Fig. 3

Principal component 6 loading spectrum extracted from long-term treatment application first derivative spectral dataset for the stall length and manger wall trial. Shaded regions can be assigned as follows: 1–3) peaks at ~ 1033, 980 and 946 cm⁻¹ are found in FTIR spectra of milk samples spiked with histamine and BHB and their aqueous solutions, 4) peak at ~ 1408 cm⁻¹ is observed in FTIR spectra of milk samples spiked with BHB, 5) peak at ~ 1460 cm⁻¹ is observed in FTIR spectra of milk samples spiked with urea and ammonium, 6) peak at ~ 1575 cm⁻¹ is observed in FTIR spectrum of histamine in aqueous solution.