Editor's note: In Part 1 of this two-part article, the author discusses the sensation of flavor, the development of meat flavor through taste and aroma, and how nitrites affect the flavor of cured meats. Next month, in Part 2, the author defines factors that affect meat flavor and outlines the implications for product development.

From a consumer perspective, appearance, flavor, and texture are key food quality attributes. The relative contributions of each of these attributes to the acceptance of meat and meat products will depend on the chemical and physical states of the meat and its constituents, which are, in turn, the result of numerous complex interactions that take place as a result of intrinsic and extrinsic factors that act upon the meat. Of these attributes, flavor (term sometimes used interchangeably with taste) has, for many years, been at or near the top among drivers of food preference and purchase intent.

Flavor and its perception

Flavor is the sensation that results primarily from the chemical senses of taste, olfaction (or smell), and the trigeminal system. Gustation, or taste, is perceived when a taste-active compound binds to specific proteins known as taste receptors, which are found in the taste buds of papillae in the tongue, or in other parts of the oral cavity, including the soft palate. This event leads to cell membrane depolarization, neurotransmitter release, and the eventual propagation of sensory information to the central nervous system via an action potential.

Olfaction, or smell, is initiated when volatile odorous molecules (or odorants) reach the olfactory epithelium located in the back of the nasal cavity and come into contact with the olfactory receptors located in the cilia of olfactory sensory neurons. There, membrane depolarization causes an action potential that is transmitted, via the olfactory and trigeminal nerves, to the brain. While it is known that humans possess between 10 and 20 million olfactory sensory neurons, each expressing one of more than 400 different olfactory receptors, the mechanisms by which their activity translates to sensory odor perception are not well understood.

The trigeminal system is a chemical sense involved in the perception of somatosensory sensations, such as touch (e.g., itching, tickling), temperature (e.g., cooling, warming), and pain (e.g., burning, stinging) and involves activation of the trigeminal nerve endings. Because most odorants that stimulate the olfactory system also stimulate the trigeminal system, their trigeminal effects cannot be ignored.

Meat flavor

Meat flavor develops primarily during cooking. Though almost devoid of flavor, raw meat contains nonvolatile components that provide all five basic tastes (salty, sour, bitter, sweet, and umami) as well as the necessary flavor precursors that contribute to the characteristic flavor of cooked meat. These flavor precursors can be either water-soluble (amino acids, peptides, nucleotides, carbohydrates, etc.) or lipid components. During thermal processing, very complex interactions between these precursors, as well as their thermal degradation, give rise to a large number of flavor compounds, which lead to a wide variety of different flavors.

The types and concentrations of specific flavor compounds formed will depend on factors such as (i) the types and concentration of taste compounds and nonvolatile precursors of aroma components present in the meat, (ii) thermal processing conditions such as temperature, time, and humidity (in other words, the cooking method), and (iii) the presence of nonmeat ingredients, such as sugars, spices, flavorings, or smoke. In order to have a better understanding of meat flavor, let us focus on its two primary determinants, taste and aroma.

Taste

The majority of taste compounds in meat are nonvolatile, low–molecular-weight components, typically amino acids, organic acids or their salts, and inorganic salts. Collectively, these components provide all five basic tastes: sweet, sour, bitter, salty, and umami. Hydrophilic peptides provide sweetness; hydrophobic peptides contribute sourness and bitterness; inorganic salts and salts of glutamate and aspartate are associated with saltiness; certain 5'-nucleotides (e.g., 5'-inosine monophosphate and 5'-guanosine monophosphate), amino acids and their salts (e.g., glutamic acid and monosodium glutamate), and certain peptides provide umami taste. Umami compounds do not possess unique characteristic flavors but can enhance, potentiate, or modify existing flavors. They have also been described as “savory,” “beefy,” or “brothy”.

Aroma

Over 1,000 volatile aroma compounds have previously been identified in beef, pork, chicken, and mutton. They include many types of organic compounds, such as hydrocarbons, alcohols, carboxylic acids, aldehydes, ketones, esters, lactones, ethers, furans, pyridines, pyrazines, pyrroles, oxazoles, oxazolines, thiazoles, thiazolines, thiopenes, and other sulfur- and halogen-containing compounds.

These volatiles form during thermal processing by the interactions of nonvolatile, low–molecular-weight precursors, such as amino acids, peptides, reducing sugars, nucleotides, vitamins, and unsaturated fatty acids, through a series of many complex reactions. The most important of these reactions are the Maillard reaction; oxidation and degradation of lipids; thermal degradation of vitamins (primarily thiamin), sugars (including caramelization), and ribonucleotides; pyrolysis of amino acids and peptides; and interactions of Maillard reaction products with lipids.

Although the number of identified volatile compounds in meats is very large (>1,000), only a relatively few have been shown to contribute “meaty” aromas. A few others contribute notes such as buttery, caramel, roast, burnt, sulfurous, green, fragrant, oily/fatty and nutty — and have thus been designated as “aroma modifiers” — and the majority are considered to be relatively unimportant. For instance, only 25 of 880 aroma compounds in cooked beef have been described as possessing a meaty aroma. The most important meat flavor volatiles are sulfur-containing compounds that occur at low concentrations but have odor detection thresholds that are very low and lipid-derived volatile compounds, which have higher aroma thresholds. The former are predominant in meat cooked at temperatures greater than 149°C (300°F), whereas the latter predominate in meat cooked to lower temperatures. Therefore, both sulfur-containing flavor precursors (e.g., the amino acids cysteine, cystine, and methionine; the peptide glutathione; and thiamin) and fatty acids are very important.

It has been observed that most basic “meaty” aroma compounds are common to meat from various animal species, because flavor precursors from different animal species are roughly similar. Noteworthy among these are the thiol-substituted furans (furanthiols) and thiophenes (thiophenthiols), which form from the reaction of cysteine and ribose via the Maillard reaction and the thermal degradation of thiamin and that provide strong meaty and roast aromas and very low odor threshold values. As would be expected, there are flavor compounds that are responsible for flavor differences across animal species. These are believed to result primarily from degradation of the meat’s phospholipid fraction, and from the interaction of this fraction with other meat components.

Flavor of cured meats

It has been thought for some time that nitrite’s antioxidant properties are involved in cured meat flavor formation. It was first postulated in 1965 (Cross and Ziegler) that the flavor of cured meat is derived from non-lipid precursors, whereas the flavor of uncured cooked meat is heavily dependent on carbonyl compounds (hexanal and others) that result from lipid oxidation. In subsequent years, it was shown that cooked cured meat contains fewer volatiles than uncured cooked meat, due mostly to a significant reduction in the number and relative concentrations of the carbonyls and hydrocarbons that are normally found in cooked meat.

Therefore, it was proposed that nitrite affects meat flavor by inhibiting lipid oxidation during cooking (and therefore formation of these carbonyls), as well as warmed-over flavor. However, it has been pointed out that if cured meat flavor were the result of the antioxidant activity of nitrite alone, other commonly used antioxidants would also generate it, but they do not, suggesting that it is due to more complex reactions of nitrite in the meat matrix.

More recent research on ham confirms a nitrite-induced reduction in hexanal, in the highly odorous thiamin-derived sulfur-containing compound 2-methyl-3-(methyldithio)furan, and in overall odor intensity (attributed to fatty acid oxidation products) but not in perception of aroma compounds derived from degradation of sulfur-containing precursors. These authors hypothesized that nitrite does not affect the production of specific flavor compounds, but rather that the higher levels of hexanal in nitrite-free ham mask the “cooked ham” flavor notes that would otherwise be present in hams without nitrite. This does not, however, rule out the possibility that intermediates formed by the reaction of nitrite with other flavor precursors are associated with cured meat flavor, as previously proposed.

— By Rodrigo Tarté, Ph.D., assistant professor, Department of Animal Science, and director of certificate studies in meat science, Iowa State University

Editor’s note: This is part of an occasional series of exclusive articles provided by authors commissioned by the American Meat Science Association in cooperation with Meatingplace. The article is taken from a presentation given at the AMSA 74^th Reciprocal Meat Conference (RMC) August 2021 and excerpted from the review paper published in the AMSA journal Meat and Muscle Biology.

The AMSA staff and host team are planning for an impactful, educational and exciting 75th RMC set to take place June 12-15, 2022 in Des Moines, Iowa. Get program details here.

AMSA Exclusive: Leveraging understanding of meat flavor for product success, Part 1

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