Biochemical and thermal characterization of crude exo-polygalacturonase produced by Aspergillus sojae

Crude exo-polygalacturonase enzyme (produced by Aspergillus sojae), significant for industrial processes, was characterized with respect to its biochemical and thermal properties. The optimum pH and temperature for maximum crude exo-polygalacturonase activity were pH 5 and 55 °C, respectively. It retained 60–70% of its activity over a broad pH range and 80% of its initial activity at 65 °C for 1 h. The thermal stability study indicated an inactivation energy of E_d = 152 kJ mol⁻¹. The half lives at 75 and 85 °C were estimated as 3.6 and 1.02 h, respectively. Thermodynamic parameters, ΔH^*, ΔS^* and ΔG^*, were determined as a function of temperature. The kinetic constants K_m and V_max, using polygalacturonic acid as substrate, were determined as 0.424 g l⁻¹ and 80 μmol min⁻¹, respectively. SDS-PAGE profiling revealed three major bands with molecular weights of 36, 53 and 68 kDa. This enzyme can be considered as a potential candidate in various applications of waste treatment, in food, paper and textile industries.     

Migration of α-tocopherol from an active multilayer film into whole milk powder

Antioxidant active packaging is a promising technology for whole milk powder (WMP) protection. In this study, the migration of α-tocopherol from a multilayer active packaging (made of high density polyethylene, ethylene vinyl alcohol and a layer of low density polyethylene containing the antioxidant) to WMP was studied. A model based on the Fick’s diffusion equation was used to calculate the diffusion coefficients (D) of α-tocopherol as 2.34 × 10⁻¹¹, 3.06 × 10⁻¹¹, and 3.14 × 10⁻¹¹ cm² s⁻¹ at 20, 30 and 40 °C, respectively. The D at 20 °C was different from those at 30 and 40 °C (P < 0.05); but it was similar at 30 and 40 °C. This low influence of temperature on the migration of α-tocopherol from 20 to 40 °C assures the release at real storage and commercialization conditions in regions with warm/hot climate. The antioxidant delivering system delayed the lipid oxidation of WMP and it was more effective at 30 and 40 °C since the rate of oxidative reactions was higher at these temperatures than at 20 °C.     

Environmental factors affect efficacy of some essential oils and resveratrol to control growth and ochratoxin A production by Penicillium verrucosum and Aspergillus westerdijkiae on wheat grain

This study determined the efficacy of three essential oils (bay, clove and cinnamon oil) and the antioxidant resveratrol (0–500 μg g⁻¹) on the control of growth and ochratoxin A (OTA) production by Penicillium verrucosum and Aspergillus westerdijkiae (=A. ochraceus) under different water activity (a_w, 0.90, 0.95, 0.995), and temperature (15, 25 °C) conditions on irradiated wheat grain. The most effective treatment (resveratrol) was then tested on natural grain. The ED₅₀ values for growth inhibition by the oils were 200–300 μg g⁻¹ at the a_w and the temperatures tested. For resveratrol, this varied from <50 μg g⁻¹ at 0.90–0.95 a_w to >350 at 0.995a_w at both temperatures. The ED₅₀ values for the control of OTA were slightly lower than for control of growth, with approx. 200 μg g⁻¹ required for the oils and 50–100 μg g⁻¹ of the antioxidant, at 0.90/0.95a_w and both temperatures. In wet grain (0.995a_w), higher concentrations were required. For growth there were statistically significant effects of single-, two- and three-way interactions between treatments except for concentration×temperature and concentration×temperature×essential oil/antioxidant treatment. For OTA control, statistically significant treatments were a_w, temperature×a_w, concentration×temperature, treatment×concentration, and three-way interaction of concentration×a_w×treatment for P. verrucosum and A. westerdijkiae. Subsequent studies were done with the best treatment (resveratrol, 200 μg g⁻¹) on natural wheat grain with either P. verrucosum or A. westerdijkiae at 0.85–0.995a_w and 15/25 °C over 28 days storage. This showed that the populations of the mycotoxigenic species and OTA contamination could be reduced by >60% by this treatment at the end of the storage period.     

Effect of heat and thermosonication treatments on watercress (Nasturtium officinale) vitamin C degradation kinetics

The use of ultrasound in food processing creates novel and interesting methodologies, which are often complementary to classical techniques. In this work, the effect of heat and the combined treatment heat/ultrasound (thermosonication) on the thermal degradation kinetics of vitamin C in watercress (Nasturtium officinale) was studied in the temperature range of 82.5 to 92.5 °C. First order reaction kinetics adequately described the vitamin C losses during both blanching processes.The activation energies and the reaction rates at 87.5 °C for heat (H) and thermosonication (Ts) treatments were, respectively, E_avitCH = 150.47 ± 42.81 kJ mol^− 1 and E_avitCTs = 136.20 ± 60.97 kJ mol^− 1, and k_{87.5 °CvitCH} = 0.75 ± 0.10 min^− 1 and k_{87.5 °CvitCTs} = 0.58 ± 0.11 min^− 1. No significant differences (P > 0.05) were detected between both treatments. The thermosonication treatment was found to be a better blanching process, since it inactivates watercress peroxidase at less severe blanching conditions and consequently retains vitamin C content at higher levels. The present findings will help to optimise the blanching conditions for the production of a new and healthy frozen product, watercress, with heat and a new blanching process methodology.

Industrial relevance

Thermosonication blanching can be useful since it reduces processing times, and consequently minimizes the adverse effects of heating on watercress quality. This new application will provide good material, in terms of vitamin C, for further processes, and can be an excellent alternative to the traditional heat treatment.     

Sensory shelf life determination of a processed meat product ‘rullepølse’ and microbial metabolites as potential indicators

Sensory profiling was performed for a Danish lightly fermented heat-processed cold cut pork product termed ‘rullepølse’. Product samples were stored under modified atmosphere (MAP, 30% CO₂/70% N₂) for 0, 28 and 34 days and with subsequent aerobic storage for 4 days (MAP–OPEN) at temperatures of 4 °C and 8 °C. Microbial growth and metabolism was also measured with a focus on lactic acid bacteria (LAB) and their organic acid metabolites including lactic acid, acetic acid and α-ketoisocaproic acid. These acids were examined for sensory shelf life indexing potential for the ‘rullepølse’. Storage temperature exerted distinct impacts on the sensory characterised shelf life of ‘rullepølse’ stored under MAP and MAP–OPEN conditions. The MAP stored ‘rullepølse’ with subsequent 4 days storage in air (MAP–OPEN) could be stored for at least 28 days at 4 °C without a decrease in the sensory quality when opened. Whilst MAP stored ‘rullepølse’ at 8 °C with subsequent open storage (MAP–OPEN), compared to the lower temperature displayed a reduced shelf life of less than 28 days if sensory quality of the ‘rullepølse’ was to be maintained. The stage of sensory deterioration was correlated with high bacterial counts exceeding 10⁶ CFU g⁻¹. With respect to indexing ability of the examined organic acids none were found to have clear potential for prediction of the sensory deterioration.     

Rheological behavior of aqueous dispersions of cashew gum and gum arabic: effect of concentration and blending

Rheological properties of cashew gum (CG) and gum arabic (AR), the exudate polysaccharides from Anacardium occidentale L. and Acacia, at different solutions (0.4–50% w/v) were studied. The intrinsic viscosity, [η], of CG in water at 20°C was ≈0.1 dl g⁻¹, while that of AR was ≈0.6 dl g⁻¹. The apparent viscosity of the unheated and the heated (at 80°C for 30 min) CG and AR solutions showed a progressive increase with increasing concentration. The flow curves of blends with equal viscosity solutions of AR/CG: 25/75, 50/50 and 75/25, showed no major interaction. The apparent viscosity (η_a) vs. shear rate data for both the AR and CG dispersions (4–50% w/v) exhibited shear-thinning characteristics at low shear rates (< about 10 s⁻¹) and Newtonian plateaus at shear rates >100 s⁻¹, and the Sisko model described well the η_a vs. data of all the dispersions.     

Release and identification of angiotensin-converting enzyme-inhibitory peptides as influenced by ripening temperatures and probiotic adjuncts in Cheddar cheeses

The aim of the study was to examine the release of angiotensin-converting enzyme (ACE)-inhibitory peptides in Cheddar cheeses made with starter lactococci and Bifidobacterium longum 1941, B. animalis subsp. lactis LAFTI^® B94, Lactobacillus casei 279, Lb. casei LAFTI^® L26, Lb. acidophilus 4962 or Lb. acidophilusLAFTI^® L10 during ripening at 4 and 8 °C for 24 weeks. ACE-inhibitory activity of the cheeses was maximum at 24 weeks. Cheeses made with the addition of Lb. casei 279, Lb. casei LAFTI^® L26 or Lb. acidophilus LAFTI^® L10 had significantly higher (P < 0.05) ACE-inhibitory activity than those without any probiotic adjunct after 24 weeks at 4 and 8 °C. The IC₅₀ of cheeses ripened at 4 °C was not significantly different (P > 0.05) to that ripened at 8 °C. The lowest value of the IC₅₀ (0.13 mg mL⁻¹) and therefore the highest ACE-inhibitory activity corresponded to the cheese with the addition of Lb. acidophilus LAFTI^® L10. Several ACE-inhibitory peptides were identified as κ-CN (f 96–102), α_s1-CN (f 1–9), α_s1-CN (f 1–7), α_s1-CN (f 1–6), α_s1-CN (f 24–32) and β-CN (f 193–209). Most of the ACE-inhibitory peptides accumulated at the early stage of ripening, and as proteolysis proceeded, some of the peptides were hydrolyzed into smaller peptides.     

Inactivation of Escherichia coli O157:H7 on surface-uninjured and -injured green pepper (Capsicum annuum L.) by chlorine dioxide gas as demonstrated by confocal laser scanning microscopy

Cells of Escherichia coli O157:H7 on uninjured and injured surfaces of green pepper were inactivated by 0·15–1·2 mg l⁻¹ClO₂gas treatments. A membrane-surface-plating method was used for resuscitation and enumeration of E. coli O157:H7 treated with ClO₂. The location and viability ofE. coli O157:H7 on uninjured and injured green pepper surfaces after ClO₂gas treatments were visualized using confocal laser scanning microscopy (CLSM). Live and dead cells of E. coli O157:H7 on pepper surfaces were labeled with a fluorescein isothiocyanate-labeled antibody and propidium iodide, respectively. A 7·27 log reduction of E. coli O157:H7 on uninjured green pepper surfaces was obtained with a 0·60 mg l⁻¹ClO₂gas treatment for 30 min at 20°C under 90–95% relative humidity. For injured surfaces, a 6·45 log reduction was achieved with a 1·2 mg l⁻¹ClO₂gas treatment. Each ClO₂gas treatment (0·15–1·2 mg l⁻¹ClO₂) for inoculated bacteria on uninjured surfaces showed significantly more reductions (1·23–4·24 log) than for those on injured surfaces (P<0·05). The microphotographs of CLSM showed that bacteria preferentially attached to injured surfaces and those bacteria could be protected from bacterial reduction by the injuries. This study indicates that ClO₂gas treatment can be a potential effective method of pathogen reduction for fresh fruits and vegetables.     

Effect of temperature on the life cycle of Aleuroglyphus ovatus (Acari: Acaridae) at four constant temperatures

The effect of four constant temperatures (20, 24, 28 and 32 °C) on the physiological properties (survival, developmental time, sex ratio, fecundity and longevity of females), and population growth of Aleuroglyphus ovatus was examined in the laboratory at 85% relative humidity. The total developmental time, longevity and oviposition period of A. ovatus shortened as temperature increased. The shortest developmental time (14.70 ± 0.34 days) was obtained at 32 °C. At 20, 24, 28 and 32 °C, mated females laid on average 0.87 ± 0.10, 2.57 ± 0.13, 3.14 ± 0.27 and 1.29 ± 0.16 eggs per day, respectively. Maximum fecundity was recorded at 28 °C with 70.83 ± 10.16 eggs per female. The highest intrinsic rate of increase (r_m) was found to be 0.16 at 28 °C.     

Influence of freeze-drying conditions on survival of Oenococcus oeni for malolactic fermentation

Malolactic fermentation (MLF) is an important process in wine production. Oenococcus oeni is most often responsible for MLF. Starter culture technology, involving the inoculation of O. oeni into wines, has been developed for inducing MLF. In this study, the effects of cell washing, pH of suspension medium, preincubation in sodium glutamate, initial cell concentration and freezing temperature on viability of freeze-dried O. oeni H-2 were investigated. The cell viability of samples without washing with potassium phosphate buffer was significantly lower than those samples undergone washing. When pH of suspension medium was 7.0 the cell survival was the highest. The cell viability was enhanced when the cells were preincubated at 25 °C before freezing. When 2.5% sodium glutamate was used as protective agent in suspension medium, the optimal initial cell concentration was 10⁹ CFU/ml. The cell viability increased by 21.6% as freezing temperature decreased from − 20 °C to − 65 °C. However, when the cells were frozen in liquid nitrogen (− 196 °C), the cell survival significantly decreased.     

Modeling within the Bayesian framework, the inactivation of pectinesterase in gazpacho by pulsed electric fields

The inactivation of pectinesterase (PE) activity in gazpacho (a Spanish ready-to-use cold vegetable soup) under pulsed electric fields (PEFs) was studied. Samples were exposed to 4 μs monopolar or bipolar square-wave pulses at 5–35 kV cm⁻¹ electric field intensity for up to 1500 μs and 200 Hz (temperature below 40 °C). Inactivation of PE was greater when treatment time and electric field intensity increased, and bipolar pulses were more effective inactivating PE than monopolar ones. Estimation of parameters and quantities involved in the tested models were performed within the Bayesian framework. The kinetic evolution of the enzyme was explained using a 3-parameter biexponential model based on a mechanism involving two irreversible consecutive steps. Rate constant k₁ was not dependent on neither electric field intensity nor pulse polarity. Rate constant k₂ and ratio between the activities of intermediate forms and the native ones of the enzyme Λ were affected by those conditions.     

Supercritical fluid extraction of β-carotene from crude palm oil using CO2

The aim of this study was to ascertain the influence of pressure, temperature and time on the supercritical fluid extraction of β-carotene from the crude palm oil. The operating conditions were shown as follows: pressures of 75, 125 and 175 bar, temperatures of 80, 100 and 120 °C and extraction time of 1, 3 and 5 h. The extracts were analyzed using UV spectroscopy at a wavelength of 450 nm. Then the experimental data was compared with the data obtained using a statistical method. The results from the model showed a good agreement with the experimental data. The results (obtained from the statistical model) demonstrate that a pressure of 140 bar, temperature of 102 °C and extraction time of 3.14 h are required to obtain optimum yield of β-carotene (1.028 × 10⁻²%) from the extraction process, however the maximum yield of the β-carotene (1.741 × 10⁻²%) was experimentally obtained at a pressure of 75 bar, temperature of 120 °C and extraction time of 1 h.     

Effect of surface-active stabilizers on the surface properties of coconut milk emulsions

Previously we have demonstrated improved stability of coconut milk emulsions homogenized with various surface-active stabilizers, i.e., 1 wt% sodium caseinate, whey protein isolate (WPI), sodium dodecyl sulfate (SDS), or polyoxyethylene sorbitan monolaurate (Tween 20) [Tangsuphoom, N., & Coupland, J. N. (2008). Effect of surface-active stabilizers on the microstructure and stability of coconut milk emulsions. Food Hydrocolloids, 22(7), 1233–1242]. This study examines the changes in bulk and microstructural properties of those emulsions following thermal treatments normally used to preserve coconut milk products (i.e., −20 °C, −10 °C, 5 °C, 70 °C, 90 °C, and 120 °C). Calorimetric methods were used to determine the destabilization of emulsions and the denaturation of coconut and surface-active proteins. Homogenized coconut milk prepared without additives was destabilized by freeze–thaw, (−20 °C and −10 °C) but not by chilling (5 °C). Samples homogenized with proteins were not affected by low temperature treatments while those prepared with surfactants were stable to chilling but partially or fully coalesced following freeze–thaw. Homogenized coconut milk prepared without additives coalesced and flocculated after being heated at 90 °C or 120 °C for 1 h in due to the denaturation and subsequent aggregation of coconut proteins. Samples emulsified with caseinate were not affected by heat treatments while those prepared with WPI showed extensive coalescence and phase separation after being treated at 90 °C or 120 °C. Samples prepared with SDS were stable to heating but those prepared with Tween 20 completely destabilized by heating at 120 °C.     

Associative and segregative interactions between gelatin and low-methoxy pectin: Part 2—co-gelation in the presence of Ca

The effect of segregative interactions with gelatin (type B; pI=4.9; 0–10 wt%) on the networks formed by low-methoxy pectin on cooling in the presence of stoichiometric Ca²⁺ at pH 3.9 has been investigated by rheological measurements under low-amplitude oscillatory shear. Samples were prepared and loaded at 85 °C, cooled (1 °C/min) to 5 °C, held for 100 min, and re-heated (1 °C/min) to 85 °C, with measurement of storage and loss moduli (G′ and G″) at 10 rad s⁻¹ and 2% strain. The final values of G′ at 5 °C for mixtures prepared at the same pH without Ca²⁺ were virtually identical to those observed for the same concentrations (0.5–10.0 wt%) of gelatin alone, consistent with the conclusion from the preceding paper that electrostatic (associative) interactions between the two polymers become significant only at pH values below 3.9. Increases in moduli on cooling in the presence of Ca²⁺ occurred in two discrete steps, the first coincident with gelation of calcium pectinate alone and the second with gelation of gelatin. Both processes were fully reversible on heating, but displaced to higher temperature (by 10 °C), as was also observed for the individual components. The magnitude of the changes occurring over the temperature range of the gelatin sol–gel and gel–sol transitions demonstrates that the gelatin component forms a continuous network; survival of gel structure after completion of gelatin melting shows that the calcium pectinate network is also continuous (i.e. that the co-gel is bicontinuous). On progressive incorporation of NaCl (to induce phase separation before, or during, pectin gelation) the second melting process, coincident with loss of calcium pectinate gel structure, was progressively abolished, indicating conversion to a gelatin-continuous network with dispersed particles of calcium pectinate. These qualitative conclusions are supported by quantitative analyses reported in the following paper.     

Enumeration, isolation and characterization of Bacillus cereus strains from Spanish raw rice

Bacillus cereus was present in 61 samples of raw rice analysed representing unhusked, husked and commercial origins. B. cereus in husked and white rice samples did not reach 10² cfu g⁻¹, while in the unhusked rice B. cereus densities exceeded 10³ cfu g⁻¹. Processing steps such as drying, husking and polishing reduced the number of B. cereus in the final product. Eight strains with typical morphology of B. cereus on Polymyxin–Mannitol–Egg Yolk–Phenol Red Agar (PMYPA) were isolated. According to ISO confirmatory tests, the API System tests and supplementary tests of motility, oxidase activity and enterotoxin production, these isolates were characterized and identified as B. cereus. All strains were motile, oxidase-negative and produced diarrheal enterotoxin in TSB. D and z -values were used to characterize heat resistance of spores obtained from the eight strains ofB. cereus characterized. A large diversity in heat resistance was observed among the isolates. At 90°C, D -values ranged from 2·23 to 23·26 min, with five groups of D -value means significantly different at the 95% confidence level. D₉₅- and D₁₀₀ values calculated for the eight strains ranged from 0·69 to 5·17 min and from 0·43 to 1·09 min, respectively. Statistical analysis revealed that there was significant difference between the D -value means obtained for the strains at each temperature. The z -values for the eight strains of B. cereus tested in this study ranged from 7·42°C to 8·20°C with an average of 7·7°C.     

On the stability of oil-in-water emulsions to freezing

Oil in water emulsions (40 wt%) were prepared from a homologous series of n-alkanes (C10–C18). The samples were temperature cycled in a differential scanning calorimeter (two cycles of 40 °C to −50 °C to 40 °C at 5 °C min⁻¹) and in bulk (to −20 °C). The emulsions destabilized and phase-separated after freeze–thaw if the droplets were solid at the same time as the continuous phase and were more unstable if a small molecule (SDS or polyoxyethylene sorbitan monolaurate) rather than a protein (whey protein isolate or sodium caseinate) emulsifier was used. The unstable emulsions formed a self-supporting cryo-gel that persisted between the melting of the water and the melting of the hydrocarbon phase. Microscopy provides further evidence of a hydrocarbon continuous network formed during freezing by a mechanism related to partial coalescence which collapses during lipid melting to allow phase separation.     

Acceleration of soluble matter extraction from chicory with pulsed electric fields

This work discusses effects of thermal and PEF treatments on efficiency of soluble solids extraction from chicory tissues. The effects of temperature, PEF electric field strength and time of treatment on damage degree and acceleration of the soluble matter extraction kinetics are discussed. The PEF treatment with field strength 100–600 V/cm, treatment time 10⁻³–50 s, and temperature 20–80 °C, was applied. The activation energy of usual thermal damage was rather high (W_τ ≈ 263 kJ/mol), however, it can be noticeably reduced to W_τ = 30–40 kJ/mol by application of PEF treatment. The moderate electric energy consumption (U < 10 kJ/kg) at room temperatures demands application of relatively high electric field strength (400–600 V/cm), however, the value of U noticeably decreases with temperature increase. The benefits of PEF application for enhancement of the soluble matter extraction from chicory were demonstrated. The PEF-pretreatment noticeably accelerated diffusion even at low temperatures within 20–40 °С. Proposed technique appears to be promising for future industrial applications of “cold” soluble matter extraction from chicory roots.     

Inhibitory effect of clove oil on Listeria monocytogenes in meat and cheese

The antilisteric activity of clove oil was examined in meat and cheese at both 30°C and 7°C. At concentrations of 0·5% and 1% clove oil restricted the growth of Listeria monocytogenes in the food items at both temperatures. The inhibitory activity of clove oil was more pronounced at a concentration of 1%.Listeria counts in treated samples were 1–3 log₁₀cfu g⁻¹less compared to controls at different intervals during storage. The results revealed the potential of clove oil as a natural preservative in meat and cheese.     

Effect of lactic acid on Listeria monocytogenes and Edwardsiella tarda attached to catfish skin

This study evaluated the use of lactic acid to decontaminate Listeria monocytogenes andEdwardsiella tarda attached to catfish skin with or without mucus. At the highest inoculum levels (10⁴–10⁵cfu skin⁻¹), lactic acid (0·5–2·0%) exposure for 10 min reduced counts of L. monocytogenes firmly attached to catfish skin by 0·9–>1·9 log₁₀cfu skin⁻¹and cells loosely attached by 2·7–>3·7 logs. Counts of E. tarda firmly attached to catfish skin were reduced by 0·9–>3·0 logs and cells loosely attached by 1·5–>3·5 logs. Overall bacterial numbers of lactic acid-treated cells that were firmly attached to skin with mucus were higher than on skin without mucus. Firmly attached L. monocytogenes was more resistant to lactic acid than was firmly attached E. tarda. Catfish skin mucus decreased the antimicrobial effect of lactic acid against attached L. monocytogenes and E. tarda.     

Inhibition of Clostridium sporogenes growth in mascarpone cheese by co-inoculation with Streptococcus thermophilus under conditions of temperature abuse

The ability of a biological control system to inhibit the outgrowth of Clostridium sporogenes spores during storage of mascarpone cheese under temperature-abuse conditions was investigated. Challenge studies were carried out on mascarpone cheese artificially contaminated with spores of C. sporogenes (10 cfu g⁻¹), and with or without the coinoculum of a Streptococcus thermophilus strain (10⁵cfu g⁻¹). During storage at 4, 12, and 25°C, the outgrowth of clostridia spores, the growth of S. thermophilus, and the pH changes were evaluated at 10, 20, 30, and 40 days. In mascarpone cheese stored at 4° and 12°C, S. thermophilus and C. sporogenes did not show any growth. The initial pH (6·14) of the product also remained unchanged. During storage at 25°C S. thermophilus grew up to about 10⁷cfu g⁻¹after 10 days, resulting in a pH decrease of mascarpone cheese to values close to 4·5. The cell number decreased progressively during storage reaching values near to 10¹cfu g⁻¹after 40 days, whereas product acidity remained constant. C. sporogenes, when inoculated alone, also grew at 25°C. The cell number increased to levels of about 10⁷cfu g⁻¹after 20–40 days of storage according to the different mascarpone cheese lots used. No growth was found when C. sporogenes was co-inoculated in mascarpone cheese with S. thermophilus and stored at 25°C. The study on the behaviour of C. sporogenes, known as a non-toxigenic variant of Clostridium botulinum, allowed us to obtain useful information for setting up an effective biological control system to inhibit growth of the toxigenic species as well. The use of an additional barrier, besides refrigerated storage, may help to maintain the safety of mascarpone cheese in the event it was exposed to elevated temperatures.