Lactosylated casein phosphopeptides as specific indicators of heated milks |
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Authors: | Pinto Gabriella Caira Simonetta Cuollo Marina Fierro Olga Nicolai Maria Adalgisa Chianese Lina Addeo Francesco |
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Institution: | (1) Department of Food Science- Faculty of Agriculture, University of Naples “Federico II”, via Universit? 100, Parco Gussone, 80055 Portici, Italy;(2) Food Science Institute of the National Research Council (C.N.R.), Via Roma, 83100 Avellino, Italy |
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Abstract: | Casein phosphopeptides (CPP) were identified in small amounts in milks heated at various intensities by using matrix-assisted
laser desorption/ionization (MALDI) time-of-flight mass spectrometry. CPP selectively concentrated on hydroxyapatite (HA)
were regenerated using phosphoric acid mixed in the matrix. Unphosphorylated peptides not retained by HA were removed by buffer
washing. This procedure enhanced the MALDI signals of CPP that are ordinarily suppressed by the co-occurrence of unphosphorylated
peptides. CPP, belonging to the β-casein (CN) family, i.e., (f1-29) 4P, (f1-28) 4P, and (f1-27) 4P, and the αs2-CN family, i.e., (f1-21) 4P and (f1-24) 4P, were observed in liquid and powder milk. The lactosylated counterparts were specific
to intensely heated milks, but absent in raw and thermized/pasteurized milk. Most CPP with C-terminal lysines probably arose
from the activity of plasmin; an enzyme most active in casein hydrolysis. A CPP analogue was used as the internal standard.
The raw milk signature peptide β-CN (f1-28) 4P constituted ~4.3% of the total β-CN. Small amounts of lactosylated peptides,
which varied with heat treatment intensity, were detected in the milk samples. The limit of detection of ultra-high-temperature
milk adjunction in raw or pasteurized milk was ~10%. |
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