Study on Thermosonication and Ultraviolet Radiation Processes as an Alternative to Blanching for Some Fruits and Vegetables

The impacts of ultraviolet-C radiation, blanching by heat, and combination of heat/ultrasounds (thermosonication) were studied for Listeria innocua (inoculated) in red bell peppers, total mesophiles in strawberries and total coliforms in watercress, in the temperature range 50–65 °C. Quality attributes such as colour and firmness were studied for all products, and total anthocyanins content was additionally determined for strawberries. Results showed that ultraviolet-C radiation was the least effective treatment in terms of microbial load reduction and was equivalent to a simple water washing. Log reductions were 1.05 ± 0.52 for L. innocua, 0.53 ± 0.25 for total coliforms and 0.26 ± 0.18 for total mesophiles. This treatment had the lowest impact on the quality parameters analysed. Thermosonication treatment was similar to heat blanching for all microorganism/product tested, excepted for total coliforms in watercress at 65 °C, in which thermosonication had a higher effect (p < 0.05). Heat blanching at 65 °C allowed 7.43 ± 0.12 log-cycles reduction, while loads were diminished by 8.24 ± 0.13 log-cycles if thermosonication at the same temperature was applied. Thermosonication also allowed better quality retention, when compared to heat blanching at the same temperatures. The impact of thermosonication on microbial load reductions was statistically significant and thermosonicated samples retained quality attributes better than heat blanched ones at the same temperatures (p < 0.05). Hence, it can be concluded that thermosonication is a promising process and may be a favourable alternative to the conventional thermal treatments.     

Effect of heat and thermosonication treatments on watercress (Nasturtium officinale) vitamin C degradation kinetics

The use of ultrasound in food processing creates novel and interesting methodologies, which are often complementary to classical techniques. In this work, the effect of heat and the combined treatment heat/ultrasound (thermosonication) on the thermal degradation kinetics of vitamin C in watercress (Nasturtium officinale) was studied in the temperature range of 82.5 to 92.5 °C. First order reaction kinetics adequately described the vitamin C losses during both blanching processes.The activation energies and the reaction rates at 87.5 °C for heat (H) and thermosonication (Ts) treatments were, respectively, E_avitCH = 150.47 ± 42.81 kJ mol^− 1 and E_avitCTs = 136.20 ± 60.97 kJ mol^− 1, and k_{87.5 °CvitCH} = 0.75 ± 0.10 min^− 1 and k_{87.5 °CvitCTs} = 0.58 ± 0.11 min^− 1. No significant differences (P > 0.05) were detected between both treatments. The thermosonication treatment was found to be a better blanching process, since it inactivates watercress peroxidase at less severe blanching conditions and consequently retains vitamin C content at higher levels. The present findings will help to optimise the blanching conditions for the production of a new and healthy frozen product, watercress, with heat and a new blanching process methodology.

Industrial relevance

Thermosonication blanching can be useful since it reduces processing times, and consequently minimizes the adverse effects of heating on watercress quality. This new application will provide good material, in terms of vitamin C, for further processes, and can be an excellent alternative to the traditional heat treatment.     

The Impact of Thermosonication and Pulsed Electric Fields on Staphylococcus aureus Inactivation and Selected Quality Parameters in Orange Juice

The effect of thermosonication (TS) and pulsed electric fields (PEF) on inactivation of Staphylococcus aureus (SST 2.4) and selected quality aspects in orange juice was investigated. Conventional pasteurization (HTST, 94 °C for 26 s) was used as a control. TS (10 min at 55 °C) applied in combination with PEF (40 kV/cm for 150 μs) resulted in a comparable inactivation of S. aureus to that achieved by conventional HTST. TS/PEF did not affect the pH, conductivity, or °Brix and had a milder impact on the juice color than thermal treatment. Furthermore, the non-enzymatic browning index was significantly affected by HTST (P < 0.05) but not by TS and PEF. Ascorbic acid retention was almost complete after TS and PEF (96.0%), but it was substantially lower (P < 0.05) after HTST (80.5%). Residual activity of pectin methyl esterase (PME) decreased as PEF field strength and treatment time increased; however, applying TS and PEF in combination left a greater residual PME activity than HTST (12.9 vs 5.0%, respectively).     

The Impact of Blanching and High-Pressure Pretreatments on Oil Uptake of Fried Potato Slices

The effect of high-pressure (HP) pretreatment on oil uptake of potato slices is examined in this paper. Potato slices were treated either by HP or thermal blanching, or a combination of thermal blanching followed by HP prior to frying. The effect of HP on starch gelatinization and potato microstructure was assessed by differential scanning calorimeter and environmental scanning electron microscope (ESEM), respectively. After treatments, the slices were fried in sunflower oil at 185 °C for a predetermined time. Frying time was either kept constant (4 min) or varied according to the time needed to reach a desired moisture content of ≈2%. The high pressure applied in this study was found not to be sufficient to cause a significant degree of starch gelatinization. Analysis of the ESEM images showed that blanching had a limited effect on cell wall integrity. HP pretreatment was found to increase the oil uptake marginally. When frying for a fixed time, the highest total oil content was found in slices treated at 200 MPa for 5 min. The oil content was found to increase significantly (p < 0.05) to 41.23 ± 1.82 compared to 29.03 ± 0.21 in the control slices. The same effect of pressure on oil content was found when the time of frying varied. On the other hand, HP pretreatment was found to decrease the frying time required to achieve a given moisture content. Thus, high-pressure pretreatment may be used to reduce the frying time, but not oil uptake.     

Improvement of color and limpness of fried potatoes by in situ pectinesterase activation

 Low-temperature, long-time blanching (LT–LT blanching) was performed on potato strips prior to frying. Application of this treatment actived the pectinesterase enzyme in situ resulting in a decrease in the limpness of the fried potatoes; likewise, an improvement in color was obtained as the result of a decrease in reducing sugar content. LT–LT blanching at 65  °C for 45 min gave the greatest improvement in the color and limpness of french fries. Received: 1 December 1998     

Effect of Blanching and Drying Temperature on Polyphenolic Compound Stability and Antioxidant Capacity of Apple Pomace

The effects of blanching and drying treatments on stability, physical properties, and antioxidant activity of apple pomace polyphenols were evaluated. Blanched and unblanched apples were extracted, and the pomace was dried in a cabinet dryer at a speed of 3 m/s at 50 °C, 60 °C, 70 °C, and 80 °C. The color, total phenolics, flavonoids, individual polyphenolic compounds, anthocyanins, and total antioxidant activity were analyzed. The blanching process caused a major retention in color, total polyphenolic content, and total flavonoid content for fresh apple pomace when compared with fresh unblanched pomace. Drying of either fresh blanched or fresh unblanched pomace caused a significant reduction (P < 0.05) in total polyphenol and flavonoid content leading to a reduction in the total antioxidant activity. When compared with the unblanched treatment, drying the blanched pomace at 80 °C resulted in a product with significant amounts of total phenolics, flavonoids, and antioxidant activity. The individual phenolic compounds were significantly increased (P < 0.05) in blanched pomace that was not dried when compared with unblanched samples. Drying blanched apple pomace did not cause a significant change in the concentration of individual polyphenolic compounds, but drying unblanched apple pomace caused a reduction in the concentrations of epicatechin and caffeic acid, with an important reduction in p-coumaric acid at temperatures higher than 60 °C. However, the drying process caused a significant reduction in the antioxidant capacity. Therefore, a combination of blanching and drying processes for apple pomace results in a product that maintains antioxidant capacity.     

Modelling kinetics of watercress (Nasturtium officinale) colour changes due to heat and thermosonication treatments

Watercress (Nasturtium officinale) colour changes due to blanching by heat and a combined treatment of heat/ultrasound (thermosonication) were studied in the temperature range of 82.5 to 92.5 °C. The application of thermosonication was intended to enable less severe blanching treatments and, therefore, improve the quality of the blanched product. The thermosonication blanching processes promoted changes of the green colour (aⁿ parameter) at a higher rate (P < 0.05), when compared with the heat blanching processes. No significant differences (P > 0.05) were detected between heat and thermosonication blanching processes in terms of the colour parameters Lⁿ, bⁿ and TCD changes. In both treatments, a fractional first order model fitted well the experimental data for Lⁿ, aⁿ and bⁿ (R_H² = 0.99; R_Ts² = 0.99) and TCD (R_H² = 0.92; R_Ts² = 0.96) colour parameters.The chlorophylls content showed no significant differences (P > 0.05) between thermally treated and thermosonicated watercress samples.The present findings will help to evaluate the effectiveness of thermosonication as a novel process to replace the classical heat treatment.Industrial relevanceConventional blanching commonly results in severe losses or destruction of nutrients due to process intensity and extended process times. Consequently, the attempts to use the synergistic effects of heat and ultrasound (at least) for enzyme inactivation are of high relevance. The results, although not conclusive, indicate, that they may aid optimization of blanching processes.     

Thermosonication and inactivation of viable putative non‐culturable Lactobacillus acetotolerans in beer

This work compares the inactivation by thermosonication of exponentially growing Lactobacillus acetotolerans cells with viable putative non‐culturable (VPNC) cells in beer. The critical process parameters were optimised using response surface methodology using a three‐factor three level Box–Behnken design. The three independent variables were volumetric power (2.7, 5.8 and 8.9 W/mL), temperature (40, 50 and 60°C) and treatment time (2, 4 and 6 minutes) with the output of log reduction in viable cell number of L. acetotolerans cells growing exponentially or in the VPNC state. The results showed that under different conditions of volumetric acoustic power–temperature–time combination, cells of L. acetotolerans in the VPNC state were more resistant to thermosonication than exponential cells. This insight will be of value to the design of appropriate thermosonication conditions to pasteurise beer and other beverages. © 2018 The Institute of Brewing & Distilling     

An Evaluation of the Potential of High-Intensity Ultrasound for Improving the Microbial Safety of Poultry

The application of sonication and thermosonication (53 ± 1 °C) was investigated as potential methods for reducing numbers of Campylobacter, enterobacteriaceae and total viable counts (TVC) on raw poultry. Sonication equipment included a high-intensity unit (HI) and a low-intensity unit (LI), which produced 20,000 and 20 W/L, respectively. The susceptibility of ten Campylobacter isolates in liquid media to thermosonication treatment was also investigated to determine whether differences between isolates existed. All Campylobacter strains were susceptible to thermosonication in the HI unit with inactivations ranging from 2.97–4.15 log₁₀ CFU/mL. Campylobacter jejuni was more susceptible to thermosonication than to thermal or sonication treatment with mean inactivations of 4.72, 1.45 and 3.17 log₁₀ CFU/mL, respectively. Following 16 min thermal, sonication and thermosonication treatments of broiler skin pieces in the HI unit, no viable Campylobacter or enterobacteriaceae were detected and TVC were reduced by 1.93, 1.34 and 2.49 log₁₀ CFU/g, respectively. Thermosonication treatment in the LI unit reduced enterobacteriaceae and TVC populations by 2.74 and 1.69 log₁₀ CFU/g, respectively. Thermosonication treatment was generally more effective against Campylobacter in liquid matrices in comparison to inoculated poultry products.     

Effect of Air Temperature on Drying Kinetics,Vitamin C,Antioxidant Activity,Total Phenolic Content,Non-enzymatic Browning and Firmness of Blueberries Variety O´Neil

Effect of air temperature on drying kinetics, vitamin C, antioxidant capacity, total phenolic content (TPC), colour due to non-enzymatic browning (NEB) and firmness during drying of blueberries was studied. Drying curves were satisfactorily simulated with the Weibull model at 50, 60, 70, 80 and 90°C. The scale parameter (β) decreased as air temperature increased and an activation energy value of 57.85 kJ mol⁻¹ was found. Important losses of vitamin C were reported during drying for all the working temperatures (p < 0.05). Although TPC decreased as air-drying temperature increased (p < 0.05) in comparison to its initial value, the dehydration at high temperatures (e.g., 90°C) presented high values for these antioxidant components. Discoloration due to NEB reaction was observed at all the working temperatures showing a maximum value at 90°C (p < 0.05). The radical scavenging activity showed higher antioxidant activity at high temperatures (80 and 90°C) than at low temperatures (50, 60 and 70°C) (p < 0.05). A tissue firmness reduction was observed with increasing temperature (p < 0.05).     

Effect of Infrared Blanching on Enzyme Activity and Retention of β‐Carotene and Vitamin C in Dried Mango

The objectives of this work were to evaluate infrared (IR) dry blanching in comparison with conventional water blanching prior to hot air drying of mango to inactivate polyphenol oxidase (PPO) and ascorbic acid oxidase (AAO) enzymes, and to study its effect on color change and retention of vitamin C and β‐carotene. Mango cylinders were blanched under similar temperature–time conditions either by IR heating or by immersion in a water bath during 2 min at 90 °C (high‐temperature‐short‐time—HTST) or for 10 min at 65 °C (low‐temperature‐long‐time—LTLT). After blanching mango was hot air dried at 70 °C. PPO was completely inactivated during the blanching treatments, but AAO had a moderate remaining activity after LTLT treatment (～30%) and a low remaining activity after HTST treatment (9% to 15%). A higher retention of vitamin C was observed in mango subjected to IR dry blanching, 88.3 ± 1.0% (HTST) and 69.2 ± 2.9% (LTLT), compared with water blanching, 61.4 ± 5.3% (HTST) and 50.7 ± 9.6% (LTLT). All‐trans‐β‐carotene retention was significantly higher in water blanched dried mango, 93.2 ± 5.2% (LTLT) and 91.4 ± 5.1% (HTST), compared with IR dry blanched, 73.6 ± 3.6% (LTLT) and 76.9 ± 2.9% (HTST). Increased levels of 13‐cis‐β‐carotene isomer were detected only in IR dry blanched mango, and the corresponding dried mango also had a slightly darker color. IR blanching of mango prior to drying can improve the retention of vitamin C, but not the retention of carotenoids, which showed to be more dependent on the temperature than the blanching process. A reduction of drying time was observed in LTLT IR‐blanching mango.     

Effects of different pre-freezing blanching procedures on the physicochemical properties of Brassica rapa leaves (Turnip Greens, Grelos)

For optimal freeze storage, green vegetables should first be blanched. The present study compared four different procedures for the blanching of grelos (leaves of Brassica rapa L.): steaming for 2 min, immersion in boiling water for 2 min, immersion in boiling water containing 1% citric acid for 1 min, and immersion in boiling water containing 5% citric acid for 1 min. After blanching, the grelos were stored for up to 120 days at ?18 °C, with sampling at two‐weekly intervals for analysis of physicochemical properties (ash weight, vitamin C content, pH, acid value, moisture content and CIE_L*a*b* colour variables). In almost all respects steam blanching gave the best results: notably, vitamin C losses were markedly lower, while moisture content and colour remained closer to those of the fresh product.     

Effect of Air-Drying Conditions on Physico-chemical Properties of Osmotically Pre-treated Pomegranate Seeds

The drying of pomegranate seeds was investigated at 40 °C, 50 °C and 60 °C with air velocity of 2 m/s. Prior to drying, seeds were osmodehydrated in 55 °Brix sucrose solution for 20 min at 50 °C. The drying kinetics and the effects of osmotic dehydration (OD) and air-drying temperature on antioxidant capacity, total phenolics, colour and texture were determined. Analysis of variance revealed that OD and air-drying temperature have a significant influence on the quality of seeds. Both anthocyanin and total phenolic contents decreased when air-drying temperature increased. The radical diphenylpicril-hydrazyl activity showed the lowest antioxidant activity at 60 °C. Both chromatic parameters (L*, C* and h°) and browning index were affected by drying temperatures, which contributed to the discolouring of seeds. The final product has 22%, 20% and 16% of moisture; 0.630, 0.478 and 0.414 of a _w; 151, 141 and 134 mg gallic acid equivalent/100 g fresh matter (FM) of total phenolics; 40, 24, 20 mg/100 g FM of anthocyanins and 46%, 39% and 31% of antioxidant activity, for drying temperatures of 40 °C, 50 °C and 60 °C, respectively. In view of these results, the temperature of 40 °C is recommended as it has the lowest impact on the quality parameters of the seeds. Differential scanning calorimetry data provided complementary information on the mobility changes of water during drying. Glass transition temperature (Tg′) depends on moisture content and as consequence, on drying conditions. In fact, Tg′ of seeds dried at 60 °C (Tg′ = −21 °C) was higher than those dried at 50 °C (Tg′ = −28 °C) or 40 °C (Tg′ = −31 °C) and osmodehydrated seeds (Tg′ = −34 °C). During OD and drying process, the texture of seeds changed. The thickness of seeds shrank by 55% at 60 °C.     

Optimization of stepwise blanching of frozen-thawed potato tissues (cv. Monalisa)

 Response surface methodology was used to compare the effect of temperature and time of the first step of blanching on compression, shear, tension and stress-relaxation parameters of frozen-thawed potato tissues. A central, composite rotatable design was used to study the effects of variation in levels of temperature (52.93–67.07  °C) and time (15.86–44.14 min) on rheological parameters. Blanching temperature was the most important factor affecting the mechanical properties tested. The models fitted for the apparent modulus of elasticity in compression, maximum tension force, and relaxed force in the first cycle (F _r1); all had R ²>0.85 (P≤0.01) and were used for doing predictions. Optimum conditions were with in the ranges of temperature (60–65  °C) and time (25–35 min) used for each factor. In the experimental verification of the models at 65  °C during 30 min, the lowest percentage residual between experimental and predicted values was obtained for F _r1 (0.644), which was therefore the most appropiate parameter for detecting the firming effect that the pectinesterase activity produced on frozen potato tissues as a consequence of stepwise blanching under these conditions. Received: 3 February 1999 / Revised version: 12 April 1999     

Deformation properties of Finnish spruce and pine wood in tangential and radial directions in association to high temperature drying Part II. Experimental results under constant conditions (viscoelastic creep)

Picea abies ) and Scots pine (Pinus sylvestris) wood under conditions relevant in the high temperature drying process. This paper reports on the experimental results obtained concerning creep in tension under constant conditions, primarily in wet (saturated, green) state at temperatures 95 °C–125 °C. The results are compared to some other researchers' measurements in a trial of the applicability of the time–temperature–moisture-content superposition principle. Based on these results, a master curve is determined by curve-fitting for use in practical calculation of the elastic and viscoelastic compliance in different conditions.

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The effect of blanching on the mechanical and rehydration properties of dried potato slices

 Short-time blanched (2 min, 90  °C), long-time blanched (30 min, 90  °C) and non-blanched potato slices were dried in a convective air drier and their mechanical and rehydration properties were compared. Blanching increased the flexibility and strength of dried potato slices, although the effects of short and long blanching were not significantly different. Unblanched potato slices did not have larger rehydration ratios than blanched ones. After rehydration for 30 min, samples from all treatments had higher strength and flexibility than cooked potatoes. Received: 2 November 1998 / Revised version: 15 February 1999     

Effect of preheating on internal checking in boards of different dimension and grain orientation inEucalyptus regnans

Eucalyptus regnans resulted in a decrease in both area of internal checking and number of checks after drying. Grain orientation was significant in determining the extent of reduction. For tangential grain, checking decreased linearly with increasing temperature; for intermediate grain, checking was relatively constant to 70 °C before declining at 90 °C ; and for radial grain, checking increased at 50 and 70 °C before declining at 90 °C . At 90 °C , reduction in area of checking and number of checks averaged 89.8 and 53.3% respectively for tangential grain, 62.7 and 62.2% for intermediate grain and 69.1 and 53.9% for radial grain, a reduction overall of 75.1 and 56.2%. Shrinkage in 5 × 10 cm cross-sections was also modified by preheating such that increased shrinkage in board width and reduced shrinkage in board thickness tended to be associated with reduced checking. Since these relationships were largely irrespective of grain orientation, they were attributed to specimen geometry. However, the major factor in check reduction was an increase in the rate of moisture loss, or ostensible permeability. When the effect of rate of moisture loss was nullified in regression analysis, check reduction tended to be related to an increase in tangential shrinkage overall and a decrease in radial shrinkage, irrespective of grain orientation. There was little effect on check reduction in smaller sized material (5 × 5 and 2.5 × 10 cm cross-sections) through preheating, although initial checking in this material was very low by comparison with 5 × 10 cm cross-sections.

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Kinetics of Crude Peroxidase Inactivation and Color Changes of Thermally Treated Seedless Guava (Psidium guajava L.)

Thermal treatment of seedless guava (Psidium guajava L.) cubes was carried out in the temperature range of 80–95 °C. The kinetics of peroxidase inactivation and color changes due to thermal treatments were determined. Peroxidase inactivation followed a first-order kinetic model, where the activation energy was 96.39 ± 4 kJ mol⁻¹. Color was quantified in terms of L, a, and b values in the Hunter system. The color changes during processing were described by a first-order kinetic model, except total color difference which followed a zero-order kinetic model. The temperature dependence of the degradation followed the Arrhenius relation. The activation energies (E _a) for L, a, b, and total color difference (ΔE) were 122.68 ± 3, 88.47 ± 5, 104.86 ± 5, and 112.65 ± 5 kJ mol⁻¹, respectively. The results of this work are a good tool to further optimize seedless guava thermal treatment conditions.     

Sorption Isotherms of Barnyard Millet Grain and Kernel

The moisture sorption isotherms of grain and kernel of barnyard millet (Echinochloa frumentacea) were determined at 20, 30, 40, and 50 °C. A gravimetric static method was used under 0.112–0.964 water activity (a _w) range for the determination of sorption isotherms. The models were compared using the coefficient of determination (r ²), reduced chi-square (χ ²) values, and on the basis of residual plots. In grain, modified Chung–Pfost (r ² > 0.99; χ ² < 0.7) and modified Oswin (r ² > 0.99; χ ² < 0.55) models were found suitable for predicting the M _e –a _w relationship for adsorption and desorption, respectively. Modified Henderson model was found to give the best fit (r ² > 0.99 and χ ² < 0.55) for describing the adsorption and desorption of the kernel. The isosteric heat, calculated using Clausius–Clapeyron equation, was varied between 46.76 and 61.71 kJ g⁻¹ mol⁻¹ at moisture levels 7–21% (d.b.) for grain and 47.11–63.52 kJ g⁻¹ mol⁻¹ at moisture level between 4% and 20% (d.b.) for kernel. The monolayer moisture content values ranged from 4.3% to 6% d.b. in the case of adsorption of barnyard millet grain and 5.2–6.6% d.b. in the case of desorption at the temperature ranges of 50–20 °C. The monolayer moisture values of barnyard millet kernel ranged from 4.4% to 6.67% d.b. in adsorption and 4.6% to 7.3% d.b. in desorption in the temperature ranges of 50–20 °C.     

Inactivation of peroxidase and lipoxygenase in carrots, green beans, and green peas by combination of high hydrostatic pressure and mild heat treatment

The efficiency of high hydrostatic pressure (HHP) with the combination of mild heat treatment on peroxidase (POD) and lipoxygenase (LOX) inactivation in carrots, green beans, and green peas was investigated. In the first part of the study, the samples were pressurized under 250–450 MPa at 20–50 °C for 15–60 min. In the second part, two steps treatments were performed as water blanching at 40–70 °C for 15 and 30 min after pressurization at 250 MPa and 20 °C for 15–60 min. Carrot POD was decreased to 16% residual activity within the first 30 min at a treatment condition of 350 MPa and 20 °C and then it decreased to 9% at 60 min. When the carrots were water blanched at 50 °C for 30 min after HHP treatment of 250 MPa at 20 °C for 15 min, 13% residual POD activity was obtained. For green beans, the most effective results were obtained by two steps treatment and approximately 25% residual POD activity was obtained by water blanching at 50 °C for 15 min after pressurization at 250 MPa and 20 °C for 60 min. An effective inactivation of POD in green peas was not obtained. For carrots, LOX activity could not be measured due to very low LOX activity or the presence of strong antioxidants such as carotenoids. After pressurization at 250 MPa and 20 °C for 15 or 30 min, water blanching at 60 °C for 30 min provided 2–3% residual LOX activity in green beans. The treatment of 250 MPa for 30 min and then water blanching at 50 °C for 30 min provided 70% LOX inactivation in green peas.