The correct answer is option 4, Ajinomoto. Ajinomoto is a commonly used flavour enhancer that is added to noodles to enhance their taste. It is a brand name for monosodium glutamate (MSG), which is a type of salt that contains the amino acid glutamate.

Option 1, saffron, is not commonly used as a flavouring agent in the preparation of noodles. Saffron is a spice that is known for its unique flavor and aroma, but it is more commonly used in dishes like rice and desserts.

Option 2, cinnamon, is a spice that is used in various dishes, but it is not commonly used as a flavouring agent in noodles. Cinnamon is often used in sweet dishes or in certain types of savory dishes, but it is not typically found in noodle preparations.

Option 3, olive oil, is a type of cooking oil that is used in a variety of dishes, but it is not commonly used as a flavouring agent in noodles. Olive oil is often used for its health benefits and its distinct taste, but it is not usually added to noodles for flavoring purposes.

Therefore, the correct answer for the commonly used flavouring agent in noodles is Ajinomoto or MSG