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The proximate, mineral element, vitamin, flavonoid and tannin composition of raw and cooked onion (Allium cepa)




The study is on “The nutrient contents, flavonoid and tannin composition of raw and cooked onion (allium cepa)”. The study has four objectives which are to determine the nutrients present in raw and cooked onion, assessment of flavonoid and tannin level in raw and cooked onion. To know if raw onion or coked onion has the highest amount of nutrients, flavonoid and tannin content, to understand the importance of onion in the diet. The data obtained from different analysis was subjected to various statistical analyses which include simple descriptive mean, standard deviation and Student t – Test. Duncan’s test was used to separate the means and Pearson’s correlation, among the sample’s attributes was determined using SPSS17.0 Software inc. USA. Findings reveal that onion provides nutrients whether eaten cooked or raw; however raw onions have higher level of sulfur compounds. Onion should be eaten raw for maximum sulfur content, as cooking onion significantly decreases the quantity of the compound but lightly cooking onion may actually increase the concentration of the nutrients. This work recommends that the intake of raw and cooked onion should be encouraged as it helps in providing nutrients, phytochemicals such as flavonoid and tannin which helps to protect the body from diseases such as cancer, cardiovascular diseases, lowers blood sugar and also prevent anti-inflammatory problems. It also contains minerals and vitamins which are needed by human to promote growth and development and strengthen immune system.



Onion (Allium cepa) also known as the bulb onion is a vegetable and can be utilizes as a food ingredient to give flavor, and aroma to a great variety of dishes. It is the most widely cultivated species of the genus Allium (Gaitam et al., 2000). Its close relative includes the garlic, shallot, leek, chive and Chinese onion (Brewster et al., 1998). The onion is used as a basic ingredient to add flavor, but is also excellent on its own. Onion is a common vegetable that can be served cooked or raw (Brewster et al., 1998).It is a member of the Allium family, and it is rich in sulfur-containing compounds that are responsible for its pungent odors and for many of its health promoting effect (Cao et al., 1996). A wide variety of Allyl sulfides are found in onion. Botanically, onion belongs to the Alliacease family in the genus Allium and known scientifically as Allium cepa, which is on the surface, a humble brown, white or red, paper – skinner bulb. Yet despite its plain look, it has an intense flavor and it is a beloved part of the cuisine of almost every region of the world (Haneltet al., 2001).

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Onions are a major source of polyphenols in general and also as flavonoids (a very important sub-division of polyphenols) (Bros et al., 2008, Bajpal M. 2005). There are three types of onions; Red, yellow, and white. The red onions are higher in total flavonoids than white onions (with yellow onions falling somewhere in-between). For medicinal purposes, onion is available for internal use as a capsule or tablet containing dehydrated onions or onion extract. The recent study of the antioxidant activity of onion juices indicates that it is not affected by heating or boiling. For external use, the juice of fresh onion is used.

Onion (both cooked and raw) has also been shown to contain anti-inflammatory, anti-cholesterol and antioxidant (Michael et al., 2002) which are compounds that protects the body against free radicals. Free radicals are highly reactive molecules that destabilize other molecules and are associated with a number of degenerative diseases. Onion provides vitamins and minerals such as biotin, manganese, vitamin B6, vitamin C, vitamin B1, B2, B3 dietary fiber, phosphorus, potassium, folate and copper (Paul S, 2005). They are low in calories (50kcal/100g). It has special qualities which add taste and flavor to food and hence it is mainly used in India for cuisine culinary preparation. Sulfides in onions contain necessary amino acids. Sulfur is one of the most common minerals in our body that assists with protein synthesis and building of cell structures. Onions serve as a good source of medicinal compound for cataract, cardiovascular diseases, cancer and other diseases due to its hypocholesterolemic thrombolytic and antioxidant effect (Cao et al., 1996). Quercetin is a plant polyphenol from the flavonoid group, found in many fruits, vegetables, leaves and grains. It can be used as an ingredient in supplements, beverages, or foods. It is the most abundant flavonoid in the human diet (Duthie and Dobson 2001). And it is found mainly in onions. The flavonoid – quercetin has shown much promise as an antioxidant agent imparting a protective effect in reducing the risk of developing cardiovascular disease (Hertog and Hollman 1996).

  • Statement Of Problem
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Onions are excellent sources of dietary fiber, vitamins and minerals (Splittstosser P. 2008). Inadequate consumption of vegetable (onion) can result in some nutritional deficiencies such as vitamin A, vitamin C, and iron deficiencies. Vitamin C deficiency leads to scurvy which causes bleeding of the gum and the inability to chew things most especially proteinous food, like meat, beans, fish etc. this will lead to protein-energy malnutrition (P.E.M). Iron deficiency leads to anaemia. Nutritional deficiency in children would not allow them to attain their endowed potentials and this can affect the future development of the nation as the children are considered to be the future of any nation.

The society is a place where vegetable is been consumed everyday and it is found out that most people are used to throwing away the skin of onions when cooking. Saving the skin of onion may be important for your health and diet. It is also a way of getting quercetin (a phytochemical – flavonoid) in our diet without supplement and the presence of quercetin in our body helps to prevent us from some certain diseases. While most people may avoid using onion while cooking because it always make them cry, so they avoid using it, thereby lacking the nutrient and phytochemicals or antioxidants contained in onion which helps bestow health and prevent diseases.

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Most people believe that cooked onion contains more nutrients and antioxidant than raw onion so they overcook it in order to get the nutrient without the knowledge that overcooking of onion totally reduced the amount of nutrient and antioxidants.

  • Objectives Of The Study

The aim of this study is to determine the nutrient contents, flavonoid and tannin composition of raw and cooked onion (Allium cepa).

  • Specific Objectives
  • To determine the nutrients present in raw and cooked onion.
  • Assessment of flavonoid and tannin level in both raw and cooked onion.
  • To know if raw onion or coked onion has the highest amount of nutrients, flavonoid and tannin content.
  • To understand the importance of onion in the diet.

 Significant Of Study

The result of this study will help the consumer to be aware of the nutrient, flavonoid, and tannin content that is contained in raw and cooked onion. This knowledge will assist us in knowing the importance of onion in our diet. This will create awareness on source of micronutrients which its deficiency have severe consequences. It will help in eliminating micronutrients deficiency as people will know the value of onion in their diet. It will also help the consumer to know if raw onion or cooked onion has the highest value of nutrient, flavonoid and tannin content.

Pages:  59

Category: Project

Format:  Word & PDF         

Chapters: 1-5                                 

Material contains Table of Content, Abstract and References


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