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Abstract:

Pretzel production includes alkali dipping prior to baking to gelatinize the starch at the surface and to result in the desired smooth surface of the final product. Hard pretzels are typically dipped in 1.0 % NaOH at a temperature of about 90 °C for 10 to 60 s. Chemical changes during this treatment also result in the unique taste, and color of the end product. However, alkali treatment may also result in protein degradation and affect nutritional quality. Model system studies recently showed that beta-elimination reaction of cystine occurs when gluten proteins are heated at alkaline pH. As a follow up to that study, the objective of the present work was to investigate whether an alkaline treatment typical for that during pretzel production, would also affect the gluten at the surface of the product . Gluten/water dough and pretzel dough were dipped in NaOH solution [0.5, 1.0, or 1.5% (w/v)] for different times (30, 45, and 60 s) and at different temperatures (50, 65, 80, and 95 °C), and subsequently baked. Protein extractability and levels of intermediate and end products of beta-elimination reactions of cystine were determined in the dough before and after the alkali dip, and after baking. Protein extractabilities decreased during pretzel production, even after reduction of disulfide bonds, which indicated that some non-disulfide cross-links were formed. Further investigation showed that beta-elimination from cystine resulted in the formation of dehydroalanine, which reacted with cysteine and lysine to lanthionine and lysinoalanine, respectively. It was concluded that the concentration and temperature of the lye solution and the dipping time impact protein cross-linking and beta-elimination reactions during laboratory scale pretzel production.