scholarly journals Stability of tryptophan during food processing and storage

1985 ◽  
Vol 53 (2) ◽  
pp. 281-292 ◽  
Author(s):  
Henrik K. Nielsen ◽  
D. De Weck ◽  
P. A. Finot ◽  
R. Liardon ◽  
R. F. Hurrell

1. The stability of tryptophan was evaluated in several different food model systems using a chemical method (high pressure liquid chromatography after alkaline-hydrolysis) and rat assays. Losses of tryptophan were compared with the losses of lysine and methionine.2. Whey proteins stored in the presence of oxidizing lipids showed large losses of lysine and extensive methionine oxidation but only minor losses of tryptophan as measured chemically. The observed decrease in bioavailable tryptophan was explained by a lower protein digestibility.3. Casein treated with hydrogen peroxide to oxidize all methionine to methionine sulphoxide showed a 9% loss in bioavailable tryptophan.4. When casein was reacted with caffeic acid at pH 7 in the presence of monophenol monooxygenase (tyrosinase; EC 1.14.18.l), no chemical loss of tryptophan occurred, although fluorodinitrobenzene-reactive lysine fell by 23%. Tryptophan bioavailability fell IS%, partly due to an 8% reduction in protein digestibility.5. Alkali-treated casein (0.15 M-sodium hydroxide, 80°,4 h) did not support rat growth. Chemically-determined tryptophan, available tryptophan and true nitrogen digestibility fell 10, 46 and 23% respectively. Racemization of tryptophan was found to be 10% (D/(D+L)).6. In whole-milk powder, which had undergone ‘early’ or ‘advanced’ Maillard reactions, tryptophan, determined chemically or in rat assays, was virtually unchanged. Extensive lysine losses occurred.7. It was concluded that losses of tryptophan during food processing and storage are small and of only minor nutritional importance, especially when compared with much larger losses of lysine and the more extensive oxidation of methionine.

1985 ◽  
Vol 53 (2) ◽  
pp. 293-300 ◽  
Author(s):  
Henrik K. Nielsen ◽  
A. Klein ◽  
R. F. Hurrell

1. Tryptophan losses in stored milk powders and in different model systems representing the major reactions of food proteins during processing and storage were determined using four different chemical methods and in a rat assay.2. Similar tryptophan values were obtained by the three chemical methods which included high pressure liquid chromatography (HPLC) after sodium hydroxide hydrolysis. colorimetric reaction withp-dimethylamino- benzaldehyde (p-DAB) after barium hydroxide hydrolysis, and fluorescence of the Norharman derivative after NaOH hydrolysis.3. Tryptophan losses in the treated proteins as measured by the alkaline-hydrolysis methods were generally smaller than those determined by the rat assay. Good agreement however was obtained when the chemical value was multiplied by the true nitrogen digestibility.4. Determination of tryptophan by reaction withp-DAB after papain (EC 3.4.22.2) digestion gave lower values in the processed proteins than the other chemical methods or the rat assay.5. A method using alkaline-hydrolysis is recommended, preferably combined with HPLC-measurement of the liberated tryptophan.


2005 ◽  
Vol 8 (4) ◽  
pp. 413-422 ◽  
Author(s):  
S. Xianquan ◽  
J. Shi ◽  
Y. Kakuda ◽  
J. Yueming

2004 ◽  
Vol 22 (SI - Chem. Reactions in Foods V) ◽  
pp. S80-S83 ◽  
Author(s):  
J. Pokorný ◽  
Š. Schmidt ◽  
H. T T Nguyen

Food raw materials and products contain inhibitors of oxidation reactions, both in the lipidic phase and the aqueous phase. The most important inhibitors are phenolic antioxidants. During food processing and storage, concentrations of antioxidants in the two phases reach an equilibrium. Phenolics react with lipidic free radicals, being converted into antioxidant free radicals, quinones, polymers and copolymers. Some degradation products possess an antioxidant activity, too. The relative antioxidant activity decreases with decreasing concentration of oxygen in the system and with increasing temperature. Antioxidants are more rapidly decomposed in surface layers. Health aspects of antioxidant degradation products are often neglected as the safety of antioxidant degradation products is mostly unknown.


Foods ◽  
2019 ◽  
Vol 8 (10) ◽  
pp. 494
Author(s):  
Vibeke Orlien ◽  
Tomas Bolumar

Domestic food processing goes a long way back in time, for example, heat for cooking was used 1 [...]


1997 ◽  
Vol 62 (2) ◽  
pp. 331-337 ◽  
Author(s):  
S. MC CLUSKEY ◽  
J.F. CONNOLLY ◽  
R. DEVERY ◽  
B. O'BRIEN ◽  
J. KELLY ◽  
...  

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