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: 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.Article Citation - WoS: 20Citation - Scopus: 18Control of Polyphenol Oxidase in Whole Potatoes by Low Temperature Blanching(Springer Verlag, 2002) Yemenicioğlu, AhmetRusset Burbank potatoes can be blanched up to 60 min at 50 °C without any loss in firmness and without appearance of browning on their peels, eyes or infected areas. Low temperature blanching (LTB) for 45 min did not cause a significant reduction in crude polyphenol oxidase (PPO) activity (12%). However, when heating time was extended to 60 min, the activity and specific activity of the enzyme were reduced by 27-45% and 22-43% respectively. The remaining enzyme extracted from heated potatoes was partially purified 3.3-3.75-fold by 0-95% ammonium sulphate precipitation and dialysis, and its kinetic parameters were determined. The comparison of the kinetic parameters of PPO in control (Km=10.3 mM and Vmax/Km=0.15) and in 60 min heated potatoes (Km=13 mM and Vmax/Km=0.054) indicated the reduced affinity of the remaining enzyme to its substrate. Thus, LTB at 50 °C for 60 min not only inactivated part of the PPO activity but also reduced the kinetic capacity of remaining enzyme. Extending heating time to 75 min caused the appearance of slight browning on the peels and eyes of potatoes and reduced their firmness. The observed browning was due to the sharp drop in the Km that caused the activation of the PPO. Heating at 50 °C did not affect lipoxygenase activity, but the Km of the enzyme dropped from 0.4 to 0.15 mM and the enzyme became kinetically more reactive at low substrate concentrations. Covalently bound pectin methylesterase considerably activated (38%) by heating and this caused the drop of pH in potato tissues.