Low Temperature Blanching Affects Firmness and Rehydration of Dried Cauliflower Florets

Cauliflower florets were blanched at 55, 60, 65, and 70°C, held without cooling for 15, 30, 45, 60, and 90 min, blanched again at 100°and then dried in a hot air dehydrater. The coefficient for the rate of rehydration (?) was calculated using a diffusion model. Rehydrated samples were divided into two equal parts, one part was boiled in water and the other was uncooked. Firmness of rehydrated samples was measured by back extrusion. Blanching cauliflower between 55°and 70°before dehydration caused a substantial increase in extrusion forces after rehydration. Cooking the rehydrated cauliflower decreased firmness of all samples. However, the degree of softening caused by cooking was proportionally less for the low temperature blanch treatments than for the controls.     

Frozen Carrots Texture and Pectic Compotients as Affected by Low-Temperature-Blanching and Quick Freezing

Carrots preheated for 2 hr at 60°C and then cooked became firmer than raw or cooked carrots. After preheating, the amount of high methoxyl pectin decreased, and low methoxyl pectin increased. Firmness of carrots decreased through freezing then thawing, but preheated carrots retained firmer texture than those blanched in boiling water. Quick-freezing resulted in better texture than slow-freezing. Loss in texture was accompanied by release of pectin. Slow-freezing accelerated release of pectin as compared to quick-freezing. Preheated carrots were slower in release of pectin. The degree of esterification of pectin substances in raw carrots decreased during preheating, freezing and thawing. Cell damage in quick frozen carrots was slight. Optimum preheating occurred with 30 min at 60°C or 5 min at 70°C. Preheating and then quick freezing were effective in improving texture of frozen carrots.     

High-Pressure-Freezing Effects on Textural Quality of Carrots

Raw or 3 min blanched carrots were pressurized for 45 min at ?18°C ～–20°C and then thawed at 20°C. When carrots were frozen at 100Mpa (ice I), firmness decreased and strain increased. Textural values of carrots pressurized at 200MPa (liquid), 340MPa (ice III), 400MPa (ice V) at ca. –20°C were acceptable. When pressure was increased above 500MPa, the strain increased. Release of pectin and histological damage in carrots pressurized at 200, 340 and 400MPa were less than carrots frozen at 100 and 700MPa (ice VI). After pressurization at 200 and 340MPa at —20°C, carrots were stored in a freezer (–30°C). Firmness decreased and strain increased, but textural values were higher and histological structure were more intact than those frozen at –30°C (0.1MPa) then stored. Thus, high-pressure-freezing at 200, 340 and 400MPa appeared to be effective in improving both the texture and histological structure of frozen carrots.     

Programmed Freezing Affects Texture, Pectic Composition and Electron Microscopic Structures of Carrots

Raw and blanched carrots (3 min, boiling water) were frozen at ?2°C, ?3°C, ?4°C or ?5°C/min (final ?20°C or ?50°C) then thawed at 20°C or 100°C. Firmness of thawed raw carrots was: ?5°C > ?4°C > ?3°C > ?2°C/min. Effect of freezing rate on blanched carrots was less than that on raw carrots, but firmness of thawed carrots was not affected by final temperature of freezing. When raw carrots were thawed at 20°C, high methoxyl pectin decreased. Pectin decrease in blanched carrots caused by freezing was greater than that in frozen raw carrots. Effects of slow-freezing, programmed-freezing (slow + quick + slow) and quick-freezing showed quick freezing (—5°C/min) best for texture. As freezing rate decreased, drip increased. A wide difference among experimental samples in fine structure was revealed by cryo-scanning electron microscopy.     

Effect of Blanch Temperature on Kinetics of Thermal Softening of Carrots and Green Beans

Cut green beans and diced carrots were blanched at 100°C and 74°C then canned and processed for 5 min to 300 min at 100°C. In every case the rate of thermal softening was consistent with the two substrate first-order kinetic theory of thermal softening of vegetable tissue. The low temperature blanch caused some changes in the apparent firstorder rate constants for both substrates, but the major difference was a much higher intercept of the extrapolated substrate S_S line on the firmness axis. We define S_S at zero process time as the “thermal firmness value” because it is a good indicator of what the firmness of the vegetable will be after canning.     

Textural Properties and Sensory Quality of Processed Sweetpotatoes as Affected by Low Temperature Blanching

Sweetpotatoes (SP) stored for 9–12 mo after harvest were cut into cylindrical pieces and, following factorial experiments and response surface design, were blanched at 50–80°C for 15–274 min. Instrumental textural properties were measured by uniaxial compression and texture profile analysis. Samples of selected blanching treatments were canned in syrup for textural and sensory evaluations. Both blanching temperature and time had significant effects on firmness. Optimal temperature for maximal firmness retention was about 62°C. For canned SP, the 62°C blanched samples were more intact (2–3-fold) and firmer (2–7-fold) than controls. Sensory texture and overall acceptability were greatest for samples blanched at 62°C for 30 or 45 min before canning.     

Pulsed electric field treatment of carrots before drying and rehydration

BACKGROUND: In this study the effects of pulsed electric field (PEF) pretreatment were evaluated during drying and rehydration of carrots. Carrots pretreated with an electric field intensity of 1 kV cm^?1 (capacitance 0.5 µF, 20 pulses) or 1.5 kV cm^?1 (capacitance 1 µF, 20 pulses) as well as blanched (100 °C, 3 min) carrots were used for the study. Following pretreatment, samples were oven dried at 70 °C and then rehydrated in distilled water (1:30 w/v) at room temperature (24 ± 1 °C). RESULTS: PEF pretreatment increased the drying rate of carrots. However, the rehydration rate of PEF‐pretreated carrots was lower than that of blanched carrots. There were no colour differences between PEF‐pretreated and blanched carrots before drying and after rehydration. In terms of texture, PEF‐pretreated carrots were firmer than blanched carrots. PEF pretreatment reduced the activity of peroxidase by 30–50%, while blanching completely inactivated the enzyme (>95%). CONCLUSIONS: Overall, the results suggest that PEF could be an effective pretreatment during drying and rehydration of carrots. Copyright © 2009 Society of Chemical Industry     

Pectinesterase Activity, Pectin Methylation, and Texture Changes During Storage of Blanched Cucumber Slices

Pectin methylation in blanched cucumber slices after 6 months’storage in acid brine (pH 3.7) ranged from 9% (no blanch) to 48% (99°C, 3 min blanch). An 81°C blanch caused complete pectinesterase inactivation, but 15 - 20% reactivation occurred during storage. After a 99°C blanch, only slight reactivation was observed. Pectinesterase was not inactivated at 66°C or less, but up to 85% of the activity was lost during storage. Firmness changes were complex. A clear relationship between pectin methylation and firmness changes was not observed. A 66 or 81°C blanch resulted in best firmness retention. Calcium ion was very effective in prevention of firmness loss regardless of the extent of pectin methylation.     

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     

Optimization of Blanching for Crispness of Banana Chips Using Response Surface Methodology

Whole green bananas were blanched in water at 50, 60, 70, 80, 90, and 100°C for 2, 15, and 30 min using a factorial design then peeled, sliced and fried in oil to make chips. Crispness was measured using a bending-snapping test in the TA.XT2 Texture Analyzer. Significant interactions were found between blanch time and temperature and crispness of chips. A second experiment was then performed using a central composite design and blanch temperatures from 41.7 to 98.3°C. Response surface analysis predicted that crispiest chips should be produced at blanching conditions of 69°C and 22 min.     

Low-temperature Blanch Improves Textural Quality of French-fries

Potatoes, CV. Alpha, were sorted (specific gravity), peeled, cut, and blanched at four temperatures (55—70°C) for several times (0—60 min.) before frying in vegetable oil (200°C, 4 min). Multiple puncture (raw potatoes) and single puncture and Texture Profile Analysis (TPA) of French-fries were used. Limpness angle and oil retention (Carver press) were also evaluated. Firmness and some TPA parameters (chewiness, cohesiveness) were increased (>200%) by blanch. Limpness and oil content were reduced by treatment. Improvement of French-fries texture resulted after blanching for 30—45 min. at 60—65°C.     

Pectin methylesterase catalyzed firming effects on low temperature blanched vegetables

The effect of low temperature blanching on firmness of eight vegetables was studied. Preheating vegetables at low temperatures prior to a conventional blanch resulted in firmer products. Temperature and time had significant effects on texture, with temperature the most influential. Under optimal conditions, firmness improvements in preheated vegetables as compared to blanched controls were: Bok choy—3.0 × (65 °C, 45 min); Chinese cabbage—1.8 × (55 °C, 45 min); cabbage—1.6 × (65 °C, 15 min); green bell peppers—1.36 × (70 °C, 15 min); sugar snap peas—1.7 × (65 °C, 30 min); carrots—2.1 × (60 °C, 15 min) and broccoli—2.9 × (60 °C, 15 min). Thermal stability and optimal temperature for pectin methylesterase in homogenates from these vegetables were also analyzed. The relationship between optimum preheating conditions for textural integrity and pectin methylesterase activity is discussed.     

Effects of low temperature blanching on texture,microstructure and rehydration capacity of carrots

The effect on quality of stepwise blanching (first 10 min at 65 °C, 50 min holding time, and 1 min at 95 °C) prior to drying of carrot slices was compared with conventional blanching (95 °C, 1 min). As quality parameters, rehydration capacity (effective diffusivity D_e, equilibrium moisture content W_e), texture (puncture test) and microstructure (SEM and Cryo‐SEM) were chosen. Non‐significant differences were found between the W_e of stepwise blanched samples and conventionally blanched ones, both values being similar to the moisture content of fresh carrots. D_e of conventional blanched carrots was higher than for stepwise blanched ones. Maximum force of stepwise blanched samples was higher than those of conventionally blanched ones and not significantly different from fresh carrots. Microstructural observations showed that stepwise blanching preserved cell to cell contacts better than conventional blanching; this fact was attributed to pectin‐methyl‐esterase activation at 65 °C, resulting in the differences in the maximum force between both treatments. Conventionally blanched samples tended to separate along their cell walls, forming voids among the phloem parenchyma cells. These voids would be filled with water during rehydration, thus showing the slightly higher W_e and the higher D_e for conventionally blanched carrots. Copyright © 2005 Society of Chemical Industry     

Processing of cauliflower by ohmic heating: influence of precooking on firmness

The feasibility of processing cauliflower by ohmic heating was investigated. Firstly, cauliflower florets were precooked in tap water at low temperatures (40–70 °C) for 0 to 60 min. A control sample was cooked at 95 °C for 5 min. No significant textural differences were found between samples treated at 40 or 50 °C and fresh samples, but the firmness of samples cooked above 60 °C decreased. The effect of precooking time was not found to be significant. Secondly, low temperature precooking was performed in salted water for 30 min and followed by ohmic heating (holding time 30 s at 135 °C). After ohmic heating, florets pretreated at low temperatures were firmer than control samples. The firmness of florets precooked at 40 °C or 50 °C was considerably increased (>300%) compared to those precooked at 95 °C. Low-temperature precooking increased the firmness of cauliflower subjected to ohmic heating. The experimental results show that ohmic heating combined with low-temperature precooking in saline solutions offers a viable solution to high temperature/short time sterilisation of cauliflower florets. © 1999 Society of Chemical Industry     

Inactivation of peroxidase and lipoxygenase in carrots, green beans, and green peas by combination of high hydrostatic pressure and mild heat treatment

The efficiency of high hydrostatic pressure (HHP) with the combination of mild heat treatment on peroxidase (POD) and lipoxygenase (LOX) inactivation in carrots, green beans, and green peas was investigated. In the first part of the study, the samples were pressurized under 250–450 MPa at 20–50 °C for 15–60 min. In the second part, two steps treatments were performed as water blanching at 40–70 °C for 15 and 30 min after pressurization at 250 MPa and 20 °C for 15–60 min. Carrot POD was decreased to 16% residual activity within the first 30 min at a treatment condition of 350 MPa and 20 °C and then it decreased to 9% at 60 min. When the carrots were water blanched at 50 °C for 30 min after HHP treatment of 250 MPa at 20 °C for 15 min, 13% residual POD activity was obtained. For green beans, the most effective results were obtained by two steps treatment and approximately 25% residual POD activity was obtained by water blanching at 50 °C for 15 min after pressurization at 250 MPa and 20 °C for 60 min. An effective inactivation of POD in green peas was not obtained. For carrots, LOX activity could not be measured due to very low LOX activity or the presence of strong antioxidants such as carotenoids. After pressurization at 250 MPa and 20 °C for 15 or 30 min, water blanching at 60 °C for 30 min provided 2–3% residual LOX activity in green beans. The treatment of 250 MPa for 30 min and then water blanching at 50 °C for 30 min provided 70% LOX inactivation in green peas.     

Comparison of Vacuum Treatments and Traditional Cooking Using Instrumental and Sensory Analysis

The purpose of this work was to compare carrots with similar firmness cooked by traditional cooking and two vacuum treatments: sous-vide (SV) and cook-vide (CV). As a first step, consumers determined the preferred level of firmness for carrots cooked by traditional cooking (boiling). This level corresponded to instrumental firmness of 2.8 N in phloem tissue and 4.1 N in xylem tissue. Response surface methodology (RSM) established the pairing conditions of time (22 to 78 min) and temperature (78 to 92 °C) to study the effect of both factors on the firmness of carrots with sous-vide and cook-vide treatments. In both treatments, the instrumental firmness of phloem and xylem samples was measured and modeled. No significant differences were found in firmness values between phloem and xylem tissue of samples cooked by vacuum treatments (CV and SV). For CV treatment, firmness decreased linearly with time and temperature, while for SV treatment it followed a second-order model. Based on the model, conditions of time and temperature to achieve the preferred firmness (2.8 N) were selected for both treatments. Finally, consumers compared the sensory properties of carrots cooked by traditional cooking, sous-vide, and cook-vide with paired comparison tests evaluating three pairs of samples. Carrots cooked by cook-vide were considered less tasty than sous-vide and traditional cooking carrots. Carrots using traditional cooking were firmer than those obtained with SV and CV treatments. Carrots cooked by traditional and sous-vide treatments were preferred to cook-vide ones for the taste.     

Processing to Improve Quality of Dehydrated Precooked Pinto Beans

The firmness of precooked and rehydrated beans after soaking in water at 30°C/2 hr and 82°C/1 hr was lower than that after soaking at 82°C/1 hr or 22°C/12 hr. The 22°C/12 hr soaking yielded the lowest butterflying (8.0%). Steam precooking at 100°C/1 hr produced less splitting, lighter color, and firmer texture than pressure precooking. High initial humidity dehydration reduced splitting. Beans after soaking at 30°C/2 hr and 82°C/1 hr, precooking at 100°C/1 hr, and dehydrating at 65°C/6 hr with initial 95% relative humidity were better regarding firmness, butterflying (11.6%), and moisture content (10.4%).     

STABILIZATION OF ANTHOCYANINS IN FROZEN TART CHERRIES BY BLANCHING

SUMMARY— Unpitted red tart cherries (Prunus cerasus L. cv. Montmorency) were blanched in steam (100°C) for 0, 30, 45 and 60 sec, then frozen at −20°C. The anthocyanin color of the fruit was determined periodically during frozen storage for 3 months in one experiment and 10 months in another. When the cherries were not allowed to thaw before the analysis, no color loss due to anthocyanin destruction was observed in either the blanched or unblanched cherries. When they were thawed at room temperature (22° C) in single layer for 2 and 4 hr, the unblanched cherries lost 14 and 25% anthocyanin color, respectively; cherries subjected to 45- or 60-sec blanching showed no significant color loss. When the cherries were disintegrated in a Waring Blendor for up to 30 min, the unblanched cherries lost considerable color (70%) after 30 min under oxygen or air, but those blanched for 45 or 60 sec suffered no color loss. Some anthocyanin destruction was Observed in the 30-sec blanch lot. Blending under oxygen was slightly more deleterious to the color than blending under air. Blending under nitrogen minimized the color loss but did not eliminate it. Blanching resulted in a 4–7.5% loss of weight.     

Low Temperature Blanching Effects on Chemistry, Firmness and Structure of Canned Green Beans and Carrots

Green beans and carrots were canned using extended blanching at 64–65°C and added calcium and/or acid. Firmer products resulted from all treatments but lowered pH was most effective. Blanched green beans were firmer with lower pectin esterification, indicating pectin methyl esterase activity. Green beans and carrots treated with calcium and/or acid and then cooked were firmer than controls. Acid exhibited a firming effect, perhaps by loosening tissue, while calcium reduced the influence of heat. Instrumental bioyield values correlated with sensory results of canned green beans; bioyield may result from a scleriformic layer. Microscopy showed firmer beans had intact middle lamellae while softer samples contained separated cells. These data suggest that the treatments rendered pectates in the middle lamella less heat labile.     

The Effect of Endogenous Pectinases on the Consistency of Tomato–Carrot Purée Mixes

Tomato and carrot were subjected to a split-stream process designed to produce a tomato–carrot suspension with reduced consistency. Raw tomatoes, containing pectinmethylesterase and endo-polygalacturonase, were mixed with thermally pretreated (blanched versus cooked) carrots containing different levels of solubilized pectin. After mixing the vegetables, tomato pectinases were shown to act on both tomato and carrot pectin in case an incubation step at medium temperature level (30 min, 40 °C), to allow enzyme action, was performed. Carrot pectin, when present in a mix of tomato and blanched (5 min, 95 °C) carrot, was solubilized as well as depolymerized, whereas depolymerization of the thermo-solubilized carrot pectin by the tomato pectinases was observed in the tomato–carrot purée containing cooked (30 min, 95 °C) carrots. The final serum pectin properties were however similar for both purée types. Carrot contributed more to the consistency of the purée mix compared with tomato but by stimulating the action of the tomato pectinases at mild temperature (30 min, 40 °C), this contribution was lost which resulted in a consistency reduction of the purée mix. This purée liquefaction was larger for the tomato–carrot purée containing blanched instead of cooked carrots. Based on the results, it is suggested that the liquefying effect is related to solubilization and degradation of pectin that is counteracted by a reduction in particle size. The purée mix containing cooked carrot showed in this respect smaller particle sizes than the mix containing blanched carrot.