Microbiological, physicochemical and organoleptic changes of shredded carrots stored under modified storage

The effect of initial head spaces of air, 4.9% CO₂/2.1% O₂/93% N₂ and 5% CO₂/95% N₂ on the microbial flora of shredded carrots was studied at 4 and 10°C. The microbial flora of shredded carrots comprised lactic acid bacteria, pseudomonads and yeasts. Lactic acid bacteria were the predominant organisms in all samples. The pH dropped during the storage of carrots and this was more pronounced at 10°C. The concentration of different organic acids such as lactic, acetic, tartaric, citric and succinic increased in all samples stored under modified atmosphere packaging conditions at both temperatures. The spoilage of carrots stored under 5% CO₂/95% N₂ was delayed, as indicated by the changes in their texture, colour and odour, compared with those samples stored under air or 4.9% CO₂/2.1% O₂/93% N₂.     

LINKING MICROBIOLOGICAL CRITERIA FOR FOODS WITH QUANTITATIVE RISK ASSESSMENT

The current annual risk of acquiring a foodborne disease in the United States is estimated at 2.7 × 10^-2. The risk of associated death is estimated at 3.7 × 10^-5. These represent a health care burden >$3 billion. Using a risk assessment model one can identify levels of microbial contamination which may be unacceptable in foods and appropriate controls needed to reduce these levels. Salmonella bacteria continue to represent a large percentage of the identifiable infections. A model developed from human dose-response studies predicts the probability of infection for Salmonella at 7.5 × 10^-3 with exposure to a single CFU of the organism. Risks of severity (hospitalization), mortality, reactive arthritides, and mortality in the elderly are estimated at 3.1 × 10^-6, 7.5 × 10^-6, 1.7 × 10^-5, and 2.8 × 10^-4. Exposure to microbial contaminants needs to be evaluated on a single meal basis. For chicken, exposure may range from a single drum stick (38g) to a half broiler (176g) but averages around 80g. For beef between 51 and 85g may be consumed during a single meal. Therefore, methods for monitoring must be able to detect at least 1 CFU/80g. Risks for some pathogenic E. coli are estimated at 1,000 to 10,000 less than Salmonella. Therefore, use of coliforms as indicators needs to be assessed and related to occurrence and survival and regrowth potential of the enteric bacteria of greater public health concern. Because, 20% of the U.S. population may be considered to be in a special population category and at an increased risk of severe outcomes, no more than 20% failure of a standard should be acceptable .     

CHANGES IN EQUILIBRIUM MODULUS AND αsl-CASEIN BREAKDOWN DURING THE RIPENING OF PORT SALUT ARGENTINO CHEESE AS AFFECTED BY FROZEN STORAGE

The effect of the freezing, frozen storage and thawing on textural parameters and α_sl-casein breakdown during the ripening of Port Salut Argentino cheese was studied. Moisture content, salt concentration, casein profiles and asymptotic equilibrium modulus were monitored in control cheeses ripened at 5C and in cheeses, stored at -22C for 30 days, thawed and ripened at 5C, for different ripening times (1, 6, 13, 27 and 56 days) and two sampling zones (central and external). The freezing process significantly increased the rate of α_sl-casein and α_sl-I-casein hydrolysis. This process may affect the susceptibility of α_sl-casein to chymosin attack and also the availability of hydrolytic enzymes released by damaged microorganisms, which may contribute to the faster hydrolysis of α_sl-I-casein. The freezing process did not significantly affect the decay rates of asymptotic equilibrium modulus. First order kinetics constants for decay of the asymptotic equilibrium modulus were 3.71 10^-2day^-1 (control cheeses, central zone), 8.48 10^-2 day^-1 (control cheeses, external zone), 4.52 10^-2 day^-1 (frozen cheeses, central zone), and 11.43 10^-2 day^-1 (frozen cheeses, external zone). Significant differences in the decay rates of asymptotic equilibrium modulus were found between central and external zones in control and frozen cheeses primarily due to differences in moisture contents of the sampling zones.     

The yeast flora of stored ready-to-use carrots and their role in spoilage

Spoilage of ready-to-use grated raw carrots packaged in polymeric films and stored at 10°C was investigated for involvement of yeasts. Cryptococcus albidus was only isolated during the first 3 days of storage, increasing to levels of 10⁵–10⁶g^-1. Candida lambica was more commonly isolated after 3–7 days of storage, and reached 10⁷–10⁸g^-1 after 12 days. Candida sake was present throughout storage, increasing from 10⁵–10⁶ after 3 days to 10⁷–10⁸ after 12 days. In some samples, Candida parapsilosis and Candida tropicalis were also isolated at levels similars to C. sake . All the yeasts isolated at the end of storage were fermentative species and their metabolism was characterized with a Warburg apparatus. Neither the number of yeasts nor the composition of the yeast flora were related to the deterioration of the product. Although Candida lambica inoculated on grated carrots caused spoilage after 12 days at 10°C, the high O₂ permeable film was most effective in reducing exudate.     

Moisture diffusivities for bran and endosperm during soaking of long-grain brown rice

A three-dimensional transmission line matrix (TLM) model, using axisymmetric elements, was developed for describing moisture diffusion during the soaking of long-grain brown rice. On the basis of this model, moisture diffusivities for bran and endosperm were calculated as a function of temperature. Endosperm diffusivities of 0.92, 1.08 and 1.26X10^-10 m² s^-1 and bran diffusivities of 0.11, 0.18 and 0.37x10^-10 m² s^-1 were found, both at 30, 40 and 50°C respectively. The activation energies for moisture diffusion were calculated to be 13.08 and 49.85 kJ mol^-1 for endosperm and bran respectively.     

Modelling the deep-fat frying of beef meatballs

Mathematical models describing heat, moisture and fat transfers during deep-fat frying of beef meatballs were developed and validated against experimental data consisting of temperatures at two locations in the product, and average moisture and fat contents. Fat diffusivity in the product was 0.287 × 10^-7m²s^-1 while fat conductivity followed Eyring's model with frequency factor of 0.137 × 10^-6m s^-1 K^-1 and activation energy of 2.70 kJ mol^-1.     

High Oxygen and High Carbon Dioxide Modified Atmospheres for Shelf-life Extension of Minimally Processed Carrots

The impact of high O₂+ high CO₂ modified atmospheres (MA), on the preservation of minimally processed carrots was studied. A combination of 50% O₂+ 30% CO₂ prolonged the shelf life of sliced carrots compared to storage in air by 2 to 3 d. When the carrots received a pre-treatment with a 0.1% citric acid dip and a sodium alginate edible coating prior to packaging, shelf life was extended by 5 to 7 d. Advantages and disadvantages of the proposed MA over previously recommended MA (1% O₂+ 10% CO₂), related to a range of physicochemical and microbiological characteristics of carrots are discussed.     

MEASUREMENT OF THE HARDNESS AND MOUTHFEEL OF CHEESE USING A SLIDING PIN CONSISTOMETER

A sliding pin consistometer (SPC) was used to differentiate between six commercial cheese products, including a hard, mature Cheddar and a soft, cream cheese, at a number of temperatures in the range 0.8 to 25.0°C. Average force values (F_f) decreased with increasing temperature and with decreasing relative cheese hardness. Measurements were also made on six Cheddar cheeses with a range of salt to moisture (s/m) ratio (2.95 × 10^-2 to 5.57 × 10^-2) at a sample temperature of 16°C at maturation periods of 22, 58, 100 and 183 days. A panel of 27 adults scored the hardness and mouthfeel of these samples at these maturation periods using 9-point scoring scales. The SPC discriminated between samples and maturation periods and was more discriminating than the subjective evaluation of panelists. Mean F_f values decreased with maturation and increased linearly with increasing s/m. Panelists' hardness scores increased with s/m but were not influenced significantly by maturation. Mouthfeel increased with maturation and was a maximum at a s/m of between 4.36 × 10^-2 and 4.57 × 10^-2. The SPC provides objective information that could be useful in assessing the effect of treatment on cheese.     

Apparent diffusivities of reducing sugars in potato strips blanched in water

The mechanism of reducing sugar losses was investigated in potatoes cut into 9.5 × 9.5 mm and 13 × 13 mm strips and blanched for 300–2400s at different temperatures between 70°C and 100°C. Experiments were carried out using large amounts of well-agitated water. Assuming no chemical reaction and using appropriate solutions of the unsteady state diffusion equation for square parallelpiped geometry, the apparent diffusivities, D_a, of reducing sugars in the potato matrix were determined at different temperatures. the incorporation of the dimensions of the strips in the solution of the diffusion equation was sufficient to explain the effect of size on losses. Values of D_a were found to be in the range 1.2 × 10^-11 1.7 × 10^-11 m²s^-1 and could be correlated with temperature according to the Arrhenius law.     

Modified atmosphere packaging of shredded lettuce

A retail package system was used to study the atmosphere modification which developed within packages of shredded Iceberg lettuce, sealed in trays with a range of polymer films of different gas permeabilities (oxygen permeability of 3000 to 10,000 ml/m²/day/atm. at 25°C). Modified atmospheres were produced both naturally by respiration, and by application of gas flushing techniques.
The effects of these modified atmosphere conditions on visual and sensory quality of shredded lettuce was observed by monitoring colour change and development of off-odours. An equilibrated modified atmosphere containing 1–3% O₂ and 5–6% CO₂was established with 35 um low density polyethylene film after flushing with 5% O2, 5% CO₂ in N₂. This resulted in a shelf-life of approximately 14 days at 5°C, almost double that of the controls.     

Technical Approach to Simplify the Purification Method and Characterization of Microbial Transglutaminase Produced from Streptoverticillium ladakanum

In order to fast and economically purify MTGase from Streptoverticillium ladakanum , a stepwise elution method was developed and compared with linear gradient elution method. MTGase was purified to electrophoretical homogeneity by using CM Sepharose CL-6B and Blue Sepharose Fast Flow chromatographies by linear gradient or stepwise methods. The recovery of MTGase by linear gradient and stepwise methods were 68.4% and 81.0%, respectively. The optimal temperature and pH were 40 °C and 5.5, respectively. It was stable at pH 5.0 to 7.0 and had a rate constant (KD) of 6.21 °o 10^-5 min^-1 for thermal inactivation at 45 °C. The purified MTGase was activated by K⁺ Na⁺, Ca²⁺, Mn²⁺, and Mg²⁺, not affected by Fe³⁺, EDTA, but inhibited by Cu²⁺, Zn²⁺, Hg²⁺, Ni²⁺, Co²⁺, Cd²⁺, PCMB, NEM, IAA, and PMSF. A simple stepwise method was developed for the purification of MTGase from S. ladakanum.     

Mathematical Evaluation of Effective Moisture Diffusivity in Fresh Japanese Noodles (Udon) by Regular Regime Theory

The effect of moisture content and temperature on the effective moisture diffusivity was investigated to have the optimal drying condition of Japanese noodles (Udon) using regular regime theory. The drying of fresh Udon of different moisture contents was carried out under constant conditions of relative humidity and airflow at 20, 30, and 40 °C. The existence of regular regime periods for fresh noodles was experimentally verified. Effective moisture diffusivity obtained ranged from 2.1 × 10 ^-7 to 3.7 × 10 ^-7 cm² s^-1. The effect of temperature on effective moisture diffusivity was adequately modeled by the Arrhenius relationship, although the effect of moisture content was quite small.     

Moisture Diffusivity in Sponge Cake as Related to Porous Structure Evaluation and Moisture Content

ABSTRACT: Water diffusivity within sponge cake was determined at 5, 20, and 25 °C by identification from a water sorption kinetic and using a mathematical model based on Fick's 2nd law. Water diffusivity at 20 °C within sponge cake varied from 0.5 × 10^-10 m²/s to 7.5 × 10^-10 m²/s as a function of sponge cake moisture content. Influence of temperature on the concentration-dependent diffusivity was investigated. The activation energy was found to vary with sponge cake moisture content from 84 to 128 kj/mole. Effective diffusivity variations were correlated with the changes in microstructure of the material that was observed by using environmental scanning electron microscopy. The level of porosity in the material played a dominant role in determining the effective diffusivity.     

Changes in Phenolic Content in Fresh Ready-to-use Shredded Carrots during Storage

Phenolic compounds of shredded carrots were characterized and quantified by HPLC and their concentrations were measured during storage in air at 4°C. Trans 5′-caffeoylquinic acid amounted to 60% of total phenolic content and accumulated rapidly. Para-hydroxybenzoic acid and p-hydroxybenzoic esters were not found in freshly prepared shredded carrots and their content increased after the first day. Patterns of accumulation varied, between samples from the same carrot cultivar grown in different geographical areas. When shredded carrots were stored in polypropylene film pouches or in controlled atmospheres containing 30% CO₂ and/or 0% 0₂, phenolic compounds accumulated very slowly. The increase in phenylalanine ammonialyase activity was consistent with accumulation of phenolic compounds and may relate to microbial spoilage.     

RELEASE OF PROPYL PARABEN FROM A POLYMER COATING INTO WATER AND FOOD SIMULATING SOLVENTS FOR ANTIMICROBIAL PACKAGING APPLICATIONS

The release phenomena of propyl paraben from a polymer coating to water and three food simulating solvents (10% aqueous ethanol, 50% aqueous ethanol, n-heptane) were studied for antimicrobial packaging applications. The effects of food simulating solvent, initial concentration in the coating and temperature on the propyl paraben release were examined. The initial concentration of propyl paraben in the coating ranged from 1.26 × 10⁴ to 10.52 × 10⁴ g/m³ and the temperature from 5.5 to 30C. For water, the release was controlled by Fickian diffusion with constant diffusion coefficient (7±11 × 10^-11 cm²/s at 30C), and independent of the initial concentration. For 10% ethanol, the release followed again the Fickian model with constant diffusion coefficient (30±40 × 10^-11 cm²/s at 30C). For 50% ethanol and n-heptane, the release was instantaneous and not controlled by Fickian diffusion. For the release into water, the activation energy for diffusion from the Arrhenius relationship was around 88 kJ/mole.     

Blanching Effects on the Chemical Composition and the Cellular Distribution of Pectins in Carrots

ABSTRACT: Carrots were blanched using 4 time-temperature combinations. Galacturonic acid and sugar contents of pectin extracts were determined, and immunocytochemistry experiments elucidated changes in the cell membrane. Blanching decreased galacturonic acid and total sugar contents for all treatments. Carrots subjected to high-temperature short-time (HTST) blanching contained more total galacturonic acid and total sugars in pectins than carrots blanched for a long time at low temperatures (LTLT). Similar trends were observed for methylated pectin and neutral sugars. Immunocytochemistries showed separation of the 3-way junction of cell walls, and LTLT-blanched carrots showed higher levels of JIM 7-labeled pectin (1.6 × 10⁻⁴ particles/nm²) than HTST-treated carrots (5.9 × 10⁻⁵ particles/nm²).     

Potassium Sorbate Diffusivity in American Processed and Mozzarella Cheeses

The diffusivity of potassium sorbate in cheeses was determined by using diffusion models and computer programming for examining the residual surface concentration and the penetration of surface-applied potassium sorbate into cheese. To determine diffusivity, the concentration of potassium sorbate in sliced cheese was measured by penetration time and distance from surface. The diffusivity was calculated by nonlinear regression with experimental data based on Fick's law. The diffusivity of potassium sorbate through American processed cheese was 1.31∞10^-6 cm²/sec and for Mozzarella cheese 6.74∞10^-7 cm²/sec. This indicated that Mozzarella cheese would maintain surface concentration of potassium sorbate above the critical fungistatic level two times longer than American processed cheese.     

EFFECT OF SEVERAL EXPERIMENTAL PARAMETERS ON COMBINATION OF RED KIDNEY BEAN (PHASEOLUS VULGARIS) α-AMYLASE INHIBITOR WITH PORCINE PANCREATIC α-AMYLASE

Purified red kidney bean (Phaseolus vulgaris) amylase inhibitor forms a 1:1 stoichiometric complex with porcine pancreatic α-amylase leading to complete loss of enzyme activity on starch. Rate of complex formation is pH dependent and is maximal at pH 5. The rate constants for complex formation, as measured by loss of amylase activity, were 2.85 × 10⁴ M^-1 sec^-1 at pH 6.9 (ionic strength of 0.918) and 2.55 × 10⁵ M^-1 sec^-1 at pH 5 at 30°C. At pH 6.9, rate of complex formation was 4.8 times faster at 0.918 ionic strength as compared with the rate at 0.138 ionic strength. At 30°C, pH 6.9 and ionic strength of 0.168 the dissociation constant of the enzyme-inhibitor complex was determined to be 3.5 × 10^-11 M. The rate constant for dissociation of the complex was calculated to be 8.7 × 10^-8 sec^-1 under the same conditions. The rate constant for complex formation, at ionic strength of 0.168, was 1.1 × 10⁴ M^-1 sec^-1 at 37⁰ and 9.77 × 10² M^-1 sec^-1 at 25.7°C. The calculated activation energy for complex formation is 39.5 kcal/mole suggesting a rate-controlling conformational change. Oxidation of the carbohydrate moiety of the glycoprotein inhibitor caused complete loss of activity. Maltose, a competitive inhibitor of α-amylase, bound as readily to the enzyme-inhibitor complex as to free α-amylase. Trypsinized α-amylase, although still able to bind to Sephadex, did not bind inhibitor. The experiments with maltose and trypsinized amylase suggest the inhibitor may not bind at the active site of α-amylase.     

Isolation and characterization of polygalacturonase and invertase from a yeast Endomycopsis fibuligera (3812) bioconversion of date wastes

Properties of polygalacturonase [E.C. 3.2.1.15] (E₁) and invertase (E.C. 3.2.1.26] (E₂) isolated and purified in powdered form from Endomycopsis fibuligera grown on date wastes were measured.
The molecular weights were estimated to be about 32000 and 69500, and they were highly specific for hydrolysing (1–4) and (1–2) glycosidic links respectively. the K_m value of E₁ was 7.1 × 10^-2M for soluble-pectic acid and that for E₂ was 6.7 × 10^-2M for sucrose at pH4.5, and optimal pHs were 3.5 for E₁ and 4.0 for E₂. the purified enzymes are stable on storage for more than one year at - 20°C.     

Effect of Minimal Processing Conditions on Respiration Rate of Carrots

ABSTRACT: Measurement, analysis, and modeling of respiration rate (RR) of fresh produce are fundamental for the engineering design of MAP. This study investigates the effect of type of cutting (sliced in circular shape, batons in rectangular shape, and shredded into thin strips) on the respiration rate of carrots at different temperatures (4, 8, 12, 16, and 20 °C) with ambient atmosphere. The higher respiration rates were found for shredded carrots and the lowest for whole carrots at all the temperatures tested. The RR increased from 9 ± 1 to 26 ± 3, 10 ± 1 to 53 ± 2, 11 ± 1 to 55 ± 2, and 18 ± 1 to 75 ± 3 mL of O₂ per kilogram hour for whole, sliced, baton, and shredded carrots, respectively, as the temperature increased from 4 to 20 °C. On an average, RO₂ and RCO₂ were increased by 85% and 64%, 100% and 72%, and 151% and 124% for sliced, baton, and shredded carrots, respectively, compared to the RR values of whole carrots. The temperature dependence of RR followed an Arrhenius‐type relationship for all types of carrots, with activation energies in the range of 35 ± 3 to 62 ± 2 kJ/mol. Type of cut was the major factor for both RO₂ and RCO₂, with shredded carrots having the highest rates and whole carrots the lowest. RR of whole carrots did not vary during storage, whereas it increased for cut carrots and especially for shredded carrots. The respiratory quotient (RQ) increased with temperature and did not vary during storage in all types of carrots, except the RQ of whole carrots decreased significantly over time.