The authors, who published their findings in Food Chemistry, said that kefir degrades at lower rates compared to conventional baker’s yeast breads and as it can ferment lactose, and consequently, cheese whey, the main liquid waste of the dairy industry, it is a an extremely sustainable ingredient.
“The fundamental idea behind the use of kefir for food production, apart from its proven positive effect on quality and preservation, is the utilisation of a low cost, yet seriously polluting raw material,” they argue.
The food scientists explained that kefir is a natural mixed culture in which lactic acid bacteria (LAB), yeasts and other bacteria co-exist in symbiotic associations.
The starter culture originates from the Caucasus region in Russia, is popular in Eastern and Central Europe but is also gaining awareness among West European consumers for its probiotic and nutraceutical properties.
The losses of aroma volatile compounds during storage – staling - are part of the overall physicochemical changes that occur in bread from the moment of production and during storage.
Controlling staling and maintaining the quality and freshness of bread for longer periods, obviously lead to financial gain, and the researchers thus argue that the rate of staling, including the rate of flavour loss, is one of the most intriguing concerns for investigation in bread manufacture research.
Studies on the changes of bread flavour during storage have indicated that within three to four days most of the volatile compounds are dramatically lost. The use of sourdough seems to be able to efficiently control this problem, slowing down bread flavour losses, compared to yeast leavened breads, said the authors.
“However, there are other factors to be taken into account, such as the type of flour, the sourdough fermentation conditions (pH and temperature) and the selection of starter cultures with specific and desirable metabolic properties (e.g. production of specific volatile compounds),” they added.
The scientists said that while previous studies have shown that kefir is able to improve the overall quality of bread, there is no research published on monitoring of changes in the aroma volatile compound profiles of sourdough breads made with kefir during storage, and thus they aimed to evaluate the efficiency of the culture in this regard.
The aroma volatile compositions of sourdough breads containing kefir grains were monitored by SPME GC–MS analysis during a five day ambient storage period.
The researchers explained that breads were made with 20 per cent and 10 per cent kefir sourdough (Breads A and B respectively), and were compared with breads made with commercial sourdough (Bread C) and sourdough prepared in the laboratory without the addition of a starter culture (Bread D).
A dramatic decrease of volatiles was observed during storage for all samples, but the kefir sourdough breads (A and B) exhibited more complex profiles of volatiles with lower loss rates during storage, noted the authors.
They also reported observed differences in the percentages of esters on total volatiles - 6.2 per cent, 5 per cent, 2.8 per cent and 2 per cent in the case of breads A, B, C, and D, respectively.
And the researchers said that the customer oriented sensory evaluation revealed significant differences among the tested samples, with best results scored in the case of bread A in all days of storage, agreeing with the analytical data.
The authors concluded that their findings reveal the superiority of kefir sourdough over conventional yeasts in terms of bread aroma and the losses observed during storage.
Source: Food Chemistry
Published online ahead of print: doi: 10.1016/j.foodchem.2010.06.086
Title: Examination of freshness degradation of sourdough bread made with kefir through monitoring the aroma volatile composition during storage
Authors: S. Plessas, A. Alexopoulos, A. Bekatorou, I. Mantzourani, A. A. Koutinas, E Bezirtzoglou