Application of mild pulsed electric fields on starter culture accelerates yogurt fermentation

Electric stimulation: a versatile manipulation technique mediated microbial applications

Electric stimulation (ES) is a versatile technique that uses an electric field to manipulate microorganisms individually. Over the past several decades, the capabilities of ES have expanded from bioremediation to the precise motion control of cells and microorganisms. However, there is limited information on the underlying mechanisms, latest advancement and broader microbial applications of ES in various fields, such as the production of extracellular polymers with upgraded properties. This review article summarizes recent advancements in ES and discusses it as a unique external manipulation technique for microorganisms with wide applications in bioremediation, industry, biofilm deactivation, disinfection, and controlled biosynthesis. One specific application of ES discussed in this review is the extracellular biosynthesis, regulation, and organization of extracellular polymers, such as bacterial cellulose nanofibrils, curdlan, and microbial nanowires. Overall, this review aims to provide a platform for microbial biotechnologists and synthetic biologists to leverage the manipulation of microorganisms using ES for bio-based applications, including the production of extracellular polymers with enhanced properties. Researchers can engineer, manipulate, and control microorganisms for various applications by harnessing the potential of electric fields.

Effect of pulsed electric field treated on quality of curd

Pulsed electric field (PEF) is a potential pre-treatment technique to improve the quality of milk by reducing its microbial load. The present study aims at addressing this issue with respect to a popular fermented dairy product, that is, curd. Milk was treated with high voltage and frequency (55 kV and 90 Hz) square waves of pulse width 900 µs for 100 s. Curd samples were prepared with conventional heat treatment (CHT), PEF-treated milk subjected to CHT (PT-CHT), and PEF-treated milk (PT). PT samples resulted in curd with higher acidity (0.17 ± 0.005% LA) and microbial load (6.65 ± 0.27 log CFU/g), while the PT-CHT samples resulted in curd with better whey holding capacity. The firmness recorded for CHT, PT-CHT, and PT was 1.15 ± 0.05, 1.32 ± 0.04, and 0.91 ± 0.03 N, respectively. PT-CHT showed a higher viscosity index, that is, 0.207 ± 0.005 g. Sensorial properties showed the acidic nature of PT-curd with greater syneresis and softer texture resulted in its poorer sensory scores for texture. Shelf-life analysis showed no significant difference between curd prepared using the CH and PT-CHT up to 12 days. The study demonstrated the potential of employing PEF with CHT for improving the texture and shelf life of curd without impacting its quality.

Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Pre-Treatment of Starter Cultures with Mild Pulsed Electric Fields Influences the Characteristics of Set Yogurt

The aim of this study was to investigate the effect of pulsed electric field (PEF) pre-treatment of a dairy starter culture of Lactobacillus delbrueckii subsp. bulgaricus LB186 and Streptococcus thermophilus ST504 on the fermentation and final product characteristics of set-style yogurt. The effects of PEF treatment parameters, voltage (4-20 kV), pulse number (20-80 pulses), frequency (1-21 Hz), and pulse (5-8 µs) width on pH development, cell counts, and proteolytic activity, as well as on texture and degree of syneresis in yogurt were investigated by use of a two-level full factorial design. Pulse frequency and pulse width had a significant effect on the yogurt stiffness (p < 0.05) and the interaction of voltage and frequency had a significant effect on both stiffness and proteolytic activity (p < 0.05). Further experiments confirmed that pre-treatment of the dairy culture with specific PEF parameters immediately before addition to milk could accelerate fermentation of, increase stiffness of, and reduce syneresis in the final yogurt. This effect of the PEF-pre-treated culture was partially retained even after flash-freezing and 14 days of storage of the culture at -20 °C. The effects were attributed to responses to oxidative stress induced by the PEF pre-treatment.

Enhancing yogurt products’ ingredients: preservation strategies, processing conditions, analytical detection methods, and therapeutic delivery—an overview

As a dairy product, yogurt delivers nourishing milk components through the beneficial microbial fermentation process, improved by bioavailability and bioaccessibility–an exclusive combined food asset. In recent decades, there has been considerable attention to yogurt product development particularly in areas like influence by antioxidant-rich fruits, different factors affecting its probiotic viability, and the functionality of inulin and probiotics. Essentially, many published reviews frequently focus on the functionalities associated with yogurt products, however, those articulating yogurt ingredients specific to associated preservation strategies, processing conditions, and analytical detection techniques are very few, to the best of our knowledge. The knowledge and understanding of preservation strategies that enhance the ingredients in yogurt products, and their function as modern drug delivery systems are essential, given the opportunities it can provide for future research. Therefore, this overview discussed how yogurt product ingredients have been enhanced, from preservation strategies, processing conditions, analytical detection methods, and therapeutic delivery standpoints. The survey methodology involved major stages, from the brainstorming of research questions, search strategy, effective utilization of databases, inclusion and exclusion criteria, etc. The innovative successes of yogurts would be enhanced via the physicochemical, nutritional and therapeutic aspects of the ingredients/products. Besides processing conditions to influence the yogurt constituents, overall acceptability, quality, and shelf-life, the analytical assays would help detect the hidden product constituents, toxins, and other storage-related changes. The therapeutic role of yogurt-a modern drug delivery system, would be demonstrated via the supplementation (of yogurt) either alone or with bioactive ingredients. The future of yogurt requires the collective action of stakeholders to formulate unique variants with different natural blends, where synthetic ingredients become completely replaced by the plant’s derivatives, which enhance the acidification rate and extend shelf life.