Probing the Structural Effects of Pasteurization and Spray Drying on Soy Protein Isolate in the Presence of Trehalose Using FT-IR-ATR and FT-Raman Spectroscopy

摘要

Fourier transform infrared-attenuated total reflectance (FT-IR-ATR) and FT-Raman spectroscopies were used to probe the effects of pasteurization and spray drying on the secondary structure of soy protein isolate (SPI). Deconvolution of the infrared Amide I band was accomplished using a curve-fitting method based upon a simple model and experimentally determined constraints. This method indicated 57percent beta-sheet and beta-turn, 5percent alpha-helix, and 38percent random coil for pasteurized, spray-dried SPI. These values are compared with those for "native" SPI, where "native" SPI is estimated using the weight-averaged values for native glycinin and beta-conglycinin. From this comparison, we conclude that pasteurized, spray-dried SPI contains less alpha-helix, more random coil, and similar amounts of beta-sheet relative to the "native" SPI. Problems with dispersibility of pasteurized, spray-dried SPI in beverages were attributed to denaturation of native alpha-helix segments of SPI with subsequent formation of aggregated beta-sheets. FT-IR-ATR and FT-Raman results showed that co-drying SPI with trehalose inhibits both the amount of protein denaturation and beta-sheet aggregation associated with pasteurization and spray drying. Because denaturation and aggregation are directly correlated to dispersibility (and other bulk properties), controlling these parameters will enable beverage manufacturers to produce products with greater consumer acceptability and improved shelf life.