Degradation kinetics of sugars (glucose and xylose), amino acids (proline and aspartic acid) and their binary mixtures in subcritical water: Effect of Maillard reaction.

A systematic kinetic study was conducted in subcritical water medium in the temperature range from 150 to 200 °C for pure glucose, xylose, proline and aspartic acid as well as binary mixtures of sugars + amino acids to understand the reaction kinetics and interactions among biomass components and to discern the influence of Maillard reaction (MR) on the overall reaction kinetics. The main degradation products identified for glucose and xylose were the respective dehydration products, hydroxymethyl furfural and furfural, yielding an increasing solid residue with temperature (15.9 wt% at 200 °C) with an augmented heating value. The degradation of sugars and amino acids in binary systems was faster compared to pure compounds due to MR and the production of dehydration products was delayed when considering total sugar conversion. Higher relative reactivity in MR was observed for xylose over glucose showing also higher antioxidant activity.

Production of small peptides and low molecular weight amino acids by subcritical water from fish meal: Effect of pressurization agent.

The hydrolysis of the water-soluble protein (WSP) fraction from tuna fish meal was evaluated by subcritical water (subW) by using N2 and CO2 as different pressurization agents in the temperature range from 140 to 180 °C. For both gases, the amino group release increased by increasing working temperature while the Lowry response decreased due to production of smaller-size peptides and free amino acids. The free amino acid content was higher with CO2 than with N2. At 180 °C, 344 ± 5 and 275 ± 3 mg of free amino acids per g of WSP were released, respectively; although, in both systems the smallest molecular weight amino acids, glycine and alanine, were preferentially released. The free amino acids content obtained by enzymatic hydrolysis with commercial proteases Alcalase and Novozym was much lower with the highest hydrolysis yield determined for histidine. These results have been supported by size exclusion chromatography analysis.

Aromatization of testosterone to estrogen varies between strains of mice.

The nuclear uptake and retention of [3H]testosterone or one of its metabolites and the aromatization of testosterone to estrogen were examined in the Swiss--Webster mouse. Castrated male mice were injected with 0.2 micrograms of either [1 alpha, 2 alpha-3H(N)]testosterone or [1 beta, 2 beta-3H(N)]testosterone per 100 g of body weight and killed one and one-half hours later. The brains were removed and processed for autoradiography. A nuclear localization of testosterone or one of its metabolites was found in the nucleus (n) interstitialis striae terminalis, n. preopticus medialis, n. premamillaris ventralis and n. amygdaloideus medialis in animals injected with [1 alpha, 2 alpha-3H(N)]testosterone. In animals injected with [1 beta, 2 beta-3H(N)]testosterone a nuclear localization was found in only n. interstitialis striae terminalis, n. premamillaris ventralis and n. amygdaloideus medialis. The results suggest testosterone is aromatized to estrogen in n. preopticus medialis ventralis in the Swiss--Webster mouse. Together with previous data, these data suggest (1) the uptake and retention of testosterone or one of its androgenic metabolites and the aromatization of testosterone to estrogen varies between strains of mice and (2) there are two separate uptake and retention systems (receptors?) for testosterone and dihydrotestosterone in the brain in all animals studied thus far with autoradiographic techniques.