Flavor release and rheology behavior of strawberry fatfree stirred yogurt during storage.

The influence of storage on the aroma release in headspace and rheological properties in strawberry-flavored fatfree stirred yogurts was determined. Three periods of storage at 10 degrees C were chosen for analysis: 7, 14, and 28 days. The headspace composition was assessed in a flask in static mode. The SPME fiber was carefully chosen, and results are presented in detail (choice and degradation). The flow properties of the final product were measured in order to follow n (flow behavior index) and K (consistency index), and the apparent viscosity was determined (eta in Pa.s). The quantity of flavors in the headspace of products at the 28 days of aging was significantly weaker for methyl 2-methyl butanoate, ethyl hexanoate, and hexyl acetate. The decrease was half of that in comparison with the seventh day. It was supposed that modification in rheological parameters can partly explain these results. Indeed, the apparent viscosity of the products significantly increased during the three times of storage. The composition of the flavored yogurt, proteins, exopolysaccharides, and fruit preparation, seemed to have a great impact on the release of aroma compounds. The aroma compound amount in the headspace decreased when the matrix changed from water to yogurt. With the fruit preparation, the headspace amounts for esters were significantly lower than in water alone, respectively, 23, 27, 29, and 17% less for methyl 2-methylbutanoate, ethyl hexanoate, hexyl acetate, and benzyl acetate. In flavored yogurt, the amount of aroma compounds in the headspace decreased again in comparison with the result obtained with the fruit preparation. Ethyl hexanoate and hexyl acetate presented the higher decreases of 48 and 53%, respectively.