Review: Adaptation of Beneficial Propionibacteria, Lactobacilli, and Bifidobacteria Improves Tolerance Toward Technological and Digestive Stresses

Abstract

This review deals with beneficial bacteria, with a focus on lactobacilli, propionibacteria, and bifidobacteria. As being recognized as beneficial bacteria, they are consumed as probiotics in various food products. Some may also be used as starters in food fermentation. In either case, these bacteria may be exposed to various environmental stresses during industrial production steps, including drying and storage, and during the digestion process. In accordance with their adaptation to harsh environmental conditions, they possess adaptation mechanisms, which can be induced by pretreatments. Adaptive mechanisms include accumulation of compatible solutes and of energy storage compounds, which can be largely modulated by the culture conditions. They also include the regulation of energy production pathways, as well as the modulation of the cell envelop, i.e., membrane, cell wall, surface layers, and exopolysaccharides. They finally lead to the overexpression of molecular chaperones and of stress-responsive proteases. Triggering these adaptive mechanisms can improve the resistance of beneficial bacteria toward technological and digestive stresses. This opens new perspectives for the improvement of industrial processes efficiency with regard to the survival of beneficial bacteria. However, this bibliographical survey evidenced that adaptive responses are strain-dependent, so that growth and adaptation should be optimized case-by-case.

The Inoculation of Probiotics In Vivo Is a Challenge: Strategies to Improve Their Survival, to Avoid Unpleasant Changes, or to Enhance Their Performances in Beverages

“…Phenotyping is one of the most commonly used methods to modify the properties of probiotics and food-grade microorganisms; this approach has been referred to by many authors as "adaptive evolution" or "pre-adaptation or cross-protection" and has some applications for the inoculation of probiotics in fruit-juices [19,21,23].…”

“…Bacterial cells possess a multitude of defense mechanisms, such as chaperones to assist folding of misfolded proteins, proteases which degrade proteins which are irreversibly damaged, transport systems, catalases, and superoxide dismutases to counteract ROS, as well as proton pumps, decarboxylases, and transporters to combat decreases in intracellular pH [19,21,23]. Isolation and identification of naturally-tolerant strains can ensure robustness during processing and storage (thermal treatments, freeze-drying, chilled or cold storage, presence of antimicrobial compounds such as phenols, etc.…”

“…), and gastrointestinal transit. Alternatively, exploiting the inherent probiotic stress response to improve tolerance capacities of existing probiotic strains could make them amenable to large-scale production and storage [21].…”

“…(a) pH modification to trigger acid adaptation [21,[26][27][28]: Probiotics are cultured in media adjusted to suboptimal pH (4.5-5.5) for several passages before inoculation in acid matrix (for example, fruit juices); (b) Osmoadaptation [29,30]: Microorganisms are grown in hyperosmotic media (for example, hyperconcentrated sweet whey) to trigger adaptation to drying; (c) Media supplementation with sugars (mannose, trehalose, sucrose) [31,32] to improve viability during freeze-drying; (d) Media supplementation with protective compounds (arginine, Tween 80, aspartate, gluthatione) [19,21] to improve acid resistance; (e) Media supplementation with prebiotics [33,34] generally increases viability throughout storage; (f) Starvation [28] for a general increase of viability during storage: Probiotics are cultured in media with a few nutrients (amino acids and/or sugar) before inoculation in food. This practice could increase viability during refrigerated storage; (g) Cold-adaptation [35]: Probiotics and/or starter strains are cultured at suboptimal temperatures (15-20 • C), thus increasing their technological performances in food; (h) Media supplementation with phenols (for example, vanillic acid) to improve strain viability in juices [26]; (i) Strain culturing in presence of increasing amount of the final food matrix [26]: Probiotics could be cultured in the presence of increasing amounts of juices (from 10% to 50%), thus increasing their viability in the product.…”

“…Table 1. Stresses encountered by food-grade microorganisms during food production and storage [19][20][21].…”