A denosine triphosphate (ATP) is the principal energy source for cellular processes. When cellular activity ceases, ATP is naturally depleted through a combination of autolytic enzyme and bacterial action that sequentially degrade ATP into smaller nucleoside and purine end products starting with adensoine diphosphate (ADP) and following progressively through adenosine monophosphate (AMP), inosine monophosphate (IMP), Inosine (Ino), and hypoxanthine (Hx) respectively (Figure 1).
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Explore this issueApril/May 2015
Because these catabolites are produced early post-mortem, their measurement in animal tissue can determine food QC parameters such as muscle age and storage time, important indicators of freshness. The quantity of these nucleotides in tissue products can also influence sensory attributes, such as taste and texture.
The freshness of fish tissue was first quantified by a Japanese team of food scientists more than 50 years ago using a six parameter equation that solved to a value K based on all of the freshness pathway products shown in Figure 1. Another team of Japanese scientists later abbreviated this to a three parameter equation solving for a Ki (%) value by using the latter stage catabolites of IMP, Ino, and Hx (Figure 2). The %IMP and %Hx can be expressed as an equivalent freshness index by their relationship in Ki such that the higher the %IMP the fresher the fish, whereas higher %Hx values indicate a transition from freshness to spoilage in muscle tissue.
Recently, the Precice Freshness assay has been developed by NovoCIB that quantifies the levels of these three latter catabolites in a microplate format by enzymatic conversion of each catabolite to nicotinamide adenine dinucleotide (NADH), which can be measured colorimetrically at 340 nanometers using a microplate reader. Figure 2 illustrates the methodology used in the microplate assay.