Comparison of high pressure treatment and thermal pasteurization effects on the quality and shelf life of guava puree

The effects of high pressures and thermal pasteurization on the survival of microorganisms, enzyme inactivation and quality changes of guava puree during storage at 4°C were investigated and compared with untreated samples. After treatment at a pressure of 600MPa and 25°C for 15 min, the microorganisms in guava puree were inactivated to less than 10 cfu mL⁻¹ and the product exhibited no change in colour, pectin, cloud and ascorbic acid content as compared with fresh samples. The inactivation of enzymes in guava puree by thermal pasteurization was greater than by high pressures. The microbial count in guava puree reduced to 200 cfu mL⁻¹ and the product showed marked changes in viscosity, turbidity and colour when heated at 88–90°C for 24s. The content of pectin, cloud and ascorbic acid as well as colour in untreated and high pressurized (400MPa) guava puree gradually decreased, whereas these changes were not observed in pasteurized (88–90°C) and high pressurized (6000MPa) puree during storage at 4°C for 60 days. The guava puree treated at 600MPa and 25°C for 15 min retained good quality similar to the freshly extracted puree after storage at 4°C for 40 days.     

Effect of High Hydrostatic Pressure on Cashew Apple (Anacardium occidentale L.) Juice Preservation

ABSTRACT:  High hydrostatic pressure is an alternative to thermal processing to inactivate spoilage and pathogenic microorganisms. Cashew apple juice has a pleasant flavor and is rich in vitamin C. Studies to determine the effect of high pressure on microorganisms in cashew apple juice are still lacking. In this study, the inactivation of natural micropopulation and inoculated Escherichia coli by high pressure was evaluated in fresh cashew apple juice. The microbiological stability of pressure-treated juice was also evaluated. The applied high pressure levels ranged from 250 to 400 MPa for periods of 3 to 7 min. Treatments with 350 MPa for 7 min and 400 MPa for either 3 or 7 min reduced the aerobic mesophilic bacteria count to a level below the detection limit. Pressure treatments were also efficient in inactivating yeast and filamentous fungi. The inoculated E. coli (10⁶ CFU/mL) was reduced to below 10 CFU/mL after a pressure treatment of 400 MPa for 3 min. The inactivation of this microorganism followed a 1st-order reaction kinetics. The decimal reduction time ( D- value) ranged from 1.21 to 16.43 min, while pressure resistance value ( z -value) was 123.46 MPa. Neither natural micropopulation growth nor E. coli repair was observed in postprocessed (400 MPa for 3 min) cashew apple juice kept under refrigerated storage (at 4 °C) during 8 wk. The results of this study demonstrated the efficacy of high-pressure treatment for preserving cashew apple juice.     

Mechanism of inactivation of heat-tolerant spores of Bacillus stearothermophilus IFO 12550 by Rapid Decompression

The effect of three rapid decompression methods to clear the mechanism of inactivation of heat tolerant spores of Bacillus stearothermophilus IFO 12550 was investigated. Pressurization of the spores at 200 MPa and 75°C for 60 min caused a kill of 10⁴ CFU/mL by the link-motion system but the nonrotational rod valve and E.G. seal methods gave a kill of about 10³ CFU/mL. Sterilization was due to the physical breakdown of spore coat, and was induced by its physical permeability of water at high pressure and temperature. Rapid decompression by the link-motion system at 200 MPa decreased the D-value of the spores from 3000 min (100°C, one atmosphere) to 6 min, 11 min, and 17 min at 95, 85, and 75°C, respectively.     

Efficacy of Pressure-Assisted Thermal Processing, in Combination with Organic Acids, against Bacillus amyloliquefaciens Spores Suspended in Deionized Water and Carrot Puree

ABSTRACT:  Effect of organic acids (acetic, citric, and lactic; 100 mM, pH 5) on spore inactivation by pressure-assisted thermal processing (PATP; 700 MPa and 105 °C), high pressure processing (HPP; 700 MPa, 35 °C), and thermal processing (TP; 105 °C, 0.1 MPa) was investigated.  Bacillus amyloliquefaciens  spores were inoculated into sterile organic acid solutions to obtain a final concentration of approximately 1.3 × 10⁸ CFU/mL.  B. amyloliquefaciens  spores were inactivated to undetectable levels with or without organic acids after 3 min PATP holding time. At a shorter PATP treatment time (approximately 2 min), the inactivation was greater when spores were suspended in citric and acetic acids than in lactic acid or deionized water. Presence of organic acids during PATP resulted in 33% to 80% germination in the population of spores that survived the treatment. In contrast to PATP, neither HPP nor TP, for up to 5 min holding time with or without addition of organic acids, was sporicidal. In a separate set of experiments, carrot puree was tested, as a low-acid food matrix, to study spore recovery during extended storage following PATP. Results showed that organic acids were effective in inhibiting spore recovery in treated carrot puree during extended storage (up to 28 d) at 32 °C. In conclusion, addition of some organic acids provided significant lethality enhancement ( P  < 0.05) during PATP treatments and suppressed spore recovery in the treated carrot puree.     

Ohmic heating of Japanese white radish Rhaphanus sativus L.

Ohmic heating was applied to Japanese white radish, Rhaphanus sativus L. at 50 Hz-10 kHz and 40 V cm⁻¹ to examine the effects of frequency on the heat generation. Of the frequencies examined, 50 Hz gave the sharpest initial rise of temperature and the shortest time to raise the temperature at the mid-part of radish to 80°C. The heating rates above 60°C were found to be almost the same and linear for all the frequencies. The pressurization (400 MPa, 25°C, for 10 min) of radish eliminated the sharp initial increase of temperature observed at 50 Hz, and gave an almost linear rise of temperature similar to those above 60°C. When radish was treated with a square wave (10 ms with 10 ms interval) of 45 V cm⁻¹ for 30 s, its impedance decreased and never recovered even after storage at room temperature for 20 h. When radish was treated at 50 Hz and 40 V cm⁻¹ until its mid-part reached 30°C, or heated to 80°C in hot water and then cooled to 30°C, ¹H-NMR imaging analysis showed more free movement of liquid components than in untreated radish. These results suggest that the initial rapid heating up at low frequency is caused by the electroporation of radish tissue membrane, resulting in the reduction of its impedance.     

Inactivation of Aspergillus niger in Mango Nectar by High-Pressure Homogenization Combined with Heat Shock

ABSTRACT:  This research evaluated the inactivation of a heat-resistant  Aspergillus niger  conidia in mango nectar by high-pressure homogenization (HPH) combined with heat shock.  A.niger  were inoculated in mango nectar (10⁶ conidia mL⁻¹) and subjected to HPH (300 to 100 MPa) and heat shock (80 °C for 5 to 20 min) before or after HPH. Processes were evaluated according to number of decimal reductions reached by each isolated or combined process. Scanning electron microscopy was performed to observe conidia wall after pressure treatment. Pressures below 150 MPa did not inactivate  A. niger  while pressures of 200 and 300 MPa resulted in 2 and more than 6 log reductions, respectively. D_{80 °C} of  A. niger  was determined as 5.03 min. A heat shock of 80 °C/15 min, reaching 3 decimal conidia reductions, was applied before or after a 200 MPa pressure treatment to improve the decimal reduction to 5 log cycles. Results indicated that HPH inactivated  A. niger  in mango nectar at 300 MPa (>6.24 log cycles) and that, with pressure (200 MPa) combined with post heat shock, it was possible to obtain the same decimal reduction, showing a synergistic effect. On the other hand, pre heat shock associated with HPH resulted in an additive effect. The observation of  A. niger  conidia treated by HPH at 100 and 200 MPa by scanning electron microscopy indicated that HPH promoted intense cell wall damage, which can sensitize the conidia to post heat shock and possibly explain the synergistic effect observed.
Practical Application : The results obtained in this paper are relevant to elucidate the mechanism of conidia inactivation in order to develop the application of HPH as an alternative pasteurization process for the fruit nectar industry.     

Storage stability of a stimulant coconut water–acerola fruit juice beverage

The objective of this work was to study the stability of a beverage formulated with acerola fruit juice and green coconut water with added caffeine. The beverage was prepared with 25% acerola pulp, 75% green coconut water and sugar up to 12°Brix, and caffeine (125 mg L⁻¹), heat processed at 90 °C for 30 s and packed in 250-mL glass bottles. Chemical, physicochemical, microbiological and sensory analyses of the beverage were performed just after processing and during 6 months of storage at room temperature (27 °C). The vitamin C content decreased significantly throughout storage, from 399.5 to 189.6 mg 100 mL⁻¹, although it has remained relatively high. The anthocyanins initially present (0.025 mg 100 mL⁻¹) were completely lost during the storage at a mean rate of 4 μg 100 mL⁻¹ month⁻¹. The product was microbiologically stable during storage. Colour changes were also observed with absorbance at 420 nm, with average values ranging from 0.19 to 0.24. However, according to the sensory analyses the product was acceptable during the 6 months of storage, presenting sensory scores (colour, taste and global acceptance) from 6.5 to 5.5, which suggests its potential for market.     

Preservation and shelf-life extension of shrimps and clams by high hydrostatic pressure

Clam ( Venus gallina ) and shrimp ( Parapenaeus longirostris ) samples were high hydrostatic pressure (HHP) treated at 200, 220 and 250 MPa at 25, 30, 40 and 50 °C for 10 and 20 min. Based on the results of microbial reduction, the best combinations of HHP treatments were determined as 250 MPa, 50 °C, 10 min for shrimps and 220 MPa, 50 °C, 10 min for clams. HHP-treated samples stored at 25 °C (room tempertur) and 4 °C (refrigeration temperature) were analysed. According to the results evaluated, shelf-life of shrimps was found to be 12 and 16 days for storage at room and refrigeration temperatures, respectively, as compared with 4 days for non-HHP-treated samples at 4 °C. Similarly shelf-life for the clam samples was found to be 12 days for storage at room temperature and 18 days for storage at refrigeration temperature as compared with 4 days for non-HHP-treated samples at 4 °C.     

Improving antioxidant capacity of fresh-cut mangoes treated with UV-C

ABSTRACT:  The effect of UV-C irradiation time on total phenol, flavonoids, β-carotene, ascorbic acid contents, and antioxidant capacity (ORAC, DPPH^•) of fresh-cut "Tommy Atkins" mango stored for 15 d at 5 °C was investigated. Fresh-cut mango was irradiated for 0, 1, 3, 5, and 10 min prior to storage at 5 °C. UV-C irradiation for 10 min induced a hypersensitive defense response resulting in the phenols and flavonoids accumulation which was positively correlated with ORAC and DPPH^• values. However, β-carotene and ascorbic acid content of fresh-cut mangos decreased with irradiation time during storage. Antioxidant capacity (ORAC, DPPH^•) was increased in fresh-cut mangoes treated with UV-C irradiation. In conclusion, UV-C irradiation appears to be a good technique to improve the total antioxidant capacity of fresh-cut mango.     

Effects of Hydrostatic Pressure/Heat Combinations on Water Uptake and Gelatinization Characteristics of Japonica Rice Grains: A Kinetic Study

ABSTRACT:  The combination effects of pressure (200 to 500 MPa) and temperature (20, 40, and 50 °C) on the water uptake and gelatinization characteristics of japonica rice (Tainung 71) grains were investigated. Pressure greater than 200 MPa at all temperatures increased the moisture content and volume of rice grains; meanwhile, the increase content of rice grain volume showed a high correlation with that of moisture content ( r ²= 0.96). The highest degree of gelatinization of 73% was observed at 500 MPa and 50 °C for 120 min, while gelatinization did not occur at pressures below 300 MPa and temperatures of 20 and 40 °C. The rate of gelatinization followed the 1st-order kinetics at each temperature and pressure. The higher pressures and temperatures would result in higher values of rate constant  k  which could be correlated with both pressure and temperature by combining Arrhenius and Eyring models.     

Microbial growth and colour of minimally processed shiitake mushroom stored at different temperatures

The effect of storage temperature on the microbiological and sensory characteristics of minimally processed shiitake was investigated. Shiitake mushrooms were washed, sanitised, packed in polystyrene trays, overwrapped with plastic film and stored at 7, 10 or 15 °C. Microbial counts, polyphenoloxidase activity, external lightness ( L* ) and acceptance tests were conducted. Mesophilic, aerobic psychrotrophic bacteria, yeasts and moulds predominated during storage. Pseudomonas was detected after 10 days' storage showing an increase of, approximately, 7 log cycles at 15 °C. Mushroom rejection occurred when the microbial population was lower than 10⁶ CFU g⁻¹, suggesting that, other factors, such as browning, affect mushroom spoilage more than microbial activity. Mushrooms treated with citric or ascorbic acids maintained high L * value during 10 days. The shelf life of minimally processed shiitake mushrooms was 10 days at 7 °C, but less than 5 days at 10 °C, and approximately 3 days at 15 °C.     

Rheological behaviour of acorn starch dispersions: effects of concentration and temperature

Rheological properties of acorn starch dispersions at different concentrations (4%, 5%, 6% and 7%) were evaluated under steady and dynamic shear conditions. The flow behaviours of the acorn starch dispersions at different temperatures (25, 40, 55 and 70 °C) were determined from the rheological parameters provided by the power law model. The acorn starch dispersions at 25 °C exhibited high shear-thinning fluid characteristics ( n  = 0.23–0.36). Consistency index (K) and apparent viscosity (η_a,100) increased with an increase in starch concentration, and were also reduced with increasing temperature. Within the temperature range of 25–70 °C, the η_a,100 obeyed the Arrhenius temperature relationship with a high determination coefficient ( R ² = 0.97–0.99), with activation energies (E_a) ranging between 16.5 and 19.0 kJ mol⁻¹. Both the power law and exponential type models were employed in order to establish the relationship between concentration and apparent viscosity (η_a,100) in the temperature range of 25–70 °C. Magnitudes of storage ( G' ) and loss ( G ") moduli increased with an increase in the starch concentration and frequency (ω). The magnitudes of G ' were higher than those of G " over most of the frequency range (0.63–62.8 rad s⁻¹). The dynamic (η*) and steady shear (η_a) viscosities of acorn starch dispersion at 7% concentration follow the Cox–Merz superposition rule.     

The effects of different incubation temperatures on the acetaldehyde content and viable bacteria counts of bio-yogurt made from ewe's milk

Yogurt and bio-yogurt were manufactured from ewe's milk using a starter culture and a probiotic culture. Incubation was carried out at 37°C and 42°C until pH 4.6 was reached and the yogurts were stored at 4 +1°C for 14 days. Analysis after 1, 7 and 14 days showed that incubation temperature and storage time significantly influenced overall properties of the samples. During the storage, whey separation and pH decreased, but titratable acidity, lactic acid and volatile fatty acid contents increased. Viable bacterial counts in all bio-yogurts were above 10⁷ cfu g⁻¹ at the end of storage.     

Quenching Mechanism and Kinetics of Ascorbic Acid on the Photosensitizing Effects of Synthetic Food Colorant FD&C Red Nr 3

ABSTRACT:  The pH effect on the oxidative stability of ascorbic acid in the presence of food colorant FD&C Red Nr 3 during storage with or without light was investigated. The quenching mechanism and kinetics of ascorbic acid on the FD&C Red Nr 3 photosensitized oxidation in an aqueous system at 25 °C were also studied by measuring the degradation of ascorbic acid or depletion of headspace oxygen. Red Nr 3 had no influence on the oxidation of ascorbic acid under dark storage, but accelerated its oxidation rate under light storage. The oxidative stability of ascorbic acid decreased as the pH increased from 4 to 7 under light without FD&C Red Nr 3. The quenching rates of ascorbic acid on the singlet oxygen by measuring the degradation of ascorbic acid in the presence of Red Nr 3 under light storage were 1.53 ± 0.15 × 10⁸, 1.86 ± 0.25 × 10⁸, and 1.19 ± 0.12 × 10⁸ M⁻¹S⁻¹ at pH 4, 5.6, and 7, respectively.     

EFFECT OF CONCURRENT HIGH HYDROSTATIC PRESSURE, ACIDITY AND HEAT ON THE INJURY AND DESTRUCTION OF LISTERIA MONOCYTOGENES

The effect of concurrent use of high hydrostatic pressure, heat and acidity on Listeria monocytogenes Scott A and CA was investigated. In general, lethality was enhanced when cells were pressurized at higher temperatures or lower pH. Strain CA demonstrated an additional 3-log₁₀ reduction when pressurized at pH 4.0 as compared with pH 6.0 at 353 MPa, 45C for 10 min. Scott A was reduced an additional 1 log₁₀ by increasing the temperature from 25C to 45C with pressurization at 252 MPa, pH 6.0 for 30 min. Exposure to 404 MPa at 45C for 30 min demonstrated complete injury or death of CA cells with an initial concentration of >10⁸ CFU/mL. At least an 8-log₁₀ reduction was observed for both L. monocytogenes strains Scott A and CA when exposed to the combined treatments of 252 MPa, 45C, pH 4.0 for 30 min .     

Evaluation of thermal properties of food materials at high pressures using a dual-needle line-heat-source method

ABSTRACT:  Thermal properties of food systems at high pressure (HP) are important in the design and operation of HP processing equipment. Available techniques for thermal property evaluation under HP conditions are still very limited. In this study, a dual-needle line-heat-source (DNL) device was installed in an HP vessel to evaluate thermal conductivity ( k ), diffusivity (α), and volumetric heat capacity ( C _pV) of foods at high pressure. The DNL probe was calibrated using glycerin (0.1 MPa) and 2% (w/w) agar gel (0.1 to 350 MPa) at 5 and 25 °C. Calibration results showed a good correlation with the reference data of pure water: R ²= 0.966 for thermal conductivity and R ²= 0.837 for diffusivity, and a small standard deviation of relative error (3.18%) for the volumetric heat capacity. Fresh potato and cheddar cheese were used as test samples at 5 °C at selected pressure levels (0.1 to 350 MPa). The potato samples gave thermal properties very close to those of pure water, but much higher than those of the cheese. The k and α values of both potato and cheese increased with pressure and a 2nd-order polynomial well fitted their pressure dependency. The volumetric heat capacity data did not show a clear pressure-dependency trend. The experimental system worked well for the evaluation of thermal properties at pressures up to 350 MPa.     

Osmotic Dehydration of Tomato in Sucrose Solutions: Fick's Law Classical Modeling

ABSTRACT:  Osmotic dehydration of tomato was modeled by the classical Fick's law including shrinkage, convective resistance at the interface and the presence of water bulk flow. Tomato slices having 8 mm thickness were osmotically dehydrated in sucrose solutions at 50, 60, and 70 °Brix and at 35, 45, and 55 °C. Other experiments were done in a 70 °Brix sucrose solution at 35 °C with tomato slices of 4, 6, and 8 mm thickness and at different motion levels (velocities 0, 0.053, and 0.107 m/s). Tomato weight, water content, and °Brix of the products were measured as a function of processing time (20, 40, 80, 160, and 320 min). Results showed that temperature, concentration, thickness, and solution movement significantly influenced water loss and sucrose gain during the osmotic dehydration of tomato. The model predicted the modifications of soluble solid content and water content as a function of time in close agreement with the experimental data. Experimental Sherwood number correlations for sucrose and water were determined as Sh _s = 1.3 Re ^0.5 Sc _s^0.15 and Sh _w = 0.11 Re ^0.5 Sc _w^0.5, respectively. The effective diffusion coefficients of water (4.97 10⁻¹¹– 2.10 10⁻¹⁰ m²/s) and sucrose (3.18 10⁻¹¹– 1.69 10⁻¹⁰ m²/s) depended only on temperature through an Arrhenius-type relationship.     

Factors controlling the growth of Clostridium botulinum types A and B in pasteurized, cured meats III. The effect of potassium sorbate

The growth of Clostridium botulinum types A and B spores, at 10¹ or 10³ per container, was studied in a pork slurry system containing nitrite (40 μg/g), sodium chloride (2.5, 3.5, 4.5% w/v) sodium isoascorbate (550 μg/g) at varying pH levels, with or without potassium sorbate (0.26% w/v), without heating and after two heat treatments (80°C for 7 min, and 80°C for 7 min + 70°C for 1 hr) followed by storage at 15, 17.5, 20 or 35°C for up to 6 months. At a given spore inoculum, potassium sorbate significantly decreased toxin production, as did increasing NaCl, decreasing pH or decreasing storage temperature. Heat treatment did not significantly affect spoilage or toxin production overall, but interacted significantly with some factors. The effect of sorbate was greater at 3.5% NaCl than at 2.5%, at pH values below 6.0, and at low storage temperature.     

Microwave Oven Heating for Inactivation of Listeria Monocytogenes on Frankfurters before Consumption

ABSTRACT:  Microwave oven heating was evaluated for inactivation of  Listeria monocytogenes  on inoculated and stored frankfurters. Frankfurters formulated without/with 1.5% potassium lactate and 0.1% sodium diacetate were inoculated with  L. monocytogenes  (1.9 ± 0.2 log CFU/cm²), vacuum-packaged, and stored (4 °C) to simulate conditions prior to purchase by consumers. At storage days 18, 36, and 54, packages were opened and placed at 7 °C, simulating aerobic storage in a household refrigerator. At 0, 3, and 7 d of aerobic storage, 2 frankfurters were placed in a bowl with water (250 mL) and treated in a household microwave oven at high (1100 W) power for 30, 45, 60, or 75 s, or medium (550 W) power for 60 or 75 s. Frankfurters and the heating water were analyzed for total microbial counts and  L. monocytogenes  populations. Exposure to high power for 75 s reduced pathogen levels (0.7 ± 0.0 to 1.0 ± 0.1 log CFU/cm²) to below the detection limit (<−0.4 log CFU/cm²) on frankfurters with lactate/diacetate, even after 54 d of vacuum-packaged storage followed by 7 d of aerobic storage. For frankfurters without lactate/diacetate, high power for 75 s caused reductions between > 1.5 and 5.9 log CFU/cm² from control levels of 1.5 ± 0.1 to 7.2 ± 0.5 log CFU/cm². Depending on treatment and storage time, the water used to reheat the frankfurters had viable  L. monocytogenes  counts of <−2.4 to 5.5 ± 0.5 log CFU/mL. The results indicated that frankfurters should be reheated in a microwave oven at high power for 75 s to inactivate up to 3.7 log CFU/cm² of  L. monocytogenes  contamination.     

Effect of protein additives, sodium ascorbate, and microbial transglutaminase on the texture and colour of red tilapia surimi gel

Beef plasma protein (BPP) and egg white, at levels of 10, 20 and 30 g kg⁻¹, and sodium ascorbate (SA) and microbial transglutaminase (MTGase), at levels of 1, 2 and 3 g kg⁻¹, were individually added into red tilapia surimi. This gel was set at 40 °C for 90 min followed by heating at 90 °C for 30 min. Gel qualities were analysed and compared with those of non-supplemented red tilapia control gel. Compared with the control, each additive significantly affected gel strength due to an increase in breaking force. Although BPP could improve texture characteristics, higher addition levels of BPP significantly affected gel whiteness. The addition of SA and MTGase were found to increase surimi gel strength and improve whiteness. Amongst all treatments, the addition of 2 g kg⁻¹ MTGase was found to provide the best gel qualities.