The effects of Ca ions, EGTA and storage time on myofibrillar protein degradation, levels of Ca(2+)-dependent proteases and cathepsins B, H, L and D of ostrich skeletal muscle

The effect of Ca ions and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) on myofibrillar protein degradation showed that when ostrich iliotibialis lateralis muscle was incubated with 10 mM EGTA at 2–4 °C for 24 hr, the activity of extracted cathepsin H was unchanged compared with a buffer-incubated sample. Ca⁺⁺ had no effect on extracted cathepsin H activity, while that of Ca²⁺-dependent protease (CDP) decreased significantly (p < 0.05). Ca²⁺-treatment enhanced post-mortem changes observed in myofibrillar protein patterns (production of fragments around 30 K) that were not observed in EGTA-incubated myofibrils. The effect of storage time on shear force, CDP activity, cathepsin B, D, H and L activities and the SDS-PAGE pattern of myofibrils showed a time-dependent reduction in CDP activity. Of the cathepsins studied only cathepsin H showed a reduction (40%) in activity. The most prominent component appearing on storage at 2–4 °C had a M_r of 27 K. The incubation of myofibrils with CDP mimicked the post-mortem changes. CDP may be responsible for some of the post-mortem changes observed, although shear force measurements suggest these changes do not lead to significant tenderisation.     

Determination of bromate in bread additives and flours by flow injection analysis

A new, simple, rapid and sensitive spectrophotometric flow injection analysis (FIA) method was developed for the determination of bromate based on its reaction with 3,5-dibromo-PADAP and thiocyanate in a strongly acidic medium. This produced an unstable violet product with a maximum absorption at 602 nm. The calibration curve was linear in the range of 2.00×10⁻⁶–2.10×10⁻⁵ mol/l and the detection limit was 8.00×10⁻⁷ mol/l. The sampling frequency was 90 h⁻¹. The method has been successfully applied to the determination of bromate in commercial bread additives and flours.     

Effect of curing salt and phosphate on the activity of porcine muscle proteases

The effect of curing salt on the activity of porcine muscle proteases was evaluated, within the salt concentration range found in the manufacturing process of Spanish cured ham. Salt (NaCl) acts as a strong inhibitor of proteolytic activity; sodium nitrate and potassium nitrate do not affect cathepsin D activity; cathepsin L is inhibited at levels of the salts not found in cured ham, and Ca-dependent proteolytic activity is enhanced by nitrate concentrations below 800 ppm.

The appearance of phosphate precipitates in several areas of ham has led to the study of phosphate effect on enzymatic activity. Results show that phosphate is an inhibitor of proteolytic activity.     

Effect of nitric oxide on ethylene production in strawberry fruit during storage

Strawberry is a non-climacteric fruit, with low ethylene production rate after harvest. Its response to nitric oxide (NO), which can be released from sodium nitroprusside (SNP), was studied. We have examined the effect of 1.0, 5.0 and 10.0 μmol l⁻¹ SNP aqueous solution on ethylene production, respiration rate, 1-aminocyclopropane-1-carboxylic acid (ACC) content and the activities of ACC synthase and ACC oxidase in post-harvest strawberry (“Fengxiang”). The most remarkable effect was obtained with 5 μmol l⁻¹ SNP aqueous solution, which significantly inhibited ethylene production, respiration rate, the activity of ACC synthase and reduced the content of ACC, but did not significantly affect the activity of ACC oxidase. SNP at 10 μmol l⁻¹ harmed the fruits; 1 μmol l⁻¹ SNP was too low to significantly extend strawberry storage life. It was suggested that NO could decrease ethylene output, through inhibiting ACC synthase activity reducing ACC content.     

Effect of pretreatment and temperature on air-drying of Dioscorea alata and Dioscorea rotundata slices

Effects of pretreatment and drying conditions on yam varieties, namely Dioscorea alata and Dioscorea rotundata, in a fabricated laboratory scale hot air drier at temperature range of 50–80 °C and constant air velocity of 1.5 m²/s were investigated. Mass transfer during air-drying of yam slices was described using Fick’s diffusion model. Drying took place entirely in the falling rate period. Temperature dependency of moisture on diffusivity was illustrated by the Arrhenius relationship. Over the range of temperature, moisture diffusivities varied from 9.92 × 10⁻⁸ to 1.02 × 10⁻⁷ and 0.829 × 10⁻⁶ to 1.298 × 10⁻⁵ m²/s for D. alata and D. rotundata, respectively. Activation energy for drying of D. alata and D. rotundata varied from 25.25 to 46.46 and 41.75 to 72.47 kJ/mol, respectively.     

Prediction of moisture transfer parameters for microwave drying of lactose powder using Bi–G drying correlation

The mass transport properties characterising the drying of lactose powder were determined using a correlation proposed by Dincer and Hussain [Dincer, I. & Hussain, M. M. (2004). Development of a new Bi–Di correlation for solids drying. International Journal of Heat and Mass Transfer, 47, 653–658]. Experimental moisture content data for lactose samples dried under convective, microwave, combined convective-microwave and combined vacuum-microwave conditions were collected. The drying coefficients and lag factors were calculated from the experimental data and incorporated into the model. The Bi numbers were in the range 0.185–439, and moisture diffusivities and diffusion coefficients in the range from 0.135 × 10⁻⁹ to 102 × 10⁻⁹ and from 0.194 × 10⁻⁶ to 118 × 10⁻⁶ m/s, respectively. The predicted moisture profiles showed adequate agreement with the experimental observations, with the average error between experimental and predicted results being ±13.7%.     

Diffusion of thiocyanate and hypothiocyanite in whey protein films incorporating the lactoperoxidase system

The diffusion of the thiocyanate (SCN⁻) and hypothiocyanite (OSCN⁻) components of a lactoperoxidase system (LPOS) in whey protein isolate (WPI) films was investigated. Diffusion coefficients for these molecules were measured for the LPOS-incorporated WPI films prepared with different WPI:glycerol ratios (1:1, 3:1, and 5:1). WPI film disks were coated on the surfaces of smoked salmon samples, and the samples were stored at 4, 10 and 22 °C. The diffusion coefficients were determined by fitting a mathematical model to the amounts of SCN⁻ and OSCN⁻ released from the disks during a period of time. The diffusion coefficients for SCN⁻ (D₁) and OSCN⁻ (D₂) in the films were 0.19–5.2 × 10⁻¹² m² s⁻¹ and 0.13–6.5 × 10⁻¹³ m² s⁻¹, respectively. The D₁ and D₂ decreased as the WPI:glycerol ratio increased and the storage temperature decreased. The E_a values for diffusion in 1:1, 3:1, and 5:1 WPI:glycerol films were 13.3, 29.5, and 35.6 kJmol⁻¹, respectively, for SCN⁻ and 15.8, 30.1, and 39.9 kJmol⁻¹, respectively, for OSCN⁻.     

Effect of Chemical and Physical Dry-curing Parameters on Cathepsins B, H and L from Ostrich Muscle

The effects of curing agents (NaCl, nitrate, ascorbic acid and glucose) and processing parameters (pH, temperature and cooking temperatures) on cathepsins B, H and L activities were investigated. NaCl, nitrate, ascorbic acid and glucose exhibited different influences on ostrich cathepsin B, B+L and H activities. In the range 20-60gl(-1), NaCl inhibited cathepsin B+L and H activities. All three cysteine proteinase activities were inhibited by up to 8g ascorbic acid l(-1). With the exception of cathepsin B activity, which was inhibited by glucose, nitrate and glucose had very little effect on cathepsin B, B+L and H activities. Cathepsins B and D were active at 65 and 69°C and might play an important degradative role during the cooking of meat and meat products. Cathepsins B, B+L and H were optimally active at temperatures of 40-45°C and 50°C, and were still quite active at the low temperatures used in the dry-curing process; they showed maximum activity in the pH range 5·5-7. A simulation of the three stages of the dry-curing process of hams revealed that cathepsins B and B+L might play an important role throughout the complete process, whereas cathepsin H could only participate in the middle and at the end of the dry-curing process. Although ostrich cathepsins show many properties similar to those from other species, the present study also revealed some interesting distinguishing features.     

Modelling the mass transfer during convective, microwave and combined microwave-convective drying of solid slabs and cylinders

In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient, of slab and cylindrical potato samples were evaluated by adopting the analytical model proposed by Dincer and Dost [Drying Technology, 13,1/2 (1995), 425]. As part of the experimental work, the moisture contents of slab and cylindrical potato samples dried under convective, microwave and combined convective–microwave conditions (air temperature, 30–60 °C; air velocity, 1–2 ms⁻¹; microwave output power, 30–650 W) were measured. From the data collected the drying coefficients and lag factors were calculated and incorporated into the model. The results showed a reasonably good agreement between the values predicted from the correlation and the experimental observations; average error between experimental and predicted results less that 10%. The experimental system exhibited mass transfer Bi numbers in the range 0.038–11.4, thus indicating the presence of finite internal and external resistances. Moisture diffusivity values in the range 0.13×10⁻⁸ to 24.22×10⁻⁸ m²s⁻¹ were calculated.     

Uniaxial compression of Swiss-type cheese at different strain rates

Rheological behaviour of 48 Swiss-type cheese samples in lubricated uniaxial compression was evaluated at three initial strain rates ranging from 4·76 × 10⁻³ to 7·62 × 10⁻² s⁻¹. Modulus, apparent fracture stress and apparent fracture strain increased significantly with increasing strain rate, which is attributed to the viscoelastic nature of cheese. The influence of strain rate on apparent fracture strain strongly depended on the shape of the stress-strain curves. The relationship between the rheological parameters evaluated at different strain rates proved to be significant. The strain rate dependency of the apparent fracture strain is further explained by the contribution of elastic and viscous components, which was evaluated in relaxation experiments in the linear viscoelastic region.     

Determination of flavonoids and ascorbic acid in grapefruit peel and juice by capillary electrophoresis with electrochemical detection

Grapefruit (Citrus paradisi Mact. (Rutaceae)) has been known for its accumulation of flavonoids and ascorbic acid. These contents are important because of their nutritional and antioxidant properties. Five flavonoids (hesperidin, naringin, hesperedin, narigenin and rutin) and ascorbic acid were separated and determined in grapefruit juice by capillary electrophoresis with electrochemistry detection (CE-ED). Two flavonoids (hesperidin, naringin) and ascorbic acid were found in extract of grapefruit peel with the same method. And the distribution comparision of the ingredients between juice and peel was discussed. The effects of several CE parameters on the resolution were studied systematically. Under the optimum conditions, the analytes could be well separated within 25 min in a 60 mmol L⁻¹ borate buffer (pH 9.0). The response was linear over four orders of magnitude with detection limits (S/N = 3) ranging from 1.4 × 10⁻⁷ to 1.0 × 10⁻⁶ g ml⁻¹ for the analytes. The method has been successfully applied for the analysis of grapefruit with satisfactory results.     

Effect of vapors from fractionated samples of propolis on microbial and oxidation damage of rice during storage

The efficacy of vapors from polar and non-polar sub-fractions of propolis on microbial and oxidation control during rice (Oryza sativa, hinohikari var.) storage was evaluated. The sub-fractions (absolute ethanol, methylene chloride, hexane extracts: AEPEV, MCPEV and HEPEV, respectively) were infused in synthetic adsorbents and their volatiles released during storage (6 months). HEPEV, MCPEV and AEPEV treatments inhibited molding and post-inoculation bacterial colonization (1.1, 1.1, 0.9 and 1.3, 1.2, 1.1 log₁₀ cfu/g reductions, respectively) on brown rice. AEPEV treatment suppressed fat acidity damage of milled rice at 30 °C to conventional cold storage level (5 °C) and differential Gram staining of bacteria isolated after the treatment indicated a dominant Gram-positive bacterial distribution. The concentrations providing 50% inhibition of 2′,2′-diphenylpicrylhydrazyl free radical scavenging were 9.8, 3.2 and 2.8 μg/μl for hexane (HEPE), absolute ethanol (AEPE) and methylene chloride (MCPE) extracts, respectively. The oxidative degradation rate was lowest for AEPE (4.3 × 10⁻⁴ min⁻¹) and highest for HEPE (1.9 × 10⁻³ min⁻¹) in the β-carotene bleaching assay. Gas chromatograph mass spectrometry revealed that AEPE had the highest amount of caffeic acid and caffeic acid phenethyl ester. Ultimately, the volatiles from the propolis sub-fractions had varied potential in rice quality preservation.     

Influence of various preservatives on the quality of minced beef under modified atmosphere at chilled storage

The effect of preservatives on microbial quality, pH, drip-loss, roasting-loss, colour, and sensorial properties of modified atmosphere packaged (70% O₂ and 30% CO₂) minced beef (M. semimembranosus) stored at (2 ± 0.5 °C) for 12 days was investigated. Beef cubes (approx. 20 × 20 × 20 mm size) were immersed in solutions of 2% and 5% lactic acid, 2% lactic acid combined with 0.5% sodium ascorbate, 20% potassium lactate and 20% potassium sorbate before mincing. Addition of lactic acid was associated with pH drop, which increased drip-loss and roasting-loss. Application of all additives inhibited aerobic micro-organisms (10³–10⁴ CFU g⁻¹ on day 12) compared to reference sample (9 × 10⁵ CFU g⁻¹ on day 12). Lactic acid discoloured samples, while sodium ascorbate seemed to improve colour stability. Despite good visual colour characteristics, potassium sorbate treated samples were organoleptically unacceptable with massive off-flavour.     

Total and soluble contents of calcium, magnesium, phosphorus and zinc in yoghurts

This paper examines the content of major minerals (calcium, magnesium, phosphorus and zinc) and its distribution between soluble (non-sedimentable) and micellar fractions of 16 commercial yoghurts from five different branches. These elements were determined by atomic absorption spectrometry after mineralisation by dry ashing. Total mineral contents showed wide intervals of variation (calcium 1090–2050 mg l⁻¹, magnesium 101–177 mg l⁻¹, phosphorus 878–1560 mg l⁻¹ and zinc 4.0–7.3 mg l⁻¹) due to the addition during manufacturing of different dairy products or fractions. Most of the minerals were found in the non-sedimentable fraction. Practically all calcium was measured in the supernatants of ultracentrifugation. Lower proportions of magnesium and zinc were determined in the non-sedimentable fraction (between 87 and 96%) whereas the lowest ones (63–77%) were found for phosphorus.     

Relationship between nitrate/nitrite reductase activities in meat associated staphylococci and nitrosylmyoglobin formation in a cured meat model system

Quantitative determination of catalase, nitrate reductase, nitrite reductase and nitric oxide synthase activities (NOS) was performed on 11 different bacterial strains, mainly staphylococci, isolated from fermented sausages, bacon brine or cured meat products. All except one strain possessed catalase activity in the range from 1.0 to 6.1 μmol min^− 1 ml^− 1. Ten out of 11 bacteria strains showed nitrate reductase activity in the range between 50 and 796 nmol min^− 1 ml^− 1 and nine showed nitrite reductase activity in the range between 6 and 42 nmol min^− 1 ml^− 1. No evidence of NOS activity of the selected strains was detected. In a colour formation assay containing myoglobin all strains affected nitrosylmyoglobin (MbFe^IINO) formation in assays containing nitrite, whereas only strains having nitrate reductase activity generated MbFe^IINO in assays containing nitrate as the sole nitrosylating agent. The quantitative nitrate and nitrite reductase activity did not fully explain or correlate well with the observed rate of formation of MbFe^IINO, which seemed to be more affected by the growth rate of the different strains. The mechanism of the reduction of nitrite into NO of strains not having nitrite reductase activity remains to be fully elucidated, but could be due to a dual-mode action of nitrate reductase capable of acting on nitrate.     

Levels of heavy metals in candy packages and candies likely to be consumed by small children

Ninety two samples of child-consumed candies and candy packages were analyzed for seven heavy metals. Lead (Pb) was detected at concentrations of 110.3–6394.1 mg kg⁻¹ in ten of 92 candy packages. The directive factor of Pb contamination had originated in the lead-based ink of the outer cover. Particularly, Pb was detected at high concentrations in case of green- or yellow-colored packages. Chromium (Cr) was detected at high concentrations in cases where Pb was also detected at high concentrations, and the Cr levels ranged from 136.9 mg kg⁻¹ to 1429.3 mg kg⁻¹ in seven of the 92 candy packages. Hexavalent chromium [Cr(VI)] was detected at 87–105.0% of the total Cr in polypropylene-coated wrappers with printed outer covers. The migration of Cr(VI) increased with elution time up to 0.20 μg (cm²)⁻¹ for 30 days in basic (pH 10.0) solution; however, there were no migrations in acidic (pH 4.0) and neutral (pH 7.0) solutions. The migration of Pb increased with elution time up to 0.65 μg (cm²)⁻¹ and 0.28 μg (cm²)⁻¹ in basic (pH 10.0) and acidic (pH 4.0) solutions, respectively. However, any migration was hardly observed in neutral (pH 7.0) solution.     

A flow-injection spectrophotometric method for nitrate and nitrite determination through nitric oxide generation

A flow injection method with novel spectrophotometric detection for the determination of nitrite and nitrate in foodstuffs is presented. The method is based on the reduction of nitrite and nitrate to nitric oxide, with subsequent reaction with iron (II) and thiocyanate in an acid medium, forming FeSCNNO⁺. The absorbance of the complex, with a maximum at 460 nm, is proportional to the nitrite and nitrate concentrations. The NO is generated in two stages: (1) reduction of nitrate to nitrite in a cadmium copper reductor column and (2) reduction of the nitrite to NO in a sulfuric acid medium. The influence of reagent concentrations and manifold parameters were evaluated. Nitrite and nitrate can be determined in the range of 0.30–3.00 and 1.00–10.00 mg l⁻¹, respectively. The sampling rate of analyses was 30–40 h⁻¹ and, considering a sample of 5.0 g, the determination limit of the method was 20 and 13 mg kg⁻¹ of nitrate and nitrite, respectively. Nitrite and nitrate were determined in vegetables and meat products by the proposed method. The precision and accuracy of the proposed method were comparable to those of the reference spectrophotometric method (official AOAC reference method for the determination of nitrate in foodstuffs).     

Thin-layer drying behaviour of sludge of olive oil extraction

Drying characteristics of sludge were examined for average moisture content from 2 to approximately 0.7–0.08 kg water/kg dry matter using hot air of the range of 20–40–80 °C and simulating the interval that can be provided by an air solar heater and by air velocities of 1 m/s at a laboratory scale dryer. Different mathematical models were used for the simulation of the sludge drying curves, such as Lewis, Page, Modified Page, Henderson and Pabis, Wang and Singh, Logarithmic, Two term, Two Term exponential, Modified Henderson and Pabis, Midilli, Approximation of diffusion, Verma et al. and Simplified Fick’s diffusion models. The performance of these models was investigated by comparing four statistical parameters: the square of the coefficient of determination (r²), reduced chi-square (χ²), root mean square error (RMSE) and sum of residuals between the observed and predicted moisture ratio. The Midilli model represented the drying characteristics better than the others. The effective diffusivity coefficient of moisture transfer varied from 2.224 × 10⁻¹⁰ to 6.993 × 10⁻¹⁰ m²/s over the temperature range. The temperature dependence of the effective diffusivity coefficient was expressed by Arrhenius type relationship. The activation energy for the moisture diffusion was found to be 15.77 kJ/mol.     

Antibacterial activity of extracts from some edible plants commonly consumed in Asia

Extracts of edible plants (26 species) from China, Japan, Thailand and Yemen were screened for their antibacterial activity against Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella infantis. Buffered methanol (80% methanol and 20% PBS) and acetone extracted inhibitory substances against tested bacteria from 16 plants, as revealed by the disc assay. The minimum inhibitory concentrations (MICs) of extracts determined by the agar dilution method ranged from 165 to 2640 mg l⁻¹. The most sensitive microorganism to extracts from Azadirachta indica, Cinnamomum cassia, Rumex nervosus, Ruta graveolens, Thymus serpyllum and Zingiber officinale was B. cereus, with MIC of 165 to 660 mg l⁻¹. E. coli and S. infantis were only inhibited by Cinnamomum cassia extracts at the highest MIC (2640 mg l⁻¹). L. monocytogenes (Tottori) was more resistant than the ATCC 7644 strain to extracts from Ruta chalepensis, Artemisia absinthium and Cissus spp. EDTA (0.85 mM) reduced the MICs of Cinnamomum cassia and Cissus rotundifolia by at least 50% when tested against E. coli, S. infantis, S. aureus and L. monocytogenes.     

Cloud point extraction and spectrofluorimetric determination of aluminium and zinc in foodstuffs and water samples

Cloud point methodology was successfully used for the extraction of trace amounts of aluminium and zinc as a prior step to their determination by spectrofluorimetry. Aluminium and zinc react with 8-hydroxyquinoline in a surfactant solution yielding a hydrophobic complex, which then is entrapped in surfactant micelles. Optimization was performed of the variables affecting complexation and phase separation. Under the experimental conditions used, preconcentration of 25 ml of sample in the presence of 0.12% (v/v) Triton X-114 permitted the detection of 0.79 μg l⁻¹ of aluminium and 1.2 μg l⁻¹ of zinc, respectively. The relative standard deviation for five replicate determinations of aluminium and zinc at 40 and 100 μg l⁻¹ concentration level, were 2.72 and 2.1%, respectively. Good recoveries in the range of 95–104% were obtained for spiked samples. The proposed method was applied to the determination of aluminium and zinc in different samples.