of glycerol
There are also mono and di glycerides with one and two fatty acids, respectively.
What are phospholipids made of?
A hydrophilic head with a phosphate group and two hydrophobic fatty acid tails
What is a sterol?
A gonane molecule with a hydroxyl (OH) group attached
What are free fatty acids?
Fatty acids found on their own, consisting of chains of carbon atoms terminating in a carboxyl group
How is a saturated fatty acid defined?
If every carbon in the chain has the maximum number of hydrogen atoms attached
How is an unsaturated fatty acid defined?
If not every carbon in the chain has the maximum number of hydrogen atoms attached
What do saturated fatty acids make up?
Fats
What do unsaturated fatty acids make up?
Oils
What are the negative effects of excess lipids in beer?
- Reduce foam potential
- Reduce flavour stability
- Cause gushing in beer
- Cause inconsistent ester formation during fermentation
What beneficial role do unsaturated fatty acids and sterols play in yeast?
Improve fermentation performance, yeast viability, and tolerance of alcohol
What percentage of lipids by weight does malted barley contain?
Around 3%
Where are the majority of lipids in barley concentrated?
In the aleurone and embryo of the grain
What percentage of malt lipids typically makes it into wort?
Less than 5%
What is the primary lipid found in wort?
Free fatty acids
What catalyzes the hydrolysis of malt triglycerides to form free fatty acids?
Lipase enzymes from malt
What factors increase the extraction of lipids during mashing?
- Using finer grist
- Increased agitation
- Producing turbid worts
- Thinner mashes
What affects the composition of fatty acids in wort?
The variety of malt used and the activity of enzymes during mashing
What is a significant factor in how quickly beer goes stale?
Lipids
What unsaturated fatty acid is thought to play a major role in beer staling?
Linoleic acid
What is formed when linoleic acid is oxidized during mashing?
A precursor to E-2-nonenal
What is the effect of E-2-nonenal on beer?
Gives the beer a stale, cardboard-like aroma
What conditions can minimize the oxidation of lipids during mashing?
- Mash in at high temperatures (> 65°C)
- Mash at low pH (around 5.1)
- Mill more coarsely
- Condition malt with 80°C water
- Mash in as rapidly as possible
- Mash at high temperature
- Mill and mash in an oxygen-free environment
- Use antioxidant sulphur dioxide
- Use barley with null LOX activity
