Background: The polyphenol oxidase (PPO) responsible for the enzymatic browning of fruits and vegetables, has been involved in the undesirable brown discolouration of food products that resulted in negative effects on colour, taste, and nutritional value. This is a generally undesired process and needs to be prevented in food technology.
Objective: The present work was carried out to evaluate the effect of chemical and thermal treatments on browning inhibition of eggplant fruit (Solanum melongena L.).
Materials and Methods: A screening of PPOs activities from eggplant was carried out. The physicochemical characteristics and thermal stability of main PPOs activities were determined in order to develop methods of anti-browning.
Results: Dopamine oxidase and pyrocatechol oxidase activities were the most active main eggplant fruit PPO activities. Maximal PPO activity was found at 30°C, pH 7.0 for dopamine and 25°C, pH 6.6 for pyrocatechol. The enzymes were stable and retained almost all of their catalytic activity at their optimum temperature (30 and 25°C) for 120 min and their pH stability was in the range of 5.0 - 7.0. Polyphenol oxidases (dopamine oxidase and pyrocatechol oxidase) remained their full activity in the presence of ion Na+, Cu2+, Pb2+ (1 mM) but were inhibited strongly by the ion Fe2+ and Pb2+ (5 mM). On the other hand, the ion K+, Ba2+ and chemical agents, EDTA, citric acid have virtually no effect on dopamine oxidase and pyrocatechol oxidase activities. Energy for inactivation (Ea) obtained using dopamine and pyrocatechol were 30.8 kJ/mol and 7.1 kJ/mol from respective substrates.
Conclusion: Ascorbic acid was a better inhibitor where 82.32% of PPOs inhibition was achieved. At 65°C, their D-values ranged from 44.72 to 72.72 min. Hence, heat treatment at 65°C for 30 min reduced browning of eggplant fruit. These data regarding the properties of PPO should enhance understanding of the browning reaction in eggplant and lead to the development of techniques for controlling this undesirable process.
For optimization of biochemical processes in food and pharmaceutical industries, the evaluation of enzyme inactivation kinetic models is necessary to allow their adequate use. kinetics and thermodynamic analysis of cellulase (GS-CX) from salivary glands of Macrotermes subhyalinus little soldier were studied, using carboxymethylcellulose as a substrate. Optimal conditions for enzymatic studies were determined to be pH 5.0 and 60 °C. Thermal inactivation of GS-CX was examined in more detail between 50 and 65 °C and in relation to exposure time. The investigation suggests the existence of a non-sensitive heat fraction on the enzyme structure, which is relatively stable up to temperatures close to 55 ºC. Denaturation of this enzyme, measured by loss in activity, could be described as a first-order model, with k-values between 0.0052 and 0.0337 min -1 . D-and k-values decreased and increased, respectively, with increasing temperature, indicating faster cellulase (GS-CX) inactivation at higher temperatures. Results suggested that GS-CX is a relatively thermostable enzyme with a Z-value of 18.08 °C and Ea of 115.81 kJmol -1 . The results of the thermodynamic investigations indicated that the hydrolytic reactions w : (1) (∆ > 0) and (2) (∆H > 0). Positive values of entropy (ΔS > 0) for GS-CX indicated that this enzyme is found in a chaotic state at the end of the reaction. The high value obtained for the variation in enthalpy indicated that a high amount of energy was required to initiate denaturation, probably due to the molecular conformation of this enzymes. Results shown that the enzyme is quite stable for biotechnological applications.
The present study aims to demonstrate the influence of extraction processes on the oil obtained from the mature albumen of the nut of the coconut hybrid NJM x GVT. Three oil extraction processes were studied. These are the traditional variable temperature extraction methods, at constant temperature (105 ° C) and then the soxlhet extraction method (control method). The physicochemical characteristics of the extracted oil such as pH, density, acid number (Ia), iodine number (Ii), peroxide number (Ip), index of saponification (Ip) and the contents of two major fatty acids, lauric acid (C12) and myristic acid (C14), were determined there. The results indicated that the oil yield obtained with the soxlhet reference method (65.79%) is high than that of the two traditional methods at variable and constant temperature (respectively 38.28 to 39.9%). The oil extracted using these three techniques is acidic (pH<7) with a more pronounced acid number compared to traditional variable temperature extraction (10.41 mg KoH / g). The traditional constant temperature method has an acid number close to that of soxlhet (1.34 mg KoH / g oil) This acidity thus obeys the standards of the Codex Alimentarius (Ia ≤ 4 mg KoH / g of oil). The extraction methods had no influence on the peroxide value. Thus, traditional extraction is best at constant temperature.
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