Meal preparation involves preparing meals ahead of time for a short
or period of time. This practice may occur among people who desire to
lose weight, gain muscle mass, or maintain a healthy lifestyle. Advance
preparation can serve to standardize food portions. Meals preparation
are fully cooked. Meals may be prepared in small containers such as
Tupperware, and are sometimes labeled and dated to remain
Freshly cut onions often cause a stinging sensation in the eyes of
people nearby, and often uncontrollable tears. This is caused by the
release of a volatile liquid, syn-propanethial-S-oxide and its aerosol,
which stimulates nerves in the eye. This gas is produced by a chain of
reactions which serve as a defence mechanism: chopping an onion causes
damage to cells which releases enzymes called alliinases. These break
down amino acid sulfoxides and generate sulfenic acids. A specific
sulfenic acid, 1-propenesulfenic acid, is rapidly acted on by a second
enzyme, the lacrimatory factor synthase (LFS), producing the
syn-propanethial-S-oxide. This gas diffuses through the air and soon
reaches the eyes, where it activates sensory neurons. Lacrimal glands
produce tears to dilute and flush out the irritant.
Cooking onions and sweet onions are better stored at room
temperature, optimally in a single layer, in large mesh bags in a dry,
cool, dark, well-ventilated location. In this environment, cooking
onions have a shelf life of three to four weeks and sweet onions one to
two weeks. Cooking onions will absorb odours from apples and pears.
Also, they draw moisture from vegetables with which they are stored
which may cause them to decay.
Sweet onions have a greater water and sugar content than cooking
onions. This makes them sweeter and milder tasting, but reduces their
shelf life. Sweet onions can be stored refrigerated; they have a shelf
life of around 1 month. Irrespective of type, any cut pieces of onion
are best tightly wrapped, stored away from other produce, and used
within two to three days.