Application of the Freshness Quality Index (K Value) for Fresh Fish to Canned Sardines from Northwestern Mexico

Adenosine triphosphate (ATP) and its breakdown products (ADP, AMP, IMP, HxR, Hx) contents in three commercial brands of canned sardine from Northwest Mexico were determined by HPLC. From this data the so called “K” value (a freshness quality index) was calculated. A homogenate of sardine extract in 0.6Mperchloric was used for the separation in a simple run on a μBondapak RP-C18 commercial column. The six compounds were separated in 12 min. The retention time of nucleotides could be measured within +0.2 relative standard deviation (CV < 2.2%). The coefficient of variation of the relative peak areas and calibration factors, based on the external standard calculation methodology were within 6% or less. Canned sardines from the different commercial brands showed aKvalue in the range from 34.7 to 56.3%. Even though processors claimed that sardines are canned prior to 36 h postcatch, results suggested that the fish processed had an equivalent biochemical age at 0°C, from 9 to 15 days postcapture at the time of processing. The methodology should be useful for measuring the original freshness of canned fish and as indicator of postcapture handling operations.