Not everyone has access to healthy and nutritious food; especially the economically backward section of the society. The Midday meal scheme was introduced in the year 1995 by the Indian government. It was introduced for the children of economically backward section of our society.
 

$\bullet$ Preservatives are the substances that are generally added to kill or inhibit the growth of microorganisms in a food item.
$\bullet$ Common salt(NaCl) and sugar are natural preservatives, vinegar and sodium benzoate are chemical preservatives.
$\bullet$ Common salt removes the water content in the pickled mangoes. In the absence of water, bacteria can't multiply and hence it act as a preservative.
$\bullet$ Similarly, fishermen add salt to fish to keep them fresh for a longer period of time.

The process of collecting the ripe crops from the field is known as harvesting. This is the final step before the product is ready to be sold in markets. 

Root and tuber crops are a type of food crops. These crops usually have the edible part under the ground. They are a good source of energy. Potato is an example.