首页|Understanding freezing-induced changes in the protein and fat phases of aged Gouda cheese using Fourier transform infrared and Raman spectroscopy
Understanding freezing-induced changes in the protein and fat phases of aged Gouda cheese using Fourier transform infrared and Raman spectroscopy
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NETL
NSTL
Elsevier
Freezing and thawing are known to cause structural modifications in proteins and fats at a molecular scale. How these modifications affect the texture and functional attributes of cheeses is not fully understood. Thus, the impact of frozen storage (FrS: -18 degrees C, 3 months) and rapid freeze-thawing cycles (FTC: 1 to 5 cycles from -18 degrees C to 6 degrees C) on the proteins and lipids in aged Gouda cheese was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and Raman spectroscopy. Both FrS and FTC treatments significantly increased the n-sheet and n-turn structures compared to unfrozen control samples, while random structures were reduced significantly. However, FTC treatment caused significantly greater increases in n-sheets and a decline in random structures than FrS treatment. Raman spectroscopy indicated higher sensitivity for alpha-helices and n-turns, with notable differences in n-sheets and random coils as compared to infrared analysis. Also, repeated FTC treatment (3-5 cycles) induced structural stability in the polypeptide backbone. Repeated FTC treatment (3-5 cycles) also caused fat coalescence and increased fluidity in the hydrocarbon chain of lipids. This was supported by an observed increase in the fat pools in FTC (3-5 cycles) samples from confocal laser scanning micrographs and an increase in the melting and oiling-off properties. Principal component analysis on the second derivative of FTIR and Raman spectra clearly indicated the differences in FTC and FrS freezing treatments. The textural attributes of cheese had moderate positive and negative correlations with total n-sheet and random coils fraction, respectively. No correlation of functional attributes (melting and oiling-off) of cheese with protein secondary conformations could be found. Overall, this study explains how freezing affects the protein and lipid phases of cheese and how these changes influence its texture and functionality.
NETL
NSTL
Elsevier
