Reduction of protease activity in milk by continuous flow high-intensity pulsed electric field treatments

High-intensity pulsed electric field (HIPEF) is a non-thermal food processing technology that is currently being investigated to inactivate microorganisms and certain enzymes, involving a limited increase of food temperature. Promising results have been obtained on the inactivation of microbial enzymes in milk when suspended in simulated milk ultrafiltrate. The aim of this study was to evaluate the effectiveness of continuous HIPEF equipment on inactivating a protease from Bacillus subtilis inoculated in milk. Samples were subjected to HIPEF treatments of up to 866 micros of squared wave pulses at field strengths from 19.7 to 35.5 kV/cm, using a treatment chamber that consisted of eight colinear chambers connected in series. Moreover, the effects of different parameters such as pulse width (4 and 7 micros), pulse repetition rates (67, 89, and 111 Hz), and milk composition (skim and whole milk) were tested. Protease activity decreased with increased treatment time or field strength and pulse repetition rate. Regarding pulse width, no differences were observed between 4 and 7 micros pulses when total treatment time was considered. On the other hand, it was observed that milk composition affected the results since higher inactivation levels were reached in skim than in whole milk. The maximum inactivation (81%) was attained in skim milk after an 866-micros treatment at 35.5 kV/cm and 111 Hz.     

Development and shelf-life determination of pasteurized,microfiltered, lactose hydrolyzed skim milk

The segment of the world population showing permanent or temporary lactose intolerance is quite significant. Because milk is a widely consumed food with an high nutritional value, technological alternatives have been sought to overcome this dilemma. Microfiltration combined with pasteurization can not only extend the shelf life of milk but can also maintain the sensory, functional, and nutritional properties of the product. This studied developed a pasteurized, microfiltered, lactose hydrolyzed (delactosed) skim milk (PMLHSM). Hydrolysis was performed using β-galactosidase at a concentration of 0.4 mL/L and incubation for approximately 21 h at 10 ± 1°C. During these procedures, the degree of hydrolysis obtained (>90%) was accompanied by evaluation of freezing point depression, and the remaining quantity of lactose was confirmed by HPLC. Milk was processed using a microfiltration pilot unit equipped with uniform transmembrane pressure (UTP) ceramic membranes with a mean pore size of 1.4 μm and UTP of 60 kPa. The product was submitted to physicochemical, microbiological, and sensory evaluations, and its shelf life was estimated. Microfiltration reduced the aerobic mesophilic count by more than 4 log cycles. We were able to produce high-quality PMLHSM with a shelf life of 21 to 27 d when stored at 5 ± 1°C in terms of sensory analysis and proteolysis index and a shelf life of 50 d in regard to total aerobic mesophile count and titratable acidity.     

Evaluation of pulsed electric field and minimal heat treatments for inactivation of pseudomonads and enhancement of milk shelf-life

Pulsed Electric Field (PEF) treatment of milk provides the opportunity to increase the shelf-life of fresh milk for distribution to distant markets. PEF treatments were evaluated in sterile (UHT) milk to determine the inactivation of added spoilage Pseudomonas isolates and the subsequent gains in microbial shelf-life (time taken to reach 10⁷ CFU mL^− 1). Little inactivation of Pseudomonas was achieved at 15 or 40 °C compared with 50 or 55 °C. The greatest inactivation (> 5 logs) was achieved by processing at 55 °C with 31 kV cm^− 1 (139.4 kJ L^− 1). Heat treatment at the application temperature without PEF treatment caused minimal inactivation of Pseudomonas (only 0.2 logs), demonstrating that the inactivation of the Pseudomonas was due to the PEF treatment rather than the heat applied to the milk. At added Pseudomonas levels of 10³ and 10⁵ CFU mL^− 1, the microbial shelf-life of PEF-treated milk was extended by at least 8 days at 4 °C compared with untreated milk. The total microbial shelf-life of the PEF-treated milk was 13 and 11 days for inoculation levels of 10³ and 10⁵ CFU mL^− 1 respectively. The results indicate that PEF treatment is useful for the reduction of pseudomonads, the major spoilage bacteria of milk.Industrial relevancePseudomonads are the major psychrotrophic spoilage microflora of refrigerated, stored HTST pasteurised milk. Long-life (UHT) products are an important component of milk sales in South-East Asia, but in recent years there has been an increasing demand for less processed milk products with extended shelf-life. The recent practice of shipping fresh bulk milk from Australia to South-East Asian countries has necessitated additional heat treatment prior to export and on arrival, to achieve the required shelf-life. Pulsed electric field treatment of HTST milk, applied alone or in combination with mild heat under optimised conditions, offers the opportunity of shelf-life extension, while limiting the reduction in quality attributes of milk associated with more severe additional heat treatments.     

Voltage spike and electroconvective vortices generation during electrodialysis under pulsed electric field: Impact on demineralization process efficiency and energy consumption

Electrodialysis (ED) with pulsed electric field (PEF) has never been tested on complex food system such as sweet whey. In this study, seven PEF pulse-pause combinations were compared with DC current to assess their impacts on whey demineralization. High-frequency PEF improved the demineralization rate by 81% while reducing the energy consumption by about 16%. This was explained by the emergence of electroconvective vortices (ECV) at the beginning of each pulse due to the appearance of a voltage spike. Since their lifetime are around 0.5 s, these ECV did not have time to fade off during the whole process in the case of high-frequency PEFs increasing consequently the mass transfer. Furthermore, PEF ratio of 1 decreased pH changes and thus could prevent scaling and organic fouling formation. Hence, ED with PEF is a new advantageous energy-efficient approach for the demineralization of whey that could be used in the dairy industries.Industrial relevanceThis study highlights the beneficial effects of using pulsed electric field (PEF) during ED in comparison to the DC current condition currently used everywhere in industry. First, for the same demineralization rate of sweet whey, PEF requires 16% less energy. This could allow the industries to better deal with the regulatory issues arising from the sustainable development goals. In addition, the use of PEF also prevents the fouling and scaling formation on the membrane, and thus could decrease the load of cleaning agent and the cleaning time required per amount of processed whey. High-frequency PEF such as 0.1 s-0.1 s is a promising greener alternative to conventional ED for demineralization of the million tons of whey generated by the cheese industry every year.     

Design and evaluation of a continuous flow microwave pasteurization system for apple cider

The purpose of this project was to design a continuous flow microwave pasteurization system and to evaluate the following process parameters: volume load size (0.5 and 1.38 l), input power (900–2000 W), and inlet temperature (3°C, 21°C, and 40°C). Water and two apple ciders, one from a cold press and the other from a hot press extraction, were the fluids used to study the heating characteristics. Volumetric flow rate and absorbed power were criteria in the evaluation. The microwave pasteurization system consisted of helical coils throughout a large cavity oven, which was shown to produce uniform and reproducible heating throughout the cavity. Fluid viscosity of water and cider was measured at temperatures between 20°C and 70°C to characterize the flow in helical coils based on the Dean number. Process lethality was verified based on inoculation of Escherichia coli 25922 in apple cider, in which the pasteurization process resulted in a 5-log₁₀ reduction.     

Inactivation of spoilage microorganisms in apple cider using a continuous flow pulsed electric field system

The effect of pulsed electric field (PEF) in inactivating naturally occurring microorganisms (yeast and molds) in freshly squeezed apple cider was investigated in a continuous flow system. The microbial count decreased with an increase of applied pulses (17.6-58.7 total) and treatment temperature (45-50 °C), and a decrease of flow rate (3-10 l/h). At field strength of 27-33 kV/cm (3 mm electrode gap in a concentric chamber), 200 pulses/s, 3 l/h flow rate, and 50 °C process temperature, there was a 3.10 log reduction in microbial counts. By PEF treatment in the presence of a mixture of nisin and lysozyme (27.5 U/ml for nisin and 690 U/ml for lysozyme), there was an increase in the microbial count from 1.12 to 1.78 log reductions for 10 l/h flow. When cider samples were treated in the presence of clove oil (3 or 5 ml/100 ml), an additive reduction of 1.99 log cycles in microbial counts was observed.     

Non-thermal pasteurization of milk by an innovative energy-saving moderate electrical field equipped with elongated electrodes and process optimization

Environmental concerns and consumer demand necessitate alternative pasteurization techniques that sustainably produce safe and high-quality milk. To this end, a new non-thermal (<42 °C) moderate electric field (MEF) system was developed with elongated electrodes and a reduced electrode gap. Response surface methodology optimized technical and thermo-physical attributes, including viscosity, density, freezing point, solid non-fat (SNF), temperature, power usage, and specific energy consumption (SEC), by altering electrical field intensities (EFI) and mass flow rates (ṁ) from 25 to 30 V/cm and from 0.017 to 0.033 kg/s, respectively. The results were then compared with the conventional thermal pasteurization (CP, 63 °C for 30 min). Besides, process cost analysis in terms of electricity consumption was performed to identify cost reduction opportunity for the industry, and milk samples were analyzed by scanning electron microscopy to elaborate on the mechanisms involved. MEF optimal processing conditions were 29.8 V/cm EFI and 0.018 kg/s ṁ, which reduced 98.58% of energy consumption, 98.51% of SEC, and 99.09% of processing time in comparison with CP. Also, MEF possessed higher productivity than CP. D-value for total count bacteria (TCB) in MEF was significantly lower than CP (0.06 vs. 14.80 min), and MEF and CP reduced TCB by 99% and 88.61%, respectively. Compared with the previously reported MEF milk pasteurizer, the MEF system developed in this study saved energy, cost, and time by 99.2%, 99.0%, and 78.4%; therefore, this emerging technology could further contribute to sustainable manufacturing of foods.     

A systematic review and meta-analysis of the effects of pasteurization on milk vitamins, and evidence for raw milk consumption and other health-related outcomes

Pasteurization of milk ensures safety for human consumption by reducing the number of viable pathogenic bacteria. Although the public health benefits of pasteurization are well established, pro-raw milk advocate organizations continue to promote raw milk as "nature's perfect food." Advocacy groups' claims include statements that pasteurization destroys important vitamins and that raw milk consumption can prevent and treat allergies, cancer, and lactose intolerance. A systematic review and meta-analysis was completed to summarize available evidence for these selected claims. Forty studies assessing the effects of pasteurization on vitamin levels were found. Qualitatively, vitamins B12 and E decreased following pasteurization, and vitamin A increased. Random effects meta-analysis revealed no significant effect of pasteurization on vitamin B6 concentrations (standardized mean difference [SMD], -2.66; 95% confidence interval [CI], -5.40, 0.8; P = 0.06) but a decrease in concentrations of vitamins B1 (SMD, -1.77; 95% CI, -2.57, -0.96; P < 0.001), B2 (SMD, -0.41; 95% CI, -0.81, -0.01; P < 0.05), C (SMD, -2.13; 95% CI, -3.52, -0.74; P < 0.01), and folate (SMD, -11.99; 95% CI, -20.95, -3.03; P < 0.01). The effect of pasteurization on milk's nutritive value was minimal because many of these vitamins are naturally found in relatively low levels. However, milk is an important dietary source of vitamin B2, and the impact of heat treatment should be further considered. Raw milk consumption may have a protective association with allergy development (six studies), although this relationship may be potentially confounded by other farming-related factors. Raw milk consumption was not associated with cancer (two studies) or lactose intolerance (one study). Overall, these findings should be interpreted with caution given the poor quality of reported methodology in many of the included studies.     

Effects of continuous flow microwave treatment on chemical and microbiological characteristics of milk

Raw cows' and goats' milks were heated by microwave in a continuous flow unit up to temperatures ranging from 73.1 to 96.7°C. The effects of the heat treatments were estimated by measurements of lactose isomerization, protein denaturation, inactivation of alkaline phosphatase and peroxidase and the total bacterial count. Negative phosphatase tests and low bacterial counts, together with low degrees of whey protein denaturation, were achieved under several temperature/time combinations. The results indicate that continuous microwave processing may be an efficient and mild approach for the pasteurization of milk.     

Effect of corona wind,current, electric field and energy consumption on the reduction of the thawing time during the high-voltage electrostatic-field (HVEF) treatment process

Electric energy plays an important role in reducing the thawing time and accelerating the entire thawing process. Corona wind speed was increased by increasing the applied voltage and current, which were 0.87 ± 0.19, 1.22 ± 0.19, 1.49 ± 0.13 m/s under 8, 10, 12 kV with 3, 5, 10 μA; 1.01 ± 0.12, 1.24 ± 0.17, 1.49 ± 0.10 m/s under − 8, − 10, − 12 kV with 5, 9, 14.5 μA. The models T1, T2, and T3 were designed to study the effects of current, corona wind and electric field on thawing, respectively. T1: a thin stainless-steel sheet covered the top of stainless-steel box with 10 g frozen distilled water; T2: a plastic sheet was placed under the stainless-steel box; T3: a plastic sheet covered the top of plastic box. Electric field alone cannot affect thawing time, which could be maximally reduced by 1/2 compared to that of air thawing.Industrial relevanceWe have studied HVEF thawing for several years because of its many advantages, such as the quick thawing of frozen meat with little energy consumption and good post-thawing quality. The mechanism of HVEF thawing and the reduction of the thawing time, which are important for the industrial application of new technology from principle to design, must be clarified. Meanwhile, this emerging technology will be beneficial for the food-thawing field.     

叶轮角度与流体黏度对高剪切罐内流体影响的模拟研究

采用标准k-ε模型及多重参考系法研究高剪切搅拌罐中叶轮角度与流体黏度改变对搅拌罐内混合流场、功率消耗、泵吸流量的影响。结果表明,高剪切搅拌罐中采用60°斜叶轮时流场具有较强烈的漩涡,泵吸流量和功率消耗也较大,同时定子射流半径也有所增加,具有较明显的优势。高剪切搅拌罐搅拌轴功率随着流体黏度的增大呈现先增大后减小的变化规律,在黏度为0.1～0.5Pa.s时功率最大;剪切头流量随着黏度的增大呈现出先降低后增大的趋势。     

Ultrasonication as a novel processing alternative to pasteurization for camel milk: Effects on microbial load,protein profile,and bioactive properties

Ultrasonic technology presents a promising novel tool in the food industry for the processing of milk and dairy products. In this study, we investigated the effects of ultrasonication (US) as an alternative to thermal pasteurization for stabilization of the bioactive properties of camel milk. Camel and bovine milk samples were subjected to US at 6 different power levels (US1–US6), and 1 set of each type of milk was concurrently subjected to flash heat pasteurization (FHP) for comparative analysis (100 mL; n = 4). The microbiological and bioactive parameters of the samples were analyzed during 7 d of storage at 4°C. In both milk types subjected to US ≥ 140 W (US3), the bacterial load was reduced by almost 4 log cycles and complete reduction of microbial load was achieved with US = 170 W and US = 210 W (US5 and US6 treatments, respectively). No significant changes in protein patterns were observed with either FHP or US treatment. In addition, bioactive properties (cholesteryl esterase and pancreatic lipase inhibition) were either enhanced or retained at US3 or higher. 2,2′-Azino-bis-3-ethylbenzthiazoline-6-sulfonic acid and ferric reducing antioxidant power activities in camel milk were decreased after FHP treatment but increased or retained upon US, particularly at US3 and US4 (160 W). Overall, under our experimental conditions, US4 was effective in completely reducing the microbial count, while concomitantly retaining different bioactive properties of both camel and bovine milk. These outcomes highlight the potential of US at 160 W as an efficient nonthermal alternative processing method for milk.     

Simulation of the temperature increase in pulsed electric field (PEF) continuous flow treatment chambers

The application of intense pulsed electric fields (PEF) in foods is intended to be a non-thermal method to inactivate microorganisms. However, it is well known that an increase in temperature is present in this process due to ohmic heating, where the pulsed electric field energy input is transformed into heat. The aim of this study was to investigate the computer modeled temperature increase in the outflow for different flow-through PEF treatment chamber designs. Given equal experimental conditions, the temperature increase is indicative of the PEF dose, and a more uniform temperature profile is thus indicative of a more homogeneous PEF treatment. The radial distribution of the temperature increase was simulated in computer models of four different chambers. The temperature increase was found to be more homogeneous in the treatment chambers making use of a decrease in the insulator diameter, i.e. a design letting the insulators and electrodes intersect at angles close to 90°. The maximum temperature increase was found close to the wall, where the flow velocity is low. Cooling of the electrodes and electric insulators is recommended to avoid too high a temperature increase. The minimum temperature increase found was 29% of the calculated average in the worst case studied here. The minimum PEF dose to which the food was subjected would thus is less than the intended dose, since the food clearly was not subjected to the intended electric field strength during the intended exposure time. This is an important result in terms of food safety in the sense that a minimum PEF treatment should be guaranteed. The microbiological inactivation was experimentally evaluated using two of the treatment chamber designs. The result is consistent with the simulations and shows a small increase in inactivation and less needed energy input giving less average temperature increase for the chamber implementing a contraction of the diameter of the insulating spacer.     

Effects of pulsed electric field on fat globule structure,lipase activity,and fatty acid composition in raw milk and milk with different fat globule sizes

To modify the structure of milk fat globules (MFGs), raw milk (RM) with native MFGs, and milk with small (MS) and large (ML) MFGs, were subjected to moderate pulsed electric field (PEF) treatment at 9 and 16 kV·cm⁻¹ for 30 μs. The changes caused by PEF on MFG structure leading to MFG-MFG and MFG-protein aggregation were found to depend on the size, composition and/or previous damage caused by the separation and mixing processes during production of MS and ML, in addition to the intensity of the PEF treatment. Although, PEF treatment had a more pronounced effect on MFGM proteins of MS, these MFG were less affected by PEF due to significant adsorption of milk proteins. The structural changes caused by PEF were accompanied by changes in lipase activity and fatty acid (FA) profiles, i.e. increase in the proportion of C6:0, C8:0, C10 and some long-chain FAs and a decrease in medium and other long chain FAs.Industrial relevancePEF is gaining attention in the dairy industry. However, information regarding the effect of PEF processing on milk components and functionality is still limited. The present investigation contributes to understand the potential of PEF at moderate field intensities to modify the MFGs and consequences for milk stability, lipolysis and composition of FAs. The new insight is relevant in development of new products and ingredients containing milk fat.     

Pulsed electric field and mild heating for milk processing: a review on recent advances

Pulsed electric field (PEF) treatment consists of exposing food to electrical fields between electrodes within a treatment chamber, which can improve the preservation of fresh-like products such as milk. Although several studies support the use of PEF technology to process milk at low temperature, these studies reported microbial reductions of around 3 log₁₀ cycles and also indicated a limited impact of PEF on some endogenous and microbial enzymes. This scenario indicates that increasing the impact of PEF on both enzymes and microorganisms remains a major challenge for this technology in milk processing. More recently, combining PEF with mild heating (below pasteurization condition) has been explored as an alternative processing technology to enhance the safety and to preserve the quality of fresh milk and milk products. Mild heating with PEF enhanced the safety of milk and derived products (3 log₁₀–6 log₁₀ cycles reduction on microbial load and drastic impact on the activity enzymes related to quality decay). Moreover, with this approach, there was minimal impact on enzymes of technological and safety relevance, proteins, milk fat globules, and nutrients (particularly for vitamins) and improvements in the shelf-life of milk and selected derived products were obtained. Finally, further experiments should consider the use of milk processed by PEF with mild heating on cheese-making. The combined approach of PEF with mild heating to process milk and derived products is very promising. The characteristics of current PEF systems (which is being used at an industrial level in several countries) and their use in the liquid food industry, particularly for milk and some milk products, could advance towards this strategy. © 2019 Society of Chemical Industry     

Factors affecting milk flow traits in dairy cows: results of a field study

The study of milk flow curves provides useful information for enhancing milking efficiency and protecting udder health by adapting milking machine and milking procedures to the physiological requirements of the cow. The aim of this experiment was to investigate, using field data, the relationships among traits of the milk flow curves, their sources of variation, and milking performances in terms of milk production, machine-on time, and udder health. A total of 2,486 milk flow curves of the whole udder were collected in 82 Italian Holstein-Friesian dairy herds in the Lombardy region of Italy. Approximately one-third (35.1%) of milk flow curves were classified as bimodal. Most flow characteristics were influenced by lactation number, days in milk, and peak flow but also strongly affected by premilking operations. Proper udder preparation, including forestripping and predipping, resulted in better milking performances compared with poor preparation, with greater milk yield per milking, shorter milking time, and lesser bimodality. Premilking delay time, between the start of teat stimulation and cup attachment, affected milking time significantly: The shortest milking time was obtained for a range of delay time between 1 and 60 s. As the delay time increased, the percentage of bimodality dropped significantly. Increasing the number of clusters per operator led to greater percentages of bimodal curves. The greater somatic cell count of cows with bimodal curves supports the hypothesis of the negative effect of bimodality on udder health and indicates the importance of avoiding its occurrence using proper pre-milking procedures.     

Conventional and ohmic heating pasteurization of fresh and thawed sheep milk: Energy consumption and assessment of bacterial microbiota during refrigerated storage

This study aimed to assess the energy consumption of ohmic heating (OH) and conventional heating (CH) for pasteurization of fresh and thawed sheep milk and their impact on bacterial microbiota throughout refrigerated shelf-life (4 °C ± 1, 15 days). OH pasteurization using 8.33 and 5.83 V/cm electric field strength spent 72–73% less energy than CH pasteurization (515 KJ). The cultivation-dependent approach showed that at least 4.2 log cycle reductions were achieved in sheep milk submitted to CH and OH pasteurization, regardless sheep milk was fresh or thawed. Data from amplicon sequencing indicated that Staphylococcus was the most prevalent genus in raw samples at day 1 (F1_D1: 58.35%; T1_D1: 69.50%), while Pseudomonas became the most abundant after 15 days under cold storage (F1_D15: 50.15% and T1_D15: 54.50%). The relative abundance of all bacterial genera assessed remained similar on pasteurized samples by CH and OH throughout refrigerated storage.Industrial relevanceOhmic heating (OH) presents as a critical advantage rapid and uniform heating of fluid food material. No studies assessed the use of OH for pasteurization of sheep milk and to evaluate the impact of this technology on sheep milk bacterial microbiota during refrigerated storage. The findings of this study prove the feasibility of sheep milk pasteurization using OH_{8.33 V/cm}. OH also ensured the bacteriological stability of sheep milk during 2 weeks of storage under refrigeration conditions prior to dairy products manufacturing. This approach comprises a cheaper and easier way to store milk when compared to frozen storage, with potential benefits to small farmers and dairy industries.