Lactalbumin alkali treated

Metabolic Transit of Lysinoalanine. Urinary and Fecal Excretion of Protein-Bound Lysinoalanine (113). Three different alkali-treated proteins (lactalbumin, fish protein isolate, and soya protein isolate) containing, respectively, 1.79, 0.38, and 0.14 g of lysinoalanine/16 g nitrogen were given to rats and the urines and feces were collected. Lysinoalanine was measured before and after acid hydrolysis. The fecal excretion varied from 33 to 51% of the total ingested lysinoalanine and the urinary excretion varied from 10 to 25%. The higher level of lysinoalanine found after acid hydrolysis indicates that a certain quantity is excreted in the urines as combined lysinoalanine (see Table VII). The total recovery was inferior to the ingested quantity (50 to 71%) indicating that the molecule is transformed or retained in the body of the rat. 

Sane laboratories (38, 55) reported severe nephrocytanegaly from alkali-treated soy protein while a similar protein, having the same IAL content, does not produce lesions (56). Karayiannis (55) has found that alkali-treated soy protein (supplying 1400-2600 ppm IAL) resulted in nephrocytanegaly whereas 2500 ppm IAL derived from alkali-treated lactalbumin did not induce the lesions. 

Another difficulty in formulating a simple relationship between LAL and nephrocytomegaly is that proteins of equivalent LAL content produce different biological responses. O Donovan (1976) reported that feeding rats alkali-treated soy protein led to severe nephrocytomegaly, while a different protein with the same LAL content did not produce lesions. Karayiannis (1976) found that alkali-treated soy protein (supplying 1400-2600 ppm LAL) resulted in nephrocytomegaly, whereas 2500 ppm LAL derived from alkali-treated lactalbumin did not. 

The key to the problem seems then to be the measurement of the enzymatic releasability of protein-bound LAL, as mentioned by Slump (1978). Little on this topic can be found in the literature. Using a closed system (pepsin-pancreatin and pepsin-pronase-prolidase-aminopeptidase), Slump (1978) found an LAL release with treated soybean of 3% (1.3 g LAL/16 g N), and of 2% with treated casein (5.5 g LAL/16 g N content) or 0.5% (1.0 g LAL/16 g N content). Using a different vitro digestion system, Finot et al. (1978) reported a 27% release of LAL from alkali-treated lactalbumine. 

For example, the respective values at pH 10.6 are 0.262, 0.494, and 1.04 mole per cent (ratio of about 1 2 4) at pH 11.2 the values are 0.420, 0.780, and 1.32 mole per cent and at pH 12.5 (pH of 1% protein solution in 0.IN NaOH), the respective values are 0.762, 0.780, and 2.62 mole per cent. (Note that the value of casein approaches that of gluten at this pH). The observed differences in lysinoalanine content of the three proteins at different pH values are not surprising since the amino acid composition, sequence, protein conformation, molecular weights of protein chains, initial formation of intra- versus intermolecular crosslinks may all influence the chemical reactivity of a particular protein with alkali. Therefore, it is not surprising to find differences in lysinoalanine content in different proteins treated under similar conditions. These observations could have practical benefits since, for example, the lower lysinoalanine content of casein compared to lactalbumin treated under the same conditions suggests that casein is preferable to lactalbumin in foods requiring alkali-treatment. 

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