Canning Quality Evaluation of Pinto and Navy Beans

Thermal processing of pinto and navy beans at 121.1°C for 16 or 14 min in a still retort gave similar sterilization value (F_o= 10) as the processing at 115.6°C for 45 min. The 121.1°C/16 or 14 min process produced beans with greater firmness than the 115.6°C/45 min process. The addition of CaCl₂ and EDTA improved firmness and color of canned beans. Calcium chloride also reduced clumping and splitting of the canned beans. Sensory evaluation showed that the acceptability of canned beans was reduced when CaCl₂ was increased up to 10 mM. High correlation between firmness and soluble pectin in various bean cultivars implied that soluble pectin content could be used as a parameter for screening bean cultivars with desirable firmness.     

Ultrastructural and Changes in Pectin Composition of Sweet Cherry from the Application of Prefreezing Treatments

ABSTRACT: Thermal and calcium pretreatments applied to preserve the sweet cherry texture by the freezing/thawing process produced biochemical changes in the pectic substances and ultrastructural alterations to the cells and tissues, which were visible under scanning electron microscopy. Partial dehydration of the epidermic tissue caused by calcium (100 m M CaCl₂) and thermal (50 °C/10 min) pretreatment attenuated the surface damage produced by freezing. However, pretreatment at 70 °C/2 min caused partial destruction of the epidermic tissue and plasmolysis of the parenchymatic cells. After freezing, the cell walls in the parenchymatic tissue of the fruits pretreated with 100 m M CaCl₂ exhibited swelling as a result of gelling of the cell-wall pectic material. Thermal pretreatments increased the ethylenediaminetetraacetic acid (EDTA)-soluble pectin fraction and reduced the degree of pectin esterification. Thermal treatments at 70 °C, without immersion in calcium, reduced the water- and pectinase-soluble pectin fractions, whereas immersion in calcium prevented depolymerization of these fractions. Immersion in 100 m M CaCl₂ increased the water-soluble pectin fraction.     

Freezing of strawberries by immersion in CaCl2 solutions

The present investigation studied the freezing of strawberries by immersion in CaCl₂ solutions, analysing drip loss, pectin content and the degree of esterification of the pectins, total and cell-wall bonded calcium contents, the ratio bonded calcium/total calcium, and textural parameters. In addition, the effect of immersion in pectin methylesterase (PME) solutions prior to immersion freezing (IF) was analysed. The firmness of thawed fruit decreased by approximately 74% with respect to fresh strawberries, and neither IF-CA (freezing by immersion in CaCl₂ solution) nor PME–IF-CA (immersion in PME solution + freezing by immersion in CaCl₂ solution) provided significant benefit in maintaining firmness when compared to slow freezing (SF). However, IF provided a significant benefit in reducing drip loss of thawed strawberries when compared to SF, but pre-treatment with PME did not provide any additional benefit.     

Quality attributes and cell wall properties of strawberries (Fragaria annanassa Duch.) under calcium chloride treatment

Effects of CaCl₂ (0%, 1% and 4%) treatment on quality attributes and cell wall pectins of strawberry fruits stored at 4 °C for 15 d were investigated. Strawberry firmness was not significantly affected by CaCl₂ treatment. Compared to the other groups, the 1% CaCl₂ group had better quality attributes, including decay rate, weight loss and soluble solids content. The treatment with 4% CaCl₂ inhibited weight loss but caused phytotoxicity. During storage, the chain widths and lengths of water-soluble pectin (WSP), chelate-soluble pectin (CSP) and sodium carbonate-soluble pectin (SSP) decreased. Strawberry softening seemed to be due to modifications of CSP and SSP, especially the side chains. CaCl₂ treatment significantly slowed the breakdown of CSP and SSP chains by strengthening the ionic crosslinkages among these pectin molecules. These results illustrate the fundamental CaCl₂ effects and will help improve the application of CaCl₂ to postharvest fruits.     

Firmness and Cell Wall Characteristics of Pasteurized Jalapeño Pepper Rings as Affected by Preheating and Storage

Changes in cell wall pectic substances, degree of pectin methylation, bound calcium and firmness were determined in preheated and nonpreheated fresh pack jalapeño pepper rings stored for 5 mo. Pepper rings preheated for 60 min at 50°C in a brine solution (8% NaCl and 0.2% CaCl₂, were firmer, had more nonextrctable pectins (NXP), more bound calcium, less water-soluble and chelator-soluble pectins (CSP), and less pectin methylation than nonpreheated pepper rings. The greater formation and maintenance of nonextractable pectins, which resisted acid hydrolysis during pasteurization and storage is probably an important factor in firming.     

Enzymatic Firming of Processed Red Pepper by Means of Exogenous Pectinesterase

Abstract

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.     

CELL WALL CHARACTERISTICS AND FIRMNESS OF FRESH PACK CUCUMBER PICKLES AFFECTED BY PASTEURIZATION AND CALCIUM CHLORIDE1

Changes in cell wall pectic substances, degree of pectin methylation, bound Ca⁺⁺, neutral sugar composition, and firmness were determined in mesocarp tissue of pasteurized and nonpasteurized fresh pack cucumber pickles. Large changes in solubility characteristics of pectic substances occurred in cell walls of nonpasteurized pickles that were attenuated by pasteurization. In particular, water and alkali soluble pectins declined, and nonextractable pectins increased during the first month of storage. The major changes in pectic substance solubility appeared to be related to reductions in the degree of pectin methylation with a minor influence of CaCl₂. Galactose in cell walls of nonpasteurized pickles was substantially reduced, and the reduction in galactose was hindered by CaCl₂ or pasteurization. The amount of bound Ca⁺⁺ appeared to be associated with tissue firmness after one month in storage, since firmer tissue had more cell wall bound Ca⁺⁺. While firmness was associated with the amount of bound Ca⁺⁺, the amount of bound Ca⁺⁺ was dependent on the supply of Ca⁺⁺ and the degree of pectin methylation.     

Changes in firmness,cell wall composition and cell wall hydrolases of grapes stored in high oxygen atmospheres

To investigate the effects of high oxygen (O₂) atmospheres on the firmness of ‘Kyoho’ grapes (Vitis vinifera L. X V. labrusca L.), changes in cell wall constituents and hydrolase activities were examined during 60 days of controlled atmosphere storage in air (control), 40% O₂ + 30% CO₂ or 80% O₂ (high O₂) at 0 °C and 95% relative humidity. Grapes stored in high O₂ retained greater firmness than grapes stored in air. The cell wall contents of high O₂-stored fruits contained less water-soluble pectin (WSP), more Na₂CO₃ soluble pectin (SSP) and higher hemicelluloses than air-stored fruits. The levels of cellulose and CDTA-soluble pectin (CSP) did not significantly change. The effects of high O₂ on enzyme activity were dramatic for polygalacturonase and β-galactosidase, moderate for cellulase, and very low for pectinesterase. No pectate lyase was detected. Taken together, WSP, SSP and hemicelluloses appeared to have major structural roles in retaining the firmness and preventing the deterioration of fruits kept in high O₂.     

Changes in Pectic Substances and Enzymes during Ripening and Storage of "Keitt" Mangos

The relationship of the distribution of pectic substances to tissue softening was examined in ripening mangos at four stages of ripeness. Water-soluble and alkali-soluble pectin declined and ammonium oxalate soluble pectin increased as the mango lost its firmness and became soft. Polygalacturonase and cellulase activities of cell wall preparations increased markedly during ripening. The decline in alkali-soluble pectin and the increase in polygalacturonase activity correlated well with the loss of firmness. Alkali-soluble pectin declined slowly in ripe mangos stored at 4°C. This decline correlated with loss of firmness of the stored mangos. The cellulase activity of cell wall preparations from ripe mangos increased during 4°C storage and the increase correlated with the decrease in firmness.     

Purification and characterisation of carrot (Daucus carota L) pectinesterase

A pectinesterase isoform with an alkaline isoelectric point of over 8.66 was detected in crude extracts of carrot. The enzyme was purified by ion exchange and molecular exclusion chromatography. The molecular weight of the isoform was 25 kDa, determined in native conditions by filtration through Sephadex G‐75 SF. The enzyme showed a high affinity for its substrate, with K_m and V_max values of 0.031 mg ml^?1 and 6.77 units respectively for apple pectin. The pectinesterase activity exhibited an optimum around pH 7.4 and was activated by metallic ions, with optimum activities at NaCl concentrations between 130 and 330 mM and at CaCl₂ concentrations between 15 and 50 mM . The enzyme was activated most by Ca²⁺ and exhibited a greater tolerance of high concentrations of Na⁺. Comparison of its heat stability with other pectinesterases of vegetable origin indicated that the purified isoform was very thermolabile, being rendered inactive by heating for 5 min at 70 °C. The enzyme was inhibited by high concentrations of polygalacturonic acid and competitively inhibited by D ‐galacturonic acid, with a K_i value of 1 mM . Copyright © 2003 Society of Chemical Industry     

Impact of Thermal and Chemical Pretreatments on Physicochemical,Rheological, and Functional Properties of Sweet Potato (Ipomea batatas Lam) Flour

The impact of thermal and chemical pretreatments on the physicochemical, rheological, and functional properties of sweet potato flour was investigated. The chemical pretreatment consisted in dipping peeled sweet potatoes in 1 % (w/v) calcium chloride (CaCl₂), while the thermal pretreatment was achieved by blanching them in tap water at 90 °C for 1 min. Composition in flour moisture, protein, fat, non-reducing sugars, and starch was determined using standard methods. Particle size, color, gelatinization, and rheological properties were analyzed. The water absorption index (WAI) and water solubility index (WSI), as well as the swelling capacity (SC) and sorption isotherms, were determined. The reducing sugar content of sweet potato flour was slightly higher in CaCl₂-pretreated (SSPCaCl₂) samples than that in blanched (SSPB) and control (SSP) samples. However, the lightness of the SSPB sample was lower than that of the SSPCaCl₂ and SSP samples. SSPCaCl₂ sample had the higher value of enthalpy of gelatinization and elasticity modulus G′. The SC was higher in blanched samples. A slight increase in the constant of water binding energy (C _BET) was observed after the CaCl₂ treatment and a marked increase for the blanched sample. Owing to the differences induced by blanching and CaCl₂ pretreatments, CaCl₂-pretreated flour samples are more suitable for bread-making processes and can also be used in food formulations.     

Improving textural quality in frozen jalapeño pepper by low temperature blanching in calcium chloride solution

The effects of low temperature blanching in calcium chloride solution of jalapeño peppers prior to freezing, on firmness retention, pH, methanol, colour and calcium ions of the product, were evaluated by response surface methodology. Texture, methanol content and pH were affected by all of the variables studied (P = 0.05). The optimum response was obtained at temperatures of 63.3–66 °C, calcium chloride concentrations of 0.17–0.21 m , immersion time of 11.6–14.4 min, with a holding time after blanching of 56.6–66.1 min. Microscopic evaluation of the thawed pepper showed that blanching in CaCl₂ solution provided a protective effect in maintaining cell wall integrity.     

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.     

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.     

Improving the hardness of thermally processed carrots by selective pretreatments

The aim of this study was to improve the texture of thermally processed carrots by selective pretreatments modifying plant-intrinsic properties. Pretreatments were a combination of a thermal or high-pressure (HP) treatment followed by a 1 h soak in a specific solution. Lowering the degree of methyl-esterification (DM) of the carrot pectin was confirmed to be one strategy to reduce texture degradation. The thermal or HP pretreatment resulted in pectin with a lower DM which is less susceptible to β-eliminative depolymerization. A subsequent Ca²⁺ soak resulted in an even better texture by enhancing the amount of pectin cross-links within the cell wall. Lowering the pH of the carrots was proven to be another strategy. A thermal or HP pretreatment followed by soaking carrots in solutions of low pH proved to be effective in lowering the internal carrot pH, hereby retarding β-elimination and consequently texture degradation. The composition of the low pH solution was shown to be of importance; soak solutions containing cations and/or Ca²⁺ complexing agents have to be avoided. Ferulic acid proved to be a good acidifying candidate. In conclusion, for texture improvement of thermally processed carrots, lowering the susceptibility for β-elimination and enhancing cell wall cross-links are two main targets which both can be reached by manipulating different plant-intrinsic properties.     

Effect of processing on the texture and structure of raspberry (cv. Heritage) and blackberry (cv. Thornfree)

This paper reports separate studies of the effect of pre-treatments (CaCl₂, low methoxyl pectin (LMP), and combined solutions) and the effect of freezing method (at four different rates) and thawing mode (at two different rates) on objective parameters, structure and sensory characteristics of fresh raspberries and blackberries. After that, the effect of a complete freezing process combining the best pre-treatments with the best freezing/thawing conditions found for each fruit was investigated. Kramer Shear Cell (KSC), back extrusion, compression and multiple penetration tests were used to measure fruit texture objectively. For calcium and LMP pre-treatments, which were applied separately, texture parameters were significantly higher in samples treated at the highest concentrations (100 mM of CaCl₂ for both fruits and 0.3 and 3% of LMP for raspberry and blackberry, respectively) compared to fresh controls. Blackberry structure was more susceptible than raspberry structure to the effect of pre-treatments. For the combined pre-treatments, the highest texture parameters were found in the samples treated with CaCl₂ (100 mM) and LMP (0.1%) in the case of raspberries and CaCl₂ (100 mM) and LMP (3%) in the case of blackberries. Combined pre-treatment did not increase firmness with respect to that of samples treated only with calcium, which indicates that CaCl₂ preserved the raspberry structure more efficiently during processing. Fruits frozen by forced convection with liquid nitrogen vapour at –40 °C were significantly firmer. Raspberries should be thawed at 5 °C, whereas blackberries may be thawed at room temperature. Sensory analysis showed that the blackberry structure was more resistant to freezing. In both fruits, over the complete process parameter values were again highest in the samples treated with 100 mM CaCl₂, applied either separately or in combination with LMP. In raspberry, panellists detected no significant differences between sensory texture parameters of the different samples, and in blackberry, panellists found no significant differences between any of the sensory characteristics. Multiple penetration maximum force (F _MP) was the parameter that best expressed product firmness for both fresh and frozen raspberries, whereas compression slope (S _C) best reflected changes in blackberries. SEM mainly corroborated results from objective texture parameters.     

Effects of Vacuum Impregnation with Sucrose Solution on Mango Tissue

The influences of vacuum impregnation (VI) on the tissue of mango cubes during atmospheric immersion in sucrose solution were investigated. Results showed that VI effectively facilitated water loss (WL) and sugar gain (SG) during the 300min immersion process, with increases of 20.59% and 31.26%, respectively. A pectin solubilization/degradation phenomenon was observed in the immersion process. The intercellular space and cross section area in the VI‐treated mango tissue increased immediately after being released to atmospheric pressure. And it was noted that after experiencing shrinkage‐relaxation period twice in the 300 min immersion process, the size of VI‐treated mango cells recovered to the original level of fresh ones. Major variations in WL, protopectin content, water soluble pectin content, firmness and microstructure of mango cubes appeared within the first 60 min. In addition, the firmness of mango cubes was positively correlated with the protopectin content (P < 0.01), but negatively correlated with WL and the water soluble pectin content (P < 0.01), indicating that WL and degradation of protopectin contributed greatly to the loss of firmness.     

INFLUENCE OF VARIOUS SALTS IN THE COOKING WATER ON PECTIN LOSSES AND COOKED TEXTURE OF COWPEAS (VIGNA UNGUICULATA)

The effects of processing with solutions of calcium chloride, magnesium chloride, sodium bicarbonate and a local tenderizer known as ‘Kanwa’ (sodium sesquicarbonate) on pectin losses and cooked texture of cowpea seeds were investigated. For comparison, the cowpeas were processed in double distilled water and a local tap water. Analysis included total pectin, calcium and magnesium content, leached solids, texture and water absorption. The results show that CaCl₂, MgCl₂ and the local tap water increased firmness, Ca and Mg content in the cooked beans compared to distilled water; however, water absorption, leached solids and pectin solubilization were decreased by these salts. Kanwa and NaHCO₃ increased water absorption, leached solids and softness in the cooked beans and also increased pectin solubilization but decreased Ca and Mg when compared to distilled water or the other salts. These changes are discussed with respect to the effects of divalent and monovalent cations on the texture of the bean tissue.     

Towards a better understanding of the pectin structure–function relationship in broccoli during processing: Part II — Analyses with anti-pectin antibodies

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. Anti-homogalacturonan antibodies were used to perform in situ (microscopy) and ex situ (immuno-dot assays) analyses on broccoli pectin which resulted in information concerning the localisation of defined pectic domains in broccoli cell walls and pectin's structure. Water-soluble pectin appears to contain unbranched, high-esterified pectin and some pectic polymers with abundant side chains that are less esterified. Ionically cross-linked pectin, on the other hand, contains low-esterified pectin with either highly branched or unbranched domains. The in situ visualisation of pectin in broccoli suggested that de-esterification of pectin by PME during LTB as well as during HP mainly takes place in the tricellular junctions of adjacent cells in broccoli tissue. Ca²⁺-cross-linked pectin could be found in cell walls lining intercellular spaces and was particularly abundant at the corners of intercellular spaces, indicating its important role in cell–cell adhesion. Both LTB and HP created pectin–Ca²⁺-cross-links in parts of the cell wall where these cross-links were originally absent. The influence of thermal processing and the effect of pressurisation on the pectic components in the cell wall could also be visualised using the antibodies.