M.A. Thesis:

The effect of quince puree on the physicochemical properties organoleptic and functional in shelf life of fat yogurt.

Yogurt is the most widely consumed fermented milk products in the world. The yogurt's wholesomeness effect is cleared on curing of some diseases like diarrhea and high cholesterol, because of considerable amount of organic acids and some other effective material in it. As yogurt is a pragmatist food by nature because its positive effects on digestive system, but many researchers could improve its pragmatic properties by adding some useful ingredients. In order to evaluate the effect of adding "quince cooked puree" into stirred yoghurt, we did an experiment as factorial experiment in a completely randomized design with three replications in Islamic Azad University of Sabzevar. The main factor in the puree was the "quince" (zero or control sample, 3, 6, 9%) and the subside element was time (1, 7, 14 and 21 days). The physicochemical properties, rheological, sensory and colorimetric product was evaluated. In measuring acidity changes, by passing time the amount of acid was increased but the amount of acidity was decreased by adding puree in each step. The least amount of acidity belonged to treatment by 9%mashed quince. The results of PH changes showed that the PH amount was decreased in spite of acidity by passing time and by adding the puree it decreased. By reviewing viscosity changes, time caused decreasing viscosity. The control samples and samples containing 6% puree showed the highest amount of viscosity comparing to the other samples. In sinusoidal variation, passing time caused increasing sinus and adding the percentage of puree in each step caused decreasing the sinus. The least sinus rate was reported for 9% mashed quince at the first day and the highest rate was occurred on the control sample at 21st day. In reviewing carbolic acid (phenol) compounds' changes, the most amount was found in 7th day for all samples and by increasing the percentage of puree in each step, we saw growing of phenolic compounds, in which, the most amount was related to sample with 9% puree on 7th day and the least one related to control sample at the first day. The antioxidant results had an approximate correspondence with phenolic results. The highest antioxidant activity was observed on sample with 9% puree on 7th day. In colorimetric results, over time and increasing the puree, the amount of changes in ?E is increased. The highest amount related to sample with 9% puree on 21st day and the least amount refer to sample with the 3% puree on the first day. Sensory evaluation such as taste, smell, texture, appearance, color, mouth feel and overall acceptability were evaluated. Ultimately in all parameters except for odor, the control sample and then yogurt contains 6 percent puree have gained more acceptance. In the parameters of our samples contain 9% puree roasted gain more popularity. Over the time, during the storage time, all of the organoleptic properties of the samples and their final acceptance was reduced.

Keywords: organoleptic, reology propertise,quince fruit , fat yogurt