Table 2 Main factors decreasing viability of probiotic microorganisms in ice cream and their mechanisms of impact
From: Probiotic ice cream: viability of probiotic bacteria and sensory properties
State of damage | Stress factors | Resultant damage(s) | Methods of viability improvement | Selected sources |
|---|---|---|---|---|
During the fermentation process (fermented ice cream) | Low pH values (especially less than ∼5.5) | Mass transfer disruption through the cells, inactivation of some bacterial enzymes (cell starvation) | Selection of tolerant probiotic strains as well as suitable probiotic and/or non-probiotic starter cultures, addition of growth factors as well as growth promoters including prebiotics, finishing the milk fermentation at relatively higher pH values (∼5.5) | Akalin and Erişir 2008; Alamprese et al. 2002; Champagne and Rastall 2009; Crittenden et al. 2001; Hagen and Narvhus 1999; Haynes and Playne 2002; Homayuni et al. 2008a; Medici et al. 2004; Stanton et al. 2003; Ziemer and Gibson 1998 |
High titrable acidity | Bacteriocidic impact after entrance into bacterial cells | |||
High redox potential (anaerobic bacteria) | Restriction and inactivation of cellular metabolic pathways | |||
High concentration of sugars | Osmotic stress | |||
Presence of food additives that are detrimental to probiotic cells | Damage to cell walls or other parts of the cells | |||
Antagonistic interactions among starter cultures (fermented ice cream) | Loss of cell viability due to production of detrimental chemical compounds as well as nutritional competition | |||
During the freezing process | Mechanical damage caused by formation of ice crystals (including freezing rate) and by scraping of the cylinder wall | Bacteria cell walls rupture | Selection of probiotic strains tolerant to freezing, use of microencapsulated probiotic cells, use of cryoprotective carbohydrates, applying adequate technology of freezing regarding ice cream freezers | Akalin and EriÅŸir 2008; Akin et al. 2007; Champagne and Rastall 2009; Gill 2006; Jay et al. 2005; Homayouni et al. 2008a, b; Krasaekoopt et al. 2003; Lankaputhra and Shah 1996 |
Temperature-related stresses | Temperature decrease shock as well as the effects of frozen temperatures | |||
Chemical and biochemical stresses | Condensation of detrimental solutes, dehydration of cells | |||
During the overrun process | Oxygen toxicity for anaerobic bacteria | Sensitivity of bacterial cells to metabolically produced hydrogen peroxide | Selection of oxygen-tolerant strains, use of microencapsulated probiotic cells, use of oxygen scavengers and redox potential reducing agents, use of packaging materials impermeable to oxygen | Akalin and EriÅŸir 2008; Davies and Obafemi 1985; Haynes and Playne 2002; Laroia and Martin 1991; Miller et al. 2003; Ravula and Shah 1998; Vasiljevic and Shah 2008; |
During frozen storage period | Time | Cells damaged during freezing die gradually during storage | Selecting tolerant probiotic strains, utilizing microencapsulated probiotic cells, avoiding temperature oscillations during storage of the product, using oxygen scavengers and redox potential reducing agents, applying packaging materials impermeable to oxygen | Akalin and EriÅŸir 2008; Dave and Shah 1998; Davies and Obafemi 1985; Haynes and Playne 2002; Laroia and Martin 1991; Miller et al. 2003; Ravula and Shah 1998; Shah 2000; Vasiljevic and Shah 2008; |
Oxygen toxicity for anaerobic bacteria | Sensitivity of bacterial cells to metabolically produced hydrogen peroxide | |||
During melting/thawing of the product | Chemical stresses | Osmotic stress, condensation of detrimental solutes |