KINETIC OF SOFTENING OF CARROT BY GAMMA RADIATION

Raw carrots were diced into 9.5 mm cubes, and subjected to gamma radiation between an array of Co⁶⁰ pencils. A series of doses ranging from 0 to approximately 50 kGy was given. A plot of log (extrusion force) versus dose showed two distinct regions; the first is a rectilinear plot with a steep negative slope for doses up to about 15 kGy. The second is also a rectilinear plot with a shallow negative slope beyond 15 kGy. Sixty-seven percent of the firmness is lost with the first 15 kGy but only 4% of the firmness is lost with the highest 15 kGy increase in dose. This two-stage softening rate curve is consistent with the model of two first-order kinetic rate processes and is qualitatively similar to that for thermal softening of carrot. The term "radiation firmness" is proposed to describe the amount of firmness that is resistant to degradation by irradiation.     

EFFECT of LOW TEMPERATURE BLANCHING, CYSTEINE-HCi, N-ACETYL-L-CYSTEINE, Na METABISULPHITE and DRYING TEMPERATURES ON the FIRMNESS and NUTRIENT CONTENT of DRIED CARROTS

Low temperature long time (LTLT) blanching (70C for 20 min) together with calcium treatment can be used to significantly improve the texture of rehydrated dried carrots when compared to high temperature short time (HTST) blanching (100C for 3 min). LTLT blanching allows pectin methyl esterase to deesterify pectin which can then react with calcium to form salt bridges. 0.3% L-cysteine-HCl was found to be most effective in preventing ascorbic acid loss and obtaining a product with the highest rehydration ability, compared to pretreatments with 0.3% N-acetyl-L-cysteine and 0.1% sodium metabisulphite. On the other hand 0.1% sodium metabisulphite was most effective in preserving the carotenoids content of dried carrots. Ascorbic acid and rehydration ability were more adversely affected by long drying time than high drying temperature, while carotenoids were more sensitive to high drying temperature than drying time. Hence, 60C drying temperature was good for ascorbic acid and rehydration ability, while 40C drying temperature was good for carotenoid and color of dried carrots.     

物性分析仪在食品质构测定方面的应用

质地特性是食品极其重要的品质因素。一般采用的感官评定方法主观因素偏重，而物性分析仪所反映的主要是与力学特性有关的食品质地特性，其结果具有较高的灵敏性与客观性，故其使用越来越广泛。本文综述了物性分析仪的原理及其在小麦粉制品、肉制品、水产品和乳制品中的应用，以及存在的问题与展望。     

Carrot texture degradation kinetics and pectin changes during thermal versus high-pressure/high-temperature processing: A comparative study

Texture degradation kinetics of carrots during traditional thermal and novel high-pressure/high-temperature (HP/HT) processing were compared. Carrots were thermally (0.1 MPa) or HP/HT (600 MPa) treated in a temperature range from 95 to 110 °C. The residual texture (hardness) was determined using a texture analyzer. Kinetic parameters were estimated using a fractional-conversion model. In comparison to the thermal treatments, the HP/HT treatments resulted in a 10-fold slower texture degradation. The retarded texture loss was accompanied by a significantly lower degree of methyl-esterification (DM) of the cell wall pectin. Additionally, the effect of lowering the DM (by applying an HP pretreatment) and adding exogenous calcium ions prior to the HP/HT treatment on the texture of carrots was investigated. It was observed that this combined pretreatment resulted in a notably harder texture of HP/HT-treated carrots. However, a similar outcome was obtained by HP/HT treating carrots directly in a calcium chloride solution without preceding DM reduction and calcium soak. Excluding a separate pretreatment step will lead to time savings and a lower cost. This study demonstrated that HP/HT processing has great potential, concerning texture preservation of processed fruits and vegetables.     

Influence of Acidification on Texture of Canned Carrots

Texture of acidified canned carrots was evaluated using a shear compression procedure. Carrots canned with as little as 0.77% gluconic acid in the brine retained firmer texture than those packed without acid. Softening phenomena of acidified carrots do not appear to be consistent with a two substrate first order rate expression model.     

INSTRUMENTAL TEXTURE OF SET AND STIRRED FERMENTED MILK. EFFECT OF A ROPY STRAIN OF LACTOBACILLUS DELBRUECKII SUBSP. BULGARICUS AND AN ENRICHED SUBSTRATE

Texture profile analysis (TPA) of stirred and set cultured milk were evaluated, using an exopolysaccharide producing strain of Lactobacillus delbrueckii subsp. bulgaricus (NCFB 2772) and a protein enriched substrate (retentate). In both cases, samples were compared respectively with a nonropy strain (NCFB 1489) and reconstituted skim milk substrate. The retentate fermented products were firmer in comparison with skim milk products, both at 10% of total solids. A loss of structure occurred when the retentate products were stirred causing a nine-fold decrease in hardness, whereas in cultured milk products the loss was of around three-fold. The main differences were found in adhesiveness and fracture characteristics. Set retentate ropy product was five times more adhesive than the nonropy one, whereas in stirred retentate and set skim milk products the difference was two-fold. No differences in adhesiveness were detected when skim milk products were stirred using either strain. The fracture force on ropy retentate samples increased after fracture while the nonropy ones showed a decrease, implying more structural breakdown in the latter. On set products, cohesiveness increased slightly due to the ropy strain. Changes in texture observed between ropy and nonropy strains can be attributed to exopolysaccharide attachment to the casein matrix being increased when the protein content is higher.     

Effect of low‐dose irradiation on shelf life and microbiological safety of sliced carrot

Minimally processed non‐irradiated carrots (sliced) exhibited diverse microflora at initial level. During storage, bacterial number increased with the presence of pathogenic bacteria accompanied by a loss of total solids. On the other hand γ‐irradiation at an optimal dose of 2 kGy offered a pathogen‐free, hygienic product with insignificant losses in nutrients such as in sucrose, total carotenes and ascorbic acid content in comparison to controls and 2‐ to 4‐fold increased in shelf‐life at refrigeration temperature. The D₁₀ values of pathogens like Escherichia coli and Yersinia enterocolitica in carrot paste were in a lower range (0.12–0.26 kGy) compared with that of Listeria monocytogenes (0.3–0.5 kGy). The validity of the processing treatment (2 kGy) was challenged by artificially inoculating Listeria monocytogenes in the product. Thus, minimally processed carrots (sliced) are amenable to radiation treatment for extended storage stability and microbial safety. Copyright © 2005 Society of Chemical Industry     

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.     

PROCESSING PARAMETER EFFECTS ON TEXTURAL CHARACTERISTICS OF REDUCED-FAT PORK SAUSAGE

The objective of this study was to evaluate the effects of fat (10, 20, and 30%, postrigor; 10 and 30% pre-rigor), rigor state, plate size (3 and 5 mm), and mixing time (2 and 5 min) on cooking loss and instrumental texture characteristics of reduced-fat pork sausage. High-fat products exhibited greater cook loss and lower breaking force than low-fat products. Rigor state of raw materials had no effect on the characteristics evaluated. Increasing plate size and mixing time increased initial force required to compress a 2.5 cm core to 20% of its original height but had no effect on other characteristics. Reduction of fat content can be accomplished without addition of nonmeat ingredients by limiting plate size to 3 mm and mixing time to 2 min.     

HISTOLOGICAL AND PHYSICAL CHANGES IN CARROTS AS AFFECTED BY BLANCHING, COOKING, FREEZING, FREEZE DRYING AND COMPRESSION

SUMMARY— The effect of processing variables on the cell structure and physical characteristics of carrots were determined. The phloem portion of fresh carrots was subjected to one of the following treatments: blanching; cooking for 10 min; freezing at 0°F, −30°F or −320°F; freeze drying, compressing after freeze drying at approximately 1500 psi. Carrots at each treatment were tested for: (1) texture by means of the Ailo-Kramer Shear Press; (2) water holding capacity by centrifuging at 500, 1000, 1500, 2000 and 2500 rpm; (3) histological changes by microscope observation of the tissue structure. Results indicate that among all treatments, freezing temperature is the most critical factor affecting the cell structure of the carrots. Freezing at 0°F or −30°F results in considerable disruption of the cellular structure, whereas it was minimal at −320°F. Carrots frozen at −320°F showed firmer texture as well as higher water holding capacity than the rest. Significant correlation coefficient was established between the shear press values and percent weight loss measured by centrifugation. This suggests that the latter may be used as an objective test for measuring textural changes in processed carrots and perhaps other foods.     

PROCESSING PARAMETER EFFECTS ON SENSORY AND INSTRUMENTAL TEXTURE CHARACTERISTICS OF REDUCED-FAT GROUND BEEF PATTIES

Effects of fat content (8 or 24%), processing temperature (–2, 1, 4C), plate size (2, 5, 5 mm), mixing time (3, 5, 8 min), and patty formation pressure (50, 100, or 150 kg) on characteristics of low-fat ground beef patties were evaluated. Reduced fat patties required less force to break when ground at –2C (2 mm plate) than when ground at 4C. Rubberiness increased as plate size increased. Rubbery scores were lowest at 4C/2 mm plate. Reduced-fat patties had lower cook losses. Increasing grinding temperature from –2 to 4C decreased break force, Kramer shear and cohesive texture. Break force was highest for patties mixed 8 min at –2C. Patty forming pressure affected breaking strength, cohesiveness, and cook loss. Production of reduced-fat ground beef patties by grinding through a 2mm plate at 4C, mixing for 2 min and forming patties at 150 kg pressure minimized rubbery texture and instrumental measures of patty hardness.     

EVALUATION OF THE TEXTURE OF FRIED POTATOES

Texture of potatoes with different shapes (slices and strips) were evaluated after frying and in some cases after baking. Blanched and unblanched potato slices (Bintje variety) were fried at four oil temperatures: 160, 170, 180 and 190C until reaching a moisture content of ∼1.7%. A puncture test with three point support for the slices was applied to measure the texture of potato chips using the following parameters extracted from the force versus distance curves: maximum force of break (MFB) and deformation of break (DB). These two parameters were useful to follow the changes in texture of the fried slices with moisture content at different frying temperatures. Blanched and unblanched potato strips were partially fried at 160C and 190C for 60, 90 and 120 s. The par-fried potatoes were frozen at -20C for one day after which they were baked at 200C for 15 min. The texture of the baked potato strips was evaluated using a bending test with two support points. From the force versus distance curves, two parameters were extracted: maximum force of deformation (MFD) and maximum deformation (MD). Significant higher MFB and lower DB values (P > 0.1) for unblanched fried slices indicate that these are crispier than blanched chips for moisture contents lower than 4% (6.59 N and 0.62 mm vs 5.74 N and vs 0.75 mm for unblanched and blanched chips, respectively, average values for the four frying temperatures employed). There was no effect of the frying temperature and the pretreatment (blanching or unblanching) on the texture of the frozen par-fried potatoes after baking when compared at the same residual moisture content, but blanched potato strips lost moisture more slowly both in frying and in baking.     

Effects of Gamma Irradiation on the Texture of Minimally Processed Apple Slices

ABSTRACT: Fresh-cut apples with or without calcium treatments were irradiated at doses up to 5 kGy at 0.4 and 2 kGy.h^-1 dose rates with a Co⁶⁰ source in 0, 21, and 100% O₂ atmospheres. Firmness decreased as irradiation dose increased beyond a 0.34 kGy threshold. High dose rate initially resulted in less softening compared to low dose rate, but dose rate became insignificant upon storage. Irradiation atmosphere did not affect firmness. Softening of irradiated slices correlated positively with water-soluble pectin, and negatively with oxalate-soluble pectin content. Calcium prevented irradiation-induced softening of thin slices (3-4 mm thick), but was not effective with thicker wedges due to limited penetration.     

PHYSICAL AND SENSORY CHARACTERISTICS OF LOW-FAT ITALIAN SAUSAGE PREPARED WITH HYDRATED OAT

Low‐fat Italian sausage was prepared with hydrated oat flakes at 10, 20 and 30% (w/w), and precook times of 0, 2 and 4 min. Cook loss and expressible moisture, cutting force and texture profile analysis, color and consumer sensory analysis were analyzed by response‐surface methodology. Minimum cook loss occurred at 16.3% of the hydrated oat and 0.76 min precook time, while expressible moisture decreased with increasing oat levels and decreasing precook time. In general, both cutting force and hardness decreased with hydrated oat level. Measurements of L*, a* and b* showed a slightly lighter product and a shift to more red and yellow cooked product at intermediate oat levels and precook times. For sensory attributes, both oat level and precook time were significant. Greatest flavor and texture likeability were attained with hydrated oat levels of 3–12%, and precook times of 1.5–3 min. Greatest overall likeability occurred over a region of 0–14% hydrated oat, and 1.1–3.3 min precook time.     

Effect of Novel Processing Techniques on Texture Softening and β-Carotene Content of Thermally Processed Carrots

Effect of novel processing methods was evaluated on product texture and β-carotene content of carrots following acidification to reduce pH from 6.0 to 4.4. Thermal treatments under Conventional (CH-T) and Ohmic heating (OH-T) conditions at 87, 92, and 97 °C, individually and/or in combination with high-pressure processing (HP-T; 400–600 MPa/40–60 °C), were given up to 90 min. A fractional conversion model was used to compute texture softening rate constant, k, and activation energy, E _a. Acid-infused carrot samples had lower k values than the control, implying a better texture retention in acidified products. In order to explore this further, acid-infused and control samples were subjected to selected processing methods for 0, 7, and 25 min representing minimal, optimum, and over-processing conditions, respectively. Texture value, pectin depolymerization by β-elimination, demethoxylation, cell microstructure modification, and β-carotene content were evaluated. Results showed that acid-infused samples retained significantly (p?≤?0.05) better texture than the untreated ones. Pectin depolymerization by β-elimination was greater (p?≤?0.05) in control samples than acid-infused samples. In contrast, pectin depolymerization by demethoxylation showed no such differences (p?>?0.05) with acid-infused samples. This indicates that pectin degradation was more dominated by β-elimination than demethoxylation, and these results concurred with the cell microstructure observations of processed carrots. Thermal and HP-T processing after acid infusion reduced the β-carotene content of carrots more than in control. However, mild heat treatment of carrots at 97 °C under CH-T and OH-T enhanced the β-carotene levels to higher than in raw control carrot samples.     

EVALUATION OF ISOMALT AND HYDROGENATED STARCH HYDROLYSATE IN SUGARLESS CARAMEL POPCORN1

Five formulations of sugarless caramel popcorn sweetened with different proportions of hydrogenated starch hydrolysate and isomalt were developed. Control and test products were evaluated for changes in physical, chemical and sensory properties over a 3‐month storage period at 33C and 50% humidity. Moisture content and water activity values increased for all products, but color values did not change with time. Texture compressibility measurements were highly correlated with liking of texture values gathered from a consumer study. The fonnula with 100percnt; isomalt was liked significantly more by consumers than the other formulas.     

Influence of Pretreatment Conditions on the Texture and Cell Wall Components of Carrots During Thermal Processing

ABSTRACT: Diced carrots ( Daucus carota var. Nerac) were subjected to different pretreatment conditions. The pretreated carrots were subsequently thermally processed in an oil bath (100°C) and in a static retort (equivalent processes [F_oΔ 6 min] at 115°C, 120°C, and 125°C). Changes in texture were analyzed as well as changes in the degree of methylation (DM) of pectin. From all the pretreatment conditions tested, high-pressure pretreated carrots (400 MPa, 60°C for 15 min) exhibited the highest resistance to texture loss. The textural properties were significantly improved when calcium infusion was combined with low-temperature blanching condition (60°C for 40 min). A significant reduction in the DM of carrot pectin was observed for all pretreatment conditions that resulted in a reduced texture loss after thermal processing. A strong negative correlation (r ≥−0.90) exists between the changes in the degree of methylation of carrot pectin and the observed changes in texture.     

PREDICTION OF APPLE FIRMNESS FROM MASS LOSS AND SHRINKAGE

Prediction of firmness from mass loss and shrinkage was investigated in apples (Malus x domestica Borkh.) under regular atmosphere (RA) storage conditions. Apples (‘Delicious’ and ‘Fuji’) were repeatedly weighed to determine mass loss. Shrinkage was measured with a strain gauge sensor. ‘Delicious’ apples lost firmness (73 to 58 N) while ‘Fuji’ apples maintained firmness at 69 N over 57 days in storage. Apples lost mass at a constant rate with ‘Delicious’ losing mass slower (0.6 % per month) than ‘Fuji’ (1.1% per month). ‘Delicious’ apple shrank less (0.28 mm) than the ‘Fuji’ (0.70 mm) over 57 days. The relationship between firmness and mass loss, or shrinkage was dependent on apple cultivar. Firmness was significantly and linearly related to mass loss and to shrinkage in ‘Delicious’ apples. It is possible to predict firmness of ‘Delicious’ apples under RA storage conditions by tracking mass loss or shrinkage.     

EFFECTS OF GAMMA RADIATION ON NUTRITIVE AND SENSORY QUALITIES OF SWEET POTATO STORAGE ROOTS

Jewel and Georgia Jet sweet potato storage roots were treated with gamma radiation doses of 0.1, 0.5, 0.8, 1.5 and 2.0 kGy and compared to the untreated control. Analyses showed that ascorbic acid and starch decreased at 1.5 and 2.0 kGy. Total carotenoids in both cultivars were unaffected by radiation treatment. Gamma radiation caused softening of Jewel and Georgia Jet sweet potato roots and the texture score decreased at 1.5 and 2.0 kGy. Color was not affected by radiation in either cultivar and differences in L, a and b values were not observed. The total sugar content of the Jewel sweet potato was higher at 0.8 kGy than at other doses but for Georgia Jet it tended to increase as the radiation dose increased. The sensory evaluation test indicated that acceptability of baked sweet potatoes was severly affected by gamma radiation at doses of 0.5 kGy and above.