Effect of Lactobacillus plantarum on functional characteristics and flavor profile of fermented walnut milk

Walnut milk is characterized by a high content of aldehydes which provide a heavier grassy taste and bad flavor for walnut milk. Mild fermentation can effectively modify the walnut milk flavor. To evaluate the effect of Lactobacillus plantarum LP56 on the free amino acids, the free fatty acids, and aroma compounds in the walnut milk after mild fermentation were analyzed using the amino acid analyzer, gas chromatography-flame ionization detector-mass spectrometry, and headspace-gas chromatography-mass spectrometry. Results showed that the contents of the sweet amino acids, umami amino acids, essential amino acids, and unsaturated fatty acids in the walnut milk reached up to 53.9 mg/L, 787.98 mg/L, 23.15 mg/L, and 2774.51 mg/L, respectively, after 12 h fermentation by Lactobacillus plantarum LP56. The flavor of the fermented walnut milk was improved with the increase in the umami compounds and sweet compounds, and the increase in unsaturated fatty acids content improved the functional characteristics of fermented walnut milk. The decrease in the aldehydes and the increase in the alcohols, acids, esters, and ketones promoted the aroma quality of walnut milk. The study provides a theoretical basis for the industrially producing fermented walnut milk.