The stability of enzymes during breadmaking and their influence on staling characteristics

Baked products continue to enjoy popularity in many parts of the world. This reflects the appealing sensory attributes of the fresh products, including the soft textural characteristics of the freshly baked goods. Staling remains a significant cause of economic loss in breads due to the loss of saleability resulting from crumb firming. The aims of the current project have been to investigate some of the factors which may impact on staling, particularly the stability of amylolytic enzymes in bakery formulations. In addition, the role enzymic hydrolysis of starch in producing partial hydrolysis products and the potential of microencapsulation as a means of studying these effects is investigated. Recently developed assay methods which are able to specifically measure α-amylase and ß-amylase, in the presence of the other potentially interfering activity, have been evaluated. These have been applied to an investigation of enzyme levels at various stages during the breadmaking process, using a cereal source of the enzyme α-amylase. For this a rapid dough formulation and processing procedure were used. α-Amylase activity levels appeared to gradually increase during the proofing stages and then to decline upon heating of the dough. However, the activity remaining in the final baked loaf was readily measurable indicating that not all of the enzyme had been inactivated. Free and total ß-amylase activities were also measured. Most of the enzyme was found to be in the free form although a higher proportion was bound in the dough than in the wheat flour used for baking. ß-Amylase was heat labile with only relatively low activities remaining in the final baked loaf. It appears that of the two amylolytic enzymes, α-amylase is sufficiently stable that it may exert some impact on the crumb characteristics in the freshly baked product and during subsequent storage. In order to assess the likelihood that amylolysis is of significance in influencing crumb characteristics, samples were also extracted and analysed for the levels of low molecular weight carbohydrates. For this purpose high-performance liquid chromatography was used to analyse the aqueous extracts for maltose, glucose, fructose, lactose and sucrose. Commercial flours were found to contain low levels of sugars with maltose being the predominant sugar present. For comparative purposes, a number of commercial breads were also analysed and the composition found to vary between the different samples. Typically maltose was present at higher levels than the other sugars. When experimental loaves were analysed, the patterns showed that other sugars declined during proofing whereas maltose remained at readily measurable levels. Upon baking and subsequent storage the amounts of maltose increased. These results are consistent with the findings that some amylolytic activity remains in the baked product. In the third phase of this study, a potential means of investigating the role of particular carbohydrates in product textures and staling rates was examined. The approach of spray drying was used to prepare microencapsulated maltodextrin. The encapsulating agents used were based upon rice starch and guar galactomannan. When these microcapsules were incorporated into the breadmaking formulation and baked, it appeared that softer crumb characteristics were achieved. The data also indicates an effect of delay in the staling rates. From these studies it is concluded that cereal grain a-amylase may be more stable during breadmaking than previously thought. There appears to be an increase in the level of some low molecular weight sugars in the final, baked product. Microencapsulation may offer a useful technique for the study of the role of specific low molecular weight carbohydrates and dextrin fractions during baking and storage of breads. These finding could form the basis of further research into staling of breads.