The safety and acceptance of microbial protein products has to be strictly controlled, as in the case of all foods. The concepts underlying the acceptance and safety of novel protein sources including mycoprotein products were developed between 1970 and 1974 by the Protein Advisory Group of the United Nations (PAG), initially based on established toxicological experience. During the 70s the experience was accumulating with the incorporation of an increasing number of preparations of microbial origin, with more extensive trials in experimental and farm animals and preclinical and clinical testing (Scrimshaw 1985; Stringer 1985). The main concepts contemplated in these guidelines (Anonymous 1975; Anonymous 1983a,b,c; Scrimshaw 1985), which define the acceptance and quality control of microbial protein products are outlined below.
(1) GRAS status organisms. Generally recognized as safe (GRAS) status may be granted to an organism by qualified experts either on the grounds of: (a) scientific studies which confirm absence of toxic compounds and non-pathogenicity, and (b) in the case of a substance used prior to January 1, 1958, through experience based on common use in food (Code of Federal Regulations, 21 CFR 170.30, 182, 184, and 186). (2) Absence of health hazards and toxic compounds in the product. No living cells derived from the fermentation process (original strain or contaminants) can be present in the final product. Medium components that may be health hazards must also be absent. In case antifoams, detergents, or flocculants are used in the fermentation process, they have to comply minimum safety requirements or be removed completely (Anonymous 1983c; Scrimshaw 1985). Constraints are placed upon the heavy metal content of the final product. Typical maximum values are: fluoride (F) 150 ppm, lead (Pb) 5ppm, arsenic (As) 2ppm, mercury (Hg) 0.1 ppm, although experience shows that the standard levels fit well below these limits. In products of fungal origin, chemical analysis of absence of mycotoxins is considered essential (Scrimshaw 1985; Stringer 1985). (3) Pathogenicity. The potential pathogenicity of a microorganism used for feeding, has been evaluated by the injection of the viable organism into the body cavity or body fluids of a mammalian species. In this way the nonpathogenicity of a large number of microorganisms (S. cerevisiae, C. utilis; C. maltosa, C. lipolytica, and Torulopsis) has been evaluated (Stringer 1985). (4) Integrity of the original strain. The maintenance of the integrity of the original strain and absence of undesirable contaminants has to be proved by specific microbiological and biochemical tests (Anonymous 1983c). (5) Continuous monitoring and control of process variables. To ensure quality and uniformity of the product the process variables (temperature, pH, aeration, cell concentration) have to be carefully monitored, and proof of such monitoring has to be presented. (6) Nucleic acid content. For animals or humans, nucleic acids coming from microbial protein sources added to the daily diet should not exceed 2 g per day (Anonymous 1975; Scrimshaw 1985). This restriction does not apply for nonprimate mammalian species or other vertebrates (Stringer 1985). (7) Toxicological and biochemical studies in animals. The required procedures for testing toxicology of microbial protein products are similar irrespective of whether the product is intended for animal and human feeding (Stringer 1985). First, the tests include short and long-term classical animal toxicology tests, with rodents and other target species (e.g. broiler chicken and pig) and the species that will finally consume the product in its diet (Stringer 1985). They consist of a complete battery of biochemical studies including effects on gross pathology, organ weight, and histopathological examination of the main organs and tissues (Anonymous 1983a). (8) Tolerance studies in humans. Clinical trials. Tolerance studies are used to determine the acceptance and the frequency of allergic and other undesirable reactions. The most common symptoms to be studied are gastrointestinal intolerance, skin rashes, and presence of other allergic reactions (Anonymous 1983b). The trials are conducted with a number of 50 or 100 individuals randomly assigned to experimental and control groups, stratified by sex, with careful report of all significant effects, symptoms, changes in mood, appetite, libido or sleep patterns, monitored in a diary along two sets of four-week study periods (Scrimshaw 1985; Udall et al. 1984). The official recommendations and guidelines of the PAG, part of them which have been briefly described here, are made specific in the form of official specifications for each microbial protein product, which are finally referred in the Code of Federal Regulations, Codex Alimentarius (http://www.codexalimentarius.net), AAFCO and other official publications, which are updated regularly.
The final control of the quality of the food product is regulated by specific official organizations and state food agencies through their respective directives. An example of this is the Food and Drug Administration (FDA, http://www.fda.gov) in collaboration with the Association of American Feed Control Officials (AAFCO) and Centre for Food Safety and Applied Nutrition (CFSAN, http://www.cfsan.fda.gov). The food agencies have to establish among others, the Compliance Policy Guides, current Good Manufacturing Practices (cGMP), official methods and mechanisms of inspection and control to be used to evaluate the quality and safety of food products. As an example of the AAFCO and FDA policy, a direct-fed microbial product listed by the AAFCO Official Publication and not labeled or promoted with any therapeutic function will be regulated as a "food" and usually will not require FDA regulatory attention. However, a direct-fed microbial product with claims for disease cure, mitigation, treatment or prevention (e.g. a dietary product containing a specific bioactive compound) will be considered an "unapproved drug" and required for regulatory action, the initial proceeding being a warning letter (FDA, Compliance Policy Guide CPG 7126.41, Directed-Fed Microbial products). In a global perspective, taking into account the existing regulations and quality control procedures, the compactness and high degree of control achieved in production of microbial protein processes, which can be manufactured under controlled factory conditions in compliance with GMP requirements, may provide a high degree of safety to the consumer, against the uncertainties which regularly surround other food products.
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