Inactivation of Salmonella typhimurium and Lactobacillus plantarum by UV-C light in flour powder

This research evaluates the potential use of ultraviolet C light (UV-C) as a decontamination method for powdered foods, particularly of refined flour. This technology's lethal effectiveness was evaluated on Salmonella enterica subsp. Enterica serotype Typhimurium and Lactobacillus plantarum in wheat flour, and in laboratory liquid media of different a_w and turbidities to evaluate the action mechanisms of UV-C light in powdered products. Initial results showed a large variability of lethality in flour, obtaining between 0.2 and 3.0 log₁₀ cycles of inactivation. Results obtained in laboratory media and SEM analysis of contaminated flour indicated that the variability was due to a shadow effect on the efficacy of UV-C light and not due to the low water a_w of the flour or starch content. Based on these conclusions, a 2-m vertical tunnel with twelve 480 W UV-C lamps was designed to treat flour by forming a continuous cloud of dust (0.05–2.4 kg/h). Inactivation levels of 4.0 to 1.7 log₁₀ cycles of the population of L. plantarum in flour were achieved at flow rates of 0.2 and 2.4 kg/h respectively, with a maximum residence time of 4 s.Industrial relevanceThis investigation demonstrated the lethal efficacy of the application of UV–C light to inactivate microorganisms, both pathogenic and spoilage, present in flour. 4-log10 cycles of inactivation of both Salmonella Typhimurium and Lactobacillus plantarum were inactivated with UV-C treatments. A UV-C facility was built up which enabled to treat flour in continuous conditions creating a cloud of dust with treatments of 4 s and lethalities of 4-log10 reductions.     

Modeling the effect of natamycin,pine-resin and environmental factors on the growth and OTA production by Aspergillus carbonarius using response surface methodology

The effect of two antifungal compounds (natamycin, pine-resin), temperature and water activity, on the growth rate, lag phase duration and Ochratoxin A (OTA) production by three Aspergillus carbonarius isolates (Ac-28, Ac-29, and Ac-33), was studied by means of Response Surface Methodology (RSM) based on a Central Composite Design (CCD). Two different experimental designs were performed as a function of temperature (16.6–33.4 °C), water activity (0.90–0.97 a_w), natamycin (0–1000 ng ml^− 1) or pine-resin (0–2.61%, w/v) on a Synthetic Grape-juice Medium (SGM). OTA production was analyzed after 5, 10 and 15 days of incubation. A second-order polynomial model was fitted to each response parameter to assess the growth and OTA potential of all fungal isolates. Results showed that natamycin, a_w and temperature had significant effects on the lag phase duration of all isolates, as well as on OTA accumulation after 10 days of incubation for Ac-29 and 15 days for Ac-28 and Ac-33 isolates. The same results were obtained for OTA production after treatment with pine-resin. However, fungal growth rates were not statistically significant in both experiments, with the exception of Ac-29 and Ac-33 after treatment with pine-resin. Overall, high natamycin concentrations (800 and 1000 ng ml^− 1) delayed fungal growth depending on the environmental factors assayed. Moreover, treatment with pine-resin at 16.6 °C/0.94 a_w/1.1% w/v, as well as at 25 °C/0.90 a_w/1.1% w/v, completely inhibited fungal growth up to 15 days of incubation.     

Effect of pre-incubation conditions on growth and survival of Staphylococcus aureus in sliced cooked chicken breast

In this work, the effect of pre-incubation conditions (temperature: 10, 15, 37 °C; pH 5.5, 6.5 and water activity, a_w: 0.997, 0.960) was evaluated on the subsequent growth, survival and enterotoxin production (SE) of Staphylococcus aureus in cooked chicken breast incubated at 10 and 20 °C. Results showed the ability of S. aureus to survive at 10 °C when pre-incubated at low a_w (0.960) what could constitute a food risk if osmotic stressed cells of S. aureus which form biofilms survive on dried surfaces, and they are transferred to cooked meat products by cross-contamination. Regarding growth at 20 °C, cells pre-incubated at pH 5.5 and a_w 0.960 had a longer lag phase and a slower maximum growth rate. On the contrary, it was highlighted that pre-incubation at optimal conditions (37 °C/pH 6.5/a_w 0.997) produced a better adaptation and a faster growth in meat products what would lead to a higher SE production. These findings can support the adoption of management strategies and preventive measures in food industries leading to avoid growth and SE production in meat products.     

Radio frequency heating of corn flour: Heating rate and uniformity

Non-uniform heating is a major challenge for using radio frequency (RF) heat treatment in pasteurization of low moisture food products. The objective of this study was to evaluate the effect of different electrode gaps, moisture content (MC), bulk density and surrounding materials on RF heating uniformity and rate in corn flour. Additionally, the dielectric and thermal properties of corn flour were determined as affected by MC, temperature (°C), and frequency (MHz). Changes in MC, water activity (a_w) and color in the sample after RF heating were measured to evaluate treatment effect on food quality. A precision LCR meter and a liquid test fixture were used to study DP of the sample at RF frequency ranging from 1 to 30 MHz. The RF heating uniformity and temperature profiles of corn flour as exposed to RF heating were obtained with an infrared camera and a data logger connected to a fiber optic sensor. The DP values increased with increasing MC and temperature, but decreased with frequency. The heating rate increased from 3.5 to 6.8 °C min^− 1 with increasing MC (from 10.4 to 16.7%), but decreased from 12.7 to 5.2 °C min^− 1 with increasing electron gap (from 11 to 15 cm). The corner and edge heating were observed at all layers of the samples for all the distances, and the hottest and the most uniform layer were determined as the middle layer at an electrode gap of 15 cm. Glass petri dish provided better uniformity than those of polyester plastic petri dish. Covering by foam led to more uniform RF heating uniformity in corn flour, and better moisture and a_w distribution. This study provided useful information to develop an effective RF process as an alternative of conventional thermal treatments for pasteurization of low-moisture products.Industrial relevanceThis paper describes a novel methodology based on Radio Frequency heating to pasteurize food powder while maintaining the quality. The study addresses the ever-increasing global demand from consumers for safe food products.     

Moisture sorption isotherms of high pressure treated fruit peels used as dietary fiber sources

High hydrostatic pressure (HHP) treatments can improve the potential of orange, mango, and prickly pear peels as food formulation fiber sources. Akaike Information Criteria differences identified Peleg and GAB as the best model alternatives to describe experimental moisture isotherms. HHP (600 MPa/10 min/22 and 55 °C) effects on moisture isotherms expressed as relative water sorption content change with respect to controls (RWSC_aw) showed that in the 0.1–0.93 a_w range, HHP improved the adsorption water retention of orange peels. The same was true for the desorption water retention for all HHP-treated fruit peels except for prickly pear HHP-treated at 22 °C and > 0.35 a_w. The area under the hysteresis curve (A_H) in the 0.15–0.51 a_w range showed that HHP increased hysteresis for all fruit peels tested. All this illustrates the HHP potential to modify the hygroscopic properties of fruit peels at lower temperature and in less processing time than conventional processes.Industrial relevanceOrange, mango, and prickly pear peels are potential food fiber formulation sources with differentiated hygroscopic and functional properties. In this study, 600 MPa treatments at 22 and 55 °C for 10 min modified the adsorption and desorption moisture retention capacity of all fruit peels tested in this study. HHP technology can improve the potential of fruit peels as dietary fiber sources with the advantage of shorter processing times and lower temperatures than conventional technologies used to treat food fibers.     

X-ray diffraction analysis of lactose crystallization in freeze-dried lactose–whey protein systems

Water sorption, time-dependent crystallization and XRD patterns of lactose and lactose–WPI mixtures were studied with glass transition data. The results indicated that the sorbed water of lactose–WPI mixtures was fractional and water content of individual amorphous components in lactose–WPI mixtures at each a_w from 25 °C to 45 °C could be calculated. Crystallization occurred in pure lactose whereas partial crystallization was typical of lactose–WPI mixtures (protein content ≤ 50%) at intermediate and high a_w (> 0.44 a_w) from 25 °C to 45 °C. The extents of crystallization were significantly delayed by WPI. The T_g values of lactose–WPI systems showed the composition-dependent property in systems and might indicate the occurrence of phase separation phenomena during 240 h storage. XRD showed no anhydrous β-lactose and mixed α-/β-lactose with molar ratios of 4:1 crystals in crystallized lactose–WPI systems (70:30 and 50:50 solids ratios). Reduced crystallization in the presence of WPI was more pronounced possibly because of reduced nucleation and diffusion during crystal-growth. The present study showed that WPI could present an important role in preventing sugar crystallization.     

Improvement of radio frequency (RF) heating uniformity on low moisture foods with Polyetherimide (PEI) blocks

Radio frequency (RF) heating is rapid, volumetric, and can penetrate most food packaging material. Thus, it is suited for in-packaged food pasteurization applications. However, the non-uniform heating problem needs to be resolved. In this study, a method of adding Polyetherimide (PEI) cylindrical blocks on top of and at the bottom of peanut butter samples in a cylindrical jar (d = 10 cm, h = 5 cm) was evaluated to improve RF heating uniformity. A computer simulation model built with COMSOL Multiphysics® was used for heating pattern prediction, and a new temperature uniformity index was proposed to suitably evaluate pasteurization process heating uniformity. Results showed that a pair of PEI blocks with a diameter of 8 cm among all five diameters (2, 4, 6, 8, and 10 cm) added to the cold spots of a given peanut butter sample could make the sample reach the best heating uniformity. Furthermore, the best height of PEI blocks with a diameter of 8 cm that allows the sample to be heated most uniformly was found to be 1.3 cm after sweeping from 0.1 to 2.3 cm with a step of 0.1 cm. Simulation results also showed that the combination of PEI surrounding and the addition of 8 cm diameter PEI blocks could further control the temperature distribution range in peanut butter within 7.1 °C when the peanut butter was heated from 23 to 70 °C. The newly developed temperature uniformity index provided a more reasonable evaluation on heating uniformity of pasteurization process than the traditional uniformity index.     

Effect of reducing nitrate and nitrite added to dry fermented sausages on the survival of Salmonella Typhimurium

Salmonella is one of the pathogens that most frequently contaminate pork processing lines. Several hurdles can control this organism in dry fermented sausages, among them is nitrite. However, the traditional use of nitrate/nitrite in the meat industry is being questioned due to their involvement in nitrosamine formation. In this study, minced pork and sausages inoculated with Salmonella Typhimurium were prepared with 150 ppm NaNO₃ and 150 ppm NaNO₂ (maximum amounts allowed by EU), and with a reduction of 25% and 50%. The absence of nitrate/nitrite favored Salmonella growth, with 2–2.5 log cfu/g higher counts at the end of ripening, compared to nitrate/nitrite added batches. The 50% reduction showed the same inhibitory effect as the maximum amounts. Nitrate/nitrite represented an essential hurdle to control Salmonella even when pH and a_w were below the values considered as minimum for its growth. The effect of this reduction on other pathogens should be considered.     

Thermodynamic analysis of the sorption isotherms of pure and blended carbohydrate polymers

The adsorption isotherms of gum Arabic (GA), mesquite gum (MG), and maltodextrin DE 10 (MD), and a blend of the three gums (17%GA–66%MG–17%MD) were determined at 25, 35, and 40 °C. All isotherms were fitted using the GAB model and the thermodynamic properties (enthalpies and entropies, differential and integral) were estimated by the Clausius–Clapeyron method. The minimum integral entropy was considered as the point of maximum stability where strong bonds between the adsorbate and adsorbent occurred, and water is less available and likely to participate in spoilage reactions. The point of maximum stability was found between 12.24 and 14.68 kg H₂O/100 kg d.s. (corresponding to water activity, a_w, of 0.32–0.57) for GA, 12.12–14.27 kg H₂O/100 kg d.s. (a_w = 0.33–0.55) for MG, and 11.37–13.84 kg H₂O/100 kg d.s. (a_w = 0.28–0.55) for the biopolymer blend, in the temperature range studied.     

Destruction of Salmonella Enteriditis inoculated onto raw almonds by high hydrostatic pressure

The effects of continuous (50,000, 60,000 and 70,000 psi with holding times of 5 and 10 min) and discontinuous (oscillatory) (six cycles at 60,000 psi with a holding time of 20 s) high hydrostatic pressure (HHP) treatments on the viability of two Salmonella Enteriditis strains (FDA and PT30) inoculated onto raw almonds were evaluated at 25, 50, and 55 °C. Complete inactivation of the S. Enteriditis was achieved in 0.1% peptone water after continuous pressurization at 60,000 psi and 25 °C for 5 min. Continuous pressurization of raw almonds inoculated with S. Enteriditis at 60,000 psi and 50 °C for 5 min resulted in less than a log reduction (log₁₀ 0.83) of vegetative cells. The decimal reduction time using the continuous pressurization parameters was determined to be 9.78 min. A discontinuous process consisting of six cycles of pressurization at 60,000 psi and 50 °C for 20 s provided greater than a one log reduction (log₁₀ 1.27 for FDA and log₁₀ 1.16 for PT30) of the S. Enteriditis concentration. The low water activity (a_w) of the almonds was found to impart baroprotective attributes on the S. Enteriditis cells. When the almonds were directly suspended in water and then pressurized, a log₁₀ reduction of 3.37 was achieved. HHP of certain dry foods appears to be feasible if the food is directly suspended in the pressurizing medium (water).     

Survival of Salmonella Enteritidis PT 30 on inoculated almond kernels in hot water treatments

Almonds are blanched by exposure to hot water or steam-injected water to remove the pellicle (skin) from the kernel. This study evaluated the survival of Salmonella Enteritidis PT 30, Salmonella Senftenberg 775W and Enterococcus faecalis on whole raw almond kernels exposed to hot water. Whole, inoculated (7 to 9 log CFU/g) Nonpareil almonds (40 g) were submerged in 25 L of water maintained at 60, 70, 80 and 88 °C. Almonds were heated for up to 12 min, drained for 2 s, and transferred to 80 mL of cold (4 °C) tryptic soy broth. Almonds in broth were stomached at high speed for 2 min, serially diluted, plated onto tryptic soy and bismuth sulfite agars (Salmonella) or bile esculin agar (Enterococcus) and incubated at 37 °C for 24 and 48 h, respectively. D values of 2.6, 1.2, 0.75 and 0.39 min were calculated for exposure of S. Enteritidis PT 30 to water at 60, 70, 80 and 88 °C, respectively; the calculated z value was 35 C°. D values determined for Salmonella Senftenberg 775W and E. faecalis at 88 °C were 0.37 and 0.36 min, respectively. Neither Salmonella serovar could be recovered by enrichment of 1-g samples after almonds inoculated at 5 log CFU/g were heated at 88 °C for 2 min. These data will be useful to validate almond industry blanching processes.     

Growth of Listeria Monocytogenes in Traditional Austrian Meat Jelly Products

Individual components of a traditional meat jelly (cooked meat chunks, gelatin and preboiled vegetable) with differences in pH and a_w can constitute a niche for the multiplication of Listeria. Listeria monocytogenes counts remained stable in jelly over 21 days at 2 and 8 °C, whereas in meat and vegetables, a >1 log₁₀ unit increase was observed after 7 days at 2 °C (or >5 log₁₀ at 8 °C). In the composed product, Listeria numbers remained stable at 2 °C (21 days), but increased more than 1 log₁₀ during 7 days at 8 °C. Improving safety of jellied meat by lowering pH is discussed.     

Desorption isotherms of salted minced pork using K-lactate as a substitute for NaCl

The aim of this study was to obtain and compare water desorption isotherms of ground meat containing NaCl (0.107 kg NaCl/kg raw-meat dry matter) and/or K-lactate as NaCl substitute at two different levels of molar substitution (30% and 100%). A thin layer of salted ground meat was dried and sampled at pre-determined times. The moisture content of the samples and their water activities (a_w) were measured at 5 °C and 25 °C. Results showed that ground meat with NaCl and/or different K-lactate contents had a similar water desorption isotherm for a_w ranging from 0.7 to 1.0. Below 0.7, the water equilibrium content fell with small decreases in a_w faster for meat with NaCl than for meat with K-lactate. K-lactate could reduce the excessive hardening at the surface of salted meat products. Experimental desorption isotherms were compared to those estimated using two approaches of the Ross equation. Models provided a good fit for the experimental data.     

Comparison of multiple chemical sanitizers for reducing Salmonella and Escherichia coli O157:H7 on spinach (Spinacia oleracea) leaves

Effectiveness of multiple chemical sanitizers on the reduction of Salmonella spp. and Escherichia coli O157:H7 on spinach was compared. Fresh spinach (Spinacia oleracea) was inoculated with a bacterial suspension containing multiple strains of rifampin-resistant Salmonella and E. coli O157:H7. Inoculated spinach leaves were treated with a water wash or water wash followed by 2% L-lactic acid at 55 °C, peroxyacetic acid (80 mg/L), calcium hypochlorite (200 mg/L), ozonated water (mg/L) or ClO₂ gas (1.2 or 2.1 mg/L). The l-lactic acid produced a 2.7 log CFU/g reduction for E. coli O157:H7 and a 2.3 log CFU/g reduction for Salmonella, statistically significant compared to water wash alone (P < 0.05), which resulted in a reduction of 0.7 log CFU/g for both pathogens. These findings indicate that 2% l-lactic acid at 55 °C may be an effective treatment for reducing pathogens on spinach leaves.     

Influence of storage period and packaging method on sliced dry cured beef “Cecina de Leon”: Effects on microbiological,physicochemical and sensory quality

Quality aspects of sliced dry-cured beef “Cecina de León” preserved in vacuum and gas mixtures (20%/80% CO₂/N₂ and 80%/20% CO₂/N₂) were studied. The evolution of microbiological, physicochemical and sensory parameters were analysed during storage (210 days) at 6 °C. Although microbial counts at 60 days of the gas-packaged samples were lower than the vacuum-packed ones, they were never higher than the spoilage limit (7 log ufc/g). A slight increase (p < 0.05) in pH was observed throughout storage of “Cecina de León” packaged under vacuum and in gas mixtures. However, a decrease (p < 0.05) in a_w was observed during storage of “Cecina de León” packaged under vacuum but a_w did not vary (p > 0.05) during storage in the gas-packaged samples. No changes were observed (p > 0.05) in lightness (L¹), redness (a¹) and yellowness (b¹) in vacuum and gas packaged samples during storage. However, sensorially evaluated colour showed lower values in gas packaged samples during 30 days storage. This difference was decisive in establishing the shelf-life of “Cecina de León” slices preserved in gas mixtures (20%/80% CO₂/N₂ and 80%/20% CO₂/N₂). Therefore, from a microbiological point of view, gas mixtures are more effective in extending the shelf-life of “Cecina de León” slices. It is concluded that vacuum packaging allows longer storage than gas-packaging as it maintains a good visual appearance of “Cecina de León”, the main parameter in consumers’ perception of meat quality.     

Effect of temperature,pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

The aim of this investigation is to evaluate the concurrent influence of temperature (4–50 °C), pH (3.5–7.0), and the presence of nisin (up to 200 μg/mL) on the inactivation of two PEF-resistant Gram-negative, pathogenic bacteria, Salmonella Typhimurium STCC 878 and Escherichia coli O157:H7, using a PEF treatment of 30 kV/cm and 99 μs. A response surface model using a central composite design was developed for the purpose of understanding the individual effects and interactions of these factors.The models showed that temperature was the factor with the greatest influence on the PEF inactivation in the two strains investigated. Increasing the treatment temperature from 4 to 50 °C increased the lethality of PEF up to at least 4 Log₁₀ reductions for both microorganisms at all pH levels investigated. PEF lethality varied with the square of the pH observing the highest microbial PEF sensitivity at pH 5.25 at all temperatures. The addition of nisin to the treatment medium did not influence the PEF lethality independently of the temperature.PEF induced 1.0–1.5 Log₁₀ cycles of damaged cells at pH 3.5 for Salmonella Typhimurium STCC 878 and at pH 5.25 for E. coli O157:H7, independently of the temperature or the presence of nisin in the treatment medium.The application of PEF at 50 °C permitted the achievement of 5 Log₁₀ reductions of Salmonella Typhimurium STCC 878 and E. coli O157:H7 in a range of pH from 4.2 to 6.7 and from 4.5 to 6.0, respectively. Therefore, the application of PEF at moderate temperatures has great potential for achieving effective control of Gram-negative pathogenic microorganisms in the range of pH found in most foods.     

Resistance of Enterobacter sakazakii to pulsed electric fields

The influence of various environmental factors on Enterobacter sakazakii inactivation by pulsed electric fields was studied and the mechanisms underlying the changes in resistance were also explored. E. sakazakii PEF resistance was higher upon entering the stationary growth phase, but it did not significantly change with growth temperature. E. sakazakii cells were also more resistant to PEF in both acidified and low water activity media. Thus, for stationary-phase cells grown at 30 °C a treatment of 50 pulses at 31 kV/cm led to 5.1 log₁₀ cycles of inactivation in media of pH 7.0 (a_w > 0.99), 1.4 log₁₀ cycles in media of pH 4.0 (a_w > 0.99) and 0.3 log₁₀ cycles in media of a_w = 0.98 (pH 7.0). However, whereas the higher PEF tolerance in acid media was coincident with an increased number of cells capable of repairing their sublethally-injured cytoplasmic membranes, the higher resistance in media of lower water activity was not. To the best of our knowledge, this is the first time that sublethal injuries in outer membrane after PEF treatments have been found.Industrial relevanceThis work provides data about PEF inactivation kinetics and PEF resistance of E. sakazakii under several conditions that might be useful for designing food pasteurization processes by PEF technology. The occurrence of sublethal injuries in cytoplasmic and outer membranes under the most protective treatment conditions, gives the chance to develop combined processes that might increase the effectiveness of the PEF process.     

Binding of retinyl acetate to whey proteins or phosphocasein micelles: Impact of pressure-processing on protein structural changes and ligand embedding

A whey protein isolate (WPI) and native phosphocaseins (PC) at pH 6.5–6.6 were processed with retinyl acetate (RAC) using pressure-assisted technological tools to improve RAC embedding through processing-induced protein structural changes. To this end, protein-RAC dispersions were submitted to ultra-high pressure homogenisation (UHPH) at 300 MPa and an initial fluid temperature (T_in) of 14 °C or 24 °C, or isostatic high-pressure at 300 MPa and 14 °C or 34 °C for 15 min. A short-time thermal treatment (STTT, 73 °C for 4 s) able to generate WPI aggregates was assessed for comparison. Processing effects were investigated in terms of protein particle sizes and molecular weights (M_w). M_w calculated using protein size determination obtained from light scattering measurements were in agreement with the known values. The amounts of RAC retained in WPI particles (unfolded and/or aggregated proteins) or in PC assemblies were quantitated after protein precipitation by ammonium sulphate. A 2.3–3.7 nmol RAC was carried per mg of pressure-denatured whey proteins, significantly less than after STTT (6.3 nmol RAC per mg of heat-denatured whey proteins) indicating that RAC embedding varied according to the technological tool, pressure or temperature. A 3.8–5.4 nmol RAC was carried per mg of PC assemblies through pressure-induced dissociation/reassociation of PC micelles. Combined pressure and mild temperature increased RAC embedding in PC assemblies.     

Investigation of equilibrium solubility of a carob galactomannan

The equilibrium aqueous solubility of a commercial carob flour was investigated by determining the percentage of soluble and insoluble components as a function of dissolution temperature. The cumulative polysaccharide yield was ca. 50% at 5 °C, increasing approximately as a linear function of temperature to ca. 90% at 85 °C. Overall molecular weight and intrinsic viscosity of the soluble polysaccharide were determined by size-exclusion chromatography. With increasing dissolution temperature, there was weak trend towards higher overall molecular weight and intrinsic viscosity: M_w from 1060 to 1150 kg/mol, and [η] from 11.8 to 12.5 dl/g, between 5 and 65 °C, respectively. Broad, amorphous peaks were evident in the wide-angle X-ray scattering profiles, indicating no role for polysaccharide melting. The continuous increase of molecular weight and decrease of DS_gal with dissolution temperature is interpreted as the result of thermodynamic partitioning based on a classical polymer-solvent fractionation, a mechanism that applies only for polysaccharide components with DS_gal<0.35 within the accessible temperature range.     

Effect of water activity on the crispiness of a biscuit (Crackerbread): Mechanical and acoustic evaluation

The objective of this study was to use mechanical and acoustic methods developed in our laboratory to monitor the changes in crispiness of a Crackerbread biscuit following equilibration at different water activities (a_w). Crackerbread samples were equilibrated at a_w of 0.113–0.98. The equilibrated Crackerbread samples were punctured with a cylindrical probe (5 mm) using an Instron Universal Testing Machine. The force and acoustic signals were simultaneously captured using Labview software. Changes in parameters associated with crispiness were modelled using Fermi’s equation. The number of sound peaks, force and sound curve lengths and area under sound amplitude–time curve decreased with increasing a_w. The sound frequency decreased linearly (R² = 0.926) with increasing a_w. The critical water activity (a_wc) of Crackerbread ranged between 0.51 and 0.59. Acoustic parameters were more sensitive to a_w-induced changes in Crackerbread occurring at a_wc than mechanical parameters.