Nucleic acids may be considered as biogenic substances and are repeatedly blamed for major limitations in the use of algae and other microorganisms as sources of food.35 Because uric acid is produced in humans and other mammals when purines are metabolized and since high levels of this metabolite may result in pathological conditions such as gout while also representing a risk factor for coronary heart disease, the high content of nucleic acid in microbial cells used as food or feed is a constant source of concern.41 Gout and hyperuricemia usually occur after the age of 30 and are more frequently found in men.42 Gout affects about 3 out of 1000 people43 and is characterized by deposits of monosodium urate crystals in tissues.44
The normal plasma uric acid concentration in men is 5.1 ± 0.9 mg 100 mL-1 and that in women is about 1 mg less. Most authorities agree that 6.0 mg of uric acid per 100 mL plasma is the lower limit for the high-risk population.35 Thus the daily intake of nucleic acids resulting from single cell protein (SCP) should not be more than 2 g with the total nucleic acid from all sources not exceeding 4 g per day. Accordingly, a maximum daily intake of 30 g algae is recommended in order to have a safety margin.11
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