Mineral and Sensory Characteristics of Osmotically Dehydrated Okazi (Gnetum Africanum) Leaves

CHAPTER ONE

INTRODUCTION

1.1     Background to the study

          Okazi leaves (Gnetum afrianum) is a climbing leafy vegetable that belong to the family of Gnetaceae. It is prevalent in the tropical regions (Ali et al., 2011). In Nigeria it is very popular among the ethnic groups of Southern and Southeastern part of the country. Okazi leaves being a vegetable contribute a crucial source of nutrient in human daily diet. Dehydration is one of the most important preservation technique that is widely used for leafy vegetables because of considerable saving in packaging, storage, labour, among others.

          Osmostic dehydration is a complementary treatment in the processing of dehydrated foods, since it presents some advantages such as minimizing heat damage to the colour and flavour, inhibiting enzymatic browning and reducing energy costs (Alakali, et al., 2006,: Torres et al., 2006, 2001). In addition, it has proved to be a good method to obtain minimally processed vegetables, due to the great sensory similarity between the dehydrated and untreated  products ( Lerici et al., 1985: Sousa et al, 2003).

          Osmotic dehydration techniques dehydrate food products by immersing them in a hypertonic solution. Water is removed due to the difference of osmotic potential between the food and the osmotic solution, reducing the water activity of the food and consequently the water availability for chemical and biological deterioration. During the process two simultaneous flows through the cell walls are created in counter current: Water leaves the vegetable to the osmotic solution and  solute (usually salt or sugar) moves from the solution into the vegetable leaves (Ordonez, 2006).

1.2     Justification

          Although various methods for extending shelf life of vegetables such as  fermenting, pickling, canning or cold storage, freeze-drying and use of convective hot air drying have been extensively employed as a preservation technique for leafy vegetables. However dehydration exposes the vegetable to elevated temperatures which leads to an increase in shrinkage and toughness, and also causes serious damage to flavour, colour and nutrient contents.

          So there is a need for simple and inexpensive alternative processes that are not only energy intensive and low capital investment but offer a way to  make available these low cost, highly perishable and valuable crops available for the masses in regions away from the production zones and also during off season.

          Given that vegetables are very crucial in human diets and that because Okazi leaf is a tropical vegetable and vegetable, there is need to carry out a study on Its preservation with minimal changes in colour, flavour, nutrient contents and also low energy cost; hence, this study.

1.3     Objectives of the study

The objectives of this study are to:

  1. dehydrate Okazi leaves using osmotic method.
  2. evaluate the mineral contents of the dehydrated leaves.
  3. evaluate the sensory quality of the dehydrated Okazi leaves.

 

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