L-citrulline is a non-essential (conditionally essential) amino acid micro nutrient that the body cannot produce in sufficient quantities typically under greater strain, therefore replenishment might become necessary. When it comes to fruit, citrulline is found in large quantities in watermelon, for example. The synergistic combination of L-citrulline amino acid and malic acid is L-citrulline malate. Malic acid (malate) is an organic acid, which can be found in nature (for example in apple). L-citrulline amino acid is what L-arginine and L-ornithine amino acids are made of.