Effective Thermal Conductivity of Cellular Tissues During Drying: Prediction by a Computer Assisted Model

Effective thermal conductivity, k*, of cellular tissues during drying is predicted as a function of moisture content. A computer model based on a planar tessellation is employed to simulate the tissue. The heat conduction equations are written on the tessellation and solved by means of a finite element technique. The whole technique, implemented in a computer package THERCOND, yields upper and lower bounds for k* which are compared to experimental values available for apples and pears.     

Thermal Conductivity Measurement and Prediction of Particulate Foods

There is reason to question some of the published thermal conductivity data for particulate foods. It is argued in this article, based on thermal conductivity bounds analysis, that the thermal conductivity of particulate foods should range between 0.03 W m^–1 K^–1 and 0.30 W m^–1 K^–1 (provided the porosity is greater than 25%), and that any data outside this range should be rejected. This argument was supported by data for five foods measured as part of this study (cocoa powder, corn starch, whole milk powder, sucrose, and wheat flour), and the majority of published data for particulate foods do indeed fall within this range. The geometric model was found to provide the most accurate thermal conductivity predictions of the models considered, and is recommended for use in first approximation predictions.     

Pasteurization of Fruit Juices by Means of a Pulsed High Pressure Process

ABSTRACT: The use of pulsed high hydrostatic pressure was investigated as a possible approach to stabilize foodstuffs. The objective of this article was to investigate the effect of the main processing variables (pressure [150 to 300 MPa], temperature levels [25 to 50 °C], and pulse number [1 to 10]) on the sanitation of nonpasteurized clear Annurca apple juice as well as freshly-squeezed clear orange juice. The aim of the article was the optimization of the process parameters in step-wise pressure treatment (pressure holding time of each pulse: 60 s, compression rate: 10.5 MPa/s, decompression time: 2 to 5s). The shelf life of the samples, processed at optimized conditions, was evaluated in terms of microbiological stability and quality retention. According to our experimental results, the efficiency of pulsed high pressure processes depends on the combination of pulse holding time and number of pulses. The pulsed high pressure cycles have no additive or synergetic effect on microbial count. The efficacy of the single pulses decreases with the increase of the pulse number and pressure level. Therefore the first pulse cycle is more effective than the following ones. By coupling moderate heating to high pressure, the lethality of the process increases but thermal degradation of the products can be detected. The optimization of the process condition thus results in a compromise between the reduction of the pressure value, due to the synergetic temperature action, and the achievement of quality of the final production. The juices processed under optimal processing conditions show a minimum shelf life of 21 d at a storage temperature of 4 °C.     

Enzymatic Clarification of Fruit Juices by Fungal Pectin Lyase

The activity of pectic enzymes was measured in culture filtrates of four selected fungal strains. Pectin lyase (PL) activity was produced by all fungi, but pectinesterase activity was not detected in culture filtrates of the strain Penicillium expansum F16. The use of crude enzymes resulted in good clarification of apple juice as evaluated by an increase in transmittance at 660 nm. PL activities were partially purified by dye-affinity chromatography on Blue Sepharose. The enzyme was bound to the column and eluted in a single peak, free of PE activity, and not coinciding with the major amount of protein. Apple, grape, and passion fruit juices were effectively clarified by these partially purified enzymes. Methanol content was determined by gas-liquid chromatography, being undetectable in the clarified juices. These pectic enzymes demonstrate potential for use in fruit juice processing.     

Thermal Inactivation of Yeasts in Fruit Juices Supplemented with Food Preservatives and Sucrose

Thermal inactivation of five yeasts (Candida krusei, Hansenula anomala, Saccharomyces bailii, S. cerevisiae and Torulopsis magnoliae) suspended in five fruit juices (apple, apricot, grape, orange and pineapple) as affected by potassium sorbate, sodium benzoate and sucrose was investigated. Yeasts were most sensitive to heat when suspended in orange juice. Both preservatives, at a concentration as low as 100 ppm, enhanced the rate of inactivation in juices containing no added sucrose. Supplementation of juices with sucrose (30 and 50%) resulted in protection against death of yeasts. The detrimental effects of potassium sorbate and sodium benzoate were reduced in the presence of high concentrations of sucrose. While neither preservative exhibited a consistent superior lethal effect compared with the other, overall, sodium benzoate was generally more effective than was potassium sorbate.     

Prediction of Thermal Conductivity of Vegetable Foods by the Effective Medium Theory

The Effective Medium Theory (EMT), known in the field of physics to model conductive properties of heterogeneous chaotic media, has been applied to predict the thermal conductivity of sugar-based fruits and of potatoes as a function of the water content. With the thermal conductivity of the constituents, the composition and porosity as data, the equation derived from the EMT for continuous media was applied to apples, pears, and potatoes. The results when compared with experimental values obtained by the probe method and from the literature showed good agreement, with differences not larger than 8%, though the model appeared to be over predictive, particularly for higher water contents.     

Enzymatic Clarification of Fruit Juices by Fungal Pectin Lyase

The activity of pectic enzymes was measured in culture filtrates of four selected fungal strains. Pectin lyase (PL) activity was produced by all fungi, but pectinesterase activity was not detected in culture filtrates of the strain Penicillium expansum F16. The use of crude enzymes resulted in good clarification of apple juice as evaluated by an increase in transmittance at 660 nm. PL activities were partially purified by dye-affinity chromatography on Blue Sepharose. The enzyme was bound to the column and eluted in a single peak, free of PE activity, and not coinciding with the major amount of protein. Apple, grape, and passion fruit juices were effectively clarified by these partially purified enzymes. Methanol content was determined by gas-liquid chromatography, being undetectable in the clarified juices. These pectic enzymes demonstrate potential for use in fruit juice processing.     

Thermal Treatments for Fruit and Vegetable Juices and Beverages: A Literature Overview

Fruit and vegetable juices and beverages are generally preserved by thermal processing, currently being the most cost‐effective means ensuring microbial safety and enzyme deactivation. However, thermal treatments may induce several chemical and physical changes that impair the organoleptic properties and may reduce the content or bioavailability of some nutrients; in most cases, these effects are strongly dependent on the food matrix. Moreover, the efficacy of treatments can also be affected by the complexity of the product and microorganisms. This review covers researches on this topic, with a particular emphasis on products derived from different botanical sources. Technologies presented include conventional and alternative thermal treatments. Advances toward hurdle‐based technology approaches have been also reviewed.     

Prediction of Total Antioxidant Capacity of Fruit Juices Using FTIR Spectroscopy and PLS Regression

The total antioxidant capacity (TAC) of 23 fruit juice samples was determined using the TEAC assay, and also, it was predicted by FTIR–PLS, the plot of measured and predicted values showing a good correlation (R = 0.97). Thus, FTIR spectroscopy is a promissory technique for rapid screening of TAC of fruit juices.     

Thermal Conductivity of Pear, Sweet-cherry, Apricot, and Cherry-plum Juices as a Function of Temperature and Concentration

ABSTRACT:  The thermal conductivity of 4 fruit (pear, sweet-cherry, apricot, and cherry-plum) juices was measured with a coaxial-cylinder (steady-state) technique. Measurements were made, temperature range 20 to 120 °C, at concentrations between 12.2 and 50 °Brix. The uncertainty of the thermal conductivity measurements was estimated to be less than 2%. A semitheoretical method for the prediction of thermal conductivity of juices was proposed. It was found that the prediction Model IV,  λ ( T , x )/λ ( T ₀, x ) = ( T / T ₀) ⁿ   , where  λ  is the thermal conductivity, x is the concentration, and T is the temperature, developed in this work can be adopted with satisfaction. The thermal conductivity of juices can be predicted just by knowing the thermal conductivity  λ₀  at a reference temperature   T ₀  .     

Inactivation of Spoiling Yeasts of Fruit Juices by Pulsed Ultrasound

This paper reports on the use of ultrasound (US) as a suitable strategy to control the growth of spoiling yeasts in fruit juices. In a first phase, US technique was tested towards Saccharomyces cerevisiae inoculated in different juices (strawberry, orange, apple, pineapple and red-fruits): the treatment was performed by modulating the level of the power (20–60 %), the duration of the treatment (2–6 min) and the pulse (2–6 s), according to a fractional design. Then, the best treatment was applied against some other spoiling yeasts (Pichia membranifaciens, Wickerhamomyces anomalus, Zygosaccharomyces bailii, Zygosaccharomyces rouxii, Candida norvegica). Finally, a challenge test for a commercial beverage (red-fruit juice), inoculated with Z. bailii and containing a citrus extract, was conducted evaluating the effect of US on the sensory scores of the beverage. The results showed that the effect of US was mainly influenced by the power and the duration of the treatment; on the other hand, the effect of pulse was less significant and slight. The highest reduction of S. cerevisiae was found in the following combination of the design: power 60 %/time 4 min/pulse 2 s and power 60 %/time 6 min/pulse 6 s; this result was confirmed for the other spoiling yeasts. US and citrus extract could be combined to prolong the shelf life of the red-fruit juice and control the growth of Z. bailii. The two hurdles exerted a different role and acted in different times: US reduced the initial contamination, whilst citrus extract controlled the yeast within the storage.     

Analysis of Aliphatic Organic Acids in Commercial Fruit Juices by Capillary Electrophoresis with Indirect UV Detection: Application to Differentiation of Fruit Juices

A simple, cheap, and reliable capillary zone electrophoresis (CZE) method with indirect UV detection to determine the main organic acids in several fruit juices has been developed in this work. The parameters affecting CZE separation including the chromophore reagent (2,6-pyridinedicarboxylic acid, PDC) concentration and pH in background electrolyte (BGE), temperature, and applied voltage were studied. The analytical parameters of the method as linearity, precision, and detection and quantification limits were also investigated. The proposed method was applied to the evaluation of organic acid contents of commercial fruit juices from apple, grape, mandarin, orange, and pineapple and compared with the levels allowed by European legislation. A chemometric technique such as linear discriminant analysis (LDA) was also applied to differentiate fruit juices based on CZE data. This simple and reliable developed procedure allows a rapid control of adulteration of high-value commercial fruit juices, which constitutes an important tool for authenticity texting in food industries and regulatory agencies.     

Color Stability of Apple and Pear Juices Blended with Fruit Juices Containing Anthocyanins

Apple and pear juices blended with anthocyanin pigmented juices developed haze and color stability during commercial marketing. To determine factors contributing to these problems, juice from apple and d'Anjou pear (prepared from whole fruit) and‘Bartlett’pear (peels and cores) were blended with 5, 10, 20%‘Concord’grape,‘Bing’cherry, or red or black raspberry juice. During storage at 25°C for up to 48 wk, turbidity, polymeric color, and % color due to tannin increased, while anthocyanin concentration decreased. As % anthocyanin pigmented juice increased, turbidity and polymeric color increased and % color due to tannin decreased. Within a given base juice, turbidity was highly correlated with polymeric color (r = 0.78 to 0.97).     

Development of a Biosensor for Controlling of Thiourea in Fruit Juices

A simple and sensitive biosensor based on mushroom (Agaricus bisporus) tissue homogenate that contains polyphenol oxidase is described for the determination of thiourea. The mushroom tissue homogenate was immobilized to the sensitive top of a Clark-type oxygen electrode with gelatin and glutaraldehyde. The linear range of the system was 1–20 μM with a detection limit of 1 μM at pH 7.5 and 30 °C. The repeatability experiments were carried out, and the average value, standard deviation, and variation coefficient were calculated as 9.875 μM, ±0.279, and 2.83%, respectively. Interference studies revealed that the substances tested did not interfere with the biosensor. Finally, the proposed biosensor was applied to the determination of thiourea in fruit juices.     

Improving the Stability of Probiotic Bacteria in Model Fruit Juices Using Vitamins and Antioxidants

Abstract: This study examined the survival of probiotic bacteria in a model fruit juice system. Three different strains of probiotic bacteria were used in this study: HOWARU Lactobacillus rhamnosus HN001, HOWARU Bifidobacterium lactis HN001, and Lactobacillus paracasei LPC 37. The probiotic bacteria were inoculated into model juice with various vitamins and antioxidants, namely white grape seed extract, green tea extract, vitamin B2, vitamin B3, vitamin B6, vitamin C, and vitamin E. The model juice without any additives was used as a control. Their viability was assessed on a weekly basis using plate count method. The model juice was made with sucrose, sodium citrate, citric acid powder, and distilled water and was pasteurized before use. Our findings showed that probiotic bacteria did not survive well in the harsh environment of the model fruit juice. However, the model juice containing vitamin C, grape extract, and green tea extract showed better survival of probiotic bacteria. The model juice containing grape seed extract, green tea extract, and vitamin C had the same initial population of 8.32 log CFU/mL, and at the end of the 6-wk storage period it had an average viability of 4.29 log CFU/mL, 7.41 log CFU/mL, and 6.44 log CFU/mL, respectively. Juices containing all other ingredients tested had viable counts of <10 CFU/mL at the end of the 6-wk storage period.     

Thermal Conductivity of Fresh and Dried Squid Meat by Line Source Thermal Conductivity Probe

Thermal conductivities (TC) of fresh and dried squid mantle meat determined using a line source probe method varied from 0.52 to 0.04 w/m°C at 30°C. TC decreased with decreasing moisture. TC data correlated with moisture content by an exponential form equation.     

超高压(UHP)技术在果汁灭菌中的应用

超高压处理技术被认为食品非热杀菌技术中最有潜力和发展前途的一种处理技术。我国的食品工业发展计划中超高压杀菌技术已经被列为重点开发的技术之一,超高压前几年一直处在小型试验研究阶段,如李里特与日本国际农林水产业研究中心的辰巳英三合作,对超高压下生产的豆腐凝胶进行了多方面的研究。     

Thermal Conductivity of Liquid Foods by the Thermal Comparator Method

The thermal comparator is shown to be a rapid, accurate method for determining the thermal conductivity of liquid foods. Increasing solids content decreased thermal conductivity for apple juice concentrate, orange juice concentrate, and milk samples. Equations for predicting the thermal conductivity of apple juice, orange juice, and milk are shown to be specific for each commodity. A comparison of apple juice and orange juice suggests that qualitative attributes of the solids fraction as well as the quantity present are important in determining thermal conductivity.     

几种超滤果蔬汁的稳定性

本文探讨了四种果蔬汁的两种孔径(50KD,150KD)聚丙烯腈膜超滤液的稳定性。结果表明:50KD的黄瓜汁和萝卜汁超滤液及两种孔径的锦橙汁超滤液杀菌后贮藏,三个月后依然保持澄清。