KINETICS AND HYDROLYSIS PARAMETERS OF TOTAL FRUCTOOLIGOSACCHARIDES OF ONION BULBS: EFFECTS OF TEMPERATURE REGIMES AND CULTIVARS

This work studied the percentage of hydrolysis, observed hydrolysis rate constant (k_obs), half‐life time (t_1/2) and kinetics of degradation of the total fructooligosaccharides (FOS) of three different onion bulb cultivars (Yellow Spanish, Red Amposta and Tenshin) kept during 6 months under three temperature regimes, 10, 15 and 20C. The percentage of hydrolysis of FOS was higher at 20C than at 10C and ranged from 47 to 58% at 10C, from 63 to 68% at 15C and from 74 to 83% at 20C. The k_obs ranged from 27 × 10^?3 to 36 × 10^?3/week at 10C and from 41 × 10^?3/week to 47 × 10^?3/week at 15C, while at 20C, it was high and was about k_obs 56 × 10^?3/week.. The t_1/2 decreased when temperature increased, and varied from 19.5 to 26.0 weeks at 10C, from 14.6 to 16.8 weeks at 15C and from 9.4 to 12.3 weeks at 20C, indicating that high degree of polymerization (DP) FOS have shorter lives than low DP FOS. Linear regression and kinetics of hydrolysis have shown that FOS hydrolysis is higher at 20C, with a coefficient of regression ranging between 0.87 and 0.99. Apparently, FOS hydrolysis is temperature independent, and storage time had more effect on the higher DP FOS than on the lower DP FOS.     

SODIUM BICARBONATE AND THE MICROSTRUCTURE, EXPANSION AND COLOR OF EXTRUDED BLACK BEANS

Seed microstructure provides complementary information to physicochemical determinations. Scanning electron micrographs of cross sections of black bean extrudates illustrated the increase in volume expansion, with an increase of sodium bicarbonate (NaHCO ₃ ) in the extrudate. This increase in volume expansion is attributed to the increase in air cell size and corresponding decrease in air cell wall thickness with additional concentrations of NaHCO ₃ . The measured increase in diameter and expansion ratio of extrudates with NaHCO ₃ addition may be explained by the increase in number of air cells within the extrudate and the increase in pores in the gelatinized starch matrix of air cell walls. Extrusion conditions, which involved the use of heat and moisture, provided the necessary conditions for the release of CO ₂ from NaHCO ₃ during processing. Expansion ratio increases between the control extrudate, and extrudate with 0.5% NaHCO ₃ addition were twofold at the node and 1.8‐fold at the area between the nodes. Statistical analysis of color data exhibited no significant change in L*, hue or chroma across concentrations of NaHCO ₃ for nonextruded flours. A simple linear regression adequately described changes in L* and hue for extruded flours. However, a curvilinear relationship was needed to explain changes in chroma versus NaHCO ₃ for extruded flours, making changes in chroma measurements less easy to interpret. The color data in this study serve as primary information for future establishment of cut‐off values of color for the development of an acceptable legume snack.     

VITAMIN AND SELENIUM CONTENT OF RIBEYE CUTS FROM GRASS- AND GRAIN-FINISHED BISON OF THE SAME HERD

Individual ribeye cuts from 10 grass‐ and 8 grain‐finished bulls of the same herd were analyzed for vitamin and selenium content. Vitamin A, vitamin E, thiamin, vitamin B₆, vitamin B₁₂ and selenium concentrations of ribeye cuts from grass‐ and grain‐finished bulls were similar. Vitamin C and folic acid levels were not detectable in ribeyes from both groups. Ribeyes from grass‐finished bulls contained significantly higher quantities of β‐carotene (P < 0.0005) and niacin (P < 0.01) and significantly lower (P < 0.0001) quantities of riboflavin than those from grain‐finished bulls. Bison ribeyes from both groups were rich sources (>20% Daily Values) of vitamin B₁₂ and selenium and good sources (10–19% Daily Values) of thiamin, niacin and vitamin B₆.     

SPATIAL DISTRIBUTION OF POPULATION OF LISTERIA MONOCYTOGENES DURING MANUFACTURING AND RIPENING OF CAMEMBERT CHEESE

The spatial distribution of the survival and growth of Listeria monocytogenes during manufacturing and ripening of Camembert cheese was studied. All cheeses were artificially inoculated with L. monocytogenes and ripened in three stages: room temperature (～20C) and relative humidity (RH) of 60% for 36 h, 13C and RH of 93% for 2 weeks, and 7C and RH of 85% for 3 weeks. During ripening, different locations were analyzed for population of L. monocytogenes. The data were collected on days 1, 5, 10, 15, 20, 25, 30 and 35 of ripening. Results showed that the population of L. monocytogenes on day 1 was 6.06 log₁₀ cfu/g, which was 1.96 log₁₀ cfu/g increasing over the initial inoculation of 4.08 log₁₀ cfu/g. For the subsequent 20 days, the L. monocytogenes population declined to 5.33 log₁₀ cfu/g. Thereafter, the L. monocytogenes population increased to 6.07 log₁₀ cfu/g on day 35 of ripening. Generally, the growth of L. monocytogenes is faster in locations near the surface than in the center. There were no significant differences between batches and sections of cheese, whereas the ripening time and locations had a significant effect on the survival and growth of L. monocytogenes. The survival and growth data for L. monocytogenes during ripening of Camembert cheese can be used to develop dynamic predictive models for possible use in risk assessment and Hazard Analysis and Critical Control Point implementation.     

APPLICATION OF WLF AND ARRHENIUS KINETICS TO RHEOLOGY OF SELECTED DARK-COLORED HONEY

The rheological properties of Common Black Horehound, Globe Thistle, and Squill types of dark‐colored Jordanian honey were examined. The types of honey used were identified via assessing the source of nectar using pollen analysis (Melissopalynology). The apparent viscosity, η, was measured as a function of the shear rate, γ. In addition, the apparent viscosity was measured, at constant shear rate (6.12 s^?1), as a function of shearing time. Newton's law of viscosity (i.e., τ=ηγ) was found to adequately (R²～ 0.99) describe the flow behavior of honey samples. The apparent viscosity was found to decrease with temperature, and the temperature dependence of viscosity was contrasted versus both Arrhenius model (η=η_oe^Ea/RT) and WLF model (η/η_G= 10 (C₁(T–T)/C₂+(T–T_G))). Although Arrhenius kinetics may fit the viscosity versus temperature data for the examined types of honey, nevertheless, it gives a relatively high value of activation energy that is quite comparable with, if not even larger than, that of a typical chemical reaction. On the other hand, WLF‐model was found to adequately describe the data while at the same time it gives quite reasonable values of both T_G and η_G, which are in agreement with those cited in literature.     

EFFECT OF pH ON ANTIOXIDATIVE ACTIVITY AND OTHER CHARACTERISTICS OF CARAMELIZATION PRODUCTS

Antioxidative activity and other characteristics of caramelization products (CPs) from fructose or glucose solutions prepared at pHs ranging from 7.0 to 12.0 with heating at 100C for various times (0–180 min) were investigated. The degradation of both sugars increased with increasing pH levels and heating time (P < 0.05). The intermediate degradation products and browning intensity also increased when pH and heating time increased (P < 0.05) as evidenced by the increase in A₂₇₀, A₂₈₅ and A₄₂₀, respectively. The reducing power and 2–2‐diphenyl‐1‐picrylhydrazyl radical scavenging activity of CPs were coincidental with the browning development and the intermediate formation. Generally, CPs from fructose showed greater antioxidative activity as shown by the higher reducing power and scavenging effect than CPs from glucose. Therefore, CPs from both sugars with pronounced antioxidative activity can be prepared by heating fructose or glucose solutions at very alkaline pH for an extended time.     

PURIFICATION AND CHARACTERIZATION OF A CATALASE FROM THE LIVER OF BULLFROG, RANA CATESBEIANA SHAW

A catalase was purified from the liver of bullfrog, Rana catesbeiana Shaw, after extraction, ammonium sulfate precipitations, DEAE‐Sephadex A‐50 chromatography, gel filtration chromatography on a Sephadex G‐150 column, ion exchange chromatography on a DEAE‐Sephacel column and Sephacryl S‐300 column. The yield and purification from the starting crude extract were 0.25% and 73.57‐fold, respectively. The purified catalase with an apparent molecular mass of 186 kDa was shown to be composed of four identical subunits of apparent molecular mass of 47.7 kDa. The purified catalase is active over a broad pH range of 6.0–10.0, and it has an isoelectric point of 6.3. The enzyme showed a K_mfor H₂O₂of 20 mM and an apparent V_maxof 51.91 U/mg, and its maximum absorption was at 408 nm in the visible portion of the spectrum. In addition, the purified enzyme was markedly inhibited by azide, cyanide and hydroxylamine.     

REGULATION OF PHENYLALANINE AMMONIA-LYASE ENZYME IN ANNONA FRUIT: KINETIC CHARACTERISTICS AND INHIBITORY EFFECT OF AMMONIA

In this work, we analyzed the kinetic properties of phenylalanine ammonia‐lyase (PAL) extracted from “cherimoya” (Annona cherimola Mill.) fruits ripened at ambient temperature (20C) and stored under several environmental conditions, including high CO₂ levels (20%) and low temperature (6C). The effect of different ammonia‐related compounds on cherimoya PAL activity was also evaluated. PAL exhibited two different K_mvalues for L‐phenylalanine (L‐Phe ) and negative substrate cooperativity, with Hill coefficient (n_app) values reaching 0.64 and 0.71 for low temperature and high CO₂ levels, respectively. The kinetic analysis revealed that ammonia produced mixed inhibition of PAL enzyme, with inhibition constants (K_i and K_i′) values of 0.57 ± 0.2 mM and 2.54 ± 0.2 mM. We propose that the regulation of PAL by ammonia inhibition and the negative cooperativity may be essential in adjusting the active phenylpropanoid metabolism in Annonas to the requirement of L‐Phe and in consequence, to the carbon skeleton demand for other anabolic pathways.     

ISOLATION AND IDENTIFICATION OF A NOVEL ASPERGILLUS JAPONICUS JN19 PRODUCING β-FRUCTOFURANOSIDASE AND CHARACTERIZATION OF THE ENZYME

A novel strain, Aspergillus sp. JN19, producingβ‐fructofuranosidase (FFase), was isolated from soil. According to the physiological and biochemical characteristics and its 18S rDNA gene sequence analysis, it was identified as Aspergillus japonicus. The optimal conditions for production of fructofuranosidase by A. japonicus JN‐19 were investigated. The initial concentration of sucrose was 15 to 18%. Yeast extract was the best nitrogen source. K₂HPO₄ was effective in increasing enzyme production. The enzyme activity was increased to about 1.3 times by addition of 0.2% carboxymethylcellulose in the medium. The highest FFase activity was 55.42 U/mL at pH 5.5 and 30C, and production yield of fructooligosaccharides was 55.8%. Some characteristics of purified FFase were also studied.     

PURIFICATION AND PROPERTIES OF TRYPSIN-LIKE ENZYMES AND A CARBOXYPEPTIDASE A FROM EUPHAUSIA SUPERBA

ABSTRACT Five proteases designated as A_1, A_2, B, C and D were isolated from Euphausia superba by the succesive steps of ammonium sulfate fractionation, acetone precipitation, gel filtration and DEAE-Sephadex A-50 chromatography, A_1, B, C and D were purified to homogeneity in disc gel electrophoresis by means of rechromatography on the DEAE-Sephadex A-50 column. Studies on substrate specificity of these enzymes revealed that A_2, B, C and D were trypsin-like enzymes and A₁ a carboxypeptidase A. A_1, B, C and D had molecular weights of about 24,000, 24,000 28,000 and 27,000; optimal pH at 9.0, 8.0, 7.5 and 7.5–8. 0; and optimal temperature at 48, 50, 55–60 and 55°C, respectively. The activity of B, C and D were not inhibited by sulfhydryl reagents and N-α-tosyl-L-phenylalanylchloro-methyl ketone, but inhibited by reducing agents, N-α-tosyl-L-lysylchloromethyl ketone and soybean trypsin inhibitor. The activity of protease A₁ was stimulated 3.5 fold by cobalt, but inhibited by 3-indolepropionate and D-phenylalanine.     

INFLUENCE OF SAMPLE SIZE AND SHAPE ON TRANSPORT PARAMETERS DURING DRYING OF SHRINKING BODIES

An experimental investigation on the influence of sample size and shape on heat and mass transport parameters under natural convection air‐drying is presented. Potato cylinders with length of 0.05 m and thicknesses of 0.005, 0.008, 0.010 and 0.016 m, and circular slices with diameter of 0.05 m and thickness of 0.01 m were dried in a laboratory scale hot‐air cabinet dryer. Results indicate that each transport parameter exhibits a linear relationship with sample thickness. Convective heat and mass transfer coefficients (h_cand h_m) decreased whereas moisture diffusion coefficient (D_eff) increased with increasing thickness. Considering no sample shrinkage effect in the parameter analysis, for the thickness range considered, the values of h_care found to be underestimated in the range of 29.0–30.6%, whereas those of h_mand D_eff are overestimated in the range of 33.7–38.0% and 75.9–128.1%, respectively. Using Levenberg–Marquardt algorithm for optimization, a correlation for Biot number for mass transfer (Bi_m) as a function of drying time and sample thickness is proposed. A close agreement was observed between dimensionless moisture contents predicted by this relation and those obtained from experiments for different sample thicknesses at drying air temperature of 60C. For the same thickness and drying conditions, circular slices caused an increase in each transport parameter significantly.     

31—THE EFFECT OF VARIABILITY OF FIBRE DIAMETER ON WORSTED PROCESSING. PART II. THE USE OF COMPARISON SAMPLES OF COMMERCIAL TOPS AND THEIR BLENDS

Changes in the coefficient of variation of fibre diameter (V _d ) were made by blending top qualities (a) 70s and 56s, and (b) 60s and 56s, and comparing these with a 58s. In this way, a range of values of V _d from 21.4 to 24.9% was obtained over three top samples whose mean fibre diameters and fibre lengths were closely similar. These tops were worsted-spun to determine their performance at the spinning limit and other yarn counts and to measure the yarn properties. The three samples did not give any important differences in chemical composition or in spinning limit, but did show a trend to significant differences in yarn breaking strength and elongation, the lower-V _d sample being favoured. Over this range of values of V _d at mean diameters of 25–26 μm, although there are hints of slight differences in spinning and in the product, the trend is not important. The range of V _d values for European tops of mean fibre diameter 25.3 μm appears to lie between 22 and 28%. The Australian tops investigated gave V _d values over the lower half of this range.     

A PHYSICO-CHEMICAL STUDY OF THE MECHANICAL PROPERTIES OF LOW AND INTERMEDIATE MOISTURE FOODS*

A number of textural properties of precooked, freeze-dried beef were examined by a cutting-extrusion test (force) and by a compression test (seven different properties). The tests were performed at different points of the moisture sorption isotherm over the complete range of water activity, A_w. In cutting-extrusion experiments (Allo Kramer Shear Press), a maximum in the force vs. A_w curve was observed at about A_w= 0.85. In compression experiments (Instron Universal Testing Apparatus), important changes of the textural properties were found in the range A_w= 0.15–0.30. These changes were paralleled by changes in the thermodynamic functions of water vapor sorption, especially in the standard differential entropy. Thermodynamic theory and mechanical measurements were used to interpret the textural changes in terms of increased crystallinity and subsequent swelling of the food structure.     

17—QUANTITATIVE ANALYSES OF WEFT-KNITTED STRUCTURES PART IV: THE DETERMINATION OF THE MAGNITUDES OF B1, B2, AND B3 AND THE EXTENSION OF THE WORK TO GENERAL MULTI-COLOUR-JACQUARD STRUCTURES

The optimum design of experiment for the determination of the magnitudes of the component units of the weft-knitted jacquard structures, B ₁, B ₂, and B ₃, is discussed in detail. Some experimental results are reported. The prediction accuracy of using the technique of independent distinct units (IDU), by means of a suggested optimum experiment, proved to be very satisfactory in predicting the length of yarn of one design repeat of an arbitrary two-colour-jacquard example. The extension of the work to general multi-colour-jacquard structures is given.     

PURIFICATION AND CHARACTERIZATION OF AN ENDOPEPTIDASE FROM PSEUDOMONAS FLUORESCENS ATCC 948

Intracellular, ca 55 kDa monomeric endopeptidase (PsPepO) from Pseudomonas fluorescens ATCC 948 was purified to homogeneity by chromatography on Q-Sepharose, Sephacryl 200, Phenyl-Superose and Mono Q. It was strongly inhibited by the metalloproteinase inhibitor, 1,10 phenanthroline and by dithiothreitol, but less strongly by EDTA; it was stimulated by Co²⁺. Activity was optimal at pH 7.0 and 40–45C, with considerable activity at pH 5.0 and 12C. The enzyme was relatively heat-stable with a D_80Cvalue of 1.2 min. It did not hydrolyze α_s1-, β-or κ-casein (CN) and peptides with less than 5 amino acids but readily hydrolyzed α_s1-CNfl-23, α_s1-CN f157-164, α_s1-CN f165-199 and various β-CN fragments and peptide hormones. On α_s1-CN fl-23, α_s1-CN f165-199, insulin B-chain and bradykinin, it mainly catalyzed the hydrolysis of peptide bonds in which a hydrophobic amino acid (most commonly Phe or Leu) residue occupied the P'₁position. β-CN f193- or 194-209, which are the source of bitter peptides in cheese ripening, were hydrolyzed slowly or not at all. β-CN fragments from the sequence 58-70 were degraded or did not inhibit the endopeptidase activity as well as β-CN f193-209. The characteristics of the endopeptidase of Ps. fluorescens ATCC 948 were compared with those of lactococcal endopeptidases.     

IN VITRO SURVIVAL AT LOW pH AND ACID ADAPTATION RESPONSE OF CAMPYLOBACTER JEJUNI AND CAMPYLOBACTER COLI

The survival of Campylobacter jejuni and Campylobacter coli at pH 7.0, 6.0, 5.0 and 4.0 for up to 24 h, and the induction of an acid adaptation response in 12 C. jejuni and 10 C. coli strains in early exponential or late stationary phases in tryptic soy broth (TSB) and Brucella broth were investigated. C. coli strains were more sensitive than C. jejuni in media adjusted to pH 5.0 or 4.0 with hydrochloric acid. Five log₁₀ cfu/mL of C. coli were inhibited at 12 h in pH 5.0, but only 2.5 log₁₀ cfu/mL of C. jejuni cells were inhibited under the same conditions. No viable cells were detected at 4 h in pH 4.0 from an inoculum of 6 log₁₀ cfu/mL of C. coli. Late stationary phase cells of C. jejuni exposed to pH 5.0 for 4 h in TSB exhibited a significant (P ≤ 0.05) acid tolerance response when compared to nonexposed cells. Late stationary phase cells of C. coli exposed to pH 5.0 for 3 h in TSB and late stationary and early exponential phase cells exposed to pH 5.0 for 3 h in Brucella broth showed a significant (P ≤ 0.05) acid tolerance response when compared to nonexposed cells. The acid tolerance responses observed for C. jejuni and C. coli conferred adapted cells no more than 1 log₁₀ cfu/mL survival advantage over nonadapted cells. Brucella broth appeared to be more protective than TSB for the survival of C. jejuni and C. coli at pH 4.0.     

INACTIVATION OF LISTERIA MONOCYTOGENES, SALMONELLA ENTERITIDIS AND ESCHERICHIA COLI O157:H7 AND SHELF LIFE EXTENSION OF FRESH-CUT PEARS USING MALIC ACID AND QUALITY STABILIZING COMPOUNDS

ABSTRACT

Inactivation of Listeria monocytogenes, Salmonella enteritidis and Escherichia coli O157:H7 and shelf life extension of fresh‐cut pears using malic acid (MA) and quality stabilizing compounds (N‐acetyl‐L‐cysteine, glutathione and calcium lactate; CGLW) were investigated. Trays of treated fresh‐cut pears were wrap sealed with a thick polypropylene film (64 µm) semipermeable to water vapor, O₂ and CO₂, and stored at 5C for 30 days. Changes in headspace gas, firmness and color of the fresh‐cut pears were also determined. Large reductions of L. monocytogenes (6.57 log₁₀ cfu/g), S. enteritidis (6.60 log₁₀ cfu/g) and E. coli O157:H7 (2.62 log₁₀ cfu/g) just after processing were achieved in those fresh‐cut pears dipped in CGLW + MA. Microbiological shelf life of pear pieces dipped in CGLW + MA was extended by more than 21 days in comparison with those cut pears immersed in water used as control sample. Lower consumption of O₂ and production of CO₂, ethylene and ethanol of fresh‐cut pears dipped in CGLW + MA were also observed. In addition, the color and firmness of pear pieces in CGLW + MA were maintained by more than 21 days in comparison with control samples. In conclusion, the combination of MA with quality stabilizing compounds can be a good alternative for assuring the safety and quality of fresh‐cut pears.

PRACTICAL APPLICATIONS

The use of natural substances generally recognized as safe (GRAS) such as malic acid and N‐acetyl‐L‐cysteine, glutathione and calcium lactate as antimicrobials and quality stabilizing compounds, respectively, can result suitable to fresh‐cut products industry, since they can assure the safety and quality of those products, while improving their sensory attributes and maintaining the fresh‐like and healthy properties of these products greatly demanded by the consumers.     

THERMAL INACTIVATION OF SALMONELLA ENTERITIDIS BY BOILING AND FRYING EGG METHODS

Salmonella enteritidis was cultivated in egg yolks and submitted to boiling and frying methods commonly used in domestic conditions in the south of Brazil. The results have demonstrated a rapid growth of the microorganism reaching counts of 9.0 log₁₀at 168 h. When contaminated shell eggs were placed in water and slowly heated, a population of approximately 7.0 log₁₀was completely inactivated after boiling for 1 min. However, in eggs placed directly in boiling water, the reduction was only 1.35 log₁₀after 1 min, and the entire population was eliminated after 3 min. A reduction of approximately 2.78 log₁₀was observed after frying for 1.5, 2.0 and 2.5 min. Even though the solidification of yolk has been pointed out as an indicator of S. enteritidis elimination in egg yolks, attention should be given to frying procedures, as considerable high levels of this microorganism could be recovered even from solidified yolks.     

FATTY ACIDS AND ESTERS PRODUCED DURING THE SPONTANEOUS FERMENTATION OF LAMBIC AND GUEUZE

Lambic and gueuze are Belgian beers obtained by spontaneous fermentation of wort. During previous studies it was found that they result from the successive development of enterobacteria, Kloeckera and Saccharomyces yeasts, bacteria of the genus Pediococcus, and Brettanomyces yeasts. The beers are characterized by high concentrations of acetic and lactic acid, ethyl acetate and ethyl lactate. This study of the content of the higher fatty acids during a 20 month fermentation period confirms the succession of the different micro-organisms. Pure cultures of isolated yeasts and bacteria produced fatty acids which were also found in the fermenting wort at periods when these organisms were active. Lambic and Gueuze are especially rich in caprylic (C₈) and capric (C₁₀) acids. These are probably produced by Saccharomyces and Brettanomyces. Important amounts of ethyl caprylate and ethyl caprate were also found. As ethyl caprate is almost absent in other beers, it might be considered as another typical aroma component of lambic and gueuze.     

THERMAL INACTIVATION KINETICS OF ALKALINE PHOSPHATASE IN BUFFER AND MILK

A detailed kinetic study on the thermal inactivation of alkaline phosphatase (ALP) added into buffer and pasteurized milk and for ALP naturally present in raw cow's milk has been performed. Kinetic parameters (rate constant, k; decimal reduction time, D; activation energy, E_a; and z value) were evaluated based on the first‐order rate model at 50–80C. The temperature sensitivity of the kinetic parameters was evaluated considering the Arrhenius‐type E_a model. All kinetic behaviors were well described by the first‐order model (r² > 0.91). The D values increased with increasing temperature. Higher temperatures resulted in higher rates of enzyme inactivation as indicated by lower D values and higher k values. There are significant differences (P < 0.01) among the D values for ALP in buffer and milk at treated temperatures. The rate of enzyme inactivation was much more rapid in buffer than in pasteurized milk. The evaluated E_a values for ALP added into the buffer and pasteurized milk, and for ALP naturally present in raw milk were 97.2, 149.9 and 207.8 kJ/mol, respectively. The inactivation kinetics of ALP during heat treatment was found to be dependent on the composition of the medium, and the time and temperature of the heat treatment.