Viscoelastic characterization of quality changes during staling of white bread | |
| Author | Chitsukon Puttanapichean |
| Call Number | AIT Thesis no.FB-04-05 |
| Subject(s) | Viscoelastic materials Bread |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. FB-04-05 |
| Abstract | The viscoelastic behaivor of bread was evaluated from the commonly used indentation test, creep and stress relaxation tests. The effects of experimental test conditions were investiged for each method. For indentation, crusted and crustless sample with 12, 24, and 36 mm thickness were evaluated to study the effect of slice thickness and the presence of crust on the modulus of elasticity. Four different indenter diameters of 10, 20, 30, and 36 mm were used to evaluate its effect on the modulus of elasticity determined from uniaxial test. Bread samples were tested from initial stress levels of 0.4, 0.5 and 0.6 N at crosshead speed of 200 mm/min for creep testing. Initial strains of 5%, 10% and 15% at two different crosshead speeds of 5 and 200 mm/min were used for stress relaxation testing. Several techniques for analyzing experimental stress relaxation data were investigated using the data obtained from the tests with the crosshead of 5 mm/min. The modulus of elasticity of bread was influenced by slice thickness but presence of the crust did not apparently affect it. The increase in the diameter of indenter resulted in a progressive increase in the values of tangent modulus for all compression levels, and the tangent modulus obtained form indentation test was higher than that obtained from uniaxial test. The trends of changes in the tangent modulus evaluated from uniaxial test were similar to the changes in the tangent modulus obtained from compression by 30 and 36 mm indenters. The creep responses were adequately represented by the four-element model with the R2 values ranging from 0.995 to 0.998. The initial stress did not affect the viscoelastic parameters. The individual stress relaxation curves were fitted with a fiveelements Maxwell model using the conventional and modified approaches. The conventional and the modified fittings showed similar results with R2 = 0.9963 to 0.9981. However, the modified equation resulted in improved values of viscoelastic parameters. The actual ramp responses were better fitted when using the parameters determined from the modified equation in comparison with the conventional equation with R2 of 0.974 and 0. 726, respectively. The changes in the texture of bread stored at 5, 15, 25 and 35°C were investigated on 0, 1, 3, and 5 days after baking in terms of initial and tangent moduli in indentation test, and elasticity and viscosity parameters in creep and stress relaxation tests. The creep and stress relaxation responses of individual bread sample were represented by the fourelements Burger model and the modified stress relaxation equation (R2 = 0.991 to 0.999). The values of all viscoelastic parameters increased with an increase in storage time and decreased with increasing storage temperature. The test parameters were fitted with an appropriate function of temperature and time with the R2 values ranging from 0.8686 to 0.9621. The accuracy and the potential in monitoring and comparison of each test parameter was based on the values of R2 • A comparison of initial and tangent modulus from indentation test and creep test indicated the tangent modulus to be more accurate. Based on an overall comparison, the parameters from stress relaxation test were found to be the most accurate in describing the textural changes during staling of white bread. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. FB-04-05 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Jindal, Vinod K.; |
| Examination Committee(s) | Athapol Noomhorm; Rakshit, Sudip K. ; |
| Scholarship Donor(s) | Royal Thai Government Fellowship |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2004 |