In numerous papers I have I read that before the extraction of lipids the oleaginous microalgae was dried via lyophilisation process. Will oven drying of microalgae affect the quality ( oxidation problems) and yield of fatty acids? Is that the reason to go for freeze drying or lyophilisation of oleaginous microalgae ?
Yes, you are assuming correctly :) Lyophilisation is always done to evaporate water at a low temperature, to avoid oxidations and other unwanted reactions, this is a general principle. For instance, to make instant coffee granules, it is done to preserve flavour, aroma and coffeine. To make cellulase or pectinase powders from fungal cultures it is done to preserve enzyme activity.
Another example is to make crystal sugar in vacuum pans. That's not freeze drying, but it is evaporation of water at temperatures lower than 65 degrees with moderate vacuum generators to avoid caramelisation and browing (something you get when you evaporate water from sugar cane juice over wood fire in India, but then I guess the brown caramel colour is desired because it tastes nice:). At the large scale of crystal sugar manufacturing, strong vacuum for freeze drying would be too costly because the tanks are so big (and the walls would have to be very thick), so mild vacuum and 60 degrees celsius boiling point is a compromise. The principle is always the same, evaporation of water at lower temperatures to preserve bio-molecules.
Thanks Denecke for your amswer and explanation..... But can you suggest some other method in case lyophilizer is not available?
Depends how you plan to extract the lipids and which lipids you are looking for. Are you using solvents (like hexane) then you could do it on fresh samples and obtain your lipids from the organic phase (like people extract vegetable oil from oilseed, or sunflower...). Keep everything cool (working in a cold room, or using large ice buckets and keep everything on ice using ice-cold solvents).
Is lyophilization expensive to apply to large scale of algae drying compared to other methods used?
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