## 6 Prebiotics, Synbiotics, Paraprobiotics, Postbiotics, and Psychobiotics  
The definition of prebiotic has evolved over time. Gibson and Roberfroid [296] defined prebiotic as \"non-digestible food ingredients that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacterial species already resident in the colon\". More recently, the definition of prebiotic has been modified to \"a substrate that is selectively utilized by host microorganisms conferring a health benefit\" [297]. Examples of prebiotics include inulin, fruct-oligosaccharides, galacto-oligosaccharides, isomalot-oligosaccharides, human milk oligosaccharides, xylo-oligosaccharides, xylan, lactulose, oat fiber (\(\beta\)-glucan), pectin, guar gum, resistant starch, stachyose, select polyphenols, bacteriophage, omega-3 fatty acids, and yeast hydrolysate [298; 299; 219]. Prebiotics are discussed in detail by Gibson and Roberfroid [300]. Synbiotics were defined by a panel from the International Scientific Association for Probiotics and Prebiotics as \"a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host\" [301]. Therefore, the proper type of prebiotic must be used with a given probiotic. Stronger health benefits occur when a product contains synbiotics rather than either a probiotic or prebiotic alone [302]. Dairy products incorporating synbiotics in research studies include yogurt and a yogurt-based drink, fermented skim milk, cheeses, ice cream, and infant formula. Some of the probiotics and prebiotics that have been incorporated into symbiotic yogurt are listed in Table 4. For non-dairy based products, this list includes bread buns, chocolate, candy, mousse, Andean blackberry slices, soybean beverage, fermented soy food, cereal mix, traditional Indian dry snack, dry malted drink, and salad dressing [302]. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Probiotic** & **Prebiotic** & **Reference** \\ \hline _L. acidophilus_ ATCC 4357 & Fructooligosaccharide and Isomaltooligosaccharide & [303] \\ _L. acidophilus_ LA-5 & Oligofructose-enriched inulin & [304] \\ _L. acidophilus_ LA-5 & Honey and aqueous cinnamon extract & [305] \\ _L. acidophilus_ ATCC 4356 & Faxseed & [306] \\ _L. acidophilus_ & White oyster mushroom flour and Taro flour & [307] \\ _L. acidophilus_ 100021 and _L. helveticus_ 501699 & Inulin and maltodextrin & [308] \\ _L. acidophilus_ LA-5 and _B. animalis_ subsp. _lactis_ BB-12 & Monk fruit extract, inulin, and pectin & [309] \\ _L. acidophilus_ ATCC 4356 and _B. longum_ & Purple Sweet Potato & [310] \\ _L. acidophilus_ and _B. animalis_ subsp. _lactis_ & Black carrot pulp and Exudate acacia gum & [311] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Some of the probiotics and prebiotics that have been incorporated into symbiotic yogurt. Paraprobiotics (ghost probiotics) are \"non-viable microbial cells (intact or broken) or crude cell extracts (i.e., with complex chemical composition), which, when administered (orally or topically) in adequate amounts, confer a benefit on the human or animal consumer\" [328]. A wide variety of probiotics can be used for paraprobiotic production [328,329]. Techniques for inactivating probiotics to produce paraprobiotics include the use of irradiation, high pressures, sonication and high-intensity ultrasound, ultraviolet rays, ohmic heating, pulsed electric field, supercritical carbon dioxide, drying, pH changes, and thermal treatments [329,330]. Paraprobiotics can be produced by ohmic heating at electric field magnitudes of 8 V/cm for inactivating probiotic cultures (_Lactobacillus acidophilus_ LA-5, _Lacticaseibacillus casei_ 01 and _Bifidobacterium animalis_ subsp. _lactis_ Bb-12) [331]. However, ohmic heating performed at sub-lethal conditions can increase cellular permeability and improve nutrient absorption leading to faster cellular growth [332].