REDUCTION OF SACCHAROMYCES CEREVISIAE, ESCHERICHIA COLI AND LISTERIA INNOCUA IN APPLE JUICE BY ULTRAVIOLET LIGHT

Apple juice was inoculated separately with Saccharomyces cerevisiae, Listeria innocua (ATCC 51742) or Escherichia coli (ATCC 11775) for treatment in a double tube ultraviolet (UV) disinfection system. The apple juice was treated at six flow rates (0.073–0.548 L/min) for selected fluences (75–450 kJ/m²). The juice was also inoculated with a mixture of these three microorganisms and UV light treated from 0.548 to 0.735 L/min for 30 min. The microbial reduction was described with a first order kinetic model. Average D_uvvalues of 23.1–40.5, 8.2–20.6 and 6.0–17.7 min were obtained for S. cerevisiae, L. innocua and E. coli, respectively. A linear model was used to describe the relationship between log D_uvversus flow rate for S. cerevisiae and L. innocua. However, a third order polynomial model was more adequate for describing the E. coli D_uvvalues versus flow rate. Less than 10 (no growth), 190 and 200 cfu/mL of S. cerevisiae, L. inocua and E. coli, respectively, were observed in UV‐treated apple juice inoculated with a mixture of microorganisms.     

SURVIVAL AND GROWTH OF LISTERIA MONOCTYOGENES ON BEEF TISSUE SURFACES AS AFFECTED BY SIMULATED PROCESSING CONDITIONS

The numbers of Listeria monocytogenes Scott A were followed on experimentally inoculated lean and fat beef tissue handled under a variety of simulated storage conditions at 5°C, including high and low moisture storage, simulated spray chilling, and vacuum packaging. Under high moisture storage conditions, L. monocytogenes increased approximately 3 log cycles on both lean and fat tissue after 21 days. Similar growth was observed with vacuum packaged lean tissue. Under dry storage conditions, the population decreased approximately 2 logs during the first 14 to 21 days, but the counts remained constant for 42 days. Simulated spray chilling did not affect the growth or survival of L. monocytogenes on either lean or fat tissue .     

VISCOSITY AS AFFECTED BY VARIOUS CONSTITUENTS OF TOMATO JUICE

SUMMARY— Degradation of proteins of tomato juice with pronase caused a relatively small loss of viscosity. Commercial cellulase freed of pectolytic activity with 8 M urea greatly decreased the viscosity of washed tomato solids. Further degradation with pectinase was ineffective in reducing viscosity. Cellulase extracted from the tomato lowered viscosity of tomato juice. Enzymatic degradation as indicated by chemical analysis did not always result in a loss of viscosity. By extracting the solids with water, viscosity of tomato juice was lowered drastically. The extent of the reduction was not affected by previous treatment with cellulase or pectinase. Viscosity was not affected by extraction with versene. The greater reduction in viscosity of tomato juice by extraction of the solids with water than with ethanol indicates that the high molecular polymers associated with the insoluble solids contribute greatly to viscosity. The data did not indicate a significant contribution of the uronides to the viscosity of tomato juice.     

APPLE JUICE QUALITY AS INFLUENCED BY ULTRAFILTRATION

Objective quality of ultrafiltered (UF) apple juice compared favorably to apple juice filtered by conventional plate and frame filtration (PF). Agtron red and green values were higher for the UF juice, indicating a lighter colored product. Agtron green values were lower after 4 months of storage and compared well to juice from conventional methods over the remaining 8 months of storage. Green color of the UF juice remained steady at storage temperatures of either 1° or 21°C and was equal to the color values of the conventional juice stored at 1°, 21° or 32°. Clarity of the UF juice was excellent and remained stable over the entire storage period at either 1 or 21° with only a slight drop in clarity at 32°. UF juice was rated significantly lower in sensory flavor than PF juice. Sensory color of the UF juice was not rated as high as the PF juice at the start of the study, but as time in storage progressed sensory color improved. Initial panel reaction to UF apple juice was that the UF juice was too light in color and watery in flavor.     

VISCOSITY AND QUALITY OF TOMATO JUICE AS AFFECTED BY PROCESSING METHODS

ABSTRACT

Quality and viscosity of tomato juice is strongly governed by mechanical and thermal abuse during processing. The effect of processing and storage duration on the viscosity and quality parameters of tomato juice was evaluated in the present work. Tomato juice was obtained by two different methods, normal method (NM) and variable method (VM), and was heated by both conventional and microwave hot break treatments. Tomato juice was evaluated for various quality characteristics including precipitate weight ratio, degree of serum separation (DOSS), Brookfield viscosity, lycopene levels, vitamin C, phenols and antioxidant activity. Changes observed in several quality parameters during storage were statistically insignificant. The methods and processing had the greatest contribution toward viscosity, whereas storage duration had no significant effects. Viscosity parameters viz precipitate weight, DOSS and Bostwick consistency revealed that juice processed by VM was more viscous than that of NM, irrespective of the hot break processing used. Ascorbic acid and lycopene content varied significantly with mechanical methods and processing conditions. However, phenolic content and antioxidant activity remained stable. The variable process represents an improvement over the conventional by enabling tomato processors to improve the consistency of the tomato product.

PRACTICAL APPLICATIONS

Quartering or slicing tomatoes followed by hot break processing techniques can significantly improve the quality of tomato juice in terms of reduced degree of serum separation and precipitate weight ratio. The modified technology could be considered as a viable and economical method for small‐ and medium‐scale tomato processors with limited resources and facilities at their disposal.

     

RHEOLOGY OF APPLE AND POTATO TISSUE AS AFFECTED BY CELL TURGOR PRESSURE

Experiments were performed on two varieties of apple tissue and one variety of potato tissue, in which cell turgor pressure was varied and the concomitant mechanical properties of the tissue were tested. Turgor pressure was controlled by immersion in solutions of various mannitol concentrations, and the degree of swelling or contraction of the tissue samples was measured. Under constant-strain-rate loading, mode of failure varied among the different commodities, and underwent a transition as the turgor pressure was varied. Rate of loading also caused a transition in failure mode. The stress and strain at failure and tissue stiffness were related to mode of failure, turgor pressure, and strain rate. From the osmotic swelling data, estimates were made of the cell wall stress-strain behavior and of the probability distribution for cell-wall strength in Ida Red apple tissue.     

THERMAL PROPERTIES OF PASSION FRUIT JUICE AS AFFECTED BY TEMPERATURE AND WATER CONTENT

The specific heat, thermal conductivity and density of passion fruit juice were experimentally determined from 0.506 to 0.902 (wet basis) water content and temperatures from 0.4 to 68.8C. The experimental results were compared with existing and widely used models for the thermal properties. In addition, based on empiric equations from literature, new simple models were parameterized with a subset of the total experimental data. The specific heat and thermal conductivity showed linear dependency on water content and temperature, while the density was nonlinearly related to water content. The generalized predictive models were considerably good for this product but the empiric, product‐specific models developed in the present work yield better predictions. Even though the existing models showed a moderate accuracy, the new simple ones would be preferred, because they constitute an easier and direct way of evaluating the thermal properties of passion fruit juice, requiring no information about the chemical composition of the product, and a reduced time of the estimation procedure, as the new empiric models are described in terms of only two physical parameters, the water content and the temperature.     

DEVELOPMENT OF STRESS AND SURVIVAL OF SALMONELLA TYPHIMURIUM ATCC 7136 IN A TAPIOCA SOYSTARCH PRODUCT CONTAINING POTASSIUM SORBATE

The effects of reduced water activity and 0.1% sorbate on Salmonella typhimurium ATCC 7136 in a soy-starch product were examined. The formulated product (final pH 6.7), was inoculated with cells to give a final concentration of approximately 2 × 10⁶ cells/g. Ten gram samples were placed in a series of desiccators over saturated salt solutions and stored at either 22°C or 40°C. Water activities ranged from 0.79 to 0.97. Samples were withdrawn at prescribed intervals and appropriate dilutions made. A dual plating procedure was used to monitor growth (tryptic soy agar) and development of injury (Levine's Eosin Methylene Blue Agar supplemented with 2% NaCl and 0.05% sodium desoxycholate). Cells stored at 22°C remained viable longer at an a_w of 0.79 than at a_w values of 0.96 to 0.97. As storage time increased, cells were stressed at a faster rate at higher a_w values. This effect was accelerated at 40°C and as storage time increased.     

QUALITY CHANGES IN APPLE JUICE AS RELATED TO NONTHERMAL PROCESSING

Fresh apple juice was preserved using ultrafiltration and high voltage pulsed electric fields as nonthermal preservation techniques. Changes in quality attributes such as soluble solids, pH, acidity and color were verified for both processes. Changes were tested in terms of membrane pore, transmembrane pressure and recovery percentage for the ultrafiltration treatments, as well as in terms of electric field strength and number of pulses for the pulsed electric fields experiments. Among the quality attributes investigated, soluble solids, pH and acid content did not show significant differences, while color was significantly different for both nonthermal techniques. For the ultrafilteredjuice, a browning trend was observed, whereas for the pulsed electric treated juice an opposite, lightening, tendency was present.     

INACTIVATION OF LISTERIA INNOCUA AND PSEUDOMONAS FLUORESCENS BY PULSED ELECTRIC FIELDS IN SKIM MILK: ENERGY REQUIREMENTS

Pulsed electric field energy applied over a short duration of time was effective in the inactivation of Listeria innocua and Pseudomonas fluorescens inoculated into 0.2% skim milk. Additionally, the energy consumption was reasonable for industry applications compared with the alternative of thermal pasteurization. The energy densities required to achieve three log reductions of the microorganisms were 120, 212 and 270 kJ/L for L. innocua corresponding to input voltages of 30, 35 and 40 kV, and 88, 105 and 128 kJ/L for P. fluorescens under the same input conditions. Treatment times were, respectively, 145 µs and 290 µs, and exponentially decaying wave pulses with time duration of 3 µs were selected. For L. innocua, the inactivation of viable cells was significantly different (P < 0.05) between energy inputs of 120, 212 and 270 kJ/L. Meanwhile, the inactivation of P. fluorescens exhibited significant differences (P < 0.05) between energy inputs of 88 and 128 kJ/L, but not between inputs of 105 and 128 kJ/L. These results consistently indicated that microbial inactivation in skim milk increased as the energy intensity and the treatment time increased.     

COLOR, POLYPHENOLOXIDASE, AND SENSORY CHANGES IN BANANA JUICE AS AFFECTED BY HEAT AND ULTRAFILTRATION

A study was conducted to determine the effects of banana maturity (less mature; maturity stage 3, more mature; maturity stage 7), heat treatment of banana puree, heat pasteurization of juice, and ultrafiltration (UF) of juice on color, polyphenoloxidase (PPO) activity, and flavor of puree and juice. Heating puree to 90C inactivated PPO and reduced browning in puree and juice, especially in puree from more mature bananas which had greater PPO activity. PPO activity decreased considerably during cold-setting and filtration of juice, and was not detectable in unheated, pad-filtered juice from less mature bananas. UF of juice through a 10,000 mwco membrance, but not a 30,000, removed all PPO activity and reduced juice browning. Pasteurization of juice (hot fill at 90C) increased browning, but not as much as PPO activity in the puree. Pasteurization had no effect on juice flavor if the puree had been heated to 90C previously as puree, but altered the flavor (i. e., more cooked banana flavor) of juice that had not been previously heated to 90C. Pasteurized juice that had not been heated to 90C as puree had similar flavor (no significant difference) as pasteurized juice that had been heated to 90C as puree.     

REMOVING MICROORGANISMS IN FRESH APPLE JUICE BY BACTERIAL CENTRIFUGATION

SUMMARY— Bactofugation, a continuous centrifugal process of removing microorganisms from liquid foods, was applied at 9.000 g force to chilled and heated apple juice at a rate of 1,600gph. A reduction 99.8% in total bacterial count and 99.9% yeast-mold count of fresh apple juice processed at 7° was obtained. Bactofugating chilled apple juice was more effective than bactofugating apple juice heated to 54°C and presented certain operational advantages. Bactofugated, chilled apple juice retained the same flavor as untreated, fresh apple juice and remained fresh 22 days at 5°C, compared to about 5 days for the untreated apple juice. The simplicity of bactofugation, its relatively high put-through capacity and its effective reduction of microbial populations in fresh apple juice suggest that the process has potential application toward improving the keeping quality of this food.     

THE EFFECT OF PH, ACIDITY, AND LOW LEVEL SORBATE ON THE SHELFLIFE OF INOCULATED APPLE JUICE

A model was derived to predict changes in optical density and changes in the number days to sensory failure for apple juice. Samples of juice were treated to produce varying levels ofpH, titratable acidity, and sorbate. Only low doses of sorbate, up to 100 ppm, were used in the study. Results indicated that apple juice with varying levels of pH and sorbate concentrations, will have varying effects on the growth of yeasts, and ultimately on the shelflife of the juice. Titratable acidity apparently did not have a significant effect over the range studied in the experiment.     

COLOR AND VITAMIN C CONTENT IN MANDARIN ORANGE JUICE AS AFFECTED BY PACKAGING MATERIAL AND STORAGE TEMPERATURE

Mandarin orange (Citrus reticulata) juice was packed in two different non-transparent cartons made of polyethylene, cardboard and (1) aluminum foil (Tetrapak ^® ) or (2) ethylene vinyl alcohol copolymers (Pure-pak ^® ) and was stored at 4C or room temperature (25  ±  3C). During the shelf life of these juices (35 days), changes in the headspace gas composition, vitamin C and CIEL*a*b* color coordinates were evaluated. In addition, a consumer panel evaluated the sensory color of the juices. Mandarin orange juices darkened and ascorbic acid content decreased with storage time. Type of carton and storage temperature played a predominant role in determining the final juice quality, with Tetrapak ^® carton providing the juice with the best quality (intense orange color and high vitamin C content and consumer preference) throughout their shelf life.

PRACTICAL APPLICATIONS

This study was a clear example of how research can help real food companies in selecting the right materials for their production lines. In this particular case, the results presented show how Tetrapak^® packaging led to a final mandarin orange juice of higher quality compared to Pure-pak^® packaging. Therefore, citrus processing companies have some scientific data comparing the behavior of these two types of non-transparent cartons. Besides, the companies manufacturing these cartons also have some information about their materials and can use it to improve them.     

RHEOLOGICAL BEHAVIOR AND PHYSICOCHEMICAL CHARACTERISTICS OF GOLDENBERRY (PHYSALIS PERUVIANA) JUICE AS AFFECTED BY ENZYMATIC TREATMENT

Goldenberry (Physalis peruviana) juice was prepared and enzymatically treated with two dosages (300 and 600 ppm) of Pectinex Ultra SP‐L, then, the juice was concentrated to 30 and 40°Brix. Rheological properties of juices were studied at a wide range of temperatures (5 to 100C) and shear rate range from 0.3 to 100/s using Brookfield Digital Viscometer. The Herschel–Bulkley, Casson and Bingham rheological models were applied to describe the rheological properties of different juices. These properties are key parameters required to solve food industry problems in numerous areas such as quality control, evaluation of consumer acceptance and texture. The results indicated that juice concentrates behave as non‐Newtonian fluids (pseudoplastic) and have a definite yield stress. The Bingham and Casson, plastic viscosity, yield stress, consistency index and flow index decreased with increasing enzyme dosage and temperature. The effect of temperature on the viscosity described by means of an Arrhenius‐type equation. The activation energy for viscous flow depends on the total soluble solids. Moreover, sensory evaluation for juices was carried out. In consideration of industrial utilization, detailed knowledge on the rheological and physicochemical characteristics of cape gooseberry juice is of major importance.