Proximate and Sensory Characteristics of Osmotically Dehydrated Bitter Leaves (Vernonia Amygdalina)

ABSTRACT

This work investigated the proximate and sensory properties of osmotically dehydrated bitter leaf. Bitter leaves were sorted, washed, drained, dehydrated osmotically using 30% sucrose, 40% sucrose, 30% sucrose + 10% NaCl and 40% sucrose + 10% NaCl. Proximate analysis and sensory evaluation were carried out on the osmotically treated and non-osmotically treated samples. The results showed that moisture content ranged from 7.98 – 8.60 %, protein(41-47%), fat (11.49-11.23%), ash (11.15-12.33%), crude fibre (7.23-9.47%) and carbohydrate (17.14-18.04%). The sensory scores showed that there was no statistical difference (p >0.05) among all samples. The results showed the feasibility of dehydrating bitter leaf using osmotic treatment without significant change in proximate and sensory qualities.

 

CHAPTER ONE

INTRODUCTION

1.1    Background to the Study

          Leafy vegetables are nutritional leaves which contains vitamins minerals and phytonutrients. They are rich in chlorophyll, which alkalinizes the blood, and fiber, which keeps the colon healthy. US DA recommends eating one-half cup of green leafy vegetables each day to prevent nutrient deficiencies and serious illnesses (Olson, 1980).

Bitter leaf scientifically known as Vernonia amygdalina is a small perennial shrub that grows in tropical Africa. It belongs to Asteraceal family. It was originated from tropical Africa (Tindall, 1988).

          Vernonia amygdalina can be propagated by cutting or by seedling. The leaves are green with a characteristics odour and a bitter taste. It does not produce fruits (Farombi et al., 2003). The bitter taste is due to anti-nutritional factors such as alkaloids, saponins, taninins and glacosides (Erasto et al., 2003).

          It is known as Onugbu, Shiwaka and Ewun by the Igbos, Hausa and Yorubas in Nigeria respectively (Kokwaro, 2009). Bitterleaf occurs widely in most countries of tropical Africa from guinea East to Somalia and south to North Eastern South Africa and in Yemen. It is commonly grown as a vegetable in Benin, Cameroon, Gabon and Dr Congo and to a lesser extent in their neighbouring countries (Kokwaro, 2009).

          Bitter leaf is highly nutritive, containing nutrients such as vitamins, (A, B, C, E, B12), proteins, fibre, Caretenoids, minerals (Ca, Fe, K,P, Mn, Cu, Cobalt) etc. The leaves of vernonia amygdalina can be consumed raw or used in soup preparation. It can also be used to cure many skin diseases and also of great benefit to health generally (Eleyinmi et al., 2008). It helps in reducing the high sugar level in the blood, making it moderate and also repair the pancreas because of it’s natural bitterness which contains vitamins (Akah and Okafor, 1992).

          Bitter leaf is a shrub or small tree of 2 – 5m with petiolate leaf of about 6mm diameter and elliptic in shape. There are about 200 species of Vernonia amygdalina. Some bitter leaf  have comparatively smaller leaves while some have broad leaves. The smaller leaves are very bitter. The bitterness is usually removed by boiling before the leaves are used to prepare soups. The leaves of the broad bitter leaves are less bitter and can be chewed raw, without cooking in hot water.

          Osmotic dehydration is a process that practically removes water from food material by means of food immersion in a hypertonic solution (such as sugar and salt). It is a counter-current mass transfer process, in which water is drained from the anterior of the food to the hypertonic solution and the solute flow into the food (Amami et al., 2007).

          The osmotic dehydration process has often been used for the development of new products of fruit and vegetable because it positively affects the sensorial and nutritional properties of the fresh product (Correa et al., 2010). It also increases the sugar to acid ratio and improves the texture and stability of pigments during dehydration and storage. It is effective even at ambient temperatures, so heat damage to texture, colour and flavour can be minimized (Rastogi et al., 2005). It also has low influence on mineral content and there is a loss in vitamin and hence, osmotically dehydrated fruits and vegetables have a good retention of flavour, aroma and nutritional content. It also helps to prevent enzymatic and non-stabilize the fruit colour (Gonzalez – Aguilar et al., 2001).

          Dehydration is a process of removing water from good material through application of heat under controlled conditions to remove, by evaporation, in order to extend the shelf life of the food material (fruits and vegetables) etc. dehydration affects the food texture, colour and causes the loss of volatile components.

          The design and operation of dehydration equipment aims to minimize these changes by selecting appropriate drying conditions for individual foods. As far as the malting process is concerned, the drying step is essential and is refused to create the desired colour and flavour.

1.2    Justification  

          Bitter leaves are prone to deterioration when kept at ambient temperature. The physiological break down of the tissues leads to modern storage/preservative facilities that is employed today, such as freezers and refrigerators.

          Its bulkiness increases it’s cost in some seasons of the year. However, there is need to provide a suitable means by which bitter leaves can be well preserved in order to keep them safe from deterioration and to extend it’s shelf life, reduce bulkiness for easy transportation and distribution.

1.3    Objective of the Study

          The main objectives of the study are to;

  1. dehydrate bitter leaf using osmotic method.
  2. evaluate the proximate content of the dehydrated bitter leaf.
  3. evaluate the sensory quality of the dehydrated bitter leaf.

 

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