Considerable knowledge has been accumulated on the volatile compounds contributing to the aroma and flavor of yogurt. This review outlines the production of the major flavor compounds in yogurt fermentation and the analysis techniques, both instrumental and sensory, for quantifying the volatile compounds in yogurt. The volatile compounds that have been identified in plain yogurt are summarized, with the few key aroma compounds described in detail. Most flavor compounds in yogurt are produced from lipolysis of milkfat and microbiological transformations of lactose and citrate. More than 100 volatiles, including carbonyl compounds, alcohols, acids, esters, hydrocarbons, aromatic compounds, sulfur-containing compounds, and heterocyclic compounds, are found in yogurt at low to trace concentrations. Besides lactic acid, acetaldehyde, diacetyl, acetoin, acetone, and 2-butanone contribute most to the typical aroma and flavor of yogurt. Extended storage of yogurt causes off-flavor development, which is mainly attributed to the production of undesired aldehydes and fatty acids during lipid oxidation. Further work on studying the volatile flavor compounds-matrix interactions, flavor release mechanisms, and the synergistic effect of flavor compounds, and on correlating the sensory properties of yogurt with the compositions of volatile flavor compounds are needed to fully elucidate yogurt aroma and flavor.

Volatile Flavor Compounds in Yogurt: A Review

The present work studied the production of carbonyl compounds and saturated volatile free fatty acids by pure cultures of Streptococcus thermophilus and Lactobacillus bulgaricus, and by starter cultures for Bulgarian yogurt during cultivation and cooling. The mixed cultures formed volatile aromatic compounds more actively than the pure cultures. A guiding factor in the preparation of the starter cultures was the biochemical activity of Lactobacillus bulgaricus in synthesizing the major carbonyl compounds, acetaldehyde, diacetyl and the volatile fatty acids C2–C10. The activity of the yogurt cultures in synthesizing carbonyl compounds was at its highest during milk coagulation and cooling, up to 7 h. However, maximum concentration was reached by 22–31 h. In the cooled 22–h starter cultures, acetaldehyde predominated (1415.0–1734.2 μg per 100 g) followed by diacetyl (165.0–202.0 μg per 100 g), acetoin (170.0–221.0 μg per 100 g), acetone (66.0–75.5 μg per 100 g), ethanol (58.0 μg per 100 g), and butanone-2 (3.6–3.8 μg per 100 g). The thermophilic streptococcus and lactobacillus cultures, and the starter cultures contained predominantly acetic, butyric and caproic acids.

Production of flavour compounds by yogurt starter cultures

Production of sulfur compounds by several yeasts of technological interest for cheese ripening

Estimation of human exposure to styrene and ethylbenzene.

The potential of different commercially used starter cultures to form volatile organic compounds were determined. Special interest was laid on the so-called minor constituents compounds that are present in the low μg/kg-range in the end-product aroma of the investigated starter cultures. The variability of the tested single strain cultures was very wide within the investigated species. It was not possible to group the strains according to the species by applying statistical procedures such as principal component analysis or cluster analysis on the GC-MS-data of the samples. Applying the concept of odour unit values to all cultures tested, it was possible to estimate the impact of each volatile organic compound investigated on the resulting aroma of the end product. Of 32 quantified compounds only 2,3-butanedione (odour unit values between 6 and 362), 2,3-pentanedione (between 0 and 363), and to a lesser extent demethyl sulfide (between 6 and 12), and benzaldehyde (between 0 and 3) are supposed to have such an impact. Mixed cultures were formed, using three strains of Lb. delbruckii ssp. bulgaricus and S. salivarius ssp. thermophilus , respectively, to produce yogurt. The most interesting finding was that 2,3-pentanedione is produced by all mixed strain cultures in three to five times the amount of the sum produced by the respective single strains.

Volatile organic compounds produced by thermophilic and mesophilic single strain dairy starter cultures

The aim of this study was to apply a standard addition method to quantify volatile organic compounds in pasteurized milk and fermented dairy products. Thirty-three volatile organic compounds detected in the headspace of milk or fermented dairy products were added in various concentrations to pasteurized milk as a reference and chromatographically analysed by a combination of dynamic headspace analysis and GC-MS. The original concentrations in milk of the added compounds and their respective 95% confidence intervals were calculated by means of linear regression analysis. With the exception of ethanal all tested compounds resulted in usable linear regressions and the calculated concentrations in milk generally agree with data found in literature. Ethanal excepted, the applied dynamic headspace GC-MS method provides accurate results for the quantification of volatile organic compounds in milk. Response factors calculated from data of the linear regression analysis in milk also allow quantitative determination of volatile compounds in fermented milks, since their matrix effect appears to be the same as for milk.

Quantitative GC-MS Analysis of Volatile Flavour Compounds in Pasteurized Milk and Fermented Milk Products Applying a Standard Addition Method

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Quantitative GC-MS Analysis of Volatile Flavour Compounds in Pasteurized Milk and Fermented Milk Products Applying a Standard Addition Method