Spices and perfumes – driving forces of humans

Lab exercise: something to behold for the eye: onion
When onions are sliced or eaten, cells are
broken, allowing the enzyme alliinase to break
down amino acid sulphoxides and generate
sulphenic acids.
A specific sulfenic acid, 1-propenesulfenic
acid, is rapidly rearranged by a second enzyme,
to syn-propanethial-S-oxide, a volatile gas
known as the onion lachrymatory factor or
LF.The gas diffuses through the air and
eventually reaches the eye, where it activates
sensory neurons, creating a stinging sensation.
Tear glands produce tears to dilute and flush
out the irritant. Similar Chemicals are known as
lachrymatory agents
cutting onions under running water or
submerged in a basin of water. Another way to
reduce irritation is by freezing, or by not cutting
off the root of the onion which has a higher
concentration of enzymes
Task1:
1. Cut onion while partner holds a
large sheeth of pH (or yellow red
beet) paper to catch flares of sulfenic
acid.
2. Test for active lachrimatory
factor by cutting an onion + bringing
it near your partner’s head
3. Cut onion under slightly alkaline
water pH 9-10 and test again.