BACKGROUND INFORMATION OF ONION
Onion (Allium cepa L.) is one of the most popular vegetable that form of the daily diet. These are native to Central Asia and Mediterranean coast areas. Featured by cold resistance, preferring warm climate, high yield, good storage, long supply period; fleshy bulbs with fine texture, soft fiber and delicate flavor, they are regarded as Vegetable Queen in Europe. In Pakistan, onion an important commercial crop widely grown is different parts of the country. At present, Pakistan stands seventh largest producer of onion in the world, China is the leading country followed by India. Onions produced by Pakistan and India are famous for their pungency and are available round the year. Onions are able to improve appetite and help digestion, as they are of relative high nutritional value and medicinal value. With the popularity of health care around the world, the food scientists, medical experts and biologists have been trying to do wide and deep study of onions. The pungency in onion is due to a volatile oil known as allyl-propyl disulphide.
Onions are high in moisture, carbohydrates, protein, fiber, vitamin C, B1 and B2. In the mean time, onions also have 18 types of amino acid and selenium, zinc, copper, iron, etc. Micro-elements, so onions are kind of treasured health food welcomed by many people, and exported increasingly.
Onion is a famous spice commodity grown all over the world and consumed in the various forms. Onion is a major ingredient in Pakistani food and commodity is typically cultivated thrice a year in monsoon, winter and summer. Onion adds taste and flavor to a food and hence it is invariable used in several cuisines and culinary preparations. Onion possesses good medicinal values and is recommended on medical ground also. Onion is processed in various products such as ketchup, chutney, sauce, puree, salsa, dry soup mixture etc. Onion can be processed into a wide variety of products. Minimally processed ready to use or ready to cook fresh onions, onion paste, dehydrated onion flakes, onion powder, onion oil, onion vinegar, onion sauce, pickled onion, onion wine and beverage etc. The demand for the processed products is increasing day by day due to its convenience to handle and use. As per the estimate, approximately 6.75% of the onion produced is going for processing (by counting total losses, consumption, export and bulb seed requirement the remaining percentage is considered for processing).
Value addition of Onion
- Minimally processed onions: These are peeled and/or cut onions for ready to use that retain its freshness, packed in suitable packaging material and stored at refrigerated conditions or frozen conditions.
- Onion paste: Onion is grounded yet retaining its freshness. Preparation of minimally processed onions and onion paste entails optimization of proper preservatives and packaging materials to increase the shelf life of these products.
- Dehydrated onions: Dehydration of onions reduces the bulk to transport and also increases the shelf life of onions significantly due to less moisture, which arrests the growth of microorganism. Dehydrated onion flakes can be processed into onion powder by proper grinding.
- Onion Powder: Onion powder dissolves very easily and reconstitute quickly compared to onion flakes. Onion powder incorporates the flavour of onion in a variety of foods. Use of suitable packaging techniques is the most important to increase the shelf life of dehydrated onion flakes and powder as these are very hygroscopic in nature.
- Pickles: An age old practice to preserve the onions is by means of a process called pickling. Most widely used pickling for onions are vinegar based pickling and oil based pickling. While vinegar based pickling is popular in the United States and Europe, oil based pickling is widely adopted in Asia and Africa.
- Fried onion: onions can be preserved in fried form. Onion slices are fried in pre-heated oil and fried till light brown color of onion flakes. After frying onion flakes are placed on paper towel to remove extra oil and packed in polythene bags or plastic jars for further use. Fried onions can also be stored in ground form.
- Vinegar/Beverage/Sauce: As the onions are rich in sugars and other nutrients they can be processed into onion vinegar and onion sauce. Onion can also be processed into onion beverage and onion sauce.
- Onion waste processing
- Large amount of onion waste is produced by consumption of onion both domestically and industrially, making it necessary to search for their utilization. The main onion waste include onion skins, two outer fleshy scales and roots generated during industrial peeling and undersized malformed or damaged bulbs. These can be used in different ways.
- Source of fiber: The skin of an onion bulb was found to be a rich fibre. After harnessing the color from the dry skin by discoloration, the resultant product is converted into a fibrous material which can be used as a fiber supplement. The same fibrous material can be used as a thickening agent and an exemplary use is in making soup.
- Natural colour: The color extracted from onion skin can be used as a natural dye. The dry skin of onion is found to contain flavonoids. Onion essence which is used as a flavoring agent can also be extracted from the skin of an onion bulb.
- Bio-gas: Other resultant materials like outer layers, roots and stalks can be anaerobically digested in a bio-digester to produce alternative energy sources like bio-gas.