Structure–functionality relationships of porcine plasma proteins probed by FTIR spectroscopy and texture analysis

FTIR spectroscopic and texture analysis studies were undertaken to elucidate the molecular basis of structure–functionality relationships of porcine plasma proteins in solution and the gel state at varying pH. At room temperature, porcine plasma proteins aggregated as a function of decreasing pH. A parallel decrease in the intensity of amide I′ bands at 1652 cm−1 in the infrared spectra of the protein solution (assigned to α-helix, predominant in serum albumin) and 1688/1638 cm−1 (assigned to intramolecular antiparallel β-sheet, predominant in immunoglobulins) along with an increase in the band at 1644 cm−1 (assigned to unordered or random structure) was observed to take place with decreasing pH. Bands assigned to intermolecular antiparallel β-sheet structures (1683 and 1617 cm−1) were observed in infrared spectra of porcine plasma protein solutions heated to the point of gel formation. Texture and water holding capacity were also very sensitive to pH. The results indicate that the lower the remaining native secondary structure and the faster the heat-induced aggregation (observed by FTIR spectroscopy) with decreasing pH, the weaker and more exudative the gels.