Calcium-Aggregated Milk: a Potential New Option for Improving the Viability of Lactic Acid Bacteria Under Heat Stress

The Effect of Decreased Ca++/Mg++ ATPase Activity on Lactobacillus delbrueckii subsp. bulgaricus sp1.1 Survival during Spray Drying

Compared with the commonly used technique of freeze-drying, spray drying has lower energy costs. However, spray drying also has a fatal disadvantage: a lower survival rate. In this study, the survival of bacteria in a spray-drying tower decreased as the water content was reduced. The water content of 21.10% was the critical point for spray drying Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) sp1.1 based on sampling in the tower. Based on the relationship between the moisture content of spray drying and the survival rate, the water content of 21.10% was also the critical point for the change in the survival rate during spray drying. Proteomic analysis was used to investigate the reasons for L. bulgaricus sp1.1 inactivation during and after spray drying. Gene Ontology (GO) enrichment revealed that differentially expressed proteins were mainly associated with the cell membrane and transport. In particular, proteins related to metal ion transport included those involved in the transport of potassium, calcium and magnesium ions. The protein-protein interaction (PPI) network revealed that Ca⁺⁺/Mg⁺⁺ adenosine triphosphatase (ATPase) may be a key protein. Ca⁺⁺/Mg⁺⁺ ATPase activity decreased substantially during spray drying (p < 0.05). Supplementation with Ca⁺⁺ and Mg⁺⁺ significantly increased the expression of ATPase-related genes and enzyme activity (p < 0.05). The Ca⁺⁺/Mg⁺⁺ ATPase activity of L. bulgaricus sp1.1 was enhanced by increasing the intracellular Ca⁺⁺ or Mg⁺⁺ concentration, thus increasing the survival of spray-dried LAB. Bacterial survival rates were increased to 43.06% with the addition of Ca⁺⁺ and to 42.64% with the addition of Mg⁺⁺, respectively. Ca⁺⁺/Mg⁺⁺ ATPase may be the key to the damage observed in spray-dried bacteria. Furthermore, the addition of Ca⁺⁺ or Mg⁺⁺ also reduced bacterial injury during spray drying by enhancing the activity of Ca⁺⁺/Mg⁺⁺ ATPase.

Alginate/Fish Gelatin-Encapsulated Lactobacillus acidophilus: A Study on Viability and Technological Quality of Bread during Baking and Storage

In the present study, Lactobacillus acidophilus LA-5 was microencapsulated in sodium alginate, followed by fish gelatin coating (0.5, 1.5, and 3%). The survival of L. acidophilus in bread before and after encapsulation in alginate/fish gelatin during the baking and 7-day storage was investigated. Moreover, the effect of alginate/fish gelatin-encapsulated L. acidophilus on the technological properties of bread (hardness, staling rate, water content, oven spring, specific volume, and internal texture structure) was evaluated. Compared with control (free bacteria), encapsulated L. acidophilus in alginate/fish gelatin showed an increase in the viability of bread until 2.49 and 3.07 log CFU/g during baking and storage, respectively. Good viability of (10⁶ CFU/g) for probiotic in encapsulated L. acidophilus in alginate/fish gelatin (1.5 and 3%, respectively) after 4-day storage was achieved. Fish gelatin as a second-layer carrier of the bacteria had a positive effect on improving the technical quality of bread. Furthermore, the staling rate of bread containing encapsulated L. acidophilus alginate/fish gelatin 0.5, 1.5, and 3% decreased by 19.5, 25.8, and 31.7%, respectively. Overall, the findings suggested encapsulation of L. acidophilus in alginate/fish gelatin capsule had great potential to improve probiotic bacteria’s survival during baking and storage and to serve as an effective bread enhancer.

Exploring the interactions between Lactobacillus rhamnosus GG and whey protein isolate for preservation of the viability of bacteria through spray drying

Protective agents used in spray drying protect the activity of lactic acid bacteria (LAB) by stabilizing the subcellular structures, constituting a protective layer at the cellular surface, or having mild drying kinetics. The effects of a reputed protectant, whey protein isolate (WPI), on Lactobacillus rhamnosus GG (LGG) were examined by exposing the cells to WPI solution to induce protein adsorption at the cellular surface prior to spray drying. WPI-treated LGG demonstrated enhanced thermotolerance with cell survival increased by 1.64 log after heat treatment. The survival after spray drying was significantly decreased from 45.75% to 8.6% and from 32.96% to 10.44%, when the WPI-treated cells were resuspended in trehalose solution or reconstituted skimmed milk as protectant, respectively, associated with decreased growth capability and metabolic activity. The contact with WPI appeared to stimulate the cellular response of LGG. With well-maintained cell viability and intact cellular membrane, the metabolic activity of WPI-treated LGG was decreased, and subsequent resuspension of the cells in trehalose solution led to a reduction in the stability of the cellular surface charge. The WPI-treated cells showed marginally increased surface roughness, indicating possible WPI attachment, but there was no thick protein coverage at the cellular surface and the size distribution of cells was unaffected. It was proposed that the enhanced thermotolerance and the decreased survival of spray-dried LGG could be linked to the cellular response toward WPI and protectant media, which may vary among individual LAB strains. Modulating the strain-specific interactions between the LAB cells and the protectant constituents could be crucial to maximizing cell viability retention after spray drying.

Influence of Pulsed Electric Field on Accumulation of Calcium in Lactobacillus rhamnosus B 442

Calcium is an element that performs many important functions in the human body. A study was conducted on the use of a pulsed electric field (PEF) to enrich cells of Lactobacillus rhamnosus B 442 in calcium ions. The highest concentration of calcium ions in bacterial cells (7.30 mg/g d.m.) was obtained at ion concentration of 200 µg/ml of medium and with the use of the following PEF parameters: field strength 3.0 kV/cm, exposure time 10 min, pulse width 75 ms and 20 h of culturing after which bacteria were treated with the field. Cell biomass varied in the range from 0.09 g/g d.m. to 0.252 g/g d.m., and the total number of bacteria ranged from 10¹⁰ CFU/ml to 10¹² CFU/ml. Microscope photographs prove that calcium ions were situated within the cells of the bacteria, and electroporation contributed to an increase in the effectiveness of the ion bioaccumulation process. Samples containing calcium and subjected to electroporation displayed intensive fluorescence. The significance of this research was the possibility of using probiotic bacteria enriched with calcium ions for the production of functional food in subsequent studies.

Comparison of microbial community and metabolites in spontaneous fermentation of two types Daqu starter for traditional Chinese vinegar production

Daqu starter, an important saccharifying and fermenting agent for the brewing process of traditional vinegar, is manufactured by spontaneous solid-state fermentation which routinely undergoes low or medium incubation temperature. Previous studies have demonstrated that the temperature plays a pivotal role in Daqu quality. Hence, to explore the feasibility of high temperature fermentation applied in the vinegar Daqu brewing and provide guidelines of controlling environmental parameters in traditional vinegar industries, the microbial community and metabolites of vinegar Daqu during medium-temperature and high-temperature fermentation processes (namely, MTFP and HTFP) were compared. The results indicated that the glucoamylase activity, amylase activity and microbial community showed no significant difference in the end of two batches (P > 0.05). Enterobacteriales, Lactobacillales, Bacillales, Saccharomycetales and Mucorales were the dominant orders during MTFP and HTFP. Redundancy analysis revealed that incubation temperature showed positive correlation with the microbial composition from days 3-14 of the fermentation process and was positively associated with the predominant phylotypes of Bacillales, Mucorales, Xanthomonadales and Rickettsiales. The acidity and moisture showed major correlations with microbial composition on day 1 of MTFP and were positively related with the predominant phylotypes of Mucorales and Lactobacillales at the order level. Moreover, higher relative contents of all volatiles were shown in the end of HTFP (13.91 mg/100 g Daqu) compared to MTFP (10.01 mg/100 g Daqu). This work illustrates high temperature (approximately 60°C) fermentation is promising to improve the vinegar Daqu flavor and shall likely contribute to preferably make traditional Daqu by modulating steerable environmental parameters.

Producing Powders Containing Active Dry Probiotics With the Aid of Spray Drying

Probiotics are microorganisms capable of conferring health benefits to humans and animals when ingested. Probiotic products that prevail in food market usually contain viable bacteria from Lactobacillus and Bifidobacterium genera. Bacterial strains in these genera often have complex nutrient requirements and tend to be fragile under environmental stresses. How to incorporate the cells into food matrix without causing undesired viability loss is a key issue for developing products of viable probiotics. Spray drying offers a rapid way to produce powders encapsulating probiotics in a matrix of protectant(s), which may extend the term of viability preservation and expand the application of probiotic products. In spray drying, feed solution that contains probiotic cells and dissolved or suspended protectant solids are atomized into droplets, which are quickly converted into particles by drying in a hot airflow. The harsh conditions and interplaying stresses make the maintenance of cell viability a challenging task. To enhance cell survival in dried powders, various approaches have been attempted, including the enhancement of the intrinsic stress tolerance of cells, adjustment of protectant composition, and optimization of the production process and dryer settings. This chapter discusses important factors influencing probiotic viability during spray drying from aspects of microbiology, food chemistry, and drying process. The mechanisms underlying the influences at the droplet and cellular levels and strategies taken to protect cell viability at the process level are discussed.

Thermal Aggregation of Calcium-Fortified Skim Milk Enhances Probiotic Protection during Convective Droplet Drying

Probiotic bacteria have been reported to confer benefits on hosts when delivered in an adequate dose. Spray-drying is expected to produce dried and microencapsulated probiotic products due to its low production cost and high energy efficiency. The bottleneck in probiotic application addresses the thermal and dehydration-related inactivation of bacteria during process. A protective drying matrix was designed by modifying skim milk with the principle of calcium-induced protein thermal aggregation. The well-defined single-droplet drying technique was used to monitor the droplet-particle conversion and the protective effect of this modified Ca-aggregated milk on Lactobacillus rhamnosus GG. The Ca-aggregated milk exhibited a higher drying efficiency and superior protection on L. rhamnosus GG during thermal convective drying. The mechanism was explained by the aggregation in milk, causing the lower binding of water in the serum phase and, conversely, local concentrated milk aggregates involved in bacteria entrapment in the course of drying. This work may open new avenues for the development of probiotic products with high bacterial viability and calcium enrichment.

Hyperconcentrated Sweet Whey, a New Culture Medium That Enhances Propionibacterium freudenreichii Stress Tolerance

Propionibacterium freudenreichii is used as a cheese-ripening starter and as a probiotic. Its reported physiological effects at the gut level, including modulation of bifidobacteria, colon epithelial cell proliferation and apoptosis, and intestinal inflammation, rely on active metabolism in situ Survival and activity are thus key factors determining its efficacy, creating stress adaptation and tolerance bottlenecks for probiotic applications. Growth media and growth conditions determine tolerance acquisition. We investigated the possibility of using sweet whey, a dairy by-product, to sustain P. freudenreichii growth. It was used at different concentrations (dry matter) as a culture medium. Using hyperconcentrated sweet whey led to enhanced multistress tolerance acquisition, overexpression of key stress proteins, and accumulation of intracellular storage molecules and compatible solutes, as well as enhanced survival upon spray drying. A simplified process from growth to spray drying of propionibacteria was developed using sweet whey as a 2-in-1 medium to both culture P. freudenreichii and protect it from heat and osmotic injury without harvesting and washing steps. As spray drying is far cheaper and more energy efficient than freeze-drying, this work opens new perspectives for the sustainable development of new starter and probiotic preparations with enhanced robustness.

IMPORTANCE

In this study, we demonstrate that sweet whey, a dairy industry by-product, not only allows the growth of probiotic dairy propionibacteria, but also triggers a multitolerance response through osmoadaptation and general stress response. We also show that propionibacteria accumulate compatible solutes under these culture conditions, which might account for the limited loss of viability after spray drying. This work opens new perspectives for more energy-efficient production of dairy starters and probiotics.