Casein in milk and milk products has been a major component of the diet of man for centuries. Long term animal feeding studies have shown that extremely high dietary levels of casein, in common with other food proteins, may be injurious to the kidneys. However, per capita daily consumption of casein and caseinates added to foods is less than 0.2g and represents a minor contribution to the total average daily intake of protein, about 99g, by the U.S. population.
Heating casein under strongly alkaline conditions at 90°C or autoclaving at higher temperature under near neutral conditions has been shown to result in the formation of lysinoalanine as a component of the protein molecule. Lysinoalanine has been reported in commercial samples of casein, calcium caseinate, and sodium caseinate. Lysinoalanine also has been detected at relatively low concentration in a number of commercial food products and in home-cooked frankfurters, chicken, and egg white.
Sensitivity to lysinoalanine differs among animals species and is dependent on the protein nature of the diet; feeding free lysinoalanine at dietary levels of 1000 ppm to five mammalian species other than the rat, including subhuman primates, failed to produce renal cytomegalic changes. Renal cytomegalic changes have been demonstrated in rats fed free lysinoalanine, or alkalitreated soy protein isolate, lactalbumin or casein containing bound lysinoalanine. The alkali-treated proteins were fed as the sole source of protein at dietary levels of 20 to 30 percent; cytomegaly did not occur or was markedly reduced in rats fed diets in which alkali-treated protein was supplemented with an untreated protein, suggesting that the renal syndrome was caused by protein bound lysinoalanine in diets deficient or imbalanced with respect to one or more amino acids. Although the available information indicates that the present consumption levels of casein and caseinates, less than 0.2g per capita as currently used, pose no hazard to the consumer,a limitation with respect to lysinoalanine content in specifications for food grade products would avoid possible future problems in this regard.
A small proportion of infants and lesser numbers of children and adults experience untoward reactions to casein and other milk proteins. Casein is only mildly antigenic but the presence of whey proteins in commercial casein may increase the frequency of hypersensitivity reactions. However, the relatively low consumption of casein, sodium and calcium caseinates added to processed foods, as compared to consumption of casein in milk, cheese, other dairy products, and foods containing dairy products as an ingredient, does not appear to significantly exposure to this antigen.
Although few nitrite analyses of caseinates dried in direct fired spray driers were available to the Select Committee, the available data and the finding of nitrite in samples of other products dried in similar equipment indicates that nitrite can occur at low levels in spray-dried products. According to available information, casein and some caseinates are dried in indirectly heated driers and would not be exposed to nitrite from the drying gases. Nitrite content is of concern because of its toxicity, per se, and because it can react with other nitrogen containing compounds to produce nitrosamines, many of which have been shown to be carcinogenic in experimental animals. It is important to ensure that preformed nitrosamines are not present in caseinates and are not formed in processed foods containing caseinates.
Consideration must be given to the potential for nitrosamine formation in vivo from ingestion of foods containing nitrite, and the latter reacting with other nitrogen containing compounds in foods, drugs, and endogenous amines, must be considered. Many natural and processed foods, including spraydried products, contribute to the total human intake of nitrite even though bacterial reduction of nitrate to nitrate in saliva is the mejor source of nitrite entering the stomach.
It has been reported from recent unpublished work with rats fed nitrite that the frequency of lymphoreticular tumor was increased. The possibility that nitrite has a direct adverse effect of this type raises questions about the total body burden of nitrite and the relative contributions from food, saliva, and the estimated larger amount produced by bacteria in the intestinal tract. A study of these sources and their relative importance is required for individuals of different age groups and dietary habits to obtain reliable figures. Specifications should be developed for food grade caseinates which limit the content of nitrite and nitrosamines.
Caseinates appear to contribute a minor quantity of nitrite to total human exposure. Preliminary estimates of per capita exposure indicate they account for less than 0.2 percent of that taken in as an ingredient of food and present in saliva, and less than 0.005 percent of the total taken in as food ingredient, present in the saliva, and generated in the intestinal tract. From the standpoint of relative contributions to the controllable nitrite load and/or total body burden, caseinates do not appear to be cause for concern at this time. Nevertheless, the possible adverse effects of nitrite call for more explicit knowledge and actions for maintaining a low level of the compound in the commercial product and for continued monitoring of its relative contributions, with adjustments as necessary, as the major sources of commercially added nitrites are progressively decreased through regulatory procedures underway.
The Select Committee has weighed the foregoing information and concludes that: It is essential that food grade specifications for casein, sodium caseinate, and calcium caseinate be established including provisions for acceptable levels of lysinoalanine, nitrite, and nitrosamines.
Assuming that acceptable levels of lysinoalanine, nitrite, and nitrosamine are established, there is no evidence in the available information on casein, sodium caseinate, or clacium caseinate that demonstrates or suggest reasonable grounds to suspect a hazard when they are used at levels that are now current or that may reasonably be expected in the future.
There is no evidence in the available information on casein that demonstrates or suggests reasonable grounds to suspect a hazard when it is used in paper and paperboard products for food packaging at levels that are now current or that might reasonably be expected in the future.