Thesis (Ph. D.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references. Also available online.

No description available.

by Suen Tsang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 96-103). / Abstract also in Chinese. / Chapter Chapter 1: --- Literature review --- p.1 / Chapter 1.1 --- "Straw mushroom, Volvariella volvacea" --- p.1 / Chapter 1.2 --- Problems which restrict the market of straw mushroom --- p.3 / Chapter 1.3 --- Non-enzymatic browning --- p.5 / Chapter 1.4 --- Enzymatic browning --- p.7 / Chapter 1.5 --- Impact of browning --- p.12 / Chapter 1.6 --- Mechanism of inhibition of PPO --- p.13 / Chapter 1.7 --- Sulfites --- p.13 / Chapter 1.8 --- Classification of PPO inhibitors based on chemical property --- p.14 / Chapter 1.9 --- Classification of PPO inhibitors based on inhibitory mechanism --- p.17 / Chapter 1.10 --- Physical methods for prolonging shelf-life --- p.18 / Chapter 1.11 --- Significance of this research --- p.20 / Chapter Chapter2: --- Characterization of PPO in straw mushroom --- p.21 / Chapter 2.1 --- Introduction --- p.21 / Chapter 2.2 --- Materials and Methods --- p.22 / Chapter 2.2.1 --- PPO content in straw mushroom compared to other food sources: potato and pear --- p.22 / Chapter 2.2.2 --- "Optimal pH, enzyme kinetics and localization of PPO in straw mushroom" --- p.24 / Chapter 2.2.3 --- PPO isoenzymes in straw mushroom --- p.25 / Chapter 2.3 --- Results --- p.29 / Chapter 2.3.1 --- PPO content in straw mushroom compared to other food sources: potato and pear --- p.29 / Chapter 2.3.2 --- "Optimal pH, enzyme kinetics and localization of PPO in straw mushroom" --- p.29 / Chapter 2.3.3 --- PPO isoenzymes in straw mushroom --- p.32 / Chapter 2.4 --- Discussion --- p.43 / Chapter Chapter3: --- Several attempts to solve browning problem of straw mushroom --- p.55 / Chapter 3.1 --- Inhibitors of PPO in straw mushroom --- p.55 / Chapter 3.1.1 --- Investigation of inhibitors of PPO in straw mushroom --- p.55 / Chapter 3.1.1.1 --- Materials and methods --- p.55 / Chapter 3.1.1.2 --- Results --- p.56 / Chapter 3.1.2 --- The potential of using a combination of different PPO inhibitors --- p.58 / Chapter 3.1.2.1 --- Materials and methods --- p.58 / Chapter 3.1.2.2 --- Results --- p.59 / Chapter 3.1.3 --- Direct application of PPO inhibitors --- p.61 / Chapter 3.1.3.1 --- Materials and methods --- p.61 / Chapter 3.1.3.2 --- Results --- p.62 / Chapter 3.1.4 --- PPO and lipase content in straw mushroom under post harvest storage --- p.62 / Chapter 3.1.4.1 --- Materials and Methods --- p.74 / Chapter 3.1.4.2 --- Results --- p.75 / Chapter 3.2 --- Vacuum packaging --- p.75 / Chapter 3.2.1 --- Materials and methods --- p.75 / Chapter 3.2.2 --- Results --- p.78 / Chapter 3.4 --- Discussion --- p.78 / Chapter Chapter 4: --- Future work --- p.87 / Chapter 4.1 --- Suggested improvements of experiments --- p.87 / Chapter 4.2 --- Suggested experiment in future: application of calcium chloride --- p.88 / Chapter Chapter 5: --- Conclusion --- p.94 / References --- p.96

Polyphenol oxidase (PPO) enzymatic extracts were recovered from apple fruit and potato tubers and enriched by an acetone precipitation. The enriched PPO extracts were immobilized by adsorption onto a wide range of inorganic supports, including chitin, alumina oxide, glass beads, Celite, Dowex and Silica gel using selected media, including water, sodium phosphate buffer and a ternary micellar system. The highest immobilization efficiencies and specific activities were obtained when the PPO extracts were suspended in sodium phosphate buffer and adsorbed onto alumina oxide. Biocatalysis of the free and immobilized PPO extracts was investigated in selected organic solvent media, including hexane, heptane, toluene and dichloromethane, using chlorogenic acid, catechin, and the endogenous phenolic compounds from apple fruit and potato tubers as substrate models. In the organic solvent media, the free PPO extracts from apple and potato demonstrated optimal enzymatic activities at 28°C and between 25 to 35°C, respectively, whereas the immobilized extracts both showed optimal enzymatic activities at 30°C. The free and immobilized extracts from apple and potato also showed similar pH values for optimal enzymatic activity in the range of 6.0 to 6.5. The immobilized apple and potato PPO extracts demonstrated a 1.5 to 1.8 and 2.1 to 3.2-fold increases in PPO activity, respectively, compared to those observed with their free counterparts, and the lowest Km values were obtained with chlorogenic acid followed by catechin and the endogenous phenolic compounds. The immobilized and free PPOs from apple and potato also showed higher Vmax values in the hexane medium followed the heptane, toluene and dichloromethane media. The end products of PPO biocatalysis were purified by size-exclusion chromatography and detected at 280 nm for the residual catechin and endogenous phenolic compounds, and at 320 nm for the PPO-catalyzed end products. Spectroscopic scanning

Thesis (Ph. D.)--Institute of Paper Chemistry, 1980. / Bibliography: leaves 100-107.

Digestive proteases were isolated from the pancreas of the stomachless cunner fish (Tautogolabrus adspersus) and characterized in terms of their physicochemical properties, their ability to hydrolyze native pectin methylesterase (PME) from orange and polyphenol oxidases (PPO) from mushroom and the ability of the cunner enzyme(s) to maintain the stability of orange juice cloud. / The cunner trypsin fraction exhibited exceptional capacity to hydrolyze native proteins versus the bovine trypsin. Incubation of native PME with cunner or bovine trypsin resulted in a loss of 75% or 35% in PME activity respectively. Similarly, a 75% or 55% loss in PPO activity was observed after treatment with cunner and bovine trypsin respectively. Bovine trypsin, however, hydrolyzed the heat-denatured PME and PPO better than the cunner trypsin. Also, there was no reactivation of both PME and PPO activity after treatment with either the cunner or bovine enzyme during storage at 4$ sp circ$C for 3 weeks. However, PPO retained up to 20% or 50% of the initial activity after treatment with cunner or bovine trypsin, respectively. / A 3 x 3 factorial design involving the factors of temperature, enzyme concentration and incubation time carried out gave an r$ sp2$ of 0.92 and 0.95 for cunner and bovine trypsin treated PME respectively. On the other hand, an r$ sp2$ of 0.91 and 0.94 was obtained for the combined effects using cunner and bovine trypsin for PPO inactivation. Validation of the model of PME inactivation measured as the % cloud remaining revealed that the cunner trypsin fraction upheld the cloud stability of cloud juice better than bovine trypsin, with cunner trypsin retaining more than 90% of the cloud whereas the juice treated with bovine trypsin only resulted in a 70% retention of the juice cloud. (Abstract shortened by UMI.)

Orientador: Valdir Augusto / Banca: Valdir Augusto Neves / Banca: José Paschoal Batistuti / Banca: Jonas Contiero / Resumo: A família das anonáceas é composta por muitos gêneros e espécies; dentre essas, a atemóia (Annona cherimola Mill. X Annona squamosa L.), resultante do cruzamento entre a fruta-do-conde (Annona squamosa L.) e a cherimóia (Annona cherimola Mill.). No Brasil, a atemóia vem despertando grande interesse na produção/comercialização dos seus frutos; no entanto um dos obstáculos enfrentados é a facilidade de escurecimento enzimático que a fruta apresenta. Esse tem como responsável a polifenoloxidase (PPO, E.C. 1.14.18.1); que sob diferentes condições de armazenamento e processamento de vegetais na sua fase póscolheita pode atuar sob substratos naturais e resultar na formação de compostos escuros, acarretando diminuição do valor nutricional, modificação das propriedades organolépticas e sensoriais, com consequente rejeição. Os objetivos desse trabalho foram isolar, purificar e caracterizar algumas propriedades da polifenoloxidase de atemóia. Condições de extração para a PPO foram estabelecidas e a enzima foi isolada por precipitação com sulfato de amônio e eluição em Sephadex G-100. Somente um pico de atividade foi eluído no processo de purificação com um fator de purificação de 7,12. O peso molecular determinado foi 82 kDa com valores ótimos de pH 6,0 e 7,0 para 4-metil catecol e catecol, respectivamente; sendo estável por 12 e 24 horas à incubação na faixa de pH 4,0-8,0. A temperatura ótima de atividade foi 35°C e 28°C para 4-metil catecol e catecol, respectivamente. Os valores calculados de energia de ativação (Ea) para esses substratos foram 87,29 cal/mol-1 e 180,97 cal/mol-1. As constantes cinéticas Km e Vmax foram 5,52mmol/L e 1428,57 UA/mL, para 4-metil catecol, e 79,3 mmol/L e 5000 UA/mL, para catecol. A relação Km/Vmax determinou uma maior afinidade da enzima pelo primeiro substrato. A enzima mostrou desprezível atividade... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The family of annonaceae is composed of many genus and species, among these, the atemoya (Annona cherimola Mill. X Annona squamosa L.), resulting from a cross between custard apple (Annona squamosa L.) and cherimoya (Annona cherimola Mill.). In Brazil, the atemoya is attracting great interest in the production / marketing of its fruits, however one of the obstacles faced is the ease of enzymatic browning that gives the fruit. This is as responsible for polyphenoloxidase (PPO, EC 1.14.18.1), which under different conditions of storage and processing plant in its post-harvest can act on natural substrates and result in the formation of dark compounds, causing decrease in nutritional value, modification of the organoleptic and sensory properties, with consequent rejection. The objectives of this study were to isolate, purify and characterize some properties of polyphenoloxidase from atemoya. Conditions for the extraction of PPO were established and the enzyme was isolated by precipitation with ammonium sulfate and elution on Sephadex G-100. Only one peak of activity was eluted in the process of purification with a purification factor of 7.12. The molecular weight of 82 kDa was determined with the optimum values of pH 6.0 and 7.0 for 4-methylcatechol and catechol, respectively. The enzyme was stable for 12 and 24 hours incubation in the pH range 4.0-8.0. The optimum temperatures for activity were 35 °C and 28 °C for 4-methylcatechol and catechol, respectively. The values of activation energy (Ea) for these substrates cal/mol-1 were 87.29 and 180.97 cal/mol-1. The kinetic constants Km and Vmax were 5.52 mmol/L and 1428.57 UA/mL for 4-methylcatechol, and 79.3 mmol/L and 5000 AU / mL for catechol. The Km/Vmax determined a higher affinity of the enzyme by the first substrate. The enzyme showed negligible activity for caffeic acid and chlorogenic as any for L-DOPA, catechin... (Complete abstract click electronic access below) / Mestre

No description available.

No description available.

No description available.