مجله علوم غذایی و تغذیه
سال هفتم شماره 1 (بهار 1389)

Among fermented milk products, yogurt is more famous than others and might be regarded as an acceptable and popular product. In this study, native microbial strains isolated from two traditional yogurt samples were used for yogurt production. The aim of this study was to evaluate the variations of acetaldehyde content of produced yogurts during cold storage. Microbial strains were isolated from native yogurt cultures. The acetaldehyde contents of yogurts were determined by combined methods of distillation and final injection to GC. The results indicated that there was a significant increase (p<0.05) in acidity and a significant decrease (p<0.05) in pH of produced yogurts during cold storage. Moreover, acetaldehyde content increased significantly (p<0.05) and reached a maximum concentration after 21st day. The application of native cultures in yogurt production improves the keeping quality and organoleptic characteristics of the product.

By application of different methods of extraction, variations in the extraction rate and chemical composition of the extracted essential oils might be observed. Essential oil of Carum copticum cultivated in Iran was obtained by hydrodistillation (HD) and microwave free solvent (SFME). Oils were analyzed by GC/MS and a firm identification of the components were preformed by comparison of relative retention indices and mass spectra with authentic reference(1).. Eleven components 99.31% were identified in the oil which was isolated by hydrodistillation. The major components of oil of C.copticum were γ-terpinene (37.40%), p-cymene (28%), thymol (24.96%), β- pinene (5.78 %.), myrcene (1.31%). Eleven components (96.91%) were characterized in the oil which was obtained by free-solvent microwave extraction. The major components of the oil were thymol (35.28), γ- terpinene (32.49%), p-cymene (23.51%), β-pinene (3.47%), carvacrol (2.46). Antimicrobial activity of the essential oils were examined against Escherichia coli, using Agar dilution method and minimum inhibitory concentration (MIC) was preformed at 500ppm.

Due to the shortage of edible oils in Iran and the high quantity imported annually and the fact that Colza is becoming popular, it is the aim of this investigation to evaluate the oils extracted from modified samples. Eleven samples of developed colza were chosen accidentally from Karaj institute of seed improvement. The extracted oils were subjected to a series of chemical tests consisting of the determination of fatty acids composition, identification and quantification of fractions present in the nonsaponifiable matter and measurement of phosphorus and phospholipids concentration. The results indicated that beta-sitosterol, gama-tocopherol and oleic acid were the predominant sterol, tocopherol and fatty acid present in the oils examined respectively. Traces of erucic acid was identified in the samples examined. The results showed that the differences between eleven varieties investigated were significant.

Kombucha beverage is a fermentation product produced by kombucha mushroom in sweet tea. One of the most important ingredient in this beverage that plays a critical role in detoxification of the body and preventation of cancer, is glucuronic acid. In this research, the effect of environmental conditions such as pH, time,temperature and sugar substrate, in production of this beverage and its glucuronic acid content were studied. Three levels of pH 4, 5 and 6;temperature 25, 30 and 35 oC;time 3, 5 and 7 days and different sugar substrates, corn syrup, molasses and sucrose were applied. Glucuronic acid content was measured spectrophotometrically in the presence of naphthoresorcinol. Optimum conditions for growth of kombucha mushroom and production of high level of glucuronic acid (44.5 mg/l) were reported using MATLAB programming to be 31 oC with sucrose on pH=6. The results show that if kombucha beverage is fermented in controlled condition, it might be regarded as a healthy and nutrient beverage.

Response Surface Methodology (RSM) was used to determine the optimum processing conditions that yield maximum water loss, minimum solid gain, maximum rehydration ratio and minimum shrinkage by osmo-convective drying of edible button mushroom. Temperature (25-40°C), immersion time (120-300 min), salt concentration (0-15%), sucrose concentration (40-60%), pressure (500-700 mbar) and drying temperature (30-60°C) were the factors investigated with respect to water loss, rehydration ratio, solid gain and shrinkage. Experiments were designed according to Central Composite Design with these six factors each at five different levels. Applying response surfaces and contour plots, optimum operation conditions were found to be temperature of 39°C, immersion time of 164 min, salt concentration of 14%, sucrose concentration of 53%, pressure of 600 mbar and drying temperature of 40°C. At the optimum point, water loss, solid gain, rehydration ratio and shrinkage were found to 63.38 (g/100 g initial sample), 3.17 (g/100 g initial sample), 2.26 and 7.15, respectively. Apart from the optimum condition which provides desirable products, color, texture, flavor and other quality indices might be investigated to produce higher quality products.

By considering the importance of wheat gluten worldwide, gluten is evaluated by several methods which the choice of assessment might be influenced by several factors such as country, wheat classification and intended application. The application of Alveogarph is a new method as compared to other routine assessment methods for testing flours quality. In this project the quality of gluten from 4 different kinds of wheat flour with different extraction rates were assesed by application of Alveograph and Farinograph methods and the results were compared. 4 different varieties of wheat flours were obtained and subjected to chemical and rheological tests. the results indicated that W, L, Ie and G paremeters of Alveograph method decreased in flours with extraction rate of 64%, 82%, 90% and 93% respectively. The P parameter in flour with extraction rate 93% which contains more bran than others was higher. On the basis of Farinograph parameters, in flour with extraction rate of 64%, the stability time was higher and water absorption and degree of softening (after 10 min, 12 min) were lower and in flours containing higher amounts of bran, this parameters acted differently. Although Alveograph is a newer method as compared to Farinograph, the results indicated that for most of the factors investigated, the correlation coefficient is equal to one.

A report of FAO shows that 25% of agriculture products are contaminated by mycotoxins and aflatoxins might be considered the most important as compared to others. Aflatoxins are secondary metabolites of Aspergillus and are divided into B1, B2, G1 and G2 types and other classes namely M1 and M2 are derived from these. In this study, inhibitory effect of Saccharomyces cerevisiae on G1 and G2 were examinated in two substrates (culture media and Kilka fish meal). In culture media, two concentrations of aflatoxin (8 and 12 ppb) and two doses of the yeast (3 and 4%) were applied. Changes of aflatoxins and the yeast growth were evaluated by HPLC and Spectrophotometer (OD: 600 λ) respectively. The results from both culture media and fish meal indicated that G1 and G2 concentrations have been decreased considerably. It is shown that Saccharomyces cerevisiae might be employed as biological tool to lower aflatoxin concentration.

Rosa canina is one of the Rosa species which grows wildly in various regions of Iran. The fruit of this plant "Rose hip" is well-known for its efficacy in strengthening the body's defense against infection and particularly the common cold. Furthermore it has preventive and remedial properties in cardiovascular and renal diseases. In this study the oil extracted from Rose hip seed collected from Ardabil province was extracted by soxhlet application. Chemical composition concerned with crude fiber, moisture, dried matter, protein and ash contents were determined. Rancimat apparatus was used to measure the stability of extracted oils. The results showed high quantities of linoleic and linolenic acids, 44% and 22% were present respectively. Rancimat method indicated that the oil has a low resistance to oxidation. Chemical properties of the seeds concerning moisture, ash, fat, protein and crude fiber indicated a high percentage of fiber and acceptable concentration of protein in the residue of defatted seed which might be used as animal feed. The oil extracted from Rose hip might be regarded as a unique oil due to its fatty acid composition particularly Omega3 content and the desirable ratio of Omega6 to omega3.