Antifoaming Agents For Mushroom Liquid Fermentation: Selection, Application and Control

Antifoaming Agents For Mushroom Liquid Fermentation: Selection, Application and Control

In the deep-tank liquid fermentation of edible fungi (such as shiitake, oyster mushrooms, Armillaria mellea, morels, and Ganoderma lucidum), culture media often contain ingredients like soybean flour, corn flour (or slurry), peptone, yeast extract, and sugars. Under conditions of aeration and agitation, thick and highly stable foam tends to form rapidly.

Excessive foam can lead to liquid overflow, clogging of exhaust filters, increased risk of contamination, and a reduction in the effective working volume. The foam layer acts as a barrier to gas-liquid exchange, indirectly lowering dissolved oxygen levels and inhibiting the formation and growth of mycelial pellets; in severe cases, the entire batch may be lost.

Antifoaming technology has evolved from simple physical methods to mechanical antifoaming, chemical antifoaming, combined approaches, and finally to novel green antifoaming techniques (including new physical technologies, biological antifoaming, and process-based foam control at the source). This evolution meets the scaling-up requirements from laboratory-scale and pilot-scale trials to industrial-scale fermentation.

This section outlines the development of fermentation antifoaming technologies and details their practical applications, advantages, disadvantages, and suitable scenarios across different scales (shake flasks, seed tanks, and large-scale fermenters).

1. Mechanism of Action of Antifoaming Agents
Antifoaming agents primarily function by reducing the surface tension of the foam's liquid film. Upon contact with the foam, the agent rapidly spreads across the bubble surface, displacing the original foaming substances and creating a point of lower surface tension. This low-tension point destabilizes the liquid film, causing it to thin and rupture, thereby eliminating the foam. Additionally, effective antifoaming agents possess "foam-suppressing" capabilities, continuously preventing the formation of new foam.

Foam control methods have evolved from early process adjustments (controlling foam at the source—still a fundamental approach today) to mechanical antifoaming (with rake-style antifoam paddles being the mainstream configuration and external centrifugal antifoaming used less frequently), and finally to the chemical antifoaming agents most commonly used today (the standard method for edible fungi liquid fermentation).

① Natural vegetable oils (soybean oil, corn oil, cottonseed oil)
Widely used in the early days of liquid spawn production for edible fungi; they can also serve as a carbon source.

Usage:

Added prior to sterilization or fed in small amounts during fermentation; dosage: 0.1%–0.5%.

Advantages:

Food-safe; compatible with liquid spawn for cultivation; no toxic residues.

Disadvantages:

Low defoaming efficiency; depletes quickly, requiring repeated replenishment; excessive addition can coat mycelia, drastically reducing kLa and dissolved oxygen levels, thereby inhibiting mycelial growth; oils oxidize easily, increasing the risk of contamination; unsuitable for high-density, long-duration fermentation.

Current role: Emergency/supplementary use in small-to-medium spawn workshops; no longer used as the primary defoamer.

② Polyether defoamers (polyoxypropylene glycerol [GP], polyoxyethylene-polyoxypropylene glycerol [GPE])
Food-grade polyethers; withstand sterilization at 121°C.

Usage:

Can be added to the medium before sterilization or automatically fed via foam sensor linkage; typical dosage for edible fungi: 0.05–0.2‰.

Advantages:

Defoaming and foam-suppression efficiency far exceeds that of vegetable oils; low dosage required; low toxicity to the mycelia of most edible fungi; suitable for liquid spawn of Shiitake (*Lentinula edodes*), King Oyster (*Pleurotus eryngii*), and Morel (*Morchella* spp.); downstream separation is easier compared to silicone-based agents if mycelial polysaccharides or metabolites are to be extracted.

Disadvantages:

Excessive addition significantly reduces kLa and dissolved oxygen; sensitive strains (e.g., *Armillaria mellea*) may exhibit slowed growth and increased browning; tolerance varies greatly among strains, so small-scale gradient tests in shake flasks are essential before full-scale production to determine the safe dosage range.

③ Silicone / Polyether-silicone composite defoamers
Extremely strong defoaming power, but generally used with caution for edible fungi spawn; testing is required before large-scale application. Example: Polydimethylsiloxane (PDMS); typical dosage for edible fungi: 0.01–0.2‰.

Risks:

Silicon components tend to leave residues, and the mycelia of certain edible fungi are sensitive to silicon; furthermore, if the mycelia are to undergo downstream processing (such as for health supplements or polysaccharide extraction), silicon residues can interfere with filtration and membrane separation processes.

Operational Guidelines for Edible Fungi Cultivation:

Apply in small amounts over multiple intervals—preferring repeated additions rather than a single large dose; prioritize automated fed-batch addition and strictly avoid manual, bulk dumping.