# Encapsulated Probiotics: Potential Techniques and Coating Materials for Non-Dairy Food Applications
## 3 Probiotic Encapsulation Techniques
### Emulsion  
In the emulsion (also known as internal ionic gelation, which produces capsules with sizes of 200 nm to 1 mm) encapsulation processes, the suspension containing probiotics cell and polymer (disperse phase) is first dispersed into vegetable oil (continuous phase) and  
Figure 1: Different types of probiotics encapsulation techniques and the morphologies of corresponding microcapsules obtained: (**a**) ionic gelation (emulsion, extrusion); (**b**) coacervation; (**c**) fluidized bed coating; (**d**) freeze-drying; (**e**) spray-drying; (**f**) spray chilling; (**g**) layer-by-layer method; (**h**) co-encapsulation. homogenized to form a water-in-oil (W/O) emulsion in the presence of a surfactant (emulsifier). After emulsification, calcium chloride (cross-linking agent) is added to insolubilize and harden (fast gelling process) the water-soluble biopolymer. The gel beads can then be harvested by filtration or centrifugation [40, 43]. Compared to the extrusion technique, the emulsion technique is easier to scale up for mass production. Hence, it is more suitable for application at the industrial level [45]. Additionally, high survival of probiotics was also reported after encapsulation using the emulsion technique [43]. [PERSON] et al. [48] found that probiotic _L. rhamns_ GG encapsulated in a homogeneous system of carboxymethyl cellulose/gelatin blend survived better under simulated intestinal tract conditions compared to free probiotics. [PERSON] et al. [49] revealed that encapsulated _L. rhamns_ in gelled water-in-oil emulsions had a survival rate of more than 77% against in vitro digestion. Probiotics (_B. bifidum_[7], _L. acidophilus_ PTCC1643, _B. bifidum_ PTCC 1644 [15], _L. plantarum_, _L. fermentum_, _L. casei_, _L. pharicus_, _S. boulardii_[16], and _Lactobacillus salivarius_ spp. _salixarius_ CECT 4063 [10] encapsulated using the emulsion technique have also been reported as suitable to be used in non-dairy food matrices such as grape [7, 15], tomato, and carrot [16] juices, and apple matrix [10]. Furthermore, the emulsion encapsulation technique is flexible since it can adjust and control the beads' size. According to [PERSON] et al. [40], the diameter of the beads produced through the emulsion technique can be reduced to 25 um, which cannot be achieved using extrusion methods. However, the emulsion technique has a high operational cost due to the high price of vegetable oil (such as soy, sunflower, corn-millet, and light paraffin oil) [40, 45]. In addition, the microcapsule produced is not suitable for use in low-fat food products due to the oil residual in the capsule [39]. Considering that conventional emulsions are thermodynamically unstable, advanced emulsion technologies such as nano-emulsion, Pickering emulsion, and Pickering high internal phase emulsion are implemented for efficient probiotics encapsulation. Nano-emulsion is a relatively stable emulsion system with smaller droplet sizes ranging from 50 to 200 nm. In the study by [PERSON] and [PERSON] [50], nano-emulsions containing soy protein isolate, Tween 80, and gum Arabic were prepared for encapsulating _L. delbrueckii_ subsp. _bulgaricus_. The stability and survivability of the probiotics loaded in nano-emulsions were well-maintained throughout the storage period of 40 days. Contrary to nano-emulsions, Pickering emulsion is an emulsion system that does not require emulsifiers in the stabilization process. Pickering emulsion is stabilized rather by solid particles (more effective with hydrophobic particles). Pickering-type double emulsion (water-in-oil-in-water, stabilized with polyglycerol polyricinoleate) has also been used to encapsulate probiotics (_L. acidophilus_) [51]. The viability (gastric digestion = 93.59%, intestinal digestion = 84.24%) and colon-adhesion efficiency (43.27%) of probiotics entrapped in the double emulsion were higher than the free probiotics (viability after 1 h gastric digestion = 0%, colon-adhesion efficiency = 14.20%) during storage (14 days) and after exposure to simulated gastrointestinal conditions.