Effect of temperature,pH and film thickness on nisin release from antimicrobial whey protein isolate edible films

BACKGROUND: An active packaging film based on whey protein isolate (WPI) was developed by incorporating nisin to promote microbial food safety. The effect of temperature and pH on the release of nisin from edible films of different thickness was investigated. The film mechanical properties and inhibitory effect were also evaluated. RESULTS: Nisin release was significantly favoured by low pH, with the highest release after 24 h (1325 IU), which was not significantly affected by temperature (5 or 10 °C). Thickness significantly affected film elongation, with thicker films showing the highest elongation (54.3 ± 2.7%). Water vapour permeability (0.15 ± 0.4 g mm m^?2 kPa^?1 h^?1) and elastic modulus were not significantly affected by thickness. The highest nisin effective diffusivity (5.88 × 10^?14 m² s^?1) was obtained using a solution at pH 4, 112 µm film thickness and a temperature of 5 °C. More than four log cycles of Brochotrix thermosphacta were reduced from the surface of a ham sample after 8 days of incubation at 4 °C by the active WPI film containing 473 IU cm^?2 nisin. CONCLUSION: Nisin diffusivity from WPI edible films was favoured at lower pH and film thickness. This active packaging film may be used to preserve the quality and safety of meat products. Copyright © 2009 Society of Chemical Industry     

Biodegradable Polymeric Films Incorporated with Nisin: Characterization and Efficiency against <Emphasis Type="Italic">Listeria monocytogenes</Emphasis>

Nisin (0.2 IU per cm² films) containing biodegradable films were produced from pea protein isolate (PPI), whey protein isolate (WPI), and polylactic acid (PLA). Nisin was released over 4 h at 22 °C and 8 h at 4 °C. PPI released more nisin compared to other films suppressing the growth of Listeria monocytogenes (P?<?0.05) based upon diffusion into agar and liquid culture media. The population of bacteria after 48 h in liquid media was 6 CFU/mL (1 log₁₀ increase) in PPI, 8.47 CFU/mL (3.47 log₁₀ increase) in WPI and 9 CFU/mL (4 log₁₀ increase) in PLA, which was significantly lower in protein based films compared to PLA (P?<?0.05). The inhibition zone in agar test was significantly higher (P?<?0.05) in PPI and WPI, compared to PLA film, which might be due to the higher hydration in protein based films. Fourier transform infrared spectroscopy (FTIR) showed that nisin altered the intensity of amide I peaks in protein based films suggesting that nisin can bind to the protein functional groups in PPI and WPI. Thermogram showed that nisin did not influence the glass transition and melting temperatures of the films. Nisin containing films exhibited significantly lower enthalpy compared to control films (P?<?0.05). PeakForce Quantitative Nano Mechanical Property Mapping (PeakForce QNM) was applied to extract material and mechanical properties in PPI, WPI and PLA films with and without nisin. Results showed significant reductions in material and mechanical properties of protein based films containing nisin compared to PLA films.     

Optimization of Nisin Production by Lactococcus lactis UQ2 Using Supplemented Whey as Alternative Culture Medium

Abstract: Lactococcus lactis UQ2 is a nisin A-producing native strain. In the present study, the production of nisin by L. lactis UQ2 in a bioreactor using supplemented sweet whey (SW) was optimized by a statistical design of experiments and response surface methodology (RSM). In a 1st approach, a fractional factorial design (FFD) of the order 2^5-1 with 3 central points was used. The effect on nisin production of air flow, SW, soybean peptone (SP), MgSO₄/MnSO₄ mixture, and Tween 80 was evaluated. From FFD, the most significant factors affecting nisin production were SP (P = 0.011), and SW (P = 0.037). To find optimum conditions, a central composite design (CCD) with 2 central points was used. Three factors were considered, SW (7 to 10 g/L), SP (7 to10 g/L), and small amounts of added nisin as self-inducer (NI 34.4 to 74.4 IU/L). Nisin production was expressed as international units (IU). From RSM, an optimum nisin activity of 180 IU/mL was predicted at 74.4 IU/L NI, 13.8 g/L SP, and 14.9 or 5.11 g/L SW, while confirmatory experiments showed a maximum activity of 178 ± 5.2 IU/mL, verifying the validity of the model. The 2nd-order model showed a coefficient of determination (R²) of 0.828. Optimized conditions were used for constant pH fermentations, where a maximum activity of 575 ± 17 IU/mL was achieved at pH 6.5 after 12 h. The adsorption-desorption technique was used to partially purify nisin, followed by drying. The resulting powder showed an activity of 102150 IU/g. Practical Application : Nisin production was optimized using supplemented whey as alternative culture medium, using a native L. lactis UQ2 strain. Soybean peptone, SW, and subinhibitory amounts of nisin were successfully employed to optimize nisin production by L. lactis UQ2. Dried semipurified nisin showed an activity of 102150 IU/g.     

Inhibition of Listeria monocytogenes and Salmonella by Combinations of Oriental Mustard,Malic Acid,and EDTA

The antimicrobial activities of oriental mustard extract alone or combined with malic acid and EDTA were investigated against Salmonella spp. or Listeria monocytogenes at different temperatures. Five strain Salmonella or L. monocytogenes cocktails were separately inoculated in Brain Heart Infusion broth containing 0.5% (w/v) aqueous oriental mustard extract and incubated at 4 °C to 21 °C for 21 d. For inhibitor combination tests, Salmonella Typhimurium 02:8423 and L. monocytogenes 2–243 were individually inoculated in Mueller Hinton broth containing the mustard extract with either or both 0.2% (w/v) malic acid and 0.2% (w/v) EDTA and incubated at 10 °C or 21 °C for 10 to 14 d. Mustard extract inhibited growth of the L. monocytogenes cocktail at 4 °C up to 21 d (2.3 log₁₀ CFU/mL inhibition) or at 10 °C for 7 d (2.4 log₁₀ CFU/mL inhibition). Salmonella spp. viability was slightly, but significantly reduced by mustard extract at 4 °C by 21 d. Although hydrolysis of sinigrin in mustard extract by both pathogens was 2 to 6 times higher at 21 °C than at 4 °C to 10 °C, mustard was not inhibitory at 21 °C, perhaps because of the instability of its hydrolysis product (allyl isothiocyanate). At 21 °C, additive inhibitory effects of mustard extract with EDTA or malic acid led to undetectable levels of S. Typhimurium and L. monocytogenes by 7 d and 10 d, respectively. At 10 °C, S. Typhimurium was similarly susceptible, but combinations of antimicrobials were not more inhibitory to L. monocytogenes than the individual agents.     

Enzymatic Production of Ribonucleotides from Autolysates of Kluyveromyces marxianus Grown on Whey

After 20h fermentation of medium containing 5% (w/v) dehydrated whey, at 30°C, pH 4.5, yeast cells were harvested, diluted in 0.1M KH₂PO₄, and autolyzed at different pHs (6.5–7.5) and temperatures (45–55°C). Phosphodiesterase (0.2–1.0% w/v, 65°C, pH 6.5, 6h) and adenyl deaminase (0.5-1.0% w/v, 60°C, pH 5.5, 4h) were added to the autolysates. After heat treatment (100°C, 15 min), samples were analyzed by RP-HPLC and LC/MS. Production of 5′-ribonucleotides was maximized at 50°C, pH 6.5. Yields of 5′-AMP (800 μg/g of biomass) and 5′-GMP (2000 μg/g) increased considerably after addition of 1.0% phosphodiesterase. 5′-IMP increased only after addition of 1.0% adenyl deaminase.     

Inhibition of Listeria monocytogenes by Nisin Combined with Grape Seed Extract or Green Tea Extract in Soy Protein Film Coated on Turkey Frankfurters

The objective of this study was to evaluate the inhibitory effect of grape seed extract (GSE), green tea extract (GTE), nisin and their combinations (nisin with either GSE or GTE) against Listeria monocytogenes. The inhibitory effect of these natural compounds was evaluated in phosphate buffer solution (PBS) medium containing approximately 10⁹ colony‐forming units (CFU/mL) of L. monocytogenes. The effectiveness of these compounds in a meat model system was evaluated by surface inoculation (approximately 10⁶ CFU/g) of L. monocytogenes onto turkey frankfurters. The inoculated frankfurters were dipped into soy protein film‐forming solutions with and without the addition of antimicrobial agents (GSE 1% or GTE 1% or nisin 10000 IU or combinations). Samples were stored at either 4 °C or 10 °C. The inhibitory effects of edible coatings were evaluated on a weekly basis for 28 d. The greatest inhibitory effect was observed in the PBS medium containing GSE (1%) and nisin (10000 IU/mL), which caused a 9‐log cycle reduction of L. monocytogenes population after 3 h incubation at 37 °C. In the meat system, the L. monocytogenes population (7.1 CFU/g) was decreased by more than 2 log cycle after 28 d at 4 °C and 10 °C, in the samples containing nisin (10000 IU) combined with either GSE (1%) or GTE (1%). This research has demonstrated that the use of an edible film coating containing both nisin and natural extracts is a promising means of controlling the growth and recontamination of L. monocytogenes on ready‐to‐eat meat products.     

Combination Inhibition Activity of Nisin and Ethanol on the Growth Inhibition of Pathogenic Gram Negative Bacteria and Their Application as Disinfectant Solution

Nisin and ethanol have been used as antimicrobial agents in food industry. However, nisin alone could not inhibit the growth of gram‐negative bacteria, except in combination with a chelating agent, EDTA, or organic acid. This research aimed to study the survival of Escherichia coli O157: H7, Salmonella Typhimurium TISTR 292 and Salmonella Enteritidis DMST 17368 after treatment with nisin at 100, 200, 300, 500, 800, or 1000 IU/mL and ethanol at 70%, 50%, 30%, 20%, or 10% (v/v) alone and in combination. None of all nisin concentrations could reduce the growth of target strains. While 20% ethanol (v/v) having no negative effect on human health, could slightly reduce the growth of target strains. However, the combination of nisin at 500, 800 or 1000 IU/mL and 20% ethanol displayed significant growth reduction at 15 min were below 1 log CFU/mL. Thus, the minimum inhibitory concentration of nisin and ethanol was 500 IU/mL and 20% (v/v), respectively. The release of fatty acid, genetic materials and scanning electron microscope suggested that nisin‐ethanol treated cells have altered permeability causing bacterial growth inhibition. Comparison treatment of combined solution and commercial chloride based sanitizer were done for all target strains on stainless steel surface. Survivals of three target strains were below 1 log CFU/mL. The result suggested that combined solution of nisin and ethanol may be a beneficial sanitizer for food industry to inhibit the growth of E. coli O157:H7 and Salmonella sp.     

Optimization of Enzymatic Hydrolysis of Pearlmillet for Glucose Production

Commercial α‐amylase preparation (Biotempase) and crude glucoamylase from Aspergillus sp. NA21 were used to hydrolyse pearlmillet, a non‐conventional starchy substrate. Various concentrations of starch (15—35% w/v) were used for liquefaction; 25% slurry was found to be judicious and optimal. Liquefaction in steam under pressure 2.06—2.75 N/cm², 104—105 °C) was found to be more economical than in a water bath at 95 °C. In the first case a 25% (w/v) slurry was liquefied in 60 min. A pH of 5.0 was found to be optimum for liquefaction. Biotempase dose was cut down by 33% to the prescribed one by addition of 150 ppm CaCl₂ to the slurry. Ninety percent saccharification of liquefied pearlmillet occurred under optimum conditions (24 h and pH 5.0). The optimum temperature for saccharification of pearlmillet was found to be 45 °C. Additions of Ca²⁺, Mg²⁺ and Zn²⁺ were found to have no effect on saccharification. Glucose was found to be the main hydrolysis product as indicated by paper chromatography.     

Antimicrobial Effects of Nisin,Essential Oil,and γ‐Irradiation Treatments against High Load of Salmonella typhimurium on Mini‐carrots

This study aimed at using essential oil (EO) alone or combined EO with nisin and γ‐irradiation to control Salmonella Typhimurium during the refrigerated storage of mini‐carrots. Peeled mini‐carrots were inoculated with S. Typhimurium at a final concentration of approximately 7 log CFU/g. Inoculated samples were coated by 5 different coating solutions: (i) nisin solution at final concentration of 10³ IU/mL; (ii) mountain savory EO solution at 0.35%; (iii) carvacrol solution at 0.35%; (iv) mountain savory EO at 0.35% plus nisin solution of 10³ IU/mL; or (v) carvacrol at 0.35% plus nisin solution of 10³ IU/mL. Coated mini‐carrots were then irradiated at 0.5 or 1.0 kGy and compared to an unirradiated control sample. Samples were kept at 4 °C and microbial analyses were conducted at days 1, 3, 6, and 9. The results showed that mini‐carrots coated by carvacrol plus nisin solution or mountain savory EO plus nisin solution in combination with irradiation at 1.0 kGy completely eliminated S. Typhimurium to under the detection limit during the storage. Thus, the combined treatments using carvacrol plus nisin or mountain savory EO plus nisin coating solution and irradiation at 1.0 kGy could be used as an effective method for controlling S. Typhimurium in mini‐carrots.     

Antimicrobial Effects of Essential Oils,Nisin, and Irradiation Treatments against Listeria monocytogenes on Ready‐to‐Eat Carrots

The study aimed at using essential oil (EO) alone or combined EO with nisin and low dose γ‐irradiation to evaluate their antibacterial effect against Listeria monocytogenes during storage of carrots at 4 °C. Minicarrots were inoculated with L. monocytogenes at a final concentration of approximately 7 log CFU/g. Inoculated samples were coated by nisin at final concentration of 10³ International Unit (IU)/mL or individual mountain savory EO or carvacrol at final concentration of 0.35%, w/w) or nisin plus EO. The samples were then irradiated at 0, 0.5, and 1.0 kGy. The treated samples were kept at 4 °C and microbial analysis of samples were conducted at days 1, 3, 6, and 9. The results showed that coating carrots by carvacrol plus nisin or mountain savory plus nisin and then irradiating coated carrots at 1 kGy could reduce L. monocytogenes by more than 3 log at day 1 and reduced it to undetectable level from day 6. Thus, the combined treatments using nisin plus carvacrol or nisin plus mountain savory and irradiation at 1.0 kGy could be used as an effective method for controlling L. monocytogenes in minicarrots.     

Pomelo Citrus grandis (L.) osbeck peel as an economical alternative substrate for fungal pectinase production

Polygalacturonase production by Aspergillus niger LFP-1 was studied in solid state fermentation (SSF) using pomelo (Citrus grandis) peel as a substrate. This local agricultural waste product is rich in lignocellulolytic material, including pectin, which can act as an inducer of pectinase production. Using the parameters of 5 g of 0.75 mm (particle size) pomelo peel as a substrate, moisture content ratio of 1:1 (w/v), inoculum size of 1×10⁷ spores/mL, cultivation temperature of 30°C, and no mixing, static fermentation conditions with addition of 1.2% ammonium nitrate produced the highest polygalacturonase production rate of 8.90 U/g of substrate and a fungal growth rate of 2.07mg of glucosamine/g of substrate on day 5 of cultivation. A large increase (1,434.5%) in enzyme production occurred after improvement of the growth parameters. Under optimum bioprocess conditions, pomelo peel can be used as solid substrate for production of pectinase.     

USE OF FLEXIBLE POLYMER MATERIAL FOR PACKAGING FRESH PEACHES

Fresh peaches (Prunus persica) were overwrapped in trays with 1 of 3 formulations of flexible polyvinyl chloride (PVC) film that differed in gas transmission rate or they were held in nonwrapped trays (controls). The CO₂ transmission rate at 0°C for PVC type III film was 280 mL/m^2. h (1 atmos); that of type II was 4 times greater and that of type I, about 5 times greater. The peaches were stored either 14 days at 0° or 7.5°C, or 7 days each at 0° and 7.5°C plus 2 days at 20°C to simulate retail display. The mean CO₂ levels were 10, 7.2 and 4.7% in packages that were wrapped with PVC III film and held at 7.5°, 0°/7.5° and 0°C, respectively. CO₂ in packages wrapped with PVC I or II was below 3% at each storage temperature. O₂ concentration remained about 4% in all packages. Weight loss was less and fruit was firmer among those packaged in PVC III than among nonwrapped controls at each of the 3 storage temperatures. Storage temperature had no effect on weight loss or of fruit held in PVC III film. External appearance of fruit packaged with the 3 types of film was significantly better than that of the controls. Internal appearance of the peaches was unaffected by any of the treatments. A microatmosphere favorable for fresh peaches can be maintained within packages overwrapped with polymer films that are selectively permeable to respiratory gases.     

Isolation and characterisation of collagen from the outer skin waste material of cuttlefish (Sepia lycidas)

In an investigation into making more effective use of underutilized resources, collagen was prepared from the outer skin of cuttlefish (Sepia lycidas). Initial extraction of the cuttlefish outer skin in acetic acid yielded only 2% of collagen (dry weight basis). On subsequent digestion of the residue with 10% pepsin (w/v), a solubilized collagen (PSC) was obtained in a yield of 35% (dry weight basis). With respect to PSC, it had a chain composition of (α 1)₂α2 heterotrimer similar to Japanese common squid. Moreover, the denaturation temperature of this collagen was 27°C which is about 10°C lower than that of porcine collagen. This report indicates that cuttlefish waste materials have potential in supplementing the skin of land vertebrates as a source of collagen.     

A modified laboratory canning protocol for quality evaluation of dry bean (Phaseolus vulgaris L)

The effects of calcium (Ca²⁺) level in the soak water, blanch water and brine, blanching temperature, and total seed solids on dry bean canning quality were investigated to optimise a laboratory canning protocol. A linear increase in the Ca²⁺ level of soak water, blanch water and brine resulted in a linear decrease in hydration coefficient and percent washed drained weight but a linear increase in texture. Low Ca²⁺ level (10 mg kg⁻¹) reduced the hydration time for dry bean seed from 14 to 1 h. Blanching temperatures of 50, 70 and 88 °C had non‐significant effects on canning quality traits. Blanching for 30 min at 70 °C for black bean or at 88 °C for navy bean and pinto bean resulted in percent washed drained weight ≥ 60, as required by the Canada Agricultural Products Standards Act. Seed solids levels of 95–97 g per 300 × 407 (14 fl oz) can were sufficient to attain a percent washed drained weight of 60. It was confirmed that the thermal processing conditions (115.6 °C retort temperature, 45 min) used in this study were sufficient to achieve commercial sterility. The optimised lab protocol for evaluation of the canning quality of dry bean breeding lines is as follows. Seed containing 95 g of solids for pinto bean, 96 g for navy bean and 97 g for black bean is soaked in water for 30 min at 20 °C and blanched for 30 min at 70 °C for black bean and 88 °C for navy bean and pinto bean in water containing 10 mg kg⁻¹ of Ca²⁺. The seed is then transferred to a 300 × 407 can, filled with brine containing 10 mg kg⁻¹ of Ca²⁺, 1.3% (w/v) of NaCl and 1.6% (w/v) of sugar. The can is then sealed, processed in steam at 115.6 °C for 45 min and cooled at 20 °C for 20 min. Cans are stored for at least 2 weeks prior to quality evaluation of the canned product. Canning of dry bean seed according to this protocol results in precise estimation of canning quality traits, particularly percent washed drained weight. © 2000 Society of Chemical Industry     

Modification of Crude Canola Lecithin for Food Use

Crude canola lecithin was fractionated by removal of neutral lipids with acetone followed by ethanol extraction with or without supercritical carbon dioxide (SC-CO₂). Two extraction steus of 60 min each at 35°C with 500 mL acetone were optimum for maximum yield of acetone solubles and maximum phospholipid (PL) concentration (66.7%) in the acetone insoluble (AI) fraction. AI were separated into 26.5% ethanol soluble and 68.7% ethanol insoluble fractions. PL concentration in the extract increased with increasing amounts of ethanol used. Yields were low for SC-CO₂/ethanol extraction, of which extracts from 55.2 MPa/ 70°C contained 32% PL (83% phosphatidyl choline).     

Antimicrobial activity of Ginkgo biloba leaf extract on Listeria monocytogenes

ABSTRACT: The antimicrobial activities of Ginkgo biloba leaf extract (GBE) and the combined effects of GBE and sodium EDTA (sodium Ethylenediaminetetraacetic acid) against Listeria monocytogenes were determined at 4 °C, 25 °C, and 37 °C. Listeria monocytogenes grown at 37 °C for 24 h was inoculated (6 to 7 log CFU/mL) into BHI broth containing either GBE or GBE and EDTA (1.6 mg/mL) with various GBE concentrations of 0.1, 0.25, 0.5, 1, 2.5, 5.0, 7.5, 10.0, 15.0, or 20.0% vol/vol and stored at 4 °C, 25 °C, and 37 °C. The inhibitory effect of the GBE was more pronounced at low temperature of 4 °C. GBE was effective in inhibiting microbial growth. Addition of EDTA enhanced antimicrobial activity of GBE.     

Production and Application of a Maltogenic Amylase by a Strain of Thermomonospora viridis TF-35

An extracellular and thermostable maltogenic amylase-producing moderate thermophile (Thermomonospora viridis TF-35), which grew well at 28–60°C, with optima at 45°C and pH 7, was isolated from soil. Maximal enzyme production was attained after aerobical cultivation for 32 h at 42°C with a medium (pH 7.3) composed of 2% (w/v) soluble starch, 2% gelatin hydrolyzate, 0.1% K₂HPO₄ and 0.02% MgSO₄ · 7H₂O. The partially purified enzyme, which was most active at 60°C and pH 6.0 and stabilized with Ca²⁺, converted about 65, 80, 75, 75, 65 and 60% of maltotriose, maltotetraose, maltopentaose, amylose, amylopectin and glycogen into maltose as a major product under the conditions used, respectively. Glucose and small amounts of maltooligosaccharides were also formed concomitantly as by-products. The molar ratio of maltose to glucose from maltotriose were larger than 1 during all stages of the hydrolysis. About 70 and 76% of 25% (w/v) potato starch liquefites having a 3.5 DE value were converted into maltose by the enzyme in the absence and presence of pullulanase during the saccharification, respectively. About 90 and 94% of the starch liquefites were also converted into maltose with relatively low contents of maltooligosaccharides by the cooperative 2 step reaction with the enzyme after obtaining starch hydrolyzates containing about 85 and 90% maltose by the simultaneous actions of soybean ß-amylase and debranching enzymes.     

Combined Effect of Dimethyl Dicarbonate (DMDC) and Nisin on Indigenous Microorganisms of Litchi Juice and its Microbial shelf life

The individual and combined influences of dimethyl dicarbonate (DMDC) and nisin (200 IU/mL) at mild heat on the inactivation of indigenous microorganisms in litchi juice, including bacteria, molds and yeasts (M&Y), were investigated. The fresh litchi juice with or without nisin were exposed to 250 mg/L DMDC at 30, 40, or 45 °C for 0.5, 1, 2, 3, 4, or 6 h. A complete inactivation of M&Y in the litchi juice with or without nisin was achieved as exposed to 250 mg/L DMDC at 30, 40, or 45 °C for 0.5 h. The bacteria, especially Bacillus sp. and Leuconstoc mesenteroides showed higher resistance than M&Y in the litchi juice. Bacillus sp. and Leuconstoc mesenteroides in the litchi juice was not completely inactivated by 250 mg/L DMDC at 30, 40, or 45 °C. However, nisin addition can enhanced the inactivation of these bacteria by DMDC, and nisin and DMDC also showed a synergistic effect on the inactivation of bacteria. M&Y and bacteria were not detected in the litchi juice added with 200 IU/mL nisin as exposed to 250 mg/L DMDC at 45 °C for 3 h. In addition, microbial shelf life of the litchi juice during storage at 4 °C also was evaluated as treated by 250 mg/L DMDC or combination with nisin at 45 °C for 3 h.     

A study on the preparation and some functional properties of a cross‐linked casein–gelatin composite by a microbial transglutaminase

A microbial transglutaminase (TGase) was used in this work as biocatalyst to prepare a cross‐linked casein–gelatin composite, a modified protein product with 4‐hydroxyproline about 41 mg g^?1 peptides. Some cross‐linking conditions such as total protein content, the ratio of caseinate to gelatin and original pH were fixed at 5% (w/v), 4:1 (w/w) and 7.5, respectively. Other suitable conditions selected by single factor trials were TGase addition of 20 U g^?1 peptides, reaction temperature of 45 °C and reaction time of 4 h. Peptide profiles from SDS‐PAGE analysis showed the composite was peptide polymers. Compared to that of the original caseinate or the cross‐linked caseinate, the dispersion of the composite exhibited a markedly enhanced apparent viscosity, storage modulus and viscous modulus. Meanwhile, the composite also showed a better water holding capacity, unchanged oil binding capacity and lower enzymatic digestibility in vitro, conferring its applicability as a new protein ingredient.     

Alternative Pressing/Ultrafiltration Process for Sugar Beet Valorization: Impact of Pulsed Electric Field and Cossettes Preheating on the Qualitative Characteristics of Juices

Alternative process of sugar beet transformation is investigated by tuning experimental conditions. A three-step process has been set-up: (1) sugar beet cossettes pretreatment by pulsed electric field (PEF) and (or) short preheating to different temperatures; (2) extraction of juice from pre-treated cossettes by pressing; and (3) purification of the expressed juice by ultrafiltration. The PEF treatment was applied to cold (10 °C) and preheated (to 20, 50, 60, 70, and 80 °C) sugar beet cossettes with intensity of E?=?600 V cm^?1 using rectangular monopolar pulses of 100 μs during t _PEF?=?5–20 ms. Experiments were performed with cossettes of three sizes. Control experiments were done without PEF treatment using cold (10 °C) and preheated (to 20–80 °C) cossettes. PEF-treated and (or) preheated cossettes were pressed at 5 bars during 15 min. Afterward, expressed juices obtained from the PEF-treated cossettes at 20 °C and from the untreated ones at 80 °C were purified by dead-end ultrafiltration with stirring (500 rpm) at the temperature of 20 °C by using polyethersulfone membrane with MWCO of 30 kDa. Application of PEF (E?=?600 V cm^?1, t _PEF?=?10 ms, T?=?20 °C) with following pressing of cossettes at 5 bars during 15 min permits to obtain the juice yield Y?=?66,5 %, which is equivalent to that obtained from cossettes preheated to 80 °C and untreated electrically (Y?=?64 %). The energy consumption of cold PEF treatment (≈2–3 Wh/kg) is very attractive as compared to preheating at high temperatures (≈138–194 Wh/kg). Combination of thermal and electrical pretreatments leads to additional softening of sugar beet tissue and to a slightly higher (on 5–10 %) juice yield, but the electroporation of preheated cossettes is more energetically costly. The raw juice expressed from PEF-treated cossettes at 20 °C has higher purity (93.5 %) than juices expressed at 50 °C (92.9 %) and at 80 °C (92.3 %). The temperature increasing from 20 to 80 °C results in a higher juice coloration (5680 IU at 20 °C and 7820 IU at 80 °C) and leads to a higher (on about 35 %) colloids concentration in the expressed juice. The filtrate obtained from the juice expressed at 20 °C with PEF treatment has a higher purity (96 %) than the filtrate obtained from the juice expressed at 80 °C (95.3 %) and its coloration is considerably lower (330 IU versus 1930 IU). In addition, the quantity of proteins and colloids in the filtrate of juice expressed at 20 °C is lower than that in the filtrate of juice expressed at 80 °C