Staff PhD

Mechanisms of off-flavour development in bread with extended shelf-life

Sidsel Bennedbæk-Jensen

Background

The shelf-life of bread is most often limited by moisture loss due to starch retrogradation, which affects the texture significantly. The use of enzymes in bread production has made it possible to extent the shelf-life of bread mainly due to decreased rate of starch retrogradation. Consequently, other parameters determine shelf-life, and off-flavour development is believed to be a shelf-life limiting factor of high importance. Flavour development in bread products is well characterized. However the character and origin of off-flavour development is not very well described in the literature and the few publications considers the influence of fat, hydrocolloids and preserving agents on off-flavours. Furthermore, the influence of enzyme addition on the development of off-flavours during pro-longed storage of bread is unknown.

Aim

The aim of the PhD project is to set up sensory and analytical methods for characterizing and quantifying flavour active components in bread added enzymes to achieve prolonged storage. Subsequently, these analytical tools should be used to 1) elucidate the mechanism behind off-flavour development in such bread types with prolonged shelf-life and 2) the relationship between off-flavour development and a range of parameters included quality of raw materials, dough/bread types, storage conditions, chemical additives and enzymes addition.

Research Outline

The project will focus on development of a combined platform for sensory and analytical flavour analysis in bread and identify the chemical mechanisms behind development of off-flavour in bread and subsequent develop strategies to prevent deterioration of bread quality.

The project work plan is organised into:

1. Identification of bread types. Different wheat bread types (including whole wheat) and raw material qualities are selected to ensure that as many variations in qualities and shelf-life are obtained.

2. Analytical and sensory methods are developed. The sensory profile will include both the flavour and texture attributes. Texture is included as it is a significant key factor for monitoring staling. A GC-MS method will be developed to identify and quantify the volatile flavour components. A HLPC method will be used for identifying and quantifying the non-volatile flavour components. During the development of analysis one type of dough/bread will be analysed with variation in enzyme addition to get initial results on how the sensory and chemical profile are influenced by prolonged storage.

3. Overview of chemical and sensory changes during shelf-life: Breads are produced in a factorial design with variation in the following factors: 1) flour qualities, 2) dough and bread types, 3) types of enzymes (amylases, lipases, xylanases etc.) and 4) enzymes doses for selected enzyme activities. The breads are produced and stored for various storage times and analysed by sensory-, GC-MS, sniff and HPLC analysis. Multivariate data analysis will be applied to the data to 1) identify the chemical key components with significant influence on the sensory profile and 2) determine the effect of enzymes, enzyme activity, chemical additives, raw material quality and dough/bread type on chemical and sensory changes in order to get an idea about the mechanism behind flavour/off-flavour development.

4. Mechanistic-studies: The identified chemical components related to flavour/off-flavour will subsequently be investigated in a study which focuses on elucidating the mechanisms behind off-flavour development in bread.

5. Optimisation study: The obtained knowledge will form the basis for optimising production, storage and enzyme addition in bread with respect to control and limit of off-flavour development.

Thus, the following hypothesis and scientific problems will be addressed

• Increased shelf-life in bread obtained by application of enzymes increases off-flavour development
• Off-flavours originate from oxidative changes in the bread
• Some types of enzymes produce pre-cursers that may increase the formation of off-flavours during storage

Off-flavour in bread can be controlled/optimised by the 1) type of added enzymes and activities and 2) addition of different compounds that can prolong shelf-life