Open Access
Yao, Ni
Graduate Program:
Food Science
Doctor of Philosophy
Document Type:
Date of Defense:
October 06, 2004
Committee Members:
  • Koushik Seetharaman, Committee Chair
  • John D Floros, Committee Member
  • Richard K Owusu Apenten, Committee Member
  • Joseph Irudayaraj, Committee Member
  • Drying
  • Extrusion
  • Flour
  • Dough
  • Screening
  • Optimization
  • Alkali
  • Pretzel
  • Baking
Pennsylvania ranks first in the nation in the production of snacks including potato chips and pretzels with over 23 pretzel-manufacturing companies in Pennsylvania, that contribute significantly to the rural economy. Despite technical advances in hard pretzel production since the 1980s, which include several patents granted for new methods in hard pretzel manufacturing, very little research has been conducted with regard to raw materials and process conditions on pretzel shelf life and quality. Based on a previous research to understand the causes of pretzel breakage, research elaborated in this dissertation was initiated first to evaluate flour property variation used in hard pretzel manufacturing, and then progressed with the development of a statistical model for optimizing process parameters in an effort to enhance the quality and consistency of the product. Seetharaman et al (2004) reported that water played an important role in controlling hard pretzel breakage. Pretzel quality appeared to be a function of appropriate gluten development and starch gelatinization in the product. In investigating the causes for differences in pretzel qualities under similar levels of water addition, as is the practice in the industry, we evaluated the variation in flour properties received at various companies. Studies indicated that significant variations existed in flour properties. The properties of hard pretzels made by using flours with different protein contents indicated that hard wheat flour would produce a harder pretzel but would not affect the surface color of final product. However, soft wheat flour with a lower amount of damaged starch, low water absorption levels and lower water binding powers was found to be desired for making hard pretzels. The significant variations in flour properties revealed in this study suggest that a more thorough understanding of the effects of processing steps on the pretzel quality is necessary. Since obtaining flours with prescribed quality is not a practical consideration for small-sized, low profit-margin pretzel companies, research was launched to see if the variability in flour properties could be accommodated by manipulating process conditions. Therefore, a screening experimental design was used to identify critical processing parameters influencing pretzel quality. Eleven process variables were selected and a two-level-eleven-factor (211) fractional factorial experimental design was used to screen a variety of process variables. Several responses were measured for dough before and after extrusion, for half-baked and fully baked pretzels. The responses selected are important indicators of consistency and quality during pretzel production. Results indicated that flour protein content, the amount of water added to make dough, and dough mixing time were important variables influencing dough behavior. Caustic concentration affected the brightness of half-baked pretzels but did not influence the color of final products. Baking time was the most important factor for both half-baked and final product quality. The hardness of fully baked pretzels was influenced by baking time, temperature in baking oven zone 1, drying time and drying temperature under the experimental conditions investigated in this study. A key observation of this study was that none of the raw material or dough processing parameters, within the range tested, influenced final pretzel quality as defined by pretzel moisture content, hardness or color. Based on the above results, four process parameters; baking time, temperature in baking oven zone 1, drying time and drying temperature, were further selected for optimization. Desirability Function Approach (DFA) was applied in optimizing multiple responses including moisture content, ∆Eab value and pasting time. Hardness was not included in the analysis since the model was not significant although the transformed model was significant. Although process parameters showed a significant effect on hardness of final products in screening experiment design, under the narrow range of values used in the optimization design, the four processing parameters did not show significant effects on pretzel hardness. The analysis of variance for the eight responses indicated that models developed did not show significant lack of fit except for color a* values. The models for moisture content, ∆Eab value and pasting time explained 99%, 87% and 91% of the variability, respectively. The coefficients of each response showed baking time had a significant effect on each response measured, while the other factors had a minor effect on the responses. Most of the interaction effects were not significant. The overall effect analysis of the four parameters on the responses also suggested that baking time had the most significant impact on all responses investigated among the four factors. Validation experiments results revealed that the two most important qualities of pretzel, moisture content and ∆Eab, can be reliably predicted, but pasting time was not predicted reliably. The study showed that Response Surface Methodology was effective in producing predictive models and establishing relationship between processing factors and key responses of hard pretzel production. DFA was an effective and convenient multiple response optimization method in achieving different optimization goals. Effects of alkali cooking on starch, protein and color changes in products were also investigated in this study. Experiments were conducted in the laboratory to mimic reactions occurring on the pretzel surface and also in a pilot plant with products. Surface starch granules were gelatinized following treatment with alkali or water at 80„aC, but the interior of the product was not gelatinized when treated with hot alkali or water at the pilot plant. Furthermore, the amylose-lipid complex dissociated even at low temperature of alkali treatment, but the dough hydration property did not show a significant increase until the temperature increased to 80„aC. Dough surface color after dipping was different but was not significantly different following baking when pigments were extracted from the flour. The results suggest that significant changes occur following treatment with alkali. The development of pretzel color could not be attributed to any pigments present in the flour but possibly is due to reactions within or between the starch or protein hydrolysis derivatives during baking.