This study aims to propose a new method for derivatizing fatty acids (FAs) from human milk (HM), eliminating the lipid extraction step, and simplifying the preparation for gas chromatography with a flame ionization detection (GC-FID) analysis to quantify the FAs. The Design Expert software optimized the reaction times, concentrations, and sample amount. The proposed method (PM) was validated for lyophilized HM and results for the figures of merit for precision in relative standard deviation (RSD) (RSDintra-day 1.34-4.03% and RSDinter day 2.08 5.16%), accuracy (99.87-102.16%), and robustness are within a linear range of 3 to 38% lipids in HM samples. The atmospheric solids analysis probe tandem mass spectrometry (ASAP-MS/MS) technique confirmed the efficiency of PM by expressing the molecular composition of triacylglycerol formed by FAs from the GC-FID technique. The PM requires a small sample size and conducts derivatization directly in the sample matrix, minimizing extraction errors. (FAs HM, , (HM) step GCFID GC FID (GC-FID times concentrations amount (PM RSD (RSD RSDintraday RSDintra 1.344.03% 134403 1.34 4.03% 1 34 4 03 1.34-4.03 208 2 08 2.0 5.16%, 516 5.16% 5 16 5.16%) 99.87102.16%, 998710216 99.87 102.16% 99 87 102 (99.87-102.16%) 38 samples ASAPMS/MS ASAPMSMS ASAP MS/MS MS (ASAP-MS/MS matrix errors (HM 344 1.344.03 13440 134 1.3 403 4.03 0 1.34-4.0 20 2. 51 5.16 87102 99.87102.16% 99871021 9987 99.8 10216 102.16 9 8 10 (99.87-102.16% ASAPMS MSMS 1.344.0 1344 13 1. 40 4.0 1.34-4. 5.1 8710 99.87102.16 9987102 998 99. 1021 102.1 (99.87-102.16 1.344. 4. 1.34-4 5. 871 99.87102.1 998710 102. (99.87-102.1 1.344 1.34- 99.87102. 99871 (99.87-102. 99.87102 (99.87-102 99.8710 (99.87-10 99.871 (99.87-1 (99.87- (99.87 (99.8 (99. (99 (9 (

The present work intends to obtain and characterize a milk by-product: the human whey (HW), in order to avoid the excessive disposal of human milk (HM). The characterization was performed through analyzes of the chemical composition and fatty acids (FAs) and the triacylglycerol (TAG) lipid profile. The results indicated that the chemical composition altered significantly after the HW obtained, except for the percentage of ash and carbohydrates. About the FA composition, it was observed that strictly essential FA, essential FA and other FAs found in HM remained present in HW. For the nutritional lipids quality, the atherogenicity and the thrombogenicity indices presented desirable values, and the TAGs lipid profile revealed a variation in the analyzed samples. Therefore, it can be concluded that the characterized HW has potential for application in isolated form or to be used as an ingredient in other foods.