M.A. Thesis:

Yoghurt enriched with plant oils and extracts of carrot

Doogh is an Iranian traditional drink based on yoghourt. Dairy products are generally recognized as healthful food stuffs. Their negligible content of polyunsaturated fatty acids (PUFAs) has prompted investigators to consider fortifying them with long chain PUFAs. In this study, Doogh were fortified with soy oil and extracts of carrot. Soy oil and extracts of carrot- fortified Doogh was prepared using yoghurt, water, salt, mint essential oil, extracts of carrot, soy oil and stabilizer. The fortified Doogh (a mixture of oil, extracts of carrot, stabilizer and yoghurt) were homogenized using ultrasound. To optimize the formulation of fortified Doogh and effects of the above factors, microbial test, rheological properties, phase separation, colorimetric, sensory analysis and physicochemical properties were investigated. To this end, soy oil was formulated at the level of (5-20%) and extracts of carrot (5-20%) according need daily. All tests samples of the fortified Doogh during storages (21 days) at temperature 5 oc were determined. 13 samples obtained from the above treatments were produced in form of centeral composite design. Statistical Analysis was carried out using Design-Expert software. The results of chemical tests showed that the amount of fat, salt, pH, total solid, acidity and protein of Doogh fortified were influenced by the above factors. Soy oil and extract of carrot a significant effect on the rheological properties and phase separation of fortified Doogh. The results of microbial tests showed microbiological contamination fortified Doogh were not influenced by the above factors. The results of color analysis indicated that extracts of carrot reduced the lightness parameter and yellow parameter but soy oil increased lightness parameter and yellow parameter went up. Redness parameter decreased as soy oil increased, and it increased as the extracts of carrot went up. The results of sensory tests showed the fortified Doogh sample containing 20 Percent soy oil and 5 Percent extracts of carrot had highest texture, taste, odor, color score and the maximum total acceptance was belonged to fortified Doogh sample made from 5 Percent soy oil and 20 Percent extract of carrot.

Keywords: Doogh, Enrichment, RSM, Shelf Life