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Thermal degradation of 1-amino-1-deoxyketoses and their role in flavour development : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University
(Massey University, 1981) Birch, Edward John
Sugars undergo caramelisation reactions at relatively high temperatures but when amino compounds are present, Maillard browning reactions are possible and these occur under less severe conditions. The reaction conditions and the basic character of the amino compounds determine the range of flavour compounds formed. The first step during Maillard browning is the condensation of a reducing sugar with an amine to form a glycosylamine and this compound may then undergo the Amadori rearrangement to form a 1-amino-1-deoxyketose. The pyrolysis of two 1-amino-1-deoxyketoses (1-deoxy-1-glycino-D-fructose and 1-β-alanino-1-deoxy-D-fructose) was studied in this investigation to examine their participation in a low energy route to aroma formation. Thermal analysis and parallel chemical investigations showed that the formation of these Amadori compounds facilitates the thermal degradation of their sugar and amino acid moieties. In addition increased quantities of various aroma compounds are produced, compared with the controls. In particular, the toxic compound protoanemonin is formed and a degradation pathway leading to its production is proposed. Most of the work involving the elucidation of degradation pathways during Maillard browning have involved studies in aqueous systems. Browning reactions between glucose and amino acids were also observed during heating in the dry-state in this study. These reactions are very vigorous once initiated and this precluded the study of a glucose plus amino acid control by the techniques used to study the pyrolysis of the 1-amino-1-deoxyketoses. Such reactions occur at temperatures below those required for the thermal degradation of the corresponding Amadori rearrangement compound thus questioning the involvement of these compounds in the lowest energy thermolysis pathway in the absence of moisture. The results of experiments designed to investigate the role of Amadori compounds during the browning of sugar-amino acid systems in the dry-state demonstrated however that the reactions reported to occur in aqueous systems can also account for the dry-state processes at temperatures up until the spontaneous decomposition of the 1-amino-1-deoxyketose can occur. That the 1-amino-1-deoxyketose does not brown by itself or in the presence of glucose as readily as a glucose plus amino acid system is presumably a basicity effect. The stronger base (the amino acid) may promote a solid-state enolisation of the glucose and hence initiate browning at a somewhat lower temperature. The results of these experiments also demonstrate the stability of the 1-amino-1-deoxyketoses and show that their formation is not a rate-limiting step during browning. In the third section of this thesis the effect of changing the amine moiety on the degradation pattern of 1-amino-1-deoxyketoses is assessed. Previous research has indicated that glucose by itself and Amadori compounds formed from weak primary bases degrade via an initial 1,2 enolisation step to form mainly 2-furaldehydes and pyrrole derivatives while 1-amino-1-deoxyketoses containing a strong basic moiety (usually formed from a secondary base) degrade via a 2,3 enol intermediate and give rise to fragrant caramel aroma compounds. Several 1-amino-1-deoxy-ketoses were prepared using primary and secondary bases covering a range of pkb values. These compounds were pyrolysed and their decomposition characteristics monitored by thermal analysis methods. Parallel analysis of the volatiles produced and a comparison of the results from previous investigations generally endorsed the reported hypotheses on the degradation of Amadori compounds. It was found that the structure of the base and functional groups present influenced the degradation phenomena as well as the basicity. The thermal decomposition of amino acid - derived Amadori compounds for instance, did not fit into the pattern of that observed for 1-amino-1-deoxyketoses derived from other bases. The amino acid influences the degradation traits by promoting 1,2 enolisation and charring rather than aiding 2,3 enolisation similar to bases of comparable pkb.
Physicochemical changes in intermediate-moisture protein bars made with whey protein or calcium caseinate.
(Elsevier, 2010) Loveday, SM; Creamer, Lawrence K.; Singh, Harjinder; Hindmarsh, Jason P.
This study examined model protein bars made with whey protein isolate (WPI) or calcium caseinate and stored at 20 °C for 50 days. WPI bars remained very soft and, throughout storage, confocal micrographs showed a continuous matrix containing soluble protein and increasing quantities of glucose crystals. In contrast, calcium caseinate bars had a firm texture within 1−5 days of manufacture (fracture stress 199 ± 16 Pa) and hardened progressively during storage (final fracture stress 301 ± 18 Pa). Electrophoresis showed no evidence of covalent protein aggregation, but there were substantial changes in microstructure over the first day of storage, resulting in segregation of a protein phase from a water−glucose−glycerol phase. Proton nuclear magnetic resonance (1H-NMR) relaxometry and nuclear Overhauser effect spectroscopy (NOESY) experiments showed that water migration away from protein towards glucose and glycerol occurred 10−18 h after manufacture, lowering the molecular mobility of protein. Phase separation was probably driven by the high osmotic pressure generated by the glucose and glycerol. These results confirm that the hardening of protein bars is driven by migration of water from protein to glucose and glycerol, and microstructural phase separation of aggregated protein.
Physicochemical changes in a model protein bar during storage
(Elsevier, 2009) Loveday, SM; Hindmarsh, Jason; Creamer, Lawrence K; Singh, Harjinder
High-protein snack bars (protein bars) contain high-quality protein, sugars and other low molecular weight polyhydroxy compounds (PHCs), high-energy confectionary fats, and a minimum of water (water activity ≤ 0.65). The consequence of the intimate mixing of these components in protein bars is that they can react together, creating sensory characteristics that are unacceptable to consumers. This study examined the changes occurring in a model protein bar during storage for 50 days at 20 °C. Over this time, fracture stress increased from 20.1 +/- 1.8 Pa to 201 +/- 75 Pa at a rate that decreased slightly over time. 1H nuclear magnetic resonance (NMR) showed that the molecular mobility of PHCs decreased dramatically over the first 5 days as the batter set into a solid bar. Over the first 17 hours after manufacturing, protein particles became more clustered, and soluble protein appeared to precipitate, as shown by confocal microscopy. Reactive lysine fell 38% in the first 10 days of storage and was approximately constant thereafter. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed little change in protein molecular weights. Following the initial ‘setting’ phase of 5-10 days, fracture stress continued to increase and the molecular mobility of PHCs decreased. Changes in PHC molecular mobility were consistent with glucose crystallisation. Chemical changes were minimal during this phase, which suggests that chemical reactions play little part in the hardening of protein bars and that changes in molecular mobility and changes in microstructure driven by moisture migration may be more important.

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