Effect of high pressure/high temperature processing on cell wall pectic substances in relation to firmness of carrot tissue

Thermal processing for food preservation results in undesired softening of fruits and vegetables. To explore the potential of high pressure sterilization in food processing, the effects of combined high pressure/high temperature (HP/HT) treatments on carrot pectic polysaccharides and the related textural properties were investigated and compared with that of samples thermally processed at atmospheric pressure. Disks of fresh carrot (Daucus carota var. Yukon) tissue were subjected to three different treatments (80 °C–0.1 MPa, 100 °C–0.1 MPa and 80 °C–600 MPa) for varying time intervals. Subsequently, the residual texture and microstructural changes of the carrots were evaluated. Alcohol-insoluble residues were prepared from the samples and sequentially fractionated with water, cyclohexane-trans-1,2-diamine tetra-acetic acid (CDTA) and Na₂CO₃ solutions. Thermal treatments at 0.1 MPa caused extensive tissue softening. This was marked by increased cell separation, an increase in water soluble pectin (WSP) paralleled by a decrease in chelator (CSP) and sodium carbonate (NSP) soluble pectin. HP/HT treated carrots showed minimal softening and negligible changes in intercellular adhesion. This was accompanied by a significant reduction in the degree of methyl esterification of pectin, low WSP in contrast to the high CSP and NSP fractions, minor changes in the different pectin fractions during treatment, and a substantial amount of pectin in the fractionation residue. There was a clear difference between HP/HT and thermally processed carrot pectin; HP/HT showing pronounced texture preservation.     

Textural Changes of Yellow Peach in Pouches Processed by High Hydrostatic Pressure and Thermal Processing During Storage

Textural changes of yellow peach in pouches (YPP) treated by high hydrostatic pressure (HHP) and thermal processing during storage at 4?±?1 °C and 25?±?1 °C for 180 days were studied. Hardness, syrup viscosity, pectin compositions, and cell structure of YPP samples were evaluated in this study. The hardness of YPP stored at 4?±?1 °C exceeded 50–70 % as compared to those stored at 25?±?1 °C. Moreover, the higher flesh hardness and lower syrup viscosity were obtained at longer pressure-holding time of HHP processing. Water-soluble pectin (WSP), sodium carbonate-soluble pectin (NSP), and total pectin contents in flesh decreased, while chelate-soluble pectin (CSP) in flesh and water-soluble pectin in syrup (WSPS) increased after 180 days storage. The texture degradation in YPP was mainly caused by solubilization and depolymerization of WSP and NSP. The temperature of 4?±?1 °C inhibited pectin degradation and delayed the softening of flesh and the increase of syrup viscosity more effectively than 25?±?1 °C. Comparing with the flesh tissue microstructure of HHP-processed YPP stored at 25?±?1 °C, better cell structures of YPP were retained during storage at 4?±?1 °C. Since the breakdown of intercellular cementing pectin was obviously delayed at lower storage temperature, thus cell wall loosening and distortion were prevented.     

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%.     

High-humidity hot air impingement blanching (HHAIB) enhances drying behavior of red pepper via altering cellular structure,pectin profile and water state

In order to exploring a feasible pretreatment technology of red pepper, an emerging thermal pretreatment technology namely high-humidity hot air impingement blanching (HHAIB) was employed and its effect on drying behavior and related mechanisms were explored through analyzing the ultrastructure, the contents and composition of cell wall pectins, water state of red pepper during the blanching process under blanching temperature of 110 °C and relative humidity of 35%–40% for various exposure times ranging from 0 to 150 s. Results indicated HHAIB can extensively reduce the drying time from 11 h for the un-blanched samples to 8 h for the samples blanched for 90 s. In addition, HHAIB reduced the products' hardness by 8.19%–47.91% compared to the untreated samples. The cellular structure and water state experienced a significant alternation with the increasing blanching time. The content of water-soluble pectin (WSP) increased, while the contents of chelate-soluble pectin (CSP) and sodium‑carbonate-soluble pectin (NSP) decreased during the blanching process. Overall, HHAIB treatment is a promising blanching technology for red pepper as it can accelerate the drying process through softening tissue and altering the ultrastructure and moisture binding state.Industrial practiceDrying is one of the most frequently used methods for red pepper preservation as it can effectively reduce the moisture content so as to hinder the growth and reproduction of microorganisms and the moisture-mediated deteriorative reactions. While the existence of waxy hydrophobic layer covered the surface of red pepper results in long drying time and poor products' quality. In industrial practice chemical dipping is often used to remove the wax layer and enhance the drying rate of red pepper. However, the chemical residues can trigger food safety issues and how to deal with the highly corrosive chemical dipping solution is also a challenge. Therefore, it is very tempting for industry to explore innovative pretreatment for red pepper drying. The current work indicated that HHAIB is a promising alternative technology to replace the chemical dipping method as it extensively enhances the drying process of red pepper.     

Low‐Temperature Blanching as a Tool to Modulate the Structure of Pectin in Blueberry Purees

Blueberry composition was characterized for 6 cultivars. It contains a good amount of dietary fiber (10% to 20%) and pectin (4% to 7%) whose degree of methylation (DM) is sensitive to food processing. A low temperature blanching (LTB: 60 °C/1 h) was applied on blueberry purees to decrease pectin DM, in order to modulate puree properties and functionalities (that is, viscosity and stability), and to enhance pectin affinity toward other components within food matrices. Fiber content, viscosity, pectin solubility, DM, and monosaccharide composition were determined for both pasteurized, and LTB+pasteurized blueberry purees. The results showed that neither the amount of fiber, nor the viscosity were affected by LTB, indicating that this treatment did not result in any significant pectin depolymerization and degradation. LTB caused a decrease both in pectin DM from 58–67% to 45–47% and in the amount of water‐soluble pectin fraction, the latter remaining the major fraction of total pectin at 52% to 57%. A LTB is a simple and mild process to produce blueberry purees with mostly soluble and low‐methylated pectin in order to extend functionality and opportunities for interactions with other food ingredients.     

Characterising polysaccharides in cherimoya (Annona cherimola Mill.) purée and their enzymatic liquefaction

Polysaccharides isolated in the alcohol-insoluble residues (AIR) from cherimoya (Annona cherimola Mill.) were characterised for contents of soluble pectin, cellulose, hemicellulose and lignin, and the distribution of neutral sugars and uronides in water-soluble pectin (WSP) and water-insoluble AIR (WAIR) fractions. For WSP, the predominant neutral sugar was arabinose and, for WAIR, cellulosic glucose and xylose. Two enzyme preparations were tested for their capacity to release neutral sugars and uronides from WAIR. The optimal incubation temperature (45 °C) and the most effective preparation—rich in pectinase, cellulase and xylanase activities—were selected according to a central composite rotatable design (CCRD). Enzyme was also applied to native cherimoya purée according to another CCRD, varying the enzyme concentration and incubation time. Native purée exhibited strong shear-thinning behaviour with high, extrapolated, yield stress. During enzymatic treatment, behaviour was less shear thinning, and yield stress, consistency index and Bostwick consistency tended to decrease, giving rise to purées of different rheological properties.     

In vitro bioaccessibility of β‐carotene in dried carrots pretreated by different methods

The effects of selected pretreatment methods, i.e. soaking in citric acid, blanching in water and blanching in citric acid, as well as hot‐air drying (at 70, 80 and 90 °C), on the retention and relative in vitro bioaccessibility of β‐carotene in dried carrots were investigated. The results indicated that the selected pretreatments and drying could enhance the relative bioaccessibility of β‐carotene in dried carrots. The relative bioaccessibility of β‐carotene in dried carrots increased to 47–73%, while the values in the fresh (13%) and dried untreated (31–47%) carrots were lower. Although significant losses of β‐carotene occurred during both the pretreatment and drying processes, bioaccessible β‐carotene contents of dried pretreated carrots were in a similar order to those of the fresh carrots, indicating the ability and hence the benefit of appropriate pretreatment and drying processes in maintaining the nutritive quality of a food product.     

High‐temperature conditioning induces chilling tolerance in mandarin fruit: a cell wall approach

BACKGROUND: High‐temperature conditioning (3 days at 37 °C and 95% relative humidity), which protects ‘Fortune’ mandarins from chilling injury (CI), manifested as pitting in the outer part of the peel (flavedo), was applied prior to cold storage (2 °C) in order to investigate the involvement of cell wall composition in the chilling tolerance of mandarins. RESULTS: Both low‐temperature storage and high‐temperature conditioning barely modified the alcohol‐insoluble substance (AIS) content or the degree of pectin esterification in the flavedo. Water‐soluble pectins (WSP) were higher in heat‐conditioned than in non‐conditioned fruits at the onset of CI. In addition, the heat‐conditioning treatment was able to increase chelator‐soluble pectins (CSP) after short cold storage periods. Covalently bound polyuronides in alkali‐soluble pectins (ASP) increased only in fruits with high incidence of CI. Cellulose and hemicellulose increased at 2 °C in both conditioned and non‐conditioned fruits, indicating that these polysaccharides may be altered by low temperature but are not related to chilling‐induced damage. CONCLUSION: High‐temperature conditioning may reduce chilling‐induced flavedo pitting in ‘Fortune’ mandarin fruit by maintaining normal levels of WSP and increasing putative sites for calcium bridge formation within the cell wall, but not by inducing changes in other matrix cell wall components. Copyright © 2012 Society of Chemical Industry     

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.     

高静压对黄桃质构相关组分模拟体系的影响

以黄桃质构相关组分(细胞壁物质)为模拟体系,探究了高静压处理、热处理以及贮藏过程对细胞壁物质持水性及其果胶各组分和纤维素含量变化的影响。结果表明:与热处理相比,高静压处理对细胞壁物质的持水性、果胶各组分含量和纤维素含量均无显著影响。与常温贮藏相比,低温贮藏对高静压处理及热处理的细胞壁物质的持水性、各果胶组分含量和纤维素含量无显著影响。相关性分析显示:碱溶性果胶与水溶性果胶之间,碱溶性果胶、水溶性果胶与持水性之间相关性较高。     

Pectin Transitions During Blueberry Fruit Development and Ripening

Quantitative and qualitative changes in the pectin composition of “Bluetta” blueberries were determined during fruit development between 30 and 57 days after full bloom. The contribution of alcohol insoluble solids (AIS) to the total fruit mass decreased threefold with maturation, while the pectin contribution decreased twofold in the fruits. Within the AIS fractions during ripening there was a reduction in dilute alkali soluble pectin (DASP) from about 65% to 20% of the AIS. A corresponding increase was observed in water soluble pectin (WSP), from about 20% to 60%, while chelator soluble pectin (CSP) increased slightly.     

CaCl_2对采后不同成熟度冬枣抗氧化及细胞壁代谢的影响

为探讨CaCl_2处理对不同成熟度冬枣(Zizyphus Jujuba Mill.cv.Dongzao)抗氧化能力及细胞壁代谢的影响,试验采用1%和2%CaCl_2浸泡处理白熟期(WM)和半红期(HM)冬枣果实,以水处理为对照,测定20±2℃贮藏过程中果实硬度、过氧化氢(H_2O_2)、丙二醛(MDA)、超氧化物歧化酶(SOD)、过氧化物酶(CAT)、抗坏血酸(As A)、还原型谷胱甘肽(GSH)、多聚半乳糖醛酸酶(PG)以及细胞壁组分(水溶性果胶(WSP)、离子结合果胶(ISP)和共价结合果胶(CSP))变化。结果表明,在贮藏过程中1%和2%CaCl_2处理可显著延缓WM和HM期果实硬度下降,抑制H_2O_2和MDA积累,维持较高水平的SOD和CAT活性以及As A和GSH含量,同时,降低PG活性以及WSP和ISP含量,增加CSP含量,其中1%CaCl_2处理对HM期果实作用效果最显著,通过提高其抗氧化活性和抑制细胞壁降解过程,使其在贮藏期间保持较好的果实品质。     

Quality Characteristics and Glass Transition Temperature of Hydrocolloid Pre-Treated Frozen Pre-Cut Carrot

The effect of hydrocolloid pre-treatment, i.e., pectin, carboxy methyl cellulose, xanthan gum and sodium alginate on textural properties, drip losses and sensory quality as well as on glass transition temperature (T_g′′′) of the frozen-thawed pre-cut carrots was studied. Untreated frozen samples showed detrimental effects in texture and also excessive drip losses while the carrot tissue integrity was well retained in the hydrocolloid pre-treated samples. As the concentration of the hydrocolloid increased, hardness and fracturability were also found to increase. However, adhesiveness was observed to follow a reverse trend. Xanthan gum (0.4%) resulted in higher texture retention than other hydrocolloids used as well as than the control samples. Hydrocolloids imparted lightness and higher red and yellowness to the carrot samples due to reduced solute mobility and moisture conditioning effects. Overall acceptability of the hydrocolloid pre-treated samples was found to be more than the experimental control samples. All the hydrocolloids were found to be effective in increasing the T_g′′′ to an extent, ?2.73 to ?0.28°C compared with T_g′′′ (?5.4°C) of untreated carrot samples. T_g′′′ increased to almost 74% in CMC (0.4%) pre-treated samples. The maximum enhancement was found in carboxy methyl cellulose followed by pectin, sodium alginate, and xanthan gum. The threshold concentrations in terms of sensory attributes were determined for optimal conditioning of the product prior to freezing.     

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     

Dietary fibre fractions in hulled and naked winter oat grain: effects of cultivar and various agronomic factors

The dietary fibre fractions in two winter cultivars each of hulled oats and naked oats grown on three sites under different agronomic conditions in two years were studied. Overall, soluble non‐starch polysaccharides (NSP) represented some 540 g kg⁻¹ of total NSP, and this did not vary greatly among cultivars. There was a significant (P < 0.001) positive relationship between total and soluble NSP. Within cultivars there was much greater variability in the concentrations of β‐glucans than in soluble NSP, and overall there was no relationship between the concentrations of the two related fractions. Oat cultivar and factors such as year and site where grown significantly (P < 0.01) affected soluble NSP contents. There were some indications that environmental factors such as temperature, rainfall and sunshine hours may have been responsible for the apparent effects of site and year. On a dehulled basis, traditional hulled cultivars contained significantly (P < 0.05) more β‐glucans than the naked types, and the results suggest that selection of oats for dietary or plant‐breeding purposes should be based on β‐glucan rather than soluble NSP concentrations. © 2000 Society of Chemical Industry     

SOFTENING AND BIOCHEMICAL CHANGES OF SAPOTE MAMEY FRUIT (POUTERIA SAPOTA) AT DIFFERENT DEVELOPMENT AND RIPENING STAGES

We investigated some of the physicochemical and biochemical factors associated with flesh softening of sapote mamey fruit during development and ripening. The activities of pectinmethylesterase (PME), polygalacturonase (PG) and β‐galactosidase (β‐GAL) enzymes were measured in fruits harvested at different development stages, and postharvest in two production seasons. The textural changes were most noticeable at the preclimacteric stage in ripening fruit. The water‐soluble pectin (WSP) increased at a different rate than firmness decreased. No correlation between PG or PME activity and changes in firmness was observed in ripening fruits, though a low correlation was seen between β‐GAL activity and softening in climacteric stage. Greatest loss of firmness occurred in climacteric stage. Fruit pulp softening was not dependent on a single enzyme activity.     

超声波辅热联合抗坏血酸对胡萝卜钝酶效果的影响

利用超声波辅热联合抗坏血酸(ultrasonic-assisted blanching combined with ascorbic acid,UBA)的方法对胡萝卜进行预处理。以过氧化物酶和多酚氧化酶为灭酶指标,通过单因素试验以及响应面分析法得出UBA预处理的最佳作用参数;比较UBA预处理、漂烫预处理以及抗坏血酸浸泡预处理对胡萝卜品质的影响。预处理工艺优化结果为超声波功率强度0.29 W/m L、作用时间3 min、作用温度60℃、抗坏血酸质量分数1%;相较于其他的预处理方法,UBA预处理在保证灭酶效果的基础上不仅能显著提高胡萝卜样品中的VC含量,还能最大程度地维持胡萝卜细胞的原有结构,是一种温和且高效的预处理方式。     

Towards a better understanding of the pectin structure-function relationship in broccoli during processing: Part I—macroscopic and molecular analyses

To investigate the structure-function relationship of pectin during (pre)processing, broccoli samples (Brassica oleracea L. cultivar italica) were subjected to one of the following pretreatments: (i) low-temperature blanching (LTB), (ii) LTB in combination with Ca²⁺ infusion, (iii) high-pressure pretreatment (HP), (iv) HP in combination with Ca²⁺ infusion, or (v) no pretreatment (control sample), whether or not in combination with a thermal treatment of 15 min at 90 °C. The macroscopic attributes of broccoli were linked to the chemical structure of broccoli pectin. By enhancing the cross-linking of pectic polymers, both LTB and HP reduced the texture loss that occurred during thermal processing of broccoli. During these pretreatments, homogalacturonan was de-esterified by pectin methylesterase, which led to changes in pectin solubility. When LTB or HP was combined with Ca²⁺ infusion, changes in the structure of pectin occurred, however not always reflected at the macroscopic level. The degree of esterification of pectin in Ca²⁺-soaked broccoli samples was lower compared to non-Ca²⁺-soaked samples and, in addition, a higher amount of ionically cross-linked pectin was retrieved.     

Influence of the Enzymatic Modification of the Nonstarchy Polysaccharide Fractions on the Baking Properties of Reconstituted Rye Flour

The effect of the nonstarchy polysaccharide (NSP)-hydrolases on the properties of rye bread was established by enzymatic modification of the enriched soluble and insoluble NSP fractions, followed by flour recombination and bread baking (20g flour per minibread). Two microbial enzyme preparations were used for the modification (incubation 2 hr at 28°C, 15 min at 75°C, and 10 min at 95°C; pH 4.6). Modification of the insoluble NSP decreased crumb firmness and increased specific volume. Hydrolysis of the soluble NSP decreased the specific volume. Treatment of both fractions improved crumb structure, decreased crumb firmness and increased the width/height ratio of the minibreads.     

Changes in texture,microstructure and nutritional quality of carrot slices during blanching and freezing

Thermal processing of vegetables has pronounced effects on the cell structure, often lowering the final textural properties of the product. In order to investigate the effect of thermal processing on carrot, slices were subjected to different blanching and freezing treatments before frozen storage. Microwave-, steam- or water-blanched material was frozen and then stored at −24 °C. Steam-blanched carrots were subjected to blast freezing or cryogenic freezing at different temperatures before frozen storage. The influence of these process conditions on the texture (maximum load and slope), microstructure, dry matter, sugars, carotene and drip loss was investigated. Microwave blanching differed from the other blanching methods by resulting in a heterogenic cell structure. The content of dry matter, carotene and sucrose was higher following microwave blanching. Blast freezing resulted in low maximum load which seemed to be caused by major tissue damage. Concerning cryogenic freezing, lowering the temperature from −30 °C to −70 °C resulted in better preservation of the native microstructure together with an increase in maximum load, which was most pronounced after one month of storage. No significant effect was observed when lowering the temperature from −30 °C to −70 °C for any of the other measured parameters. © 1999 Society of Chemical Industry