Lysinoalanine content

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. 

Lysinoalanine Content of Proteins and Foods Alkaline Treated Proteins... 

Table 6. Effect of additives on lysinoalanine content of alkali-treated wheat gluten. ...

Possible effects of D-amino acid and lysinoalanine contents on food casein digestibility was examined (Friedman et al., 1981). The following variables, which were expected to influence amino-acid composition and utilization, were evaluated (a) pH (8-14) (b) temperature (25-75 C) and (c) time of treatment (10 min to 24 hr). An approximately inverse relationship was observed between D-amino acid... 

Racemization reactions also lead to protein cross-linking reactions. These reactions occur because of the formation of cross-linking compounds such as lysinoalanine (LAL). The formation of LAL not only renders the Lys that participates in the reaction unavailable to the animal, but it also decreases the digestibUity of total protein and other AA because LAL impairs the approach of proteolytic enzymes to the peptide chain (Boschin et al, 2003). However, because LAL formation occurs more readily at a higher pH, this reaction is more prevalent in alkali treated proteins compared with proteins simply exposed to heat treatments (Bunjapamai et al, 1982). Lysinoalanine content of a feed can be determined when analyzing feeds for AA content. 

Boschin, G., A. D Agostina, A. Rinaldi and A. Amoldi, 2003. Lysinoalanine content of formulas for enteral nutrition. J. Dairy Sci. 86, 2283-2287. 

De Groot and Slump (40) studied the influence of alkali on soy protein isolates, monitoring the production of lysinoalanine and changes in amino acid content. They found that above pH 10, treatment at 40 C for 4 hours resulted in decreased cystine and increased LAL (Figure la). They also found that at pH 12.2 for 4 hours, lysine and cystine content steadily decreased with increasing temperatures from 20° to 80 C, and LAL content increased dramatically. At pH 12.2 and 4O C they reported that the greatest loss in cystine and increase in LAL occurred in the first hour (Figure lb). Thus they concluded that exposure of soy protein isolate at pH 12.2 for only a short time would destroy some cystine and decrease the nutritive value. 

The inspection of cinnamycin (4) and duramycin (5)—prompted by their content in lanthionine and /3-methyllanthionine—for the presence of ,/3-unsaturated amino acids was negative. However, cinnamycin as well as duramycin contain lysinoalanine, among other amino acids rarely seen in nature. Did the peptides at one time contain dehydroalanine and did it serve as a precursor for lysinoalanine If the answer to this question were yes, which amino acids, in turn, are potential precursors of dehydroalanine ... 

Exposure of a % (w/v) solution of soy protein to 0.1 N NaOH for 1 hr at 45 to 75"C in the absence and presence of 5 to 20 (w/v) glucose did not affect the amount of lysinoalanine produced (Figures 2,3 Tables 4). Glucose, however, did produce two noticeable effects 1) a sharp decrease in the arginine content, which varied directly with the amount of glucose present and 2) the formation of a new compound eluting just before lysinoalanine. 

Tables 6 and 1 compare the effects of several organic and inorganic compounds on the lysinoalanine and lysine contents of alkali-treated wheat gluten and soybean protein. These results show that all these compounds partly inhibit lysinoalanine formation. The extent of inhibition may vary from protein to protein and should be related to both the content and reducibility of the disulfide bonds (Friedman, 1978a Finley et al., 1978 a,b Masri and Friedman, 1982).

Table 7. Effect of thiols on content of alkali-treated lysinoalanine soy protein.1...

Table 11. Aspartic acid racemization and lysinoalanine (LAL) content of alkali-treated casein and acetylated casein.

Relationship between vitro digestibility of casein and its content of lysinoalanine and D-amino acids. J. Food Sci.> 127. 

Table 1.31 lists the contents of lysinoalanine in food products processed industrially or prepared under the usual household conditions . 

Fig. 1.39. Lysinoalanine (LAL) formation from wheat gluten (2) and corn gluten (1). Protein contents of the glutens 70% heated as 6.6% suspension at 100 °C for 4 h. (according to Sternberg and Kim, 1977)...

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