Background

Flavor is an important attribute that greatly impacts beef eating experience. Beef flavor is perceived by the senses in response to flavor compounds which develop during cooking. The development of cooked beef flavor compounds is driven by chemical reactions between precursor compounds present in raw beef (Mottram, 1998). Beef flavor compounds are developed primarily through thermal lipid degradation and the Maillard reaction (Mottram, 1998). Thermal lipid degradation of phospholipids and triglycerides results in volatile compounds that have been shown to influence flavor (Larick, Turner, Koc, & Crouse, 1989). Likewise, compounds resulting from the Maillard reaction have been shown to influence flavor (Farmer & Patterson, 1991). The Maillard reaction is initiated between amino acids and reducing sugars. This initial reaction results in a series of reactions which may produce a variety of flavor compounds (Mottram, 1998). Additional flavor contributions have been shown to be made through the degradation of Thiamin and nitrogen containing nucleotides which participate in the Maillard reaction (Aliani & Farmer, 2005). Identification of beef flavor compounds allows the determination of the route by which they are formed and the influence of flavor precursor compounds. Flavor has been shown to be highly important to consumers. Current knowledge about the mechanisms of beef flavor is somewhat lacking. Therefore it was the objective of this study to broaden the understanding of those mechanisms which drive beef flavor. In addition it was an objective of this study to use the obtained information to create a means of predicting beef flavor.   

Methodology

Experimental design:
Treatments: 3 USDA Prime, Low Choice, and Standard
Experimental unit: 24 subprimals (n = 8)
Sampling: 2 steaks per subprimal with 2 analyses per steaks

Chemical analysis:
Lipids: fatty acids from neutral and polar lipid fractions – gas chromatography flame ionization detector
Water soluble compounds: determination of free amino acids, reducing sugars, creatine, nucleotides and their degradation products, and thiamin – reverse phase high performance liquid chromatography fluorescence or UV detection
Volatile flavor compounds: head space solid phase microextraction and gas chromatography mass spectrometry

Findings

This study has yielded a number of significant observations for known flavor precursors  and volatile flavor compounds. Differences were observed among lipid fractions and USDA  quality grades which may be contributing to volatile flavor compounds. Polar lipid fatty acids  were found to be degraded differently during cooking compared with neutral lipid fatty acids.  Among Low Choice and Standard quality grade amino acids, greater concentrations of Strecker aldehyde forming amino acids were found. Additionally, cooking increased the concentration of all free amino acids except cysteine. Quality grade was found to have no effect on many important reducing sugars. However, cooking dramatically decreased the concentration of reducing sugars. Ribose was found to be more affected by cooking in Low Choice and Standard quality grade steaks, than Prime steaks. 

Among nucleotide compounds, it was found that raw Standard steaks possessed greater amounts of taste contributing compounds than Low Choice and Prime graded steaks. Cooking was found to dramatically increase adenosine-5-monophosphate, which when degraded may ultimately provide the reducing sugar, ribose. In addition, thiamin was found to not be affected by quality grade and decreased with cooking. 

Specific volatile compounds were identified, which have previously been shown to contribute to beef flavor. Many of the determined compounds are known to be the results of degradation or interactions of precursor compounds. Regardless, positive flavor contributing compounds were observed to be greater among Prime quality grade steaks.

Implications

The results of this research have documented the effects of cooking and USDA quality grade on the compounds and precursors that determine beef flavor. The present and future use of this data in predicting meat flavor will continue to be explored as we consider the complexity of the chemical properties measured and their correlation to scheduled trained and consumer sensory flavor analysis in the coming year.