Fermented Dairy Products: From Artisanal Production to Functional Products and Beyond

Fermented dairy products have been a staple food commodity throughout recorded human history. Even before the discovery of microorganisms, humans had tamed fermentation and through its exploitation, had been able to produce a wide range of dairy products. Through trial and error, a wealth of technical wisdom was generated and passed through generations, reaching present times.

Over the past century, the microorganisms that drive dairy fermentation, the factors that affect their growth and persistence, and the effect of their metabolic end products on human health have been extensively assessed. In recent years, the development of techniques that can produce large amounts of data allowed the exploration of understudied aspects of microbial subsistence, facilitating our understanding of the biotic and abiotic factors that direct dairy products’ microcommunity development. In addition, several bioactive compounds generated through microbial metabolism that have a direct or indirect effect on human health have been described. All these factors have inevitably led to the current trend of product customization. The capacity for product customization depends upon our ability to understand and effectively control microbial growth and metabolism. Early attempts in this direction have provided very promising results, indicating that we are one step closer to the next target, which is personalized nutrition. At the same time, dairy waste valorization through microbe-mediated production of value-added products has also been intensively assessed. The composition of waste materials directs the necessity of upstream processes before their microbial biotransformation, which in turn directs any downstream refining procedures. The valorization of both dairy effluents and residual products has been exploited, and in many cases, economically viable procedures have been described.

Assessment of the dairy microbiome, from raw milk through the production procedure to the final product, has been the epicentre of intensive study in recent decades. Biçer et al. provided a comprehensive synthesis of the factors that affect the composition of raw milk’s microecosystem and direct its evolution during its transformation into dairy products, with particular emphasis on kefir and cheese. The authors also described the effects of the microcommunity composition on flavour and texture. In addition, they provided an overview of the methods currently employed to determine microbiota structure and perform functionality assessment, including their advantages and disadvantages. The geographical diversity of artisanal cow’s milk kefir microbiome was presented by Ströher et al. along with the factors that shape the composition of the microcommunity and their effect on sensorial and functional properties. The authors highlighted the regional adaptation of the microcommunities and presented the directions that need further assessment.

Microbiota assessment is followed by thorough evaluation of the isolates obtained against a series of technological and functional properties. Isolates are often reported to exhibit comparable, and sometimes superior, properties compared to commercially available starter cultures. As a result, the development of products using such isolates is often reported. The development of a semi-industrial Kefalotyri-type cheese using thermized milk from native Epirus sheep breeds and autochthonous starter and adjunct cultures was reported by Bosnea et al. They exhibited the capacity of a starter culture to drive fermentation and result in a final product of excellent quality. This started culture consisted of native isolates, namely Streptococcus thermophilus ST1 and two wild Lactococcus lactis strains, in the presence or absence of an adjunct culture also consisting of native isolates, namely Lactiplantibacillus plantarum H25 and two wild Leuconostoc mesenteroides strains. Keser and Ozcan demonstrated the capacity of native isolates belonging to the Levilactobacillus brevis, Lacticaseibacillus paracasei, and Lacticaseibacillus rhamnosus species to develop and modify the textural and sensorial properties of high-fat dairy products. The authors highlighted the efficacy of these native cultures in developing customized high-fat dairy products that could meet market needs. The functional properties of traditional yoghurt and yoghurt-based products resulting from enrichment with bioactive compounds, such as fibres, phenolic compounds, terpenes, fatty acids, and proteins, were thoroughly presented and discussed by Munteanu-Ichim et al. They also addressed the possible modification of yoghurt physicochemical properties and storage stability resulting from their incorporation in the yoghurt formula. The authors highlighted the capacity of yoghurt as a substrate to include a wide variety of functional ingredients of both biotic and abiotic nature. Chávez-Alzaga et al. investigated the antioxidant activity of water-soluble kefir postbiotics obtained with different substrates, namely whole milk, skim milk, and whey, and methods of obtaining them, namely high-intensity ultrasound and thermosonication. The authors reported that the water-soluble kefir postbiotics obtained from whey had higher antioxidant activity, water-soluble protein content, and proteolysis degree and a lower percentage of dead cells, suggesting also a way to produce value-added products from whey.

Dairy waste valorization has also been intensively studied. Bencresciuto et al. studied the capacity of dairy effluent, without any nutrient addition or adjustment, to support the growth of Lipomyces starkeyi strain DSMZ 70295 towards the production of single-cell oils for biodiesel and biolubricant production. The authors reported the production of single-cell oils at higher fermentation temperatures was accompanied by the production of single-cell oils with remarkable oxidation stability and tribophysical features. However, it was also highlighted that increasing the fermentation yield, through substrate composition adjustment or through application of continuous or semi-continuous fermentation, was necessary to improve the economic sustainability of the process.

The aim of this Special Issue was to collect articles that improve our knowledge of fermented dairy products’ microecosystem development, the metabolism of related microorganisms, product design and evaluation of their safety and functional potential, as well as dairy waste valorization. The Guest Editors are confident that this goal was achieved, as new insights have been provided and research gaps have been addressed by the high-quality manuscripts that were published. These manuscripts not only improve our understanding of dairy products as a whole but may also serve as a guide for future research.