Enzymatic Firming of Processed Red Pepper by Means of Exogenous Pectinesterase

The objective of this investigation was to demonstrate that the firmness of a commercial vegetable product, diced and frozen red pepper (Capsicum annum var. Sendt), could be improved by the use of exogenous pectinesterase in an industrially relevant process. The diced pepper pieces 10 × 10 × 7 mm³ were infused under vacuum with a commercially available pectinesterase. The range of optimal process conditions was: 15-20°C, 45 min infusion time, a 10-25 mM CaCl₂ infusion brine, a w/w ratio of pepper fruit to infusion brine of 1.5:1, and an enzyme dosage of 30-60 pectinesterase units (PEU) per kg pepper fruit. The firmness as measured by back extrusion was improved by a factor of two to three. The effect of firming was robust and conserved after freezing and heating in a simulated household cooking process. The firming process seems easily adaptable to industrial conditions and may be applicable to other vegetable and fruit products.     

Thermal inactivation of the frozen thawed traditional meat starter culture, Pediococcus pentosaceus, in a meat model system

The equation, y_(t) = y₍₀₎e^kt, was fitted (R = 0.9281, 0.9220 and 0.9117, respectively) to thermal inactivation data (55, 60 and 65 °C) of the traditional meat starter culture Pediococcus pentosaceus (10⁷ cfu/ml) in a meat model system. The population reduction constant (‘k’) increased (about 2.5- and 3-fold) with an increase in the treatment temperature (from 55 to 60 °C and from 60 to 65 °C, respectively). The Q₁₀ (55–65 °C) for ‘k’ was 7.63. Thermal treatments of 19.1, 9.0 and 3.1 min (55, 60 and 65 °C, respectively) reduced the population of P. pentosaceus by 2.0 logs. The value of ‘k’ and the duration of the thermal treatment played an important role in the extent of the inactivation of the culture. The “zero inactivation” temperature (T₀) for P. pentosaceus was 49.9 °C. About 5 logs of the culture would be destroyed at 63 and 68 °C within about 15.5 and 6.5 min, respectively.     

Design, fabrication, and testing of a returnable, insulated, nitrogen-refrigerated shipping container for distribution of fresh red meat under controlled CO2 atmosphere

In today's market, fresh red meat is cut and packaged at both the wholesale and retail level. Greater economies could result if the wholesaler prepared all consumer cuts centrally, but the short storage life of meat limits distribution. Use of CO₂-controlled atmosphere, master packaging, and strict temperature control (−1.5±0.5°C) can enhance storage life and, therefore, distribution ease. An insulated shipping and storage container was designed and tested for its suitability to distribute master-packaged meat. Shelves in the container supported 36 master trays (508 × 381 × 60 mm), with the source of refrigeration being injected liquid nitrogen (N₂). Electric fans dispersed the N₂ gas throughout the container. To reduce costs, 36 saline water bags (10% w/v NaCl) were used to thermally simulate the meat. Temperatures of 20 bags were recorded during storage experiments. The container was tested at outside temperatures of 15, 0 and −15°C with 4 internal fans and at 30°C with 2, 4 and 6 fans. In all instances, bags cooled from 10°C to an equilibrium temperature of −1.5°C within 5.5 h. Minimum equilibrium temperatures during any 8 h trial were −2.6, −2.0 and −2.0°C for 2, 4 and 6 fans, respectively. Correspondingly, maximum temperatures were −0.2, −0.7 and −0.3°C. Initial chilling of the product required, on average, 19 kg of N₂, while equilibrium was maintained at a N₂ consumption rate of 5.5, 4.0, 2.6 and 0.93 kg/h at outside temperatures of 30, 15 0 and −15°C, respectively, with 4 fans. The N₂ use for 2 and 6 fans was 5 and 6.3 kg/h, respectively, at an outside temperature of 30°C. During simulated power failure or when the N₂-tank ‘ran dry', temperatures in the container rose 0.9 and 2.0°C/h, respectively. When the door to the container was opened long enough to remove three trays, temperature was restored within 5 min. Convective heat transfer coefficients between saline water bags and circulating N₂ were in the range of 80–100, 115–135, and 140–155 W/(m²·K) for 2, 4 and 6 fans, respectively. Heat transfer to meat will be limited by conduction in master packaged meat if similar convection coefficients prevail.     

The effect of air temperature, velocity and visual lean (VL) composition on the tempering times of frozen boneless beef blocks

Beef blocks of two compositions, 100% and 50% visual lean (VL), in standard commercial packaging with nominal dimensions of 510 × 390 × 150 mm were tempered from −18 °C to −3 °C using air at temperatures from 3 °C to −3 °C and velocities of 0.5 and 5 ms⁻¹. These conditions were then modelled using a finite difference mathematical model and the accuracy of the model assessed by comparison with the experimental results. An extended range of conditions (including an intermediate air velocity of 2 ms⁻¹ and an intermediate composition of 75% VL) was then modelled to produce data that can be used to design tempering processes.

The results show that single stage air tempering of even single blocks within their cartons needs to be a long process. In air at 3 °C and 5 ms⁻¹, blocks of 50% VL rose to deep temperatures of −10 °C and −3 °C after 4.0 and 22.5 h, respectively, while with 100% VL 4.6 and 27.3 h were required. Under these conditions, the surface layers of the meat would have spent many hours in a thawed condition that would be detrimental to both drip and optimal processing. Using lower temperatures avoids thawing and at the same time produces an optimum temperature difference for subsequent processing. However, tempering times are substantially extended. For example, times to the above temperatures using air at −1 °C and 5 ms⁻¹ were 4.8 and 37.5 h for 50% VL and 5.1 and 44.5 h for 100% VL.     

Structural and physical properties of dried Anaheim chilli peppers modified by low‐temperature blanching

The effect of low‐temperature blanching and drying processes on the ultrastructural and physical properties of Anaheim chilli pepper was studied and optimum conditions to provide a final product with maximum firmness were determined. Lots of Anaheim pepper were blanched in water for 4 min at 48, 55, 65, 75 and 82 °C and maintained for hold times of 35, 45, 60, 75 and 85 min, blanched again for 4 min at 96 °C and dehydrated at 53, 60, 70, 80 and 87 °C. After treatment the samples were rehydrated in water at 30 °C. Rehydration ratio, texture and structural changes were evaluated. Optimisation used a second‐order rotatable central composite design. Texture and rehydration ratio were affected by blanching temperature and the interaction of blanching temperature with hold time (p ≤ 0.05); drying temperature did not show a significant effect. The best results, ie those which gave greatest firmness, were obtained by blanching at 64 °C for 4 min, holding for 55 min after blanching, followed by a second blanching at 96 °C for 4 min and then drying at 70 °C. Evaluation of the rehydrated dried pepper by microscopy showed that low‐temperature blanching close to the optimum conditions provided a protective effect in maintaining cell wall integrity. The results of processing increased firmness in the rehydrated product by a factor of 1.97. Copyright © 2003 Society of Chemical Industry     

Effects of low‐temperature blanching on tissue firmness and cell wall strengthening during sweet potato flour processing

Free starch rate has been one of the most important criterions to evaluate the quality of sweet potato flour. Low‐temperature blanching (LTB) of sweet potatoes before steam cooking has shown significant increase in tissue firmness and cell wall strengthening. This research indicated that pectin methylesterase (PME) activity decreased by 87.8% after 30 min of blanching in water at 60 °C, while polygalacturonase (PG) and β‐amylase activity decreased 69.4% and 7.44%, respectively, under the same condition. Both PME and β‐amylase played important roles in tissue firmness. Further studies of tissue firmness and methyl esterification showed that the combination of LTB and Ca²⁺ could increase the activity of PME and significantly enhance the pectin gel hardness to strengthen the cell walls and decrease free starch rate from 12.83% to 7.28%.     

Low-Temperature Blanching of Sweetpotatoes to Improve Firmness Retention: Effect on Compositional and Textural Properties

ABSTRACT: Low-temperature blanching of sweetpotatoes (SP) prior to cooking has been shown to significantly increase firmness retention. This research investigated the effect of blanching on firmness, pectin methylesterase activity (PME), pectin methylation, and galacturonic acid and cell wall material concentrations in SP tissue subjected to blanching and cooking treatments. PME activity decreased 82% after 20 min of blanching in water at 62°C, while sample firmness continued to increase with blanching time (3.5 N for unblanched and 19.0 N for 90 min blanched, and cooked tissue), indicating that firming due to pectin demethylation explains part of the observed increased firmness retention caused by low-temperature blanching, but unknown factors also play a role.,     

Two-dimensional diffusion of Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) populations in stored wheat under constant environmental conditions

Insect movement inside a stored-grain bulk increases the chance for the pests to find biologically suitable locations for their development and multiplication. The movement of rusty grain beetle, Cryptolestes ferrugineus, adults was determined in a 0.1×1×1 m wooden box filled with wheat. There were 12 combinations of temperature (20, 25, 30, or 35 °C), number of adults (125, 250, or 500), moisture content (12.5, 14.5, or 16.5%), and time periods (3, 6, 12, 24 or 72 h) over which movement could occur. The diffusivities in each set of environmental conditions were calculated using a developed procedure (program) and experimental data. The diffusivity at 14.5% m.c. and 20 °C in the 24 h movement period was 2.5±0.3×10⁻⁴ m²/h. The diffusivity increased with increasing temperature, decreasing moisture contents, decreasing movement periods, and increasing insect numbers. Adult numbers in each section of the wooden box were predicted using an analytical model and calculated diffusivities. There were no significant differences between measured and predicted adult numbers. This research suggests that distribution and dispersal of the C. ferrugineus adults in stored wheat follow a diffusion pattern under constant environmental conditions.     

Texture of rehydrated dried bell peppers modified by low-temperature blanching and calcium addition

Diced green bell pepper was blanched twice, once at 51–79 °C for 19–61 min, and once at 95 °C for 3 min, and dried. The firmness of rehydrated samples was measured by puncture, and optimum conditions assessed by response surface methodology. The optimized model showed that, blanching at 65 °C for 49 min gave a 64% increase in puncture force over the control. The optimum temperature was used to evaluate the effect of adding CaCl₂. The dices were blanched twice, once at 65 °C for 3 min in either 0 or 4% CaCl₂, secondly in either 0 or 2% CaCl₂ solution at 95 °C for 3 min. In the second case the dices had been held at room temperature for 0–30 min before treatment. Adding CaCl₂ increased puncture force significantly ( P  ≤ 0.05). The best results, those which gave greatest firmness, were obtained by blanching at 65 °C for 3 min in 4% CaCl₂, holding for 16 min after blanching, followed by a secondary blanching at 95 °C in 2% CaCl₂.     

Pre-selection of protective colloids for enhanced viability of Bifidobacterium bifidum following spray-drying and storage, and evaluation of aguamiel as thermoprotective prebiotic

The objective of this work was to demonstrate that Bifidobacterium bifidum viability to spray-drying and with storage time could be substantially enhanced by pre-selecting protective colloids offering resistance to oxygen diffusion (high activation energy) and adding aguamiel as a thermoprotector prebiotic. Three different protective colloids blends exhibiting relatively high, medium and low activation energies were mixed with B. bifidum harvested in the late log phase, with or without aguamiel, spray-dried at 130, 140 and 155 °C, and stored at 4 °C at a water activity of 0.32. Viability was determined by cell total count in MRS agar. Best viability was achieved when microencapsulating the microorganism in the protective colloids blend exhibiting highest activation energy (40.7 kJ mol⁻¹), with aguamiel, and dried at 140 °C. Viability ranged from 1.26 × 10⁸ cfu g⁻¹ immediately after drying to 6.0 × 10⁶ cfu g⁻¹ after 5 weeks storage time at 4 °C.     

Effect of thermal blanching and of high pressure treatments on sweet green and red bell pepper fruits (Capsicum annuum L.)

The effect of pressure treatments of 100 and 200 MPa (10 and 20 min) and of thermal blanching at 70 °C, 80 °C and 98 °C (1 and 2.5 min), on sweet green and red bell peppers was compared. Pressure treated peppers showed a lower reduction on soluble protein and ascorbic acid contents. Red peppers presented even an increased content of ascorbic acid (15–20%), compared to the untreated peppers. Peroxidase and pectin methylesterase (whose activity was only quantifiable in green peppers) showed a higher stability to pressure treatments, particularly the latter enzyme, while polyphenol oxidase was inactivated to the same final level by the thermal blanching and pressure treatments. Pressure treatments resulted in comparable (in green pepper) to higher (in red pepper) microbial loads compared to blanching. Pressure treated green and red peppers presented similar to better firmness before and after tunnel freezing at −30 °C, compared to thermally blanched peppers, particularly those blanched at 98 °C. The results indicated that pressure treatments of 100 and 200 MPa can be used to produce frozen peppers with similar to better nutritional (soluble protein and ascorbic acid) and texture (firmness) characteristics, comparable activity of polyphenol oxidase and higher activity of pectin methylesterase, while pressure treated peppers show a higher level of peroxidase activity. It would be interesting to use higher pressures in future studies, as an attempt to cause a higher reduction on microbial load and on enzymatic activity.     

Effect of pretreatment and temperature on air-drying of Dioscorea alata and Dioscorea rotundata slices

Effects of pretreatment and drying conditions on yam varieties, namely Dioscorea alata and Dioscorea rotundata, in a fabricated laboratory scale hot air drier at temperature range of 50–80 °C and constant air velocity of 1.5 m²/s were investigated. Mass transfer during air-drying of yam slices was described using Fick’s diffusion model. Drying took place entirely in the falling rate period. Temperature dependency of moisture on diffusivity was illustrated by the Arrhenius relationship. Over the range of temperature, moisture diffusivities varied from 9.92 × 10⁻⁸ to 1.02 × 10⁻⁷ and 0.829 × 10⁻⁶ to 1.298 × 10⁻⁵ m²/s for D. alata and D. rotundata, respectively. Activation energy for drying of D. alata and D. rotundata varied from 25.25 to 46.46 and 41.75 to 72.47 kJ/mol, respectively.     

Extraction of polycyclic aromatic hydrocarbons from cookies: A comparative study of ultrasound and microwave-assisted procedures

The chromatographic determination of 15 polycyclic aromatic hydrocarbons (PAHs) in cookies has been improved in order to obtain a fast method with a low limit of detection through the combination of microwave-assisted extraction (MAE), oil saponification and solid-phase extraction clean-up before the injection of purified extracts in a C18 201TP52 (5 µm, 250  × 2.1 mm) column. Using acetonitrile-water as mobile phase, with a 50% to 95% w/w acetonitrile gradient for a fixed flow of 0.250 ml min^-1, 15 PAHs were separated in 45 min. The column temperature was maintained at 15°C; and fluorimetric detection was made at a fixed excitation wavelength of 264 nm and emission measurements at the best wavelength for each analyte, from 352 nm for 11H-benzo[b]fluorene to 500 nm for indeno[1,2,3-c,d]pyrene. Recoveries for all 15 PAHs varied between 96  ± 4 and 105%  ± 4%; and the limits of detection ranged from 0.015 ng g^-1 for chrysene to 0.7 ng g^-1 for phenantrene. Results were compared with those obtained by conventional Soxhlet extraction during 8-h refluxing with toluene, demonstrating that the methodology proposed is appropriate to quantify PAHs in cookies. Furthermore, the microwave-assisted method was faster and used less solvent than the conventional and ultrasound-assisted methods. The extraction time was reduced to 9 min compared with the 8 h required for Soxhlet extraction and 60 min required for ultrasound-assisted treatment, and the solvent consumption has been reduced to 25 ml compared with the 155 and 90 ml required using Soxhlet and ultrasound, respectively.     

Conventional freezing plus high pressure-low temperature treatment: Physical properties, microbial quality and storage stability of beef meat

Meat high-hydrostatic pressure treatment causes severe decolouration, preventing its commercialisation due to consumer rejection. Novel procedures involving product freezing plus low-temperature pressure processing are here investigated. Room temperature (20 °C) pressurisation (650 MPa/10 min) and air blast freezing (−30 °C) are compared to air blast freezing plus high pressure at subzero temperature (−35 °C) in terms of drip loss, expressible moisture, shear force, colour, microbial quality and storage stability of fresh and salt-added beef samples (Longissimus dorsi muscle). The latter treatment induced solid water transitions among ice phases. Fresh beef high pressure treatment (650 MPa/20 °C/10 min) increased significantly expressible moisture while it decreased in pressurised (650 MPa/−35 °C/10 min) frozen beef. Salt addition reduced high pressure-induced water loss. Treatments studied did not change fresh or salt-added samples shear force. Frozen beef pressurised at low temperature showed L, a and b values after thawing close to fresh samples. However, these samples in frozen state, presented chromatic parameters similar to unfrozen beef pressurised at room temperature. Apparently, freezing protects meat against pressure colour deterioration, fresh colour being recovered after thawing. High pressure processing (20 °C or −35 °C) was very effective reducing aerobic total (2-log₁₀ cycles) and lactic acid bacteria counts (2.4-log₁₀ cycles), in fresh and salt-added samples. Frozen + pressurised beef stored at −18 °C during 45 days recovered its original colour after thawing, similarly to just-treated samples while their counts remain below detection limits during storage.     

Improved Firmness in Calcified Diced Tomatoes by Temperature Activation of Pectin Methylesterase

ABSTRACT: The effects of temperature and calcium on pectin methylesterase (PME) activity and texture in tomato pericarp material were examined. Heating thin slices of pericarp to temperatures between 50°C and 75°C led to the rapid evolution of methanol from the material, indicating an activation of PME. This activity was further stimulated when CaCl₂ (up to 2.0% w/v) was added. When applied to half-inch diced tomato pericarp, the same conditions that led to the activation of PME also improved firmness. Diced tomatoes treated for 5 min with 0.5% CaCl₂ at 70°C were 2.5 times firmer than diced tomatoes treated with CaCl₂ at room temperature. This improvement in texture by treating with CaCl₂ at elevated temperatures was only apparent when the tomatoes received a subsequent 100°C treatment. Heating tomatoes to 70°C either before or after the CaCl₂ treatment also improved firmness through a subsequent high-temperature treatment, but to a lesser extent than heating during the CaCl₂ treatment. These results are consistent with the model that heating to 70°C greatly increases PME activity, leading to extensive pectin de-esterification and increased calcium cross-linking of the pectins in the middle lamella. Production of thermally processed diced tomatoes with improved firmness should be possible by increasing the temperature during and after calcium treatment.     

Texture and Rehydration of Dehydrated Carrots as Affected by Low Temperature Blanching

Whole carrots were blanched at four temperatures for five time periods, then blanched again for 6 min at 100°C. A control sample was blanched 8 min at 100°C. All samples were then dehydrated. Very slight differences in rehydration ratios between treatments were observed. The 50°C blanch gave a firmness equal to or less than the control for all blanch times. The carrots blanched at 55°C for 15, 30 and 45 min were less firm than the control while the 60 and 90 min blanched samples were firmer than the control. The 60 and 65°C blanched samples had significantly firmer texture than the control when blanch time was > 30 min. Blanching carrots for 45 min at 65°C increased firmness of the rehydrated product by 51% for uncooked and 27% for cooked.     

Effect of Vacuum Impregnation Combined with Calcium Lactate on the Firmness and Polysaccharide Morphology of Kyoho Grapes (<Emphasis Type="Italic">Vitis vinifera</Emphasis> x <Emphasis Type="Italic">V. labrusca</Emphasis>)

The effects of vacuum impregnation (VI) with 2% calcium lactate treatment on the VI properties (obtained from hydrodynamic mechanism and deformation–relaxation phenomena models), firmness, and pectin of Kyoho grapes were investigated. Fruit pectin was analysed by atomic force microscopy (AFM). VI was applied for 10–35 min at 25–45 °C and 5 kPa. The maximum values of effective porosity, ε_e (0.606%), and volume fraction, X (0.588%), occurred at 35 °C when the VI time was 15 min. No change was observed in the volumetric deformation (γ ≈ 0) of the grapes after the impregnation. The firmness significantly increased at 35 °C VI (from 12.93 to 14.47 N). According to the AFM results, calcium mainly inhibited the degradation of chelate-soluble pectin and sodium carbonate-soluble pectin short branches during the VI. Under the studied conditions, the validity of VI to incorporate calcium into fruit to improve the quality of grapes was verified, and a final corresponding product was obtained by VI.     

Effect of feed texture, meal frequency and pre-slaughter fasting on carcass and meat quality, and urinary cortisol in pigs

The gelation characteristics of myofibrillar proteins are indicative of meat product texture. Defining the performance of myofibrillar proteins during gelation is beneficial in maintaining quality and developing processed meat products and processes. This study investigates the impact of pH on viscoelastic properties of porcine myofibrillar proteins prepared from different muscles (semimembranosus (SM), longissimus dorsi (LD) and psoas major (PM)) during heat-induced gelation. Dynamic rheological properties were measured while heating at 1 °C/min from 20 to 85 °C, followed by a holding phase at 85 °C for 3 min and a cooling phase from 85 to 5 °C at a rate of 5 °C/min. Storage modulus (G′, the elastic response of the gelling material) increased as gel formation occurred, but decreased after reaching the temperature of myosin denaturation (52 °C) until approximately 60 °C when the gel strength increased again. This resulted in a peak and depression in the thermogram. Following 60 °C, the treatments maintained observed trends in gel strength, showing SM myofibrils produced the strongest gels. Myofibrillar protein from SM and PM formed stronger gels at pH 6.0 than at pH 6.5. Differences may be attributed to subtle variations in their protein profile related to muscle type or postmortem metabolism. Significant correlations were determined between G′ at 57, 72, 85 and 5 °C, indicating that changes affecting gel strength took effect prior to 57 °C. Muscle type was found to influence water-holding capacity to a greater degree than pH.     

Sunflower Head Residue Pectin Extraction as Affected by Physical Conditions

Effects of extraction pH, temperature, and time on yield and quality of pectin from sunflower heads (Interstate cultivar) were investigated. The low-methoxyl pectin was extracted, using 0.75% sodium hexametaphosphate at pH 3, 4, and 5 and at 75, 85, and 95°for 20, 40, and 60 min, respectively. Yield, molecular mass, and firmness of jellies of the pectins were determined. Three-way statistical analysis on yield, molecular mass and gel firmness showed strong interactions among pH, temperature and time. Highest yields were obtained at pH 5, 95°for 20 min and pH 4, 85°for 40 min. Pectin extracted for 40 min at pH 3 and 4 and at 85°and 75°C, respectively, had the highest molecular mass. Gel firmness of sunflower pectin prepared at pH 5.4 was higher than that of a commercial citrus pectin.     

Effect of salt and transglutaminase (TG) level and processing conditions on quality characteristics of phosphate-free, cooked, restructured pork shoulder

Six treatments of phosphate-free restructured cooked pork shoulder were produced with two salt levels (2% and 1%) and three transglutaminase levels (0%, 0.075% and 0.15%) under two processing conditions (72 °C/65 min and 78 °C/65 min). Salt level significantly affected (p < 0.05) the chemical composition, the cooking losses, the colour, the sensory attributes and the overall acceptability of the product. Transglutaminase level affected (p < 0.05) only the consistency and the overall acceptability. The processing conditions on the contrary, affected the moisture and the protein content, the cooking losses, the consistency and the juiciness of restructured cooked pork shoulder. Transglutaminase can be used at a level of 0.15% with reduced salt level (1%) and processing at 72 °C/65 min to produce phosphate-free restructured cooked pork shoulder with acceptable sensory attributes.