مجله علوم غذایی و تغذیه
سال هشتم شماره 2 (بهار 1390)

Gelatinization is an important functional property in food systems. In flat breads due to different extraction rates and bran particles, the rate of staling and gelatinization is different. This study is aimed to investigate the effects of bran particles variations on the quality characteristics, gelatinization and retrogradation of Lavash and Taftoon breads. Three different flours with extraction rates of 90% (1.33% ash), 85% (1.06% ash) and 58% (0.44% ash) were selected. Taftoon and Lavash breads were baked after carrying out series of chemical tests. Starch gelatinization and retrogradation of breads were quantified using Differential Scanning Calorimetery (DSC) and showed endothermic peaks at intervals of 24 and 72hrs of storage. Bread staling was determined using shear test by Texture Profile Analyzer at intervals of 1, 3, 5, 7 days of storage. It was indicated that Lavash and Taftoon breads of high bran flours were softer at the first day of storage but breads of low bran flours were firmer at the first day of storage and the course of staling took faster. The results showed that bran has deterious effect on bread texture and high bran flours produced unpleasant soft breads. The results indicated that high bran flours also have low gelatinization and retrogradation rates due to high water absorption.

In recent years, there is a trend towards increased consumption of reduced fat products. Therefore, there has been and will continue to be a demand for reduced fat products. Reduced-fat dairy products can be produced by partially replacing the fat content of the milk base with low calorie products known as fat replacers. The present investigation was carried out to examine the effect of modified corn starch as a fat replacer on reduced-fat cream, in comparison to the full-fat cream. Low fat creams were manufactured from acid treated corn starch (ATS) and acid treated cross-linked corn starch (ATCLS) by replacing 5, 10 and 15% of their fat contents with modified starches. A 30% fat cream was considered as control. Energy values, texture firmness and sensory scores were determined during storage. Reduction of 5, 10 and 15% fat content reduced the energy content of the creams about 7.25, 14.5 and 21.6% respectively. ATS creams were firmer than ATCLS creams at the same concentrations of starch. Creams treated with ATS those ATCLS (10 and 15%) had unacceptable firm textures. Control received the highest flavor score followed by ATCLS cream and ATS cream at 5% starch concentration. Good quality low fat creams might be produced by supplementing ATCLS and ATS at 5% starch concentration. The added starch assists in providing a creamy body and minimal oil separation without the use of any other stabilizer.

From ancient time, traditional breads have been consumed in Iran and bread is considered as a major part of Iranian diet. Considering this important subject, food specialists are continuously seeking ways to improve the quality and shelf life of this traditional product. In this research the effect of hydrocolloids (guar and kappa carageenan) at 0.1% and 0.5% (W/W) concentrations on rheological properties of Barbary bread dough was studied. The study on the rheological behavior of the dough containing hydrocolloids was performed by farinograph and extensograph. In addition, initial tests of flour, namely measurements of curd fiber, fat, moisture, ash, pH, wet gluten, protein and ultimately Falling number was carried out by official standard methods. The highest absorption was observed for carageenan followed by guar at concentration of 0.5%.The dough developing time (DDT) and stability time increased with the addition of both hydrocolloids however, guar at 0.5% concentration had most increasing effect. Hydrocolloid addition increased dough resistance to deformation (R50 and Rm) and maximum change was observed with guar. Rheological properties of dough showed that guar gum had maximum effect on dough viscoelastic properties. Adding guar and carageenan hydrocolloids at 0.1% and 0.5% (W/W) caused improving water absorption, increasing consistency and tolerance of Barbary breads dough to strain force. The extensibility parameter (E) for control sample decreased with the resting time. In comparison, dough containing hydrocolloids exhibited greater stability to extensibility changes with time.

Contamination of vegetables by heavy metals namely cadmium and lead might create some health problems. In this project, the concentrations of lead and cadmium in some vegetables, which were cultivated in five regions of southern Tehran, were assessed. Concentrations of cadmium and lead were determined after digestion through microwave by ICP- AES and GFAAS. The LODs were calculated 0.12 μgg-1 and 0.06 μgg-1 for lead and cadmium respectively and repeatability of the whole procedure expressed, as the RSD were 1.56% and 0.3% for lead and cadmium, respectively. Highest contamination of lead and cadmium were found in leek samples (0.14 mg/ kg and 0.15mg/kg, respectively) which were higher than the European Union permissible values for human consumption (0.1mgkg -1 fresh weight). In this study significant differences were found among the mean concentration of cadmium for three samples of leek, lettuce and mint in five regions (P<0.05), but this was not observed for Pb.

Mayonnaise is one of the most widely used sauces in the world and gums are usually used in the industry to stabilize it. In this study, the Influence of Synergistic Utilization of Flake Tragacanth and Chitosan on the Rheological Properties of Mayonnaise was considered and compared to the blank sample contained xanthan and guar gum. mayonnaise samples containing different amounts of flake tragacanth and chitosan and a blank sample were produced. The rheological analysis comprising the evaluation of flow properties and the variations of viscosity in respect of time were carried out by Rheometer. The results of flow curves showed that all the mayonnaise samples exhibited nonnewtonian, pseudoplastic behavior which fitted by Herschel-bulkley model and the factors related to this model were specified in the samples and blank. All the samples showed thixotropic behavior at the time of testing. the results showed that flow properties of mayonnaise samples depended on both shear rate and the time. The results indicated that the sample containing 0.16% flake tragacanth and 0.04% chitosan was behaving most similar to the blank and synergistic interaction between the two hydrocolloids was observed, therefore this sample was selected as the superior sample.

Hemp seed oil has attracted the attention of many scientists due to its valuable nutritional and pharmaceutical properties. The aim of this work is to evaluate the oil extracted from hemp seed. The extracted oils were subjected to a series of chemical tests such as fatty acid composition, iodine value, saponification value, peroxide value, free fatty acid content, induction period measurement, nonsaponifiable matter content and qualitative and quantitative measurements of fractions present in the nonsaponifiable matter. The results indicated that the fatty acid composition of the extracted oil (34% of the total weight of the seed) consisted mainly of polyunsaturated fatty acids namely 54% linoleic, 18.4% α- linolenic and 1% γ- linolenic acids and some monounsaturated and saturated acids such as oleic and stearic acids. The ratio of linoleic acid to linolenic acid was 3 to 1 which might be regarded valuable in term of nutrition. The induction period of the oil was 2.9 hour at 110 °C. Although the oil contains a considerable quantities of linolenic and linoleic acids, it is stabilised by a high concentration of natural antioxidants namely γ tocopherol. The oil contains 3294 mg/kg sterol where the predominant sterol was β- sitosterol. It was concluded that hemp seed oil due to its high content of mono and poly unsaturated fatty acids might be regarded as valuable oil for consumption.

Mastitis and elevated somatic cell count are considered as factors that affect the quality of milk and milk products. The purpose of present study was to investigate the effect of mastitis on the rate of fermentation in inoculated yoghurt milk during incubation time. Yoghurt milk with three different levels of somatic cell count (<200000 (Low), 200000 to 800000 (Medium) and >800000 cells/ml (High)) was used to produce set style yoghurt. The non protein nitrogen in raw milk, titratable acidity and pH of inoculated yoghurt milk were monitored during incubation period. The results revealed that with increasing somatic cell count, the amount of non protein nitrogen increases and longer incubation time is required to reach the target pH or titratable acidity at the end of incubation period (p<0.05). It was suggested that by elevating somatic cell count, the concentrations of chloride, sodium, citrate and immunoglobulin increase while the concentrations of potassium, calcium, phosphorus, casein and lactose decrease which might cause alteration of buffering capacity, pH and titratable acidity of yoghurt milk. Beside higher proteolytic activity in mastitic milk that results in higher nonprotein nitrogen content in medium and high somatic cell samples can stimulate the growth of Streptococcus thermophilus. It has been concluded that at high level of somatic cell in yoghurt milk, longer fermentation is required to achieve the desired acidity and structure in final yoghurt.

Sodium lactate has been regarded as an antimicrobial substance for the preservation of food. The antimicrobial effect of sodium lactate at 0, 2.5 and 4.5% concentrations combined with heat treatment at different temperatures on the survival of Salmonella Typhimurium RTCC 1370 inoculated in to lean ground beef was studied. Samples were subjected to heating by immersion in a water bath stabilized at 60, 65,70 and 75oC. Statistical analysis were performed by randomized design and Duncan`s Multiple Range Test. The results indicated that heating temperature had significant effect on the thermal reduction time (D value) of Salmonella typhimurium in ground lean meat (P<0.05). The effect of Sodium Lactate was not significant (P>0.05). Interaction of heating and Sodium Lactate was only significant at 70 and 75oC (P<0.05). The results of this study indicated that antimicrobial effect of sodium lactate on Salmonella typhimurium in ground lean meat is significant only when temprature is over70 oC.

Probiotic products are useful for human health. Probiotic bacteria grow slowly in the basic cultures of fermented products. In this study, the effects of Malt extract as a growth factor on the bioability and fermentation rate was investigated. In order to determine the effect of different doses of malt extract (0, 2, 4 and 6%) on the increasing growth of probiotic bacteria; Lactobacillus acidophilus and Bifidobacterium bifidum in probiotic milk and yoghurt, first lyophilized bacteria Lactobacillus acidophilus was added to 1 liter of low fat sterilized milk and was considered as control. Malt extract at the concentrations of 2, 4 and 6% were added to the samples and incubated at 38 °C until reached the acidity at 40 degree Dornic and then left in refrigerator. Similar procedure was applied to the bacteria Bifidobacterium bifidum. Lactobacillus acidophilus and Bifidobacterium bifidum yoghurts were made from the respective milks. The shelf lives of the products were evaluated after 5, 10 and 20 days. This study showed that the growth rate of bacteria was increased by increasing the concentration of malt extract and reached the desired acidity at shorter period. By increasing the concentration of malt extract, the acidity is increased and firmer yoghurt is produced. The increasing rate of acidity in Lactobacillus acidophilus yoghurt was higher but the shelf life was shorter.

Pousti cheese, a prominent cheese made in the eastern part of Iran from the whole raw ewe’s milk without any starter cultures. The cheese has a distinctive organoleptic characteristic and properties making this product popular. The concern about this product is its susceptibility to contamination by pathogens due to the fact that this product is locally ripened and aged in goat’s skin for at least a month and consumed regardless of its microbial safety. The aim of this study is to understand the microbiological changes in this cheese during ripening. Three batches of cheese were prepared following the traditional method using whole raw ewe's milk. Calcium chloride and starters were not added to the milk. In this study microbial characteristics of unripened cheese and its changes during 90 days of ripening were investigated. The enumeration of total mesophilic bacteria, total coliforms, Lactic acid bacteria, Staphylococcus aureus as well as yeasts and molds were performed. Total mesophilic bacterial count decreased and on 60th day of ripening no mesophilic bacterium was isolated. On the 30th day of ripening coliforms and Staphylococcus aureus were isolated from samples which were totally inhibited by the 60th day. Yeasts and molds were isolated and there was a slight increase in their number during ripening. A slight increase of NALAB, was observed during the first 30 days, however the number was gradually decreased during the rest of ripening period. The results of this investigation suggested that the product does not meet national standard of ripened cheese.