CUTTING RESISTANCE OF A RESTRUCTURED FRUIT BAR AS INFLUENCED BY WATER ACTIVITY

The cutting resistance, of thin rectangular strips of a restructured dehydrated fruit bar was measured over a range of water activity, 0.30-0.97. There was a 100-fold increase in cutting force as the product was dried from an initial cutting resistance of 4.4 N at a_w, = 0.86 to a maximum of 452 N at a_w= 0.33. Below a water activity of 0.33, samples became brittle and showed lower cutting resistances; for example, 68 N at a_w= 0.30. The major ingredients in the fruit product affecting cutting resistance were the level of apple puree and maltodextrin.     

USE of UNIFAC IN the PREDICTION of WATER ACTIVITY VALUES of AQUEOUS POLYOL SOLUTIONS

The water activity (a_w) values of two commonly used aqueous polyoi solutions (xylitol and sorbitol) in the confectionery industry were estimated at 25C by using the UNIFAC (universal functional group activity coefficient) model in the a_w range 0.50–0.99. the comparison between the experimental and estimated a_w values at the high a_w region (a_w> 0.96) revealed very good agreement. However, the predicted values by the UNIFAC model did not fit well to the experimental data at a_w < 0.96, indicating that the UNIFA C method needed to be modified. the agreement between the experimental and predicted values was considerably improved at a_w < 0.96 when the modtfled UNIFAC model was used.     

EFFECT OF CHOCOLATE COATING ON OXIDATIVE STABILITY OF NORMAL AND HIGH OLEIC PEANUTS

Oxidative stability studies were performed on roasted high-oleic acid peanuts (HOP-SunOleic 95) and normal oleic acid peanuts (NOP-Florunner). Peanuts were dry-roasted to a Hunter Lab value of approximately 50. Chocolate-coated peanut bars (6"x4"×1/2") were prepared using milk chocolate, white chocolate, and reduced-fat chocolate (containing salatrim). Chocolate bars were stored at 25C and 0.60 water activity (a_w). Uncoated peanuts were stored at 0.60 and 0.19 a_w at 25C. Samples were removed from storage at 4-week intervals for peroxide value measurement. Oxidation of peanuts with chocolate coatings were higher than the peanuts that were stored uncoated at the same a_w. The peroxide values of NOP were similar for chocolate coated treatments and 0.60 a_w control but the 0.19 a_w control was 2–4 times higher than the others. Chocolate-coated peanuts had higher oxidation rates compared to uncoated peanuts.     

KINETICS OF NONENZYMATIC BROWNING IN CHEDDAR CHEESE POWDER DURING STORAGE

Nonenzymatic browning (NEB) in Cheddar cheese powder during storage was investigated in the water activity (a_w) and temperature ranges of 0.48–0.85 and 20–40C, respectively. The NEB obeyed zero-order reaction kinetics during storage. Activation energies and Q₁₀ values were in the range of 15.1–22.3 kcal/mole and 2.2–3.5, respectively. The NEB increased with increasing temperature and storage time. There was an a_w maxima at 0.63 for NEB at 20C. At 30 and 40C, NEB decreased with increasing a_w. A generalized NEB model for Cheddar cheese powder during storage was developed based on Arrhenius equation to describe NEB as a function of a_w and temperature. Powders stored at 20 and 30C were evaluated for quality aspects. Maximum storage stability was obtained in powders stored at a_w of 0.54 at 20C for five months based on an overall desirability score of 3.5 on a 7-point scale. The average score of fresh powders were 4.7 throughout the storage study 7.     

Water desorption isotherms of two varieties of sweet potato

Water desorption isotherms were determined for New Zealand sweet potato at 25, 40 and 55°C, and for Philippines sweet potato at 28°C. The isotherms were sigmoid in shape and of type II according to the BET classification. The data were fitted to eight two-parameter equations reported in the literature. The effect of water activity, a_w, and temperature, T °C, on the equilibrium moisture content, M _e g water/100g dry solids, was best described for New Zealand sweet potato by: Me = 20.51 T-^0.204 (a_w/(1-a_w)0.39 for a_w= 0.06–0.81     

EFFECT of WATER ACTIVITY ON VITAMIN A DEGRADATION IN WHEAT FLOUR (ATTA)

ABSTRACT. The effect of water activity (a_w) on the stability of vitamin A palmitate adsorbed onto wheat flour, starch, gluten, enzyme inactivated wheat flour and micro-crystalline cellulose was investigated. In wheat flour the rate of vitamin A degradation was lowest at 0.0 a_w. In gluten, starch and enzyme inactivated wheat flour, the rate was highest at 0.0 a_w and decreased with rise in a_w. the rate of lipid oxidation in wheat flour was lowest at 0.0 a_w whereas in enzyme inactivated wheat flour it was highest at 0.0 a_w and decreased with rise in a_w. In micro-crystalline cellulose system vitamin A degradation was least at 0.33 a_w and the rate of degradation increased both below and above this a_w. Among the wheat flour constituents, gluten provided better protection to vitamin A than starch. the role of lipoxygenase enzyme in accelerating the rate of degradation of vitamin A in wheat flour at higher a_w has been suggested.     

Effect of Water Activity on Lipid Oxidation and Protein Solubility in Freeze-dried Beef during Storage

ABSTRACT: Ground beef patties (15% fat) were freeze-dried to different a_w endpoints and stored at 25°C or 49°C. Water activity, total moisture (%), lipid oxidation (TBARS@450nm), and protein solubility were evaluated. TBARS @450nm was favored at 49°C, but not at 25°C except at high a_w range (p < 0.05), whereas protein solubility was greater at 25°C than 49°C (p < 0.05). TBARS@450nm values at 49°C were generally greatest at low a_w range (p > 0.05). Protein solubility was lowest at medium a_w at 49°C (p < 0.05), while at 25°C low a_w protected protein solubility better than other low or high a_w values.     

ASSESSMENT of NEAR INFRARED (NIR) DIFFUSE REFLECTANCE ANALYSIS FOR MEASURING MOISTURE and WATER ACTIVITY IN RAISINS

Near Infrared (NIR) Analysis was applied to assess its potential for measuring water activity (a_w) and moisture in California Seedless Raisins in moisture equilibrium and nonequilibrium conditions. Samples covered a wide range of anticipated moisture contents. an NIR calibration for a_w was made for whole raisins that were fully equilibrated. For ground raisins, NIR calibrations were made both a_w and vacuum oven moisture, covering a large range of moisture contents and equilibrium conditions. Direct measurement of a_w by a dewpoint device gave highly repeatable results, especially for ground raisins. Vacuum oven analysis of moisture was less precise than a_w measurements. Full spectrum NIR calibrations indicated that NIR could predict a_w of raisins in ground form, irrespective of their state of hydration beyond three hours following processing. A much larger sample population will be needed to establish precise calibrations for vacuum oven moisture.     

Molecular Dynamics of Soy-Protein Isolate Films Plasticized by Water and Glycerol

ABSTRACT: The effects of water and glycerol on the molecular mobility of a soy-protein isolate (SPI)-based film were investigated using ¹H nuclear magnetic resonance (NMR). SPI-films were prepared with different glycerol contents and equilibrated to various levels of water activity (a_w). The distributed transverse relaxation of film samples showed 2 distinct components: a solid-like fraction (T_2s*) and a liquid-like fraction (T_2m*). The peak T_2s* values of films with lower glycerol concentration were more sensitive to variation in a_w. As a_w increased, the change of solid-like to liquid-like fraction was observed in higher glycerol films. As glycerol content increased, a minimum longitudinal relaxation time (T₁) occurred at lower a_w. Our results suggest that NMR techniques can be used to quantify the plasticizing effects on biopolymer films.     

WATER ACTIVITY AND THE INACTIVATION OF ENTEROBACTER CLOACAE INOCULATED IN CHOCOLATE LIQUOR AND A MODEL SYSTEM BY PULSED ELECTRIC FIELD TREATMENT

Effects of water activity (a_w) on the inactivation of Enterobacter cloacae inoculated in chocolate liquor and in a model system of 0.1% (w/v) peptone water and glycerol by pulsed electric field (PEF) treatment were investigated. An electric field strength of 24.5 kV/cm, a total treatment time of 320 μs, a pulse duration time of 4 βs, a pulse delay time of 15 βs, and a pulse cycle time of 15 s were selected for PEF treatment. The inactivation ofE. cloacae by PEF increased significantly as a^w increased (P < 0. 05). As a^w of chocolate liquor increased from 0.48 to 0.89, the log reduction of E. cloacae increased from 0.1 to 1.3. The measured temperature change inside the PEF treatment chamber was 0.4C when the log reduction was 1. 3. Similarly, as a^w increased from 0. 51 to 0.91 in the model system, the log reduction increased from 0.4 to 1.3. E. cloacae surviving a low a_w environment had high resistance to PEF. PEF inactivated E. cloacae in the chocolate liquor with a_w of 0.85 by 1 log at O h incubation. However, the log reduction was only 0.1 when PEF treatment was applied to E. cloacae which was incubated for 2 h in the chocolate liquor with a_w of 0.85 before PEF treatment. E. cloacae surviving the low a_w environment might have resistance not only to the low a_w but also to PEF. The resistance to low a_w environment may need to be considered when the inactivation of microorganisms by PEF is evaluated.     

Thiamin Stability in Solids as Affected by the Glass Transition

The stability of thiamin was evaluated in solid polyvinylpyrrolidone model systems as a function of water activity (a_w) and the glass transition. In the glassy state, thiamin degradation rate constants correlated with the glass transition temperature (T_g), decreasing as T_g increased. Above a_w 0.4, rate constants correlated better with a_w rather than T_g. However, rate constants decreased in the rubbery state above a_w 0.4, which could be attributed to glass transition-induced structural collapse. Glass transition effects (mobility considerations, collapse) have a larger effect on thiamin stability than a_w, which should be recognized during the development of fortified food products.     

EFFECT OF WATER ACTIVITY ON THE GROWTH OF STAPHYLOCOCCUS AUREUS AT MEAT-CHEESE INTERFACES

There is increased marketing of ready-to-eat nonrefrigerated snack foods which consist of meat or sausage products with low or intermediate moisture levels combined with high moisture food products, i.e., cheese products. Packaging the intermediate moisture meat in direct contact with a high moisture food might change the water activity (a_w) of the products sufficiently to support growth of Staphylococcus aureus at contaminated interfaces. To evaluate this possibility, sterile sausage slices (a_w= 0.60 to 0.82) were surface inoculated with log 2-3 CFU/g of S. aureus, interfaced with processed cheese slices (a_w= 0.94), vacuum packaged, and incubated at 19, 28, 37C and at cyclic temperature of 19–37–19C. S. aureus levels and water activities were determined weekly for 0 to 9 weeks. The a_w at the interface changed rapidly and reached an a_w that supported S. aureus growth. Growth of S. aureus occurred under all test conditions when the samples were stored at 28 and 37C. At 19C storage S. aureus remained viable for the length of the study.     

Natural maize phenolic acids for control of aflatoxigenic fungi on maize

ABSTRACT:  Natural phytochemicals may be an alternative to synthetic chemicals for controlling fungal growth and mycotoxin production in stored maize. A key to progress in this field is to select the best natural maize phytochemicals to be applied in a storage maize ecosystem. This research was undertaken to evaluate the effects of the natural phytochemicals trans-cinnamic acid (CA) and ferulic acid (FA) alone at concentrations of 20 to 30 mM and in 5 combinations on Aspergillus flavus Link and A. parasiticus Speare populations and aflatoxin B₁ production. Studies on Aspergillus population and aflatoxin B₁ production were carried out in maize grain in relation to a water activity a_w of 0.99, 0.97, 0.95, and 0.93. CA and FA at concentrations of 25 to 30 mM, respectively, and CA-FA mixture T9 (25 + 30 mM) were the treatments most effective at inhibiting A. flavus and A. parasiticus population at all a_w assayed after 11 d of incubation. At all a_w values, the mixture CA-FA T9 (25 + 30 mM) completely inhibited (100%) aflatoxin B₁ production by both strains at a_w= 0.99, 0.97, 0.95, and 0.93. Decreased aflatoxin B₁ levels in comparison with the control were observed with mixtures CA-FA T6 (10 + 25 mM), T7 (20 + 20 mM), and T8 (20 + 30 mM) of both strains in the majority of a_w assayed. The data show that CA and FA could be considered as effective fungitoxicants for A. flavus and A. parasiticus in maize in the a_w range 0.99 to 0.93. The information obtained shows promise for controlling aflatoxigenic fungi in stored maize.     

Low Temperature Growth of Type E Clostridium botulinum Spores. 2. Effects of Solutes and Incubation Temperature

SUMMARY— The inhibition of outgrowth of spores of Clostridium botulinum Type E by the addition of different concentrations of various solutes to a trypticase-peptone-sucrose-yeast extract medium (TPSY) was studied at different incubation temperatures. Solutes added to TPSY medium were sodium chloride (NaCl), sodium formate (NaCOOH), potassium chloride (KCI), sucrose and glucose. Incubation was at 30, 21.1, 15.6, 10 and 7.2°C, and growth was confirmed by mouse toxin assay. The effect of the solutes on the equilibrium relative humidities (ERHI of the various media was measured using the graphical interpolation method and expressed as water activity (a_w). The possibility of an osmotic effect was also investigated. The molar (M) concentrations and osmotic pressures of the different solutes were calculated and related to the approximate inhibitory concentrations of 5.0% NaCl (a_w 0.975), 6.0% KCI (a_w 0.974), 5.5% NeCOOH (a_w 0.9711, 38.5% sucrose (a_w 0.976) and 22.5%. glucose (a_w 0.970).
The inhibitory salt concentrations were approximately 0.80 M and produced osmotic pressures of about 36.0 atmospheres. The approximate osmotic pressure of the inhibitory 1.12 and 1.24 M sucrose and glucose solutions were 25.08 and 27.97 atmospheres respectively.
Growth response decreased as the incubation temperature decreased as measured by delayed outgrowth times and in decreased amount of cellular material produced by the Type E strains tested.     

Water activity of culture media used in food microbiology

An improved gravimetric method was used to simultaneously determine (in a single assay) the water activity ( a_w ) of 30 solid and liquid culture media covering the entire useful range of a_w in food microbiology, including media recommended for osmophilic, halophilic and xerophilic organisms. The water activities of the media ranged between 0.999 and 0.739. As could be expected, the water activities of the solid media were not affected significantly by the presence of agar. No significant differences were observed either between the gravimetric (20°C) and the cryoscopic measurements (below 0°C) of liquid media of very high a_w .     

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.     

Nonenzymatic Browning in Amorphous Food Models: Effects of Glass Transition and Water

ABSTRACT: The effect of glass transition on nonenzymatic browning (NEB) rates of amorphous, L-lysine, and D-xylose containing maltodextrin (MD)- or polyvinylpyrrolidone (PVP)-based food models, equilibrated into a_w of 0.23, 0.33, or 0.44 was studied. Glass transition temperature, T_g, was measured using DSC and NEB rates, followed spectrophotometrically. Use of citrate buffer as a pH regulator was evaluated. The NEB rates were higher in PVP than in MD models. Arrhenius plots showed nonlinearity in the vicinity of the T_g. Increasing a_w decreased T_g, but did not affect NEB rates around the T_g. The temperature difference (T - T_g) was not a sufficient measure of material stability.     

Role of Moisture in Maillard Browning Reaction Rate in Intermediate Moisture Foods: Comparing Solvent Phase and Matrix Properties

ABSTRACT: In intermediate-moisture foods, a mechanism describing how moisture affects chemical reaction rate is unknown. Previously, research showed glycol addition to model systems allowed high rates of nonenzymatic browning below the monolayer moisture value and an a_w of 0.2. These works were replicated, focusing on a mechanism of either plasticization or reactant dissolution. T_g curves showed plasticization increased with added glycerol and sorbitol. The maximum rate of nonenzymatic browning with glycerol occurred at an a_w= 0.25 and was 1.5 times higher than the control (a_w= 0.65). Sorbitol showed rates similar to the control. Plasticization and aw were poor predictors of reaction rate. Dissolution of glucose in glycerol explained the effect.     

Mold-free Shelf-life Extension of Bakery Products by Active Packaging

ABSTRACT: Total elimination of oxygen (O₂) in modified atmosphere packaging of bakery products is difficult to achieve. Because of the typical porous texture of the packaging, air can be retained inside. The effect of O₂ absorbers alone or in combination with modified atmosphere on Eurotium amstelodami, E. herbariorum, E. repens , and E. rubrum growth was investigated. Cakes of 0.80 to 0.90 water activity ( a_w ) were packaged with different atmospheres (air, 100% N2; 70% N2:30% CO₂) and O₂ absorbers of 2 different absorption capacities. The use of absorbers with a suitable absorption capacity led to a significant increase of cakes with mold-free shelf life, regardless of a_w and pH level, at 25 °C.     

Glass Transition, Water, and Glycerol Effects on Sucrose Inversion in Pullulan-Sucrose Systems

ABSTRACT: Glass transition, water, and glycerol effects on sucrose inversion were investigated in pullulan-sucrose systems. Pullulan-sucrose (2:1), PS was dissolved into distilled water. Pullulan-sucrose-invertase, PSI, and pullulan-sucrose-invertase-glycerol, PSIG, were prepared by adding tiny amounts of invertase and glycerol, respectively, to similar PS blends. Samples were freeze-dried, further dehydrated over P₂O₅, and their physical properties were determined using water sorption isotherms and DSC. The amount of glucose formed by sucrose hydrolysis in samples stored at various RH was monitored. Water and glycerol plasticized the systems. DSC thermograms indicated complex phase behavior in PSI and PSIG depending on water content. Glycerol increased sucrose hydrolysis at 0.538 a_w, and favours it even at very moderate a_w.