Thesis (MTech (Food Technology))--Cape Peninsula University of Technology, 2016. / The Maillard reaction (MR) involves the condensation reaction between amino acids or proteins with reducing sugars, which occurs commonly in food processing and storage. Maillard reaction products (MRPs) were prepared from glucose-casein model system at pH 8, heated at 60, 75 and 90°C for 6, 12 and 24 h, respectively. Browning intensity (BI) of MRPs, as monitored by absorbance at 420 nm increased with an increase in reaction temperature. The reducing power (RP) of MRPs increased (p < 0.05) as the reaction time increased at 60 and 75°C, while at 90°C an increase in RP was observed from 6 to 12 h and thereafter a slight decrease was observed up to 24 h. The 2,2-Azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) radical scavenging activity (ABTS-RS) and Peroxyl radical scavenging (PRS) activity of glucose-casein MRPs produced at 90°C decreased as the reaction time increased. In this study, the ferrous chelation activity of MRPs was higher than that of tert-butylhydroquinone (TBHQ) (0.02%) and Trolox (1 mM), respectively. Moreover, the 1, 1-diphenyl-2-picryl-hydrazil radical scavenging (DPPH-RS) of MRPs increased (p < 0.05) as the reaction time increased irrespective of the heating temperature. The primary and secondary lipid oxidation products were measured using the Peroxide value (PV) and Thiobarbituric acid reactive substance (TBARs) assay in sunflower oil-in-water emulsion, respectively. MRPs derived at 90°C for 12 h had the lowest peroxide value, while the TBARs inhibitory by MRPs ranged from 39.05 – 88.66%. Glucose-casein MRPs displayed superior antioxidant activity than TBHQ (0.02%) and Trolox (1 mM), respectively, as measured by the TBARs assay. The differential scanning calorimetry (DSC) and Rancimat techniques set at 110°C were used to evaluate the oxidative stability the lipid-rich media containing MRPs. At the same temperature program, DSC gave significantly lower reduction times than the Rancimat. Furosine (N-ε-Fructosyl-lysine) and Pyrraline (2-amino-6-(2-formyl-5-hydroxymethyl-1-pyrrolyl)-hexanoic acid) were determined using high pressure liquid chromatography to evaluate the extent of the MR. Furosine concentration of glucose-casein MRPs ranged between 0.44 – 1.075 mg.L-1 in MRPs derived at 60°C, while at 75°C an increase as function of time was observed. MRPs derived at 60 and 75°C exhibited a varied concentration of pyrraline as the reaction time increased with higher temperatures resulted in higher concentrations (0.39 mg.L-1). The results of this study clearly indicated that MRPs possess antioxidant activity and can be used as natural antioxidants in the food industry.

The role of redox reactions in the formation of aroma volatiles, colour and other non-volatiles in the Maillard Reaction was investigated. The electrochemical properties of individual reactants and Maillard model mixtures were monitored via ORP (oxidation-reduction potential) and oxygen electrodes. All models exhibited unique electrochemical activities represented by their corresponding ORP profiles. Investigation into the redox potentials of several model systems demonstrated that the increased negative value of a redox potential is not necessarily correlated with its browning potential. An optimal redox potential range, where browning is favoured, was found to represent a balance between carbonyl and hydroxyl moieties in the structure. Adjustment of this redox potential by introducing reducing or oxidizing species can shift this balance resulting in modifications in browning capacities. However, it was concluded that there is a clear relationship between browning ability and reducing capacity of the model systems. Furthermore, a novel oxidative pyrolysis technique was developed to study the role of oxidative environment on the product distribution during pyrolysis and to investigate the mechanism of formation of non-volatiles through 13C and 15N-label incorporation. Application of this technique to glucoselglycine model system have indicated that most non-volatile Maillard reaction products can arise from glucose oxidation intermediates such as glucosone, gluconic acid and deoxyglucosones. To study the specific role of redox reactions in the formation of non-volatiles, a post-pyrolytic derivatization technique was developed and optimized. Several non-volatile end products were identified and mechanistically confirmed to involve oxidation and reduction reactions for their formation, such as lactones, hydroxylated benzenes and hydroxylated pyrazine. The latter was identified and confirmed to be generated via the dimerization of glycine and subsequent oxidation. In addition, the formation of different volatiles such as pyrazole, imidazole and oxazole was mechanistically confirmed to depend on redox reactions.

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Amadori rearrangement product (ARP) of tryptophan with glucose was synthesized according to a published procedure, and its decomposition was studied at two different concentrations and at two temperatures, 110$ sp circ$C and 140$ sp circ$C over a period of 6 hrs. A RP-HPLC system was developed to separate and quantitate the decomposition products of the ARP. The results indicated that, the ARP can decompose to form the following products, hydroxymethylfurfural (HMF), maltol, indole, $ beta$-carbolines (norharman and harman) and tryptophan. Further, using the same analytical method, the following systems were also analyzed for the presence of the above mentioned products (a) D-glucose and D-mannose with tryptophan; (b) D-glucose; and (c) tryptophan. In addition, rate constants and activation energies for the decomposition and formation reaction were calculated. Plausible mechanisms for the formation of the decomposition products are suggested.

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Proximate analysis of the commercial shrimp meat waste samples indicated the presence of 94.6% protein and 4.2% fat on a dry basis. The HPLC analysis revealed the presence of 17 amino acids (proline most abundant) and 7 sugars (ribose being the most abundant). The changes in the concentration of the amino acids and sugars after heat treatment, are explained based on their interaction through the Maillard reaction and by the thermal hydrolysis of proteins and polysaccharides present in tissue. Carotenoid pigments ($ beta$-carotene, canthaxanthin, astacene, and astaxanthin monopalmitate) were extracted and separated by thick layer chromatography. Their structures were identified tentatively by thick layer chromatography (TLC) and subsequently confirmed by Fourier transformed infrared (FT-IR) spectroscopy. Lipids were separated and categorized into glycerides, sterols, and phospholipids by thin layer chromatography while flavor-active components were extracted by different organic solvents into acidic, basic, and neutral fractions and their sensory properties determined. The flavor profile of the raw and cooked shrimp meat waste revealed the presence of 59 compounds in raw shrimp compared to 44 in cooked. The components identified were of different functional groups, including fatty acid esters, long chain alcohols, aldehydes, ketanes and hydrocarbons. Many fractions provided desirable aroma (nutty, fruity, floral, green woody, meaty) indicating the presence of important flavor compounds in the commercial shrimp waste. / Model studies were carried out under different experimental conditions (water content, pH), to observe the influence of these parameters on the formation of Maillard reaction products. Furthermore, a comparative study between direct injection of the aqueous solutions and its organic extracts was conducted. The direct injection of aqueous solutions revealed the presence of many water soluble components that were not detected by organic solvent extraction such as droserone and 3,9-diazatricyclo$ lbrack7.3.0.0 sp{*}.3 sp{*}.7 sp{ *} rbrack$-dodecan-2,8-dione while maltoxazine and acetanilide are example of compounds identified only in the dichloromethane extracts. Results also demonstrated that monosaccharides affected the yield of the compounds produced whereas the amino acids influenced the sensory properties of these models. Fructose and ribose were found to be the most reactive sugars in their respective categories. Thiazoles were found to be more water soluble whereas $ beta$-carbolines were more abundant in the organic extracts. The influence of water content was investigated in model systems containing fructose or glucose. It was found that water free systems decreased the yield of pyrazines and thiazoles while the formation of pyrrole and pyridine derivatives increased under dry heating conditions. The formation of Maillard reaction products were studied under different pH conditions in order to assess the effect of pH on the formation of heterocyclic compounds. Pyrazine and furan derivatives were the most affected by pH and alanine was found to be a better nitrogen source than lysine in the formation of pyrazines under different pH conditions. Finally, based on energy minimization studies using MM2 force field, a plausible mechanism was proposed for the formation of maltol in Maillard model systems.

The process by which foods are browned during baking and roasting is attributed to the Maillard reaction. The interaction of the $ alpha$-hydroxycarbonyl moiety of a reducing sugar with an amino compound can result in a complex series of changes. The identification and isolation of the key intermediates, known as the Amadori rearrangement product (ARP) and Heyns rearrangement product (HRP), can provide a greater understanding of the browning process. / Fourier transform infrared (FTIR) analysis of 1-hydroxyacetane provided qualitative and quantitative information of the behavior of this $ alpha$-hydroxycarbonyl compound in various aqueous and non-aqueous solutions. / The carbonyl peaks (in the 1750-1700 $ rm cm sp{-1}$ absorption region) due to the keto and aldehydo forms of 1-hydroxyacetone (acetol) in the pure state and in deuterium oxide $ rm(D sb2O)$ were assigned. Upon addition of the acid-base catalysts (triethylamine, 5% NaOD and 5% DCl) additional peaks were detected in the alkene region (1700-1650 $ rm cm sp{-1})$ due to the formation of enediols by enolization. The examination of analogous hydroxycarbonyl structures (1-hydroxy-2-butanone, glyceraldehyde, glycoaldehyde and dihydroxyacetone) provided the means to confirm the assignments of the carbonyl and enediol bands. / The integrated intensity of the carbonyl peak of 1-hydroxyacetone centered at 1720 $ rm cm sp{-1}$ was determined for dilute solutions in $ rm D sb2O.$ The integrated molar absorptivity of the carbonyl band was calculated to be 3674 L/mol/cm. In addition, the effect of concentration and temperature on dimer dissociation was investigated. The effect of solvent and temperature on enolization was also studied. Time run analysis of the carbonyl-amine reaction of 1-hydroxyacetone with pyrrolidine provided the basis for a kinetic study of the rearrangement process in the early stage of Maillard reaction.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 162-202). Also available in print.

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