PARTIAL CHARACTERIZATION OF A PEPTIDE FROM HONEY THAT INHIBITS MUSHROOM POLYPHENOL OXIDASE

Mushroom polyphenol oxidase (PPO) was inhibited by one type of honey, in a model system. Honey was a noncompetitive inhibitor of PPO catalyzed oxidation of catechol. The Anhenius activation energy (Ea) of thermal inactivation of mushroom PPO differed in the presence and absence of honey. The Ea value in the presence of honey was 27.71 kJ/mol; whereas, Ea of the control was 83.14 kJ/rnol. Thus, the temperature coefficient of PPO inactivation was lower in the presence of honey. Characterization of the inhibitor was carried out by gel electrophoresis (SDS‐PAGE and NativePAGE). An inhibitory peptide fraction was obtained after native PAGE. The molecular weight was determined to be 0.6 kDa by Sephadex G‐15 column chromatography.     

EFFECT OF COMMERCIAL PROCESSING STAGES OF APPLE JUICE ON PATULIN, FUMARIC ACID AND HYDROXYMETHYLFURFURAL (HMF) LEVELS

The effects of different stages of commercial apple juice production on the patulin, fumaric acid and hydroxymethylfurfural (HMF) contents of apple juice were investigated. Heat treatment and activated charcoal were effective for the reduction of patulin. The average reduction of patulin were 13.4% and 22.9% for heat treatment and activated charcoal, respectively. Statistical analysis showed no significant differences (P<0.05) in the presence of fumaric acid between different treatments. Filtration and heat treatment caused an apparent increase in the HMF content, while activated charcoal caused a decrease. The average increments of HMF were 40.4% and 38.0% for separation and heat treatment, respectively, while the average reduction of HMF was 23.7% for activated charcoal. Spiking of samples with known amounts of patulin and fumaric acid revealed respective recovery rates of 96.4% and 95.9%.     

CHARACTERIZATION OF POLYPHENOLOXIDASE FROM WILD PEAR (PYRUS ELAEGRIFOLIA)

Wild pear polyphenoloxidase (PePPO) was extracted and purified using a Sepharose 4B- l -tyrosine- p -amino benzoic acid affinity column. Optimum conditions for pH, temperature and heat inactivation were determined. At the optimum pH and temperature, K _M and V _max values for PePPO with catechol and pyrogallol were determined. The V _max/ K _M showed that PePPO has the greatest activity toward catechol. Optimum pH for PePPO was pH 6.0 using catechol as substrate. Optimum temperatures of PePPO for pyragallol and catechol were 65 and 35C, respectively. Enzyme activity decreased because of heat denaturation with increasing temperature. Inhibition of PePPO was investigated using p -aminobenzoic acid, ethyleneglycol, l -cysteine, l -tyrosine, sodium azide, p -aminobenzenesulfonamide, β-mercaptoethanol and dithiothreitol and catechol as substrate. Competitive-type inhibition was obtained with ethyleneglycol, l -cysteine, l -tyrosine, p -aminobenzenesulfonamide and dithiothreitol. Uncompetitive inhibition was obtained with β-mercaptoethanol, sodium azide and p -aminobenzoic acid. These results show that the most effective inhibitor for PePPO was dithiothreitol and that the type of inhibition depended on the origin of PPO.

PRACTICAL APPLICATIONS

In this present work, the properties of polyphenoloxidase in Pyrus elaegrifolia , including optimum temperature, optimum pH, substrate specificity and response to inhibitors, were studied.     

Recipe development for production of a Turkish dessert,cheese halva

Within the scope of this study, six different recipes were developed for the production of cheese halva. White unsalted cheeses were produced by using cow milk or sheep milk or a blend of cow and sheep milk, and each was produced with white flour or semolina. It was found that there was no significant difference among the recipes in terms of chemical properties, but there were significant differences in sensory properties. Moreover, the microbial quality of cheese halva were determined. It was found that the shelflife of cheese halva can be up to 10 days at ambient temperature and for up to 1 month when refrigerated.     

EFFICACY OF PULSED ELECTRIC FIELDS FOR LISTERIA MONOCYTOGENES INACTIVATION AND CONTROL IN HORCHATA

Although Listeria monocytogenes is readily destroyed by thermal treatment, the factor that makes it particularly difficult to control in nonpasteurized foods is its ability to grow at refrigeration temperatures. In heat‐sensitive products, nonthermal technologies such as pulsed electric fields (PEF) as part of hurdle technology could minimize the presence of foodborne pathogens. The influence of PEF‐treatment conditions, inoculum size and substrate conditions on the inactivation and recovery of L. monocytogenes in a traditional low‐acid, vegetable beverage was investigated. The combined effect of PEF, low temperature (5C) and low inoculum level contributed to slow down the recovery of sublethally injured cells. However, at 12 or 16C, this elongation of the lag phases after PEF treatment observed for low inoculum levels of cells was not achieved. Therefore, to prevent the development of L. monocytogenes in low‐acid products by PEF, it may be necessary to combine it with low refrigeration temperatures during distribution and storage, as well as to achieve a very low initial contamination by pathogens in the raw ingredients.     

基于小生境遗传算法的通用涡旋型线优化研究

目前涡旋型线的优化设计多数是在一些参数修改设计的基础上,简化为单目标优化问题,因而不易获得多性能最优的设计方案,涡旋型线形状的设计本质上是一个多目标优化问题,在通用涡旋型线形状优化设计中,根据关于切向角参数的基于曲率半径的Whewell固有方程的通用涡旋型线泛函表征形式,建立了多目标涡旋型线形状优化设计数学模型,应用了基于共享小生境技术的非劣优选遗传算法,给出了通用涡旋型线多目标形状优化设计实例分析.