Effect of ozone processing on the colour,rheological properties and phenolic content of apple juice

Apple juice samples were ozonated with processing variables of ozone concentration (1–4.8% w/w) and processing time (0–10 min). Effects of processing variables on colour values (L, a and b), rheological properties and phenolic content were studied. Significant reductions in these parameters were observed during ozonation. Second order polynomial regression modelling was used to investigate the main effects of ozone concentration and processing time on the changes in the selected quality parameters of ozonated apple juice. Predicted models were found to be significant (p < 0.05) with low standard error and high coefficients of determination (R²).     

Rheological Properties of Sonicated Guar,Xanthan and Pectin Dispersions

The influence of high intensity ultrasound on the rheological characteristics of guar, xanthan, and pectin dispersions was investigated. Guar 1%, xanthan 1% and pectin 2% (w/v) dispersions were sonicated at varying intensity levels of 3.7, 6.3, 8.1, and 10.1 W/cm² for 5 min at 25^oC. Significant differences were observed in the rheological characteristics of each sonicated hydrocolloid dispersion studied. Sonication affected the consistency index (k), flow behaviour index (n) and complex power law constants (a and b). No recovery was observed in the structure breakdown after a 24-h storage period. Changes in the rheological properties of guar and pectin dispersions were significantly higher than that of xanthan dispersions.     

Rheological properties of whey protein isolate stabilized emulsions with pectin and guar gum

Dynamic oscillatory and steady-shear rheological tests were carried out to evaluate the rheological properties of whey protein isolate (WPI) stabilized emulsions with and without hydrocolloids (pectin and guar gum) at pH 7.0. Viscosity and also consistency index of emulsions increased with hydrocolloid concentration. At γ = 20 s⁻¹, the value of viscosity of the emulsion with 0.5% (w/v) pectin was about fivefold higher than that of the emulsion without pectin. Flow curves were analyzed using power law model through a fitting procedure. Flow behaviour index of all emulsions except for containing 0.5% (w/v) guar gum was approximately in the range of 0.9–1.0, which corresponds to near-Newtonian behaviour. The shear thinning behaviour of emulsions containing 0.5% (w/w) guar gum was confirmed by flow behaviour index, n, of 0.396. Both storage (G′) and loss modulus (G″) increased with an increase in frequency. Emulsions behaved like a liquid with G″ > G′ at lower frequencies; and like an elastic solid with G′ > G″ at higher frequencies. Effect of guar gum was more pronounced on dynamic properties. Phase angle values decreased from 89 to <10° with increasing frequency and indicated the viscoelasticity of WPI-stabilized emulsions with and without pectin/guar gum.     

Protein changes after irradiation and ice storage of horse mackerel (Trachurus trachurus)

Anthocyanin-rich concentrates from different fruits can be used as natural food colourants. The pigments' stability is comparatively low and dependent on the composition of food matrices. Food ingredients relevant for soft drinks, jelly fruits and salad dressings were tested in model systems regarding their influence on the colour stability of elderberry and black currant concentrate determined by colour measurement (CIE L ^* a ^* b ^*). In aqueous solutions food-grade organic acids and salt were found to influence anthocyanin stability: colour stability increased with increasing pK _a of acids and decreased with increasing salt concentrations. This may be attributed to altered solvation characteristics of aqueous solutions. A stabilizing influence was found for sugars presumably by reducing water activity. However, when heat treatment was applied, e.g. in the production of hydrocolloid gels, fructose was shown to accelerate anthocyanin decay due to the formation of sugar degradation products. Comparing hydrocolloids, alginate was shown to increase colour stability in aqueous solution and pectin displayed overall highest colour stability in a gel model system, suggesting that polyuronic acids may improve anthocyanin stability by intermolecular association.     

Effects of rapid chilling of carcasses and time of deboning on weight loss and technological quality of pork semimembranosus muscle

The effect of rapid air chilling of carcasses in the first 3 h of chilling at −31 °C (then at 2–4 °C, till 24 h post-mortem) and the possibility of earlier deboning (8 h post-mortem) after rapid air chilling, compared to conventional air chilling (at 2–4 °C, till 24 h post-mortem) on weight loss and technological quality (pH value, tenderness, drip loss, cooking loss and colour - L^*a^*b^* values) of pork M. semimembranosus was investigated. Under the rapid chilling conditions, weight loss was 0.8% at 8 h post-mortem and increased to 1.4% at 24 h post-mortem when weight loss was 2.0% under conventional chilling. Carcasses that were rapid chilled had significantly lower (P < 0.001) internal temperature in the deep leg at 4 (25.7 °C), 6 (13.0 °C), 8 (6.2 °C) and 24 h (3.8 °C) post-mortem compared to conventional chill treatment (32.7, 24.2, 19.1 and 5.1 °C, respectively). Rapid chilling reduced significantly (P < 0.05) the rate of pH value decline at 8 h (6.02) post-mortem in M. semimembranosus compared to conventional chill treatment (5.88). Compared to conventional chilling, in M. semimembranosus deboned in different time post-mortem, rapid chilling had a positive significant effect on drip loss (P < 0.05, muscles deboned 8 h post-mortem), cooking loss (P < 0.001) and incidence of pale colour (L^* value). Rapid chilling i.e. rapid chilling and earlier deboning had neither positive nor negative significant effects (P > 0.05) on other investigated technological quality parameters of M. semimembranosus (tenderness, a^* value and b^* value) compared to conventional chilling.     

Properties of low methoxyl pectin‐carboxymethyl cellulose based on montmorillonite nanocomposite films

In this study, the low methoxyl pectin‐carboxymethyl cellulose‐based montmorillonite (LMP‐CMC‐MMT, LCM) nanocomposite films with nine ratios of LMP:CMC (from 10:0 to 0:10) and different MMT contents (1–8 wt%) were prepared. The mechanical properties, colour, opacity and water vapour permeability (WVP) of composite films were investigated. The maximum of tensile strength (TS) of composite films was 39.85 ± 2.51 MPa at LMP:CMC ratio of 4:6 and 4 wt% MMT (LCM47), which indicated the formation of hydrogen bonds between MMT and LMP‐CMC. The reduction of WVP of the LCM47 composite film was 333% of that of the CMC film due to the tortuous path caused by MMT incorporation. LCM composite films had the higher b*‐ and ΔE*‐values and lower L*‐values in comparison with LMP‐CMC (LC) composite films. The LCM composite films showed a decrease in transparency as MMT content increased.     

Rheological characterizations of texturized whey protein concentrate-based powders produced by reactive supercritical fluid extrusion

A powder blend comprising (by weight) 94% whey protein concentrate (WPC80), 6% pre-gelatinized corn starch, 0.6% CaCl₂, and 0.6% NaCl was texturized using a supercritical fluid extrusion (SCFX) process. The blend was extruded at 90 °C in a pH range of 2.89 to 8.16 with 1% (db) supercritical carbon dioxide (SC-CO₂) and 60% moisture content. The texturized WPC-based (TWPC) samples were dried, grounded into powder, reconstituted in water, and evaluated using a range of rheological studies. Most TWPC samples exhibited shear thinning behavior and their mechanical spectra were typical of weak gel characteristics. The TWPC produced under extremely acidic condition of pH 2.89 with SC-CO₂ yielded the highest η^* (10,049 Pa s) and G′ (9,885 Pa) compared to the unprocessed WPC (η^* = 0.083 Pa s and G’ = 0.036 Pa). The SCFX process rendered WPC into a product with cold-setting gel characteristics that may be suitable for use as a food texturizer over a wide range of temperatures.     

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.     

Effects of the proteinaceous moiety on the emulsifying properties of sugar beet pectin

The role of the proteinaceous moiety in emulsifying was investigated using pectin from sugar beet as a model polysaccharide. Physicochemical and macromolecular characteristics of sugar beet pectin were examined with or without an enzymatic modification using multiple acid-proteinases. The enzymatic modification decreased the total protein content from 1.56±0.15% to 0.13±0.02% by the Bradford method without significant change in ferulic acid or most constitutional sugars. It also decreased the weight-average molecular weight (M_w) from 517±28 to 254±20 kg/mol and the z-average root-mean-square radius of gyration from 43.6±0.8 to 35.0±0.6 nm. Emulsifying properties of the polysaccharide with or without the enzymatic modification were evaluated by emulsion droplet size and creaming stability of O/W emulsions (pH 3.0) containing 15 w/w% middle-chain triglyceride and 1.5 w/w% sugar beet pectin as main constituents. The modification increased the average diameter (d_3,2) of emulsion droplets from 0.56±0.04 to 3.00±0.25 μm immediately after the preparation, suggesting a decrease in the emulsifying activity. It caused the creaming of the emulsions during incubation at 60 °C, which was in line with the finding that macroscopic phase separation occurred only in the presence of the modified pectin after storage at 20 °C for a day, suggesting a decrease in the emulsion stabilizing ability. The modification also decreased significantly the amount of the pectin fraction that adsorbed onto the surface of emulsion droplets from 14.58±2.21% to 1.22±0.03% and the interfacial concentration of the polysaccharide from 1.42±0.23 to 0.45±0.05 mg/m², where the proteinaceous materials in the pectin molecules activated the oil-water interface. Results from the present study suggest an important role of the proteinaceous moiety to explain the emulsifying properties of sugar beet pectin as in the case of gum arabic and soy soluble polysaccharide.     

Viscoelastic properties of aqueous and milk systems with carboxymethyl cellulose

Carboxymethyl cellulose (CMC) is widely used as a stabilizer and thickener in the food industry. Previously published work has been carried out in predominantly monophasic systems, i.e. aqueous solutions, but there are few studies of complex systems like dairy desserts where CMC may interact with carbohydrates and milk proteins. Oscillatory rheological methods were used to study the influence of CMC concentration (0.75%, 1.00%, 1.25% and 1.50% w/w) and type of dispersing media (aqueous solution, skimmed milk and whole milk) on the viscoelastic properties of aqueous and milk systems. Both the type of dispersing media and the CMC concentration clearly affected the viscoelastic behaviour of samples, which ranged from fluid-like to weak gel. At the lowest CMC concentration (0.75% w/w), no significant differences in G′, G″ and η* values at 6.28 rad/s were observed between the three systems studied. At the highest CMC concentration (1.5% w/w) G′ and η* values at 6.28 rad/s were significantly higher for whole-milk samples than for skimmed-milk samples, which in turn were higher than for aqueous solutions.     

Preparation and properties of pullulan–alginate–carboxymethylcellulose blend films

Pullulan, alginate, and carboxymethylcellulose (CMC) films were solvent cast from aqueous polymer solution. At 55% RH and 20 °C, their tensile strength and elongation at break were 67 MPa and 11%, 49 MPa and 5.2%, and 45 MPa and 5.8%, respectively. Pullulan films had lower water vapor permeability than alginate and CMC films (4.4 × 10⁻⁷, 9.7 × 10⁻⁷, and 1.3 × 10⁻⁶ g m/Pa h m², respectively), but dissolved in water quicker than alginate and CMC films. By incorporating alginate and CMC into pullulan, water barrier and mechanical properties were weakened significantly. Blending pullulan with alginate or CMC up to about 17–33% (w/w total polymer) reduced film solubilization time in water. The addition of glycerol further reduced tensile strength, increased elongation at break, weakened water barrier properties, but enhanced solubilization in water. FTIR results indicated that blending pullulan with alginate and CMC resulted in weaker hydrogen bonds acting on –OH groups compared to the pure pullulan.     

Microbial, physical-chemical and sensory spoilage during the refrigerated storage of cooked pork loin processed by the sous vide method

The aim was to study spoilage during the refrigerated storage of cooked pork loin processed by the sous vide method. Samples were packaged under vacuum into polyamide-polypropylene pouches, cooked at an oven temperature/time of 70 °C/12 h, chilled at 3 °C and stored at 2 °C for 0, 5 or 10 weeks. Microbial (psychrotrophs, lactic acid bacteria, Enterobacteriaceae, moulds and yeasts), physical–chemical (pH, water activity, TBARS, acidity, L^*a^*b^* colour, texture profile analysis and shear force) and sensory (appearance, odour, flavour, texture and acceptance) parameters were determined. The results showed that sensory spoilage preceded microbiological spoilage of sous vide pork loin. Counts bellow 1 log cfu/g of psychrotrophs, anaerobic psychrotrophs, Enterobacteriaceae and lactic acid bacteria were detected in any control week, while moderate counts (2–3 log cfu/g) of moulds and yeasts were found. Minor changes in water activity, lipid oxidation, CIELab colour, hardness, cohesiveness or gumminess were associated with spoilage of pork loin, only decreases of lactic acid, springiness and shear force were observed. The pork loin was unacceptable after 10 weeks. This loss of acceptance was mainly due to the deterioration of meaty flavour and odour, although the loss of appearance, juiciness and firmness also contributed. Moderate warmed-over and rancidity were detected. The sensory analysis was the most effective method for determining the shelf life of the sous vide pork-based dishes.     

Characteristics of gelling agent substituted fruit jam: studies on the textural,optical, physicochemical and sensory properties

A series of mango jams were prepared using different hydrocolloid solutions (high methoxyl pectin (HMP), carboxymethyl cellulose (CMC), and sago starch) as gelling agents to investigate the effect of hydrocolloid type, hydrocolloid concentration, and freeze‐thaw treatment on the physicochemical, optical, textural, and sensory characteristics. The optical properties results revealed that the total colour change (ΔE) of the sago starch‐based mango jam samples displayed higher values in comparison with samples prepared with HMP and CMC. The textural parameters (hardness, work of shear, stickiness, and work of adhesion) increased with hydrocolloid concentration but decreased with the freeze‐thaw treatment except for sago starch‐based mango jams. The overall acceptability of mango jams containing 6% sago starch was rated similarly to the samples prepared with 0.7% HMP and 0.5% CMC. Principle component analysis revealed that it could be used as an effective tool to segregate characteristics related to fruit jam manufacture.     

Pectin–sucrose–Ca2+ interactions: effects on rheological properties

The effects of varying concentrations of pectin (4.5–6.5%, w/w), sucrose (40–60%, w/w) and calcium (20–60 mg/g pectin) on the viscoelastic properties of pectin dispersions at pH 3.0 were investigated. Pectin samples used were extracted from pomelo fruit peels (Citrus grandis) grown in Malaysia. The dynamic rheological parameters (G′, G″, δ and η*) of pectin–sucrose–calcium dispersion were determined at 1.5% strain from 90–20°C at a cooling rate of 3°C min⁻¹. Plots of G′ and G″ against frequency (rad s⁻¹) showed G″>G′ throughout the frequency range with no occurrence of crossover for most of the pectin dispersions. In addition both storage (G′) and loss (G″) moduli of the dispersions increase on cooling. Increasing pectin, sucrose and calcium concentrations increased G′ and G″ with pectin having the greatest effect. Interactions amongst the three factors were also studied. At lower pectin concentrations, addition of Ca²⁺ increased G′ at all temperatures. This effect was also observed at higher pectin concentrations at 20°C but not at 90°C. The opposite effect was observed with the addition of sucrose, i.e. addition of sucrose at a higher pectin concentration increased G′ whereas at a lower pectin concentration no effect was observed. Interaction between calcium and sucrose gave rise to an increase in G′ when Ca²⁺ was added at high sucrose concentrations, but a decrease in G′ was evident at low sucrose concentrations. Dispersions of pectin alone or in combination with sucrose exhibited a more liquid-like behaviour with G″>G′. However, in the presence of Ca²⁺, mechanical spectra of G′>G″ were obtained.     

Properties of enzyme modified corn, rice and tapioca starches

Corn, rice and tapioca starches were partially hydrolyzed by treating the starch dispersions with heat stable α-amylase. Dextrose equivalent (DE) of 8–12 was achieved by hydrolyzing the starch samples (10–20% w/v) for 30 min at 90 ± 2 °C. Scanning electron micrographs showed that starch granules had broken down to smaller particles. High performance liquid chromatography with refractive index detection indicated that oligosaccharides with broad molecular weight distributions are present in the reaction products. Hydrolyzed starch dispersions were analyzed for their rheological properties. The storage modulus values (G′) for 20% solid containing slurries were 7373 and 1470 Pa for untreated and enzyme treated samples, respectively, indicating a marked decrease in solid properties due to enzyme action. The complex viscosities (η^*) for native corn starch and hydrolyzed corn starch were 8243 and 1637 Pas, respectively, which indicate that the enzyme treatment decreases the overall resistance of the sample to flow such that the product can spread easily. Further 13C CP/MAS NMR and FTIR studies revealed the loss of ordered structures in the enzyme modified starches. Free flowing fat substitute in the form of fine powder was prepared by spray drying the hydrolyzed starch slurry.     

Influence of particle characteristics and E/Z‐isomer ratio on the colour of concentrated β‐carotene dispersions

The influence of particle concentrations (0.02–0.40%), mean particle sizes (0.45–1.5 μm) and all‐E‐isomer ratios (95–30%) on the CIELAB colour coordinates (L*, a*, b*) of concentrated β‐carotene dispersions was investigated. Particle concentration between 0.06% and 0.40% had a slight impact on the colour parameters. However, with decreasing the mean particle size from 1.50 to 0.45 μm, there were increases in ΔL* = 8.0, in Δa* = 2.26 and in Δb* = 13.1. And with decreasing the all‐E‐isomers ratio from 95% to 30%, there were increases in ΔL* = 8.66, in Δb* = 17.51 but decrease in Δa* = 7.42. The experimental results were explained in terms of the scattering and absorption of light by dispersions. These findings have important implications for food industry as they offer a means to control and optimise the colour of food dispersions.     

Effect of inulin on the rheological properties of silken tofu coagulated with glucono-δ-lactone

This study investigated the rheological properties of inulin-containing silken tofu coagulated with glucono-δ-lactone (GDL) upon heating. Inulin (Raftiline^® HP-gel) was added to a soy protein isolate-enriched cooked soymilk at 0%, 1%, 2%, 3% and 4% (w/v) levels along with 0.4% (w/v) GDL to prepare acid-induced silken tofu. Gelation was induced by heating the soymilk mixture from 20 to 90 °C at a constant rate (1 °C/min) or isothermally at 90 °C for 30 min. The gelling properties were measured with dynamic small-deformation mechanical analysis and static large-deformation compression tests. The rheological changes in soymilk during gelation were dependent upon both the pH decline (hydrolysis of GDL) and the specific temperature of heating. Control samples heated to 50 °C, with the pH lowered to 5.95, started to gel, showing a rapid increase in storage (G′) and loss (G″) moduli afterwards. The addition of 2% inulin lowered the on-set gelling temperature by 2.8 °C and improved (P < 0.05) both rheological parameters of the tofu gel as well as hardness and rupture force (textural profile analysis) of the formed silken tofu. The results indicated that inulin enhances the viscoelastic properties of GDL-coagulated silken tofu, and the textural effect of inulin is an added benefit to its current application mainly as a prebiotical ingredient in food.     

Anthocyanin and colour degradation in ozone treated blackberry juice

Response surface methodology (RSM) was used to investigate the effects of ozone concentration (%w/w) and treatment time (min) on the anthocyanin content and colour of fresh blackberry juice. RSM methodology based on a two factor five level central composite design was employed with control variables of ozone concentration (0 to 7.8%w/w) and treatment time (0 to 10 min) at a constant gas flow rate. Predicted models were found to be significant (p < 0.001) with regression coefficients (R²) of 0.89, 0.82, 0.95, 0.86 and 0.97 for L, a, b, TCD and anthocyanin content respectively. Ozone concentration and treatment time were found to be critical factors influencing both anthocyanin and colour degradation. This study demonstrated that response surface methodology can be employed to model colour and anthocyanin degradation of ozonated blackberry juice while minimising the number of experiments required.Industrial relevanceIn the United States (US) legislation requires fruit juice processors to achieve a 5-log reduction in the numbers of the most resistant pathogens in their finished products. Consequently a number of commercial fruit juice processors in the US started to employ ozone for fruit juice pasteurisation. Ozonation was approved by the FDA in 2001 as a direct additive to food. The FDA issued industry guidelines for fruit juice processing with ozone [FDA, (2004). FDA Guidance to Industry, 2004: Recommendations to Processors of Apple Juice or Cider on the Use of Ozone for Pathogen Reduction Purposes. Available online http://www.cfsan.fda.gov/~dms/juicgu13.html.], however this report concludes that these guidelines are based upon limited scientific data. This paper investigates the effect of ozone processing on the anthocyanin content and colour of blackberry juice. The results presented demonstrate that the effect of ozonation on the nutritional properties of blackberry juice or juice products containing blackberry should be considered by processors prior to its adoption as a preservation technique.     

Ultrasonic processing influences rheological and optical properties of high-methoxyl pectin dispersions

The effect of high-intensity ultrasound on the rheological and optical properties of high-methoxyl pectin dispersions was studied. Pectin solutions (1.15 wt% pectin, 41.4 wt% sucrose) were treated with high-intensity ultrasound at intensity levels ranging from 0 to 40 W cm⁻² for various times (0–60 min). Samples were adjusted to pH 1.5 to initiate gelation and their dynamic rheological properties (G′, G″) were recorded as a function of time using a rotational rheometer. Ultrasonically pretreated pectin dispersions formed weaker gels with increasing sonication power and time. After 4 h, log G′ of the pectin dispersion that was pretreated at the highest intensity level (40 W cm⁻² and 30 min) was approximately five times lower than log G′ of the untreated dispersion. The change in phase angle [arctan (G′/G″)] with time indicated that the rate of gelation decreased as ultrasonic intensity and application time increased. The turbidity of ultrasonically pretreated pectin dispersions decreased by 50% yielding more transparent gels. Results were attributed to an overall reduction in the average molecular weight of pectin due to cavitational effects. A power law model was fitted to the flow curves of ultrasonically pretreated pectin dispersions to determine both flow behavior index n and consistency coefficient K. With increased sonication power and application time, n increased from 0.6 to 0.97 indicating that the flow behavior changed from viscoelastic to Newtonian.