Propionibacterium freudenreichii
is a beneficial food-grade actinobacterium, widely implemented, and thus consumed, in various food products. As the main application,
P. freudenreichii
is used as a ...cheese-ripening starter, mostly in hard type cheeses. Indeed, during manufacture of “Swiss-type” cheeses (or opened-body cheeses), the technological process favors propionibacteria growth, as well as the corresponding propionic fermentation. This leads to the characteristic flavor of these cheeses, through the release of short chain fatty acids and through lipolysis, as well as to their specific texture. To fulfil this ripening, massive amounts of propionibacteria are industrially produced, dried and stored, prior to cheese making. Furthermore,
P. freudenreichii
is commercialized in various probiotic food supplements aiming at preserving intestinal health and comfort, in line with its ability to produce beneficial metabolites (short chain fatty acids, vitamins), as well as immunomodulatory compounds. Other industrial applications of
P. freudenreichii
include the production of food-grade vitamins of the B group, of trehalose, of conjugated linoleic acid, and of biopreservatives. For these different applications, maintaining survival and activity of propionibacteria during production, drying, storage and finally implementation, is crucial. More widely, maintaining live and active probiotic bacteria represents a challenge as the market for probiotic products increases. Probiotic bacteria are, for a bulk majority, freeze-dried, but spray drying is also more and more considered. Indeed, this process is both continuous and more cost-efficient, as it utilizes less energy compared to freeze-drying; on the other hand, it exposes bacteria to higher heat and oxidative stresses. Apart from process optimization and strain selection, it is possible to enhance the resistance of bacteria by taking advantage of their adaptation capacity. Indeed,
P. freudenreichii
stress tolerance can be boosted by different pretreatments applied before the drying step, thus considerably increasing its final survival. In particular, adaptation to hyperosmotic conditions improves stress tolerance, while the presence of osmoprotectants may mitigate this improvement. Thermal adaptation also modulates tolerance towards these technological challenges. The composition of the growth medium, including the ratio between the carbohydrates provided and the non-protein nitrogen, plays a key role in driving the accumulation of osmoprotectants. This, in turn, determines
P. freudenreichii
tolerance towards different stresses, and overall towards both freeze-drying and spray-drying. As an example, the accumulation of trehalose enhances its spray-drying survival, while the accumulation of glycine betaine enhances its freeze-drying survival. Growth of propionibacteria in hyperconcentrated whey was used to trigger multiple stress tolerance acquisition, underpinned by overexpression of key stress protein, accumulation of cytoplasmic storage compounds, and leading to enhanced spray-drying survival. A simplified process, from cultivation to atomization, was developed by using whey as a 2-in-1 medium in which propionibacteria were grown, protected and dried with minimal cell death. This innovative process was then subjected to scaling up at the industrial level. In this aim, a gentle multi-stage drying process offering mild drying conditions by coupling spray drying with belt drying, led to final probiotic survival close to 100% when stress tolerance acquisition was previously implemented. Such innovation opens new avenues for the efficient, cost-effective and sustainable development of new probiotic production technologies, as well as probiotic application in the context of food and feed.
Key points
•
Propionibacteria acquire multi-stress tolerance when grown in hyper-concentrated whey.
•
Spray drying of osmo-adapted probiotic bacteria is possible with limited cell death.
•
A two-in-one drying method is developed to grow and dry probiotic bacteria in the same matrix.
Microencapsulation of lactic acid bacteria (LAB) via spray drying differs from that of common bioactive substances in that the intrinsic stress tolerance of cells can be modulated to improve cell ...survival. In this study, elevated growth temperatures that were 3–5 °C above the standard conditions were used to culture
Lactococcus lactis
subsp.
cremoris
,
Lactobacillus rhamnosus
GG (LGG), and
Lactobacillus acidophilus
for spray drying. The heat-adapted cultures showed lower bacterial population than the controls by 0.45 log at stationary growth phase and produced lactobacilli cells with elongated shape, while their metabolic activities were maintained similar to the controls. Heat-adapted
L
.
cremoris
and LGG demonstrated increases in survival by 0.7–1.5 log and 0.3 log, respectively, after heat treatment at 60 °C. The thermotolerance of
L
.
acidophilus
grown at 42 °C was dependent on growth phase, and the culture entered death phase within 24 h of incubation. The survival of heat-adapted
L
.
cremoris
and
L
.
acidophilus
after spray drying was increased by 21.0% and 13.7%, respectively, whereas the increase shown by LGG was relatively insignificant (9.9%). Spray-dried powders containing heat-adapted cells showed substantial reduction of viability at the first week of storage, reaching 1.03–1.23 log, compared to 0.87–0.90 log of reduction shown by the controls. The findings demonstrated that strain-specific cellular response toward variations in growth conditions is crucial to the intrinsic properties of LAB and to cell survival during spray drying and storage. Controlling cellular response is one of the key factors in developing a viable spray drying scheme for active LAB.
Propionibacterium freudenreichii
is a beneficial bacterium widely used in food as a probiotic and as a cheese-ripening starter. In these different applications, it is produced, dried, and stored ...before being used. Both freeze-drying and spray-drying were considered for this purpose. Freeze-drying is a discontinuous process that is energy-consuming but that allows high cell survival. Spray-drying is a continuous process that is more energy-efficient but that can lead to massive bacterial death related to heat, osmotic, and oxidative stresses. We have shown that
P. freudenreichii
cultivated in hyperconcentrated rich media can be spray-dried with limited bacterial death. However, the general stress tolerance conferred by this hyperosmotic constraint remained a black box. In this study, we modulated
P. freudenreichii
growth conditions and monitored both osmoprotectant accumulation and stress tolerance acquisition. Changing the ratio between the carbohydrates provided and non-protein nitrogen during growth under osmotic constraint modulated osmoprotectant accumulation. This, in turn, was correlated with
P. freudenreichii
tolerance towards different stresses, on the one hand, and towards freeze-drying and spray-drying, on the other. Surprisingly, trehalose accumulation correlated with spray-drying survival and glycine betaine accumulation with freeze-drying. This first report showing the ability to modulate the trehalose/GB ratio in osmoprotectants accumulated by a probiotic bacterium opens new perspectives for the optimization of probiotics production.
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.
► Increasing pH for dry heating accelerates whey proteins denaturation/aggregation. ► Protein aggregation through intermolecular disulphide bonds occurs at pH 2.5. ► Disulphide bonds and other ...covalent bonds are formed at pH 4.5 and 6.5. ► Dry heating at pH 2.5 induces protein hydrolysis into peptides.
The effect of pH on the heat-induced denaturation/aggregation of whey protein isolate (WPI) in the dry state was investigated. WPI powders at different pH values (6.5, 4.5, and 2.5) and controlled water activity (0.23) were dry heated at 100
°C for up to 24
h. Dry heating was accompanied by a loss of soluble proteins (native-like β-lactoglobulin and α-lactalbumin) and the concomitant formation of aggregated structures that increased in size as the pH increased. The loss of soluble proteins was less when the pH of the WPI was 2.5; in this case only soluble aggregates were observed. At higher pH values (4.5 and 6.5), both soluble and insoluble aggregates were formed. The fraction of insoluble aggregates increased with increasing pH. Intermolecular disulphide bonds between aggregated proteins predominated at a lower pH (2.5), while covalent cross-links other than disulphide bonds were also formed at pH 4.5 and 6.5. Hence, pH constitutes an attractive tool for controlling the dry heat-induced denaturation/aggregation of whey proteins and the types of interactions between them. This may be of great importance for whey ingredients having various pH values after processing.
BL23 has a recognized probiotic potential, which includes immune modulation, protection toward induced colitis, toward induced colon cancer and toward dissemination of pathogens. In
, as well as in ...other probiotics, both probiotic and technological abilities are highly dependent (1) on the substrate used to grow bacteria and (2) on the process used to dry and store this biomass. Production and storage of probiotics, at a reasonable financial and environmental cost, becomes a crucial challenge. Food-grade media must be used, and minimal process is preferred. In this context, we have developed a "2-in-1" medium used both to grow and to dry
BL23, considered a fragile probiotic strain. This medium consists in hyper-concentrated sweet whey (HCSW).
BL23 grows in HCSW up to 30% dry matter, which is 6 times-concentrated sweet whey. Compared to isotonic sweet whey (5% dry matter), these growth conditions enhanced tolerance of
BL23 toward heat, acid and bile salts stress. HCSW also triggered intracellular accumulation of polyphosphate, of glycogen and of trehalose. A gel-free global proteomic differential analysis further evidenced overexpression of proteins involved in pathways known to participate in stress adaptation, including environmental signal transduction, oxidative and metal defense, DNA repair, protein turnover and repair, carbohydrate, phosphate and amino acid metabolism, and in osmoadaptation. Accordingly, HCSW cultures of
BL23 exhibited enhanced survival upon spray drying, a process known to drastically affect bacterial viability. This work opens new perspectives for sustainable production of dried probiotic lactobacilli, using food industry by-products and lowering energy costs.
The drying of milk concentrate droplets usually leads to specific particle morphology influencing their properties and their functionality. Understanding how the final shape of the particle is formed ...therefore represents a key issue for industrial applications. In this study, a new approach to the investigation of droplet–particle conversion is proposed. A single droplet of concentrated globular proteins extracted from milk was deposited onto a hydrophobic substrate and placed in a dry environment. Complementary methods (high-speed camera, confocal microscopy, and microbalance) were used to record the drying behavior of the concentrated protein droplets. Our results showed that whatever the initial concentration, particle formation included three dynamic stages clearly defined by the loss of mass and the evolution of the internal and external shapes of the droplet. A new and reproducible particle shape was related in this study. It was observed after drying a smooth, hemispherical cap-shaped particle, including a uniform protein shell and the nucleation of an internal vacuole. The particle morphology was strongly influenced by the drying environment, the contact angle, and the initial protein concentration, all of which governed the duration of the droplet shrinkage, the degree of buckling, and the shell thickness. These results are discussed in terms of specific protein behaviors in forming a predictable and a characteristic particle shape. The way the shell is formed may be the starting point in shaping particle distortion and thus represents a potential means of tuning the particle morphology.
•Sweet whey (SW) was used as a medium for biomass production and spray drying.•Highly concentrated sweet whey (20~30% w/w) increased initial bacteria populations.•Highly concentrated SW decreased the ...dependence of bacteria growth on casein peptone.•Highly concentrated SW increased bacteria survival after spray drying.•Bacteria in powders dried from highly concentrated SW had better storage stability.
Preservation of probiotics represents a challenge as the probiotic market increases. A simplified process from growth to drying of probiotics was investigated by utilizing sweet whey as a double-used medium. Its total solid content (TS) was increased in order to achieve one-step drying of bacterial cultures with higher levels of dry matter. Two probiotic strains, Lactobacilllus casei BL23 and Propionibacterium freudenreichii ITG P20, were used in this study. Interestingly, after increasing the TS of sweet whey from 5 to 20 or 30%, final population of both probiotic strains was higher, instead of being inhibited by the high osmolality. The final L. casei population was less dependent on casein peptone supplementation. The probiotic survival after spray drying was also improved when grown in culture media with 20 and 30% TS. Moreover, the probiotics in the powders from these higher TS culture media maintained considerably more stable viability over 4 month's storage at 4 °C.
Along with the increase in the fresh cheese production market, there is a concomitant increase in the volume of its by-product, lactic acid whey (LAW). This type of whey is especially rich in organic ...acids and ash content, making it more difficult to develop applications for human food. In view of its hygroscopicity, this type of whey is in fact clearly the most difficult to dry properly, and its high level of mineralization narrows its potential uses for nutritional reasons. The aim of this study was to evaluate the ability to use nanofiltration (NF) for the production of partially demineralized LAW powder with regard to the dryability of the concentrate and the quality of the powder at a semi-industrial scale. The strong selectivity of this demineralization process results in a 30% reduction in lactic acid content and a reduction of between 46 and 60% in monovalent ions. The dryability of the NF LAW concentrate is improved as well. Moreover, the energy cost of the overall process is reduced by 43%. These elements highlight the benefit of inserting an industrial NF step into the overall processing of LAW and should significantly contribute to the production of partially demineralized LAW powder.
•The semi-industrial scale-up of nanofiltered lactic acid whey drying is possible.•The results are similar to those obtained on a small pilot plant in the laboratory.•The nanofiltration of lactic acid whey reduces stickiness during drying.•The nanofiltration of lactic acid whey decreases the hygroscopicity of the powder.
Infant formulas (IFs) are used as substitutes for human milk and are mostly based on cow milk proteins. For sustainability reasons, animal protein alternatives in food are increasingly being ...considered, as plant proteins offer interesting nutritional and functional benefits for the development of innovative IFs. This study aimed to assess how a partial substitution (50%) of dairy proteins with faba bean and pea proteins influenced the digestibility of IFs under simulated dynamic in vitro digestion, which were set up to mimic infant digestion. Pea- and faba bean-based IFs (PIF and FIF, respectively) have led to a faster aggregation than the reference milk-based IF (RIF) in the gastric compartment; that did not affect the digesta microstructure at the end of digestion. The extent of proteolysis was estimated via the hydrolysis degree, which was the highest for FIF (73%) and the lowest for RIF (50%). Finally, it was apparent that in vitro protein digestibility and protein digestibility-corrected amino acid score (PDCAAS)-like scores were similar for RIF and FIF (90% digestibility; 75% PDCAAS),
lower for PIF (75%; 67%). Therefore, this study confirms that faba bean proteins could be a good candidate for partial substitution of whey proteins in IFs from a nutritional point of view, provided that these in vitro results are confirmed in vivo.
PDF
