The Influence of Maillard Browning and Other Factors on the Stability of Free Tryptophan

Abstract

The influence of various factors on the stability of free tryptophan was evaluated in several reaction systems. After treatment, tryptophan was measured by high performance liquid chromatography. Factors such as heating, protein, and glucose were responsible for tryptophan losses in a system undergoing Maillard browning. Hydrogen peroxide caused extensive losses while pH and light had minimal effect on tryptophan stability in solution. When the stability of tryptophan was compared to lysine and threonine during browning, threonine had the highest retention. At low water activity (0.22), tryptophan had the lowest retention (42%) while at a high water activity (0.75) lysine had the lowest retention (5%). When fortified corn tortillas were made using the typical heat treatment involved in preparation, retention of added lysine and tryptophan was 85–90%.

Chemistry, analysis, nutritional value, and toxicology of tryptophan in food. A review

“…Chemical transformations of tryptophan are essentially a function of the temperature and the duration of treatments. However, specific modifications can be induced by the presence of oxygen, water (Leahy and Warthesen, 1983; Kanner and Fennema, 1987), other food-oxidizing lipids (Krogull and Fennema, 1987;Nielsen et al, 1985a-d;Yong et al, 1980), vitamins (Kanner and Fennema, 1987), reducing sugars (Ashoor and Zent, 1984; Brautigam and Severin, 1974;Dworschak and Orsi, 1977;Finot et al, 1982; Nyhammar and Pernemalm, 1985;Orsi, 1985; Orsi and Dworschak, 1978;Sgarbieri et al, 1973;Tanaka et al, 1975), carbonyl compounds (Arai, 1980; Chu and Clydesdale, 1976;McLaren, 1977;Previero et al, 1972), nitrites (Bonnett and Holleyhead, 1974; Nakai et al, 1978;I to et al, 1979; Gruenwedel et al, 1984; Hotchkiss, 1984; Kinae, 1986;Mellet et al, 1986; Ochiai et al, 1986), halogens (Bercz and Bawa, 1986), radiation (Garrison, 1987), and sulfites (Yang, 1973).…”

“…The rate of degradation of free tryptophan during thermal treatment in a 90-140 °C temperature range is a function of pH (Leahy and Warthesen, 1983). In the presence of formate buffer, the maximum rate of decomposition occurs at pH 5.3.…”

“…The -amino group of the free amino acid reacts with carbonyl compounds such as pentoses or hexoses (Lee et al, 1979). The extent of this Maillard reaction is a function of time, temperature, and water activity (Leahy and Warthesen, 1983). Free tryptophan in the absence of other reactive compounds is relatively unaffected by heating at temperature near 100 °C for about 10 h. However, in the presence of glucose the loss reaches about 50%.…”

Non-Enzymatic Degradation Pathways of Lactose and Their Significance in Dairy Products

“…In view of the fact that tryptophan, arginine and histidine are not as abundant in milk proteins as lysine, their possible reactivity in Maillard reactions is of nutritional interest. In particular, it has been reported that tryptophan may be even less stable than lysine under some conditions (Leahy and Warthesen, 1983). Dworschak and Hegedü s (1974) reported the loss of 97% of the tryptophan in a milk powder containing 5.7% moisture that was heated at 1008C for 4 h. This conflicts with the results of Nielsen et al (1985b,c), who could not detect a decrease in tryptophan (by chemical analysis or rat bioassays) in a browned milk powder.…”

“…However, Eichner and Ciner-Doruk (1979) proposed that the 1,2-E pathway assumes increasing importance as the water content increases. Significantly, a w may influence the site specificity of Maillard reactions involving proteins (Wu et al, 1990) and also the relative reactivity of individual amino acids (Leahy and Warthesen, 1983). Ideally, a w should be used as a predictor of browning rate and other spoilage reactions in foods only in the absence of moisture sorptiondesorption hysteresis (i.e.…”