Understanding the changes in the bread component of ready to eat sandwiches where consumers observation of 'Dry and Stale' limits shelf lifeTools Fragkiadaki, Evgenia (2018) Understanding the changes in the bread component of ready to eat sandwiches where consumers observation of 'Dry and Stale' limits shelf life. MRes thesis, University of Nottingham.
AbstractThis research constitutes a scientific insight to consumers’ feedback indicating that the bread in two commercial ready-to-eat sandwiches becomes drier over storage. These sandwiches were i) ham, mustard and mayonnaise sandwich and ii) ham, farmhouse cheese and pickle sandwich. The techniques used in this project were Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Fourier Transform Infrared spectroscopy (FTIR). The provided sandwiches were packaged and cut in two equal triangles following the shape of the packaging. They were stored at 4°C and each day a different sandwich was used for analysis. During sample preparation, sandwich bread was isolated from the filling and the applied barrier (signature mustard & mayonnaise for the ready-to-eat ham, mustard and mayonnaise sandwich and butter and ploughman’s pickle layered on top of the one slice and signature 30% mayonnaise for the other slice of the ready-to-eat ham, farmhouse cheese and pickle sandwich). Samples of bread were taken from three different parts of the sandwich, namely two different samples were isolated from the slices that were in contact with the packaging and one from the slices that were in the middle of packaging. In the case of the ready-to-eat ham, mustard and mayonnaise sandwich, the analysis was taken over 4 days. A considerable increase in total amount of water in all the three samples acquired from the ready-to-eat ham, mustard and mayonnaise sandwich was noticed (oven drying results) and it is probably related to moisture migration from mustard and mayonnaise sauce to sandwich bread over storage. A significant increase of in the FW fraction and a decrease in the UFW fraction (DSC results) was monitored only in the case of middle slices of bread. TGA results detected a higher water release rate in the case of middle slices and in the one slice that was in contact with the packaging, while for the other the results were inconclusive. An upward trend in the amylopectin melting enthalpy in all samples indicated starch retrogradation over storage. Analysis of samples from the ready-to-eat ham, farmhouse cheese and pickle sandwich was taken over 3 days. The slice of bread spread with signature 30% mayonnaise showed an increase in the total amount of water (oven drying results) and an upward trend in water release rate over storage (TGA results). The slice of bread spread with butter exhibited a decrease in the same variable while the TGA results were inconclusive. FW, UFW and amylopectin melting enthalpy were statistically equal over storage. Changes in starch crystallinity could not be detected through FTIR technique for none of the samples. Overall, experiments in ready-to-eat ham, mustard and mayonnaise sandwiches implied that despite the physicochemical changes in water, amylopectin retrogradation is probably the main reason for the drier texture of sandwich bread, while consumers’ feedback on ham, farmhouse cheese and pickle sandwich could not be experimentally explained.
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