Study of butter fat content in milk on the inactivation of Listeria innocua ATCC 51742 by thermo-sonication

Ultrasound combined with heat treatment has yielded favorable results in the inactivation of microorganisms; however, the composition of food influences the rate of microbial inactivation. The objective of this research was to study the effect of butter fat content in milk on the inactivation of Listeria innocua and compositional parameters after thermo-sonication. Four butter fat contents in milk were evaluated at 63 °C for 30 min of sonication (Hielscher® UP400S, 400 W, 24 kHz, 120 μm amplitude). Results showed that inactivation of Listeria cells occurs first in fat free milk, and that the rate of inactivation decreases with increasing fat content. No degradation of protein content or color variation was observed after the treatments. The pH dropped to 6.22, and lactic acid content showed an increase of 0.015% after the treatment; solids-non-fat, density and freezing point decreased. During storage life, growth of mesophiles was retarded with sonication.Industrial relevanceUltrasound is an emerging technology that has shown positive effects in milk processing. Listeria monocytogenes represent one of the main foodborne pathogenic microorganisms in the food industry. Results of this research show that thermo-sonication is a viable technology capable of inactivating Listeria cells in milk and extending shelf-life without significant nutritional or physicochemical changes.     

COMPOSITION PROPERTIES, PHYSICOCHEMICAL CHARACTERISTICS AND SHELF LIFE OF WHOLE MILK AFTER THERMAL AND THERMO-SONICATION TREATMENTS

Raw whole milk (RM) was pasteurized with heat-pasteurized milk (TT) and thermo-sonication (US) treatments. Batch pasteurization was used for TT and 36, 72, 108 and 120 µm of the ultrasound wave intensity (24 kHz, 400 W); in addition, the heat conditions were applied together for US. Apparent protein content of US milk decreased; butter fat content was increased by US treatment. Proximal analysis showed the presence of added water in US milk and a decrease of nonfat solids, whereas pH was decreased for US milk, lactic acid was increased and density was decreased from RM to US; also, the color of US milk was whiter. The tested parameters for the TT samples were often intermediate between RM and US samples. Statistical analysis showed a significant difference ( P <  0.05) among all treatments. After 16 days, US samples (4C) did not show mesophilic growth higher than 2 log; pH, acidity and color remained constant.

PRACTICAL APPLICATIONS

Thermo-sonication (US) is an available method that can improve some sensorial and quality milk characteristics such as color and appearance, while at the same time, ultrasound pasteurizes the product. Minor changes in nutritional properties of milk (i.e., protein content) have been reported after US, with the advantage of extending the shelf life of the product for more than 16 days at 4C without the use of intensive heat treatments. This is a potential technology for use in research and development of new and current products in the dairy industry.     

Influence of high intensity ultrasound on microbial reduction,physico-chemical characteristics and fermentation of sweet whey

The aim of this study was to investigate the influence of high intensity ultrasound on quality of reconstituted sweet whey in order to substitute thermal treatments i.e. pasteurization. Also, it was intended to study the influence of ultrasound on fermentation process of pasteurized or thermo-sonicated whey with respect to culture activation and sensory properties of the fermented whey. In the first stage, whey was subjected to treatments with different power inputs (480 W, 600 W) over 6.5, 8 and 10 min at constant temperature (45 °C, 55 °C). Treated whey samples were analyzed for microbiological quality, particle size distribution, protein content, acidity, electrical conductivity, viscosity and sensory properties. All of the analyzed parameters were compared with the control sample (pasteurized) and fresh whey. Subsequently, influence of high intensity ultrasound on pasteurized or thermo-sonicated whey fermentation with yoghurt culture and with monoculture Lactobacillus acidophilus La-5 was investigated. Ultrasound treatments were applied for culture activation prior to or after the inoculation. Whey thermo-sonication by nominal power of 480 W for 10 min at 55 °C resulted in better microbiological quality and sensory properties in comparison to whey pasteurization. Ultrasound treatments with nominal input power of 84 W over 150 s resulted in the highest increase of the viable count during the activation process. Whey fermentation by ultrasonicated culture La-5 lasted 30 min shorter and resulted in higher viable cells count.Industrial relevanceAttached paper (“Influence of high intensity ultrasound on microbial reduction, physico-chemical characteristics and fermentation of sweet whey”) reports the influence of high intensity ultrasound on quality and fermentation process of sweet whey. Also, the influence of high intensity ultrasound on pasteurized or thermo-sonicated whey fermentation with yoghurt culture and with monoculture Lactobacillus acidophilus La-5 was investigated.Whey proteins are thermo-labile proteins and degradable at higher temperatures (above 60 °C), and at conventional processing (pasteurization), denaturation and precipitation of proteins occur. Ultrasound gives a great replacement for pasteurization where precipitation does not occur. Also, ultrasonic treatment of the whey results in homogenization and thus, stability is increased. When microbiological cultures for fermentation, prior to the inoculation in the samples, are treated by ultrasound their activity is higher (explained in the paper) and thus fermentation is faster.From an economical point of view, processing by ultrasound can reduce costs a lot, since fermentation time is shorter, and the same effect as pasteurization is achieved. Ultrasonic treatment is a future in the dairy industry.     

Pasteurization of tender coconut water by pulsed light treatment: Microbial safety,enzymatic inactivation,and impact on physicochemical properties

The study investigated the potential of pulsed light (PL) in the pasteurization of tender coconut water (TCW). The initial counts of E. coli, B. cereus and L. monocytogenes in the inoculated TCW were 7.00, 9.14 and 7.8 log₁₀ cfu mL⁻¹, respectively. For a PL fluence of 465 J cm⁻², E. coli, B.cereus and L. monocytogenes exhibited a log reduction of 5.12, 2.97 and 3.40, respectively. Bacillus cereus and Listeria monocytogenes exhibited greater resistance than Escherichia coli in the TCW. Peroxidase (POD) was more sensitive to PL treatments than polyphenoloxidase (PPO) in TCW. Weibull model and n^th order model exhibited excellent fit for microbial inactivation (R² > 0.96) and enzyme inactivation (R² > 0.97) kinetics, respectively. While 5-log₁₀ reduction of B. cereus and L. monocytogenes was achieved at 2.5 kV|2.5 min (1073 J cm⁻²), PPO was inactivated by greater than 99% at 2.9 kV| 5 min (2988 J cm⁻²). While the total reducing sugars increased, the changes in color (0.49 < ΔE* < 1.51), pH, total soluble solids, and acidity were insignificant after the PL pasteurization. The PL condition of 2.9 kV|5 min preserved 21 and 24% more phenolics and ascorbic acid in TCW, along with greater sensory scores than the thermal treatment (90 °C|3 min).Industrial significanceThe outcome of this study determined the intensity (fluence of 2988 J/cm²) and penetration depth (4–5 mm) required for the pasteurization of tender coconut water (TCW). On an industrial scale of large processing volumes, continuous pulsed light (PL) pasteurization of TCW can be undertaken in an annular flow reactor or thin film flat bed chamber. The thickness of the film can be mimicked from this study to ensure adequate penetration of PL in the sample to achieve adequate lethality.     

Production and quality improvement of Indian cottage cheese (Paneer) using high pressure processing

Paneer, a product of India similar to cottage cheese, was prepared from cow's milk heat-treated (90 °C/5 min) (HTMP) or high-pressure (HP) treated (500 MPa/15 min) (HPPMP) for achieving pasteurization. HTMP and HPPMP paneer samples were HP treated (500 MPa for 15 min) again after vacuum packaging to get HTMP/HPP and HPPMP/HPP samples, respectively. The third set of samples were obtained by dipping HTMP and HPPMP paneer samples in 2% lactic acid solution and then subjecting them to the same HP treatment and stamped as HTMP/LA/HPP and HPPMP/LA/HPP, respectively. All six types of vacuum-packed paneer were studied for changes in moisture, acidity, pH, color, texture, and microbiological quality during storage at 5 ± 1 °C and 25 ± 1 °C. High-pressure treatment of milk increased the yield of paneer significantly (P < 0.05) from 13.9 ± 0.59% (HTMP) to 18.2 ± 0.32% (HPPMP). Paneer treated with lactic acid and high-pressure treatment (HTMP/LA/HPP and HPPMP/LA/HPP) had higher textural stability than HTMP, HTMP/HPP, HPPMP, and HPPMP/HPP for up to 28 days, but had a reduced moisture content, higher acidity, and lower whiteness index. High-pressure treatment of vacuum-packed paneer (HTMP/HPP and HPPMP/HPP) led to the formation of a more compact paneer matrix (higher hardness), higher moisture expulsion, and yellowness (b*). Thus, high-pressure processing of paneer could pave paths for extending paneer shelf-life without any additives and thermal treatment.     

Thermosonication versus thermal processing of skim milk and beef slurry: Modeling the inactivation kinetics of psychrotrophic Bacillus cereus spores

Non-thermal processed foods are generally cold stored and distributed. The use of ultrasound for food preservation has attracted the interest of many research groups. In the current study, the thermosonication (TS, simultaneous ultrasound and thermal process) inactivation of psychrotrophic Bacillus cereus spores was investigated (24 kHz, 210 μm, 0.33 W/mL or W/g). First, the effectiveness of a 1.5 min TS process at 70 °C in skim milk, beef slurry, cheese slurry, and rice porridge was investigated. The TS was more effective than sole thermal treatment in reducing B. cereus spores in rice porridge, beef slurry and cheese slurry by 7, 6, and 4 fold, respectively. Then, the first-order D- and z-values for TS and thermal processing in skim milk and beef slurry, and the best model to fit TS inactivation of B. cereus spores in beef slurry were determined. The D_70 °C-values in skim milk were 2.9 min for TS and 8.6 min for the thermal treatment. And in beef slurry, values of 0.4 min for TS and 2.3 min for thermal were estimated. It was found that the Log-logistic model better described the TS spore inactivation in beef slurry. The ultrasound technology required 20–30 °C lower temperatures for the same spore inactivation, which resulted in better food quality and energy saving gains.     

Screening for and characterization of Lactococcus lactis bacteriophages with high thermal resistance

Fifty-six Lactococcus lactis phage isolates collected from different German dairies and obtained from a starter culture manufacturer were tested for their heat resistance. About 40% of these isolates resisted treatment at 80 °C for 5 min when they were heated in milk. The most resistant phage isolate, P1532, was collected from sour cream. Plaque-formation was still detectable even after heating at 97 °C for 5 min. The second heat-resistant one, P680, showed some plaque-forming ability after heating at 95 °C for 5 min. Kinetic parameters for the thermal inactivation of these two resistant phages were determined for temperatures ranging from 70 to 97 °C. The inactivation of phage P1532 in skim milk and in buffer medium were found to follow first-order kinetics and did not exhibit tailing, whereas in the inactivation curves of phage P680 tailing was observed. The D-value of P1532 at pasteurization temperature of 72 °C was calculated as 112 min.     

Pasteurization of carrot juice by combining UV-C and mild heat: Impact on shelf-life and quality compared to conventional thermal treatment

The combination of UV-C radiation and mild heat (UV-H) treatment is a promising strategy for synergistically increasing microbial inactivation in low UV-transmitting juices. In this research, we explored the suitability of UV-H treatment in carrot juice pasteurization and its impact on juice quality during shelf-life compared to that of thermal pasteurization. UV-H treatment at 60 °C (3.92 J/mL, 3.6 min) enabled reductions of over 5 log₁₀ cycles in the reference pathogens and a significant reduction in spoilage yeasts, bacteria, and bacterial spores. The activity of pectin methylesterase and polyphenol oxidase was reduced by UV-H treatment to levels close to those of low-temperature pasteurization (60 °C/18.1 min). The native population of total aerobic bacteria, lactic acid bacteria, and yeasts and molds of UV-H-treated juice remained undetectable during 29 days of cold storage. Furthermore, viscosity, cloud stability, and the color of fresh juice were better preserved by UV-H treatment than by thermal pasteurization throughout storage.Industrial relevanceThis study demonstrates that UV-H treatment is a beneficial alternative to conventional thermal processing in carrot juice pasteurization, since appropriate inactivation levels of pathogenic and spoilage microorganisms can be reached while better preserving the quality attributes of fresh juice throughout its shelf-life.     

Cycled high hydrostatic pressure processing of whole and skimmed milk: Effects on physicochemical properties

In this study, we compare the effects of single- and double-cycle HP treatments at 600 MPa on inactivation of the natural microflora and physicochemical properties of whole and skimmed milk of high bacterial load. The results show that two-cycled HP (2 × 2.5 min) was more effective (P < 0.05) on microbial inactivation, and caused similar or slightly less changes (P > 0.05) in physicochemical properties of milk in comparison to single cycled HP (1 × 5 min). In addition to the expected milk protein structure changes, HP at 600 MPa caused only slight effects on milk fat and lactose. Minor decreases in levels of short chain fatty acids were observed with the cycled treatments, and the volatiles in general decreased after HP treatment, depending mostly on the pressure time but also on cycling in skimmed milk. The study confirmed the superior effect of two-cycle HP on microbial inactivation, and shows a slightly better preservation of the physical-chemical milk quality.Industrial relevanceMulti-cycling HP has been shown to be advantageous for microbial inactivation, but limited information is available regarding the effect on milk components in whole milk or skimmed milk. The present study compares the psychochemical properties of whole and skimmed milk processed by multi-cycling in comparison to single cycle HP treatment. Double cycled HP presented a superior effect on microbial inactivation and slightly better preservation of milk quality than one continuous HP.     

Microbial decontamination of black peppercorns by simultaneous treatment with cold plasma and ultraviolet C

An intervention technology employing simultaneous ultraviolet (UV)-C and cold plasma (CP) treatments was developed to inactivate indigenous mesophilic aerobic bacteria in black peppercorns. At higher UV intensity of UV-CP treatment and water activity of black peppercorns, microbial inactivation levels increased up to 0.6 and 1.7 log CFU/g, respectively. Using a response surface analysis, optimum CP voltage and treatment time for inactivating indigenous bacteria in black peppercorns by UV-CP treatment were predicted to be 10.3 kV and 22.1 min, respectively; these inactivated indigenous bacteria and Bacillus tequilensis spores by 3.4 log CFU/g and 1.7 log spores/g, respectively, with minimal increase in temperature (4.5 ± 1.2 °C). The bacterial inactivation rate (3.4 log CFU/g) achieved by UV-CP treatment was higher than the sum (2.7 log CFU/g) of the inactivation rates of individual UV and CP treatments. UV-CP treatment did not alter the color of black peppercorns and shows potential for application in non-thermal microbial decontamination of black peppercorns.Industrial relevanceThis study has developed a novel system for non-thermal microbial inactivation in black peppercorns using simultaneous UV-C and CP treatment (UV-CP treatment). UV-CP treatment was effective in inactivating indigenous bacteria in black peppercorns, including Bacillus tequilensis spores, and had an additive effect on microbial inactivation. The efficacy of treatment in microbial inactivation increased with higher water activity of black peppercorns. The bacterial inactivation efficacy was also influenced by the UV intensity and treatment time. The results of this study demonstrated that UV-CP treatment has the potential to be employed as a non-thermal technology to disinfect black peppercorns and possibly other spices, without affecting their color.     

Moderate electric field pasteurization of milk in a continuous flow unit: Effects of process parameters,energy consumption,and shelf-life determination

This study presents a new non-thermal moderate electric field (MEF) process for milk pasteurization. To evaluate the applicability of this process, fresh milk was treated by MEF at electrical field strength (EFS) of 8.33, 14.58, and 20.80 V/cm and mass flow rates (MFR) of 0.018, 0.042 and 0.077 kg/s to compare the microbiological quality, alkaline phosphatase activity, chemical composition, and some physical properties of the product with those of conventionally pasteurized (15 s at 72 °C) and raw milk. The changes in the total count of bacteria (TCB) and titratable acidity of samples were observed during 18 days of storage at 5 °C for shelf-life estimation. The results showed that MEF reduced energy consumption by 63% in comparison with thermal pasteurization. Also, MEF treatment inactivated coliforms (100%), Staphylococcus aureus (100%), psychrophiles (100%), yeasts and molds (100%), and alkaline phosphatase (100%) while keeping the processing temperature below 22 °C. Also, TCB of sample was reduced by increasing the EFS from 8.33 to 20.8 V/cm and decreasing the MFR from 0.0774 to 0.0185 kg/s. The longest shelf-life of MEF samples, i.e., 15 days, was observed at EFS of 20.80 V/cm and MFR of 0.018 kg/s which was better than that of thermal pasteurization samples, i.e., 9 days.     

Inactivation of Salmonella enterica serovar Typhimurium on fresh produce by cold atmospheric gas plasma technology

Cold atmospheric gas plasma treatment (CAP) is an alternative approach for the decontamination of fresh and minimally processed food. In this study, the effects of growth phase, growth temperature and chemical treatment regime on the inactivation of Salmonella enterica serovar Typhimurium (S. Typhimurium) by Nitrogen CAP were examined. Furthermore, the efficacy of CAP treatment for decontaminating lettuce and strawberry surfaces and potato tissue inoculated with S. Typhimurium was evaluated. It was found that the rate of inactivation of S. Typhimurium was independent of the growth phase, growth temperature and chemical treatment regime. Under optimal conditions, a 2 min treatment resulted in a 2.71 log-reduction of S. Typhimurium viability on membrane filters whereas a 15 min treatment was necessary to achieve 2.72, 1.76 and 0.94 log-reductions of viability on lettuce, strawberry and potato, respectively. We suggest that the differing efficiency of CAP treatment on the inactivation of S. Typhimurium on these different types of fresh foods is a consequence of their surface features. Scanning electron microscopy of the surface structures of contaminated samples of lettuce, strawberry and potato revealed topographical features whereby S. Typhimurium cells could be protected from the active species generated by plasma.     

Processing of clear and turbid grape juice by a continuous flow UV system

The inactivation of inoculated (S. cerevisiae) and spoilage microorganisms, i.e. yeasts and lactic acid bacteria (LAB), in clear and turbid grape juice was investigated using a pilot scale UV system. The biodosimetry method was used for UV dose prediction in a continuous flow UV reactor. Weibull model was applied for fitting the inactivation data. The flow rates (774, 820 ml/min) in this system were very close to the ones used in fruit juice processing. S. cerevisiae in clear juice was reduced by 3.39 ± 0.04 at 65.50 mJ/cm² of UV dose. 1.54 ± 0.04 and 1.64 ± 0.03 log CFU/ml reductions were obtained for spoilage yeasts and LAB in turbid juice at UV dose of 78.56 and 67.97 mJ/cm², respectively. The soluble solids (°Brix) and pH of grape juice samples were not affected by UV-C treatment (p > 0.05). Although the color parameters slightly were changed after irradiation, the color of PCGJ and FSTGJ did not show visual difference compared to the untreated samples.Industrial relevanceUV light has a potential to reduce the levels of microbial contamination in liquid foods. Although grape juice has many beneficial health effects, it has a fairly short shelf life. Therefore, pasteurization is required. But the thermal pasteurization has some undesired effects on the juice quality. Consumer demands for high quality fruit juice with fresh-like characteristics have markedly expanded in recent years. In the current study, the microbial inactivation efficiency of a pilot scale UV system for non-thermal treatment of clear and turbid grape juice was evaluated under conservative conditions. Most of the physicochemical properties of grape juice samples were not significantly affected from UV-C treatment (p > 0.05). This would be a major advantage in the processing of nutritious juice products.     

Pulsed electric field processing of a pomegranate (Punica granatum L.) fermented beverage

The aim of this study was to evaluate the effect of pulsed electric field (PEF) (11.7 or 18 kV/cm) and pasteurization (batch or slow (VAT) and high-temperature-short time (HTST)) on the microbial, physicochemical, bioactive and sensory characteristics of a pomegranate (Punica granatum) fermented beverage (PFB) through storage at 4 °C. Bioactive compounds (antioxidant capacity, phenolic compounds, flavonoids, anthocyanins content) and color were measured. The microbiological counts (initial mesophilic aerobic bacteria (MAB) of 9.77 × 10³ CFU/mL and initial molds plus yeasts (MY) of 2.04 × 10³ CFU/mL) showed that applying 6 ms of bipolar PEFs at 18 kV/cm with 200 Hz repetition frequency reduced the microbial loads in approximately 4-log cycles, remaining <10 CFU/mL of both types of microorganisms in the PFB. PEF barely affected the total soluble solids, pH, ethanol, total acidity and color. All PEF-treated and pasteurization samples showed a slight reduction in bioactive compounds during storage. In sensory acceptability, the lowest score was given to the VAT pasteurized sample; however, still acceptable (between like slightly and like moderately).Industrial relevanceThis research provides essential information on the microbiological, physicochemical, bioactive and sensory characteristics of a pomegranate fermented beverage processed with pulsed electric fields. The pulsed electric field processing of fermented beverages may provide criteria to the processing industry to use this novel technology as a processing method for delivering a microbiological safe beverage with good sensory and antioxidant characteristics to consumers.     

Far infrared and ultraviolet radiation as a combined method for surface pasteurization of black pepper seeds

This study presented the potential of far infrared (FIR) and ultraviolet (UVC) radiation for surface pasteurization of black pepper seeds. FIR treatment at different exposure times and temperatures was applied followed by constant UVC treatment with an intensity of 10.5 mW/cm² for 2 h. Then, the reduction on total mesophilic aerobic bacteria (TMAB) and mold-yeast contents were determined, and quality changes of the seeds were evaluated. TMAB of the seeds decreased to the target level of 10⁴ CFU/g after 4.7 and 3.5 min FIR treatment at 300 and 350 °C, respectively. Under given conditions, complete elimination for other microorganisms (TMY, Escherichia coli and Bacillus cereus) was also obtained while there were no significant changes in volatile oil and color. UVC however, alone or in combination with FIR, did not exhibit a significant reduction in TMAB content. Consequently, FIR treatment was suggested to be a promising method for the surface pasteurization of black pepper seeds.     

Inactivation of Cronobacter sakazakii by manothermosonication in buffer and milk

The inactivation of Cronobacter sakazakii by heat and ultrasound treatments under pressure at different temperatures [manosonication (MS) and manothermosonication (MTS)] was studied in citrate-phosphate pH 7.0 buffer and rehydrated powdered milk. The inactivation rate was an exponential function of the treatment time for MS/MTS treatments (35−68 °C; 200 kPa of pressure; 117 μm of amplitude of ultrasonic waves) in both media, and for thermal treatments alone when buffer was used as heating media. Survival curves of C. sakazakii during heating in milk had a concave downward profile. Up to 50 °C, the lethality of ultrasound under pressure treatments was independent of the treatment temperature in both media. At temperatures greater than 64 °C in buffer and 68 °C in milk, the inactivating effect of MTS was equivalent to that of the thermal treatments alone at the same temperature. Between 50 and 64 ºC for buffer and 50 and 68 °C for milk, the lethality of MTS was the result of a synergistic effect, where the total lethal effect was higher than the lethal effect of heat added to that of ultrasound under pressure at room temperature. The maximum synergism was found at 60 °C in buffer and at 56 °C in milk. A heat treatment of 12 min (60 °C) or 4 min of an ultrasound under pressure at room temperature treatment (35 °C; 200 kPa; 117 μm) would be necessary to guarantee the death of 99.99% of C. sakazakii cells suspended in milk. The same level of C. sakazakii inactivation can be achieved with 1.8 min of a MTS treatment (60 °C; 200 kPa; 117 μm). Damaged cells were detected after heat treatments and after ultrasound under pressure treatments at lethal but not at non-lethal temperatures.     

Effect of high‐pressure treatments on microbial loads and physicochemical characteristics during refrigerated storage of raw milk Serra da Estrela cheese samples

This work studied the effect of high pressure processing (HPP) at 400, 500 and 600 MPa during 10, 5 and 3 min, respectively, on samples ewe cheese manufactured from raw milk, during storage (100 days) at 5 °C. Total aerobic mesophilic and lactic acid bacteria were slightly affected, decreasing by about 1.0 and 0.82 log CFU g^?1, respectively, immediately after HPP treatment at 600 MPa for 3 min, while Enterobacteriaceae, yeasts and moulds, and Listeria innocua were reduced to below the quantification limits. Lactic acid bacteria decreased further during storage, showing increasing inactivation as the pressure level increased. Physicochemical parameters (water activity, moisture content, pH and titratable acidity) were generally not affected by HPP, while lipid oxidation increased throughout storage, with HPP samples showing lower values (50–66%) at 100 days of storage. The results indicated that HPP has potential to improve cheese microbial safety and shelf‐life, with a lower lipid oxidation level than nonpressurised cheese.     

Impact of plasma-activated water washing on the microbial inactivation,color, and electrolyte leakage of alfalfa sprouts,broccoli sprouts,and clover sprouts

This study investigated plasma-activated water (PAW) as a sanitizer for the washing of sprouts. Alfalfa sprouts, broccoli sprouts, and clover sprouts were washed with PAW, chlorine (Cl, 200 ppm), or deionized water. The inactivation of aerobic mesophilic microorganisms and inoculated Escherichia coli DH5α was evaluated. The quality of sprouts was assessed based on visual color change (ΔE) and plant tissue damage (measured by electrolyte leakage). Significant reductions of 1–2 log CFU/g in aerobic mesophilic microorganisms were achieved by PAW and Cl on clover sprouts and alfalfa sprouts. Reductions of E. coli ranging between 1.4 ± 0.4 log CFU/g and 3.5 ± 0.9 log CFU/g were achieved by PAW on the sprouts (original counts: 6.4 to 8.1 CFU/g), which were comparable to Cl except for the case of alfalfa sprouts where Cl achieved the highest inactivation. No significant quality difference in terms of visual color change or electrolyte leakage was observed in sprouts washed by PAW and Cl.     

Listeria innocua Multi-target Inactivation by Thermo-sonication and Vanillin

Hurdle technology combining an emerging preservation technique such as low-frequency ultrasound is an alternative for processing juices that are susceptible to suffer a loss of quality due to traditional heat treatments. Predictive microbiology allows evaluation of the effectiveness of preservation techniques and its combinations in order to enhance both food quality and safety. Listeria innocua inactivation by thermo-sonication along with vanillin was investigated. Fermi model (R ² _adj= 0.970 ± 0.02) and surface response methodology (p < 0.05) were utilized in order to evaluate the survival of L. innocua to a multi-target treatment and to predict the interactions of studied techniques, high-intensity/low-frequency ultrasound (20 kHz/400 W) at selected wave amplitudes (60, 75, or 90 μm), temperature (40, 50, or 60 °C), and vanillin (200, 350, or 500 mg/kg). A combination of ultrasound, vanillin, and temperature enhanced L. innocua inactivation as described by Fermi parameters a and t _c, which decreased as the studied effects increased. A multi-target inactivation effect was observed for a temperature range of 45–55 °C.