Staling and Starch Retrogradation in Speciality Bread
Abstract: Bread products are one of the most common and important foods in our daily diet, and have been since ancient times. Although it has a long history and comes in many variations, the staling phenomenon of bread is still not fully known. Staling is a complex phenomenon that includes all the physical and sensorial changes occurring in bread during storage. To gain a better understanding of staling, different additives were used in the studies that make up this thesis. The additives were divided into two groups according to their mechanisms, where they had either a direct or an indirect influence on the starch retrogradation. The additives that had a direct influence on the starch retrogradation were α-amylase, lipase and monoglycerides, whereas the additives gluten, oat, wheat and rye bran, waxy wheat flour, waxy barley starch, barley flour and pre-gelatinized barley flour, oat flour and waxy barley starch had an indirect influence on the starch retrogradation. The staling process was monitored by measuring the firmness, springiness, water migration and loss, cutability and crumbliness. However, since all these parameters are affected by the water content, starch retrogradation and/or amylose-lipid complex formation, additional measurements were performed regarding these attributes. A texture analyzer was employed for analyzing the firmness and springiness while the starch retrogradation and presence of amylose-lipid complexes were measured by a DSC. A 1H-NMR was also employed to give information on the water mobility and increased solid fraction. The bread was made using different baking processes - laboratory baking, industrial baking and in a household baking machine. Two different methods were used in the laboratory baking, where the loaves were baked either as freestanding or as pan-baked loaves. The results showed that small amounts of additives, with increased water absorption compared to wheat flour, could increase the water content in dough to various extents and, in most cases, also maintain the extra amount of water during the bread making. The pre-gelatinized additives had the greatest water absorption and displayed improved water maintaining capacity during both baking and storage of laboratory-baked bread. The water content and distribution was seen to be important for the softness of the loaves. For some recipes, greater water content was seen to give a softer crumb although higher amounts of starch retrogradation were detected. Both water content and firmness displayed a variation within the slices as a result of the water migration. The firmness was also found to correlate with the starch retrogradation, proton relaxation and specific volume although the correlations were dependent on the recipe of the bread. Furthermore, the firmness influenced the cutability which improved to a certain degree of firmness, after which it became constant. Both baking process and method were seen to be of great importance for the bread quality and staling. Industrially-baked bread lost more water during the bread making than bread baked in the other two baking processes. Furthermore, pan-baked loaves lost less water during both baking and storage and resulted in less firm bread although no differences were seen in the amount of starch retrogradation. The baking method showed a greater influence on the staling of the loaves than some of the used additives, indicating the importance of the baking process and method, and not only the ingredients, for the final quality of the loaves.
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