Preparation of osmotically dried products

Aim of the experiment: To study the drying of horticultural produce.

Objectives:

1. To get acquainted with various types of drying methods of horticultural produce.

2. To prepare the dehydrated products.

Materials required:

          Fruit/ vegetables, salt, hot air oven and packaging materials

Relevant information:

Drying preserves foods by removing enough moisture from food to prevent decay and spoilage. The water content of properly dried food varies from 5 to 25 percent depending on the food. Successful drying depends on:

Ø Enough heat to draw out moisture, without cooking the food;

Ø Dry air absorbs the released moisture; and

Ø Adequate air circulation to carry off the moisture.

When drying foods, the key is to remove moisture as quickly as possible at a temperature that does not seriously affect the flavour, texture and colour of the food. If the temperature is too low in the beginning, microorganisms may grow before the food is adequately dried. If the temperature is too high, affects the flavour, texture and colour of the food. Dehydration is an alternative to canning/bottling and freezing fruits and vegetables. The practice of drying foodstuff, especially fruits and vegetables are very old.

The term drying and dehydration means the removal of water. The former term drying is generally used for drying under the influence of non-conventional energy sources like sun and wind. If fruits or vegetables are to be sun-dried, they or their pieces should be evenly spread in a single layer on trays or boards and exposed to the sun. In sun drying there is no possibility of temperature and humidity control.

Dehydration means the process of removal of moisture by the application of artificial heat under controlled conditions of temperature, humidity and airflow. In this process, by single layer of fruits or vegetables are spread on trays which are placed inside the dehydrator. The initial temperature of the dehydrator is usually 43OC which is gradually increased to 60-66°C in the case of vegetables and 50-71°C for fruits.

Principles of drying and dehydration:

The microorganisms require plenty of free water for their survival. Drying or dehydration removes biologically active water, and the growth of microorganisms is stopped. This also results in a reduced rate of enzyme activity and chemical reactions. The food value, natural flavour and characteristic cooking quality of fresh material are retained after drying. Fruits show no sign of moisture or stickiness and vegetables become brittle on drying. The residual moisture should not be more than 6-8 per cent in vegetables and 10-20 per cent in fruits. Dried fruits can be used as such or after soaking, while dried vegetables are usually soaked in water overnight before cooking.

Procedure for Dehydration:

The flow chart for dehydration of fruit and vegetables is given below.

Drying of Fruit and Vegetables

Observations to be recorded

Selected fruit/ vegetables =

Amount of fruit/ vegetable taken =

Duration of drying=

Temperature of drying =

Final dehydrated product =

Recovery rate (%) =