Determination of moisture content of dried fruits is one of the most important factors of the fruit after drying. Standard 672 of the Iranian Standards Organization, AOAC 22.013, and ISO 665: 2000 have been used to identify these methods.
Fruits are dried using traditional methods by sun rays or industrial devices and methods. All types of dryers in various capacities are used to dry fruits in high volume in the industry.
The moisture content of each dried fruit should be determined by laboratory methods. One method is as follows:
First method- method of measuring weight difference before and after drying for fruits that can be powered and have high sugar content such as dried peach, dried apple, dried banana, etc.
Required laboratory supplies for determination of dried fruits moisture:
- Lab scale with 0.01 g precision
- Metal plate with minimum diameter of 8.5 cm
- Desiccator with silica gel
- Laboratory sand
- 0.1 N hydrochloric acid
- Distilled water
Wash 2 grams of sand in 0.1 N hydrochloric acid and dry it with water after rinsing. Then pour the sand into the plate and put the lid on the plate and put it in the oven for 2 h at a temperature of 70 °C and a pressure of 100 mm Hg to dry. Then put the plate and its lid in the desiccator to reach the ambient temperature while not absorbing moisture. Then weigh it. Name the weight of this step M0.
Weigh 50 g of dried fruit, grind it 2-3 times, weigh 5 g of it in the scales with 0.01 accuracy, and spread it completely in the plate containing sand. You can mix sand and the ground dried fruit with a spatula and some warm distilled water to mix them better. Wash the remained sample on the spatula with warm water inside the plate.
Put the plate in Bain-Marie to evaporate the added distilled water and dry the plate. Then weigh the set of plates, sand, and dried fruit powder after removing the added distilled water (M1). Then put it in the oven at 70 °C and a pressure of 100 mm Hg for 6 h. Oven should not be opened during drying.
Place the metal plate always in direct contact with the metal shelf of the oven and immediately transfer the plate to the desiccator after 6 h to reach the ambient temperature while maintaining non-absorption of moisture. Then weigh the plate with the lid by the scale (M2).
Always keep in mind that the plate lid in the oven should be next to the plate so that the moisture expelled from the material can easily leave the plate.
Moisture weight percentage is obtained by the following formula:
This means that how much percent of the dried fruit (M1) contain water before losing all its moisture, and the percentage of moisture in the dried fruit (M1) can be obtained.
This test should be repeated until two recent tests have the difference below 0.2%.