فهرست مطالب naser hamdami

Freezing and thawing are complex heat transfer processes and the chemical and physical changes that occur during these processes can affect the product quality (Li and Sun, 2002). During the thawing process, physicochemical changes and microorganism activities damage the food products (Bertola et al, 1994; Kalichevsky, Knorr, & Lillford, 1995). Several factors can affect the degree of quality loss, including the rate of thawing, temperature, and microorganisms (Jia et al, 2017). The rate and quality of the thawing process are the fundamental needs of the meat industry, and accordingly, many studies have investigated the thawing conditions to achieve the best quality of meat products (Jia et al, 2017). Modern thawing methods such as high pressure, microwave, ohmic, radiofrequency, ultrasonic, and high voltage electric field thawing can improve the thawing rate at the low temperature (Hsieh et al., 2010). In recent years, the use of high voltage electric fields (HVEF) has been considered due to low thermal damage, no chemical consumption, and being economical. In HVEF thawing, a strong electric field is used between point and plate electrodes in an environment of dielectric fluid to create a force, followed by a secondary motion in the fluid. The secondary flow of fluid name ionic wind, or corona wind, results from localized air ionization around the point electrode. By increasing the corona flow, the volume fluctuation and air velocity increase, which results in an increase in the heat transfer coefficient (Singh et al., 2012). In this case, the thin electrode is an electric discharge electrode and another electrode is a ground electrode. One of the advantages of using an electric field for thawing is the antimicrobial effect of this method. In addition, the electric field can affect oxygen molecules of air and generates free radicals of ozone molecules, which is a strong oxidizing agent with a high disinfection capacity that various studies reported the effect of ozone depletion on poultry meat (Yang and Chen, 1979; Jaksch et al., 2004). The present study was conducted to study the effect of HVEF thawing of mutton on the process rate and its qualitative and microbial properties. For this purpose, three different strengths of the electric fields were produced by varying the voltage at a constant electrode distance, and the HVEF thawing was compared with the conventional air thawing.

The fresh mutton meat was cut into cube pieces (4 × 4 × 3 cm3, 35 g) and after packing in polyethylene bags were frozen by a freezing tunnel at -30° C for 1 hour and stored at -18 ° C until analysis. The HVEF system was consists of a generator with adjustable voltages between -50 and 50 kV and a maximum output current of 5 mA (Ls50KV5mA, China), multiple needle and plate electrodes, and a wooden enclosure. The copper plate electrode was connected to the negative pole and the spot electrode connected to the positive pole of the high voltage power. The thawing process was performed at an electrode distance of 4.5 cm and 3 different voltages of 7.6, 9, and 10.3 kV at a temperature of 25 ˚C. The thawing process proceeded until the center of samples reached 0˚C and an optical fiber thermocouple (FOB 651A, Canada) was used to determine the end time of thawing. The evaporation, thawing, cooking and total losses were measured by weighting the frozen samples before and after thawing and cooking (Mousakhani- Ganjeh et al., 2015). The surface color, pH value and total microbial count of meat samples were measured after thawing.

Thawing of frozen mutton was carried out at 3 voltages of 7.6, 9, and 10.35 kV, and at an electrode distance of 4.5 cm that is equal to the field strength of 1.7, 2.0, and 2.3 kV/cm. Thawing of the control sample was performed at the same condition without field application. Results showed that the thawing rate of the frozen samples significantly increased with increasing field strength so that the thawing time at the near-spark voltage in comparison with the control sample reduced 45%. Investigation of different losses of mutton samples thawed under different strengths of the electric field showed that the evaporation loss of the thawed samples under HVEF increased by arise the electric field strength, conversely, the thawing loss was reduced with increasing the electric field strength. The control sample had the lowest cooking loss and the thawed sample under the strength of 2.0 kV/cm had the highest cooking loss. As the results show, the pH value increased with increasing the strength of the electric field, but this increase was not statistically significant (p>0.05). Investigation of the color parameters of thawed samples showed a* index, as a particular index in the meat color, decreased and L* index increased with increasing the electric field strength. The results of microbial counts of thawed samples under different strengths of the electric field showed a significant decrease (P <0.05) in the total viable counts in thawed samples under HVEF compared to the control sample. Total microbial count of HVEF thawed samples under strengths of 1.7, 2.0, and 2.3 kV/cm decreased to 4.8, 4.69, and 4.5 log CFU/g, respectively.

This study investigated the HVEF thawing of frozen mutton in comparison with air thawing. The results showed that the HVEF thawing of frozen mutton improved the thawing rate and the evaporation, cooking and total loss of the conventional thawed sample was lower than the HVEF thawed samples while the thawing loss decreased by applying the electric field during the thawing process. In addition, HVEF thawing process reduced the total microbial count of thawed samples by the production of ozone and negative ions that this effect improved with increasing the electric field strength.

One of the common defects in the processing of Feta cheese made in package is softening of texture. This defect occurs mainly at low temperatures and salt levels. In the industry, by increasing the amount of syneresis from the curd, some of this defect is prevented.In addition to texture softening, quantity and quality of UF –Feta cheese affected by expulsion or absorption phenomena. Reducing or increasing moisture content of cheeses matrix effected on other compositions and physical properties of cheeses protein matrix. The most important factors that play role on syneresis and textural properties are temperature, NaCl concentration and calcium level. The mechanism of this factors is different, but in summary, any factor that increase protein aggregation in cheeses matrix, grain hardness and syneresis, and in contrast, expanding cheese matrix occur.

In this research, hardness and syneresis or absorption amount measured in six brine concentration consist 0, 2, 8, 10, 18 and 26 in 3 (200, 1700 and 3200 ppm) calcium ions levels (18 treatments) at 3, 11, 9 and 27°C (72 treatments). The 3 replicates were analyzed in triplicate. Data were analyzed using a split-plot design.

Temperature, brine composition (NaCl and calcium ions) and interaction between this factors (Salt× Ca++, T× Salt and T× Ca++) and Salt× Ca++×T, was significant effects (p<0.01) on hardness and syneresis. The absorption phenomena occur in a salt concentration and temperature less than about 8% and 11°C, respectively. At more than 8% NaCl and 11°C, gradually, hardness and syneresis improved. The most swelling was observed in range 8-10% salt. Increasing of Ca++ was shifted maximum absorption to lower brine concentration. When Ca++ ions increased, the maximum swelling was shifted to lower brine concentration. Also, the hardness results and moisture content of cheese confirmed shrinkage and swelling of the cheese matrix.

The interaction of temperature, Nacl and calcium have two different models on syneresis and textural properties in UF-Feta cheese. At below 11°C, when Nacl concentration enhanced up to 8-10%, softening and swelling cheese matrix increased, but Increasing Nacl concentration and temperature above this rang improve shrinkage and hardness cheese matrix. Also, grain in calcium ion concentration reduced swelling and softening in UF- feta cheese at all temperature and Nacl concentrations. Therefore, in order to avoid the softness of the texture of this type of cheese, the process of industrial production and storage should be designed in such a way as to prevent optimal swelling of cheese matrix.

Bamiye is kind of sweet that frying is one of the stages of making it. The purpose of this study was to evaluate the effect of pre drying on some quality features of Bamiye. Samples put in oven at 105 ° C for zero (control), 2.5, 5 and 7.5 minutes for drying, then they fried on frying oil at 160 ° C and were measured qualitative characteristics on production day and every 15 days for 1 month at during storage. The Acid and Peroxide values in the pre dried samples showed a significant decrease compared to the control samples. the lowest content were for 7.5 minutes pre dried samples and maximum amount of it were for control samples. During storage Acid and Peroxide values increased in all of samples, but this increase in control samples was more than pre dried samples. By applying pre-drying treatment, volume of Bamiye decreased but tenderness of them increased. During storage time of samples, volume, tenderness and sensory properties decreased. In this case, reduce the volume and tenderness of the treated samples was less than the control sample. The results showed, pre drying is a suitable method for production of Bamiye samples and it has advantages such as saving product time, preparation Bamiye with low calorie, healthy oils and products with a high shelf-life. Advantages such as reducing process time, producing healthy product with lower calorie (due to low oil absorption) and longer lifetime.

Rehydration typically composes of three simultaneous processes: the imbibition of water into dried material, the swelling of the rehydrated products and the leaching of soluble solids to rehydration medium. In this research, squash (Cucurbita pepo) fruits were cut into 0.4 cm thick and 4 cm diameter slices. Then, squash slices were blanched in a steam chamber for 4 min. After cooling to room temperature, squash slices were dehydrated up to moisture content of 0.1065 kg H2O per kg d.m. Dehydrated samples were stored at 4°C. Squash slices with specified weight were rehydrated by immersion in distilled water at different temperatures (25, 50, and 75°C), various dry matter-water ratios (1:25, 1:50, and 1:100), which was agitated at 100 rpm. At specified time intervals, up to 300 min, the squash samples were removed from the water, and the weight, moisture content and rehydration indices of the sample were determined. The texture characteristics were examined over a 180 min period. The results showed that moisture content, water absorption capacity (WAC) and rehydration ability (RA) of squash slices increased, whereas dry matter holding capacity (DHC) and texture firmness (maximum force and stress) decreased with rehydration time. The maximum WAC was achieved in squash slices rehydrated into 75°C water at 1:100 dry matter-water ratio. The lowest force and stress were observed in squash slices which were rehydrated into 75°C water after 180 minute. These squash slices had the maximum moisture content and RA and the minimum DHC. The lowest moisture content and RA and the highest DHC, force and stress, were observed in squash slices immersed in water at 1:100 dry matter-water ratio. In general, for all rehydration conditions of squash slices, the highest water absorption rate occurred during the first minuts of process. Then, this rate decreased. The highest rehydration rate and amount of water absorption occurred in 75°C.

Throughout the present research، squash (Cucurbita pepo) slices (0. 4 cm thickness and 4 cm diameter) were blanched in a steam chamber for 4 min. Following cooling to room temperature، the squash slices were dehydrated by use of a hotair dryer، under air temperature of 60°C up to moisture content of 0. 1065 kg H2O per kg d. m. Squash slices of specified weights were rehydrated by immersion in distilled water at different temperatures (25، 50، and 75°C). They were agitated at different speeds (0،100، and 200 rpm). For any of the experiments، the dry matter to water ratio was kept at 1:25. The squash samples were removed from water at specified time intervals of up to 300 min. Then their weight، dry matter content and water absorption content (in percent) were determined. The squash slice color was examined over a 180 min period. The results showed thatrehydration time، water temperatureand agitation speed had significant effects (p˂0. 01) on dry matter content، water absorption (percent) and color indices (L*، a*، b*، and ΔE) in the dried squash slices. Water absorption percent and total color difference (ΔE) of squash slices increased، whereas dry matter content and color indices (a*، b*، and L*) decreased with rehydration time. Maximum water absorption and ΔE، minimum dry matter content as well as color indices (a*، b*، and L*)، were observed in squash slices rehydrated into 75°C water and agitated at 200 rpm.

Flaxseed is one of the oilseeds that use as ingredient in food product due to its considerable nutritional and beneficial health effects. In this study in order to produce functional Taftoon bread, ground flaxseed was incubated at 30 ºc and microwaved for 2.5 minutes in order to reduce cyanogenic glycosides compound. Wheat flour replaced with treated ground flaxseed at 5, 15 and 25 percent levels. Results showed that cyanogenic compound reduced 84/6%. Result of rheological properties test of dough showed that, with replacing wheat flour with ground flaxseed, water absorption of dough and expansion of dough during fermentation decreased and stability time of dough increased and the difference between them was significant (p<0.01). Results of stress relaxation test showed that addition of ground flaxseed to wheat flour, increases the viscoelasticity of dough. Results of oxidative stability test showed that with replacing wheat flour with ground flaxseed, peroxide and thiobarbituric acid value increased and highest value was at 15% ground flaxseed and had significant difference(p<0.01). Results showed that bread containing flaxseed had darker color and softer texture and staling of bread containing flaxseed was lower. Results of organoleptic test showed that bread containing flaxseed had better flavor, aroma, texture and overall acceptability by panelist, although color of bread had less acceptance at 15% and 25% level of replacing ground flaxseeds.

In this study the impact of freezing rate and degree of pre-fermentation on Sangak frozen dough and its bread was assessed. The pre-fermentation was between zero and 120 min and the corresponding secondly fermentation was between 120 and 0 min، respectively، to obtain total fermentation time of 120 min. The pre-fermentation dough was formed in flat shape and frozen under -20، -25 and -30 °C. It was followed by one day storage at -18 °C. After storage period a second fermentation (in some case there was no second fermentation) was done and in order to finish the fermented dough was baked. Sangak frozen dough quality was assessed by measuring yeast survival and gassing power after thawing. Characteristics of frozen dough bread were evaluated by measuring density after baking. Results showed that viability of yeast initially increased and then decreased by increasing freezing rate، so that at -25 °C the most viability was observed. The maximum yeast viability was observed at short pre-fermentation (30 min). A direct relationship was observed between gassing power and yeast viability. The lowest bread density was obtained with the highest freezing rate and with the short pre-fermentation time.

The physico-chemical characteristics and physiological qualities of palm (Phoenix dactylifera) fruit strongly depend on the storage conditions. Storage environment and packaging type are the factors most influencing on the quality of dates during their storage. Date fruits were packed within an aerobic atmosphere, vacuumed in PA/PE pouches and stored at different temperatures (-20, 4, 25 and 40 ºC). Throughout the study, the effect of packaging type, storage temperatures as well as storage time on physical properties of the fruits were investigated. The samples were evaluated for color indices (L*,a*, b*) and as well for textural parameters (gumminess and chewiness) on a monthly basis, and during storage for a duration period of up to 6 months. Results demonstrated that the storage temperatures, storage time and packaging type greatly (p < 0.01) affect all the physical parameters (color indices, guminess, chewiness) during storage. The color index values (L*, a*, b*) of dates stored at 40 ºC were lower than those of the other date fruits. L*,a* and b* indices of atmospheric packed dates were higher than those of the vacuum packed samples. The gumminess and chewiness were higher in the dates stored at 40 ºC within all packaging types within the sixth month. An increase of gumminess and chewiness was detected for all the samples throughout the storage period. However, it was noted that the increase was significantly greater at 40 ºC as compared with those at the other storage temperatures.