Methods for disruption of microbial cells for potential use in the dairy industry—a review

Hydrothermal conditioning of oleaginous yeast cells to enable recovery of lipids as potential drop-in fuel precursors

BACKGROUND

Lipids produced using oleaginous yeast cells are an emerging feedstock to manufacture commercially valuable oleochemicals ranging from pharmaceuticals to lipid-derived biofuels. Production of biofuels using oleaginous yeast is a multistep procedure that requires yeast cultivation and harvesting, lipid recovery, and conversion of the lipids to biofuels. The quantitative recovery of the total intracellular lipid from the yeast cells is a critical step during the development of a bioprocess. Their rigid cell walls often make them resistant to lysis. The existing methods include mechanical, chemical, biological and thermochemical lysis of yeast cell walls followed by solvent extraction. In this study, an aqueous thermal pretreatment was explored as a method for lysing the cell wall of the oleaginous yeast Rhodotorula toruloides for lipid recovery.

RESULTS

Hydrothermal pretreatment for 60 min at 121 °C with a dry cell weight of 7% (w/v) in the yeast slurry led to a recovery of 84.6 ± 3.2% (w/w) of the total lipids when extracted with organic solvents. The conventional sonication and acid-assisted thermal cell lysis led to a lipid recovery yield of 99.8 ± 0.03% (w/w) and 109.5 ± 1.9% (w/w), respectively. The fatty acid profiles of the hydrothermally pretreated cells and freeze-dried control were similar, suggesting that the thermal lysis of the cells did not degrade the lipids.

CONCLUSION

This work demonstrates that hydrothermal pretreatment of yeast cell slurry at 121 °C for 60 min is a robust and sustainable method for cell conditioning to extract intracellular microbial lipids for biofuel production and provides a baseline for further scale-up and process integration.

Ultrasonic processing: effects on the physicochemical and microbiological aspects of dairy products

Dairy products that are contaminated by pathogenic microorganisms through unhygienic farm practices, improper transportation, and inadequate quality control can cause foodborne illness. Furthermore, inadequate storage conditions can increase the microflora of natural spoilage, leading to rapid deterioration. Ultrasound processing is a popular technology used to improve the quality of milk products using high-frequency sound waves. It can improve food safety and shelf life by modifying milk protein and fats without negatively affecting nutritional profile and sensory properties, such as taste, texture, and flavor. Ultrasound processing is effective in eliminating pathogenic microorganisms, such as Salmonella, Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes. However, the efficiency of processing is determined by the type of microorganism, pH, and temperature of the milk product, the frequency and intensity of the applied waves, as well as the sonication time. Ultrasound processing has been established to be a safe and environmentally friendly alternative to conventional heat-based processing technologies that lead to the degradation of milk quality. There are some disadvantages to using ultrasound processing, such as the initial high cost of setting it up, the production of free radicals, the deterioration of sensory properties, and the development of off-flavors with lengthened processing times. The aim of this review is to summarize current research in the field of ultrasound processing and discuss future directions.

A comprehensive report on valorization of waste to single cell protein: strategies, challenges, and future prospects

The food insecurity due to a vertical increase in the global population urgently demands substantial advancements in the agricultural sector and to identify sustainable affordable sources of nutrition, particularly proteins. Single-cell protein (SCP) has been revealed as the dried biomass of microorganisms such as algae, yeast, and bacteria cultivated in a controlled environment. Production of SCP is a promising alternative to conventional protein sources like soy and meat, due to quicker production, minimal land requirement, and flexibility to various climatic conditions. In addition to protein production, it also contributes to waste management by converting it into food and feed for both human and animal consumption. This article provides an overview of SCP production, including its benefits, safety, acceptability, and cost, as well as limitations that constrains its maximum use. Furthermore, this review criticizes the downstream processing of SCP, encompassing cell wall disruption, removal of nucleic acid, harvesting of biomass, drying, packaging, storage, and transportation. The potential applications of SCP, such as in food and feed as well as in the production of bioplastics, emulsifiers, and as flavoring agents for baked food, soup, and salad, are also discussed.

Hydroxy fatty acids in the surface Earth system

Lipids are ubiquitous and highly abundant in a wide range of organisms and have been found in various types of environmental media. These molecules play a crucial role as organic tracers by providing a chemical perspective on viewing the material world, as well as offering a wealth of information on metabolic activities. Among the diverse lipid compounds, hydroxy fatty acids (HFAs) with one to multiple hydroxyl groups attached to the carbon chain stand out as important biomarkers for different sources of organic matter. HFAs are widespread in nature and are involved in biotransformation and oxidation processes in living organisms. The unique chemical and physical properties attributed to the hydroxyl group make HFAs ideal biomarkers in biomedicine and environmental toxicology, as well as organic geochemistry. The molecular distribution patterns of HFAs can be unique and diagnostic for a given class of organisms, including animals, plants, and microorganisms. Thus, HFAs can act as a valuable proxy for understanding the ecological relationships between different organisms and their environment. Furthermore, HFAs have numerous industrial applications due to their higher reactivity, viscosity, and solvent miscibility. This review paper integrates the latest research on the sources and chemical analyses of HFAs, as well as their applications in industrial/medicinal production and as biomarkers in environmental studies. This review article also provides insights into the biogeochemical cycles of HFAs in the surface Earth system, highlighting the importance of these compounds in understanding the complex interactions between living organisms and the environment.

High pressure homogenization applied to fruit juices: Effects on microbial inactivation and on maintenance of bioactive components

High-pressure homogenization (HPH) is a non-thermal technology widely studied to replace, partially or in total, the conventional thermal preservation processes used in the food industry, thus minimizing undesirable changes in the nutritional and sensory characteristics of liquid products. The main effect of HPH is the size reduction of dispersed particles thus affecting physical stability of the products, despite also inactivating microorganisms, preserving bioactive compounds, and maintaining sensory characteristics. During the process, the fluid is driven under high-pressure through a micrometric gap inside the valve. Phenomena including cavitation, shear and turbulence are responsible for the changes in the fluid. From this perspective, the present paper reviews the effects of HPH on the inactivation of microorganisms and preservation of bioactive compounds of fruit juices treated with this technology. The juice matrices reported were apple, apricot, banana, blackberry, carrot, kiwifruit, mandarin, mango, orange, peach, pomegranate, rosehip, strawberry and tomato. The paper elucidates the potential application of HPH to fruit juice processing aiming at producing safe products with high nutritional and sensory quality.

Lipid Droplets from Plants and Microalgae: Characteristics, Extractions, and Applications

Plant and algal LDs are gaining popularity as a promising non-chemical technology for the production of lipids and oils. In general, these organelles are composed of a neutral lipid core surrounded by a phospholipid monolayer and various surface-associated proteins. Many studies have shown that LDs are involved in numerous biological processes such as lipid trafficking and signaling, membrane remodeling, and intercellular organelle communications. To fully exploit the potential of LDs for scientific research and commercial applications, it is important to develop suitable extraction processes that preserve their properties and functions. However, research on LD extraction strategies is limited. This review first describes recent progress in understanding the characteristics of LDs, and then systematically introduces LD extraction strategies. Finally, the potential functions and applications of LDs in various fields are discussed. Overall, this review provides valuable insights into the properties and functions of LDs, as well as potential approaches for their extraction and utilization. It is hoped that these findings will inspire further research and innovation in the field of LD-based technology.

Isolation and characterization of a high-efficiency algicidal bacterium Pseudoalteromonas sp. LD-B6 against the harmful dinoflagellate Noctiluca scintillans

The dinoflagellate Noctiluca scintillans is a harmful algal species that is globally distributed and poses a certain threat to marine ecosystems. Recent research has shown that the application of algicidal bacteria is a promising method to prevent and control such harmful algal blooms (HABs), given its advantages of safety and efficiency. In this study, a strain of algicidal bacterium LD-B6 with high efficiency against N. scintillans was isolated from the coastal waters of Lianyungang, China. 16S rDNA sequence analysis showed that the strain LD-B6 belongs to the genus Pseudoalteromonas. Furthermore, the algicidal effect of LD-B6 on N. scintillans was investigated. The results showed that strain LD-B6 exerted strong algicidal activity against N. scintillans. After 12 h of bacterial culture addition to algal cultures at a 2% final volume rate, the algicidal activity reached 90.5%, and the algicidal activity of LD-B6 was influenced by the density of N. scintillans. In addition, the algicidal bacterium LD-B6 was found to indirectly lyse algal cells by secreting extracellular compounds. These algicidal compounds were stable, indicating that they are not proteins. Importantly, strain LD-B6 was broadly general, showing varying degrees of lysing effects against five of the six algal species tested. On the basis of the described studies above, the algicidal powder was also initially developed. In summary, the isolated bacterial strain LD-B6 shows the potent algicidal capability to serve as a candidate algicidal bacterium against N. scintillans blooms.

Bioprocessing of recombinant proteins from Escherichia coli inclusion bodies: insights from structure-function relationship for novel applications

The formation of inclusion bodies (IBs) during expression of recombinant therapeutic proteins using E. coli is a significant hurdle in producing high-quality, safe, and efficacious medicines. The improved understanding of the structure-function relationship of the IBs has resulted in the development of novel biotechnologies that have streamlined the isolation, solubilization, refolding, and purification of the active functional proteins from the bacterial IBs. Together, this overall effort promises to radically improve the scope of experimental biology of therapeutic protein production and expand new prospects in IBs usage. Notably, the IBs are increasingly used for applications in more pristine areas such as drug delivery and material sciences. In this review, we intend to provide a comprehensive picture of the bio-processing of bacterial IBs, including assessing critical gaps that still need to be addressed and potential solutions to overcome them. We expect this review to be a useful resource for those working in the area of protein refolding and therapeutic protein production.

Performance indicators, coccidia oocyst counts, plasma biochemical parameters and fermentation processes in the cecum of rabbits fed a diet with the addition of black cumin seed meal

The aim of this study was to determine the effects of dietary supplementation with black cumin seed meal on growth performance parameters, coccidia oocyst counts, plasma biochemical parameters and cecal fermentation processes in growing rabbits. A total of 40 male Californian rabbits at 35 days of age were divided into two feeding groups: Control (complete rabbit diet) and Black cumin (2% of the complete diet was replaced with black cumin seed meal). Dietary supplementation with black cumin did not affect growth performance parameters, but it reduced coccidia oocyst counts in the feces of 63-day-old rabbits. Increased liver weight and elevated plasma albumin levels were noted in these rabbits. A significant decrease in small intestinal digesta viscosity was also observed in rabbits fed a diet supplemented with black cumin seed meal. The above change suppressed the formation of putrefactive compounds, i.e. ammonia and branched short-chain fatty acids (SCFAs) in the cecum, but it did not decrease the production of major SCFAs, i.e. acetic, propionic and butyric acids. The current study demonstrated that the dietary addition of 2% black cumin seed meal exerted a modulatory effect on gastrointestinal function, but it did not compromise microbial enzyme activity or SCFA production in the cecum.

Response Surface Methodology for Optimization Membrane Disruption Using Thermolysis in Lipase Lk2 and Lk3

Lk2 and Lk3 were thermostable recombinant lipase and highly expressed in Escherichia coli BL21 (DE3). However, Lk2 and Lk3 accumulated as an inclusion body. To further characterize both recombinant lipases, the soluble enzyme must be obtained first. This study aimed to optimize the disruption of the cell membrane in order to obtain soluble and active lipases. The effects of temperature lysis, pH, and SDS concentration on lipolytic activity Lk2 and Lk3 were investigated using a three-factor Box-Behnken design response surface methods. The optimum condition for the temperature variables at 50°C, pH 8, and 0.34% SDS which gave a lipolytic activity of 0.9 U for Lk2. Meanwhile, Lk3 lipolytic activity of 0.9 U obtained at the temperature of 50°C, pH 8, and 0.1% SDS. This result showed efficient one-step membrane disruption methods using thermolysis with addition of a low concentration of detergent at pH 8. The methods used were effective and applicable in the production of active and soluble thermostable recombinant lipase.

In-situ transesterification of single-cell oil for biodiesel production: a review

In recent years, biodiesel synthesis and production demands have increased because of its high degradability, cleaner emissions, non-toxicity, and an alternative to petroleum diesel. In this context, Single Cell Oil (SCO) has been identified as an alternative feedstock, having the advantage of accumulating high intracellular lipid. SCO/microbial lipids are potential alternatives for sustainable biodiesel production. The traditional technique for biodiesel production from the oils obtained from microbes generally requires two steps: lipid extraction and transesterification. In-situ transesterification is an innovative and renewable process for biodiesel production. It rules out the need to isolate and refine the feedstock lipid, as it directly uses biomass in a single step, i.e., the pretreated biomass will be subjected to in-situ transesterification in the presence of catalysts. Hence, the production cost can be reduced by eliminating the lipid extraction procedure. The current review focuses on the basic features and advantages of in-situ transesterification of SCO for biodiesel production with the aid of short-chain alcohols along with different acid, base, and enzyme catalysts. In addition, a comparative study was carried out to highlight the merits of in-situ transesterification over conventional transesterification.

Recovering Microalgal Bioresources: A Review of Cell Disruption Methods and Extraction Technologies

Microalgae have evolved into a promising sustainable source of a wide range of compounds, including protein, carbohydrates, biomass, vitamins, animal feed, and cosmetic products. The process of extraction of intracellular composites in the microalgae industry is largely determined by the microalgal species, cultivation methods, cell wall disruption techniques, and extraction strategies. Various techniques have been applied to disrupt the cell wall and recover the intracellular molecules from microalgae, including non-mechanical, mechanical, and combined methods. A comprehensive understanding of the cell disruption processes in each method is essential to improve the efficiency of current technologies and further development of new methods in this field. In this review, an overview of microalgal cell disruption techniques and an analysis of their performance and challenges are provided. A number of studies on cell disruption and microalgae extraction are examined in order to highlight the key challenges facing the field of microalgae and their future prospects. In addition, the amount of product recovery for each species of microalgae and the important parameters for each technique are discussed. Finally, pulsed electric field (PEF)-assisted treatments, which are becoming an attractive option due to their simplicity and effectiveness in extracting microalgae compounds, are discussed in detail.

A Review: Application of Enzymes in Dairy Processing Industry

Abstract:

Enzymes are proteins and bio-catalyst. They are responsible for initiating a specific response to a specific outcome. In the dairy industry numerous enzymes are used; rennet and proteolytic enzymes. These enzymes are used for the coagulation and ripening of cheese. Enzymes are also used to increase the nutritional value of dairy products to alleviate the state of malnutrition. This review paper converges on

A Simple and Efficient Mechanical Cell Disruption Method Using Glass Beads to Extract β-Glucans from Spent Brewer’s Yeast

β-glucan extraction from spent brewer’s yeast is a long process that starts with the lysis of yeast cells, this step lasting up to 36 h and can be disadvantageous when working on a small scale. In this study, a rapid cell rupture method was selected for the lysis of spent brewer’s yeast to obtain β-glucans. Optimal parameters were determined for the lysis of a cellular suspension of spent brewer’s yeast by vortexing with glass beads. Thus, parameters such as the number of 10 min vortex cycles from 1 to 3, the concentration of cell suspension (5, 10, and 15%), and the ratio of yeast/glass beads (1:1, 1:2, and 1:3) were varied in a Box-Behnken design. A cell lysis mechanism using glass beads allows the cell to rupture and permits the removal of intracellular content. An increase in yeast suspension concentration decreased the disruption efficiency, while a proportional increase was observed with the yeast/glass beads ratio and the increasing number of vortexing cycles. The optimal parameters for cell lysis were found to be a cell suspension concentration of 5%, a ratio of yeast/glass beads of 1:2, and a vortexing cycle of 3, with a disruption efficiency of 99.8%. The β-glucan fraction extracted from the optimal sample showed characteristic absorption bands at 1370.77 and 1153.92 cm−1, the content of β-glucan being 78.53%.

Effects of different pre-treatments on the properties of polyhydroxyalkanoates extracted from sidestreams of a municipal wastewater treatment plant

The paper deals with effects of two different widespread extraction methods (conventional extraction and Soxhlet extraction) and four different pre-treatments (homogenization with pressure and with blades, sonication, and impact with glass spheres) on the extraction yields and properties of polyhydroxyalkanoate (PHA) extracted from biomass coming from an innovative process (short-cut enhanced phosphorus and PHA recovery) applied in a real wastewater treatment plant. The results show that the two different extraction processes affected the crystallization degree and the chemical composition of the polymer. On the other hand, the extractive yield was highly influenced by pre-treatments: homogenization provided a 15% more extractive yield than the others. Homogenization, especially at high pressure, proved to be the best pre-treatment also in terms of the purity, visual appearance (transparency and clearness), thermal stability, and mechanical performances of the obtained PHA films. All the PHA films begin to melt long before their degradation temperature (Td > 200 °C): this allows their use in the fields of extrusion or compression moulding. SYNOPSIS: Optimizing the extraction of PHAs from municipal wastewater gives a double beneficial environmental impact: wastewater treatment and circular bio-based carbon upgrade to biopolymers for the production of bioplastics and other intersectoral applications.

Performance indicators and gastrointestinal response of rabbits to dietary soybean meal replacement with silkworm pupae and mealworm larvae meals

The objective of this study was to determine the effects of silkworm pupae meal (SPM) and mealworm larvae meal (MLM) on the production results and function of the digestive system in rabbits. Thirty male New Zealand White growing rabbits were divided into three feeding groups: control (C) (10% soybean meal [SBM] in the diet), group SPM (5% SBM and 4% SPM) and group MLM (5% SBM and 4% MLM). Compared with group C, rabbits of groups SPM and MLM, were characterised by higher final body weight and daily body weight gains. They were also found to have better apparent total tract digestibility (ATTD) of ether extract, and acid detergent fibre (ADF) and acid detergent lignin (ADL). Increased digesta viscosity was observed in these rabbits, as well as reduced extracellular activity of bacterial α-glucosidase, β-glucosidase, α-arabinofuranosidase and β-xylosidase in the caecal digesta. Similar differences between groups were also noted for the intracellular activity of β-glucuronidase, total activity of β-xylosidase and α-glucosidase. The SPM and MLM treatments contributed to an increase in the extracellular and total activity of N-acetyl-β-D-glucosaminidase (NAGase) in the caecal digesta. The SPM and MLM treatments were characterised by increased extracellular/total activity of colonic bacterial NAGase as well as increased release rates of NAGase and β-cellobiosidase, compared with group C. The rabbits fed the MLM diet had the lowest caecal concentrations of acetic acid, propionic acid, and total short chain fatty acids (SCFA). The proportion of butyric acid in the caecal SCFA profile was significantly lower in group MLM than in group C. The SPM treatment reduced the colonic concentration of iso-valeric acid. Group C had the highest colonic SCFA pool. It can be concluded that an inclusion of 4% SPM and 4% MLM in rabbit diets improved their production results, as well as beneficially increased the ATTD of fat, ADF and ADL without compromising the ATTD of other nutrients and energy. Although both dietary insect-derived products caused a mobilisation of microbiota to utilise of chitin (see NAGase activity), they stifled the metabolism of large intestinal microbiota, as manifested by decreased enzyme activity and lower SCFA concentrations.

Novel alternative for controlling enzymatic browning: Catalase and its application in fresh-cut potatoes

Surface browning is a vital phenomenon that adversely reduces the quality of fresh-cut potatoes. Although many anti-browning methods have been explored, it is unclear whether exogenous catalase (CAT) treatment influences the enzymatic browning. Our results showed that 0.05% CAT immersion for 5 min alleviated browning during cold storage (4°C, 8 days), which was accompanied by a higher lightness and lower redness; additionally, lower H₂ O₂ and O₂ ·- contents were found. The activities of CAT, ascorbate peroxidase, and glutathione peroxidase and the scavenging efficiency of 2,2-diphenyl-1-picrylhydrazyl were also increased. Moreover, CAT treatment inhibited the activities of polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase and reduced phenol accumulation. Treatment with 0.1% hydrogen peroxide (H₂ O₂ ) achieved the opposite results. This is the first report of CAT application reducing fresh-cut potato browning, providing a safe treatment alternative for enzymatic discoloration and preliminarily revealing the underlying mechanism with insight into antioxidant regulation. PRACTICAL APPLICATION: This research is helpful for fresh-cut potato producers because a novel, safe, easy-to-carry out anti-browning solution was proposed. Dipping in 0.05% catalase solution for 5 min revealed color improvement in the quality of fresh-cut potato slices. The mechanism may rely on enhancing antioxidant ability (ascorbate peroxidase, and glutathione peroxidase, and 2,2-diphenyl-1-picrylhydrazyl scavenging), reducing reactive oxygen species (H₂ O₂ , O₂ ·-, malondialdehyde) and controlling enzymatic browning reaction factors (polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase, and phenol accumulation). This method shows promise for better meeting the requirements and demands of consumers for fresh quality products.

A Review of the Extraction and Closed-Loop Spray Drying-Assisted Micro-Encapsulation of Algal Lutein for Functional Food Delivery

In this study, the physical and chemical properties and bioavailability of lutein have been summarized, with the novelty of this work being the review of lutein from production to extraction, through to preservation and drying, in order to deliver a functional food ingredient. The potential health functions of lutein have been introduced in detail. By comparing algae and marigold flowers, the advantages of algae extraction technology have been discussed. In this article, we have introduced the use of closed-loop spray drying technology to microencapsulate lutein to improve its stability and solubility. Microencapsulation of unstable substances by spray drying is a potentially useful direction that is worth exploring further.

Purified lactases versus whole-cell lactases-the winner takes it all

Lactose-free dairy products are in great demand worldwide due to the high prevalence of lactose intolerance. To make lactose-free dairy products, commercially available β-galactosidase enzymes, also termed lactases, are used to break down lactose to its constituent monosaccharides, glucose and galactose. In this mini-review, the characteristics of lactase enzymes, their origin, and ways of use are discussed in light of their potential for hydrolyzing lactose. We also discuss whole-cell lactase catalysts, which appear to have great potential in terms of cost reduction and convenience, and which are more natural alternatives to purified enzymes. Lactic acid bacteria (LAB) already used in food fermentations seem to be optimal candidates for whole-cell lactases. However, they have not been industrially exploited yet due to technical hurdles. For whole-cell lactases to be efficient, the lactase enzymes inside the cells must be made available for lactose hydrolysis, and thus, cells need to be permeabilized or disrupted prior to use. Here we review state-of-the-art approaches for disrupting or permeabilizing microorganisms. Lastly, based on recent scientific achievements, we propose a novel, resource-efficient, and low-cost scenario for achieving lactose hydrolysis at a dairy plant using a LAB whole-cell lactase.Key points• Lactases (β-galactosidase) are essential for producing lactose-free dairy products• Novel permeabilization techniques facilitate the use of LAB lactases• Whole-cell lactase catalysts have great potential for reducing costs and resources Graphical abstract.

Recent advances in the application of ultrasound in dairy products: Effect on functional, physical, chemical, microbiological and sensory properties

Alternative methods for improving traditional food processing have increased in the last decades. Additionally, the development of novel dairy products is gaining importance due to an increased consumer demand for palatable, healthy, and minimally processed products. Ultrasonic processing or sonication is a promising alternative technology in the food industry as it has potential to improve the technological and functional properties of milk and dairy products. This review presents a detailed summary of the latest research on the impact of high-intensity ultrasound techniques in dairy processing. It explores the ways in which ultrasound has been employed to enhance milk properties and processes of interest to the dairy industry, such as homogenization, emulsification, yogurt and fermented beverages production, and food safety. Special emphasis has been given to ultrasonic effects on milk components; fermentation and spoilage by microorganisms; and the technological, functional, and sensory properties of dairy foods. Several current and potential applications of ultrasound as a processing technique in milk applications are also discussed in this review.

Effect of Cryoconcentration Assisted by Centrifugation-Filtration on Bioactive Compounds and Microbiological Quality of Aqueous Maqui (Aristotelia chilensis (Mol.) Stuntz) and Calafate (Berberis microphylla G. Forst) Extracts Pretreated with High-Pressure Homogenization

The objective of this study was to evaluate the effect of cryoconcentration assisted by centrifugation-filtration on the bioactive compounds and the microbiological quality of aqueous maqui (Aristotelia chilensis (Mol.) Stuntz) and calafate (Berberis microphylla G. Forst) extracts pretreated with high-pressure homogenization (HPH). Aqueous extracts were prepared from fresh fruits which were treated with HPH (predefined pressure and number of passes). The best pretreatment was determined by aerobic mesophilic, fungal, and yeast counts. Treated extracts were frozen at −30 °C in special tubes and centrifuged at 4000 rpm for 10 min to obtain the cryoconcentrated product. The optimal pretreatment conditions for HPH were 200 MPa and one pass in which the extracts exhibited no microorganism counts. Cryoconcentration by freezing and subsequent centrifugation-filtration in a single cycle showed high process efficiency (>95%) in both soluble solids and bioactive compounds (total polyphenols and anthocyanins) and antioxidant capacity of the fresh fruits and extracts. The HPH treatment and subsequent cryoconcentration assisted by centrifugation-filtration is an efficient technology to obtain concentrates with good microbiological quality and a high content of bioactive compounds.

Live-cell ATR-FTIR spectroscopy as a novel bioanalytical tool for cell glucose metabolism research

Current novel drug developments for the treatment of diabetes require multiple bioanalytical assays to interrogate the cellular metabolism, which are costly, laborious and time-consuming. Fourier-transform infrared (FTIR) spectroscopy is a nondestructive, label-free, sensitive and low-cost technique that is recently found to be suitable for studying living cells. The aim of this study is to demonstrate that live-cell FTIR can be applied to study the differences in glucose metabolism in cells in normal culturing medium and cells treated in high glucose (a diabetes model) in order to highlight the potential of the technique in diabetes research. Live HepG2 cells were treated in normal glucose (3.8 mM; control) or high glucose (25 mM) medium and were measured directly using the FTIR approach. Principal component analysis was used to highlight any possible correlated changes 24, 48 and 72 h after treatments. FTIR spectra of live cell treated in normal and high glucose medium have shown significant differences (p < 0.05) for all treatment time. The control cells have seen an increased in the absorbance at 1088, 1240 and 1400 cm^-1, which are associated with phosphate stretching mode vibrations from phosphorylated proteins and DNA back bone; and symmetric stretching mode vibration of COO^- from fatty acids, amino acids, lipids and carbohydrate metabolites. However, the high glucose treated cells have shown a different changes in the 1000-1200 cm^-1 region, which is linked to the glycogen and ATP:ADP ratio. In conclusion, live-cell FTIR can be a low-cost method for the studies of metabolic changes in cells.

Impact of down-stream processing on functional properties of yeasts and the implications on gut health of Atlantic salmon (Salmo salar)

Yeasts are becoming popular as novel ingredients in fish feeds because of their potential to support better growth and concomitantly ensure good fish health. Here, three species of yeasts (Cyberlindnera jadinii, Blastobotrys adeninivorans and Wickerhamomyces anomalus), grown on wood sugars and hydrolysates of chicken were subjected to two down-stream processes, either direct heat-inactivation or autolysis, and the feed potential of the resulting yeast preparations was assessed through a feeding trial with Atlantic salmon fry. Histological examination of distal intestine based on widening of lamina propria, showed that autolyzed W. anomalus was effective in alleviating mild intestinal enteritis, while only limited effects were observed for other yeasts. Our results showed that the functionality of yeast in counteracting intestinal enteritis in Atlantic salmon was dependent on both the type of yeast and the down-stream processing method, and demonstrated that C. jadinii and W. anomalus have promising effects on gut health of Atlantic salmon.

Current Pretreatment/Cell Disruption and Extraction Methods Used to Improve Intracellular Lipid Recovery from Oleaginous Yeasts

The production of lipids from oleaginous yeasts involves several stages starting from cultivation and lipid accumulation, biomass harvesting and finally lipids extraction. However, the complex and relatively resistant cell wall of yeasts limits the full recovery of intracellular lipids and usually solvent extraction is not sufficient to effectively extract the lipid bodies. A pretreatment or cell disruption method is hence a prerequisite prior to solvent extraction. In general, there are no recovery methods that are equally efficient for different species of oleaginous yeasts. Each method adopts different mechanisms to disrupt cells and extract the lipids, thus a systematic evaluation is essential before choosing a particular method. In this review, mechanical (bead mill, ultrasonication, homogenization and microwave) and nonmechanical (enzyme, acid, base digestions and osmotic shock) methods that are currently used for the disruption or permeabilization of oleaginous yeasts are discussed based on their principle, application and feasibility, including their effects on the lipid yield. The attempts of using conventional and “green” solvents to selectively extract lipids are compared. Other emerging methods such as automated pressurized liquid extraction, supercritical fluid extraction and simultaneous in situ lipid recovery using capturing agents are also reviewed to facilitate the choice of more effective lipid recovery methods.

Design and optimization of a semi-industrial cavitation device for a pretreatment of an anaerobic digestion treatment of excess sludge and pig slurry

The use of hydrodynamic cavitation (HC) as a wastewater treatment and anaerobic digestion pretreatment is a well-known process. However, most of the experiments have been done at laboratory scale and using a low concentration of total solids in the sludge treated. In this study, the waste-activated sludge has been mixed with pig slurry with the aim of treating two wastes rich in nutrients and organic matter. The HC has been studied not only at laboratory scale but also at industrial scale (up to 500 L), using a novel rotating device consisting of a rotor with multiple teeth that rotate inside a grooved stator. The effectiveness of the process has been calculated using the disintegration degree (DD) and analyzing the volatile fatty acids, while the energy efficiency has been determined with specific energy of the sludge solubilization (SE_SCOD ) and the specific energy. Results show that both the SE_SCOD and the specific energy decrease when the cavitation process is scaled from laboratory scale to industrial scale. Specifically, SE_SCOD decreases from 2.71 × 10² to 0.16 × 10²  kJ/g SCOD and specific energy decreases from 3.58 × 10⁴ to 2.85 × 10³  kJ/kg TS while DD values show reasonable values up to 17%. PRACTITIONER POINTS: A new industrial hydrodynamic cavitation device has been developed to treat industrial wastewater without chemical additives A volume up to 500 L has been treated at industrial scale experiments. Sludge with 7% of total solids content was satisfactorily disintegrated. The process scale-up lead to an energy efficiency enhancement.

How Capsular Exopolysaccharides Affect Cell Surface Properties of Lactic Acid Bacteria

Some lactic acid bacteria are able to produce exopolysaccharides that, based on localization, can be distinguished in free and capsular or cell-bound exopolysaccharides (CPS). Up to now, the former were the focus of current research, mainly because of the technofunctional benefits they exhibit on fermented dairy products. On the other hand, CPS affect the surface properties of bacteria cells and thus also the textural properties of fermented foods, but data are very scarce. As the cell surface properties are strongly strain dependent, we present a new approach to investigate the impact of CPS on cell surface hydrophobicity and moisture load. CPS positive and negative Streptococcus thermophilus and Weissella cibaria were subjected to ultrasonication suitable to detach CPS without cell damage. The success of the method was verified by scanning electron and light microscopy as well as by cultivation experiments. Before applying ultrasonication cells with CPS exhibiting an increased hydrophilic character, enhanced moisture load, and faster water adsorption compared to the cells after CPS removal, emphasizing the importance of CPS on the textural properties of fermented products. The ultrasonic treatment did not alter the cell surface properties of the CPS negative strains.

Low and High-Intensity Ultrasound in Dairy Products: Applications and Effects on Physicochemical and Microbiological Quality

Milk and dairy products have a major role in human nutrition, as they contribute essential nutrients for child development. The nutritional properties of dairy products are maintained despite applying traditional processing techniques. Nowadays, so-called emerging technologies have also been implemented for food manufacture and preservation purposes. Low- and high-intensity ultrasounds are among these technologies. Low-intensity ultrasounds have been used to determine, analyze and characterize the physical characteristics of foods, while high-intensity ultrasounds are applied to accelerate particular biological, physical and chemical processes during food product handling and transformation. The objective of this review is to explain the phenomenology of ultrasounds and to detail the differences between low and high-intensity ultrasounds, as well as to present the advantages and disadvantages of each one in terms of the processing, quality and preservation of milk and dairy products. Additionally, it reviews the rheological, physicochemical and microbiological applications in dairy products, such as raw milk, cream, yogurt, butter, ice cream and cheese. Finally, it explains some methodologies for the generation of emulsions, homogenates, crystallization, etc. Currently, low and high-intensity ultrasounds are an active field of study, and they might be promising tools in the dairy industry.

Comparative assessment of pretreatment strategies for production of microalgae-based biodiesel from locally isolated Chlorella homosphaera

The yield and quality of lipids extracted from microalgal biomass are critical factors in the production of microalgae-based biodiesel. The green microalga Chlorella homosphaera, isolated from Beira Lake, Colombo, Sri Lanka was employed in the present study to identify the effect of chlorophyll removal and cell disruption methods on lipid extraction yield, fatty acid methyl ester (FAME) profile and quality parameters of biodiesel; including cetane number (CN), iodine value (IV), degree of unsaturation (DU) and high heating value (HHV). In the first section of this study, chlorophyll was removed from dry microalgae biomass prior to lipid extraction. Through the analysis of FAME profiles, it was observed that chlorophyll removal yielded biodiesel of enhanced quality, albeit with a lipid loss of 44.2% relative to the control. In the second section of the study, mechanical cell disruption strategies including grinding, autoclaving, water bath heating and microwaving were employed to identify the most effective method to improve lipid recovery from chlorophyll-removed microalgae biomass. Autoclaving (121 °C, 20 min sterilization time, total time 2 h) was the most effective cell disruption technique of the methods tested, in terms of lipid extraction yield (39.80%) and also biodiesel quality. Moreover, it was observed that employing cell disruption subsequent to chlorophyll removal has a significant impact on the FAME profile of microalgae-based biodiesel, and consequently served to increase HHV and CN although IV and DU did not vary significantly.

Autolysis, plasmolysis and enzymatic hydrolysis of baker's yeast (Saccharomyces cerevisiae): a comparative study

Saccharomyces cerevisiae is being used for long as a rich source of proteins, sugars, nucleotides, vitamins and minerals. Autolyzed and hydrolyzed yeast biomass has found numerous applications in the health food industry as well as livestock feeds. Here, we have compared three lysis methods for production of yeast lysates using autolysis, plasmolysis (ethyl acetate 1.5%), and enzymatic hydrolysis (Alcalase 0.2%). The efficiency of each process was compared according to soluble solid and protein contents, cell lysis monitoring, and release of intracellular materials, cell viability and microscopic analysis. Results showed that plasmolysis by ethyl acetate was found to be more efficient compared to autolysis, with a higher recovery of yeast extract (YE) content. In comparison, the content of released solids and proteins were higher during the enzymatic hydrolysis using Alcalase compared to autolysis and plasmolysis treatments. The highest decrease in optical density of 600 nm was monitored for the hydrolyzed cells. Besides, we defined "Degree of Leakage (DL)" as a new index of the lysis process, referring to the percentage of total released proteins from the cells and it was estimated to about 65.8%, which represents an appropriate indicator of the cell lysis. The biochemical and biophysical properties of the hydrolyzed yeast product as well as its biological activity (free radical scavenging activity and bacterial binding capacity) suggest that Alcalase could be used to accelerate the lysis of yeast cells and release the valuable intracellular components used for foodstuffs, feed and fermentation media applications. Production of baker's yeast lysates using autolysis, plasmolysis, and enzymatic hydrolysis methods.

Coagulation and disinfection by-products formation potential of extracellular and intracellular matter of algae and cyanobacteria

Coagulation and flocculation can remove particulate algal cells effectively; however, they are not very effective for removing dissolved algal organic matter (AOM) in drinking water plants. In this work, optimum coagulation conditions using alum for both extracellular and intracellular organic matter of six different algal and cyanobacterial species were determined. Different coagulation conditions such as alum dosage, pH, and initial dissolved organic carbon (DOC) were tested. Hydrophobicity, hydrophilicty, and transphilicity of the cellular materials were determined using resin fractionation method. The removal of DOC by coagulation correlated well with the hydrophobicity of the AOM. The disinfection by-product formation potential (DBPFP) of various fractions of AOM was determined after coagulation. Although, higher removal occurred for hydrophobic AOM during coagulation, specific DBPFP, which varied from 10 to 147 μg/mg-C was higher for hydrophobic AOM. Of all the six species, highest DBPFP occurred for Phaeodactylum tricornutum, an abundant marine diatom species, but is increasingly found in surface water.

Can Polyhydroxyalkanoates Be Produced Efficiently From Waste Plant and Animal Oils?

Polyhydroxyalkanoates (PHAs) are a potential replacement for some petrochemical-based plastics. PHAs are polyesters synthesized and stored by various bacteria and archaea in their cytoplasm as water-insoluble inclusions. PHAs are usually produced when the microbes are cultured with nutrient-limiting concentrations of nitrogen, phosphorus, sulfur, or oxygen and excess carbon sources. Such fermentation conditions have been optimized by industry to reduce the cost of PHAs produced commercially. Industrially, these biodegradable polyesters are derived from microbial fermentation processes utilizing various carbon sources. One of the major constraints in scaling-up PHA production is the cost of the carbon source metabolized by the microorganisms. Hence, cheap and renewable carbon substrates are currently being investigated around the globe. Plant and animal oils have been demonstrated to be excellent carbon sources for high yield production of PHAs. Waste streams from oil mills or the used oils, which are even cheaper, are also used. This approach not only reduces the production cost for PHAs, but also makes a significant contribution toward the reduction of environmental pollution caused by the used oil. Advancements in the genetic and metabolic engineering of bacterial strains have enabled a more efficient utilization of various carbon sources, in achieving high PHA yields with specified monomer compositions. This review discusses recent developments in the biosynthesis and classification of various forms of PHAs produced using crude and waste oils from the oil palm and fish industries. The biodegradability of the PHAs produced from these oils will also be discussed.

Pulsed electric field-assisted extraction of valuable compounds from microorganisms

Microorganisms (bacteria, yeast, and microalgae) are a promising resource for products of high value such as nutrients, pigments, and enzymes. The majority of these compounds of interest remain inside the cell, thus making it necessary to extract and purify them before use. This review presents the challenges and opportunities in the production of these compounds, the microbial structure and the location of target compounds in the cells, the different procedures proposed for improving extraction of these compounds, and pulsed electric field (PEF)-assisted extraction as alternative to these procedures. PEF is a nonthermal technology that produces a precise action on the cytoplasmic membrane improving the selective release of intracellular compounds while avoiding undesirable consequences of heating on the characteristics and purity of the extracts. PEF pretreatment with low energetic requirements allows for high extraction yields. However, PEF parameters should be tailored to each microbial cell, according to their structure, size, and other factors affecting efficiency. Furthermore, the recent discovery of the triggering effect of enzymatic activity during cell incubation after electroporation opens up the possibility of new implementations of PEF for the recovery of compounds that are bounded or assembled in structures. Similarly, PEF parameters and suspension storage conditions need to be optimized to reach the desired effect. PEF can be applied in continuous flow and is adaptable to industrial equipment, making it feasible for scale-up to large processing capacities.

A comparative study of extraction techniques for maximum recovery of β-galactosidase from the yogurt bacterium Lactobacillus delbrueckii ssp. bulgaricus

The study reported in this research communication evaluates the chemical (solvents) and mechanical (sonication, bead-beater) extraction methods to determine the maximum recovery of β-galactosidase from L. bulgaricus spp. Among all extraction techniques, sonication-assisted extraction yielded the highest amounts of enzyme activity (between 1892-2156 Miller Units) in cell-free extract (supernatant). Interestingly, solvent extracted enzyme activities were found to be very low (between 83-153 Miller Units) in supernatant. SDS-polyacrylamide gel electrophoresis and the total protein determination showed that mechanical methods can completely lyse the cells. Our results thus demonstrated that the mechanical extraction method of sonication is the best one for recovering the maximum amount of lactase from L. bulgaricus strains.

Improvement of carotenoid extraction from a recently isolated, robust microalga, Tetraselmis sp. CTP4 (chlorophyta)

In recent years, there has been increasing consumer interest in carotenoids, particularly of marine sustainable origin with applications in the food, cosmeceutical, nutritional supplement and pharmaceutical industries. For instance, microalgae belonging to the genus Tetraselmis are known for their biotechnologically relevant carotenoid profile. The recently isolated marine microalgal strain Tetraselmis sp. CTP4 is a fast-growing, robust industrial strain, which has successfully been produced in 100-m³ photobioreactors. However, there are no reports on total carotenoid contents from this strain belonging to T. striata/convolutae clade. Although there are several reports on extraction methods targeting chlorophytes, extraction depends on the strength of cell coverings, solvent polarity and the nature of the targeted carotenoids. Therefore, this article evaluates different extraction methods targeting Tetraselmis sp. CTP4, a strain known to contain a mechanically resistant theca. Here, we propose a factorial experimental design to compare extraction of total carotenoids from wet and freeze-dried microalgal biomass using four different solvents (acetone, ethanol, methanol or tetrahydrofuran) in combination with two types of mechanical cell disruption (glass beads or dispersion). The extraction efficiency of the methods was assessed by pigment contents and profiles present in the extracts. Extraction of wet biomass by means of glass bead-assisted cell disruption using tetrahydrofuran yielded the highest amounts of lutein and β-carotene (622 ± 40 and 618 ± 32 µg g^-1 DW, respectively). Although acetone was slightly less efficient than tetrahydrofuran, it is preferable due to its lower costs and toxicity.

Microfluidic platform for rapid screening of bacterial cell lysis

Over the past decade significant progress has been found in the upstream production processes, shifting the main bottlenecks in current manufacturing platforms for biopharmaceuticals towards the downstream processing. Challenges in the purification process include reducing the production costs, developing robust and efficient purification processes as well as integrating both upstream and downstream processes. Microfluidic technologies have recently emerged as effective tools for expediting bioprocess design in a cost-effective manner, since a large number of variables can be evaluated in a small time frame, using reduced volumes and manpower. Their modularity also allows to integrate different unit operations into a single chip, and consequently to evaluate the effect of each stage on the overall process efficiency. This paper describes the development of a diffusion-based microfluidic device for the rapid screening of continuous chemical lysis conditions. The release of a recombinant green fluorescent protein (GFP) expressed in Escherichia coli (E. coli) was used as model system due to the simple evaluation of cell growth and product concentration by fluorescence. The concept can be further applied to any biopharmaceutical production platform. The microfluidic device was successfully used to test the lytic effect of both enzymatic and chemical lysis solutions, with lysis efficiency of about 60% and close to 100%, respectively, achieved. The microfluidic technology also demonstrated the ability to detect potential process issues, such as the increased viscosity related with the rapid release of genomic material, that can arise for specific lysis conditions and hinder the performance of a bioprocess. Finally, given the continuous operation of the lysis chip, the microfluidic technology has the potential to be integrated with other microfluidic modules in order to model a fully continuous biomanufacturing process on a chip.

Increasing DNA content for cost-effective oil production in Parachlorella kessleri

The aim of this work was to study salt stress effects on DNA content and oil production processes integrating harvesting, lipid accumulation and oil extraction. Salt-induced enlargement of Parachlorella kessleri cells, with increasing content of DNA and neutral lipid were found. The 34.77% neutral lipid content and biomass concentration of 0.83 g L^-1 were obtained after 7 days of salt treatment, compared with that of 13.57% and 0.89 g L^-1 cultivated under normal condition. Sedimentation efficiency increased markedly from 15% to 90% due to the cell enlargement. Disruption fraction and the recovery rate of total lipids of wet cells under salt stress were significantly higher than that of normal conditions (100% and 82.4% for salt stress vs.76.8% and 51.1% for normal conditions). This work demonstrated that salt-induced increase in cell size and DNA content was an effective strategy for the enhancement of oil production, microalgae harvesting and oil extraction.