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K-Value (or K-Factor) is recognized for several decades as the most effective and objective indicator of the freshness of fish and seafood products (as well as of meat: beef, pork, lamb and poultry). However, no reliable and efficient system for measuring K-Value has ever been developed and marketed for a routine use by professionals of the Seafood Industry... Until now! By developing its PRECICE® K-Freshness Assay Kit, NOVOCIB is the first company to offer a very easy to use, reliable and sensitive spectrophometric system (patented) for an objective measurement of the freshness of fish product by K-Value. For a detailed description of PRECICE® K-Freshness Assay Kit
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What is K value?
How do nucleotides indicate the freshness level of flesh?
ATP (adenosine triphosphate) is the major energy currency in cell. Its content is particularly high in muscle tissue where ATP is used to power contraction. As soon as an animal dies, cell respiration stops as well as ATP formation. Once the rigor mortis stage is reached, within minutes to few hours after the animal has been slaughtered, ATP pool starts being progressively and sequentially depleted through a succession of reactions, as shown on the following figure.
Post-mortem ATP degradation in fish and subsequent formation of IMP, Inosine (Ino) and Hypoxanthine (Hx).
Post-mortem ATP depletion is mainly due to autolytic reactions and controlled by endogenous enzymes, even if the microbial flora, when developed enough, may contribute to the process. This makes the level of ATP degradation an excellent criterion for fish freshness measurement and storage age, before microbial spoilage starts and the corresponding traditional techniques for spoilage measurement become relevant.
The K value concept
In the late 1950's, a Japanese research team (Saito et al.) proposed a new concept, called "K value", for the indication of the freshness of fish flesh. The K value is based on ATP breakdown and the subsequent formation of its by-products, namely adenosine diphosphate (ADP) and monophosphate (AMP), inosine monophosphate (IMP), inosine (Ino) and, at a later stage, hypoxanthine (Hx). The K-value measures how far ATP degradation has progressed within the tissue. It is expressed as a percentage of the content of the last two final compounds resulting from ATP catabolic pathway, i.e. Ino and Hx, over the total content of ATP and its degradation by-products: ATP, ADP, AMP, IMP, Ino and Hx.
However, because ATP decomposes very quickly to IMP in most animals, a simplified K value (generally called Ki value) was soon proposed by Karube et al. (1984) and is currently considered as equivalent to the original 6-parameter equation for K-value.
| K (%) = | Ino + Hx | The K value is recognized for several decades
as the most effective and objective indicator of the freshness of fish and seafood products, as well as of meat (beef, pork, lamb and poultry). |
| IMP + Ino + Hx |
The lower the K-value, the fresher the fish.
K value offers an additional key-advantage over other freshness criteria: K value is based on the content of the by-products resulting from ATP breakdown. Since IMP), Ino and Hx are stable to heating or freezing, K value can be measured on fresh, frozen or even cooked fish products.
(^Top) Why and when measuring K-value?
Freshness is the most important quality criteria regarding fish and seafood products. If freshness can be quite easily checked on entire crude and chilled finfish by sensory analysis, freshness control remains puzzling when considering transformed fish, for instance.
Current CQ analytic tools, such as TVBN or TMA, are routinely used but they are based on the biochemical changes that appear when spoilage has started, and can be relevant for a medium- or a late-stage of the process. However, since ATP depletion is the very first biochemical process that occurs once a fish has died, long before spoilage starts, K-value changes concern the early stage of fish transformation and storage and allows professionals to anticipate the beginning of spoilage (e.g. TVBN formation) and to better control the "high" freshness level of the product.
In other words, K-value is the choice freshness marker at the early stage of the process.
Most of Japanese researchers consider that raw fish can be eaten as sashimi when the K-value is up to than 20%.
Please, contact us for any questions.
| Related Links |
| • PRECICE® K-Freshness Assay Kit: Overview
• Assay Kit description |