Elimination of aggregates of (1→3) (1→4)-β-D-glucan in dilute solutions for light scattering and size exclusion chromatography study

Methods for eliminating aggregates of cereal (1→3) (1→4)-β-D-glucan in dilute solutions were investigated using dynamic light scattering and size exclusion chromatography. Wheat β-D-glucan samples were selected and dissolved in various solvents under different preparation conditions. The molecular size distribution was monitored by dynamic light scattering measurement. In most of the solutions, there were two well separated species of different average sizes. It appeared that the specie with smaller average size represented the un-aggregated molecules (unimers) and the specie with larger particle size corresponded to the aggregates. The results showed that heat treatment, filtration, ultrasonication, and the use of urea solution (up to 6 M) could not eliminate aggregates completely. However, the percentage of aggregates in aqueous NaOH solution decreased significantly with the increase of NaOH concentration. In 0.5 M NaOH solution, no aggregation was detectable by dynamic light scattering measurement. Both dynamic light scattering and HPSEC data showed that wheat β-D-glucan was stable in 0.5 M NaOH solution without any noticeable degradation when stored at 25 °C for 12 h. The results of present study suggested that 0.5 M NaOH solution is a suitable solvent for cereal β-D-glucans. Using this solvent, the molecular characteristics of wheat β-D-glucan was studied by both dynamic and static light scattering. The weight average molecular weight (M_w), radius of gyration (R_g), hydrodynamic radius (R_h), and the second virial coefficient (A₂) were obtained with the values of 3.29×10⁵ g/mol, 45.6 nm, 26.2 nm, and 1.04×10⁻³ cm³ mol/g² respectively. This study also confirmed that wheat β-glucan in solution exhibited a random coil conformation.     

Depuration of cadmium from blue mussel (Mytilus edulis) by hydrolysis peptides and chelating metal elements

The present experiment was conducted to investigate the effects of prepared hairtail (Lepidopusc audatus) hydrolysis peptide–metal element (Fe^2 +, Zn^2 +, Ca^2 +, or Mg^2 +) complexes (PH–Fe^2 +, PH–Zn^2 +, PH–Ca^2 +, or PH–Mg^2 +) on the depuration of cadmium (Cd) from blue mussel (Mytilus edulis) tissues. Cd concentrations in anterior adductor muscle, posterior adductor muscle, gill, mantle, and visceral mass of mussels were 11.391, 15.323, 63.672, 19.509, and 109.621 μg/g, respectively, after 5 days of exposure to 0.32 mg/L Cd. Five groups of these exposed mussels were then exposed to seawater laced with four different concentrations of the peptide complexes listed above (5, 10, 15, and 20 mg/L) for 8 days. After 8 days of depuration, 5 mg/L of PH–Fe^2 +, PH–Zn^2 +, and PH–Ca^2 + showed no significant (P > 0.05) effects on Cd concentrations in mussel tissues. However, significant differences (P < 0.05) were observed in groups exposed to 20 mg/L of PH–Fe^2 +, PH–Zn^2 +, and PH–Ca^2 +. The Cd concentrations in anterior adductor muscle, posterior adductor muscle, gill, mantle, and visceral mass were significantly (P < 0.05) decreased by 29.56–35.83%, 27.51–33.62%, 31.59–40.34%, 25.83–31.28%, and 33.62–33.97%, respectively. Nevertheless, the variables of Cd concentrations in tissues treated with 5–20 mg/L PH–Mg^2 + showed no significant (P > 0.05) differences from controls at any point during the experimental period. For these reasons, PH–Fe^2 +, PH–Zn^2 +, and PH–Ca^2 + can be recommended as depuration agents in mussel feed to decrease the Cd concentrations in tissues.     

Combinations of nisin with organic acids or salts to control Listeria monocytogenes on sliced pork bologna stored at 4°C in vacuum packages

This study evaluated dipping solutions of nisin with or without organic acids or salts, as inhibitors of Listeria monocytogenes introduced on sliced cooked pork bologna before vacuum packaging and storage at 4°C for 120 days. Inoculated (10²–10³ cfu/cm²) slices were immersed in nisin (5000 IU/ml), or in lactic or acetic acid (1, 3, 5 g/100 ml), sodium acetate or diacetate (3, 5 g/100 ml), and potassium benzoate or sorbate (3 g/100 ml), each combined with nisin. Additional slices were immersed in nisin, inoculated and then immersed in acid or salt solutions without nisin. Nisin reduced L. monocytogenes by 1.0–1.5 log cfu/cm² at treatment (day-0) followed by a listeriostatic effect for 10 days. Thereafter, however, the pathogen multiplied in treatments without acid or salts, with growth being faster on slices immersed in nisin after as compared to before inoculation. Nisin in combination with 3 or 5 g/100 ml acetic acid or sodium diacetate or 3 g/100 ml potassium benzoate, applied individually or as mixtures, did not permit growth before day-90. Other treatments were of variable and lesser effectiveness (20–70 days), whereas in untreated or water-treated (control) bologna L. monocytogenes increased at 6–7 log cfu/cm² at day-20. Based on the antilisterial efficacy and effects of treatments on product pH, nisin with 3 g/100 ml sodium diacetate may be the most promising combination in dipping solutions to control L. monocytogenes on sliced cured pork bologna.     

Phytosterols and tocopherols content of pulps and nuts of Brazilian fruits

Fruits and nuts from the North and Northeast regions of Brazil were collected to determine their phytosterol and tocopherol content. The species studied were Cotia nut (Aptandra spruceana M.), Brazil nut (Bertholletia excelsa H.B.K.), Mucajá (Couma rigida M.), Red Açaí (Euterpe oleracea M.), Inajá (Maximiliana maripa D.), Jenipapo (Genipa Americana L.), Buriti (Mauritia flexuosa L.) and Uxi (Endopleura uchi C.). Phytosterols were analyzed by GC–FID using β-cholestanol as an internal standard, while tocopherols were determined by RP-HPLC-DAD. The pulps of Mucajá (26–236 mg 100 g^–1), Inajá (119–285 mg 100 g^–1) and Jenipapo (216 mg 100 g^–1) showed the highest total phytosterol contents. Considering α-tocopherol equivalents, the pulps of Buriti (346.72 μg g^–1) and Uxi (200.92 μg g^–1) contained the highest vitamin E activity. Therefore, the results indicate that these fruits and nuts have great potential to be cultivated and marketed as alternative dietary sources for these bioactive compounds.     

Modeling the inactivation kinetics of fruit bromelain in pineapple during high-pressure and thermal treatments

The stability of fruit bromelain (FBM) in pineapple pulp was studied within a high-pressure domain of 0.1–600 MPa/30–70 °C/1 s–30 min. The pulse effect was quantified as a function of pressure, temperature, pressure build-up and decompression times. A maximum of 60% reduction in FBM activity was obtained after a single pulse of 600 MPa/70 °C. Upon applying nth order model, the obtained reaction order (n) for thermal (0.1 MPa/30–70 °C) and high-pressure (100–600 MPa/30–70 °C) inactivation was 1.1 and 1.2, respectively. The inactivation rate constant (k) ranged from 1.2 to 45.0 × 10^− 3 U^n − 1 min^− 1. The activation energy was nonlinearly dependent on pressure (P); whereas, the activation volume was linearly related to temperature (T). The nonlinear dependence of k on P and T was modeled by an empirical equation. The D-values obtained from the empirical model appeared to be more realistic than those from the log-linear kinetics.Industrial relevancePineapple fruit bromelain (FBM) has numerous health benefits and therapeutic effects. It is a protease enzyme that helps in digestion. Processing of pineapple pulp needs attention towards retaining the maximum FBM activity in it. A detailed kinetic study of FBM within a broad range of pressure–temperature–time domain will help in designing a high-pressure process for the pineapple pulp with respect to its bromelain stability.     

Comparative studies on the physico-chemical properties of hemicelluloses obtained by DEAE-cellulose-52 chromatography from sugarcane bagasse

Water- and alkali-soluble hemicelluloses isolated from dewaxed sugarcane bagasse were sub-fractionated on DEAE-cellulose-52 chromatography and obtained six hemicellulosic sub-fractions by eluting with water, 0.1 M and 0.3 M NaCl aqueous solution, respectively. Sugar composition and molecular weight analysis revealed that the lower molecular weight (14,180–43,590 g mol^?1) and more branches of hemicelluloses could be extracted by the hot water, which are rich in glucose, galactose, and xylose, while the higher molecular weight (75,430–138,170 g mol^?1) and more linear hemicelluloses were able to be dissolved into 1% NaOH aqueous solution, which are rich in xylose, principally resulting from l-arabino-(4-O-methyl-glucurono)-d-xylans. In addition, it was found that with increasing the concentration of NaCl (aqueous), the hemicellulosic sub-fractions with both higher arabinose to xylose ratio and higher molecular weight were eluted. Based on the FT-IR, sugar composition and ¹H and ¹³C NMR comparative studies, the alkali-soluble hemicellulosic sub-fractions had a classical structure, with a backbone of β-(1→4)-linked xylosyl residue substituted with arabinose at C–2 and/or C–3 of main chain, whereas the difference may occur in the distribution of branches along the xylan backbone.     

Improved astaxanthin production by Xanthophyllomyces dendrorhous growing on enzymatic wood hydrolysates containing glucose and cellobiose

Eucalyptus wood samples were treated with NaOH solutions and subjected to enzymatic hydrolysis with a commercial, β-glucosidase-deficient, cellulase complex or with a mixture of cellulase and β-glucosidase. Hydrolysates containing glucose or glucose and cellobiose were supplemented with KNO₃ and nutrients, and used as culture media for the proliferation of Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) ATCC 24228. For comparative purposes, similar experiments were carried out with media made from commercial sugars. All the bioconversion experiments were carried out in a batch fermenter. At selected fermentation times, the concentrations of substrate (or substrates), biomass and carotenoids were determined. Under the best conditions assayed (hydrolysates obtained with cellulases supplemented with an inorganic nitrogen source), biomass concentrations in the vicinity of 10 g litre⁻¹, with volumetric carotenoid concentration of 2.14 mg litre⁻¹, were reached after 74 h of fermentation. These results compare favourably with those reported for carotenoid production from enzymatic hydrolysates containing glucose as the sole carbon source..     

Purification of angiotensin I-converting enzyme inhibitory peptides and antihypertensive effect of milk produced by protease-facilitated lactic fermentation

Fresh low-fat milk was fermented with five mixed lactic acid bacteria for up to 30 h at 42 °C. A protease, prozyme 6, was added 5 h after the beginning of fermentation. The whey was separated from the fermented milk and freeze-dried. As the fermentation time extended to 30 h, soluble protein content increased from 30.9 to 195.9 mg g⁻¹, free amino acid content increased from 2.8 to 192.8 mg g⁻¹, peptide content increased from 6.4 to 402.8 mg g⁻¹ and γ-aminobutyric acid (GABA) increased from 0 to 80.6 mg 100 g⁻¹, while inhibition of angiotensin I-converting enzyme (ACE) increased as indicated by a decrease of IC₅₀ from 1.18 to 0.24 mg mL⁻¹, respectively. The amino acid sequences of two ACE inhibitory peptides were Gly–Thr–Trp and Gly–Val–Trp, of which the IC₅₀ values were 464.4 and 240.0 μm, respectively. The systolic blood pressure and diastolic blood pressure of spontaneously hypertensive rat (SHR) were reduced 22 and 21.5 mm Hg, respectively, after 8 weeks of oral administration of diluted whey (peptide concentration 5 mg mL⁻¹) from the 30 h fermentation.     

Effect of monoglycerides on the thermal inactivation kinetics ofBacillus cereusF4165/75 spores

The combined effect of monoglycerides and heat on the inactivation of Bacillus cereusF4165/75 spores was investigated. Linear survivor curves were obtained for spores suspended in buffer with or without added monoglyceride, and were consistent with first-order inactivation kinetics. In the presence of 3.056 mmol l^–1monoglyceride, the heat resistance of spores was affected differently depending upon the monoglyceride. Monolaurin and monolinolenin significantly lowered the spores' heat resistance, whereas monomyristin and monolinolein increased it but less dramatically. TheD_91°Cvalues obtained increased in the following order: monolaurin (3.056 mmol l^–1)< monolinolenin (3.056 mmol l^–1)< phosphate buffer (pH 7)< monomyristin (3.056 mmol l^–1)< monolinolein (3.056 mmol l^–1). Monolaurin was the most effective monoglyceride, possibly because of its lipophilic nature and great emulsifying properties. Increasing its concentration from 1.058 to 5 mmol l^–1significantly enhanced the heat inactivation rate ofB. cereusF4165/75 spores. The thermodynamic data were used to speculate on the mechanism of heat inactivation of the spores. These thermodynamic values were not significantly different in the presence or absence of monolaurin. This suggested that the enhancing effect due to increasing concentrations of monolaurin on the thermal inactivation of spores is essentially identical at any sterilization temperature, although it allows the heating temperature for sterilization to be reduced.     

Optimization of solid–liquid extraction of phytochemicals from Garcinia indica Choisy by response surface methodology

A central composite rotatable design was employed to study the effect of ultrasound assisted extraction conditions namely sonication amplitude (10–90%), sonication cycle (0.1–1.0 s^?1), solid–liquid ratio (2–10) and extraction time (5–35 min) on the total anthocyanin extraction from Garcinia indica Choisy. Overall extractions of total anthocyanin, acidity and antioxidant activity were considered as response variables. The significant (p < 0.05) response surface models with high coefficients of determination values (R²) ranging from 0.91 to 0.93 were fitted for the experimental data, which indicated that the polynomial response models fitted well for describing the extraction efficiencies of anthocyanin, acidity and antioxidant activity. Based on the design, the optimal conditions for obtaining higher extraction were extraction time 35 min, cycle ranging from 0.44 to 0.48 s^?1, percentage amplitude ranging from 10 to 14%, and solid–liquid ratio 10. The graphical optimization of superimposed contour plots fulfilled the conditions to obtain total anthocyanin (Y₁) ≥ 135 mg/100 g DW, total titratable acidity (Y₂) ≤ 25 g/100 g DW and antioxidant activity (Y₃) ≥ 14.5 M Trolox/100 g DW. The study demonstrated that response surface methodology can be utilized for deriving the optimum conditions for extraction of anthocyanin from G. indica Choisy.     

Production of fat-derived (flavour) compounds during the ripening of Gouda cheese

Fat-derived flavour compounds in four different batches of Gouda cheese were monitored over 2 years of ripening. The total free fatty acid (FFA) concentrations increased from 200–400 to 700–1200 mg kg^–1 dry matter, in a fairly linear manner. Long-chain FFAs were predominant in the curds, but relatively more short and intermediate chain fatty acids were released during ripening. The production of δ-lactones was rapid initially, but reached a plateau at 55 mg kg^–1 dry matter in about 20 weeks. The production of γ-lactones was slower and also decreased, but was noticeable over a longer time, giving 5.5 mg kg^–1 dry matter in 90 weeks. Ethyl ester formation varied substantially. Ketone levels increased only very slightly during ripening; long chain alcohols and aldehydes were not found. Some individual FFAs and lactones exceeded reported flavour thresholds, and are expected to influence the flavour of Gouda cheese.     

Routine and sensitive SPE-HPLC method for quantitative determination of pheophytin a and pyropheophytin a in olive oils

A sensitive and specific HPLC method with tandem diode array-fluorescence detection (DAD-FL) has been developed and validated for the simultaneous determination of pheophytin a (phy a) and pyropheophytin a (pyrophy a) in olive oils. Pigments were extracted with reverse phase solid phase extraction (RP-SPE) and subsequently analysed by HPLC-DAD-FL. The chromatographic analysis was carried out isocratically on ODS2 RP column using methanol–acetone (1:1 v/v) at flow-rate of 2.0 ml min⁻¹. Specificity of the method was assured by the simultaneous detection by UV–visible (410 nm) and FL (λ_Ex: 410 nm; λ_Em: 672 nm). Both compounds could be baseline separated within 7 min. The method was validated and applied in olive oil samples recently extracted as well as stored during 12 months. The limit of detection (LOD) defined at a signal-to-noise ratio of about 3 was ∼21.6 ng g⁻¹ for pyrophy a and ∼24.6 ng g⁻¹ for phy a under FL detection, and ∼148.0 ng g⁻¹ for both analytes under UV–visible detection. The calibration graphs were linear (r² > 0.9999; p < 0.01) between 0.25–14.00 ng μl⁻¹ for pyrophy a and 0.25–19.00 ng μl⁻¹ for phy a, under both fluorescence and UV–visible detection conditions. Recoveries of phy a and pyrophy a were over 94% as estimated by the standard addition method. Relative standard deviation for the intra-day and inter-day determination of phy a and pyrophy a were lower than 3.7% and 8.0%, respectively.     

Rheological characterization of acylated and dextran conjugated African yam bean (Sphenostylis stenocarpa Hochst. Ex A. Rich.) proteins

The molecular weight distribution and rheological properties of acetylated, succinylated and dextran conjugated African yam bean (Sphenostylis stenocarpa) proteins dispersion were studied. Succinylation of the protein showed the three prominent electrophoretic bands of the unmodified protein but all the bands disappeared with acetylation. Immobile band characterized dextran conjugated S. stenocarpa electrophoregram. The flow behavior indices (n) of these modified S. stenocarpa protein dispersions were in the range 0.03–0.22. This is an indication that they were pseudoplastic in nature. This pseudoplastic nature was maintained in ionic media 0.05–0.5 mol dm^?3, pH 3–8 and temperature range of 27–75 °C. The yield stresses were 0.270, 0.302 and 0.320 Pa for acetylated, succinylated and dextran conjugated protein respectively. Activation energy of acetylated and succinylated protein were in the range 6.2–8.2 and 2–5.4 J mol^?1 respectively. Thus acetylation of S. stenocarpa protein made its dispersion viscosity more susceptible to temperature change than succinylation. These results suggest that acylation and dextran conjugation of African yam bean (S. stenocarpa) protein produce protein species with different rheological properties.     

Structural,thermal and viscoelastic characteristics of starches separated from normal,sugary and waxy maize

Starches separated from five types of maize (two normal, one sugary and two waxy) were investigated for physicochemical, thermal, amylopectin structure and viscoelastic properties. Kisan and Paras were normal maize while Parbhat and LM-6 were waxy maize type. Apparent amylose content of normal and sugary maize was 29.5–32.6 and 41.0%, respectively. Swelling power of normal, sugary and waxy maize starches was 11.6–15.2, 7.8 and 30.2–39.2 (g/g), respectively. X-ray diffraction of maize starches indicated typical A-pattern. Maize starch showed a single broad peak at 2θ=23.2° and a dual peak 2θ=17°–18.1, respectively. Waxy maize starches showed the presence of greater crystallinity than other starches while sugary maize starch showed the presence of lower crystallinity and a large amount of amylose–lipid complex. Intrinsic viscosity [η] of starches in 90% DMSO at 25 °C was 79.7–119.5 ml g⁻¹ for normal, 70.5 ml g⁻¹ for sugary and 107.2–118.1 ml g⁻¹ for waxy starches. Branch chain–length distribution of amylopectin revealed that the apparent amylose, long side chain- and short side chain-amylopectin proportion ranged between 0.0–41%, 13.4–31.5% and 41.5–66.8%, respectively, among the various maize starches. Maize sugary showed the highest apparent amylose content and the least amount of short- and long-side chains of amylopectin. LM-6 and Parbhat showed higher proportion of both long- and short-chain amylopectin as compared to other starches. Distribution of α-1, 4-chains of amylopectin (short-/long-chain) ranged between 2.1 and 3.4, the least for LM-6 and the highest for Paras starch. The transition temperatures (T_o–T_c) ranged between 60.5 and 76.1 °C for sugary, 63.5–76.3 °C for normal and 64.4–81.3 °C for waxy maize starch. The enthalpy of gelatinization (ΔH_gel) of sugary, normal and waxy maize starches was 2.47, 3.7–4.75 and 4.15–5.4 J/g, respectively. Normal and sugary maize starches showed higher G′ and G″ than waxy type starches. The change in the moduli during cooling and reheating of pastes cooked at different temperatures revealed low disintegration of granular structure in starch with higher amylose and amylose–lipid complex as well as low crystallinity. The changes in moduli during 10 h at 10 °C revealed highest retrogradation in maize sugary followed by Paras and Kisan starch.     

Survival of Listeria monocytogenes in Galotyri,a traditional Greek soft acid-curd cheese,stored aerobically at 4°C and 12°C

Galotyri is a traditional Greek soft acid-curd cheese, which is made from ewes’ or goats’ milk and is consumed fresh. Because cheese processing may allow Listeria monocytogenes post-process contamination, this study evaluated survival of the pathogen in fresh cheese during storage. Portions (0.5 kg) of two commercial types (<2% salt) of Galotyri, one artisan (pH 4.0±0.1) and the other industrial (pH 3.8±0.1), were inoculated with ca. 3 or 7 log cfu g⁻¹ of a five-strain cocktail of L. monocytogenes and stored aerobically at 4°C and 12°C. After 3 days, average declines of pathogen's populations (PALCAM agar) were 1.3–1.6 and 3.7–4.6 log cfu g⁻¹ in cheese samples for the low and high inocula, respectively. These declines were independent (P>0.05) of the cheese type or the storage temperature. From day 3, however, declines shifted to small or minimal to result in 1.4–1.8 log cfu g⁻¹ of survivors at 28 days of storage of all cheeses at 4°C, indicating a strong “tailing” independent of initial level of contamination. Low (1.2–1.7 log cfu g⁻¹) survival of L. monocytogenes also occurred in cheeses at 12°C for 14 days, which were prone to surface yeast spoilage. When ca. 3 log cfu g⁻¹ of L. monocytogenes were inoculated in laboratory scale prepared Galotyri of pH ≅4.4 and ≅3% salt, the pathogen died off at 14 and 21 days at 12°C and 4°C, respectively, in artisan type cheeses fermented with the natural starter. In contrast, the pathogen survived for 28 days in cheeses fermented with the industrial starter. These results indicate that L. monocytogenes cannot grow but may survive during retail storage of Galotyri despite its low pH of or slightly below 4.0. Although contamination of Galotyri with L. monocytogenes may be expected low (<100 cfu g⁻¹) in practice, that long-term survival of the pathogen in commercial cheeses was shown to be unaffected by the artificial contamination level (3 or 7 logs) and the storage temperature (4°C or 12°C), which should be a concern.     

Determination of moisture,solids-not-fat and fat-by-difference in butter using routine methods according to ISO 8851/IDF 191—an international collaborative study and a meta-analysis

An international collaborative study of routine methods for the determination of moisture, solids-not-fat (SNF) and fat-by-difference (i.e. fat (g 100 g^–1 product) =100−moisture (g 100 g^–1 product)−SNF (g 100 g^–1 product)) in butter was carried out to obtain estimates of the precision parameters repeatability (2.8s_r) and reproducibility (2.8s_R). Ten laboratories tested blind duplicate samples of eight different butters according to standard operating procedures jointly drafted by the International Standards Organisation (ISO) and the International Dairy Federation (IDF) (draft ISO standard 8851, parts 1–3; draft IDF standard 191, parts 1–3). Estimates of repeatability and reproducibility respectively were: moisture, 0.28 g 100 g^–1 product and 0.44 g 100 g^–1 product; SNF, 0.20 g 100 g^–1 product and 0.34 g 100 g^–1 product; fat-by-difference, 0.30 g 100 g^–1 product and 0.51 g 100 g^–1 product. These estimates are similar to those found previously in a New Zealand study. A meta-analysis, pooling the results of the present study and the New Zealand study, yielded overall estimates of repeatability and reproducibility as follows: moisture, 0.31 g 100 g^–1 product and 0.42 g 100 g^–1 product; SNF, 0.20 g 100 g^–1 product and 0.39 g 100 g^–1 product; fat-by-difference, 0.35 g 100 g^–1 product and 0.54 g 100 g^–1 product, and these are recommended for adoption in the respective methods. This study completes the validation work for the respective methods, which may now be progressed for final adoption as international standard routine methods. A protocol is proposed for dealing with situations where multiple precision estimates are available.     

Microwave-assisted digestion of β-lactoglobulin by pronase, α-chymotrypsin and pepsin

The effects of microwave irradiation (MWI) on kinetic parameters for pronase, α-chymotrypsin and pepsin hydrolysis of bovine β-lactoglobulin (β-Lg) were evaluated. The experiments were performed under MWI or conventional heat (CH) at 40 °C. The initial velocity (V₀) of peptide bonds cleavage was measured by o-phthaldialdehyde method; the peptide profile was analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE). Higher catalytic effectiveness (K_cat K_m⁻¹) values were obtained in the pronase and α-chymotrypsin digestions performed under MWI (7793 and 2073 min⁻¹ mM⁻¹, respectively) in comparison with the values in the respective CH digestions (1802 and 941 min⁻¹ mM⁻¹, respectively). The Michaelis–Menten constant (K_m) for either enzyme was reduced under MWI. Pepsin showed very low activity on β-Lg at pH 4.0 regardless of the heating procedure used. For two enzymes, pronase and α-chymotrypsin, differences in SDS–PAGE profiles were obtained due to the MWI applied during the enzymatic hydrolysis. The combined enzyme/MWI treatments could have a relevant application in the development of β-Lg hydrolysates.     

Phenolic profile and antioxidant activity of the Algerian ripe date palm fruit (Phoenix dactylifera)

The aim of this study was to determine the phenolic profile of seven different varieties of ripe date palm fruit (Phoenix dactylifera) from Algeria by LC–DAD–MS (ESI+), to investigate their respective antioxidant activities by the DPPH^· method and to estimate their phenolic content using the Folin–Ciocalteu method. The total phenolic content was in the range of 2.49 ± 0.01 to 8.36 ± 0.60 mg gallic acid equivalents (GAE) per 100 g fresh fruit. This fruit was shown to possess an antioxidant activity, giving values of antiradical efficient (AE) from 0.08 ± 0.00 to 0.22 ± 0.00. The phenolic contents and the antiradical efficiencies of the different varieties were highly correlated (R²=0.975). All the varieties were found to contain mainly p-coumaric, ferulic and sinapic acids and some cinnamic acid derivatives. Three different isomers of 5-o-caffeoylshikimic acid were detected. Different types of flavonoids were identified, mainly flavones, flavanones and flavonol glycosides.     

Biochemical changes throughout the ripening of a traditional Spanish goat cheese variety (Babia-Laciana)

The physico-chemical characteristics, proteolysis (classical nitrogen fractions, caseins and their degradation products and free amino acids), and lipolysis (fat acidity and free fatty acids) were studied throughout the ripening of three batches of Babia-Laciana cheese, a Spanish traditional variety made from raw goats’ milk. The main compositional characteristics of this cheese at the end of the ripening are its high content of total solids (TS) (78.0±2.4 g 100 g⁻¹ of cheese) and fat (61.1±1.2 g 100 g⁻¹ of TS), the presence of residual lactose (1.6±0.8 g 100 g⁻¹ of TS) and its low content of sodium chloride (1.1±0.7 g 100 g⁻¹ of TS) and ash (2.8±0.5 g 100 g⁻¹ of TS). Its pH values (4.44±0.72) are extraordinarily low. The evolution and final values of the different nitrogen fractions show that this cheese undergoes a very slight proteolysis, a fact which was corroborated when the caseins and their degradation products were quantified: β-casein did not undergo any modification throughout ripening, while only 21% of the α_s-caseins were degraded. Free amino acids content increased by a factor of about 7 throughout ripening, resulting in a high content of γ-amino butyric acid and a low content of glutamic acid at the end of the process. Fat acidity increased very slightly, approximately 4.5 times, during ripening, reaching final values of 3.5±2.2 mg KOH g⁻¹ of fat. The total free fatty acids content showed a similar evolution to fat acidity. At the end of the ripening process, the main free fatty acid was C_18:1, followed by C₁₆ and C₁₀.     

Antibiotic resistance and susceptibility to some food preservative measures of spoilage and pathogenic micro-organisms from spices

Antibiogram of 84 strains of Bacillus cereus, 26 strains of Clostridium perfringens, four strains of Staphylococcus aureus, 51 strains of Enterobacteriaceae, two strains of each of Salmonella and Shigella; isolated from spices, were studied against 20 different antibiotics that are commonly used against foodborne diseases, mainly gastroenteritis. All the tested strains of B. cereus, Cl. perfringens, Staph. aureus, Escherichia coli, Salmonella and Shigella were found resistant to at least 3, 4, 7, 6, 10 and 9 antibiotics, respectively. In brain–heart infusion broth supplemented with glucose, the D_100°C-values for B. cereus were 3.5–5.9 min, and the z-values were 17–18°C. The D_100°C-values for Cl. perfringens in fluid thioglycolate medium were higher (10.0–19.8 min) than those of B. cereus. The minimum inhibitory concentrations (MICs) of sodium chloride were 45–80 mg ml⁻¹. While the MIC of benzoic acid for Cl. perfringens, tested on perfringens agar (pH 7.3) plates by incubating anaerobially at 35°C for 24 h, was 1.9–2.2 mg ml⁻¹, for others, tested on nutrient agar (pH 6.8) plates by incubating at 35°C for 18 h in static aerobic condition, it was much less. Similarly, the MIC of sorbic acid for all the tested isolates, excepting Cl. perfringens, was 0.6–1.1 mg ml⁻¹. Of the eight isolates of Cl. perfringens, only three were inhibited at 2.0 mg sorbic acid ml⁻¹, while others were resistant. Sixty percent and 75% of the respective strains of B. cereus and Cl. perfringens were resistant to 5000 IU Nisaplin ml⁻¹, whereas the MIC values of Staph. aureus were between 3000 and 5000 IU ml⁻¹. While studying combined effect of selected hurdles on the growth of enterotoxigenic Cl. perfringens 16-C2, the judicious combination considered was low acid (pH 6.0), 30 mg sodium chloride ml⁻¹ and 1.25 mg benzoic acid ml⁻¹.