Influence of ultrasound on mass transport during cheese brining

 The effect of ultrasound on mass transfer during cheese brining has been investigated. The rate of water removal and NaCl gain increased when ultrasound was applied in comparison with brining performed under static or dynamic conditions, suggesting that ultrasound improves both external and internal mass transfer. A simple diffusional model was developed to simulate mass transport during acoustic brining. Model parameters were estimated using experimental data from acoustic brining experiments carried out on cheese cylinders of 1.7×10^–2m radius and 3×10^–2 m height at different temperatures (5, 15 and 20  °C). Effective water (D _W) and NaCl (D _S) diffusivities estimated using the proposed model ranged from 5.0×10^–10m²/s and 8.0×10^–10 m²/s at 5  °C to 1.3×10^–9m²/s and 1.2×10^–9 m²/s at 20  °C. Both D _W and D _S varied with temperature according to the Arrhenius equation. Through the proposed model, water losses and NaCl gains of the experiments used in the parameter identification were accurately simulated (average %var=98.2%) and also of two additional acoustic experiments carried out under different conditions of temperature (10  °C) and sample size and geometry [parallelepiped of (6×2.5×1.25)×10^–2 m] to those used in the parameter identification (average %var=98.4%). Received: 22 September 1998 / Revised version: 20 November 1998     

Optimization of stepwise blanching of frozen-thawed potato tissues (cv. Monalisa)

 Response surface methodology was used to compare the effect of temperature and time of the first step of blanching on compression, shear, tension and stress-relaxation parameters of frozen-thawed potato tissues. A central, composite rotatable design was used to study the effects of variation in levels of temperature (52.93–67.07  °C) and time (15.86–44.14 min) on rheological parameters. Blanching temperature was the most important factor affecting the mechanical properties tested. The models fitted for the apparent modulus of elasticity in compression, maximum tension force, and relaxed force in the first cycle (F _r1); all had R ²>0.85 (P≤0.01) and were used for doing predictions. Optimum conditions were with in the ranges of temperature (60–65  °C) and time (25–35 min) used for each factor. In the experimental verification of the models at 65  °C during 30 min, the lowest percentage residual between experimental and predicted values was obtained for F _r1 (0.644), which was therefore the most appropiate parameter for detecting the firming effect that the pectinesterase activity produced on frozen potato tissues as a consequence of stepwise blanching under these conditions. Received: 3 February 1999 / Revised version: 12 April 1999     

Kinetics of green asparagus ascorbic acid heated in a high-temperature thermoresistometer

 Thermal degradation of green asparagus ascorbic acid in high-temperature short-time conditions was studied by heating in a five-channel computer-controlled thermoresistometer. Ascorbic acid was heated to between 110  °C and 140  °C and the degradation kinetics were analyzed assuming that two different inactivation mechanisms were occurring, one aerobic and the other anaerobic. The two reactions followed first-order kinetics, with E _a=12.3(2.0) kcal/mol and k _125  °C=47.0(3.0)×10^–3 s^–1 for the aerobic oxidation, and E _a=6.1(1.4) kcal/mol and k _125  °C=4.1(0.2)×10^–3 s^–1 for the anaerobic degradation. Received: 30 January 1998 / Revised version: 11 June 1998     

Optimization of supercritical CO2 extraction of phytosterol-enriched oil from Kalahari melon seeds

Supercritical carbon dioxide (SC-CO₂) extraction of oil from Kalahari melon seeds was investigated in this study. Response surface methodology was applied to model and optimize the extraction, namely pressure (200–400 bar), temperature (40–80 °C), and supercritical fluid flow rate (10–20 mL/min). Well-fitting models were successfully established for oil recovery (R ² = 0.9672) and phytosterol concentration (milligrams per 100 g; R ² = 0.8150) through multiple linear regressions with backward elimination. The effect of supercritical fluid flow rate was the most significant (P < 0.05) factor that affected oil recovery but this factor had no significant (P > 0.05) effect on phytosterol concentration. The optimal processing conditions for oil recovery and phytosterol concentration were pressure of 300 bar, temperature at 40 °C, and supercritical fluid flow rate of 12 mL/min. These optimal conditions yielded a 76.3% oil recovery and 836.5 mg/100 g of phytosterol concentration. The oil content in the Kalahari melon seeds as estimated by Soxhlet extraction was around 30.5/100 g. The phytosterol concentration in the oil extracted with SC-CO₂ extraction was 94% higher than that obtained with solvent extraction.     

The effects of fermentation on the thermostability of the yellow-orange pigments extracted from cactus pear (Opuntia ficus-indica)

 Cactus pear (Opuntia ficus-indica) juice with a total soluble solids content of 15.94 °Brix was fermented using the wine yeast Saccharomyces cerevisiae. A 94.54% conversion of fermentable sugar was achieved with an ethanol production of 55.3 ml/l. The pigment degradation was found to be 17% at the end of the time allowed for fermentation. However, the fermentation had actually ceased due to depletion of fermentable sugars after 12 h, a point at which only 9.4% pigment degradation was observed and there was no further total soluble solids degradation. The thermal stability of the yellow-orange pigment of the fermented juice was determined as a function of temperature at pH 5.0. The kinetic experiments were carried out at three different temperatures, 50, 70 and 90  °C. For a pseudo-first order thermal degradation rate the reaction rate constants were determined to be 0.0066, 0.0206 and 0.1244 min^–1 for temperatures of 50, 75 and 90  °C, respectively. The activation energy was calculated as 15.71 kcal mole^–1. The fermentation process did not affect the thermostability of the pigment extract. Received: 10 January 2000 / Revised version: 31 March 2000     

Quality of cauliflower as influenced by film wrapping during shipment

 Throughout the season, 'Siria' cauliflower heads from three harvesting periods were film-wrapped and stored for 1 week at 1.5  °C to simulate a maximum period of commercial shipment. After cold storage, the heads were kept for 2.5 days at 20  °C to simulate a retail sale period. Different polymeric films – polyvinyl chloride (PVC) of 14 μm thickness, low-density polyethylene (LDPE) of 11, 15 and 20 μm thicknesses and a special LDPE of 11 μm thickness adapted for microwave ovenuse – were used for wrapping. Soluble solid content, pH, titratable acidity, weight loss, physiological disorders, fungal attacks, visual quality and gas composition within packages were monitored. After the shelf life simulation, among the LDPE films studied, the best results were obtained by using 11 μm LDPE. Gas composition (about 16% O₂ and 2% CO₂ during cold storage, and about 11% O₂ and 3.5% CO₂ during retail sale simulation), overall quality, yellowing and browning of the head, and Alternaria spp. development were at similar levels among the films studied. However, weight loss was considerably lower for all LDPE films than for PVC film. For commercial purposes 11 μm LDPE could be a good alternative to PVC for wrapping cauliflower. Received: 30 October 1998 / Revised version: 18 January 1999     

Use of β-hydroxyacyl-CoA-dehydrogenase (HADH) activity to differentiate frozen from unfrozen fish and shellfish

 Further work on an enzymic method to differentiate frozen from unfrozen fish and shellfish is reported. The method is based on the release of the β-hydroxyacyl-CoA-dehydrogenase (HADH) from mitochondria during freezing. Enzymic activity was evaluated in fresh and frozen thawed samples from sole (Solea solea), sea bream (Pagellus centrodontus), hake (Merluccius merluccius), gilt headed bream (Sparus aurata), sea bass (Dicentrarchus labrax), salmon (Salmo salar), prawn (Penaeus japonicus) and Norwegian lobster (Nephrops norvegicus). Changes in the HADH activity of fresh and frozen thawed samples were compared after freezing at –196  °C for 15 min. Two values were obtained: U (by dividing: HADH activity of samples frozen at –196  °C, then thawed/HADH activity of unfrozen samples) and F (by dividing: HADH activity of samples frozen at –18  °C, thawed, then frozen at –196  °C /HADH activity of samples frozen at –18  °C, then thawed). Statistical analysis showed significant differences (P≤0.05) between both quotients for gilt headed bream, salmon, sea bream, sole and prawn, and an arbitrary limit was set at 2 to differentiate frozen thawed from unfrozen samples. The application of this limit made it possible to discriminate the unfrozen from the frozen thawed state of around 90% of the total samples analysed. Best results were obtained for prawn (100% of samples differentiated). In the present paper, a laboratory routine is proposed based on the comparison of the HADH activity of a sample analysed straight away and that of a sample frozen at –196  °C and then thawed. The reported method is simple and fast. The entire laboratory procedure can be performed in 45 min. Received: 20 July 1998 / Revised version: 2 November 1998     

Clostridium sporogenes-ATCC 7955 Spore Destruction Kinetics in Milk Under High Pressure and Elevated Temperature Treatment Conditions

Clostridium sporogenes (ATCC 7955) spores inoculated in milk (2% fat) were subjected to high-pressure (HP) treatments (700–900 MPa) and at elevated temperatures (80–100 °C) for selected times up to 32 min. Samples were sealed in 1-mL plastic vials and placed in a specially constructed insulated chamber to prevent temperature drop during the treatment. Both pressure pulse (with no hold time) and pressure hold techniques were employed for treatment. Pressure pulse resulted in a small, but consistent, destruction (up to 0.5 log kill) of spores. During the pressure hold treatment, the destruction followed a first-order model (R ² > 0.90). The kinetic data were compensated for the small variations in temperature during the treatment. As expected, higher pressures and higher temperatures resulted in a faster rate of spore destruction. Temperature-corrected D values ranged from 13.6 to 2.4 min at 700 MPa and 7.0 to 1.3 min at 900 MPa, respectively, with process temperatures set at 90 and 100 °C. In comparison, thermal treatments gave D values ranging from 156 min at 90 °C to 12.1 min at 100 °C. The temperature sensitivity Z _P values (16.5 to 20.3 °C) under high pressure (700–900 MPa) were higher than under conventional thermal processing (9.0 °C), indicating the spore’s thermal resistance to increase at HP processing conditions. The pressure sensitivity Z _T values varied between 450 and 680 MPa under the elevated temperature (80–100 °C) processing conditions. Overall, C. sporogenes 7955 spores were relatively more sensitive to temperature than pressure.     

Comparison Between Systems for Synthesis of Fructooligosaccharides from Sucrose Using Free Inulinase from Kluyveromyces marxianus NRRL Y-7571

This work is focused on the synthesis of the fructooligosaccharides (FOS) from sucrose using free inulinase from Kluyveromyces marxianus NRRL Y-7571 in aqueous and aqueous–organic systems. The most significant variables for the aqueous–organic system were identified using a fractional factorial design. The evaluated variables were the temperature, pH, sucrose concentration, inulinase activity, aqueous/organic ratio, and the polyethylene glycol concentration. The use of sequential experimental design methodology was shown to be very useful in the optimization of the FOS synthesis by inulinase either in aqueous or aqueous–organic systems. For the aqueous–organic system, the maximum Y _FOS reached was 16.7 ± 1.1 wt.% with the following operational conditions: temperature of 40 °C, enzyme activity of 4 U mL⁻¹, organic solvent/total system ratio of 25/100, pH of 6.0, and sucrose concentration of 55%. In the aqueous system, the maximum conversion obtained was 12.8 ± 1.0 wt.% under the following conditions: 40 °C, pH 5.0, 55% sucrose, and inulinase activity 4 U mL⁻¹.     

The texture of low calorie grape juice jelly

 In this work the production of grape juice jellies with a low methoxyl pectin was studied. Availability of this kind of jelly will increase the range of dietetic products and is a promising alternative use for grapes surplus to the needs of the enological industry. The formulation of the jellies was optimized by response surface methodology (RSM), using as independent variables total sugar content (20 – 50°Brix), low methoxyl pectin content (0.5 – 1.5%) and processing temperature (55 – 90°C) at five levels. The dependent variable was the overall balance (B), a response obtained from sensory analysis. B was chosen from a series of sensory attributes evaluated by a test panel and the data treated by principal component analysis (PCA). The resulting polynomial equation (R ² = 0.92) showed the maximum value for B to occur for a jelly produced with 38°Brix of total sugar, 1.2% of low methoxyl pectin and a processing temperature of 69°C. The sensory-optimized jelly was objectively characterized for texture and dynamic rheological behaviour. Received: 2 October 1996 / Revised version: 7 January 1997     

Mass Transfer Coefficients for the Drying of Pumpkin (Cucurbita moschata) and Dried Product Quality

The aim of this work was to determine the mass transfer properties of pumpkin (Cucurbita moschata) exposed to air drying. The drying temperatures tested ranged between 30°C and 70°C, and the kinetic behavior was studied in this temperature band. The samples were analyzed in terms of moisture content, acidity, proteins, lipids, and crude fiber, both in the fresh state and after drying. From the chemical analyses made, it was possible to conclude that drying induces some reductions in acidity, lipids, fibers, and proteins. As to the influence of the drying temperature on the process, it was observed that a temperature rise from 30°C to 70°C led to a 70% saving in drying time. The results obtained by fitting the experimental data to the kinetic models tested allowed concluding that the best model for the present case is Henderson–Pabis, and the worst is Vega–Lemus. Furthermore, in this work, it was possible to determine the values of the diffusion coefficient at an infinite temperature, D _e⁰, and activation energy for moisture diffusion, E _d, which were, respectively, 0.0039 m²/s and 32.26 kJ/mol. Similarly, the values of the Arrhenius constant and the activation energy for convective mass transfer, respectively, h _m⁰ and E _c, were also calculated, the first being 3.798 × 10⁸ m/s and the latter 86.25 kJ/mol. These results indicate that the activation energy for convective mass transfer is higher than that for mass diffusion.     

Browning susceptibility of minimally processed Baby and Romaine lettuces

 This study was conducted to determine the effects of cultivar, tissue susceptibility and storage temperature on the keeping quality of minimally processed Baby and Romaine lettuces. Midrib and photosynthetic tissues were lightly processed and stored for up to 7 days at 5  °C and 13  °C. Changes in L ^* and a ^* values and absorbance at 430 nm were compared. The relationship between polyphenols, phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) activities and browning was examined. Measurements of L ^* and a ^* values on midribs showed that browning discoloration was the same for Baby as for Romaine lettuces and there was no relationship for temperature. In addition, L ^* and a ^* values in photosynthetic tissue indicated a decrease in green pigmentation during storage, especially at 13  °C. For both kinds of tissue at the end of cold storage an increase in soluble brown polymers was detected. In midribs, total phenolics increased significantly throughout the storage period because of the tissue-wounding response. The photosynthetic tissue had a higher phenolic content than the midrib one. For both kinds of tissue an increase in PPO activity occurred throughout cold storage. On the other hand, PAL activity in midrib tissue only increased initially, followed by a slow decline to reach normal levels. Browning potential estimated by L ^* values correlated significantly (P>95%) with PPO activity and with absorbance at 430 nm for Romaine lettuce. Based on colour and browning potential no differences between Romaine and Baby lettuce cultivars were observed. However, photosynthetic tissue was the most suitable tissue for the preparation of minimally processed salad mixes because of its high phenolic content. Received: 28 September 1998     

Sorption Isotherms of Barnyard Millet Grain and Kernel

The moisture sorption isotherms of grain and kernel of barnyard millet (Echinochloa frumentacea) were determined at 20, 30, 40, and 50 °C. A gravimetric static method was used under 0.112–0.964 water activity (a _w) range for the determination of sorption isotherms. The models were compared using the coefficient of determination (r ²), reduced chi-square (χ ²) values, and on the basis of residual plots. In grain, modified Chung–Pfost (r ² > 0.99; χ ² < 0.7) and modified Oswin (r ² > 0.99; χ ² < 0.55) models were found suitable for predicting the M _e –a _w relationship for adsorption and desorption, respectively. Modified Henderson model was found to give the best fit (r ² > 0.99 and χ ² < 0.55) for describing the adsorption and desorption of the kernel. The isosteric heat, calculated using Clausius–Clapeyron equation, was varied between 46.76 and 61.71 kJ g⁻¹ mol⁻¹ at moisture levels 7–21% (d.b.) for grain and 47.11–63.52 kJ g⁻¹ mol⁻¹ at moisture level between 4% and 20% (d.b.) for kernel. The monolayer moisture content values ranged from 4.3% to 6% d.b. in the case of adsorption of barnyard millet grain and 5.2–6.6% d.b. in the case of desorption at the temperature ranges of 50–20 °C. The monolayer moisture values of barnyard millet kernel ranged from 4.4% to 6.67% d.b. in adsorption and 4.6% to 7.3% d.b. in desorption in the temperature ranges of 50–20 °C.     

Principal component analysis to study the effect of temperature fluctuations during storage of frozen potato

 The effects of temperature fluctuation ranges, number of fluctuations carried out, and packaging during frozen storage on the texture of potato tissue in terms of compression, shear, and tension rheological parameters were assessed through data generated according to a factorial design using principal component analysis (PCA). Five ranges of fluctuation (–24  °C to –18  °C, –18  °C to –12  °C, –12  °C to –6  °C, –24  °C to –12  °C and –18  °C to –6  °C) applied 2, 4, 8, 16, 24, and up to 32 times on unpacked and pre-packed frozen potatoes, were considered. The controls were unpacked and prepacked frozen tissues thawed immediately without undergoing any fluctuation. In addition, several geometrical, technological, and chemical parameters were determined. PCA showed that maximum shear force, F_s was the best rheological parameter for differentiation of the structural damage and softening occurring in the tissue at each treatment, which was closely related to its duration, TT _d . PCA did not permit complete discrimination between the five fluctuation ranges, but it clearly separated samples subjected to –18  °C/–6   °C from those subjected to –24  °C/–18  °C. Frozen samples undergoing up to four fluctuations formed a separate cluster from those undergoing a higher number. Analysis also clearly separated unpacked from pre-packed samples in response to slower freezing rates reached in the latter. Received: 17 December 1999     

Thin Layer Drying of African Breadfruit (Treculia africana) Seeds: Modeling and Rehydration Capacity

African breadfruit (ABF) seeds are underutilized plant resources, which have been reported to have high potential for novel food and industrial uses. The kinetics of moisture removal during air drying of the whole (WS) and dehulled (DS) seeds was studied at temperatures of 40–70 °C. Five empirical models were tested for predicting the experimental data. Drying of ABF seeds followed an exponential decay pattern, while drying predominantly took place during the falling rate periods. All the drying models predicted the experimental data above 90% accuracy while the Henderson–Pabis model gave the best fit (0.95 < r ² < 0.99) at most of the experimental conditions. Effective moisture diffusivity, D _eff, ranged from 3.65 to 7.15 × 10⁻⁹ m²/s and 3.95 to 6.10 × 10⁻⁹ m²/s for WS and DS, respectively. D _eff showed significant dependence on the moisture content (p < 0.01). Rehydration capacity of DS was not significantly affected by drying temperature while that of WS increased with drying temperature.     

Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)

 A comparison of the lipid damage produced in different hake zones was carried out during frozen storage at –11 and –18  °C. Three light muscle zones and the dark muscle were considered. Lipid oxidation [conjugated dienes; thiobarbituric acid index (TBA-i); fluorescence formation] and hydrolysis (free fatty acids, FFA) were determined. The most predominant lipid damage in all zones was hydrolysis, at the end of storage reaching values of about 40% (for the light muscle zones) and 12% (for the dark muscle) of the total lipids at –11  °C. Significant (P<0.05) correlation value (r=0.67–0.85) relationships between the frozen storage time and the FFA content were obtained for the four muscle zones at both temperatures. A comparison of the regression lines slopes in the different zones showed that a lower (P<0.05) lipolitic activity was produced in the dark muscle compared to the three light zones at both temperatures. A low lipid oxidation development was produced in the three light muscle parts, so that no significant differences between them could be assessed. However, the dark muscle showed a higher oxidation development (TBA-i and fluorescence formation) as a result of a higher lipid content and the presence of prooxidant constituents. Received: 16 June 1998     

Physicochemical Properties of Caribbean Sweet Potato (Ipomoea batatas (L) Lam) Starches

The proximate compositions and physicochemical properties of 21 Caribbean sweet potato (Ipomoea batatas (L) Lam) starches were investigated. Proximate composition, amylose, reducing and non-reducing sugars were determined using standard methods. Swelling power and solubility were evaluated and pasting properties of the starches were determined using Rapid Visco Analyzer. Moisture (8.0–12.4%), protein (0.0–0.2%), ash (0.1–0.5%), and reducing (0.3–2.3%) and non-reducing sugar (0.1–0.2%) contents of starches were significantly different (P < 0.05) among the cultivars. Amylose content varied significantly between 12.8–21.3%. Swelling power and solubility ranged between 7.8–31.1% and 1.5–9.6%, respectively. Pasting properties such as peak viscosity measured in Rapid Visco Units (143.2–288.8 RVU), breakdown viscosity (29.4–162.6 RVU), and setback viscosity (15.0–78.8 RVU), pasting temperature (73.5–87.7 °C) and time to pasting temperature (3.6–4.5 min) varied significantly among the cultivars. Breakdown viscosity was poorly correlated with final viscosity attained (r = − 0.0507, P < 0.05); however, pasting temperature was correlated (r = 0.479, P < 0.05) with setback viscosity. The variability observed in the physicochemical properties of the starches was related to specific requirements for use in the production of noodles, pasta, and inclusion in bread and weaning food formulations.     

Use of carbon dioxide enriched atmospheres in the refrigerated storage (2 °C) of salmon (Salmo salar ) steaks

 Selected microbial counts (total viable microbiota, Brochothrix thermosphacta, lactic acid bacteria and Enterobacteriaceae), biochemical parameters [pH, total volatile nitrogen, nucleotide breakdown products, non-volatile amines, d(–) and l(+)-lactic acids and short-chain fatty acids] and sensory attributes (colour and odour) of refrigerated (2  °C) salmon (Salmo salar) steaks stored under CO₂-enriched [CO₂/air (20/80, v/v), CO₂/air (40/60, v/v)] and air atmospheres were determined. When compared with air, sensory results showed shelf-life extension of 6 days and 15 days for 20% and 40% CO₂-enriched atmospheres, respectively. Microbial and biochemical results also revealed that the 40% CO₂-enriched atmosphere was the most effective packaging type for refrigerated salmon. Received: 22 April 1999     

Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)

 A comparison of the lipid damage produced in different hake zones was carried out during frozen storage at –11 and –18  °C. Three light muscle zones and the dark muscle were considered. Lipid oxidation [conjugated dienes; thiobarbituric acid index (TBA-i); fluorescence formation] and hydrolysis (free fatty acids, FFA) were determined. The most predominant lipid damage in all zones was hydrolysis, at the end of storage reaching values of about 40% (for the light muscle zones) and 12% (for the dark muscle) of the total lipids at –11  °C. Significant (P<0.05) correlation value (r=0.67–0.85) relationships between the frozen storage time and the FFA content were obtained for the four muscle zones at both temperatures. A comparison of the regression lines slopes in the different zones showed that a lower (P<0.05) lipolitic activity was produced in the dark muscle compared to the three light zones at both temperatures. A low lipid oxidation development was produced in the three light muscle parts, so that no significant differences between them could be assessed. However, the dark muscle showed a higher oxidation development (TBA-i and fluorescence formation) as a result of a higher lipid content and the presence of prooxidant constituents.     

Ripening and ethylene biosynthesis in controlled atmosphere stored apricots

 Ethylene synthesis and metabolism were studied in apricot fruits (Prunus armeniaca L. cv. Búlida, under controlled atmosphere (CA) conditions (20% CO₂ and 20% O₂; 20% CO₂ and 1% O₂; 0.03% CO₂ and 1% O₂) and at a temperature of 2  °C. In control apricots stored outdoors in air containing 20% O₂ and 0.03% CO₂, the evolution of the physical and chemical parameters characteristic of ripening (loss of texture, decrease in acidity and increase in soluble solids) was slow during the storage period. However, for apricots stored in CAs containing 1% O₂ and 20% or 0.03% CO₂, these parameters did not show significant changes during the storage period. Ethylene production was completely inhibited in apricots stored in the three CAs, while control fruits showed a maximum ethylene level after 2 weeks of storage. This inhibition was accompanied by lower levels of 1-aminocyclopropane-1-carboxylic acid, free and total, which were more pronounced in apricots stored in the CAs containing 20% CO₂. In apricots stored in the CAs containing 1% O₂, the ethanol content increased after 1 week of storage, and this caused a smell and taste that made the fruits unsuitable for consumption. Received: 16 October 1998