Hydrodynamic Cavitation in Food and Fermentation Processing

8 Food Proteins and Bioproduct Recovery

8.1 Protein extraction and functional modification

Cavitation can increase protein recovery by disrupting cell walls, reducing particle size, increasing solubility, and accelerating liquid penetration. It can also alter the structure of already extracted proteins, changing emulsifying, foaming, gelation, and hydration behavior. These two objectives require different severity. Extraction often benefits from strong disruption, whereas functionalization requires sufficient unfolding without irreversible aggregation or peptide degradation [28-31,41].

A soy processing study by Preece, et al. used a two stage high pressure homogenizer at 50-125 MPa to treat soy slurry and diluted okara. A single pass at 100 MPa increased total protein extraction from soy slurry to approximately 82%. Repeated passes did not continue to improve yield because viscosity, swelling, particle interactions, and reduced centrifuge separation efficiency offset the greater protein availability. Okara extraction reached a plateau after one pass [41]. The study demonstrates the need to optimize extraction and separation as a coupled system.

Milk protein data reviewed in Section 4.2 show a milder functionalization pathway. At 6 MPa, prolonged treatment reduced aggregate size and raised solubility without new low molecular weight bands on SDS PAGE [28]. Rotor cavitation at lower pressure but high pass frequency reduced viscosity in high solids MPC80 and accelerated powder rehydration [29,30]. The choice of device must therefore reflect whether the target is cell disruption, powder deagglomeration, or controlled molecular reorganization.

To quantify protein recovery efficiency in plant based processing, the protein extraction yield ($Y_p$) to the soluble soy base stream is defined by mass balance:

where $Y_p$ is protein extraction yield to the soluble soy base stream, S and O are the masses of soy base and okara streams, and $x_{p,s}$ and $x_{p,o}$ are their protein mass fractions [41].

8.2 Intracellular polymer recovery

Hydrodynamic cavitation has been evaluated for recovery of intracellular polyhydroxyalkanoates from mixed microbial culture. Yilmaz et al. used a 3 L stainless steel loop with exchangeable orifices and short treatment. Under the selected optimum, approximately 71.7% recovery efficiency and 71.4% polymer purity were reported, compared with higher recovery and purity for conventional chloroform extraction [42].

The cavitation route provides rapid mechanical cell disruption and can reduce chemical and thermal requirements, but it does not eliminate downstream separation. Polymer molecular weight, thermal stability, residual biomass, solvent use, energy, and equipment wear must be included in the comparison. The study recommends investigation of vortex and rotor stator devices for scale up, reflecting the broader advantage of locating the active cavitation away from erosion sensitive surfaces [42].

8.3 Controlled manufacture of protein microbubbles

Not every cavitation application seeks to destroy bubbles. Bhattacharjee et al. used a vortex based hydrodynamic cavitation platform to manufacture albumin microbubbles for therapeutic delivery. The device generated microbubbles near 7 µm under mild conditions and loaded them with curcumin. Ultrasound triggered delivery produced substantially greater release or uptake than the no sonicated condition in the reported system [43].

This application illustrates a broader principle: hydrodynamic cavitation can be designed as a controlled bubble manufacturing platform when gas introduction, protein adsorption, pressure history, and collection are tuned to stabilize rather than immediately collapse the bubbles. Food analogues include aerated dairy products, beverage nitrogenation, foams, and encapsulated flavors, although food grade formulations require independent development.

Table 8.1. Protein and bioproduct applications of hydrodynamic cavitation.

Application	Device or severity	Reported result	Primary scale up constraint
Soy protein extraction [41]	High pressure homogenizer; one pass at 100 MPa	Protein extraction up to approximately 82%	Centrifuge separation efficiency and viscosity after repeated passes
Milk protein concentrate [28]	6 MPa, up to 30 min	4.82 to 1.35 µm; solubility 88.2% to 98.8%	Avoid excessive aggregation and functional property reversal
MPC80 viscosity reduction [29]	Rotor at 25-50 Hz	Viscosity reduced 20-56%	Energy, temperature rise, and evaporation or dryer integration
MPC80 rehydration [30]	Semi industrial in line HC	D90 0.45 µm versus 21.17 µm conventional	Powder feed consistency and sanitary powder induction
PHA recovery [42]	3 L loop; orifice; short treatment	71.7% recovery and 71.4% purity	Cell disruption versus polymer preservation and downstream separation
Albumin microbubbles [43]	Vortex cavitation with gas and protein	Approximately 7 µm microbubbles and triggered delivery	Bubble stability, gas control, sterile or hygienic manufacture

8.4 Adjacent high shear micron and nano formulation methods

Impinging jet and Microfluidizer processors are hydrodynamic cavitation devices. They are, however, useful benchmarks because they combine controlled high pressure flow, intense micromixing, cavitation and short residence time to produce functional food dispersions. A study reported fish oil emulsions containing 12 to 14 wt.% oil with median droplet sizes of 119 to 163 nm and no particles larger than 1 µm. The same platform reduced a vitamin C liposome formulation from a median scale near 5 µm to approximately 200 nm at the best four pass condition [65].

The study also produced soy fiber dispersions in which 99% of particles were below 15 µm and curcumin particles in the approximate 300 to 500 nm range. These results show why a technology comparison should be based on final size distribution, oxidation, temperature history, pass count, energy per unit mass, cleanability, and stability in the final food matrix. A cavitation process may be preferred for scale, lower pressure, combined heating, or extraction, while an impinging jet higher pressure system may be preferred when a narrowly controlled nano formulation is the primary objective [65].