Food Engineering / Gıda Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/12
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Article Citation - WoS: 8Citation - Scopus: 7Commercially Suitable Pectin Methylesterase From Valencia Orange Peels(Türkiye Klinikleri Journal of Medical Sciences, 2010) Şimşek, Şebnem; Yemenicioğlu, AhmetA simple and effective procedure was developed to extract pectin methylesterase (PME) from Valencia orange peels. Orange peels contain 25-34 μmol of COOH min-1 g-1 of peel PME activity. The enzyme was ionically bound to cell walls and could not be extracted with water. This enables removal of water soluble pectic substances and oils from peels via homogenization and washing with water before enzyme extraction. Enzyme extraction can be conducted simply by addition of suitable amounts of NaCl (optimum: 10 g of NaCl 100 g-1 of extraction mixture) to peel homogenate and stirring (optimum: 30 min at 200 rpm). The PME extracted from orange peels contains almost the same amount of heat-stable and heat-labile fraction, and the enzymes cannot be activated by mild heating. A slight activation of enzyme (almost 20%) was achieved by adding 1 mM CaCl2 to enzyme extracts, but this agent was inhibitory at higher concentrations. The extracts stabilized by Na-benzoate and K-sorbate maintained more than 90% of their PME activity at 4 °C for at least 5 months. The obtained PME was successfully used to prepare low-methoxyl citrus pectin used in edible film formation in the presence of CaCl2. This study shows the potential of using Valencia orange peels as a source of commercial PME. © TÜBİTAK.Article Citation - WoS: 21Citation - Scopus: 29Partial Purification and Kinetic Characterization of Mushroom Stem Polyphenoloxidase and Determination of Its Storage Stability in Different Lyophilized Forms(Elsevier Ltd., 2007) Şimşek, Şebnem; Yemenicioğlu, AhmetMonophenolase (1011 ± 626 U/g AP) and diphenolase activities (5163 ± 3059 U/g AP) of PPO in acetone powders (APs) of different mushroom stems varied considerably. However, the limited variation of average dipenolase (L-DOPA) to monophenolase (L-tyrosine) activity ratio (5.4 ± 0.7) in crude extracts showed the homogeneity of PPO from different mushroom stems. The change in extraction material or partial purification method (ammonium sulfate or acetone precipitation) did not affect the temperature stability, temperature and pH dependency and Km of monophenolase activity considerably. However, some changes were observed in pH stability and substrate specificity of PPO in different parties of mushroom stems. The most important aspects of mushroom stem PPO are its lower diphenolase to monophenolase activity ratio than mushroom cap PPO, low temperature dependency of activity between 25 and 40 °C (Ea = 30 kJ/mol), broad optimum pH between 6 and 8, but lack of activity pH ≤5, and ability to use phloridzin as substrate. The mushroom stem PPOs partially purified and lyophilized by using sucrose, dextran or alginate showed moderate to high stability at -18 °C for 6-6.5 months. Thus, the mushroom stems obtained as a waste material during mushroom processing may be used as a more homogenous source than whole mushrooms to obtain PPO used for different industrial, clinical or research purposes.Article Citation - WoS: 8Citation - Scopus: 7Potential Application of Hot Rehydration Alone or in Combination With Hydrogen Peroxide To Control Pectin Methylesterase Activity and Microbial Load in Cold-Stored Intermediate-Moisture Sun-Dried Figs(John Wiley and Sons Inc., 2004) Demirbüker Kavak, Dilek; Şimşek, Şebnem; Yemenicioğlu, AhmetSun-dried figs contain a considerable amount of pectin methylesterase (PME) activity (22 μM COOH/ min/g). The enzyme causes softening and loss of desired gummy texture in cold-stored intermediate-moisture (IM) sun-dried figs brought to a 28% to 29% moisture range. Partial reduction of PME activity (28%) delayed undesirable textural changes in IM figs rehydrated at 80°C for 16 min. The heat treatment did not cause a considerable reduction in microbial load. However, the addition of 2.5% H2O2 to the rehydratlon medium at 80°C reduced the initial total mesophilic aerobic count of figs by at least 90% and turned the figs from a brown color to a desirable and stable yellow-light brown. The in situ fig catalase remains after rehydration at 80°C. Thus, by reducing the contact period of figs with H2O2 or by pureeing figs, it is possible to eliminate residual H2O2 and to obtain safe and SO2-free light-colored fig products.