Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
Lactobacillus sakei MI806, Pediococcus pentosaceus MI810 and Pediococcus acidilactici MI807, able to produce bacteriocin-like inhibitory substances, were originally isolated from Lithuanian spontaneous rye sourdough and adapted in the novel fermentation medium containing extruded wheat material. The novel fermented products (50 and 65 % moisture content) were stored at the temperatures used in bakeries (15 days at 30–35 °C in the summer period or 20 days under refrigeration conditions at 0–6 °C). The number of lactic acid bacteria (LAB) was determined during the storage of fermented products for 15–20 days. Furthermore, the effect of novel fermented products stored under different conditions on wheat bread quality was examined. Extruded wheat material was found to have a higher positive effect on LAB growth compared to the control medium by lowering the reduction of LAB populations in fermented products with the extension of storage time and increase of temperature. During storage, lower variation and lower decrease in LAB count were measured in the novel fermented products with a moisture content of 65 % compared to those with 50 %. Furthermore, this humidity allows for the production of a product with higher moisture content in continuous production processes. The addition of the new fermented products with 65 % humidity to the wheat bread recipe (10 % of the quantity of flour) had a significant effect on bread quality: it increased the acidity of the crumb and specific volume of the bread, and decreased the fractal dimension of the crumb pores and crumb firmness. Based on the microbiological investigations of fermented products during storage and baking tests, the conditions of LAB cultivation in novel fermentation media were optimized (time of cultivation approx. 20 days at 0–6 °C and approx. 10 days at 30–35 °C).Lactobacillus sakei MI806, Pediococcus pentosaceus MI810 i Pediococcus acidilactici MI807, bakterije koje proizvode inhibitore slične bakteriocinu, izolirane su iz litvanskoga kiselog tijesta što se proizvodi od raženoga brašna, te prilagođene za uporabu u novoj fermentacijskoj podlozi s ekstrudiranom pšenicom. Da bi se ispitala mogućnost njihove primjene u pekarama, ti novi fermentirani proizvodi (s 50 i 65 % vlažnosti) skladišteni su 15 dana pri ljetnim temperaturama od 30 do 35 °C i 20 dana u hladnjaku pri 0 do 6 °C. Tijekom tih 15 do 20 dana ispitivan je broj mliječno-kiselih bakterija u fermentiranim proizvodima, te njihov utjecaj na kakvoću kruha. Dodatak ekstrudirane pšenice bitno je utjecao na rast mliječno-kiselih bakterija, u usporedbi s kontrolnom podlogom, smanjujući njihovo odumiranje u fermentiranim proizvodima tijekom duljeg skladištenja pri povišenoj temperaturi. Tijekom skladištenja primijećene su manje promjene broja mliječno-kiselih bakterija u novim fermentiranim proizvodima sa 65 % vlažnosti nego u onima s 50 % vlažnosti, pa je zaključeno da se njihovim dodatkom u kontinuiranom procesu može proizvesti kruh s većim udjelom vlage. Dodatak 10 % novih fermentiranih proizvoda sa 65 % vlažnosti pšeničnom brašnu bitno je utjecao na kakvoću kruha: povećali su se kiselost krušnih mrvica i specifični volumen kruha, a smanjila fraktalna dimenzija pora te čvrstoća mrvica. Na osnovi mikrobioloških istraživanja fermentiranih proizvoda tijekom skladištenja te pokusnog pečenja kruha optimirani su uvjeti uzgoja mliječno-kiselih bakterija u novim fermentiranim proizvodima (optimalno vrijeme uzgoja bilo je otprilike 20 dana pri 0-6 °C i 10 dana pri 30-35 °C)
