Food freshness indicator ink and method for the manufacture of a food freshness indicator ink

1. A food freshness indicator ink, which comprises:

i) a varnish that constitutes between 90-98 weight % of the total ink, said varnish comprising

i.1) between 5-25 weight % of the total amount of the varnish of at least one film-forming resin or at least one vinylic resin or a mixture thereof;

i.2) between 10-25 weight % of the amount of the resin of a plasticiser additive; and

i.3) between 50-75 weight % of the total amount of the varnish of solvents, and

ii) between 2-10 weight % of the total ink being metallic salts.

2. The ink, according to claim 1 , wherein the viscosity of the base ink measured in a Ford Cup No. 4 (FC/4) is 10″-50″ at 20° C.

3. The ink, according to claim 1 , wherein the resin is a resin derived from cellulose.

4. The ink, according to claim 3 , wherein the cellulose derived resin is selected from a wetted nitrocellulose, ethyl cellulose and cellulose aceto-propionate.

5. The ink, according to claim 1 , wherein the solvent is selected from ethyl alcohol, ethyl acetate, n-propyl alcohol, n-propyl acetate, ethoxypropanol, methoxypropanol and mixtures thereof.

6. The ink according to claim 1 , wherein the solvent is selected from a mixture of ethyl alcohol-ethyl acetate, a mixture of n-propyl alcohol-n-propyl acetate, a mixture of ethyl alcohol-ethyl acetate-methoxypropanol and a mixture of ethyl alcohol-n-propyl acetate-ethoxypropanol.

7. The ink according to claim 1 wherein the plasticizer additive is acetyl tributyl citrate.

8. The ink according to claim 1 , wherein the metallic salts are selected from copper and iron salts.

9. The ink according to claim 1 wherein the metallic salts are selected from copper carbonate and iron nitrate.

10. A method for the manufacturing of a food freshness indicator ink, the method comprises:

a) preparing a varnish by mixing at least one vinylic resin or at least one film forming resin or a mixture thereof, with at least one plasticizer additive that is compatible with the resin, the whole being added to a solvent mixture and stirred until complete solubility, the resin being between 5-25 weight % of the total varnish, the plasticizer additive between 10-25 weight % of the amount of resin and solvents between 50-75 weight % of the total varnish;

b) preparing a concentrated base ink by adding to the varnish a metal salt, wherein said metal salt is added under slow stirring in the varnish, all the components being stirred subsequently and defining a concentrated base ink, the metal salts being 15-30 weight % and the varnish being between 70-85 weight %, of the total of the ink;

c) milling the dispersion obtained in step b) in a bead-mill until a dispersion of uniform particle-size distribution smaller than 5μ is obtained;

d) diluting the concentrated base ink thus obtained in the varnish made in step a), to a metallic salt concentration between 2 and 10% of the total weight of the ink.

11. The method, according to claim 10 , wherein the stirring step b) is performed at 1200 rpm for at least 15 minutes.

12. The method, according to claim 1 , wherein the milling step is performed in a bead mill with microspheres of zirconium/yttrium oxide for 30 minutes.

13. A label comprising the food freshness indicator ink as defined in claim 1 for detecting gaseous substances comprising sulphur-containing compounds and formed by microbial food spoilage.

14. The label according to claim 13 , wherein the label is formed by printing the food freshness indicator ink on a porous substrate or a polymeric matrix.

15. A food package comprising a label as defined in claim 13 .