Lysine availability

LYSINE AVAILABILITY IN HEATED WHEAT FLOUR PROTEINlZ... 

Desol ventization techniques have been shown to influence lysine availability (62. Heating prior to oil removal had little effect on PER at 93 C, and only a slight effect at 108°C... 

As shown in Table IX, the lysine availability (%) showed changes for the three samples. However, the unavailable lysine (total lysine minus available lysine) contents in bread (whole), bread crust and crumb were only 0.04, 0.05, 0.03%, respectively. Table 7 shows that the unavailable lysine contents for all pizza crusts, baked and unbaked, varied only from 0.02 to 0.03%. These data indicate the reduction of lysine caused by baking is mainly shown by the total lysine analysis. It appears then that there is no need to run available lysine determinations for such bakery foods. This finding also suggests that the nutritive loss of bread and pizza crusts was primarily due to the destruction of lysine in those products to a lesser extent baking caused it to become unavailable. 

Of the eight amino acids essential for man and other animals, lysine is the most easily damaged by processing and/or storage of food. This damage or modification results in a reduction in nutritional availability of lysine. Available lysine can be... 

In the lower range the SA values were below FDNB values but above about 4 g lysine/16 g N, the SA levels were slightly higher. The difference may arise from the fact that FDNB tends to react with the E -Nl -linkage of blocked lysine ( 22 ). There may be also differences due to the failure of the various reagents to fully penetrate the high crosslinked material. The SA method may therefore better reflect the influence of poor digestibility on lysine availability. 

Table II. Relative percentage of the lysine availability in selected samples as determined by various methods ( unheated total lysine - 6.0 g /16 g N - = 100% ).

It is possible to assess lysine availability using an Escherichia coli lysine auxotroph,44 but further development is required before such a test can compete with furosine determination. 

L. S. Malec, A. S. Pereyra Gonzales, G. B. Naranjo, and M. S. Vigo, Influence of water activity and storage temperature on lysine availability of a milk like system, Food Res. Int., 2002, 35, 349-353. 

The hypothesis of the loss of lysine availability engaged in such peptides has been tested in animal assays with the free synthetic molecules. 

Furosine, a marker of the Maillard reaction product, is a valuable indicator of food protein quality. It is a marker for thermal treatment in foodstuffs and is directly related to the loss of lysine availability. IPC was employed to determine furosine content in beverages based on soy milk and cow milk supplemented with soy isoflavones [39]. Furosine was also analyzed in 60 commercial breakfast cereals to assess their protein nutritional values. The higher the protein content in the formulation, the higher the furosine levels [40]. A simple IPC technique that uses 1-octanesulfonic acid as the IPR allowed the selective determination of histamine levels in fermented food [41]. 

Delgado-Andrade, C., Rufian-Henares, J.A., and Morales, F.J. Lysine availability is diminished in commercial fibre-enriched breakfast cereals. Food Chem. 2007, 100, 725-731. 

After 10 days, there is a very significant decrease in lysine availability, which combines to decrease as the browning is prolonged. At 40 days, roughly 57% of the lysine is lost (10). 

On the contrary, the nutritional value of oxidized lipid-protein interaction products is substantially lower than that of the original lipoproteins. The main reason is the lower digestibility most covalent bonds formed in the interactions are not attacked by proteases under the conditions of digestion. The 6-amino group of bound lysine is particularly sensitive to interactions with carbonylic oxidation products (Janitz et al., 1990), and the resulting imine bonds substantially reduce the lysine availability. Lysine losses correlate with the increase in fluorescence. Other amino acids, such as tyrosine, tryptophan, and methionine, are also partially converted into unavailable products. Interaction products may be allergenic even when allergenic proteins have reacted (Doke et al., 1989). 

The chemical and enzymatic browning reactions of plant polyphenols and their effects on amino acids and proteins are reviewed. A model system of casein and oxidizing caffeic acid has been studied in more detail. The effects of pH, time, caffeic acid level and the presence or not of tyrosinase on the decrease of FDNB-reactive lysine are described. The chemical loss of lysine, methionine and tryptophan and the change in the bioavailability of these amino acids to rats has been evaluated in two systems pH 7.0 with tyrosinase and pH 10.0 without tyrosinase. At pH 10.0, reactive lysine was more reduced. At pH 7.0 plus tyrosinase methionine was more extensively oxidized to its sulphoxide. Tryptophan was not chemically reduced under either condition. At pH 10.0 there was a decrease in the protein digestibility which was responsible for a corresponding reduction in tryptophan availability and partly responsible for lower methionine availability. Metabolic transit of casein labelled with tritiated lysine treated under the same conditions indicated that the lower lysine availability in rats was due to a lower digestibility of the lysine-caffeoquinone complexes. 

Is is highly likely that the discoloured sunflower protein concentrates produced at alkaline pH (Pomenta and Burns, 1971 Cater et al., 1972) also have a decreased lysine availability due to the reaction of sunflower protein with chlorogenoquinone and other oxidized phenols. The conversion of phenolic acids to quinones can also occur enzymically under the action of naturally-occurring phenolase enzymes at neutral pH and these quinones appear to react with lysine in a similar manner. The enzymic reactions, however, are much less rapid than those occurring under alkaline conditions and would probably have less influence on the nutritional quality of protein concentrates. 

Bujard and Finot compared six methods for the determination of available lysine, using a set of milk samples previously submitted to different heat treatments. I will use this work to make a critical comparison of a few methods that are theoretically sound and could be applied to determine lysine availability in foods. The methods compared are ... 

Total lysine TLV (Fig. 3). This value grossly overestimates lysine availability, since for an availability of zero the TLV is still 3-3gLys/16gN. Thus, the regeneration of lysine from the blocked lysine corresponds to 40% of the lysine theoretically present (ThL = 8 2 g Lys/16 g N). This liberation from protein-bound deoxylactulosyl-lysine (DL-Lys) is less than that obtained from free DL-Lys. ... 

Lysine availability tests are useful to determine the degree of heat damage in proteins, but they do not necessarily determine potential decreases in intestinal protein digestion or information on individual AA digestibility. Although the technique may be appropriate for eomparing different samples within the same feeds, it is not recommended for use among various feeds. 

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