Fermentation starter cultures: from strains to peptides

A fermentation starter culture is a defined microbial culture, single or mixed, added to a raw material in known amounts to drive and steer its fermentation. For a formulator the interesting questions are the following: how are the strains selected, what functional fractions can fermentation generate, and what may you say about them. VF Bioscience selects starter strains with specific fermentation capacities, for dairy and specialty fermentation, and supplies them to food, functional food and ingredient manufacturers.

What is a fermentation starter culture?

In the food-science literature, starter cultures are “individual or mixed microbial cultures used in known concentrations to promote and conduct fermentation” (Laranjo et al., Frontiers in Microbiology, 2019). Most are lactic acid bacteria (LAB). As one review summarizes, the group is “gram-positive, non-sporing, non-respiring cocci or rods”, and “the main function of LAB is to produce lactic acid, that is, the acidification of the food” (Bintsis, AIMS Microbiology, 2018). That acidification is the base function on which everything else, preservation, texture, flavour, is built.

How is a starter culture different from a probiotic?

A starter culture is defined by a technological role: it drives and controls fermentation. A probiotic is defined by a health benefit (“live microorganisms that … confer a health benefit on the host”), and a postbiotic likewise by a benefit from inanimate cells (Salminen et al., 2021). Some LAB starter strains do also carry probiotic properties, but that is a separate, strain-specific claim that needs its own evidence. A culture can be an excellent starter and confer no health benefit at all.

What do starter cultures do?

Beyond acidification, starter cultures shape the product and protect it. They “contribute to the flavour, texture and nutritional value of the fermented foods”, and act as bio-protective cultures that inhibit spoilage and pathogenic microorganisms (Bintsis, 2018). The safety mechanism is competitive: “starter cultures engage in competitive exclusion, outcompeting spoilage microorganisms for nutrients and oxygen”, and they “help to standardize product properties and shorten ripening times” (Laranjo et al., 2019). Standardization is a crucial point: a characterized starter turns a variable, spontaneous process into a reproducible one.

How are industrial starter cultures selected?

Selection is based on technological performance, safety and robustness. Besides, VF Bioscience selects strains “not only for technological fermentation properties (growth capacity, acidification, texturization), but also more specific properties such as the capacity to generate health-promoting molecules”. Beyond performance, industrial strains are chosen for resilience: lactococci “are selected for use as starters based on their metabolic stability, their resistance to bacteriophage, and their ability to produce unique compounds” (Bintsis, 2018); phage resistance in particular protects a production line from collapse. Safety is assessed through EFSA’s Qualified Presumption of Safety approach.

From starter culture to bioactive peptides

The reason a characterized culture is more than an acidifier is that its enzymes can release functional fractions from the substrate. Proteolytic LAB have “a highly developed proteolytic system composed of cell envelope proteinases (CEPs), peptide transporters, and intracellular peptidases”, and through it can generate bioactive peptides described as antimicrobial, antioxidant, antihypertensive (ACE-inhibitory) and anti-inflammatory (Fabbri et al., Foods, 2024). VF Bioscience’s own starters illustrate the principle.

Precision fermentation or traditional fermentation?

Traditional fermentation uses whole living cultures to transform a substrate, which is what a starter culture does. Precision fermentation instead uses “microbial hosts as ‘cell factories’ for producing specific functional ingredients” (Good Food Institute), typically engineered hosts that make a single target molecule which is then purified from the biomass. Starter-culture fermentation is the traditional route: the culture and its enzymatic activity on the substrate are the point, not a purified single compound.

What can you claim in the EU?

Under EU law, “health claims shall be prohibited unless they … are authorised … and included in the lists of authorised claims” (Regulation (EC) No 1924/2006). The case of the ACE-inhibitory tripeptides IPP and VPP shows how high the bar is even for a well-studied fermentation-derived peptide: EFSA concluded that a cause and effect relationship with maintenance of normal blood pressure had not been established, and no claim was authorized.

Working with characterized starter cultures

The value of a starter culture is in its characterization: a strain selected for defined technological properties, documented for safety, and understood for the fractions it generates. VF Bioscience develops proprietary starter strains through its microbiology work and offers functional fermentation starters for dairy and specialty fermentation, alongside documented strains such as L. fermentum ME-3® and L. plantarum VFP46®. It also runs industrial fermentation and bioproduction projects, and supplies the resulting actives to healthcare and nutrition formulators as part of its wider ingredient range.