Kinetics of degradation of sorbic acid in aqueous glycerol solutions

Degradation of sorbic acid in aqueous glycerol solutions at pH 4·0 over the a_w range 0·71–1·00 and the temperature range 40°–60°C was found to follow first-order reaction kinetics and to conform to the Arrhenius equation. Activation energy values obtained were 5·8 kcal mol^?1 and 7·8 kcal mol^?1 for systems at 0·80 a_w with and without added Co⁺⁺, respectively. The rate of sorbic acid degradation was observed to increase with decreasing a_w (i.e. increasing glycerol concentration). The presence of added Co⁺⁺ decreased the rate of sorbic acid breakdown at any particular a_w or temperature. Browning of sorbate solutions during storage was markedly inhibited by Co⁺⁺.     

Chemical and Microbiological Studies on "Duke de Leche" a Typical Argentine Confectionery Product

“Dulce de leche” (milk sweet) is a typical Argentine confectionery product prepared with milk which is concentrated by evaporation in the presence of added sucrose. Its sugar composition, water activity (a_w) and pH values of commercial samples were studied. Water activity varied between 0.80 and 0.85 and pH between 5.6 and 6.3. The effects of practicable modification in a_w pH, storage temperature and addition of potassium sorbate on the growth of an osmotolerant yeast was studied. The best way of inhibiting the growth of the test microorganism at room temperature (25°C) was the addition of sorbate (500 ppm as sorbic acid) together with a pH adjustment to 5.5.     

Determination of Sorbic Acid Diffusivity in Edible Wheat Gluten and Lipid Based Films

Edible films using wheat gluten as the structural matrix with or without different lipid components and pure lipid films were tested for sorbic acid retention properties. A diffusion mechanism following Fick's first law was identified. An experimental procedure was developed for determining the diffusivity coefficient of sorbic acid in edible films immersed in an aqueous medium. The effect of film composition and temperature was investigated. The diffusion coefficient of sorbic acid in a gluten based film was 7.6 × 10^?12 m²/sec. The addition of a lipid component such as acetylated monoglyceride led to a 50% reduction in diffusivity. In a pure lipid film such as beeswax the diffusion coefficient of sorbic acid was 2.7 × 10 ^?16m ²/sec. The effect of temperature could be described by an Arrhenius type model, with activation energy ranging from 30.0 to 39.8 kJ/mole.     

Calcium Alginate Films: Thermal Properties and Permeability to Sorbate and Ascorbate

Calcium alginate films were prepared by the pH-controlled release of calcium ions into alginate solution or by the cooling of hot calcium alginate gels. Thermogravimetry and calorimetry showed that the controlled Ca release films contained a greater amount of high-temperature component, and required extra energy to dissociate the tightly crosslinked calcium alginate. Structural differences were reflected by the permeability of the two films to potassium sorbate: 1.06 × 10^–7 (controlled Ca release) and 1.58 × 10^–7 cm²sec^–1 (cooled). Apparent activation energy was estimated to be for the diffusion of potassium sorbate 24.1 KJ·mol^–1, sodium ascorbate 23.7, and ascorbic acid 36.2. Results suggested that the pH of the diffusant solution had an interactive effect on the alginate film.     

Influence of Potassium Sorbate and pH on Ten Strains of Type A and B Clostridium botulinum

Growth of each of ten strains of C. botulinum was measured as the average A_630nm of five replicate peptone-yeast extract-glucose (PYEG) broth cultures at 37°C. Media ranged in pH from 7.10–5.10 with potassium sorbate concentrations of 0–0.26%. Growth Ratios [GR = treatment/control] based on time to reach A₆₃₀=0.35 were calculated. The linear regressions of log [GR] vs log [undissociated sorbic acid in mg/L] or [1/GR] vs [pH] were used to predict GR's at 250 mg/L undissociated sorbic acid (pH 5.65 and 0.26% sorbate) and at pH 5.65 (0% sorbate) respectively. Among the ten strains examined, statistically significant differences (P<0.05) in resistance to pH and sorbate among strains and for the same strain from different spore suspensions were discovered. Resistance to pH and sorbate appeared to be correlated.     

High Hydrostatic Pressure as a Hurdle for Zygosaccharomyces bailii Inactivation

The combined effects of high hydrostatic pressure (HHP, 172, 345, 517 or 689 MPa), duration of HHP treatment (0, 2, 4, or 10 min), water activity (a_w 0.98 or 0.95), and potassium sorbate (PS) concentration (0 or 1000 ppm) on Zygosaccharomyces bailii inactivation were evaluated at pH 3.5 and 21°C in laboratory model systems. Inactivation of the initial inoculum (? 1.0 times; 10⁵ CFU/mL) occurred when the pressure was 689 MPa regardless of a_w PS or duration of treatment. Lower pressure was required for Z. bailii inactivation in the presence of PS.     

POTASSIUM SORBATE PERMEABILITY of POLYSACCHARIDE FILMS: CHITOSAN, METHYLCELLULOSE and HYDROXYPROPYL METHYLCELLULOSE

Edible coatings controlling preservative migration from surface to food bulk could control surface microbial growth which is often the main cause of spoilage for many food products. In this paper we examine the potassium sorbate permeability behavior of chitosan, methyl cellulose and hydroxypropyl methyl cellulose based films. to gain an understanding of the permeation process, permeability determinations were done at 5, 24, 32 and 40°C. Permeability rates followed the Arrhenius activation energy model. A lack of breaking points in Arrhenius plots indicated that no morphological changes occur within these films in the 5 to 40°C temperature range. Activation energy values were found to be independent of film composition and were affected only by the solvent embedded in the film. This behavior was confirmed by analysis of the same permeability data using a modified Stokes-Einstein equation. Methyl cellulose was the most promising diffusion barrier with a permeability constant of 3.4 and 1.4×10^?8 (mg/s cm²) (cm)/(mg/cm³) at 24 and 5°C, respectively. Electron microscopy was used to examine the morphological characteristics of these films and showed they have no visible pores or channels at magnifications up to 10,000.     

The effects of sorbates on the ensilage of chopped whole-plant maize and lucerne

The incorporation of (a) sorbic acid (0.18 and 0.90 g kg^?1, fresh weight basis) and potassium sorbate (0.90 g kg^?1) with chopped lucerne, and (b) sorbic acid (0.90 g kg^?1) and potassium sorbate (0.90 g kg^?1) with chopped maize (whole-plant) at the time of ensiling, led to a reduction in the surface spoilage associated with the ensilage of these two forages. Use of sorbic acid (0.90 g kg^?1) and potassium sorbate (0.90 g kg^?1) led to (a) a reduction of volatile nitrogen (VN), higher levels of residual water-soluble carbohydrates (WSC) in lucerne silage and more aerobically stable lucerne silage and (b) a reduction in weight loss, population of yeasts and moulds, and VN, higher levels of WSC in maize silage and more aerobically stable maize silage when compared to the untreated forages or forages treated with sorbic acid and potssium sorbate at 0.045 and 0.18 g kg^?1 (fresh weight basis), respectively.     

Potassium Sorbate Inhibition of Microorganisms Growing on Refrigerated Packaged Beef

The influence of potassium sorbate concentration (27–1325 ppm of sorbic acid) on the growth of natural flora in raw beef samples wrapped in plastic films of different oxygen permeability was studied at 0° and 4°C. Changes in aerobic plate counts, Pseudomonas spp., Brochothrix thermosphacta, Lactobacillus spp., Enterobacteriaceae and yeasts were monitored. Sorbate treatment effect on percentage increment of lag phase and reduction of growth rate during exponential phase for the different microorganisms were analyzed and antimicrobial action was evaluated by the Inhibition Index. A significant increase in the time to reach aerobic counts of 10^6.5 CFU/cm² was observed at low storage temperatures and pH values in vacuum packaged treated samples.     

Packaging Film Permeability in Conjunction with Sodium Nitrite, Potassium Sorbate or Lactic Acid Starter Culture for Control of Clostridium sporogenes (PA3679) Growth in Sliced Bologna

A sliced bologna was prepared and inoculated with Clostridium sporogenes (PA3679), packaged in films ranging in oxygen permeability from 0.1 cc/m²/24 hr to 120 cc/m²/24 hr and stored at 5°C, 15°C or 25°C. Subsequent bologna preparations included either 156 ppm sodium nitrite, 0.26% potassium sorbate or a lactic acid starter culture. Water activity, pH, TBA number and PA3679 counts were monitored during 28 days of storage. TBA numbers increased in packages with over 60 cc/m²/24 hr permeability but PA3679 counts did not change as a function of packaging film. Nitrite and sorbate were equally effective as inhibitors. At 15°C and 25°C, the lactic acid culture allowed the least PA3679 growth. Oxygen permeability did not alter any inhibitory effects even when increased TBA numbers resulted from using an oxygen-permeable film.     

A Multi-parameter Approach to Control the Growth of Saccharomyces cerevisiae in Laboratory Media

The effects of combinations of reduced water activity (a_w from 0.97 to 0.93), pH (3, 4, 5, and 6) and addition of potassium sorbate (0, 100, 500, and 1,000 ppm) on the growth of one strain of Saccharomyces cerevisiae in laboratory medium were studied. The minimal a_w for growth inhibition in the absence of sorbate and in the range of optimal pH was 0.89. Various combinations of a_w, pH and sorbate concentration prevented growth of the yeast at a_w values above 0.89. For example, at v = 0.93, addition of 100 ppm sorbate at pH = 4.0 resulted in inhibition; at a_w= 0.97 and same pH (4.0), 500 ppm of sorbate were necessary. The combined effects of the above parameters on generation time, maximum population, and lag time of the cells were also determined.     

Thermal Resistance of Bacillus coagulans in Double Concentrated Tomato Paste

Thermal resistance was determined on a strain of Bacillus coagulans in double concentrated tomato paste (a_w= 0.95 at 23°C, pH = 4.0, 30.3°Brix, 70.1% moisture and acidity 1.30 g/100g citric acid. A microsyringe method was used with an inoculum of 1.3 × 10⁴ spores/ mL. Values of D_90°c= 3.5 min and z = 9.5C° were obtained.     

Effect of Solute Type on Sorbate Resistance in Zygosaccharomyces rouxii

The effect of sorbate on the growth of Zygosaccharomyces rouxii was evaluated at reduced a_w using sucrose, glucose and polyethylene glycol (PEG). Sorbate-adapted and unadapted cells were grown aerobically at pH 5.0 in media adjusted to 0.92 a_w by addition of the solutes. Sorbate resistance by unadapted cells increased in the order of glucose < PEG < sucrose. Solute type had little effect on sorbate resistance by sorbate-adapted cells in media containing glucose and sucrose. The combination of PEG and 400 μg/mL sorbate was less inhibitory to sorbate-adapted cells than PEG with 0 μg/mL and 800 μ-g/mL of sorbate.     

The effect of temperature on microbial growth in apple cubes packed in film and preserved by use of orange juice

Red delicious apple cubes were packed in fresh orange juice containing chemical preservatives (citric and ascorbic acid, potassium sorbate) and covered with plastic films of different gas permeabilities (polyethylene and EVA‐SARAN‐EVA) before storage at 4, 10 and 20 °C. The concentration of potassium sorbate in the product was optimized with respect to colour and microbial growth. Yeast and mould growth was modelled by Gompertz and linear equations to derive parameters such as lag phase, maximum microbial population and specific microbial growth or rates of decline. Activation energies for the specific growth rates were estimated from Arrhenius‐type equations and the time required to reach microbial counts of 10^6±0.2 CFU g^?1 was determined in all cases. At 4 °C, these values were longer than 25 days in all systems tested. The use of a low gas permeability film and an adequate potassium sorbate concentration extended storage life at higher temperatures.     

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.     

Sensory Attributes and Instron Measurements of Reduced-Nitrite Poultry Frankfurters With Sorbic Acid or Potassium Sorbate

Poultry frankfurters (0 and 40 ppm nitrite) with sorbic acid or potassium sorbate were studied. Flavor characteristics were influenced by nitrite but not by ascorbic acid or potassium sorbate. Frankfurters with sorbic acid were softer and those with potassium sorbate were firmer than those without. Nitrite alone increased firmness. Sorbic acid appeared to counteract that increased firmness and potassium sorbate enhanced the increase in firmness when those compounds were used in combination with nitrite in the poultry frankfurters. Simulated-teeth attachments for the Inston gave results similar to sensory firmness scores. Frankfurters with sorbic acid added had lower pH than frankfurters from other treatments.     

Microbiological and sensory quality of stored croissant‐type bakery products depending on external (sorbic acid) and internal (dough,aw value) conditions

The work presents some results from the evaluation of microbiological (total bacterial count, coliform bacteria, moulds and yeasts) and sensory (shape, odour, colour, taste, consistency, crust, soft inside, etc.) quality and of the a_w value and pH during the 90‐day storage (interval of 0, 30, 45, 60, 75 and 90 days) under laboratory conditions at 20 ± 2°C in eight types of the bakery croissant‐type product with the nougat cream differing by the type of dough (brioche, croissant( a_w value of the cream, and by the presence or absence of sorbic acid in the spirit spray applied onto the surface of products. The above‐indicated parameters were examined also in the nougat cream samples (on the zero and 90^th day of storage). The chosen quality parameters permitted the level of the durability influence of croissants depending on external (sorbic acid) as well as internal (recipe, a_w) conditions to be estimated.     

Diffusivity of potassium sorbate in κ-carrageenan based antimicrobial film

The diffusion of potassium sorbate incorporated into κ-carrageenan based antimicrobial film was measured at 5 s intervals using a diffusion cell. The kinetics of potassium sorbate release followed Fick's law of diffusion, as shown by diffusional exponent characteristic n-value and high correlation coefficients between experimental and theoretical data. The effects of solution pH at the film surface (3.8, 5.2 and 7.0) and temperature (5, 25 and 40 °C) on diffusion were investigated. Diffusion was found to be unaffected by adjacent solution pH in the range of values tested, but a decrease in temperature from 40 to 5 °C resulted in a reduction of diffusion coefficients from 4.24×10⁻¹³ to 1.29×10⁻¹³ m²/s at pH 5.2.     

Acid Requirement for pH Modification of Processed Foods

A bench-top procedure was developed and tested for estimating the acid requirement for modifying the pH of low acid foods. Acid amounts needed to achieve desired equilibrium pH in finished products depended on total solids, protein and ash contents of foods, and on buffering capacities of acidulants and foods. Acid requirements to modify pH were calculated from titration curves. Specified equilibrium pH values were achieved within 0.08 pH unit. Effective gluconic acid diffusion (D_eff) into a buffered model food was 8.3 × 10^?10±1.5 × 10^?10 m²sec-¹.     

Microbiological changes in cottage cheese varieties during storage at +7°C

Studies have been made of microbiological changes in cottage cheese varieties during storage at 7°C. Commercially prepared products obtained directly from three manufacturers were at an initial pH in the range 4·6 to 5·1 and differed significantly in their content of sorbic acid/sorbate and of viable lactic streptococci. In many of the varieties that did not contain sorbic acid/sorbate multiplication occurred of Pseudomonas spp., Enterobacteriaceae and yeasts; spoilage occurred in some batches due to formation of a surface film of Pseudomonas fluorescens or of surface colonies of Sporobolomyces roseus and Trichosporon sp. at times equal to, or slightly greater than the recommended storage life. Where high numbers of viable lactic streptococci were present in varieties immediately after manufacture, no marked decrease in pH or increase in titratable acidity was observed during storage at 7°C. In varieties that contained sorbic acid at a concentration higher than approximately 500 mg kg^?1 little increase in numbers of bacteria or yeasts was observed during storage at 7°C. Decrease in quality due to separation of whey occurred in some products from each manufacturer, but no clear correlation was observed between separation of whey and pH or the number of lactic streptococci present.Bacteria of public health significance, Escherichia coli type I, Staphylococcus aureus and Vibrio spp. were not detected in these products.Fifty-nine samples produced by six manufacturers, purchased from retail outlets, were examined on the sell-by date; the results confirmed the conclusions drawn from studies during storage.