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The 15 - cm layer of bottom sediments of the Lake Bukowo was examined. Organic sediments make up to 32% of the Lake Bukowo bottom surface, the mixed sediments - 52% and the sandy ones - 16%. Bottom sediments of this lake displayed a high content of organic matter ca. 28%, nitrogen ca. l. 2%, silica 65% and phosphorus 0.9%. Nitrogen and phosphorus were deposit into sediments in the main form of organic compounds. These sediments were characterized by low content of metals (average: Ca 1%, Mg 0.8 %, Fe 1.3% and Al 1.1%). The pollution of Lake Bukowo increased comparison to 1987.
The aim of this study was to evaluate the influence of temperature (40, 50, 60, 70°C), flow velocity of the drying air (0,5 i 1 ms-1) and water blanching (3 min) on the specific energy during convective drying of parsley. The total process energy was also evaluated. The results showed that an increase of drying air temperature from 40 to 70 °C caused a decrease of the total process energy by about 43% (1 ms-1s) and 31% (0,5 ms-1) for non-blanching parsley, and about 52% (1 ms-1), and 42% (0,5 ms-1) for blanching material. For each drying temperature the total drying energy was lower in the case of the flow velocity 1.0 ms-1and decreased after blanching. The lowest average total drying energy (10.5 MJkg-1) was obtained for blanched parsley dried at the temperature of 70°C, and for the air flow velocity of 1.0 ms-1.
The effect of two types of modified atmosphere (MA1: 69% N2, 25% CO2, 5%O2, 1% CO; MA2: 70% N2, 30% CO2) on changes in physical and chemical parameters (pH, aw - water activity, TVBN - total volatile basic nitrogen, TMA - trimethylamine, FFA - free fatty acids, PV - peroxide value, TBA - thiobarbituric acid) in muscle tissues of the silver carp was monitored in the study. The samples were stored at temperatures +2 ± 2oC for 18 days. Changes in gas volumes (CO2 and O2) in MAs were also monitored. CO2 levels increased in MA1 but decreased in MA2. At the end of 18 days of storage, a significantly (P < 0.01) lower water activity (aw) levels were found in samples packaged under MA1, in contrast to samples packaged under MA2 where water activity values showed considerable fluctuation. Variations in pH values in the two types of MA showed similar trends. Sample pH gradually decreased until day 9 of storage. On day 11, muscle tissue pH increased markedly and then began to decrease again. The overall decrease in pH values was more profound in samples packaged under MA1. TVBN and TMA levels in samples packaged under the two types of MAs remained almost identical until day 9 of the experiment. Later, however, significantly (P < 0.01) higher levels of both parameters were found in muscle tissues packaged under MA1. FFA concentrations in silver carp samples in MA1 were significantly lower (P < 0.01) throughout the experiment. The PV increased significantly in both muscle samples tested. Greater fluctuations in this parameter’s values throughout the experiment were observed in samples packaged under MA2. Faster rates of oxidation (P < 0.01) were found in samples packaged under MA1 starting on day 9. Maximum TBA values in MA1 and MA2 were observed on days 14 and 18 of the experiment, respectively. From the course of proteolytic and oxidative changes point of view, the more appropriate combination of gases for silver carp storage seems to be the mixture of 70% N2 and 30% CO2 (MA2), which allows for muscle storage of up to 9 days. We recommend TVBN as a suitable indicator of freshness, and TBA assay as a suitable indicator of the extent of oxidative processes.
Background. Salted fish products are popular in many countries around the world. Salting is one of the oldest techniques for fish preservation, and is essentially intended to increase the shelf-life of the product depressing water activity by means of dehydration and salt uptake by the fish muscle. However, the current demand for salted fish is driven more by the flavour of the product than for preservation purposes. Vacuum-packaging represents a static form of hypobaric storage. It is widely used in the food industry because of its effectiveness in reducing oxidative reactions in the product at relatively low cost. Low temperature storage is one of the primary methods to maintain fish quality, based on the reduction in the rates of microbiological, chemical and biochemical changes. Material and methods. Fresh Golden mullets were rapidly beheaded, scaled, gutted and immediately washed with tap water then, samples were taken to the laboratory in ice box for chemical and microbial analysis of fresh fish, other samples were put in the brine (6 liter water and 2160 g salt was used for brine solution). After 14 days of brining, fish were taken out of brine solution and drained, then they were Vacuum Packed and labelled (each pack contained two fish about 1500 g weight). Ali the packs were stored in a refrigerator 4°C. Some quality aspects including Total Volatile Nitrogen (TVN), Peroxide Value (PV), Thiobarbituric Acid (TBA), Total Viable Count (TVC), Halophilic Bacteria (HB) and presence of Clostridium Botulinum were determined in fresh mullets, fresh brined mullets after 14 days of brining, and in (Vacuum Packed) VP samples stored at 4°C at intervals of 30, 60 and 90 days. Results. TVN increased from ten mg/100 g in fresh brined after 14 days to 30.80 mg/100 g in VP brined Golden mullet after 90 days of storage at 4°C, PV increased after brining from 1.50 meq/kg in fresh brined to 28.90 meq/kg in VP brined Golden mullet after 90 days of storage at 4°C, TBA increased from 0.07 mg MDA/kg in fresh brined to 0.10 after 60 days and then, decreased to 0.09 mg MDA/kg in VP brined Golden mullet after 90 days of storage and TVC decreased from 4.70 log CFU/gr in fresh brined to 4.40 log CFU/ gr after 30 days and then, increased to 5.70 log CFU/gr in VP brined Golden mullet after 90 days of storage at 4°C, FIB increased from 4.55 log CFU/gr in fresh brined to 6.30 log CFU/gr after 90 days of storage period at 4°C and exceeded the permissible level. Clostridium botulinum toxin was not detected in any of the samples throughout the storage. Conclusions. The results from this study clearly suggested that a combination of brining, vacuum packaging and storage at refrigerated temperature prolongs the shelf-life of Golden mullet to a great extent. Our findings revealed that the longest shelf-life was for VP brined Golden mullet stored at 4°C is 30 days.
The aim of this work was to determine the dependence between the content of fatty acids (especially trans isomers) and chemical changes occurring in fats during baking and storage of shortcakes. The fats containing different fatty acids (trans isomers from 4.1 to 53.2%) were used to bake the cakes. The cakes were baked at 180ºC for 20 min and next stored for 6 weeks. Fat was extracted with the Kates’ method and the composition of fatty acids was determined with gas chromatography. It was found that trans isomers content in fats had no statistically significant effect on the oxidation and hydrolytic changes occurring in fats during baking of shortcakes. In all fats, irrespective of the content of trans isomers, the primary and secondary oxidation products appeared in small quantities. Temperature during baking had no influence on the content of saturated fatty acids. Considering trans isomers and polyunsaturated fatty acids in the product in comparison with initial fats, small changes appeared, but the changes were significant from the statistical point of view. Fats with a high content of trans fatty acids – although they do not cause hydrolytic and oxidation changes during baking and storage - should not be used for baking cakes, especially shortcakes with a high content of fat.
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