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.     

An Objective Evaluation of Changes in Firmness of Ripening Bananas Using a Sonic Technique

SUMMARY— Firmness in fruits is sometimes evaluated as being the force necessary to attain a given deformation within the product. Since modulus of elasticity is defined as the ratio of stress to strain, it should measure resistance to force and, hence, the firmness of a material. Using a sonic technique, the resonant frequencies of cylindrical specimens of flesh from Valery bananas were measured and Young's modulus of elasticity was calculated. Softening of the banana during ripening was associated with a decrease in Young's modulus of elasticity from 272 × 10⁵ dynes/cm² at ripeness corresponding to a light green peel color to 85 × 10⁵ dynes/cm² at the yellow stage. Modulus of elasticity was significantly and directly correlated with starch content, but inversely correlated with luminous reflectance and the logarithm of percent reducing sugars.     

A FRACTURE MECHANICS ANALYSIS OF THE TEXTURE OF POTATOES

The generalized fracture mechanics approach (GFM) developed by Andrews (1974) was applied to measure the fracture toughness of potatoes of the cultivar Shepody . Specimens were fashioned from the centre portions of 10 tubers, and were soaked in distilled water overnight to attain full turgor pressure in the cells. Tensile tests were performed on specimens with different initial crack lengths. The function k₁(W₀) for potatoes was evaluated. This function is an explicit distribution function of input energy in the specimen (work done on unit volume of the specimen). From the form of the function, a simple mathematical model was developed to describe k₁(W₀) for potatoes. The critical apparent energy release rate defined by GFM theory was found to be constant ( T = 2650 J m⁻²) and independent of initial crack length and applied load. The fracture toughness ( T₀ ) of Shepody potato obtained from this value of T was 212 J m⁻², which is in good agreement with the results of other researchers using uniaxial compressive and tensile tests.     

Elimination of Listeria monocytogenes in soft and red smear cheeses by irradiation with low energy electrons

Soft and red smear cheeses are frequently contaminated by Listeria monocytogenes , sometimes at relatively high concentration (< 10⁵ CFUg^-1). This bacterium is radiosensitive (D₁₀ value of approximately 0.45 kGy) but irradiation of the whole cheese by X-rays induced off-flavours when the dose exceeded 1.0 kGy. Irradiation could be effective in eliminating L. monocytogenes only from lightly contaminated cheeses (> 10²CFU g^-1).
L. monocytogenes appears only in the rind (where the pH is greater than 6.3) and never grows in the core of the cheese. Under these conditions, a specific irradiation of the rind after ripening, with a low-energy electron beam at relatively high doses (up to 3.0 kGy), allows the total elimination of L. monocytogenes in heavily contaminated samples (10⁵-10⁶ CFU g^-1) without noticeable modifications of the organoleptic properties of the cheese.     

CHARACTERIZATION OF MODEL NITROSYLHEME PIGMENTS WITH VISIBLE, INFRARED AND 15N FOURIER TRANSFORM NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

Synthetic pigments that model the organic-soluble pigment in heat-processed cured ham were characterized with infrared (IR) and ¹⁵N nuclear magnetic resonance (NMR) spectroscopy. The two pigments synthesized were ¹⁵N nitrosyl (protoporphyrinato- IX) iron (II), or Fe^II PP¹⁵ NO, and ¹⁵N dinitrosyl (protoporphyrinato-IX), or Fe^II PP(¹⁵NO)₂. An NMR spectrum was obtained only for the Fe^II PP¹⁵ NO. The NMR spectrum consisted of a single peak + 1.78 ppm from the Na¹⁵ NO³ and –6.8 from the CH₃NO₂ reference. The IR spectrum included a single NO symmetric stretch at 1801 cm⁻¹. The visible spectrum of Fe^II PPNO did not match the visible spectrum of ham extracts, while it did with FE^II PP(¹⁵NO)₂. An unequivocal structural assignment of Fe^II PP¹⁵ NO was made, but longer NMR runs may be necessary to obtain a spectrum and unequivocal structural assignment of Fe^II PP(¹⁵ NO)₂.     

PURIFICATION AND CHARACTERIZATION OF TWO TOMATO POLYGALACTURONASEISOENZYMES

The properties of tomato polygalacturonases at two ripening stages were investigated. Two isoenzymes, PG I and II, were isolated from underripe fruits with an orange skin color. Fully ripe fruits contained only polygalacturonase II. PG I and II were purified by chromatography on DEAE-Sephadex A-50, Sephacryl S-200 and CM-agarose chromatography. PG I had a M_r of 199,500 as determined by Sephacryl S-300 gel filtration and was 50% inactivated at 66.5°C and pH 4.5 after incubation for 5 min. It had an activation energy (E_a) of 16.8 Kcallmol (70.3 times 10³ Jlmol), V_max of 27.7 units/mg protein and K_m value of 7.5 times 10⁻² mM polygalacturonic acid. PG II had a M_r of 45,700 and was 50% inactivated at 58°C under the same conditions. Both isozymes had a pH optimum of 4.6. PG II had an E_a value of 14.8 Kcallmol (61.9 times 10³ Jlmol), V_max value of 58.8 units/mg protein and K_m value of 3.8 times 10⁻² mM polygalacturonic acid. PGI gave rise to only one band during electrophoresis in polyacrylamide gels, whereas PG II showed one major and one minor band both with PG activity. Gel electrophoresis in the presence of sodium dodecyl sulfate resulted in two major bands (M_r= 47,500 and 41,000) for PG I and only one major band (M_r= 47,500) for PG II. PG I is composed of several subunits, all of which are glycoproteins.     

Changes in rheological and viscoelastic properties and protein breakdown during the ripening of 'Port Salut Argentino' cheese

Changes in the rheological behaviour and viscoelastic properties during ripening at 10°C of a soft cheese (Port Salut Argentino) packaged in a plastic film (EVA-EVA) were analysed. Casein degradation was measured by electrophoresis slab gels; α_s1 casein degradation was rapid and striking compared with that of β casein. Rheological parameters obtained from uniaxial compression tests changed during ripening: hardness decreased, adhesiveness and cohesiveness increased.
An exponential decay equation with two maxwellian elements and one elastic in parallel was fitted to characterize stress relaxation curves. Viscoelastic parameters (elastic moduli and relaxation times) were obtained using non-linear regression analysis. The elastic equilibrium modulus decreased 80% during the ripening period and the viscosity of the element with the highest relaxation time decreased 20%. These parameters represented the changes observed in cheese hardness and elasticity during ageing time and were related to the extent of casein breakdown.     

APPLICATION OF CHLORINE TO REDUCE POPULATIONS OF ESCHERICHIA COLI ON BEEF

The effects of chlorine against 2 strains of E. coli attached to the surface of beef carcass tissue (BCT) were examined using a model carcass washer. Lean and adipose BCT with approximately 5 log ₁₀ CFU/cm ² E. coli bacteria were spray-treated with water and sodium hypochlorite (NaOCl) to give chlorine concentrations of 50, 100, 250, 500, or 800ppm, incubated for 24 h, 4C, and E. coli populations enumerated. Spray treatments with water did significantly (P < 0.05) reduce the bacterial populations of either organism attached to lean or adipose BCT, as compared to populations of controls; however, reductions were less than 0.60 log ₁₀ CFU/cm ². Treatments with 500 and 800 ppm chlorine against E. coli ATCC 25922 attached to BCT resulted in the greatest reductions of 1.22 and 1.28 log ₁₀ CFU/cm ², respectively. At 800 ppm chlorine , E. coli O157:H7 ATCC 43895 attached to BCT was reduced by 1.04 log ₁₀ CFU/cm ², whereas spray treatments with 50, 100, 250, and 500 ppm chlorine resulted in reductions of < 1 log ₁₀ CFU/cm ². Spray treatments with chlorine from sodium hypochlorite solutions reduced populations of E. coli, however, these reductions were not sufficient to completely inactivate the bacteria attached to red meat .     

Effect of irradiation and modified atmosphere packaging on the microbiological safety of minced pork stored under temperature abuse conditions

The safety of irradiated pork packed in 25% CO₂:75% N₂ and stored at abuse temperature (10 or 15°C) was assessed by inoculation studies involving Salmonella typhimurium, Listeria monocytogenes, Escherichia coli, Yersinia enterocolitica and Clostridium perfringens . Irradiation to a dose of 1.75 kGy reduced pathogen numbers to below the detection limit of 10² cells g^-1. When higher inoculum levels were used (10⁶ cells g^-1) irradiation at 1.75 kGy reduced pathogen numbers by 1 –>5 log₁₀ cycles depending on strain. Clostridium perfringens was the most resistant, and Y. enterocolitica the most sensitive of the pathogens studied.
In all cases when high numbers (10⁶ to 10⁷g^-1) of spoilage and/or pathogenic bacteria were present initially on the pork the meat appeared spoiled, and although irradiation reduced the number of microorganisms, the meat was still unacceptable from a sensory viewpoint after treatment.
It was concluded that the microbiological safety of irradiated, modified atmosphere packaged (MAP) pork is better than that of unirradiated MAP pork.     

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.     

Quality of Shredded Carrots as Affected by Packaging Film and Storage Temperature

ABSTRACT: Different packaging films and storage temperatures were used to establish a range of equilibrium modified atmospheres for storage of shredded carrots. Quality and storage-life of the packaged shredded carrots were determined using sensory evaluation, microbial counts, and a range of physical tests. Minimal processing steps such as peeling and shredding caused physical damage, physiological stress, and enhanced microbial growth, leading to a reduced shelf life when compared to the whole vegetable. A P-plus microporous film (CO₂ permeability of 29 X 10³mL.m ^-2.d ^-1.atm ^-1) was the most suitable for the storage of shredded carrots. Findings indicated that deterioration in these products was triggered by the depletion of oxygen more than by the rise in carbon dioxide.     

Development of a simple model based on chemical kinetics parameters for predicting respiration rate of carambola fruit

The respiration model was parameterised with experimental data obtained at temperatures 10, 15, 20, 25 and 30 °C by the closed system. Reaction orders of O₂ and CO₂ determined for respiration rate are 0.912 and −0.24, respectively. Estimates of A and E _a for rate coefficient are 5.219 _× 10¹⁰ h⁻¹ and 61.397 kJ mol⁻¹, respectively. The reliability of the model was verified against new data generated from 18 °C. An enzyme kinetics based model was likewise built and verified as a contrast. Verification results indicate that the chemical kinetics model performs very well and has superiority over the enzyme kinetics one. This study demonstrates that chemical kinetics can be used to underpin the development of simple respiration model and should facilitate the prediction of respiration rate for the carambola fruit in practice.     

A RESEARCH NOTE EFFECT OF MOISTURE CONTENT AND INITIAL THIAMIN CONCENTRATION ON THIAMIN DEGRADATION KINETICS

The degradation kinetic parameters of thiamin in a pea puree system containing 80% (w/w) and 85% (w/w) water were studied at 110, 120, and 130C for three thiamin concentrations of 50, 200 and 260 mg B₁-HCl/100 g pea puree. Both moisture content and initial thiamin concentration had no significant effect on the degradation kinetics. The degradation followed a first order reaction with an average k_121C of 0.0114 min^−1. The temperature dependence was adequately described by the Arrhenius equation. The average activation energy was 25.2 kcal/mol.     

Kinetic Parameters for Thermal Degradation of Green Asparagus Texture by Unsteady-state Method

An unsteady-state method was developed for estimating texture degradation during heating-cooling of green asparagus spears. The method used a mathematical model of heat transmission for time-temperature history estimation, and a nonlinear regression of texture measurements of asparagus spears to estimate kinetic parameters. The specific heat, conductivity and convective coefficient of green asparagus were determined experimentally and used in the mathematical model for temperature estimation. Values obtained were Ea = 76.19±0.13 kJ/mol and k_1158°C= 0.00528±0.00005 s^-1. Good agreement was found between predicted and observed texture values. The method was compared with the classical steady-state method. The mathematical model and kinetic parameters estimated could be used to design and evaluate thermal processes for green asparagus.     

MICROBIOLOGICAL STATUS OF EGYPTIAN SALTED MEAT (BASTERMA) AND FRESH SAUSAGE

The microbiological quality of 125 samples of the most popular Egyptian meat products (75 Egyptian fresh sausage "EPS" and 50 basterma) was determined. The aerobic plate count (APC) and Lactobacillaceae count of basterma ranged from 1 × 10⁴ to 9 × 10⁶ CFU/g, respectively . Enterobacteriaceae, mold and yeast counts for basterma were similar (<1 × 10² CFU/g). Artificially contaminated slices of meat and garlic paste of basterma showed that the paste inhibited growth of Salmonella typhimurium. APC and Enterobacteriaceae counts of EFS ranged from 1.1 × 10⁴ to 1 × 10⁸ and from 1 × 10² to 1 × 10⁷ CFU/g, respectively. Nearly 26% and 29% of EFS were positive for Clostridium perfringens and coagulase-positive Staphylococcus aureus, respectively . Salmonella could not be detected in any examined samples. Bacteriologically, EFS might pose a potential health hazard, making it imperative to institute sanitary measures during its production and sale .; Accepted for Publication July 2, 1997     

Microbiological study of semi-hard goat's milk cheese (Majorero)

The development of microbial flora in industrially produced semi-hard cheese made from pasteurized goat's milk was studied during manufacture and over a 90-day ripening period.
Estimates of total count, streptococci, lactobacilli, leuconostocs, coliforms, micrococci and staphylococci, Staphylococcus aureus and yeasts and moulds were carried out at various stages of the ripening process; streptococci and lactobacilli were identified by species.
Initially, the total count increased rapidly, primarily as a result of the growth of mesophilic lactic streptococci mainly Streptococcus lactis and Strep, cremoris. Subsequently, both these counts stabilized or decreased. Lactobacilli increased, and by the end of the ripening period were the predominant microorganisms. Most common were Lactobacillus casei var. casei. , especially at the end of storage; L. casei var. rhamnosus , L. casei var. plantarum and L. cellobiosus were also isolated. Leuconostocs were not found in any of the cheeses, and hence no eye formation took place. Coliforms, enterococci, yeasts and moulds remained below 10²–10³ c.f.u. g⁻¹. Maximum levels of micrococci and staphylococci were found after 15–30 days of ripening and decreased gradually towards the end of the ripening period. Neither the milk curd, nor cheese contained Staph. aureus.     

Rheological behaviour of acorn starch dispersions: effects of concentration and temperature

Rheological properties of acorn starch dispersions at different concentrations (4%, 5%, 6% and 7%) were evaluated under steady and dynamic shear conditions. The flow behaviours of the acorn starch dispersions at different temperatures (25, 40, 55 and 70 °C) were determined from the rheological parameters provided by the power law model. The acorn starch dispersions at 25 °C exhibited high shear-thinning fluid characteristics ( n  = 0.23–0.36). Consistency index (K) and apparent viscosity (η_a,100) increased with an increase in starch concentration, and were also reduced with increasing temperature. Within the temperature range of 25–70 °C, the η_a,100 obeyed the Arrhenius temperature relationship with a high determination coefficient ( R ² = 0.97–0.99), with activation energies (E_a) ranging between 16.5 and 19.0 kJ mol⁻¹. Both the power law and exponential type models were employed in order to establish the relationship between concentration and apparent viscosity (η_a,100) in the temperature range of 25–70 °C. Magnitudes of storage ( G' ) and loss ( G ") moduli increased with an increase in the starch concentration and frequency (ω). The magnitudes of G ' were higher than those of G " over most of the frequency range (0.63–62.8 rad s⁻¹). The dynamic (η*) and steady shear (η_a) viscosities of acorn starch dispersion at 7% concentration follow the Cox–Merz superposition rule.     

EVALUATION OF THE HOLE PRESSURE METHOD TO MEASURE THE FIRST NORMAL STRESS DIFFERENCE OF CORN MEAL DOUGH DURING EXTRUSION COOKING

Rheological properties of food dough melt, such as steady shear viscosity (η) and first normal stress difference (N₁), were measured using an in-line slit die rheometer attached to a laboratory model single-screw extruder. The flow rate through the rheometer was varied by altering the screw speed. Alternatively, a sidestream valve, to vary the flow rate through the rheometer at fixed screw speed, was also used to obtain rheological data. The slit die rheometer was tested with corn meal at three different experimental conditions: 25% and 35% moisture contents at 180C barrel temperature and 35% moisture content at 150C barrel temperature. N₁ was measured using the hole-pressure and exit-pressure method. Exit pressure measurements were found to be erratic and unreliable. Hole pressure increased monotonically with increasing flow rate and was found to be affected by the processing history. The magnitude of the hole pressure ranged between 2% and 21% of pressure of the flush mounted transducer. For the experimental conditions used in this study, N₁ ranged from 3 × 10⁴ to 6 × 10⁵ Pa for shear rates between 30 to 400 s⁻¹. Possible sources of errors in the hole pressure measurements are discussed.     

Exogenous Polyamines and Gibberellic Acid Effects on Peach (Prunus persica L.) Storability Improvement

Peaches ( Prunus persica L., cv. Babygold 6) harvested at the stage of commercial ripening were pressure-infiltrated with putrescine (1 mM) or GA₃ (100 mg L^-1) and then stored at 2°C for 14 d. Both treatments increased fruit firmness, putrescine-treated peaches being significantly firmer than control ones. Treatments were also effective in reducing the susceptibility of the fruit to be damaged by mechanically compression with lower volume and surface of the damage zone. Ethylene emission and the respiration rate were reduced in treated fruits, which reflects a delay of the ripening process. The effects of the mechanical stress could be related to increased spermidine levels, rather than ethylene emission and respiration rate during storage.     

Adhesion modeling on rough low linear density polyethylene

ABSTRACT:  Food adhesion is an important attribute that could have both positive and negative ramifications depending on the application. Yet, its quantification remains cumbersome and as a consequence adhesion models are scarce. The effect of surface roughness, free energy, and ozone treatment on adhesion of rough low linear density polyethylene films was investigated. Adhesion was measured by a 180° peel strength test. The plastic films were roughened (surface roughness ratio, r , ranged from 1.00 to 1.15). Exposing the film to ozone treatment (0 to 300 s) modified its surface free energy, γ _s (32.4 to 37.9 mJ/m², respectively), and its polar component of the surface free energy, γ ^p _s (3.0 to 8.3 mJ/m², respectively). The films were coated with polyurethane capable of forming hydrogen bonds. Adhesion was found to be a function of the apparent contact angle of water, θ _{ap [water]}, surface roughness ratio, and surface free energy. The linear relationship between the apparent contact angle of water, θ _{ap [water]}, and γ ^p _s was incorporated in building an empirical model that quantifies peel strength as function of r and γ ^p _s . The model showed good agreement with experimental data, especially for longer ozone exposures and rougher surfaces. The empirical model provides insight into the relationships between surface roughness, surface energy, and adhesion. Quantifying these effects could facilitate reducing biofilm forming on food equipment, antisticking treatments, or easy peel packages, or reducing food residues adhering to the food packages and consequently minimize oxidation, off flavors, and waste.