纳米流体在液态食品杀菌中的应用及其作用机制研究进展

纳米流体是一种能替代热交换器中传统介质的新兴流体,其具有稳定性好、可重复利用、节约能耗等优点,以纳米流体为传热介质的热交换器有传热效率高、杀菌时间短的特点,更好地保持了食品感官和营养特性.该流体已成功应用于牛奶、果汁等液态食品的杀菌.本文概述了不同类型的纳米流体,如多壁碳纳米管(Multi-wall carbon na...     

Nano-fluid thermal processing of watermelon juice in a shell and tube heat exchanger and evaluating its qualitative properties

Due to specific thermophysical properties of nanofluids, compared with conventional thermal fluids (steam and hot water), their application in diverse industries, to improve heat transfer and to save energy, has increased. One important aspect of applying nanofluid thermal processing is shortening the process time which could have high potentials in the food industry since nutritional and bioactive components would be maintained much higher than common thermal processes. In this project, possibility of replacing water with alumina-water nanofluids (2 and 4% concentrations) during high temperature short time processing (75, 80 and 85 °C for 15, 30 and 45 s) of watermelon juice in a shell and tube exchanger regarding its qualitative properties (lycopene, vitamin C, color, pH and TSS) was investigated. Reduction in process time when applying 2 and 4% nanofluids, up to 24.88 and 51.63%, had considerable effects on maintaining qualitative properties for watermelon juices. For instance, thermal processing by 0, 2 and 4% nanofluids at 75 °C for 15 s could keep 81.15, 84.81 and 91.28% of lycopene and 61.11, 63.70 and 67.04% of vitamin C, respectively. pH and TSS indices of processed watermelon juices were in the range of 5.58–5.82 and 9.0–9.4, respectively, showing no considerable correlation with the heating media used in thermal processing. Our results revealed that nutritional and physicochemical properties of watermelon juice processed with alumina nanofluids were better than common thermal processing by water with 9.89, 6.18 and 50.38% higher lycopene, vitamin C and color retention in the final product, respectively.Industrial RelevanceEven so thermal processes are effective in preventing microbial spoilage of fruit juices, high volume of energy transfer in long durations into food products with heat sensible ingredients or properties results in biochemical and nutritional losses, development of unpleasant reactions, changes in overall quality of food products, and high energy consumption. Nowadays, consumers demand for food products with long shelf lives, high quality and proper prices are increasing. So, to meet these demands, food industries are looking for alternative thermal technologies to reduce losses in food characteristics and process costs, and introduce a fresh, nutritious, healthy and affordable food produce.Thermal conductivity of conventional fluids is much lower than metals and oxidized metals. For example, thermal conductivities of copper and alumina are 700 and 60 times higher than the thermal conductivity of water, respectively. Accordingly, fluids with suspended particles of metals or oxidized metals benefit from better heat transfer properties. The term of Nanofluid refers to each stable two-phase compound that includes both base fluids and nanoparticles (lower than 100 nm, at least in one dimension).There is no research dealing with effects of adding nanoparticles to conventional thermal fluids for fruit juices processing. So, the goal of this research was to introduce nanofluid technology for thermal processing of food products for the first time, increasing heat transfer efficiency in shell and tube exchangers by nanofluids and frugality in energy consumption for pasteurization, reducing thermal processing duration and better quality retention of food products.     

Comparative study on color,viscosity and related enzymes of tomato juice treated by high-intensity pulsed electric fields or heat

The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,500 μs using bipolar 4-μs pulses at 100 Hz) on color parameters and viscosity, as well as peroxidase (POD), pectin methylesterase (PME) and polygalacturonase (PG), were evaluated during 77 days of storage at 4 °C and compared to thermal treatments at 90 °C for 1 min or 30 s for unprocessed tomato juice. HIPEF-treated tomato juice showed higher values of lightness than the thermally processed and the untreated juice throughout storage time (P < 0.05). Viscosity of HIPEF-treated tomato juice was also greater than both thermally treated and untreated for the first 35 days of storage. POD of HIPEF-treated tomato juice was inactivated by 97% whereas in the case of the thermally treated, 90 and 79% inactivation was achieved after 1 min and 30 s, respectively. The highest PME inactivation in tomato juice was obtained by PEF (82%) and heat treatment at 90 °C for 1 min (96%). PG of PEF-treated tomato juice was inactivated by 12% whereas thermal treatments at 90 °C for 1 min or 30 s achieved 44 and 22%, respectively. Despite the low rates of PG inactivation obtained, the pattern followed in the residual activity along the storage time was similar in the tomato juice treated by HIPEF than the thermally processed.     

Volatile compounds and changes in flavour‐related enzymes during cold storage of high‐intensity pulsed electric field‐ and heat‐processed tomato juices

BACKGROUND: The effects of high‐intensity pulsed electric field (HIPEF) processing (35 kV cm^?1 for 1500 µs, using 4 µs bipolar pulses at 100 Hz) on the production of volatile compounds and flavour‐related enzymes in tomato juice were investigated and compared with those of thermal processing (90 °C for 30 or 60 s). RESULTS: Tomato juice treated by HIPEF showed lower residual lipoxygenase (LOX) activity (70.2%) than juice heated at 90 °C for 60 s (80.1%) or 30 s (93.2%). In contrast, hydroperoxide lyase (HPL) was almost completely inactivated when the juice was subjected to 90 °C for 60 s, whereas roughly 50% of the control tomato juice was depleted after HIPEF treatment or thermal processing at 90 °C for 30 s. A slight decrease was observed in the initial LOX activity of treated and untreated samples during storage, whereas initial HPL activity was strongly affected over time. CONCLUSION: HIPEF‐treated juice exhibited higher levels of compounds contributing to tomato aroma than untreated and heat‐treated juices throughout storage. Thus HIPEF processing can preserve flavour quality and stability of tomato juice compared with conventional thermal treatments. Copyright © 2010 Society of Chemical Industry     

Novel approaches to reduce brown pigment formation and color changes in thermal pasteurized tomato juice

The effects of two heat processes mild-temperature pasteurization (MTP: 75 °C, 23 s) and high-temperature pasteurization (HTP: 92 °C, 5 s) on undesirable brown color development and some quality attributes (pH, soluble solids content, and color parameters) of pasteurized tomato juice were evaluated and compared during 94 days of storage at 5 °C. Although both heat treatments combined with refrigeration prevented microbial growth for 64 days, the shelf life regarding acceptable microbial load of HTP-treated sample was higher than 94 days. Both processes produced lesser brown color formation in tomato juices than the commonly adopted thermal treatments although the MTP processing provides better color preservation than the HTP one. No effect of heat treatments on soluble solids content was observed while the HTP processing slightly increased the acidity of pasteurized tomato juice. The good relationship obtained between brown color and total color difference (TCD) suggests that TCD can be used to evaluate the visual color deterioration and browning in thermally processed tomato juice throughout refrigerated storage. Results presented in this study showed that the combination of a mild heat treatment plus refrigeration may help to ensure the microbiological safety and the nutritional value of pasteurized tomato juices.     

Modulation of thermal resistance of ascospores of Neosartorya fischeri by acidulants and preservatives in mango and grape juice

Minimal thermal processing is desirable for near natural organoleptic and nutritional qualities of fruit based products. In the present investigation, the effect of heat (85°C) in combination with acidulants or common preservatives on inactivation of ascospores of Neosartorya fischeri, a heat resistant mould isolated from grapes, has been studied in mango and grape juice. The ascospores were found to survive for >300 min of heating at 70, 75 and 80°C in these fruit juices and complete inactivation required 120 min of heating at 85°C. The synergistic effect of heat and organic acids or preservatives in fruit juices was noticed. The thermal death rate (1/k_85°C) values did not vary much in the presence of lactic (20), malic (20) and citric (19) acids, but tartaric acid showed least inactivation effect (1/k_85°C=54 min) in mango juice. The 1/k_85°Cvalues for ascospores of N. fischeri in mango juice containing 0·1% of potassium sorbate or sodium benzoate or combination of both at 0·05% were found to be 44, 35 and 29 min respectively. These values were respectively, 32, 13 and 14 min in grape juice. Nearly 50 and 67% of the heating time was reduced by the use of potassium sorbate and sodium benzoate (0·05% each) in mango and grape juice to inactivate 3 log number of ascospores of N. fischeri. These results may be useful in thermal processing of fruit juices.     

Heat resistance of Byssochlamys nivea, Byssochlamys fulva and Neosartorya fischeri isolated from canned tomato paste

Cultures of heat resistant molds (20) were isolated from spoiled canned tomato paste in order to estimate the pasteurization efficiency applied to commercially canned products. Ascospores of nine strains grown on malt extract agar for 30 days at 30°C, survived heating at 85°C for 20 min when initial numbers were near 10⁵/mL. Of these heat resistant strains were identified: two Byssochlamys nivea, three Byssochlamys fulva and four Neosartorya fischeri strains. Ascospores of all cultures were more heat resistant in tomato juice than in phosphate buffer. Thermal death rate curves were nonlogarithmic but approached logarithmic death rates at higher temperatures. The thermal destruction time for 1 log₁₀ at 90°C was 1.5 min for a Byssochlamys nivea strain, 8.1 min for a Byssochlamys fulva strain and 4.4 to 6.6 min for Neosartorya fischeri strains.     

Effect of pulsed light treatment on the phytochemical,volatile, and sensorial attributes of lactic-acid-fermented mulberry juice

Lactic-acid-fermented mulberry juice (LFMJ) was subjected to pulsed light (PL) treatment at exposure time of 2, 4, and 8 s at high insensitive pulses of 14.0 J/cm². The effect of PL treatment on the microbial inactivation, physicochemical, phytochemical, volatile, and sensory characteristics of LFMJ was evaluated. It was found that the PL was able to reduce the microbial load to acceptable levels (1.02 ± 0.04 log₁₀ cfu/mL) with no significant impact on the physicochemical properties of LFMJ. It was also observed that the PL treatment caused a slight decrease in anthocyanin concentration at 8 s exposure time. The color difference (?E) of the juice treated for 2 and 4 s fell below the slightly noticeable range 0.5<ΔE<1.5 while ?E values for the 8 s (0.55 ± 0.02) and the thermal (0.50 ± 0.02) treated samples were slightly noticeable. The volatile profile and odor activity values were positively affected by increasing the exposure time. The results depict that, under the present experimental conditions, the application of the PL resulted in a fermented juice with superior quality attributes as compared to the thermal treated juice.     

EFFECT OF pH AND SOLUBLE SOLIDS ON THE SERUM VISCOSITY AND SERUM COLOR OF TOMATO JUICE AT ELEVATED TEMPERATURES1

Effects of heating time and temperature, pH, and soluble solid levels on serum viscosity and serum color of tomato juice were studied. The samples were canned in 18 mL TDT cans and exposed to processing temperatures of 88C, 102C, and 112C for 30, 60, and 120 min. Depending upon the time and temperature of heating, and initial viscosity of the serum, the losses in viscosity ranged from 3.0–55.6% being higher in serum with higher initial viscosity. Percent losses in serum viscosity during heating of juice increased (6–60%) with increase in pH (3.8–4.9) and soluble solids (6°–24°) in the juice. An increase in pH and soluble solids also enhanced heat induced browning in the serum with values varying from 0.1–2.69.     

Synergistic Effect of Orange Essential Oil or (+)-limonene with Heat Treatments to Inactivate Escherichia coli O157:H7 in Orange Juice at Lower Intensities while Maintaining Hedonic Acceptability

This study investigates the effects of different concentrations (50–200 ppm) of (+)-limonene or orange essential oil (EO) when designing thermal treatments to pasteurize orange juice (OJ) at different temperatures (54–60 °C). The addition of 200 ppm of (+)-limonene or orange EO to commercial OJ reduced the heating time to inactivate 5 log₁₀ cycles of the target pathogen Escherichia coli O157:H7 by 3.8 or 2.5 times, respectively. Results demonstrated that EOs and heat acted synergistically. Interestingly, the synergistic effect was constant in the studied range of temperatures. OJ added with 100 ppm of (+)-limonene or 200 ppm of orange EO maintained the sensory acceptance after a heat treatment able to inactivate 5 log₁₀ cycles of E. coli O157:H7. This study opens up the possibility of designing scientific-based combined processes for OJ pasteurization founded on the controlled incorporation of orange EO or (+)-limonene.     

Dry-peeling of Tomato by Infrared Radiative Heating: Part I. Model Development

Infrared (IR) dry-peeling of tomatoes has emerged as a nonchemical alternative to conventional peeling methods using hot lye or steam. Successful peel separation induced by IR radiation requires the delivery of a sufficient amount of thermal energy onto the tomato surface in a very short duration. The objective of this study was to understand the transient heat transfer phenomena during IR dry-peeling by developing a computer simulation model. Modeled tomatoes with realistic shapes and different sizes were employed to predict the temperature distributions on their surface and interior during a typical 60 s IR heating. IR radiation was postulated as a mathematically gray-diffuse radiation problem based on the enclosure theory. Radiation heat transfer model combining heat conduction and convection was solved numerically in COMSOL by using a finite element scheme. Changes of tomato thermal properties and phase change of water inside tomato tissues due to temperature increase were considered in the model to improve the prediction accuracy. The developed model can further be used to study the effects of various engineering parameters on IR heating performance relevant to tomato peeling quality and efficiency. Numerical modeling of the heat transfer mechanism provides in-depth understanding of the rapid surface heating characteristics of IR in the tomato dry-peeling process.     

Impact of Thermal and Pressure-Based Technologies on Carotenoid Retention and Quality Attributes in Tomato Juice

The aim of this study was to investigate the impact of thermal processing (TP) (90 °C, 90 s), high-pressure processing (HPP) (600 MPa, 46 °C, 5 min), and high-pressure homogenization (HPH) (246 MPa, 99 °C, <1 s) on product quality parameters, specifically carotenoid content, and physicochemical attributes of particle size, color, viscosity, total soluble solids, and pH in tomato juice. Unprocessed tomato juice was used as control. The four major species of carotenoids (lycopene, β-carotene, phytoene, and phytofluene) in tomato juice were analyzed by HPLC. The content of total lycopene, all-trans-lycopene, cis-lycopene isomers,  phytoene, and phytofluene, in TP-, HPP-, and HPH-treated tomato juice did not significantly differ from that in unprocessed (control) juice. Significant reduction in β-carotene content was observed after TP treatment but not after HPP and HPH treatments. HPH significantly reduced tomato juice particle volume mean diameter from ～330 μm in control, HPP-, and TP-treated tomato juices to ～17 μm. A concomitant increase in apparent viscosity was observed in HPH-treated juice versus control. HPH-treated juice had increased redness (a*) and yellowness (b*) than that in control and HPP-treated tomato juices. These results indicate that high-pressure-based technologies (HPP and HPH) can preserve carotenoids as well as improve physicochemical properties.     

Inactivation Kinetics of Pectin Methylesterase,Polyphenol Oxidase,and Peroxidase in Cloudy Apple Juice under Microwave and Conventional Heating to Evaluate Non-Thermal Microwave Effects

Continuous-flow microwave pasteurization provides important advantages over conventional heat exchangers such as fast volumetric heating, lower tube surface temperature, and possible non-thermal effects that enhance enzymatic and bacterial inactivation. Conventional and microwave-assisted inactivation of pectin methylesterase (PME), polyphenol oxidase (PPO), and peroxidase (POD) in cloudy apple juice were investigated to evaluate non-thermal effects. Experiments were conducted to provide uniform heating with accurate temperature acquisition and similar temperature profiles for conventional and microwave treatments. A two-fraction first-order kinetic model was successfully fitted to the data in a procedure that took into account the whole time-temperature profile instead of assuming isothermal conditions. Predicted inactivation curves for pasteurization at 70 and 80 °C of the cloudy apple juice showed that PME has the highest thermal resistance (residual activity of 30% after 250 s at 80 °C) and that there was no evidence of non-thermal microwave effects on the inactivation of these enzymes.     

EFFECT OF DIFFERENT PASTEURIZATION CONDITIONS ON ENZYME INACTIVATION OF ORANGE JUICE IN PILOT-SCALE EXPERIMENTS1

The orange juice pasteurization is associated with enzymatic degradation (primarily pectin-methylesterase) of soluble pectin. Time-temperature curves were established to study different pasteurization conditions on enzyme inactivation, for fresh single-strength orange juice from Florida, containing natural PME enzyme. The orange juice was heated in a DeLaval, model P5-VRB plate heat exchanger with heating and cooling sections, and a 0.0101 m³ volume holding tube. The temperature in the heat exchanger was controlled by means of a pneumatic proportional controller. The residence time in the holding tube of the heat exchanger was monitored by adjusting the flow rate of the positive feed pump. The calculated holding times to obtain 90% reduction of enzyme activity ranged from 33.27 s at 80C to 17.85 s at 90C.     

Effect of thermosonication on quality improvement of tomato juice

Inactivation of pectinmethylesterase (PME) and polygalacturonase (PG) is required to minimize quality loss in tomato products. Tomato juice was subjected to thermosonication (TS) (24 kHz), at amplitudes of 25, 50 and 75 μm at 60, 65 and 70 °C or heat only treatments. The TS treatment at 60 °C, 65 °C and 70 °C for 41.8, 11.7 and 4.3 min exposure, respectively reduced PME activity by 90%. The heat only treatment at 60 °C, 65 °C and 70 °C for 90.1, 23.5 and 3.5 min, respectively inactivated PME by 90%. TS treatments with 25–75 μm amplitude had no significant impact on the inactivation efficiency between 60 and 70 °C. After TS the average particle size decreased noticeably (< 30 μm) and viscosity increased 2–4 fold, compared to the heat treated or untreated juice (180 μm)_. These results suggest that TS at 60 and 65 °C could be useful to obtain tomato juice with a low residual PME activity and high viscosity.Industrial relevanceThe processed tomato industry is constantly in search for potential alternative processes to conventional “cold break” and “hot break” treatments that could inactivate the pectic enzymes of importance. The findings of this study would help the industry to inactivate pectinmethylesterase (PME) enzyme at a lower temperature range and also achieve a higher viscosity due to the mechanical effects of thermosonication. Low temperature treatment would enable the retention of fresh-like properties of tomato juice. Based on the findings of this study, thermosonication could be considered as a potential alternative to conventional “cold break” and “hot break” treatments of tomato juice.     

Cost Analysis and Environmental Impact of Pulsed Electric Fields and High Pressure Processing in Comparison with Thermal Pasteurization

The cost of high pressure processing (HPP) and the environmental impact of pulsed electric fields (PEF), HPP and thermal pasteurization of orange juice were estimated in the US. The cost analysis was based on commercial processing conditions that were validated for a 2-month shelf-life of orange juice under refrigeration conditions. Total electricity consumption was estimated to be 38,100 and 1,000,000 k Wh/year for thermal and HPP processing, respectively. Total pasteurization cost of HPP was estimated to be 10.7 ¢/l for processing 16,500,000 l/year (3,000 l/h). Of this, capital costs accounted for 59 % (6.3 ¢/l), labor costs accounted for 37 % (4.0 ¢/l) and utility charges, mainly electricity, accounted for 4 % (0.4 ¢/l). The total HPP cost was 7-folds higher than that of conventional thermal processing (1.5 ¢/l). The equivalent CO₂ emission was 90,000 kg for thermal processing and 700,000 and 773,000 kg for PEF and HPP, respectively. This corresponds to an increase between 7- and 8-folds in comparison to the thermal processing. Increasing the production output by 2- to 6-folds reduced the total production costs of nonthermal processing by 50–75 %. A deeper knowledge of the processing costs and environmental impact of nonthermal technologies will afford companies a better understanding of the benefits and limitations of these novel systems.     

Chemical Characterization of Tomato Juice Fermented with Bifidobacteria

Abstract: The objective of this research was to characterize the chemical properties of tomato juice fermented with bifidobacterial species. Tomato juice was prepared from fresh tomatoes and heated at 100 °C prior to fermentation. Bifidobacterium breve, Bifidobacterium longum, and Bifidobacterium infantis were inoculated in tomato juice and kept at 35 to 37 °C for up to 6 h. Fructooligosaccharide (FOS) was added to tomato juice prior to fermentation. The analyses for brix, total titratable acidity (TTA), pH, color, and lycopene content were conducted to characterize tomato juices fermented with bifidobacterial species. Heat treatment of tomato juice did not cause any significant changes in brix, pH, and TTA. Only the redness of tomato juice was significantly increased, as the heating time increased to 30 min. The tomato juices fermented with B. breve and B. longum exhibited significant decreases in pH (3.51 and 3.80, respectively) and significant increases in TTA (13.50 and 12.50, respectively) (P < 0.05). B. infantis did not cause any significant change in the chemical properties of tomato juice. The addition of FOS further improved the fermentation of tomato juice by bifidobacterial species. The lycopene contents of tomato juice were significantly increased from 88 to 113 μg/g by heat treatment at 100 °C (P < 0.05), however did not exhibit any significant change after fermentation with bifidobacterial species.     

Thermal inactivation of <Emphasis Type="Italic">Alicyclobacillus acidoterrestris</Emphasis> spores under conditions simulating industrial heating processes of tangerine vesicles and its use in time temperature integrators

The aim of the present study was to characterize the thermal inactivation of Alicyclobacillus acidoterrestris spores under isothermal and non-isothermal conditions simulating industrial heating processes applied to tangerine vesicles. A microbiological time temperature integrator (TTI) suitable for estimating the severity of thermal processes applied to acid foods was also developed. The heat resistance of A. acidoterrestris was characterized by D _105 °C = 0.63 min and z = 10.8 °C in tangerine juice, showing linear survival curves, without shoulders and tails. Under non-isothermal conditions, the use of isothermal data allowed for an accurate prediction of the inactivation. The spores were included in alginate TTIs and they were used to estimate the severity of thermal treatments applied both in a thermoresistometer Mastia and in a food pilot plant scale system, which allows fast heating of the product to 93 °C and then a short holding time (2 min). In the thermoresistometer, tangerine juice was used as heating medium. In the food pilot plant scale system, thermal treatments were applied in batch to unpackaged tangerine vesicles. In both equipments, the TTIs accurately predicted the lethality of the thermal treatments applied. The percent coefficients of variation for survivor counting in TTIs showed that distribution of heat is homogeneous both in the thermoresistometer and in the reactor, being lower than 10% in all cases. The logistic and normal distributions were found to be the best for fitting the different survivor datasets.     

Mathematical modelling of vacuum ohmic evaporation process

Ohmic evaporation is a complex process in which heat and mass transfers take in place simultaneously. In this study, finite difference-FD and finite volume-FV models simulating the changes of temperature and water removed from tomato juice during the vacuum ohmic evaporation process (VOEP) were developed. Models considering the heat and mass transfer equations were combined. Experimental effective electrical conductivity and specific heat capacity relations were taken into account. For heating period, final temperature was predicted with errors of 3.4 ± 1.3 °C and 0.7 ± 1.3 °C, while the evaporation time prediction errors were 1.3 ± 1.6 min and − 2.1 ± 1.6 min for FV and FD models, respectively. It was concluded the effect of mixing was not important on temperature distribution for such a high consistency tomato paste compared to the heat generation effect during the ohmic evaporation process. The developed models could be used to predict process time, temperature history, and volume fraction at any time during the ohmic evaporation process.     

A Deviant Heat Process Applied to Canned or Packaged Liquid Food

A new procedure was developed for predicting the correction factor of a deviant thermal process applied to canned or packaged convection heating food. This development was accomplished through a combined application of a mathematical model for estimating process lethality and statistical procedures. Through a dimensional analysis of the mathematical model it was found that there were nine independent dimensionless parameters required to define uniquely correction factors. The influence of each parameter was determined by applying a statistical design of screening tests. Of the nine dimensionless parameters, only two parameters, which contained a magnitude of drop in heating medium temperature, duration of this drop, the slope index of thermal death time curve, and the slope index of heating curve influenced significantly the correction factor. Those of no significant influence included initial food temperature, retort temperature, cooling water temperature, drop location, and normal processing time. A simple polynomial equation was obtained for predicting the correction factor by applying a central composite design of experiments and a statistical regression analysis. The reliability of this equation was verified through heat transfer experiments by using canned distilled water, 0.1% bean gum aqueous solution, and tomato juice.