Academic literature on the topic 'Enzymatic browning. eng'

This study compared the effect of application of edible coating on or before ultraviolet treatment on postharvest longan fruits. The treated longan fruits were examined for weight loss, respiration rate, surface color changes, enzymatic activities (PPO, POD, and PAL), and total phenolic contents throughout the 7 storage days at ambient temperature. In addition, coat homogeneity was examined and cell structure of longan flesh at the end of storage was observed. The results showed that when UV was applied before coating (i.e., chitosan or carrageenan), it had relatively lower PPO and PAL activities and retained higher TPC in longan pericarp. However, the changes in enzymatic activities did not affect the surface lightness and browning index as they were more influenced by the type of coating, in which combination treatments with carrageenan showed higher surface lightness and lower browning index compared to treatment combinations containing chitosan. However, when UV treatment preceded coating, the combinations of UV plus chitosan coating produced lower PPO and PAL activities and retained better cell structure with less damage than the combinations of UV plus carrageenan coating. UV plus carrageenan coating showed relatively higher weight loss and respiration rate, with cell structure exhibiting bigger intercellular spaces at the end of storage. Therefore, application of UV treatment followed by chitosan coating was found to be the best treatment combination for controlling enzymatic activities and reducing senescence rate of longan fruits.

The relationship of phenolic composition and polyphenoloxidase activity (PPO, E.C. 1.14.18.1) to browning potential (BP) was studied in buffer extracts of peach [Prunus persica L. Batsch) and nectarine [P. persica var. nectarine (L.) Batsch] fruit skin. The BP varied among cultivars with `Flavorcrest' having the highest value and `Maycrest' the lowest. On average, over 83 % of the browning measured at the end of the S-hour incubation occurred during the first hour. The total soluble phenolics (TSP), the total anthocyanin (TA), and glutathione content (GLU) varied among cultivars, but were not significantly correlated to the BP. Of the phenolics determined by HPLC, only chlorogenic acid had a significant positive correlation and epicatechin a significant negative correlation with BP by the first hour of incubation. The PPO activity, ranging from 4 to 11 optical density units per gram dry weight per minute among peaches and nectarines, was not significantly correlated with BP. However, no browning was detected if the buffer extract was previously boiled. These results indicated that browning in the buffer extracts of peach and nectarine skin tissue depends on the presence of PPO activity and chlorogenic acid, which are major contributors to enzymatic browning.

In Brazil, the largest producer of sugarcane in the world, the industrial process transforms this crop into ethanol and/or granulated sugar. Some cultivars exhibit enzymatic browning in the extracted sugarcane juice at levels harmful to the manufacturing process of white granulated sugar. The objective of this study was to assess the effect of sugarcane straw used as soil coverage, the use of different planting systems, and treatments with hydrogel polymer on enzymatic activity. The cultivar RB 86 7515 was sampled for 8 months; the first sample was obtained by cutting the upper portion of the stalk at the internode, which was taken to the laboratory for determination of the enzymatic activity of polyphenoloxidase (PPO) and peroxidase (POD). The soil coverage with different forms of straw as well as the planting systems did not change the enzymatic activity of polyphenoloxidase (PPO) and peroxidase (POD). The polyphenoloxidase (PPO) activity increased with the use of a polymer due to increased polyphenoloxidase (PPO) activity in the groove system. The enzymes studied showed changes in activity during the experimental period. The production of sugar at the end of the season (August to November) avoids the periods of highest enzymatic activity.

The capacity of UV-C light to induce glycation and modify functional properties of systems containing freeze-dried egg white proteins and carbohydrates with increasing molecular weight (i.e., glucose, maltose, trehalose and maltodextrin) was studied. Color changes induced by light exposure were taken as typical indicators of glycation. Samples were then analyzed for selected physical (critical concentration, particle size and viscosity), chemical (ovalbumin content) and technofunctional properties (gelling temperature and foaming capacity). The presence of sugars during exposure to UV-C light promoted intense browning and decreased ovalbumin content by circa 30%. Concomitantly, up to a 3-fold increase in critical concentration of the aqueous suspensions of the irradiated protein-carbohydrate powders and changes in particle size were detected. These modifications were consistent with the development of non-enzymatic browning reactions upon UV-C light irradiation. Photoinduced glycation was associated to a decrease in viscosity, a tendency to form gel at temperature lower by up to 8 °C and a better capacity of foam stabilization. The intensity of these changes seems to be affected by the nature of the carbohydrates reacting with proteins, with longer carbohydrates able to produce systems with higher foam stability capacity.

Minimal processing of eggplant (Solanum melongena L.) generates loss of firmness and polyphenol oxidase catalyzes the oxidation of phenolic compounds producing enzymatic browning. The aim of this study was to evaluate the effect of 1% ascorbic acid and 2% calcium ascorbate in aqueous solution at natural pH of the antioxidant (pH 2.6 and 7.8, respectively), or adjusted to pH 5 with generally recognized as safe substances, mantaining the quality of minimally processed eggplant stored at 5 °C for 6 d. Water was used as a control. The color, firmness, polyphenol oxidase activity, and visual quality was evaluated in the freshly cut fruit at 3 and 6 d of storage. No effect of the treatments on firmness or polyphenol oxidase activity was observed. At 3 d of storage, a correlation was observed between polyphenol oxidase activity and the visual evaluation of the cut product. Samples treated with 2% calcium ascorbate and the rest of the treatments at pH 5 had a lower browning index than those treated with 1% ascorbic acid and the control. At the end of the storage period, the visual quality of the eggplant samples treated with 1% ascorbic acid at pH 5 was evaluated above the marketing limit, whereas those treated with 1% ascorbic acid at pH 2.6 had the lowest quality indicators. An adjustment to pH 5 helps to preserve the luminosity and visual quality of the eggplant, however firmness was not affected by calcium ascorbate or the pH of the medium.

This research investigates the relative importance of two roasting parameters—colour (i.e., roast degree) and time—on the sensory properties of coffee. The paper draws on data from eight studies conducted using sensory descriptive analysis with trained (in six studies) or semi-trained (in two studies) assessors, focusing on a common set of attributes. The results indicated that, while both parameters significantly affected coffee flavour, colour was the stronger predictor of the two. The effects direction for both colour and time were similar and related to the rate of non-enzymatic browning, with darker roasts/longer roasting times associated with an increase in bitterness and a decrease in acidity, fruitiness, and sweetness. With respect to roasting time, we distinguished two phases, “time to first crack”, corresponding to the time between the onset of roasting and the moment where the accumulated steam pressure causes the beans to crack, and “development time”, corresponding to the time elapsed from the first crack to the end of the roasting process. The results clearly indicated that, under the same colour, time variation also influenced flavour, and in particular, development time, rather than time to first crack, had the largest effect on coffee flavour.

Extrinsic stain resides in the dental pellicle and can be caused by introduction of chromogenic materials or therapeutic agents into the oral cavity. In contrast, intrinsic tooth stain is found within the tooth structure and can be caused by a variety of agents, including hematological and developmental abnormalities and drugs such as tetracycline. The mechanisms of extrinsic stain formation differ with respect to the causative agent. For example, stain induced by chlorhexidine (CH) can be explained by an increased rate in the non-enzymatic browning reactions occurring at the pellicle surface, while food stains are retained on the surface via ion exchange mechanisms. Although most extrinsic dental stain can be removed by abrasive and/or surface-active materials, removal of certain types of surface stain, e.g., staining due to cationic antimicrobial agents, requires specific agents such as aminoguanidine to reduce the stain. A broad-spectrum approach to reduce both intrinsic and extrinsic dental stains clinically requires oxygenating agents. To evaluate this approach and understand the mechanisms of stain removal, we developed a spectroscopic method for measuring stain in vivo. A series of clinical studies was performed to evaluate stain removal by the agents. The results showed that carbamide peroxide in combination with surfactants and anti-redeposition agents, e.g., sodium pyrophosphate, was more effective in bleaching dental stain compared with carbamide peroxide alone. A detailed examination of the tooth structure by microhardness measurements, x-ray photoelectron spectroscopy, and scanning electron microscopy showed that stain decolorization with this system did not have any adverse effects.

Biliverdin reductase (BVR) is an enzymatic and signaling protein that has multifaceted roles in physiological systems. Despite the wealth of knowledge about BVR, no data exist regarding its actions in adipocytes. Here, we generated an adipose-specific deletion of biliverdin reductase-A (BVRA) (BlvraFatKO) in mice to determine the function of BVRA in adipocytes and how it may impact adipose tissue expansion. The BlvraFatKO and littermate control (BlvraFlox) mice were placed on a high-fat diet (HFD) for 12 weeks. Body weights were measured weekly and body composition, fasting blood glucose and insulin levels were quantitated at the end of the 12 weeks. The data showed that the percent body fat and body weights did not differ between the groups; however, BlvraFatKO mice had significantly higher visceral fat as compared to the BlvraFlox. The loss of adipocyte BVRA decreased the mitochondrial number in white adipose tissue (WAT), and increased inflammation and adipocyte size, but this was not observed in brown adipose tissue (BAT). There were genes significantly reduced in WAT that induce the browning effect such as Ppara and Adrb3, indicating that BVRA improves mitochondria function and beige-type white adipocytes. The BlvraFatKO mice also had significantly higher fasting blood glucose levels and no changes in plasma insulin levels, which is indicative of decreased insulin signaling in WAT, as evidenced by reduced levels of phosphorylated AKT (pAKT) and Glut4 mRNA. These results demonstrate the essential role of BVRA in WAT in insulin signaling and adipocyte hypertrophy.

Orientador: Valdir Augusto<br>Banca: Valdir Augusto Neves<br>Banca: José Paschoal Batistuti<br>Banca: Jonas Contiero<br>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)<br>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)<br>Mestre

<strong>Apstrakt je obrađen tehnologijama za optičko prepoznavanje teksta (OCR).</strong>Nastajanje i inhibicija stvaranja melanoidina u nečistim rastvorima saharoze je ispitivana na uzorcima neafinisanog i afinisanog C produkta na 80 [&deg;C].Utvrdjena je zavisnost obrazovanja bojenih materija tipa melanoidina od vremena reakcije, od sadržaja suve materije, kao i od sadržaja i vrste aminokiselina.Smanjenje obojenosti rastvora zavisi od koncentracije natrikum-sulfita i matematički je definisano Baule-Mitscherlichovim krivama zasićenja. Maksimalni efekat odbojavanja koji se može postići iznosi 30 [%] na 560 [nm], odn. 20 [%] na 420 [nm], ne razlikuje se za rastvore neafinisanog i afinisanog C produkta, a ostaje nepromenjen u vremenu od 1620 [min].Povećanje koncentracike vodonik-peroksida je praćeno porastom količine bojenih materija prevedenih u leuko oblike, i produžavanjem vremena oksidacije. U odsustvu slobodnog vodonik-peroksida dolazi do reverzije boje rastvora.Smanjenje obojenosti rastvora neafinisanog i afinisanog C produkta je signifikantno veće pri uzastopnom delovanju oksidacionog i redukcionog sredstva od smanjenja obojenosti postignutog njihovim pojedinačnim delovanjem. Efekti uzajamnog delovanja se ne menjaju u ispitivanom vremenu.<br><strong>Abstract was processed by technology for Optical character recognition (OCR).</strong>Reaction and inhibition of melanoidine formation in inpure solutions of sucrose were investigated on affinated and unaffinated C sugar samples carried out on 80 [&deg;C].Melanoidin type colour formation dependending on reaction time, dry matter content and content and variety on amino acids has been studied.Colour decrease in solutions depended on concentration of sodium sulphite and was mathematically defined by Baule-Mitscherlich curve of saturation. Maximum effect of colour decrease wich can be obtained was 30 [%] at 560 [nm], and 20 [%] at 420 [nm] wavelength respectively, and without any difference between affinated and unaffinated C sugar solutions, but it has stayed unchanged during reaction time of 1620 [min]. Hydrogen peroxide concentration rise was followed by increasing amounts of colour compounds transferred in leuco forms and by prolonged oxidation time. Absence of free hydrogen peroxide has induced the reverse formation of colour solutions.Colour decrease in unaffinated and affinated C sugar solution was significantly larger, during subsequent treatment of oxidizing and reducing compounds, than during separate reactions. During reaction time the mutual treatment effect was unchangeable.