Microbial impact on the volatolomic profile of fermented milks: a case study with the application of industrial starter cultures

In the dairy industry, a considerable and growing interest is given to the aroma of yogurt and fermented milks (FMs), and the capability of lactic acid bacteria, applied as starter cultures, to naturally improve flavor characteristics. This case study aimed to characterize volatile organic compounds (VOCs) in fermented milks obtained by using industrial starters, either individual or in mix, composed of Lactobacillus delbrueckii subsp. bulgaricus (LB) and/or Streptococcus thermophilus (ST), with the aim to elucidate the impact of each single strain within the same species in the complexity of the microbial communities. Thus, 33 different VOCs, including ketones, acids, aldehydes, alcohols, esters and aromatic compounds were identified through headspace solid-phase microextraction coupled to GC-MS. Only LB produced acetaldehyde (green apple-like) and 2-nonanol (musty), whilst in ST-FM acetic acid (vinegar like), diacetyl (buttery), 2,3-pentanedione (sweet), acetoin (creamy), and hexanoic acid (pungent) were higher compared to LB-FM. Depending on the single strain and their different combinations, noticeable differences in the VOCs profile were observed, showing that, the selection of the proper combinations of ST and LB strains to obtain FMs with a specific final VOCs profile is a key aspect in the dairy industry sector.