KINETICS OF OSMOTIC DEHYDRATION OF MANGO

The effects of sucrose syrup concentration (40–70 g/100‐g solution) and temperature (40–90C) on water loss and sucrose uptake by mango mesocarp slices during osmotic dehydration were investigated. The effective diffusivities for mass transfer were determined using the slope method based on the Fickian diffusion model. Water loss and sucrose uptake were proportional to the square root of osmotic contact time, implying that the process is Fickian. The specific mass transfer rate constants and effective diffusivities (D_e), derived from Fick's unsteady‐state diffusion equation, increased with temperature and sucrose syrup concentration. D_e values for water loss and sucrose uptake, which ranged between 2.59 × 10^?6 to 5.12 × 10^?6 m²/h and 1.70 × 10^?6 to 4.14 × 10^?6 m²/h, respectively, were related to absolute temperature using an Arrhenius‐type relationship. The activation energies, which fell in the range previously reported for diffusion‐controlled processes, increased with sucrose syrup concentration and varied from 9.74 to15.16 KJ/mol.     

Water activity change at elevated temperatures and thermal resistance of Salmonella in all purpose wheat flour and peanut butter

Water activity (a_w) is a major factor affecting pathogen heat resistance in low-moisture foods. However, there is a lack of data for a_w at elevated temperatures that occur during actual thermal processing conditions, and its influence on thermal tolerance of pathogens. The objective of this study was to gain an in-depth understanding of the relationship between temperature-induced changes in a_w and thermal resistance of Salmonella in all purpose flour and peanut butter at elevated temperatures (80 ^oC). Equilibrium water sorption isotherms (water content vs. water activity) for all purpose wheat flour and peanut butter over the range of 20 to 80 °C were generated using a vapor sorption analyzer and a newly developed thermal cell. The thermal resistance (D₈₀-values) of Salmonella in all purpose wheat flour and peanut butter with initial a_w of 0.45 (measured at room temperature, ~ 20 °C) was determined via isothermal treatment of small (< 1 g) samples. When increasing sample temperature from 20 to 80 °C in sealed cells, the a_w of all purpose flour increased from 0.45 to 0.80, but the a_w of peanut butter decreased from 0.45 to 0.04. The corresponding estimated D₈₀-values of Salmonella in all purpose flour and peanut butter with 20 ^oC a_w of 0.45 were 6.9 ± 0.7 min and 17.0 ± 0.9 min, respectively. The significantly (P < 0.05) higher D₈₀-value of Salmonella in peanut butter than in all purpose flour may be partially attributed to the reduced a_w in peanut butter in comparison to the increased a_w in all purpose flour at 80 °C. The improved understanding of temperature-induced changes in a_w of low-moisture products of different composition provides a new insight into seemly unpredictable results, when using heat treatments to control Salmonella in such food systems.     

Environmental factors affect efficacy of some essential oils and resveratrol to control growth and ochratoxin A production by Penicillium verrucosum and Aspergillus westerdijkiae on wheat grain

This study determined the efficacy of three essential oils (bay, clove and cinnamon oil) and the antioxidant resveratrol (0–500 μg g⁻¹) on the control of growth and ochratoxin A (OTA) production by Penicillium verrucosum and Aspergillus westerdijkiae (=A. ochraceus) under different water activity (a_w, 0.90, 0.95, 0.995), and temperature (15, 25 °C) conditions on irradiated wheat grain. The most effective treatment (resveratrol) was then tested on natural grain. The ED₅₀ values for growth inhibition by the oils were 200–300 μg g⁻¹ at the a_w and the temperatures tested. For resveratrol, this varied from <50 μg g⁻¹ at 0.90–0.95 a_w to >350 at 0.995a_w at both temperatures. The ED₅₀ values for the control of OTA were slightly lower than for control of growth, with approx. 200 μg g⁻¹ required for the oils and 50–100 μg g⁻¹ of the antioxidant, at 0.90/0.95a_w and both temperatures. In wet grain (0.995a_w), higher concentrations were required. For growth there were statistically significant effects of single-, two- and three-way interactions between treatments except for concentration×temperature and concentration×temperature×essential oil/antioxidant treatment. For OTA control, statistically significant treatments were a_w, temperature×a_w, concentration×temperature, treatment×concentration, and three-way interaction of concentration×a_w×treatment for P. verrucosum and A. westerdijkiae. Subsequent studies were done with the best treatment (resveratrol, 200 μg g⁻¹) on natural wheat grain with either P. verrucosum or A. westerdijkiae at 0.85–0.995a_w and 15/25 °C over 28 days storage. This showed that the populations of the mycotoxigenic species and OTA contamination could be reduced by >60% by this treatment at the end of the storage period.     

Storage stability of pineapple slices preserved by combined methods

Storage stability during 3 months was evaluated for pineapple slices preserved by combined methods (blanching for 1 min with saturated vapour, a_w reduction by osmotic concentration in sucrose syrup, pH reduction by addition of citric acid, and the addition of 1000 parts per million (ppm) of potassium sorbate and 150 ppm of sodium bisulphite). Pineapple slices were microbiologically sound and their moisture content, °Brix, pH and a_w remained almost constant during storage with mean values of 71.8%, 26.1, 3.65 and 0.978, respectively. Total sulphite and potassium sorbate concentrations of the pineapple slices were reduced during storage at 5 and 25 °C, being final concentrations 51% and 38% and 63% and 48% of the initial concentrations, respectively. Colour, texture and sensory evaluation revealed that there were no significant (P < 0.05) changes between samples stored at 5 or 25 °C. Good overall acceptability (initial mean score 7.21) of preserved pineapple slices even after 3 months storage at 25 °C (final mean score 7.02) was observed.     

Yoghurt added with Lactobacillus casei and sweetened with natural sweeteners and/or prebiotics: Implications on quality parameters and probiotic survival

The effect of addition of natural sugar substitutes (stevia, erythritol or xylitol) and prebiotics (oligofructose or polydextrose) on physicochemical characteristics, probiotic survival (Lactobacillus casei) and sensory acceptance of yoghurts during storage (7 °C, 28 days) was evaluated. Yoghurts with sucrose or sucralose were also prepared. Xylitol and sucralose added yoghurts had physicochemical characteristics and sensory acceptance similar to those of the product with sucrose. Xylitol was more efficient in maintenance of textural characteristics and probiotic survival in simulated gastrointestinal conditions (SGIC) than sucralose. Addition of erythritol and stevia changed the textural parameters, reduced acceptance and decreased probiotic survival in SGIC. Addition of oligofructose or polydextrose improved texture and increased probiotic survival but decreased flavour acceptance. All formulations could be considered probiotic products during shelf life (7 °C, 28 days) with counts higher than 10⁷ cfu mL⁻¹ in the product and 10⁴ cfu mL⁻¹ after SGIC.     

Curing and diffusion coefficient study in pastırma,a Turkish traditional meat product

Changes in water activity (a_w), moisture and salt contents and salt effective diffusion coefficients (D_eff) of past?rma samples during the curing process were determined. At the end of the curing stage, a_w values decreased to 0.942. The average initial moisture content of the samples decreased from 74.56% to 66.64%, depending on the curing time and the average salt content increased to 15.65 g NaCl/100 g dry matter at the end of the 48-hour curing process. Past?rma samples were assumed the geometry of endless slices, and the analytical solution of Fick's second equation was used for determination of salt D_eff values. Salt D_eff values were found to vary between 1.49 × 10^− 9–4.08 × 10^− 9 m²/s.     

Optimisation of vacuum pulse osmotic dehydration of blanched pumpkin

Pulsed vacuum osmotic dehydration (PVOD) is an efficient process for obtaining semi‐dehydrated food. The effects of temperature (30–50°C), solute concentration (NaCl 0–15 kg per 100 kg solution, sucrose, 15–35 kg per 100 kg solution) and vacuum pulse application (50–150 mbar and 5–15 min) on water loss (WL), solid gain (SG), water activity (a_w) and total colour difference (?E) of previously blanched pumpkin slices were assessed through Plackett–Burman experimental design. Temperature was not statistically significant in the process. Later, with the aid of a central composite design (CCD), it was found that concentration of sucrose and NaCl was influent on the WL, SG, a_w and ?E, and the pressure and time of application of vacuum were influent on WL and SG. The optimal conditions of process were stabilised with the desirable function, and the simulated data were similar from the experimental ones.     

Heat Resistance of Salmonella typhimurium and Listeria monocytogenes in Sucrose Solutions of Various Water Activities

The heat resistance of Salmonella typhimurium was determined in sucrose solutions with a_w ranging from 0.98–0.83. The D_65.6^o_c ranged from 0.29–40.2 min (> 100-fold increase), with z value 6.5–7.7°C. S. typhimurium was also heated in four chocolate syrups purchased at retail. The D_65.6^o_C ranged from 1.2–3.2 min while the a_w of the syrups ranged from 0.75–0.84. The heat resistance of Listeria monocytogenes was determined in sucrose solutions with a_w ranging from 0.98–0.90. The D_65.6^o_C value shifted from 0.36–3.8 min (10-fold increase); the z value ranged from 7.6–12.9°C.     

Optimisation of the pulsed vacuum osmotic dehydration of cladodes of fodder palm

Fodder palm, a great source of nutrients for human and animals, grows even in arid climates. Pulsed vacuum osmotic dehydration is an efficient process for obtaining semidehydrated food. It was used to slice cladodes of fodder palm. The independent variables used were temperature (30–50 °C), pulsed vacuum pressure (50–150 mbar) and NaCl concentration (5–15 g per 100 g solution). The response variables were water activity (a_w), moisture content (X), colour parameters, water loss (WL), solid gain (SG) and weight reduction (WR). The pulsed vacuum osmotic dehydration process was optimised for minimum values of a_w, X and SG, and maximum values of chroma. The experimental data obtained with the optimum condition (100 mbar; 10 gNaCl per 100 g solution, 44 °C) were near the estimated ones. For example, WL, a_w and ?E, and their error were 8.15 g per 100 g, 11%; 0.985, 0.3% and 6.15, 15.2%, respectively.     

Effect of essential oils of cinnamon,clove, lemon grass,oregano and palmarosa on growth of and fumonisin B1 production by Fusarium verticillioides in maize

The ability of cinnamon, clove, lemon grass, oregano and palmarosa essential oils to prevent growth of and fumonisin B₁ (FB₁) production by Fusarium verticillioides at different water activity (0.95 and 0.995 a_w) and temperature (20 and 30 °C) levels in irradiated maize grain was evaluated. All the essential oils inhibited growth of F verticillioides isolates under all conditions tested, but FB₁ production was only inhibited at 30 °C and 0.995 a_w. Moreover, stimulation of toxin production was found under certain environmental conditions. None of the essential oils showed a significantly greater ability to inhibit FB₁ production when compared with the others. At 1000 mg essential oil kg^?1 maize the essential oils showed a greater inhibitory effect on growth of F verticillioides than at 500 mg kg^?1, but there was no difference in FB₁ production between the two levels of essential oil. Copyright © 2004 Society of Chemical Industry     

Improved radical scavenging activity and stabilised colour of nipa palm syrup after ultrasound-assisted glycation with glycine

The effects of ultrasound-assisted glycation with 1 m glycine at room temperature in comparison with thermal glycation on the colour and radical scavenging activity of nipa palm (Nypa fruticans Wurmb.) syrup were investigated. The pH of both treatments decreased with increasing reaction time. The browning development occurred after induction period of 10 min for thermal glycation and 60 min for ultrasound-assisted glycation. A shorter time of ultrasound rendered the syrup light brown to amber in colour with some green. With long-term ultrasound, the syrup turned brighter, yellower and greener. The increased DPPH^· scavenging activity of the thermal syrup was due to the brown pigments as shown by a marked increase in the A₄₂₀ and a* value. The scavenging activity of ultrasound-treated syrup was improved by 53–57% due to the accumulation of UV-intermediate products as shown by a higher A₂₉₄/A₄₂₀. Thus, ultrasonication for 30–60 min was recommended in order to prevent dark colour development of the final syrup.     

Kinetics Modeling of Mass Transfer Using Peleg’s Equation During Osmotic Dehydration of Seedless Guava (<Emphasis Type="Italic">Psidium guajava</Emphasis> L.): Effect of Process Parameters

Peleg’s equation was used to study the effect of process parameters on kinetics of mass transfer in terms of solids gain and water loss during osmotic dehydration using 30–50% (w/w) sucrose solution at 30, 40 and 50 °C. The experimental data were successfully fitted employing Peleg’s equation with the coefficient of determination (R ²) higher than 0.88, the root mean square error, and the mean relative percentage deviation modulus (E) of less than 0.003% and 6.40% for all treatments, respectively. In all cases, initial mass transfer rate parameter (K ₁) decreased significantly (p < 0.05) as the solution concentration and solution temperature increased suggesting a corresponding increase in the initial mass transfer rate. Initial mass transfer rate followed an Arrhenius relationship which showed that solids gain had the highest temperature sensitivity (E _a = 21.93–33.84 kJ mol⁻¹) during osmotic dehydration. Equilibrium mass transfer parameter (K ₂) decreased significantly (p < 0.05) as solution concentration increased demonstrating that the equilibrium solid and water contents increased with increase in solution concentration. The equilibrium solid and water contents were also estimated adequately using Peleg’s equation (R ² > 0.78). The results of this work allow estimating the kinetics of mass transfer during osmotic dehydration in order to obtain products with determined solid and water contents.     

Predicting suitable storage conditions for spray-dried microcapsules formed with different biopolymer matrices

Canola oil (CO)-in-soy protein isolate (SPI, 12.5 g per 100 ml of solution), CO-in-whey protein concentrate (WPC, 30 g per 100 ml of solution) and CO-in-mesquite gum (MG, 30 g per 100 ml of solution) emulsions were obtained (all with CO to biopolymers solids ratio of 25 g of canola oil per 100 g of wall material), spray dried and stored at water activities (a_w) of 0.12–0.89 at temperatures of 15, 25 and 35 °C. The powders adsorption isotherms experimental data were fitted to the GAB model. Their differential and integral enthalpies and entropies were estimated. The microcapsules point of minimum integral entropy (maximum stability) kept at 25 °C occurred at 10.40 g water per 100 g of dry solids (a_w of 0.55) for MG, 10.59 g water per 100 g of dry solids (a_w of 0.68) for SPI, and 6.38 g water per 100 g of dry solids (a_w of 0.46) for WPC. The integral enthalpy–entropy compensation indicated that the water vapour adsorption was controlled by entropic mechanisms at low a_w, but by enthalpic mechanisms at high a_w.     

Development of a device and method for the time-course estimation of low water fluxes and mean surface water activity of food products during ripening and storage

Accurate measurement of water activity (a_w) is an important goal for the food industry because a_w is a key parameter in microbial growth, biological reaction rates and physical properties. An experimental device was setup using air-product water balance to non-destructively estimate the time-course of mean a_w at the food product surface under well-controlled airflow conditions. The device is especially suited for studying the ripening of cheeses and fermented meat products, where water fluxes exchanged between products and air are very low. The validation tests performed with a_w-known model products showed that water fluxes of 10^?7 kg s^?1 can be estimated with an accuracy better than 2% over very short periods of time, and that surface a_w can be estimated with an absolute uncertainty of less than 0.01 a_w units. A handful of cheese ripening trials illustrate the potential of the method, highlighting the effects of a low air velocity and high air RH on the water exchanges occurring at a cheese surface, thus demonstrating the strong surface sensitivity to external air conditions.     

Environment,food residue,and dry cleaning tool all influence the removal of food powders and allergenic residues from stainless steel surfaces

The aim of this study was to investigate how the properties of powered food (particle size and chemical composition), food contact surface (surface roughness), and the environment (ambient relative humidity) impact the efficacy of brushing and scraping in removing wheat flour and non-fat dry milk (NFDM) from stainless steel coupon surfaces. Scraping was significantly less effective than brushing in the removal of powder under all conditions. The number of brush passes (7 ± 2) required to remove NFDM at 0.81 a_w was significantly greater than for samples at lower a_w levels. Moreover, surface protein residues were still detected following brush removal of NFDM at 0.69 and 0.81 a_w. Adhesion and cohesion in samples equilibrated at different relative humidity levels (i.e. different resulting a_w) were measured using custom test cells to quantify shear force. Greater adhesion and cohesion were detected for NFDM at higher a_w levels. Adhesion and cohesion of NFDM at 0.81 a_w were determined to be 129 ± 60 N/m² and 5418 ± 633 N/m²_, respectively. In addition, the particle size of NFDM (75, 180 and 355 μm) and the interaction between particle size and surface roughness (Ra = 0.17 ± 0.09, 0.77 ± 0.12, 1.08 ± 0.37 and 2.05 ± 0.40 μm) had significant effects on residual ATP following brushing. However, surface roughness did not significantly affect cleaning outcomes under the tested conditions. Overall, these findings highlight the potential for allergenic residue retention after conventional dry cleaning using hand tools. By better understanding the baseline efficacy of conventional hand tools used in dry cleaning under different scenarios, more effective cleaning technologies can be developed.     

Effect of water activity on the inactivation kinetics of Escherichia coli O157:H7 by electron beam in ground beef, chicken breast meat, and trout fillets

Water activity (a_w) of ground beef, chicken breast meat, and trout fillets was modified to intermediate (a_w 0.98–0.99) and lowest (a_w 0.94–0.96) levels. The meat samples with modified and unaltered (native, a_w 1.00) a_w were inoculated with Escherichia coli O157:H7 and subjected to electron beam (e‐beam). Survivor curves were plotted and the D₁₀‐values were calculated. The D₁₀‐values ranged from 0.22 kGy for trout at native a_w to 0.33 kGy for beef at intermediate, and chicken and trout at lowest a_w. Regardless of the species, a_w reduction increased E. coli resistance to e‐beam, suggesting that even small depletion of unbound water from food increases survival. The difference of the D₁₀‐values between the samples at intermediate and lowest a_w was insignificant. E‐beam could be used before a_w‐reducing techniques are applied to food products. However, this would require stringent microbial control following e‐beam processing. The ‘tailing’ of survivors was observed for some samples with reduced a_w.     

Water availability and calcium propionate affect fungal population and aflatoxins production in broiler finisher feed during storage

The aim of this study was to investigate the effects of calcium propionate, water activity (a_w) and incubation time on the total fungal count and aflatoxins B₁ (AFB₁), B₂ (AFB₂), G₁ (AFG₁) and G₂ (AFG₂) production in the broiler finisher feed. The feed was added with calcium propionate (5 g kg^–1), adjusted to 0.85, 0.90 and 0.95 a_w and stored for 28 days at 25°C, analysing for mould growth and aflatoxins production every 7 days. Analysis of variance indicated that all the factors (preservative, a_w and storage time) alone and in combination significantly (p < 0.001) affected the total fungal count and aflatoxins production in the feed. Minimum total fungal counts (1.99 × 10² CFU g^–1) were observed in calcium propionate feed at 0.85 a_w on day 1 and the highest (4.36 × 10⁹ CFUs g^–1) in control sample at 0.95 a_w on day 28 of storage. During the storage period, AFB₁ content in control samples increased from 11.35 to 73.44, from 11.58 to 81.81 and from 11.54 to 102.68 ng g^–1, whereas in preserved feed the content of B₁ increased from 11.47 to 37.83, from 11.54 to 49.07 and from 11.20 to 53.14 ng g^–1 at 0.85, 0.90 and 0.95 a_w, respectively. Similar patterns were noted for AFB₂, AFG₁ and AFG₂ contents. All the aflatoxins readily increased over storage time; however, the increase was much slower in preserved feed that contained a lower amount of available water. This study reveals that calcium propionate addition to poultry litter along with water activity amelioration is an effective tool for controlling mould incidence and aflatoxin production in poultry feed.     

Death rates of Salmonellae in fishmeals with different water activities. I. During storage

Fishmeals with different moisture contents, having water activities (a_w) ranging from 0.34 to 0.71, were infected with strains of Salmonella oranienburg or S. senftenberg and were stored at 15, 20 and 30°c, packed in nitrogen or air. The initial death rates (calculated over storage periods of 70 days) were not appreciably influenced by reduction of a_w from 0.71 to 0.54. Further reduction of a_w to 0.34 caused a decrease of the initial death rate, in particular in meals stored at 15 or 20°c. As compared with fishmeals packed in air, meals packed in nitrogen showed a decrease of initial death rates, especially in meals with the lowest a_w and stored at 15 and 20°c. Death rates calculated over longer storage periods were smaller than initial death rates, in particular in meals with a_w 0.54 stored at 15 and 20°c and meals with a_w 0.34 stored at 15, 20 and 30°c. Pelletisation of meals with a_w 0.72-0.74 caused a 10²-10³-fold reduction of initial Salmonella counts. The death rates of salmonellae which survived the pelletisation treatments were of about the same order as found for the initial death rates of salmonellae in non-pelletised meals with about the same a_w.     

The effects of dry-cured ham initial water activity on Tyrophagus putrescentiae infestations

A 5 × 2 × 2 factorial arrangement within a completely randomized design was used to evaluate the effect of a_w (0.65, 0.70, 0.75, 0.80, and 0.85), RH (65% and 75%) and temperature (24 °C and 28 °C) on Tyrophagus putrescentiae growth, on ham cubes in two separate experiments, one for treated nets (infused with propylene glycol (PG) + propylene glycol alginate (PGA) + carrageenan (CG) + water) and one for untreated control nets. For treated nets, water activity and temperature did not affect mite growth. When control nets were used, there was no difference due to aging temperature, but there were more mites (P < 0.05) at 65% RH than at 75% RH. In addition, ham cubes with 0.85 a_w had more mites (P < 0.05) than at 0.70 and 0.65 a_w, and ham cubes with 0.80 and 0.75 a_w had more mites (P < 0.05) than at 0.65 a_w. The only treatment combinations that controlled mites were the ham cubes with 0.65 a_w that were stored at 75% RH at both temperatures, with average mite counts below the initial inoculum level of 20 mites. Overall, results indicated that the treated nets were effective at controlling ham mites, regardless of ham cube a_w, storage temperature, and RH. However, if only untreated barrier nets were used, mites were only controlled when ham cubes had a a_w of 0.65 or 0.70 and were stored at 75% RH. These conditions may not be practical since drying to 0.65 or 0.70 a_w would result in more moisture loss, lower yields, and less product that could be sold.     

In-package atmospheric cold plasma inactivation of Salmonella in freeze-dried pet foods: Effect of inoculum population,water activity,and storage

Recently, Salmonella has been linked to numerous low water activity (a_w) food recalls. As an emerging technology, atmospheric cold plasma (ACP) has the potential to reduce Salmonella in low a_w foods. The objective of this study was to evaluate the effects of initial inoculum population of Salmonella (~ 10, 9 and 8 log CFU/cm²), treatment time (2.5, 5, 7.5 and 10 min), water activity (0.13, 0.34, 0.54), and post-treatment storage (0, 7 and 14 days at 21 °C) on the reduction of cocktails of S. Typhimurium and S. Senftenberg on freeze-dried pet food treats. The top surface of pet food was spot inoculated with cocktails of Salmonella with initial cell populations of 10, 9 and 8 log CFU/cm². Inoculated samples were first equilibrated to target a_w values, packaged with modified atmosphere (78% N₂ + 21% O₂ + 1% CO₂), and then in-package ACP treatments were performed. The initial inoculum population, treatment time, and post-treatment storage had significant (P < 0.05) effects on Salmonella inactivation efficacy of ACP. Regardless of the initial inoculum population and storage time, Salmonella equilibrated to 0.13 a_w pet food exhibited the greatest resistant to ACP treatment. ACP treatment for 10 min followed by 7 days storage reduced the Salmonella cells in 0.54 a_w pet food, to below the limit of detection (>4.5 log reduction), when the initial inoculum population was 8.2 log CFU/cm². Regardless of a_w of petfood, peroxide and thiobarbituric acid reactive substance values of 10 min ACP-treated pet foods were significantly increased to 3.44 meq/ kg of fat and 1.53 mg MDA/ kg pet food from 0.87 meq/ kg of fat and 0.50 mg MDA/ kg pet food, respectively. Post-ACP treatment storage of 10 min ACP-treated samples for 14 days further increased the lipid oxidation to 2.58 from 1.53 mg MDA/ kg of pet food, irrespective of the a_w of samples. This study showed that the Salmonella reduction efficacy of in-package ACP treatment in low a_w environment is influenced by various process and product factors.Industrial relevanceFreeze drying is not considered a kill step to inactivate microorganisms on foods. In the future, in-package ACP technology could be used as a potential method for post-packaging decontamination of freeze-dried pet foods in industrial settings after obtaining necessary regulatory approvals.