Flavor-improving agents

PROBLEM TO BE SOLVED: To provide a novel food or drink flavor improving agent that is a means capable of easily reproducing a taste of richness because time and cost are necessary in order to industrially reproduce the taste of richness, and that can impart the flavor that does not last more than necessary, and can easily impart the taste of richness that does not last more than necessary, that is, an un-insistent taste of richness and a taste of richness with good cleared aftertaste.SOLUTION: Provided are: a heat reaction product obtained by making a D-amino acid or D-amino acid residue-containing peptide or a salt thereof, and a carbonyl compound coexist and heating them, and a production method of a flavor improving agent comprising the heat reaction product. The D-amino acid or D-amino acid residue is a compound that has a side chain selected from aliphatic side chains, hydroxyl group-type side chains, basic side chains, amide side chains, acidic group-type side chains and aromatic type side chains, and the carbonyl compound is a reducing sugar, or a compound produced by the oxidation of lipids.