FREEZE DRYING.pptx

Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product, lowering pressure, then removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using heat.
Because of the low temperature used in processing, the quality of the rehydrated product is excellent. When solid objects like strawberries are freeze dried the original shape of the product is maintained. If the product to be dried is a liquid, as often seen in pharmaceutical applications, the properties of the final product are optimized by the combination of excipients (i.e., inactive ingredients). Primary applications of freeze drying include biological (e.g., bacteria and yeasts), biomedical (e.g., surgical transplants), food processing (e.g., coffee) and preservation.

1. FREEZE DRYING( Lyophilization )

2. PRINCIPLE The main principle involved in freeze drying is a phenomenon called sublimation , where water passes directly from solid state(ice) to the vapour state without passing through the liquid state. Sublimation of water can take place at pressure and temperature below the triple point. The material to be dried is first frozen and then subjected under a high vaccum of heat so that frozen liquid sublimes leaving only solid ,dried components of original liquid. This method is majorly used in preserving high value foods( eg -dry coffee).

3. Effects of freeze drying on nutrients Freeze-drying causes less damage to the substance than other  dehydration  methods using higher temperatures. Nutrient factors that are sensitive to heat are lost less in the process as compared to the processes incorporating heat treatment for drying purposes. Freeze dried foods have very high retention of sensory characteristics and nutritional qualities. Only minor changes to starch and other carbohydrates,proteins .

4. Open porous structure of freeze dried foods may allow oxygen to enter and cause oxidative deterioration of lipids . Thus its packaged in inert gas. Changes in thiamin(vitamin A) and ascorbic acid content during freeze drying are moderate and there are negligible losses of other vitamins. However, losses of nutrients due to preparation procedures like blaching ,may substantially affect final nutritional quality of a freeze dried foods.

5. FOOD LOSS(%) Vitamin C Vitamin A Thiamin Riboflavin Folic acid Niacin Pantothenic acid BEANS (GREEN) 26-60 0-24 - - 10 - PEAS 8-30 5 - - 10 ORANGE JUICE 3 3-5 - - - - - BEEF - - 2 + 13 PORK - - < 10 - 56 +,- APPARENT INCREASE/DECREASE