Spray-Dried Bacterial Starter Cultures Turn Oyster Mushroom Fermentation Into a GABA-Rich Functional Food

Fermented foods have surged in popularity over the past decade, driven by growing consumer interest in gut health, natural flavor development, and functional ingredients that go beyond basic nutrition. Yet behind every reliable fermented product on the supermarket shelf lies a persistent industrial challenge: how to deliver the right microbes to the fermentation tank in a form that survives storage, shipping, and the harsh thermal realities of large-scale production. A new study from researchers at Prince of Songkla University in Thailand tackles that challenge head-on, and the results suggest that oyster mushrooms, one of the world’s most widely cultivated edible fungi, could become the basis of a new generation of shelf-stable, gamma-aminobutyric acid-enriched fermented foods.

The research, published in Food Science and Biotechnology, focused on developing spray-dried starter cultures for fermenting Pleurotus ostreatus, the common oyster mushroom. The team, led by Aem Nuylert with co-authors Benjamas Cheirsilp and Suppasil Maneerat, worked with two bacterial strains with complementary roles. Lactobacillus futsaii CS3, a lactic acid bacterium originally isolated from Thai fermented shrimp, is a known producer of gamma-aminobutyric acid, or GABA, an amino acid compound prized in functional foods for its potential calming and blood-pressure-lowering effects. Staphylococcus carnosus K21S22 served as a co-starter, contributing to the flavor and aroma development that makes fermented products appealing to consumers.

The central problem the researchers faced is one that haunts the entire probiotic and starter culture industry: spray drying is an efficient, scalable, and inexpensive way to turn liquid cultures into powders, but the process itself is lethal to many bacteria. As droplets are blasted through hot air in the drying chamber, cells experience simultaneous dehydration, heat shock, and oxygen exposure. Membranes rupture, proteins denature, and intracellular components leak out. Survival rates can plummet, which is why many commercial starter producers still rely on freeze drying, a gentler but far more energy-intensive and costly process that is difficult to scale for commodity applications.

Nuylert and colleagues attacked the survival problem from two directions. The first was preconditioning the cells before they ever reached the dryer. The team adapted Lactobacillus futsaii CS3 by growing it in the presence of 10 millimolar calcium chloride, a mild stress that triggers protective responses within the cell. This calcium adaptation strategy builds on earlier findings that intracellular calcium accumulation can stabilize bacterial membranes and improve heat resistance. In the study, the adapted cells showed markedly improved thermotolerance at 60 degrees Celsius, a temperature that would normally devastate unprotected lactic acid bacteria. The mechanism is elegant in its simplicity: by pre-stressing the cells with calcium, the researchers essentially taught them to brace for the thermal assault of spray drying.

The second line of defense was the protective carrier matrix in which the cells were embedded during drying. The researchers screened formulations and found that a matrix combining monosodium glutamate and maltodextrin, each at 10 percent, delivered the best results. Monosodium glutamate has a long history as a thermoprotectant in microbial preservation, helping to stabilize proteins and membranes during dehydration, while maltodextrin acts as a bulking agent that forms a glassy matrix around the cells, limiting molecular mobility and slowing degradation during storage. With this combination, post-drying survival reached 70.3 percent for Staphylococcus carnosus K21S22 and 59.2 percent for Lactobacillus futsaii CS3, figures that represent a substantial recovery of viable cells from an otherwise punishing process.

Survival through drying is only half the battle, however. A starter culture powder is useless if the cells die on the warehouse shelf. To test long-term stability, the team stored the dried powders in vacuum-packed conditions at 4 degrees Celsius for three months. The results were impressive: the cultures retained 86.4 percent viability for Lactobacillus futsaii and 84.1 percent for Staphylococcus carnosus. Vacuum packaging removes oxygen, limiting oxidative damage to cell membranes, while refrigeration slows the residual metabolic and chemical decay processes that gradually erode viability even in dried cells. Together, the drying formulation and the storage strategy produced a starter culture that could realistically sit in a food factory’s cold room for a full quarter and still perform.

The real test, of course, was whether these rehydrated powders could actually ferment mushrooms effectively. In application trials, inoculating oyster mushroom substrates with the spray-dried starters accelerated acidification and shortened the overall fermentation time compared with uncontrolled or slower fermentations. Rapid acidification is a critical safety and quality parameter in fermented foods, because a quick drop in pH suppresses spoilage organisms and pathogens before they can establish themselves. Faster, more predictable acidification also means shorter production cycles, which translates directly into economic benefits for manufacturers.

On the functional front, the cultures delivered on their GABA promise. Fermentations conducted with Lactobacillus futsaii CS3 alone produced GABA concentrations of 12.04 milligrams per gram, while the mixed culture of both strains achieved a nearly identical 12.02 milligrams per gram. This consistency is notable because it suggests that adding the Staphylococcus co-starter for flavor purposes did not come at the expense of the functional compound. For product developers, that is a valuable combination: a single fermentation process yielding both a bioactive ingredient and an improved sensory profile.

The sensory results added an intriguing layer to the findings. Using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry, the researchers profiled the volatile compounds generated during fermentation and found that the mixed starter produced a distinct relative volatile peak-area profile compared with the single-strain fermentation. In the taste panel, the mixed starter earned the highest taste acceptance score of 7.85 and the highest overall acceptance score of 7.63. Importantly, the authors were careful to note that no causal relationship between the volatile differences and sensory acceptance was inferred, a scientifically cautious position that acknowledges the complexity of flavor perception, where non-volatile taste compounds, texture, and aroma all interact in ways that volatile profiling alone cannot fully explain.

Taken together, the study outlines an industry-relevant strategy for transforming oyster mushrooms into value-added fermented products. The workflow is practical: precondition cells with calcium, dry them in an MSG-maltodextrin matrix, vacuum pack at refrigeration temperature, and inoculate mushroom substrate for a fast, GABA-producing fermentation with strong consumer acceptance. Because spray drying is already a mature industrial technology used for everything from milk powder to instant coffee, the barrier to adoption is comparatively low. As demand grows for plant-based and fungal-derived functional foods, shelf-stable starter cultures like these could help fermented mushroom products move from artisanal novelty to mainstream supermarket staple, bringing a scientifically optimized blend of taste and function to a wider audience.

Subject of Research: Spray-dried starter cultures for GABA-enriched oyster mushroom fermentation

Article Title: Spray-dried starter cultures (Lactobacillus futsaii CS3 and Staphylococcus carnosus K21S22) improve taste acceptance and GABA production in oyster mushroom fermentation

Article References: Nuylert, A., Cheirsilp, B., & Maneerat, S. (2026). Spray-dried starter cultures (Lactobacillus futsaii CS3 and Staphylococcus carnosus K21S22) improve taste acceptance and GABA production in oyster mushroom fermentation. Food Science and Biotechnology. https://doi.org/10.1007/s10068-026-02321-7

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02321-7

Keywords: spray drying, starter cultures, Lactobacillus futsaii, Staphylococcus carnosus, oyster mushroom, fermentation, GABA, microencapsulation, calcium adaptation, vacuum packaging, sensory acceptance, functional foods