Acid whey is a liquid fraction that remains after the fermentation of milk or the addition of organic or mineral acids to milk. The processing of acid whey is much more challenging than the processing of sweet whey, mainly because of the higher lactic acid content, which obstructs the drying process. Acid whey is, therefore, more often considered as waste, and as such as an ecological burden for the environment and an unwanted cost for the manufacturer. The purpose of this study was to investigate the possibility of using acid whey as a culture medium for probiotic bacteria. The acid whey used was the by-product of an industrial-sized production of cottage cheese. We first showed on a smaller scale that the chosen bacterial strains were able to grow in an acid whey medium. The addition of yeast extract and/or a mixture of minerals improved the growth of the Lactiplantibacillus plantarum strains and the Lacticaseibacillus rhamnosus IM239 strain, but it did not affect the growth of the Lactobacillus paragasseri IM105 strain. Then we showed on a larger scale that the yield of live bacteria was higher if the pH value was not regulated during the fermentation in a bioreactor. We also showed that the bacteria samples collected at the beginning of the stationary growth phase had a higher survival rate during freeze-drying if their pH value was adjusted to 6,5 during the fermentation. However, in the samples collected after 24 hours the pH value had a smaller effect on the survival rate during freeze-drying. With the study we thus confirmed that acid whey can be used as a growth medium for the cultivation of lactic acid bacteria.
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