Some biochemical properties of polyphenol oxidase from two varieties of avocado

A study of crude polyphenol oxidases from two avocado (Persea americana Mill.) varieties, Booth 1 (b1PPO) and Julio Millán (jmPPO), were carried out to provide information useful for guiding food processing operations. Results are reported as “apparent” data because crude extracts were used, activities of which can be derived from a combination of isoenzymes. The pH-activity optimum was pH 7.5–7.6 for both extracts. Heat inactivation, between 67 and 84 °C was biphasic with activation energies ranging from 21.4 to 64.1 kcal/mol. The apparent substrate specificity was established from values V_max/K_m as: 4-methyl catechol>chlorogenic acid>pyrogallol>catechol>caffeic acid>dl-DOPA for b1PPO. The substrate specificity for jmPPO was: 4-methyl catechol>chlorogenic acid>pyrogallol>caffeic acid>catechol>dl-DOPA>protocatechuic acid. The order of inhibitor effectiveness was: l-cysteine>ascorbic acid>resorcinol>glycine>NaCl.     

Characterization of polyphenoloxidase from 2 peach (Prunus persica L.) varieties grown in Argentina

Polyphenoloxidase was extracted from September peach (_SEPPO) and Summerset peach (_SUPPO) and its physicochemical characteristics were analyzed. The optimum pH was 6.5 for _SEPPO and 5.5 for _SUPPO. The optimum temperature was 35°C for _SEPPO and 39.4°C for _SUPPO. Activation energy (Ea) from thermal activation was 41.5 kJ/mol for _SEPPO and 37.5 kJ/mol for _SUPPO. Heating at 60°C by 5 min, _SUPPO was denatured whereas _SEPPO retained 2.6% of activity. Activation enthalpy (ΔH^#) and activation entropy (ΔS^#) for _SEPPO heat-inactivation were 69.9 J/mol and −83.5 kJ/mol·K for _SUPPO, ΔH^# was 91.8 J/mol while ΔS^# was −21.0 kJ/mol·K. Substrate specificity (V_max/K_M) was 4-methylcatechol>catechol>pyrogallol for _SEPPO and 4-mehtylcatechol>pyrogallol>catechol for _SUPPO. For both enzymes, the order of inhibition effectiveness using reductor agents was metabisulphite>ascorbic acid. Benzaldehyde, 4-hydroxybenzaldehyde, and dl-dopa were competitive inhibitors, and their K_I values were 38.86, 8.43, and 2.08 mM, respectively.     

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.     

Thermal and light stabilities and antioxidant activity of carotenoids from tomatoes extracted using an ultrasound-assisted completely solvent-free method

The use of petroleum-derived solvents, particularly volatile organic compounds (VOCs), in the chemical industry has increased the contamination and residual effects of these solvents. Ionic liquids (ILs) can potentially replace VOCs, thereby reducing the risks of environmental contamination and toxicity. In this context, the objectives of this study were as follows: 1 — to obtain an ionic liquid for use in extracting carotenoids from tomatoes with ultrasound assistance; and 2 — to determine the stability and antioxidant activity of tomato carotenoid extracts. Ultrasound can also efficiently extract carotenoid compounds with ionic liquids in comparison with conventional VOC solvents (obtained from an all-trans-lycopene 7.5–8.0 μg·g^− 1 tomato sample by IL and 6.2–7.7 μg·g^− 1 by acetone). Similarly, the activation energies (E_a) in aqueous medium were obtained for the IL carotenoid extract (10.8 kJ·mol^− 1) and acetone carotenoid extract (9.4 kJ·mol^− 1). The antioxidant activities of the tomato carotenoid extract were 7.4 and 12.4 relative to α-tocopherol for the ionic liquid extract and acetone extract, respectively. The combination of chromatographic analysis and degradation kinetics provided data for positive assessment similarity of thermal and light stabilities of tomato carotenoids extracted by IL and extracted by acetone.     

Influence of emulsifier type on in vitro digestibility of lipid droplets by pancreatic lipase

The objective of this study was to investigate the influence of interfacial composition on the in vitro digestion of emulsified lipids coated by various emulsifiers by pancreatic lipase. Sodium caseinate, whey protein isolate (WPI), lecithin and Tween 20 were used to prepare corn oil-in-water emulsions (3 wt% oil). Pancreatic lipase (1.6 mg/mL) and/or bile extract (5.0 mg/mL) were added to each emulsion and the particle charge, droplet aggregation, microstructure and free fatty acids released were measured. In the absence of bile extract, the amount of free fatty acids released per unit volume of emulsion was much lower for lipid droplets coated by Tween 20 (13 ± 16 μmol ml⁻¹) than those coated by lecithin (75 ± 20 μmol ml⁻¹), sodium caseinate (220 ± 24 μmol ml⁻¹) or WPI (212 ± 6 μmol ml⁻¹). In the presence of bile extract, there was an appreciable increase in the amount of free fatty acids released in all the emulsions, with the most appreciable effects being observed in the Tween 20-stabilized emulsions. The stability of the emulsions to droplet flocculation and coalescence during hydrolysis was also strongly dependent on emulsifier type, with the WPI emulsions being the least stable and the Tween 20 emulsions being the most stable. Our results suggest that the access of pancreatic lipase to emulsified fats decreases in the following order: proteins (caseinate and WPI) > phospholipids (lecithin) > non-ionic surfactants (Tween 20). These results may have important consequences for the design of foods with either increased or decreased lipid bioavailability.     

Methyl ketone production from copra oil by Penicillium roqueforti spores

Bioconversion of copra oil by two strains of Penicillium roqueforti spores was studied in the presence or absence of exogenous lipase. Without exogenous lipase action, methyl ketone productivities were weak: 33 ± 1.9 to 61 ± 2.4 μmol g⁻¹ of oil, respectively, for strains 1 and 2. This formation results from the bioconversion of free fatty acids present in copra oil and appears strain-dependent. The major ketone was 2-undecanone, reflecting the high concentration of dodecanoic acid in the substrate. After lipolysis of copra oil by a Candida cylindracea lipase, a large increase of methyl ketone productivities (912 ± 13 and 1935 ± 26 μmol g⁻¹ of oil, respectively) is noticed with 2-heptanone predominating. This observation could result from the selectivity of the lipase used in the bioconversion process, or from the preferential oxidation due to spore specificity. When the reaction time was increased, the amount of methyl ketones decreased and other volatile compounds were formed..     

Chemical composition and potential of some underutilized tropical biomass. I: fluted pumpkin (telfairia occidentalis)

The seeds of Telfairia occidentalis have been subjected to standard chemical analysis to evaluate their properties. Proximate analysis indicated a low moisture content (6.30 ± 0.50%). The ash content was slightly higher than the range recommended for compounding of animal feed (3.44 ± 0.06%). The carbohydrate content was low (16.5 ± 0.12%). Starch, however, constituted the dominant carbohydrate (62.5 ± 0.48), while three sugars, glucose, fructose and sucrose were detected in the seed. The crude protein in the seed was high (16.0 ± 0.03%), a value which compared favourably with high protein seeds and nuts. In all, 16 amino acids were detected in the protein. Glutamic acid showed the highest concentration (16.4 g 100 g⁻¹), while lysine showed the lowest (2.6 g 100 g⁻¹). The brown oil extracted from the seed (yield 48.6 ± 0.94) had the following physicochemical properties; acid value, 3.05 ± 0.80 g, saponification value 166 ± 1.34 mg/KOH g⁻¹, free fatty acids, 0.3 g and peroxide value 3.02 ± 0.07 mg Eq kg⁻¹. The iodine value (80.1 ± 0.10)g 100 g⁻¹ indicated a preponderance of unsaturated fatty acid. Four fatty acids were detected whilst unsaturated acids constituted 61.3 g. Triglyceride was the dominant lipid species while hydrocarbons, waxes, sterols and sterol esters and higher alcohols, were detected in the unsaponifable matter. Results of nutritionally valuable mineral elements indicated that potassium occurred at the highest concentration.     

Relationship between photon emission and chemopreventive potential of tea

Photon emission from tea (610–670 nm) in the H₂O₂/KHCO₃/MeCHO system and the utility of the photon detection system in tea evaluation were investigated. Photon intensity of tea depended on manufacturing method as follows: green tea (1202 ± SD 173.51 cd/m²) > oolong tea (834 ± SD 237.44 cd/m²) > black tea (222 ± SD 87.65 cd/m²). Photon intensity corresponded with polyphenol content (r²=0.8810) rather than catechin content (r²=0.7759) and showed a high correlation with chemopreventive activities against H₂O₂ (r²=0.7516), O₂⁻ (r²=0.7998) and DPPH radical (r²=0.7516). Photon intensity from green tea leaves at each manufacturing process step gave the same decreasing curve as DPPH radical scavenging activity. Chemiluminescence of tea, which gives information on the polyphenol content and chemopreventive potential, is a useful technique for tea evaluation.     

Persistence and Biofilm Assessment of Campylobacter Jujeni in Poultry Abattoir

Persistence of Campylobacter sp and its biofilm forming ability was assessed in two poultry abattoirs at two weeks intervals. Average prevalence (63.75%) of Campylobacter spp. was observed on assessing a total of 160 samples collected from the surfaces of packaging table (80%), dressing table (75%), floor source (70%) and washing table (30%). Biofilm assessment formed by Campylobacter jejuni within 5-days at 37°C were in decreasing order of washing table > packaging table > dressing table > floor. An average rate (19.6%) of isolates to develop biofilm observed in both sites was considered relatively low. Absorbance value (Optical Density-OD_590nm) of formed biofilms ranged from 0.483 – 0.952. Wastewater from the facilities showed higher TDS (643 – 820 mgl⁻¹), TSS (1200 – 1775 mgl⁻¹), COD (152 – 141 mgl⁻¹) and BOD (30.3 – 32.5mgl⁻¹) than the WHO standards of 500 mgl⁻¹, 100 mgl⁻¹, 10 mgl⁻¹ and 6 mgl⁻¹ respectively. This is a clear indication of heavy microbial presence in the wastewater. Total bacterial count (TBC) was slightly higher in site A (4.4 × 10⁵ CFU/ml) than site B (3.5 × 10⁵ CFU/ml). Efficiency index ratio (≈/> 1) observed in all tested drugs suggests their effectiveness in campylobacteriosis management. Decreasing drug sensitivity pedigree was observed with streptomycin > erythromycin & gentamincin > tetracycline & neomycin > penicillin > riphapicin & ampicillin > norflaxicin & cephalexin. These results of frequency and biofilm forming tendencies of Campylobacter spp. observed in this study can be of value in checkmating campybacteriosis outbreak from poultry abattoir facility.     

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.     

Purification and characterisation of polyphenol oxidase (PPO) from eggplant (Solanum melongena)

Eggplant (Solanum melongena) is a very rich source of polyphenol oxidase (PPO), which negatively affects its quality upon cutting and postharvest processing due to enzymatic browning. PPO inhibitors, from natural or synthetic sources, are used to tackle this problem. One isoform of PPO was 259-fold purified using standard chromatographic procedures. The PPO was found to be a 112 kDa homodimer. The enzyme showed very low K_m (0.34 mM) and high catalytic efficiency (3.3 × 10⁶) with 4-methyl catechol. The substrate specificity was in the order: 4-methyl catechol > tert-butylcatechol > dihydrocaffeic acid > pyrocatechol. Cysteine hydrochloride, potassium metabilsulphite, ascorbic acid, erythorbic acid, resorcylic acid and kojic acid showed competitive inhibition, whereas, citric acid and sodium azide showed mixed inhibition of PPO activity. Cysteine hydrochloride was found to be an excellent inhibitor with the low inhibitor constant of 1.8 μM.     

Isolation and characterisation of a novel antibacterial peptide from bovine αS1-casein

Bovine casein was hydrolysed with a range of proteolytic enzymes including pepsin, trypsin, α-chymotrypsin and β-chymotrypsin, and assessed for antibacterial activity. The pepsin digest of bovine casein, which showed antibacterial activity, was fractionated using reverse phase high performance liquid chromatography and the antibacterial peptides isolated were characterised using electrospray ionisation mass spectrometry. Two antibacterial peptides were identified, a novel peptide (Cp1) which corresponded to residues 99–109 of bovine α_S1-casein and a previously reported peptide (Cp2) which corresponded to residues 183–207 of bovine α_S2-casein. The minimum inhibitory concentration (MIC) of Cp1 and Cp2 were determined against a range of bacterial cultures. Cp1 exhibited an MIC of 125 μg mL⁻¹ against all Gram-positive bacteria tested, and MIC ranging between 125 and >1000 μg mL⁻¹ against the Gram-negative bacteria tested. Cp2 was generally far more potent against the Gram-positive bacteria, exhibiting an MIC of 21 μg mL⁻¹, compared to MICs ranging from 332 to >664 μg mL⁻¹ against most of the Gram-negative bacteria tested.     

Effect of ohmic heating on texture,microbial load,and cadmium and lead content of Chilean blue mussel (Mytilus chilensis)

The effect of ohmic heating (OH) on the texture, microbial load, and cadmium (Cd) and lead (Pb) content was evaluated in Chilean blue mussel (Mytilus chilensis) at shucking and subsequent canning. Mussel samples were processed by OH and blanching (BLAN) at 50 ± 1 °C, 70 ± 1 °C and 90 ± 1 °C for shucking and then canning at 115 °C for 20 min. The Cd and Pb content in fresh mussels was 2.47 ± 0.18 μg g^− 1 and 5.26 ± 0.55 μg g^− 1 dry weight (dw). The greatest reduction in Cd content was reached at 90 ± 1 °C by OH with 1.67 ± 0.06 μg g^− 1 (dw) and 1.69 ± 0.08 μg g^− 1 (dw) by BLAN. At the same temperature, the Pb content was reduced to 4.18 ± 0.24 μg g^− 1 dw for OH and 4.14 ± 0.30 μg g^− 1 dw for BLAN. The cutting strength of fresh samples (21.35 ± 2.44 N) significantly decreased in samples processed by OH (15.65 ± 1.36 N) at 90 ± 1 °C compared with BLAN samples (20.41 ± 3.16 N) at the same temperature. The initial mean count for mesophilic aerobic microorganisms and Enterobacteriaceae was 3.8 log cfu/g and 2.5 log cfu/g, respectively. The mesophilic aerobic microorganism count was reduced by 1.7 logarithmical units, while Enterobacteriaceae counts were reduced to undetectable levels by OH at 90 ± 1 °C.Industrial relevanceHigh temperature short time (HTST) processes rely on rapid convection heat transfer and are thus well suited to liquid foods. But, they are, however, limited in application to particulates since, for particles more than a couple of millimeters thick, the processing time is insufficient for heat to transfer to the center to give sterility. Ohmic heating is an emerging technology and very promising in food industries. It is a thermal process in which heat is generated internally in food and acts as a resistance to the flow of alternating electric current. This type of treatment prevents overheating by producing less deterioration in food components. It is a rapid procedure that allows food to conserve its natural properties; microorganisms and enzymes are also inactivated. The purpose of the present work was to evaluate the effect of Ohmic heating on mechanical properties, microbial load, Cd and Pb content in the opening and subsequent canning of Chilean blue mussel (Mytilus chilensis). This information could be used for the seafood industries in order to improve thermal heating processes in mussels.     

Inhibition of Chymosin and the Coagulation of Para-Casein Micelles by Anions

The effect of monovalent anions on the coagulation of para-casein micelles was determined by monitoring light transmission after adding different Ca salts (40 mM) to partially hydrolyzed casein micelles. The release of macro-peptide by chymosin was quantified using fluorescamine. The average rate of the chymosin-initiated coagulation of casein micelles, approximated by the reciprocal of clotting time, was determined as a function of anion type and concentration to determine the simultaneous effects of anions on chymosin velocity and para-casein micelle aggregability.Chymosin velocity and the coagulation of para-casein micelles were progressively inhibited by anions; the larger the anion, the greater the inhibition (SCN⁻ > NO₃⁻ > Br⁻ > Cl⁻). This is attributed to the binding of anions to cationic binding sites on kappa-casein and para-kappa-casein. The relative effect of the larger anions compared with that of Cl⁻ on the average rate of the chymosin-initiated coagulation of casein micelles increased with anion concentration (6 to 120 mM) but became limited at 120 mM. In the presence of 120 mM SCN⁻, NO₃⁻ and Br⁻, the average rate of coagulation was 26, 59, and 78% of that obtained with 120 mM Cl⁻.The marked sensitivity of the interactions between chymosin and kappa-casein and between para-casein micelles to anion type support conclusions that cationic sites on kappa-casein are important in the mechanism of the chymosin-initiated coagulation of casein micelles. Thus, monovalent anions may be useful to elucidate the mechanism of protein-protein interactions in food systems.     

Effects of pulsed vacuum osmotic dehydration (PVOD) on drying kinetics of figs (Ficus carica L)

Drying kinetics of non-pretreated (fresh) and pretreated Sarılop (Ficus carica L.) variety figs were compared. In experiments, figs were performed as a whole (unsliced and unpeeled). Pretreatment was pulsed vacuum osmotic dehydration (PVOD). Osmotic dehydration was performed in sucrose solution at 50 °Brix and 50 °C with a solution/fruit mass ratio of 4/1. Vacuum impregnation in osmotic dehydration was applied at 130 mbar for 15 min then the osmotic treatment continued at atmospheric pressure for 165 min, therefore the total pretreatment period lasted for 180 min (15 min (130 mbar) + 165 min (P_atm)). Pretreated and non-pretreated figs were dried at 55, 65 and 75 °C in a convective oven. Results showed that increasing of drying temperature shortened the drying time for both non-pretreated and pretreated figs. Drying period of pre-treated figs lasted shorter than non-pretreated figs, thus PVOD shortened the drying period. Non-pretreated (fresh) figs had greater shrinkage than the pretreated figs. Effective moisture diffusivity (D_eff) values of pretreated figs are greater than the non-pretreated figs during the drying at all three temperatures. D_eff increased with drying temperature for both pretreated and non-pretreated figs. D_eff values of non-pretreated and pretreated figs ranged 2.75·10^− 10–5.69·10^− 10 m²/s and 3.57·10^− 10–10.25·10^− 10 m²/s, respectively. Activation energy (E_a) of non-pretreated and pretreated figs were obtained 34.68 (kJ/mol) and 50.27 (kJ/mol), respectively. Also, sensory evaluation of color, flavor, odor, texture and overall acceptability of the samples was made.Industrial relevanceThe use of PVOD technique is relevant for food industry. So that, PVOD treatment shortened the drying period of figs. Thus, this result can cause the economic advantage as reducing the further costs for drying process. Additionally, results of sensory evaluation show that there was no significant difference (p > 0.05) between the pretreated and traditional dried figs except for flavor. Sensory properties of pretreated figs may be improved by changing conditions of pretreatment.     

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.     

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.     

Free radical-scavenging activity of Aloe vera (Aloe barbadensis Miller) extracts by supercritical carbon dioxide extraction

The free radical-scavenging activities of extracts of Aloe vera of leaf skin by supercritical CO₂ extraction and solvent extraction were determined. An orthogonal array design matrix of L₉ (3⁴) was considered to optimize supercritical carbon dioxide extraction processing at a CO₂ flow rate of 12–36 l h⁻¹, 35–45 MPa and 32–50 °C. The optimum extracted yield of 1.47% was provided at 50 °C 36 l h⁻¹, 35 MPa and 20% of modifier of methanol. These four factors were all demonstrated to be significantly crucial in the supercritical carbon dioxide extraction operation, as two-variable interactions. The extracts of A. vera rind by supercritical carbon dioxide extraction and solvent extracts provided significantly higher free radical-scavenging activities of 33.5% and 39.7%, respectively, than extracts of A. vera gel extracted by ethanol with a free radical-scavenging activity of 14.2%. The inhibition percentage of extracts of A. vera and reference antioxidants followed the decreasing order: Trolox (76.8%) > ethanol extracts of A. vera skin (39.7%) > BHT (35.9%) > the extract of supercritical carbon dioxide extraction (33.5%) >α-tocopherol (25.6%) > ethanol extracts of A. vera pulp (14.2%). Compared to BHT and α-tocopherol, the extracts of A. vera skin, by supercritical carbon dioxide extraction and ethanol, showed stronger antioxidant activities. Components in the rind of A. vera are responsible for the higher antioxidant activity of A. vera extracts.     

In-vitro mineral binding capacity of five fiber sources and their insoluble components for magnesium and calcium1

In-vitro binding of calcium (Ca) and magnesium (Mg) by total dietary fiber, hemicellulose A (HCL A), lignocellulose (LCL), cellulose (CL), and lignin (L) fractions isolated from rice bran (RB), wheat bran (WB), oat fiber (OF), apple fiber (AF) and tomato fiber (TF) was evaluated. At pH 6.8, significant amounts of Ca were bound by whole fibers, ranging from 800 μg g⁻¹ for RB to 10 097 μg g⁻¹ for TF. Mg bound by whole fibers varied from 496 μg g⁻¹ for OF to 2177 μg g⁻¹ for WB. Re-acid washing (pH<2.0) released 95–99% of the Ca and Mg bound to the fibers. Fibers with the highest endogenous Ca and Mg concentrations bound significantly (P<0.05) the highest amounts of the minerals studied. The Ca bound by HCL A varied from 9753 μg g⁻¹ for RB to 11 337 mg g⁻¹ for TF, whereas Mg bound varied from 1151 μg g⁻¹ for OF to 5626  μg g⁻¹ for TF hemicellulose fractions, respectively. Among the fiber components, Mg binding decreased in the order HCL A>LCL>L>CL, whereas Ca bound was in the order HCL A>LCL>CL>L. A relatively strong correlation was observed between the combined effects of protein content, hemicellulose, and lignin vs total Ca and Mg bound. 1998 Elsevier Science Ltd. All rights reserved     

Structure–mechanism relationship of antioxidant and ACE I inhibitory peptides from wheat gluten hydrolysate fractionated by pH

The aims of this study were to assess bioactive properties (ACE inhibition and antioxidant capacity) from wheat gluten hydrolysate peptides fractionated by pH (4.0, 6.0 and 9.0), to determine peptide action mechanism, and to relate it to the secondary structure and functional groups of peptides. Gluten hydrolysate extracts (GHE) were enriched in peptides with medium hydrophobicity and molecular weight (≈ 60% MH and 5.5 kDa, respectively). Gluten peptides inhibited ACE I by uncompetitive mechanism and a direct relationship between α-helix structure and IC50% value was obtained (r = 0.9127). TEAC and cooper chelating activity from GHE 6.5 were the highest and directly correlated with MH peptides. GHE 9.0 had high carotene bleaching inhibition (47.5 ± 0.3%) and reducing power activity (163.1 ± 2.9 mg S₂O₃^2 − equivalent g^− 1 protein), which were directly related to disulfide bonds content of peptides (r = 0.9982 and 0.9216, respectively). pH was a good alternative to select bioactive peptides from wheat gluten hydrolysate.