Citrinin, a nephrotoxic fungal metabolite produced by several species of Penicillium and Aspergillus , has been found to contaminate foods used by humans and animals. The present study investigated potential effects of this compound on the immune system. Male CD-1 mice received 0, 0.12, 0.6 or 3.0 mg of citrinin/kg i.p. every other day for 2–4 weeks. Food consumption and body or organ weights were not affected but kidneys were enlarged. Splenic cells from mice exposed to citrinin for 2 or 4 weeks were cultured with or without the mitogens, phytohemagglutinin (PHA), pokewecd mitogen (PWM) or lipopolysaccharide (LPS). Exposure to citrinin stimulated splenic lymphocyte proliferation. Antibody production by splenic cells in animals sensitized to sheep red blood cells (SRBC) increased in the two highest dose groups. Delayed hypersensitivity reaction, measured as a foot-pad swelling, in response to SRBC sensitization and subsequent challenge were not affected by citrinin treatment. In vitro addition of citrinin (>1 × 10 −5 M ) to splenic lymphocytes was cytotoxic. These findings suggest that citrinin mildly stimulates the immune system but does not have consistent immunotoxic effects at the doses tested.
Enzymatic coagulation of milk by immobilized proteases, and their potential application to cheese manufacture, is reviewed. Particular emphasis is given to the immobilized protease catalyst and to the reactor design for coagulation of milk. Pepsin and chymotrypsin retained more activity and greater stability than the other immobilized proteolytic enzymes. Porous glass beads, several anion exchange resins, and the copolymer ethylene-maleic anhydride gave best results among the support materials that were evaluated. Covalent attachment of enzyme to support is preferable to adsorption techniques but may be too costly. Perhaps the best catalyst is one using a lengthy procedure for covalent immobilization of enzyme on glass beads but good results were also obtained with simpler adsorption techniques. Catalysts varied greatly in initial activity but all lost activity upon exposure to milk. Stirred tank, packed bed, and fluidized bed reactor designs were used. Continued research is required to make enzymic milk coagulation with immobilized proteases economically feasible.