The objectives of this study were (1) to quantify the protein inherent molecular structural features of green cotyledon (CDC Striker) and yellow cotyledon (CDC Meadow) pea (Pisum sativum L.) seeds using molecular spectroscopic technique (FT/IR-ATR); (2) measure the denaturation of protein molecular makeup in the two types of pea during dry roasting (120°C for 60 min), autoclaving (120°C for 60 min) or microwaving (for 5 min); and (3) correlate the heat-induced changes in protein molecular makeup to the corresponding changes in protein digestibility determined using modified three-step in vitro procedure. Compared with yellow-type, the green-type peas had higher (P<0.05) ratios of amide I to II peak height (1.698 vs. 1.805) and area (1.843 vs. 2.017). A significant correlation was observed between the amide I and II peak height (r=0.48) and peak area (r=-0.42) ratio with protein content. Compared with yellow-type, the green-type peas had lower (P<0.05) α-helix:β-sheet ratio (1.015 vs. 0.926), indicating varietal difference in protein secondary structure makeup. All processing applications increased α-helix:β-sheet ratio, with the largest (P<0.05) increase being observed with roasting and microwaving. The heat-induced changes in α-helix:β-sheet ratio was strongly correlated to intestinal digestibility of protein within the green (r=-0. 86) and yellow (r=0.81) pea-types. However, across the pea types the correlation was not significant. Principal component and hierarchical cluster analyses on the entire spectral data from the amide region (ca. 1727-1480 cm(-1)) were able to visualize and discriminate the structural difference between pea varieties and processing treatments. This study shows that the molecular spectroscopy can be used as a rapid tool to screen the protein value of raw and heat-treated peas.
Keywords: Intestinal digestion; Processing applications; Protein molecular structures.
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