Application of Fluorescence Spectroscopy for Monitoring Changes in Nonfat Dry Milk During Storage

Maillard emission (a), Maillard excitation (b), tryptophan emission (c), and riboflavin emission (d) spectra of the NDM samples before storage. The curves represent 3 samples each (1, 2, and 3) from each of 3 manufacturers (A, B, and C).

Factor loadings of the first 2 principal components (a) and similarity map (b) of principal component analysis (PCA) made on Maillard emission spectra of the NDM samples before storage. The lines in (a) indicate: PC1 (solid) and PC2 (dotted). The symbols in (b) represent the 9 samples collected from manufacturer A (♦), B (■) and C (▴) (3 from each manufacturer).

Factor loadings of the first 2 principal components (a) and similarity map (b) of principal component analysis (PCA) made on Maillard excitation spectra of the NDM samples before storage. The lines in (a) indicate: PC1 (solid) and PC2 (dotted). The symbols in (b) represent the 9 samples collected from manufacturer A (♦), B (■) and C (▴) (3 from each manufacturer).

Factor loadings of the first 2 principal components (a) and similarity map (b) of principal component analysis (PCA) made on tryptophan emission spectra of the NDM samples before storage. The lines in (a) indicate: PC1 (solid) and PC2 (dotted). The symbols in (b) represent the 9 samples collected from manufacturer A (♦), B (■) and C (▴) (3 from each manufacturer).

Factor loadings of the first 2 principal components (a) and similarity map (b) of principal component analysis (PCA) made on riboflavin emission spectra of the NDM samples before storage. The lines in (a) indicate: PC1 (solid) and PC2 (dotted). The symbols in (b) represent the 9 samples collected from manufacturer A (♦), B (■) and C (▴) (3 from each manufacturer).

Fluorescence spectra of NDM samples before storage and samples stored at 50°C for 1, 2, 4, and 8 wk. (a) Maillard emission spectra, (b) Maillard excitation spectra, (c) tryptophan emission spectra, (d) riboflavin emission spectra.

Principal component analysis (PCA) made on Maillard emission spectra of the NDM samples: (a) Similarity map of the NDM samples before storage and after storage at 4, 22, 35, and 50°C (C in key) for 1, 2, 4, and 8 wk (W in key); (b) factor loadings of the first 2 principal components; the lines in (b) indicate: PC1 (solid) and PC2 (dotted).

Principal component analysis (PCA) made on Maillard excitation spectra of the NDM samples: (a) Similarity map of the NDM samples before storage and after storage at 4, 22, 35, and 50°C (C in key) for 1, 2, 4, and 8 wk (W in key); (b) factor loadings of the first 2 principal components; the lines in (b) indicate: PC1 (solid) and PC2 (dotted).

Principal component analysis (PCA) made on tryptophan emission spectra of the NDM samples: (a) Similarity map of the NDM samples before storage and after storage at 4, 22, 35, and 50°C (C in key) for 1, 2, 4, and 8 wk (W in key); (b) factor loadings of the first 2 principal components; the lines in (b) indicate: PC1 (solid) and PC2 (dotted).

Principal component analysis (PCA) made on riboflavin emission spectra of the NDM samples: (a) Similarity map of the NDM samples before storage and after storage at 4, 22, 35, and 50°C (C in key) for 1, 2, 4, and 8 wk (W in key); (b) factor loadings of the first 2 principal components; the lines in (b) indicate: PC1 (solid) and PC2 (dotted).