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Degradation of Secalins During Rye Sourdough Fermentation

¹University of Helsinki, Department of Food Technology, PO Box 66, FIN-00014 University of Helsinki, Finland. ²Corresponding author. E-mail: jussi.loponen@helsinki.fi ³Current address: Suomen Viljava Oy, Finn Cereal, Kielotie 5 B, FIN-01300 Vantaa, Finland.

Rye sourdough (RSD) gives rye bread mildly acidic taste and desired flavor. Flavor precursors (amino acids and small peptides) are generated in the proteolytic breakdown of rye proteins. Our aim was to study the protein degradation during RSD fermentations. Two sourdoughs were prepared of flours derived from two rye cultivars (Amilo and Akusti). RSD samples were collected during fermentations. Three protein fractions were obtained by sequential protein extraction and these were analyzed by SDS-PAGE. Free amino nitrogen (FAN) was measured with a ninhydrin method. In addition, two rye incubations without starter microorganisms (with antibiotics) were made at pH 3.6 and 6.1, and proteinase profiles of the rye cultivars were analyzed at pH 4.3. SDS-PAGE analysis showed that during RSD fermentations, rye proteins, especially the alcohol-soluble secalins, were degraded. Secalins also evidently degraded during the incubation without starter microorganisms at pH 3.6. Aspartic proteinases were in the major proteinase group in both rye cultivars. This study confirms that endogenous proteinases of rye, mainly aspartic proteinases, hydrolyze rye proteins, especially secalins, during RSD fermentation. Protein degradation in rye sourdoughs may thus be enhanced by selecting rye flours with high proteolytic activity toward secalins.