Proline/glucose mixtures

The very potent taste compound 59 (Fig. 3.34), which has a low taste threshold of only 9 mmol/L, and several other bitter compounds were responsible for the taste of a roasted proline/glucose mixture ]84]. 

Influence of High Hydrostatic Pressure on Aroma Compound Formation in Thermally Processed Proline-Glucose Mixtures... 

To correlate differences in the aromas of different samples, first, the most-odor active compounds in the samples treated without HHP have to be identified. The subsequent application of a comparative Aroma Extract Dilution Analysis (AEDA) is a very useful tool to screen and compare odor activities of the same odorants in two different samples. To gain first insights into the influence of HHP on aroma formation in Maillard type reactions, the key odorants formed at 100°C in proline/glucose mixtures treated under HHP or at normal pressure were compared. Labeling experiments were then performed to elucidate the influence of HHP on formation of transient intermediates and an pathways leading to selected key odorants. 

The results clearly indicate that the formation of Acp in thermally degraded proline and glucose mixtures proceeds via decarboxy-... 

Nutritional Effects Due to the Presence of the Maillard Products. Many physiological or antinutritional effects have been attributed to the Maillard products. Specific effects have been attributed to the Amadori products deoxyfructosylphenylalanine (a model substance not likely to be present in large quantities in foods) appears to depress the rate of protein synthesis in chicks (32) and to partially inhibit in vitro and in vivo the absorption of tryptophan in rats (33). The compound e-deoxyfructosyllysine inhibits the intestinal absorption of threonine, proline, and glycine and induces cytomegaly of the tubular cells of the rat kidneys (34) as does lysinoalanine. In parenteral nutrition the infusion of the various Amadori compounds formed during sterilization of the amino acid mixture with glucose is associated with milk dehydration in infants and excessive excretion of zinc and other trace metals in both infants and adults (35,36,37). 

In a first experiment, two solutions of glucose and proline were separately reacted in MOPS buffer at a constant pH of 7.0 for 90 min at 100°C. One mixture was treated at HHD, the other at normal pressure (NP). The MOPS buffer was used, because it is known to be stable under HHP and, thus, was able to keep the pH constant, which is an important prerequisite in studies at HHP. 

Figure /. Aroma profiles of thermally processed glucose/L-proline mixtures. Right normal pressure (NP) left high hydrostatic pressure (HHP)...

Figure 5. mounts of 2-oxopropanol formed during thermal processing (100°Q pH 7) of a glucose/proline mixture ( high hydrostatic pressure M normal pressure)... 

A [ Cel-glucose/proline, B [ CeJ-glucose/proline and C [ Ce]- and [ Ce]-glucose/praline (1+1). The 2-oxopropanol formed from the three mixtures was derivatized with ethyl hydroxamine and the derivatives were then analyzed by MS/CI. 

Figure 8. Isotopomers of 2-hydroxypropanal (as ethoxime derivatives) formed from C -glucose/proline (A) C -glucose/proline (B) and a 7+7 mixture of C -glucose/proline (C) racted under high hydrostatic pressure...

Secondary amines and amino acids react in an entirely different way. Indeed, L-proline forms a mixture of the four possible tautomers, but, after a time, ninhydrin-positive substances may be formed by breakdown of the proUne molecule. (Other ketoses do not give this reaction.) Secondary amines, such as piperidine, will not react at 0°, but, at higher temperatures (40-60°), some D-fructosylamine is formed, together with a higher proportion of D-glucose by isomerization. Morpholine or dicyclohexylamine give a 20 to 25% yield of D-n6o-hexulose, and may be used on a preparative... 

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