Volatiles Production from Isoleucine in Fresh-cut Apple, Using Alginate Coatings As the Holding Matrix

Edible coatings (EC) have been successfully used for the preservation of fresh-cut apples, since EC create semipermeable barriers to gases and water vapor. EC are also potential carriers of additives that can help to preserve apple quality. Aroma is one of the main quality parameters in apples; naturally occurring fatty acids and amino acids are the main aroma precursors in this fruit. EC could be used as carriers of amino acids, to enhance the aroma of fresh-cut apple, where the fruit, through the amino acid pathway, could metabolize the amino acid contained in the EC to produce volatile aroma compounds (VACs). The objective of this work was to study fresh-cut apple wedges covered with alginate coatings formulated with isoleucine as a precursor for VACs. Fresh-cut apple wedges were first immersed in a CaCl2 solution followed by one of these EC: coating of pure alginate (ALG), alginate coating containing 10 mM isoleucine, or alginate coating containing 50 mM isoleucine, (LAA and HAA, respectively). Apple wedges were stored for 12 days at 4 °C and 85 % relative humidity. The development of VACs during storage was measured chromatographically utilizing HS-SPME by GC-MS. The presence of isoleucine caused an increase in the concentration of 2-methyl butanol, 2-methylbutyl acetate, butyl 2-methyl butanoate, and hexyl 2-methyl butanoate, which are branched VACs derived from the isoleucine metabolism. This increase was proportional to the amino acid content, showing higher values in HAA apples than in LAA ones. The concentration of branched VACs increased during storage for HAA and LAA apples getting the highest values at day 9 of storage, while control and ALG apples didn´t show any changes throughout the storage period. At day 9, 2-methyl butanol showed a concentration seven fold higher in HAA apples when compared to control ones.  The esters 2-methylbutyl acetate, butyl 2-methyl butanoate, and hexyl 2-methyl butanoate showed values 8, 4 and 1.6 fold higher, respectively, in HAA apples when compared to control wedges, at day 9. EC did not influence the production of straight chain volatiles since those VACs are synthesized by the fatty acid metabolic pathway. On the other hand, the content of the aldehydes hexanal and trans-2-hexenal resulted higher in control wedges, when compared to coated apples. EC containing isoleucine enhanced the production of the VACs derived from the isoleucine metabolic pathway. EC formulated with isoleucine have a great potential in the fresh-cut apple industry.