بهمن بهرامی

Oil-in-water emulsions have attracted considerable attention in food industry due to their physical and rheological properties. These systems consist of small oil droplets dispersed in an aqueous medium. Numerous factors affect rheological properties of emulsions such as emulsion composition، process and storage conditions. In this study، effect of thermal treatment on oil in water emulsions containing 40 % oil was studied. The emulsions were prepared using xanthan gum، guar gum and carboxymethyl cellulose as stabilizer and polyoxyethylen sorbitan monooleat as emulsifier. A mixture design was used to define the percentage of each stabilizer to simulate wide range of emulsions. The emulsions were pasteurized at 87ºC for 15 minutes. Rheological properties were studied using a Brookfield rotational viscometer. Thermal treatment had considerable influence on rheological properties of emulsions. Viscosity of all emulsions decreased after thermal treatment and stabilizers had a positive effect on this response. This behavior could be explained by the structural breakdown of the molecules due to the hydrodynamic forces generated and the increased alignment of the constituent molecules and hydrolization of stabilizers. All model emulsions exhibit non-newtonian pseudoplastic flow behavior often referred to as shear thinning (n<1). A non-linear relation between shear rate and shear stress can be observed. Shear stress versus shear rate data was successfully fitted to the Power-law model. Consistency coefficient (K) of emulsions decreased and flow behavior index (n) increased after thermal processing.

Hypercholesterolemia is major risk factors for heart disease. Plant sterols have been used for reduction of cholesterol since 1950 decade; so enriching food materials with such components is important. Major problems related to enrichment of products with plant sterols are high melting temperature and chalky taste. In addition, crystal form of these components in comparison with lipid-in solved forms can not significantly reduce the blood cholesterol. In this study enrichment of yogurt and optimization of the process condition were investigated. A four components (plant sterols, emulsifier, vegetable oils and water) mixture design was used to define the percentage of each mixture component to simulate wide range of mixture with different oil quantities. Emulsifier and soy oil were used for dissolving and dispersing of plant sterols in water phase. Yogurt texture, syneresis susceptibility, acidity and viscosity were measures during storage. Gel strength of enriched samples was higher than control. The mean values of syneresis and viscosity of enriched yogurts with phytosterol, were significantly (P < 0.05) lower than the control yogurt. Addition of plant sterol into yogurt did not change titrable acidity. Taste and flavor tested by panelists, where enriched yogurt was preferred to control.

Introduction and cultivation of new oilseeds، is an important step to provide needed oil for the country. Milk thistle (Silybum marianum) is an annual or biennial plant that the extract of its leaf or seed has been used for treatment of liver diseases since 2000 years ago. In spite of compatibility of this plant to climate of Iran especially resistance to dryness، there is no information about the content and quality of the seed oil. In this study، the oil content was determined by Soxhlet and it was 22. 7%، nearly similar to soybean and cottonseed (dehulled) oil content. Refractive index، Color and Specific gravity and Peroxide (1. 59)، Iodine (109. 57)، Saponification (180. 9) and Acid (1. 82) values of the oil were studied. Also، fatty acid profile of the oil was determined by GC. Linoleic acid (51. 2%) and oleic acid (28. 8%) were the most fatty acids of the oil، respectively. In regard to remarkable oil content of the seed and high nutritional value of the oil (high-linoleic acid)، cultivation of this new valuable oilseed is necessary and beneficial.