Study on the reduction of acrylamide in mixed rye bread by fermentation with bacteriocin-like inhibitory substances producing lactic acid bacteria in combination with Aspergillus niger glucoamylase

Abstract

This study mainly focuses on a strategy for reducing of acrylamide in cereal products, predominantly in bakery products. The effect of mesophilic lactic acid bacteria (LAB) strains as well as a novel fermentation media on the bases of extruded rye wholemeal on the acrylamide formation in mixed rye bread of different weight of loaf was studied. The LC–MS/MS method for acrylamide determination in bread crumb has been applied. Addition of 15% low pH (pH 3.4–4.3) fermented product to bread dough, which were produced by using commercial strain Lactobacillus casei and bacteriocin-like inhibitory substances (BLIS) producing strains Lactobacillus sakei KTU05-6, Pediococcus acidilactici KTU05-7 and Pediococcus pentosaceus KTU05-8 separately, caused significant reduction of acrylamide in mixed rye bread. All bread loafs of 1000 g contained less by 27% acrylamide concentrations versus loafs of 500 g. Acrylamide formation was affected (r² = 0.7193) by total reducing sugar content in bread and slightly correlated (r² = 0.5587) with reducing sugar content in sourdough. The treatment of extruded rye wholemeal with Aspergillus niger glucoamylase as compared to the control sample was found to have a positive effect on the acidification process lowering the acrylamide formation on an average by 59.4% and 40% in 500 g and 1000 g loafs of bread, respectively. This study demonstrates that acrylamide content could be reduced by using LAB excreting lower amylolytic activity in the medium, while the higher proteolytic activity is preferred.

Introduction

Acrylamide is formed in foods via the Maillard reaction with free asparagine and reducing sugars as the precursors, with the former generally being limiting in cereal-based products (Mottram, Wedzicha, & Dodson, 2002; Stadler et al., 2002; Zyzak et al., 2003). Moderate levels of acrylamide (5−50 μg/kg) in heated protein-rich foods and higher levels (150−4000 μg/kg) have been found in carbohydrate-rich foods, including potato, and also in certain heated commercial potato products and crisp bread (Claus, Carle, & Schieber, 2008; Dybing & Sanner, 2003; Surdyk, Rosén, Andersson, & Åman, 2004). Acrylamide occurs in many foods common to diets globally. It is formed during the heating of carbohydrate-rich foods containing the reducing sugars glucose and fructose and the amino acid asparagine, which are common to the plant ingredients used in the preparation of many foods (Lineback & Jones, 2011).

Acrylamide concentration in processed food products has become a very serious health issue. The possibility to remove acrylamide from foods by exploiting its chemical and physical properties was studied (Amrein, Schonbachler, Escher, & Amado, 2004; Anese, Suman, & Nicoli, 2010; Blom, Baardseth, Sundt, & Slinde, 2009). Lower protein (asparagines) content of bread is associated with lower acrylamide. In dough-based applications, addition of asparaginase resulted in reduction of acrylamide content in the final products of 34–92% (Hendriksen, Kornbrust, Østergaard, & Stringer, 2009). Also it is known that acrylamide content could be reduced by fermentation processes (Fink, Andersson, Rosen, & Aman, 2006; Fredriksson, Tallving, Rosen, & Aman, 2004) due to a consumption of the limiting precursor asparagine by yeast. Therefore, one of the possibilities to reduce the levels of acrylamide and herewith to ensure the safety of bakery products (Digaitiene, Hansen, Juodeikiene, Eidukonyte, & Josephsen, 2012; Juodeikiene et al., 2012) the use of bacteriocin-like inhibitory substances (BLIS) producing lactic acid bacteria (LAB) with high proteolytic activity (Elder, Fulcher, Leung, & Topor, 2007; Wehrle, Crowe, van Boeijen, & Arendt, 1999) should be envisaged.

Lactic acid bacteria are generally fastidious on artificial media, but they grow readily in most food substrates and lower the pH rapidly to a point where competing organisms are no longer able to grow. The formation of lactic acid is obtained by acidification below pH 4.2 which is a safety factor, and also gives a nice taste to whey products (Manea & Buruleanu, 2010). The leavening by LAB in association with yeast forming a softer and more palatable bread crumb, modifying flour components, e.g. swelling and partial hydrolysing proteins and polysaccharides (Salovaara, 2004). The highly promising results of these studies underline the important role that functional, bacteriocins of certain LAB strains play in the food industry as starter cultures, co-cultures, or bioprotective cultures, to improve food quality and safety (Juodeikiene et al., 2012).

The use of the lactic acid sourdough is a way to enhance dough properties, to improve flavour, texture and microbiological shelf-life of bread (De Vuyst & Vancanneyt, 2007). In the Baltic States, a traditional scald process is applied for the production of bread. In compare with rye bread making processes used in other parts of Europe, the major difference is a scalding step (15–20% of rye flour brewing up with hot water and saccharification during 3 h prior to fermentation) that contributes to the excellent quality and long shelf life of the bread. However, scalded bread preparation is a long, complicated and economically inefficient process. The alternative technological means for the intensification of sourdough production, higher stability of sourdough and improved bread quality are still being studied. Recently, considerable interest has arisen in the application of a new fermentation media composed of extruded products possessing specific physical properties (Juodeikiene et al., 2011). Extrusion cooking causes gelatinization of starch among the other physicochemical and functionality changes the grain components undergo; moreover, extrusion enhances the amount of dietary fibre and eliminates the bacterial contamination of the cereal material.

However, there is a lack of literature on the effect of scald saccharification process using enzymatic treatment of extruded rye wholemeal as well as of lactic acid fermentation on acrylamide formation in rye mixed bread.

The aim of this study was to investigate the effect of Lactobacillus and Pediococcus strains in combination with Aspergillus niger glucoamylase used for saccharification of extruded rye wholemeal on acrylamide formation in the most popular mixed rye bread of different loaf weight.