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The Effect of Formaldehyde on the Nutritive Value of Casein and Lactalbumin in the Diet of Rats

Applied Biochemistry Division, DSIR, and the NZ Dairy Research Institute, Palmerston North, New Zealand

A preparation of formaldehyde-treated casein (formol-casein) that had been shown to supply more amino acids than untreated casein for absorption when given by mouth to sheep, was fed to rats as the sole protein at 11%, 20% and 40% of the diet. The 11% formol-casein diet did not support growth and a supplement of L-lysine, L-histidine and L-tryptophan was without benefit; its protein efficiency ratio (PER) was 0, as compared to a PER of 2.8 for untreated casein. When fed at 20% of the diet it supported growth at about half the control value. Nearly normal growth and normal body weight was maintained for 13 weeks when 40% of the diet was formol-casein. The apparent protein digestibility of the formol-casein was 66% as compared with 93% for the untreated casein. A soluble lactalbumin concentrate was treated with formaldehyde at 0, 2, 4, 8 and 16 g/kg. When fed to rats to supply 6.6% protein in the diet, solubility, weight gain, PER, apparent protein digestibility and nitrogen retention progressively decreased, as did digestion by trypsin in vitro. The percentage of absorbed nitrogen retained did not decrease in the formol-lactalbumin fed rats. This indicated that the loss of nutritional value of the proteins was due to depressed digestibility only.

KEY WORDS: • formaldehyde • protein digestion • casein • lactalbumin

Manuscript received 8 September 1975.