**4.7 Drying process**

Powdered foods have much longer shelf life at an ambient temperature. Drying can be achieved by different methods such as freeze drying, spray drying, microwave drying and vacuum drying. Spray drying could be achieved at a lower cost compared with other techniques. However, spray drying could lead to a loss of viability of the probiotic cells due to encountering them to several stresses including high temperature, dehydration, osmotic pressure, gradual increase in detrimental compounds during drying and mechanical stress (shearing). Also, concentration of dissolved oxygen might also increase in dried products which could be toxic to bifidobacteria (Korbekandi et al 2011; Rybka and Kailasapathy, 1997). In the spray drying method, the most critical parameters affecting survival of bifidobacteria are the type of atomization, air pressure, and the outlet temperature (Champagne and Møllgaard, 2008). Freeze drying is the best process for maintaining the viability of the bacterial cells used for preparing starter culture cells. However, its costeffectiveness should be evaluated before usage.

#### **4.8 Microencapsulation**

Microencapsulation, as one of the new and efficient methods, has recently been under especial consideration and investigation. From microbiological point of view, microencapsulation can be defined as the process of entrapment/enclosure of microorganisms cells by means of coating them with proper hydrocolloid(s) in order to segregate the cells from the surrounding environment; in a way that results in appropriate cell release in the intestinal medium (Krasaekoopt et al., 2003; Mortazavian et al., 2007b, 2008; Picot and Lacroix, 2003; Sultana et al., 2000). Microencapsulation of probiotic cells has been shown to preserve them from detrimental environmental factors such as low pH and high acidity (Wenrong and Griffiths, 2000), bile salts (Lee and Heo, 2000), cold shocks induced by the process conditions such as deep freezing and freeze drying (Shah and Rarvula, 2000), molecular oxygen in case of obligatory anaerobic microorganisms (Sunohara et al., 1995), heat shocks caused by process conditions such as spray drying, bacteriophages (Steenson et al., 1987) and chemical antimicrobial agents (Sultana et al., 2000). In addition, other advantages such as increase improvement and stabilization of sensory properties (Gomes and Malcata, 1999) and immobilization of the cells for their homogeneous distribution throughout the product (Krasaekoopt et al., 2003) can also be achieved by this process.

This process has been recently used as an efficient method for improving the viability of probiotic bacteria in fermented milk drinks, fermented frozen dairy desserts, ice cream and juices (Adhikari et al., 2000; Krasaekoopt et al., 2004; 2005; Kailasapathy, 2006; Mohammadi et al., 2011), and simulated gastrointestinal tract (Hansen et al., 2002; Korbekandi et al., 2011; Lee and Heo, 2000; Krasaekoopt et al., 2004; Mortazavian et al., 2008; Sultana et al., 2000; Wenrong and Griffiths, 2000). Encapsulated probiotic organisms, when incorporated into fermented frozen dairy desserts, showed an improved viability of >105 cfu g-1 in the product compared to counts of <103 cfu g-1 when non-encapsulated organisms were used (Mortazavian et al., 2010 ; Shah and Ravula 2004). Studies suggest that, micro-encapsulation of free probiotic cells can increase their viability by ≥2 log cycles in fermented milks during a refrigerated storage period. As mentioned earlier, in fermented milk drinks with pH values of less than 4.2, free cells of *L. acidophilus* LA-5 lost their viability to less than 106 cfu mL-1 after 1 week; and in the case of *Bifidobacterium lactis* BB-12, a similar loss occurred after 2 weeks of storage. For encapsulated cells, viable population of *L. acidophilus* and bifidobacteria remained higher than 105 and 106 cfu mL-1 after 42 days of refrigerated storage, and counts of free probiotic free cells were not detected and 102 cfu mL-1, respectively (Mortazavian et al., 2008).

#### **4.9 Packaging materials and conditions**

132 New Advances in the Basic and Clinical Gastroenterology

intracellular ice crystals causes greater damage to the cells (Gill, 2006; Jay et al., 2005). Therefore, rapid freezing after inoculating with the probiotic microorganisms contributes to the good maintenance of the populations of these microorganisms in the product

Probiotic cells are subjected to some chemical stresses during melting (freeze-thaw) of the frozen products which can cause mortality to them. On one hand, the cells are exposed to osmotic effects (Jay et al., 2005). On the other hand, the high concentrations of detrimental factors such as hydrogen ions, organic acids, oxygen and other poisoning components to probiotic cells in melting media, associated with freezing concentration, are the factors having a great effect on viability loss of probiotics. pH has been found to exhibit a crucial

Powdered foods have much longer shelf life at an ambient temperature. Drying can be achieved by different methods such as freeze drying, spray drying, microwave drying and vacuum drying. Spray drying could be achieved at a lower cost compared with other techniques. However, spray drying could lead to a loss of viability of the probiotic cells due to encountering them to several stresses including high temperature, dehydration, osmotic pressure, gradual increase in detrimental compounds during drying and mechanical stress (shearing). Also, concentration of dissolved oxygen might also increase in dried products which could be toxic to bifidobacteria (Korbekandi et al 2011; Rybka and Kailasapathy, 1997). In the spray drying method, the most critical parameters affecting survival of bifidobacteria are the type of atomization, air pressure, and the outlet temperature (Champagne and Møllgaard, 2008). Freeze drying is the best process for maintaining the viability of the bacterial cells used for preparing starter culture cells. However, its cost-

Microencapsulation, as one of the new and efficient methods, has recently been under especial consideration and investigation. From microbiological point of view, microencapsulation can be defined as the process of entrapment/enclosure of microorganisms cells by means of coating them with proper hydrocolloid(s) in order to segregate the cells from the surrounding environment; in a way that results in appropriate cell release in the intestinal medium (Krasaekoopt et al., 2003; Mortazavian et al., 2007b, 2008; Picot and Lacroix, 2003; Sultana et al., 2000). Microencapsulation of probiotic cells has been shown to preserve them from detrimental environmental factors such as low pH and high acidity (Wenrong and Griffiths, 2000), bile salts (Lee and Heo, 2000), cold shocks induced by the process conditions such as deep freezing and freeze drying (Shah and Rarvula, 2000), molecular oxygen in case of obligatory anaerobic microorganisms (Sunohara et al., 1995), heat shocks caused by process conditions such as spray drying, bacteriophages (Steenson et al., 1987) and chemical antimicrobial agents (Sultana et al., 2000). In addition, other advantages such as increase improvement and stabilization of sensory properties (Gomes and Malcata, 1999) and immobilization of the cells for their homogeneous distribution throughout the product (Krasaekoopt et al., 2003) can also be achieved by this

(Mohammadi et al., 2011).

role in this regard.

**4.7 Drying process** 

**4.8 Microencapsulation** 

process.

effectiveness should be evaluated before usage.

The packaging of probiotic food products influences the oxygen permeability into the product, and as a result, affects the viability of bifidobacteria, *L. acidophilus* and other probiotic species during the storage period. Several aspects of food packaging materials including the type of the packaging materials (Glass and plastic) their thickness, and the application of active/intelligent packaging systems could influence survival of probiotic bacteria (Korbekandi et al., 2011). In general, two important points are worth mentioning. Firstly, apart from the packaging materials, the temperature and relative humidity of the atmosphere are the key factors affecting oxygen permeability. Secondly, besides the efficiency of packaging, the economic aspect should also be taken into account (the price of packaging materials as well as the price of packaging machines) because they can significantly influence the final price of products and their sale volumes.
