مجله علوم غذایی و تغذیه
سال دوازدهم شماره 3 (تابستان 1394)

Unbiodegradable materials used in food packaging and the microbial contaminants derived from this might create problems in our society. The application of biodegradable material that might have antimicrobial activity is desirable and is considered a priority for the researchers. Chitosan is a biopolymer that eliminates these problems. In this study، chitosan nanoparticles and chitosan films were prepared and physical and chemical characteristics of these were determined and the antimicrobial effects against Staphylococcus aureus PTCC 1431 and Listeria monocytogenesusing different methods were assessed. The size of chitosan nanoparticle was 273 nm with MIC and MBC of 3. 5 for these bacteria. Synthezied chitosan film with 43. 69 ± 2. 4 mm of thickness، 1% of moisture content and 52% film solubility caused a reduction of 100% in the number of food pathogenic bacteria in 24 hoursat 30°C. Since chitosan is a biodegradable polymer and has antimicrobial activity in the form of chitosan nanoparticle and film against food pathogenic bacteria (Staphylococcus aureus PTCC 1431 and Listeria monocytogenes)، it might be employed in the packaging industry particularly food.

Curdlan gum is a bacterial polysaccharidic biopolymer that is the result of β-(1→3)-D-glycosidic linkages. Due to its ability to curdle and the water-holding capacity, curdlan has applications in the manufacture of food products such as jelly, noodles, edible fibers. Curdlan is biodegradable, nontoxic and it has applications in the pharmaceutical industry because of its potent biological activities. For the first time, the present study is concerned with the synthesis, characterization, optimization of cultural conditions and modeling of curdlan production from Paenibacillus polymyxa using RSM. After preparation of the microorganism and the medium, Plackett–Burman design with 12 experimental runs was used to screen the effective factors through 11 variables of batch culture medium for curdlan production. Central composite design with 20 experimental runs was used for optimization of the effective variables. In addition, four characterization methods such as FT-IR, C-NMR, XRD and DSC were employed. The result of the experiments showed that three nutritional factors (glucose, yeast extract and triton x-100) had the predominant effect on curdlan production. The maximum production of curdlan was 4.75 g/l from the optimum condition consisting of glucose (100 g/l), yeast extract (3 g/l) and triton x-100(2.5 g/l). In addition, the average molecular weight of curdlan was determined at 170 kDa by GPC. The results from this study have demonstrated that Paenibacillus polymyxa PTCC 1020 with more specific growth rate (µ) than previous studies is capable to produce curdlan gum and also the production of the synthetic curdlan was confirmed using qualitative methods of identification.

The consumers demand foods with high nutritional value that are free from chemical preservatives.This has led to numerous efforts to find natural antioxidants from herbal resources. Savory essence is a colorless to pale yellow liquid that contains phenolic compounds such as carvacrol, P-cymen and thymol that exhibit anti-oxidative and antimicrobial activities. The aim of this study is to quantify the phenolic compounds present in the essential oil of Satureja hortensis as a source of natural antioxidant and to examine its stabilising effect on colza and anchovy oils. The aerial parts of plant was collected, dried and the essential oils was extracted and analysed by GC/MS. Total content of phenolic compounds of the essential oils was determined by Folin-Ciocalteu method. The extracted essential oil was added to canola and anchovy oils at the concentrations of 0.05, 0.1, 0.2 and 0.3% and the antioxidant activities were measured and compared to the control and sample containing BHA. Peroxide value and tiobarbitoric acid value and induction period measurements by Rancimate were used as means to evaluate the antioxidant activities. Carvacrol, gamma-terpinene, alpha-terpinene and p-cymene were determined as the predominant compounds in the extracted essential oil. The total concentration of the phenolic compounds in the extracted oil was 0.739±0.27 mg/ml as Gallic Acid Equivalent. The added essential oil at the concentration of 0.3% exhibited the highest antioxidant activity in canola and anchovy oils. This study has indicated that the application of the natural essential oilsto suitable substances such as canola or anchovy oils in order to improve the stability of the oils and also to replace the synthetic antioxidants is desirable and preferred.

Today, biodegradable packaging is taken more consideration due to the environmental problems of the synthetic packaging materials. Edible coating is one of the important biodegradable active packaging material and is regarded as a suitable alternative for the synthetic packaging studied. In this research the effects of edible coating based on carboxy methyl cellulose containing thyme was studied with particular reference to moisture absorption, fungal growth and sensory characteristics in coated raw hazelnut. The edible coatings were prepared at different concentration levels of carboxy methyl cellulose (0.0, 0.5, & 1.5% W/V) and thyme extracts (0.0, 0.5 & 1% V/V). The mean changes in fungal growth and sensory characteristics were determined for coated and uncoated (control) hazelnut over 21 weeks. The tests were applied in three replications using factorial design based on completely random design. The results of this research showed that non-coated samples had the most moisture absorption, fungal growth and mold development rates. Addition of hydroalcoholic thyme extract to coating solution significantly reduced the fungal growth in coated samples (p≤ 0.05). The results of the sensory tests of the samples indicated that the use of carboxy methyl cellulose coating delayed the softening of the tissues. The use of edible coatings with carboxy methyl cellulose and thyme extract reduced the moisture absorption and mold growth and increased the shelf-life of the coated hazelnuts. Carboxy methyl cellulose, a biodegradable natural biopolymer might be regarded as an alternative to the synthetic packaging.

Ketchup is a popular product and since there is a growing rate in the consumption of fast foods and the use of ketchup as the resulte, therefore elevaluation of the behaviour and characteristic value of this product with new formulations such as the addition of prebiotics is desirable. In this study, chemical properties (pH, acidity,brix and non soluble solids), physical characteristics (syneresis and color) and sensory properties of prebiotic ketchup samples containing different amounts of inulin and galactooligosaccharides along other thickeners (modified starch, xanthan and guar gum) using defined standard methods were evaluted. There was no significant difference in the chemical properties between the samples except for the acidity. Prebiotic ketchups containing modified starch had more syneresis as compared to the samples with similar amounts of prebiotic compounds along with xanthan and guar gum. Color values of L*,a*,b* were increased with increasing the prebiotic compounds. In addition, the difference in the total color was higher for prebiotic samples containing modified starch. Although the sensory properties of the prebiotic ketchup samples were influenced by the application of inulin and galactooligosaccharides, but the overall acceptance of most prebiotic samples were not significantly different as compared to the commercial ketchup. According to the results of this study, a prebiotic ketchup might be produced with the acceptable physicochemical and sensory properties by the addition of inulin and galactooligosaccharides to the formulation. The prebiotic samples containing xanthan and guar showed more similar charactristics to the commercial product particularly considering the syneresis effect.

Purslane (Portulaca oleracea) is a warm climate annual plant classified as a weed. Purslane has been described as a power food of the future due to its high nutritive and antioxidant properties. It is listed in the world health organization as one of the most used medicinal plants and it has been given the term “Global panacea”. This study is concerned with the evaluation and comparison of the chemical and fatty acids composition of the Purslane leaves from north (province of Gilan) and south (province of Fars) of Iran. In this research work purslane leaves were prepared for chemical composition tests consisting of ash, protein, fibre, carbohydrate and oil contents. The fatty acid compositions and profiles were determined by conversion of the fatty acids into their methyl esters and their application on to a GC equipped with a capillary column and Flame Ionisation Detector according to the defined methods of standard. The comparison between north and south samples indicated significant differences in the ash, protein, oil, and carbohydrate contents. Evaluation of the fatty acids compositions showed that α-linolenic acid was the predominant fatty acid present in the purslane leaves oil in both samples. It was concluded that purslane leaves oil due to its high nutritive and antioxidant values might be regarded as a valuable oil for specific applications.

The aim of this study is to investigate the effects of temperature, osmotic solution concentration and dehydration time on the mass transfer during osmotic dehydration of eggplant and then comparison of the mathematical models in order to select the best model for the mass transfer. Dehydration of the eggplant with the osmotic solutions containing 5, 10 and 15% salt and temperatures of 30, 45 and 60°C in a water bath at the ratio of eggplant slices to osmotic solution of 1:10, 1:15 and 1: 20 has taken place. Water loss and solid gain values ​​for each concentration and temperature at intervals of 0, 15, 30, 60, 90, 150, 210 and 270 minutes were determined respectively. Equilibrium values ​​ of water loss and solid gain were calculated by models as well as the rate of mass transfer. The moisture content and mass transfer kinetics are functions of temperature and salt concentration changes over the time. The model proposed by some researchers (Azura model) with maximum Regression Coefficient and minimum root mean square error and the square sum error was compared to the Magee model that can describe the mass transfer kinetics better. The Azuara model in 1:15 ratio of osmotic solution of the sample resulted in a correlation coefficient of 0.9792 for water loss and of 0.9386 for solid gain as compared with 1:10 and 1:20 ratios that showed the best fit. The proposed model of Azuara regarding the maximum correlation and the minimum root mean square error and the sum of squared errors was recommended in order to model the mass transfer kinetics during osmotic dehydration of eggplant.

Oils extracted from nuts by the cold press might be regarded as valuable oils due to their high yield, unique flavors characteristics. Due to the role of nuts in Iranian society regarding its high consumption, this preliminary study concerned with the fatty acid and sterol compositions of the oils extracted from the related nuts by cold press have been carried out. To define the chemical compositions of nut oils, four nuts consisting of pistachio, walnut, hazelnut and almond were collected from Kerman, Tuyserkan, Qazvin and Azarshahr areas respectively and the oils were extracted at 25°C using the cold press methods. Fatty acid and sterol compositions were determined using a gas chromatography equipped with a capillary column and Flame Ionisation Detector according to the defined methods of standard. The results showed that oleic acid was predominant fatty acid in hazelnut (83.3%), almond (67.6%) and pistachio (63.3%) oils while the linoleic acid had the highest concentration in walnut oil (52.5%). The analysis of the sterol fractions of the nonsaponifiable matters of the extracted oils indicated that the apparent β-sitosterol was the predominant sterol and covered 85-91% of the total sterol fractions in all the oils examined. The results showed that the oils extracted from nuts have desirable quantities of oleic and linoleic acids. The results also indicated the absence of trans acids. Due to the presence of high concentrations of oleic acid in hazelnut, almond and pistachio, these oils have a good stability against oxidation chain reactions.

Doubts about the safety and health hazard concerned with the use of synthetic antioxidants have led to a growing demand for the application of natural antioxidants. In this study the antioxidant activities of water and alcoholic extracts of shahmirzadi variety of green husk of walnut based on reducing power, total antioxidant activity and DPPH scavenging activity were evaluated. The effects of extracts on inhibition of oxidation chain reactions of soyabean oil was examined by measuring peroxide and thiobarbitoric acid values as means to evaluate the antioxidant activities. Phenolic compounds were extracted with methanol (80%), ethanol (50%) and water and the total phenolic content was measured by Folin-Ciocalteu method. The results showed that the highest total phenolic compounds were present in the methanolic extract using microwave. The results also indicated that the extracts were able to retard the oxidation and the antioxidant activity was concentration dependent and the sample with the concentration of 1000ppm extract inhibited the oxidation of soyabean oil. Walnut husk might be regarded as a potential source of natural antioxidants but further investigation might be recommended for its possible application in food and related industries.

Lactobacillus genus is classified in the large group of lactic acid bacteria. All the organisms are gram positive and produce lactic acid by fermentation. These bacteria are found naturally in various foods and have been considered as a natural preservative in some of the traditional foods since the ancient times. The aim of this study is to evaluate the technological properties and usability of lactobacilli isolated from the traditional cow and sheep cheeses as starters in cheese and other fermented products. In this study, 12 Lactobacillus strains were obtained from the six traditional sheep and cow cheeses in Sangesar area (Semnan, Iran). Lactobacillus strains were confirmed by phenotypic tests. The isolated strains were evaluated as starter by the technical tests such as growth, acid production, proteolytic, amilolytic and autolytic activities. The optimum growth temperature was at 30˚C for all the isolated strains. The highest growth rate was in the two isolated strains from cow cheese; LB2-1and LB2-5, respectively. The proteolytic activity was observed in three isolated strains from cow cheese; LB2-1, LB2-4and LB2-6, and the strain isolated from sheep cheeses (LB1-3). Amilolytic activity was observed in none of the isolated strains. The highest rate of acid production and autolytic activity was observed in isolated strain from cow cheeses (LB2-2) and the strain isolated from sheep cheese (LB1-1). In this study the isolated lactobacilli from traditional Sangesar cheeses showed desirable technological characteristics and high potential for application as a starter