Yoghurt quality is generally determined from results of both chemical and structural analyses. Components analysed include flavour compounds and milk constituents, while assays for chemical indices such as enzyme activity are also performed. The structural analysis measures textural, rheological and microstructural properties.

Flavour analysis examines those attributes perceived by taste and smell, and is highly important for the determination of yoghurt aroma profile, of use in both quality control and research and development. Key flavour components of yoghurt include lactic acid, other organic acids and various volatile compounds.

Chemical indices such as the zeta potential of casein micelles and the enzymic activity of the bacterial starter culture are important parameters for monitoring the aggregation/fusion potential during gelation and the formation of casein micelles during fermentation/incubation. Textural and rheological properties of yoghurt also influence consumer perception of the product and thus may be measured for quality control purposes. Yoghurt microstructure influences the texture and appearance of the product.

An article by Mortazavian et al.¹ provides an overview of the application of advanced instrumental methods of use for chemical and structural analyses of set and stirred yoghurt. The methods discussed include gas chromatography, high performance liquid chromatography, electronic nose methodology, assays for chemical indices, penetration and texture profile analysis, viscometric tests, oscillatory tests, creep recovery/relaxation tests, ultrasonic reflectance and diffusing wave spectrometry, image analysis and assays of microstructure.
.....................................................................................................
1 Mortazavian, AM; Rezaaei, K; Sohrabvandi, S (2009). Application of advanced instrumental methods for yogurt analysis. Critical Reviews in Food Science and Nutrition 49 (2) 153-163.

Click on the logo below to view an abstract of this article from FSTA Direct.