Process conditions influence on characteristics of holding tube fouling due to cheese sauce

Cheese sauces, with formulations of 3 g/100 g or 4 g/100 g starch and 15 g/100 g or 35 g/100 g cheese, were processed through a scraped surface heat exchanger (SSHE) under two processing temperatures of 105°C and 121.1°C and mean velocities of 0.14, 0.24 and 0.34 m/s in 3, 5 and 7 h runs. Two test sections (3.548 and 3.569 cm in i.d., and 9.70 and 9.65 cm long, respectively) were installed, one in the holding section after the heating section of the SSHE and the other after cooling section of the SSHE. The fouling deposit was removed from the test sections after each run. Concentrations of protein, phosphorus, fat and mineral were determined. The amount of fat in the deposits was very low after 3 h of processing; it increased with time and almost doubled after 7 h of processing. Process conditions with high mean velocity, regardless of temperature, did not produce detectable fouling deposit. Maximum fouling was obtained in the holding section after the heating section of the SSHE when processing at 121.1°C and for 7 h. Formation of deposit was extremely sensitive to temperature. No fouling was found in the cooling sections.     

Fluid-to-particle Heat Transfer Coefficients for Continuous Flow of Suspensions in Coiled Tube and Straight Tube with Bends

Fluid-to-particle heat transfer coefficient (h_fp) for spherical particles in continuously flowing food suspensions (0-30% v/v green peas in 1.5% sodium carboxymethylcellulose solution) in the holding section of an aseptic processing system was determined. The effects of hold tube geometry, temperature, flow rate, and particle concentration were investigated. The h_fp values ranged from 538 to 1450 W/m²·°C in the coiled tube and from 204 to 1220 W/m²·°C in the straight tube. Significantly, higher h_fp value was observed for particles in the coiled tube as compared to that in the straight tube. The h_fp value increased with temperature, flow rate, and particle concentration. Dimensionless correlations relating the Nusselt number to Reynolds and Prandtl numbers were developed. Estimation of h_fp values based on the particle resistance temperature device (RTD) data and dimensionless correlations indicated a reduction in the degree of overprocessing of average particles when a coiled tube was used instead of a straight tube for the holding section.     

Infrared pasteurization of raw almonds

Due to outbreaks of salmonellosis associated with whole raw almonds, an infrared (IR) pasteurization process was investigated for its efficacy in improving the safety of raw almonds. After almonds were heated to 100, 110 and 120 °C with IR, they were cooled at ambient temperature to a holding temperature of 70, 80 or 90 °C before being transferred to a custom-designed holding device for different time periods up to 60 min. We observed that holding almonds at 90 °C for 10-15 min reduced the Pediococcus population size by more than 5-log and holding at 80 °C for longer than 22 min provided more than 4-log reduction, thus satisfying the targeted 4-log reduction required in the almond industry. The L^∗a^∗b^∗ color values of whole almonds were not affected significantly (P > 0.05) by the IR process whereas the a^∗ and b^∗ color values of ground almonds changed significantly (P < 0.05). The sensory panel did not detect any significant difference (P > 0.01) in appearance, texture, flavor and overall quality of pasteurized almonds compared with untreated samples.     

Pressure and temperature combination for inactivation of soymilk trypsin inhibitors

High hydrostatic pressure (HHP) processing, an emerging technology for food preservation, in combination with thermal treatment (250/50, 550/19, 550/65, and 550/80 MPa/°C) was applied to soymilk made from previously soaked soybeans (in distilled water or 0.5% sodium bicarbonate solution). First order kinetics constants ranging from 0.081 to 0.217 min⁻¹, for residual trypsin, were estimated in soymilk from soaked soybeans at selected pressure–temperature combinations. Residual trypsin, at 550 MPa and 80 °C, was high at higher HHP holding times. The highest percentage of residual trypsin (76%) was estimated after a 15 min holding time. The use of sodium bicarbonate for soaking of soybeans synergistically decreased the trypsin inhibitor activity in soymilk in comparison with residual trypsin using distilled water alone.     

Lethality Distribution within Particles in the Holding Section of an Aseptic Processing System

Residence time distribution (RTD) affected lethal effects of heat on 1.27 cm diameter particles in the holding section of an aseptic processing system. The variations in particle center and particle surface F₀ were determined as a function of particle density, flow rate, and particle to fluid heat transfer coefficient, h_fp. Particles with density ratios of 1.00-1.04 relative to the carrier fluid showed diverse RTD characteristics in the hold tube. Particles with density ratio of 1.01 had the least residence time. The distribution of the particle center F₀ value increased with increase in the h_fp.     

Modelling the effect of water immersion thermal processing on polyacetylene levels and instrumental colour of carrot disks

C₁₇ polyacetylenes are a group of bioactive compounds present in carrots which have recently gained scientific attention due to their cytotoxicity against cancer cells. In common with many bioactive compounds, their levels may be influenced by thermal processes, such as boiling or water immersion. This study investigated the effect of a number of water immersion time/temperature combinations on concentrations of these compounds and attempted to model the changes. Carrot samples were thermally treated by heating in water at temperatures from 50–100 °C and holding times of 2–60 min. Following heating, levels of falcarinol (FaOH), falcarindiol (FaDOH), falcarindiol-3-acetate (FaDOAc) and Hunter colour parameters (L^∗, a^∗, b^∗) were determined. FaOH, FaDOH, FaDOAc levels were significantly reduced at lower temperatures (50–60 °C). In contrast, samples heated at temperatures from 70–100 °C exhibited higher levels of polyacetylenes (p < 0.05) than did raw unprocessed samples. Regression modelling was used to model the effects of temperature and holding time on the levels of the variables measured. Temperature treatment and holding time were found to significantly affect the polyacetylene content of carrot disks. Predicted models were found to be significant (p < 0.05) with high coefficients of determination (R²).     

Effects of supercritical fluid extraction parameters on lycopene yield and antioxidant activity

The effects of various parameters of supercritical carbon dioxide (SC-CO₂) fluid extractions of tomato skins on the extraction yields and antioxidant activities of lycopene-rich extracts were investigated. A Box–Behnken design was applied to study the effects of three independent variables (temperature ranging from 40 to 100 °C, pressure ranging from 20 to 40 MPa, and flow rate ranging from 1.0 to 2.0 mL/min) on lycopene yield. The model showed good agreement with the experimental results, by the coefficient of determination (r² = 0.9834). Temperature, pressure, and the quadratic term for the temperature of SC-CO₂ extraction were large significantly positive factors affecting lycopene yield (P < 0.05). The maximum total lycopene content of 31.25 μg/g of raw tomato was extracted at the highest temperature of 100 °C, 40 MPa and 1.5 mL/min. TEAC assay was applied to assess the antioxidant activity of lycopene-rich extracts from SC-CO₂ fluid extraction. The effects of SC-CO₂ fluid extraction parameters on the antioxidant activities of the extracts differed with the yield. For each unit of lycopene extract, the antioxidant activity level was constant below 70 °C, but then gradually decreased above 70 °C due to isomerization occurring as a result of the higher temperature. The ratio of all-trans-lycopene to the cis-isomers changed from 1.70 to 1.32 when the operating temperature was adjusted from 40 to 100 °C, indicating an increased bioavailability due to the generation of the cis-isomers. No significant effects of pressure or flow rate of SC-CO₂ fluid extraction on the antioxidant activity were observed.     

Effect of processing conditions on physicochemical properties of astaxanthin nanodispersions

A top-down approach based on an emulsification–evaporation technique was used to prepare nanodispersions of astaxanthin. Response-surface methodology was employed to investigate the effect of the main processing conditions, namely, the applied pressure (20–90 MPa), number of cycles (0–4) and evaporation temperature (16–66 °C), on the average particle size, polydispersity index and astaxanthin concentration of the nanodispersions. Second-order polynomial regression models expressing the astaxanthin nanodispersion properties as functions of the main processing variables were significantly (p < 0.05) fitted, with high coefficient-of-determination values (R² > 0.90). A multiple-optimisation procedure showed that the optimum conditions of pressure, number of cycles of homogenization and evaporation temperature, were 50 MPa, two cycles and 47 °C, respectively. A statistical assessment showed insignificant (p > 0.05) differences between experimental and predicted values, thus verifying the adequacy of the final reduced models fitted for explaining the variation of emulsion properties, as a function of homogenization and evaporation conditions.     

Influence of whey protein aggregation on the residence time distribution in a tubular heat exchanger and a helical holding tube during heat treatment process

The residence time distribution (RTD) of a whey protein (WP) suspension flowing through a heat treatment system was studied. The experimental system is the tubular heat exchanger and the helical holding section of a laboratory scale thermal process. RTD was measured in isothermal conditions at 60 °C, a temperature involving no WP aggregation, and at 87 °C, temperature at which WP aggregates. Two flow rates (20 L/h and 49 L/h) were tested with two different lengths of holding tube in order to maintain the same order of magnitude of the holding time. Methylene blue was used as tracer and spectrophotometer analysis were performed to determine the outlet concentration. These investigations yielded to great differences between the RTD in aggregation and no aggregation conditions. The minimum residence time is shorter when WP aggregation occurs due to the modification of the velocity field inside the tubular devices with the local enhancement of the viscosity. Fitting the experimental results with a new compartment model based on the generalized convection model give very good agreement contrary to the more classical RTD models. This RTD model could be used in combination with a population balance model in order to predict the WP aggregates size dispersion.     

Optimization of the antioxidant capacity of thyme (Thymus vulgaris L.) extracts: Management of the convective drying process assisted by power ultrasound

Food properties change during processing, altering the quality of the final product. Sometimes, the important causal relationships are not well known and thus process management is difficult. This is especially true when chemical changes can occur as in the case of the drying of bioactive materials. The aim of this work was to develop a management tool for the thyme drying process, assisted by power ultrasound, to allow the appropriate values of the operating conditions that maximize the antioxidant capacity (AC) of the dried thyme extracts to be determined. For this proposal, the thyme drying process was analyzed at different drying air temperatures (T) (40–80 °C), drying air velocities (v_a) (1–3 m/s) and levels of power ultrasound (US) (0, 6.2, 12.3, 18.5 kW m⁻³). The essential oil was extracted by means of a supercritical fluid extraction method, and its AC was measured by FRAP. The drying velocity and the AC of the dried thyme extracts were both influenced by the magnitude of the air velocity and temperature, and also by power ultrasound. Artificial neural networks were developed to formulate and solve the optimization problem. The developed management tool allowed the optimal conditions of the process to be established, thereby maximizing the AC values in function of the raw materials, process characteristics and room air conditions.     

Computational fluid dynamics modeling of bread baking process

A computational fluid dynamic (CFD) model was developed to study the temperature and browning profile of bread. This study differs from previous work of CFD modeling reported in literature in that phase change during evaporation as well as evaporation-condensation mechanism during baking process was incorporated in this model. Simulation results were validated with experimental measurements of bread temperature at three different positions. In this study crumb temperature does not cross 100 °C due to incorporation of evaporation-condensation mechanism in this model. Baking process completes within 25 min of processing time once the temperature of crumb becomes stable at 98 °C. Formation of crust and browning of bread surface were studied using earlier reported kinetic model and it predicted more browning at bread edges than the surfaces. However, predicted browning index was well within the range (< 52).     

Are virgin olive oils obtained below 27 °C better than those produced at higher temperatures?

Within the European Union, indications of ‘first cold pressing’ and ‘cold extraction’ can only be used for virgin olive oil (VOO) obtained below 27 °C from mechanical processing. Three different malaxing temperatures (25, 35 and 45 °C) are here evaluated for the quality of the VOO obtained in a continuous industrial plant. The oils were stored at room temperature in the dark for 12 months. Initially, oil obtained from a blend of Frantoio/Leccino cultivars (F/L) had higher acidity and peroxide levels and lower phenolic content than a Coratina cultivar (Cor). The oxidative stability of the oils positively correlated with malaxation temperature (F/L, R² = 0.818; Cor, R² = 0.987) as the phenolic content was directly proportional to the temperature (F/L, R² = 0.887; Cor, R² = 0.992). Only oils obtained at 45 °C were rejected because of ‘heated or burnt’ off-flavour. Decarboxymethylation of secoiridoids and further hydrolysis of phenolic esters occurred during storage. The oxidation products of derivatives of tyrosol and hydroxytyrosol were detected after nine months in both the F/L and Cor samples. Thus, VOO obtained at a processing temperature lower than 27 °C does not show higher chemical and sensory qualities than VOO obtained at 35 °C.     

Shear rate and cooling modeling for the study of candelilla wax organogels’ rheological properties

The rheological properties evolution, during the organogelation by cooling of candelilla wax (CW) solution in safflower oil, was studied using computational fluid dynamics (CFD). A simulated storage modulus (G′) model agreed satisfactorily with experimental observations. The gelation of 3% CW solutions was done using static conditions during the whole process (90–5 °C), or by applying a shear rate (180, 300 and 600 s⁻¹) during cooling from 90 °C to 52 °C and then continuing the cooling under static conditions up to the final temperature (i.e. 5 °C). The proposed model predicts G′ evolution as a function of temperature, and considers the final torque (Γ_f) of the sheared stage as an inductor of molecular flow alignment. Predictions revealed that the final solid-like component (i.e. G′) increases as the shear rate increases up to a maximum for a shear rate of about 400 s⁻¹. Then, final G′ value diminishes gradually, probably due to the destruction of microstructures that generate the gelation. The model was validated by graphical methods and variance measures. The results demonstrate the potential of CFD to allow the development of a model linking process variables (i.e. cooling and shearing) and rheological properties. This model can be successfully applied for process control purposes and for the design of organogels with predefined properties.     

Comparison of essential oils of clove buds extracted with supercritical carbon dioxide and other three traditional extraction methods

Supercritical fluid extraction (SFE) of essential oil from clove buds with CO₂ was explored. The effect of different parameters, such as temperature (30 °C, 40 °C, 50 °C), pressure(10 MPa, 20 MPa, 30 MPa) and particle size (three degree index), on the extraction yield and the content of eugenol in extracts was investigated using three-level orthogonal array design. The experimental results show that the temperature has the largest effect on the eugenol content of the extracts, and particle size has the maximum effect on the oil yield. The essential oil of 19.56% yield, in which the maximum content of eugenol in extracts is 58.77%, can be extracted from clove buds at pressure of 10 MPa and temperature of 50 °C. Essential oil of clove buds obtained by SFE, hydrodistillation, steam distillation and Soxhlet extraction were further analyzed by gas chromatography/mass spectrometric detection to compare the extraction methods. Twenty three compounds in the clove oils have been identified, showing that the composition of the clove oil extracted by different methods is mostly similar, whereas relative concentration of the identified compounds is apparently different. General characteristics of the clove oils obtained by different methods were further compared, and SFE is considered as the optimum process among the four processes for obtaining clove oil with high quality.     

Effect of extraction conditions on lycopene extractions from tomato processing waste skin using response surface methodology

Skin, rich in lycopene, is an important component of waste originating from tomato paste manufacturing plants. A central composite design with five independent variables, namely solvent/meal ratio (20:1, 30:1, 40:1, 50:1, and 60:1 v/w); number of extractions (1, 2, 3, 4 and 5); temperature (20, 30, 40, 50 and 60 °C); particle size (0.05, 0.15, 0.25, 0.35 and 0.43 mm); extraction time (4, 8, 12, 16 and 20 min) was used to study their effects on lycopene extraction. The experimental values of lycopene ranged between 0.639 and 1.98 mg/100 g. The second order model obtained for extracted lycopene revealed a coefficient of determination (R²) of 0.99 and a standard error of 0.03. Maximum lycopene (1.98 mg/100 g) was extracted when the solvent/meal ratio, number of extractions, temperature, particle size and extraction time were 30:1 v/w, 4, 50 °C, 0.15 mm and 8 min, respectively.     

The effect of electrical processing on mass transfer in beetroot and model gels

The diffusion between solids and surrounding liquids has been studied under the influence of different electric field strengths varying between 0–1000 V m⁻¹, characteristic both of ohmic heating and Moderate Electric Field (MEF) processing. The rate of enhancement of mass transfer between slabs of beetroot and surrounding fluid has been studied at up to 60 °C, as a function of electric field strength and the orientation of the slab to the field. Enhancements in diffusion coefficient of up to a factor of 2 are seen, with decreased enhancement at higher temperature and when the electric field does not pass through the particle. Diffusion into gels has been studied and enhancement found only for alginate (an ionically set gel) and not for gelatin and egg albumin, that are thermally set gels.     

Microbiological quality of Port Salut Argentino cheese stored at two temperature treatments

Microbiological quality of Port Salut Argentino cheese was studied during 10 days (after ripening) at two storage temperature treatments: (a) 4°C and (b) a temperature combination of both 4 and 20°C (4/20°C), which implied 12 h at 4°C and 12 h at 20°C. Total coliforms were not higher than 10³ cfu/g among samples. E. coli was detected at both treatments. Thirty three percent of the cheese contained Staphylococcus aureus. Listeria spp. and Salmonella spp. were not detected in any treatment. Bacillus spp. incidence was 50% of the cheese, being B. cereus, B. cereus variety mycoides and B. pumilus. Bacillus cereus and Staphylococcus aureus grew at 4/20°C. Mesophilic aerobic bacteria were between 10⁴ and 10⁷ cfu/g. At 4/20°C counts decreased. At 4°C the behaviour was variable. Moulds were lower than 10⁴ cfu/g and yeasts were between 10⁴ and 10⁵ cfu/g. pH, moisture content and tritatable acidity ranges of samples were 5.5-6, 51-52.3% and 1.215-1.935 g/100 g of lactic acid, respectively. Manufacturing of this cheese includes a short heat treatment and starter culture addition; consequently, our results indicate that this processing may be insufficient for achieving hygienic cheese production. The storage at refrigeration temperature will not always guarantee the cheese safety and quality.     

Off-line capillary rheometry of corn starch: Effects of temperature, moisture content and shear rate

A capillary rheometer was used to determine the rheological behaviour of corn starch with moisture contents ranging from 27 to 37 g/100 g (wet basis), at temperatures of 85, 100 and 120 °C, and true wall shear rates ranging from 100 to 2000 s⁻¹. It was found that the rheology of the system followed a pseudoplastic law and the interactions between the processing variables such as temperature, moisture content and shear rate were well correlated with viscosity for the experimental range of conditions considered in this work. The apparent viscosity decreased as moisture content, temperature and shear rate increased in agreement with previous work.     

Segregative interactions and competitive binding of Ca in gelling mixtures of whey protein isolate with Naκ-carrageenan

Gelling mixtures of Na⁺κ-carrageenan with whey protein isolate (WPI) at pH 7.0 have been studied rheologically and by differential scanning calorimetry (DSC), with comparative measurements for the individual constituents of the mixtures. The concentration of WPI was held fixed at 10.0 wt% and carrageenan concentration was varied in the range 0.05–3.0 wt%. Ca²⁺ cations, which have been shown previously to be particularly effective in inducing gelation of κ-carrageenan, were introduced as CaCl₂. The concentration of CaCl₂ used in most of the experiments was 8 mM, but other concentrations were also studied. Mixtures were prepared in the solution state at 45 °C, and showed no evidence of either phase separation or complex formation. Rheological changes were monitored by low-amplitude oscillatory measurements of storage modulus, G′, during (i) cooling (1 °C/min) and holding at 5 °C, to induce gelation of the carrageenan in the presence of non-gelled WPI; (ii) heating and holding at 80 °C to dissociate the carrageenan network and induce gelation of WPI; (iii) cooling and holding again at 5 °C, to give composite networks with both components gelled; and (iv) re-heating to 80 °C to dissociate the carrageenan network. Gel structure was characterised further by creep–recovery measurements at the end of each holding period, and by torsion measurements at 5 °C, before and after thermal gelation of WPI.     

Optimisation of osmotic dehydration process of carrot cubes in mixtures of sucrose and sodium chloride solutions

In the optimisation of the osmotic dehydration process of the carrot cubes in mixtures of sucrose and sodium chloride by response surface methodology, using face-centred central composite design (CCF), it was shown that the independent process variables for osmotic dehydration process were osmotic solution concentrations (5–15% w/v sodium chloride in 50 °Brix sucrose syrup), temperature (35–55 °C) and process duration (120–240 min). Statistical analysis of results showed that the linear terms of all the process variables have a significant effect on all the responses. The optimum osmotic dehydration process conditions for maximum water loss, minimum solute gain, maximum retention of colour, and sensory score were: 50 °Brix + 15% w/v sodium chloride solution, 54.8 °C solution temperature and 120 min process duration.