Effect of immersion and turgor pressure change on mechanical properties of pumpkin (Cucumis moschata,Duch.)

Mesocarp raw tissue of a pumpkin (Cucumis moschata, Duch.) popularly known in Argentina as ‘calabacita criolla’ was rheologically characterized by large and small deformations after a stepwise adjustment of its turgor pressure to determine the relative contributions of turgor pressure, cell wall (CW) and middle lamella (ML) to the mechanical behavior. Examinations using light microscopy (LM) and transmission electron microscopy (TEM) were performed in order to explain the textural behavior observed. In general, firmness at failure, residual relaxation force and dynamic moduli increased with turgor pressure. For all the hypotonic solutions (polyethylene glycol 400 (PEG) concentrations lower than 250 mol m^?3) a gain of tissue weight was observed, a trend that indicated a null occurrence of cell bursting as confirmed by observations using LM and TEM of undamaged cell membranes with swelled cytoplasms. However, no significative change in relative volume was detected for tissue equilibrated in PEG with concentrations of 0–130 mol m^?3, probably due to the resistance of CW to further elongation. Peaks of failure were observed during compression for tissue equilibrated under all osmotic conditions and their presence was associated with CW integrity. Plasmolysed tissue did not show a residual force at infinite time of relaxation. Incipient plasmolysis was better detected by rheological studies than by volume change and it was confirmed by LM. Significant correlations were obtained between residual relaxation force and either storage moduli or phase shift angle, revealing that relaxation out of the linear viscoelasticity range and dynamic assays provide analogous information concerning tissue behavior. Copyright © 2006 Society of Chemical Industry     

Textural,histological and biochemical changes in cucumber (Cucumis sativus L) due to immersion and variations in turgor pressure

Textural, histological and biochemical characteristics of cucumber (Cucumis sativus L) under different tissue turgor pressures were studied after equilibration of mesocarp tissue cylinders in various polyethylene glycol 400 (PEG) solutions. Tissue swelling was observed for all hypotonic solutions. Cell membrane vitality was detected in all cucumber tissues where significant values of initial firmness (f_i) and residual relaxation force (F_R) were found. Good turgor status was also associated with higher values of these parameters, observing higher values of the textural parameters for higher turgor. Cell wall integrity was observed through Calcofluor fluorescence assay in tissue equilibrated in hypotonic, isotonic and hypertonic solutions, although a lower fluorescence intensity was observed in tissue equilibrated with 0 mol m^?3 PEG solution, probably owing to some cell bursting. Calcium bridges between pectic polymers were proven to be responsible for cell–cell adhesion and tissue integrity of cucumber mesocarp tissue. Compression curves obtained for raw tissue showed a stage of fracture, and its loss after immersion might be attributed to cell–cell adhesion weakness due to immersion in calcium‐free PEG solutions. Peroxidase and polygalacturonase increased after cucumber equilibration in the solutions, probably expressing tissue injury. Cucumber textural behaviour was very much affected by immersion in calcium‐free solutions, determining the loss of fracture stage and a great influence of turgor pressure on the textural response of soaked tissue. © 2003 Society of Chemical Industry     

Comparison of hot air-drying and freeze-drying on the physicochemical properties and antioxidant activities of pumpkin (Cucurbita moschata Duch.) flours

Freeze-drying and hot air-drying were applied in the preparation of pumpkin flours to investigate the effects of drying methods on the antioxidant activities and physicochemical properties. The antioxidant activities of methanol extracts from pumpkin flours were studied in terms of total antioxidant activity, reducing power, free radical scavenging, superoxide anion radical scavenging and metal chelating activities. Hot air-dried pumpkin flour showed stronger antioxidant activities than freeze-dried flour. The percentage inhibition of peroxidation in linoleic acid system by 15 mg mL⁻¹ extracts from hot air-dried and freeze-dried pumpkin flours was found to be 92.4% and 86.1% after 120 h of incubation, respectively. Hot air-dried pumpkin flour exhibited higher reducing power, free radical scavenging and metal chelating activities than freeze-dried flour. This study also indicated that freeze-drying significantly reduced the browning and preserved the redness of pumpkin flours. Hot air-drying reduced the oil absorption capacity, water absorption and porosity of pumpkin flours, while it markedly increased the water solubility and bulk density.     

6种南瓜栽培品种体外抗氧化活性研究

目的:研究6种不同栽培品种南瓜（金钩、甜面、日本、超甜蜜本、蜜本、辽宁新民金钩）的体外抗氧化活性。方法:采用清除二苯代苦味酰基（DPPH）自由基、清除[2,2’-联氨-（3-乙基苯并噻唑啉-6-磺酸）二氨盐]（ABTS）自由基及铁离子还原/抗氧化能力（FRAP）测定法,评价南瓜体外抗氧化活性,并与阳性对照二丁基羟基甲苯（BHT）比较。结果与结论:南瓜体外抗氧化活性比较弱。六种样品中,超甜蜜本乙酸乙酯提取部分清除DPPH自由基（抑制率=38.99%）、ABTS自由基（IC50=20.90μg/mL）及还原Fe3+的能力（TEAC=（459.40±10.44）μmol/g）较好,抗氧化活性最强,但仍低于阳性对照BHT（清除率为93.93%,IC50=7.72μg/mL,TEAC=（1581.68±97.41）μmol/g）。      

Evaluation of process conditions on osmotic dehydration and quality indexes of pumpkin (Cucurbita moschata) and further polymeric film selection for packaging and refrigerated storage

We studied the influence of composition and concentration of solutions and product size on mass transfer kinetics during Anco pumpkin osmotic dehydration (OD). Once optimal conditions were determined, samples packed in commercial polymeric films were microbiologically analysed during refrigerated storage. The optimal OD time was 3 h, when the efficiency index WL/SG (water loss/solid gain) was stabilised. At this time, 1.0 and 1.5 cm cubes presented the highest index value (about 11) in binary solution (sucrose 55°Bx). WL was higher in 1.0 cm cubes for each dehydrating ternary salt solution tested, and no significant differences in firmness were observed with Calcium Lactate addition. Thus, optimal condition for OD in ternary solutions was 180 min and 55°Bx – 2% NaCl. Microbiological determinations were done for dehydrated (55°Bx without/with 2% NaCl) and untreated samples, packaged in different polymeric films. The combination with lowest mesophilic and psychrophilic counts at day 10 was: samples dehydrated with ternary solution of sucrose-salt packed in Polypropylene film.     

Characterisation and stability of quality indices on storage of pumpkin (Cucurbita moschata and Cucurbita maxima) purees

Purees of Cucurbita moschata‘Menina Brasileira’ and of Cucurbita maxima‘Exposição’ pumpkins were produced. A commercial sterilisation test confirmed the effectiveness of the thermal treatment applied in the production. The stability was monitored during storage in ambient conditions. No significant alterations in pH, titratable acidity or soluble solids were noted. Both types of puree have a good concentration of carotenoids, although a slight decrease was detected in the ‘Exposição’ pumpkin puree after 15 days of storage. In relation to the colour of the purees, there were no significant alterations in a*, b* or ΔE during storage. Decreases in L* and WI were detected after 30–60 days of storage, thus suggesting a browning in an initial period. However, the scores given by the sensory assessors remained above 7 in a 9‐point scale, thus showing no significant alterations during storage. The results showed the stability of the pumpkin purees during the 180 days of storage under the proposed conditions.     

Comparisons of physicochemical properties and antioxidant activities among pumpkin (Cucurbita moschata L.) flour and isolated starches from fresh pumpkin or flour

Physicochemical properties (pasting and thermal properties, swelling power, water solubility and antioxidant activities) and chemical composition of pumpkin flour (PF) and starches, isolated from fresh pumpkin (SFF) or flour (SFP) were compared. SFP and SFF had similar proximate composition and amylose content. Drying process during PF preparation modified starch properties. PF exhibited greater antioxidant activities (DPPH, ABTS and FRAP), but had lower β‐carotene than fresh pumpkin. SFF and SFP had higher amylose content than PF, and exhibited a B‐type X‐ray diffraction pattern with spherical and dome‐like starch granules. Peak viscosity of SFP was relatively higher than that of SFF, probably due to lower swelling power and water solubility, which indicated increased granular rigidity in the SFP starch structure. Compared with SFF and SFP, PF had significantly higher onset (T_o), peak (T_p) and conclusion (T_c) temperatures due to a lower starch content and relatively higher fibre content, which resulted in lower gelatinisation enthalpy (ΔH).     

Oligosaccharides prepared by acid hydrolysis of polysaccharides from pumpkin (Cucurbita moschata) pulp and their prebiotic activities

As a rich source of polysaccharides, pumpkin pulp was used for the production of oligosaccharides. To investigate the prebiotic potential of the oligosaccharides, prepared by acid hydrolysis of polysaccharides from pumpkin pulp, the effect of the oligosaccharides on lactobacilli growth was studied. The oligosaccharides were composed of galactose (99.03%) and glucose (0.97%). The molecular weight distribution of the oligosaccharides showed a larger part of low molecular weight fraction in a range from 5000 to 324 Da than the polysaccharides, which gave the oligosaccharides higher solubility. The oligosaccharides showed good resistance to hydrolysis by artificial human gastric juice and α‐amylase, compared to the reference prebiotic inulin, and considerable capability to stimulate the growth of lactobacilli. In vitro studies showed that the number of lactobacilli was significantly greater than those in control medium when they were cultured in the medium supplemented with the oligosaccharides (P < 0.05), and there was no significant difference at the oligosaccharides group and the inulin group (P < 0.05).     

茉莉酸甲酯和乙烯利对冷藏鲜切南瓜伤害防御响应的研究

本文以鲜切南瓜为原料,经茉莉酸甲酯(Me JA)和乙烯利处理,于4℃下贮藏,通过分析自由基清除系统中过氧化物酶(POD)、过氧化氢酶(CAT)、超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)等四种工具酶活性以及H2O2含量、多酚氧化酶(PPO)活性的变化,研究Me JA和乙烯利对鲜切南瓜机械伤害胁迫的适应性防御响应。结果表明:Me JA和乙烯利可延缓POD、SOD和APX活性的下降速度,保持CAT活性,同时减少H2O2的积累,显著抑制PPO活性(p<0.05)。茉莉酸甲酯(Me JA)和乙烯利可能通过诱导自由基清除系统工具酶的活性,启动防御反应,乙烯利的作用效果更为显著。      

Mango ripening: changes in cell wall constituents in relation to textural softening

Ripening of mango (Mangifera indica L., cv. Alphonso) fruit is characterized by a series of biochemical changes resulting in gradual textural softening. From unripe to ripe stage, the starch content came down from 18% to 0.1%; pectin from 1.9% to 0.5%; cellulose from 2% to 0.9% and hemicelluloses from 0.8% to 0.2%. Concomitantly, the total soluble solids increased from 7% to 20%, total soluble sugars from 1% to 15% and pH increased from 2.8 to 5.1. The increase in activity of several of the carbohydrate‐degrading enzymes, which resulted in solubilization of the various polysaccharide fractions, correlated with fruit‐softening phenomenon. Efficient distribution of ¹⁴C‐starch into glucose, fructose and sucrose revealed considerable sugar interconversions indicating active gluconeogenesis during mango fruit ripening. Copyright © 2005 Society of Chemical Industry     

Mass transfer kinetics and regressional‐desirability optimisation during osmotic dehydration of pumpkin,kiwi and pear

Mass transfer kinetics and optimisation of osmotic dehydration (OD) of fruits and vegetables with diverse structures were studied. Different concentrations of sucrose (20–60 °Brix) and process times (0–24 h) were used. Magee’s model was appropriate for predicting water loss (WL), while Azuara’s model fitted well solids gain (SG) data and represented more accurately the evolution of the complete process close to equilibrium. Polynomial equations for each kinetic variable [WL, SG and weight reduction (WR) – for pumpkin, kiwi and pear] using multiple linear regression were fitted for a selected range of experimental data (30–240 min, 20–60 °Brix). A complete solution algorithm for desirability function was coded in Matlab^® 7.2 (Mathworks, Natick, MA, USA) with the aim to optimise osmotic dehydration process in terms of WL, SG and WR; optimal conditions were found for each fruit. Besides, an optimal common zone was identified for OD corresponding to process time from 114 to 240 min and sucrose concentration from 54 to 60 °Brix.     

A preliminary study of monosaccharide composition and α‐glucosidase inhibitory effect of polysaccharides from pumpkin (Cucurbita moschata) fruit

In this work, crude polysaccharide extracts were extracted from pumpkin (Cucurbita moschata) fruit by hot water. After removal of proteins and purification, polysaccharides of pumpkin fruit (PP1‐1) were subjected to structural identification. Gas chromatography analysis indicated that PP1‐1 comprised of galactose (86.4%), and glucose (13.6%). The molecular weight of PP1‐1 was measured to be 0.87 × 10⁴ Da by gel permeation chromatography. The inhibitory kinetic evaluation showed that it was non‐competitive inhibition of PP1‐1 on the α‐glucosidase‐catalysed hydrolysis of PNPG. The Michaelis–Menten constant (K_m) was 0.106 m , and the inhibitory constants (K_i), 0.435 mg.     

Purification and characterization of Cu,Zn superoxide dismutase from pumpkin (Cucurbita moschata) pulp

From ethyl acetate fraction of olive pomace, solid residue from olive oil extraction, a new compound was isolated and purified through solid-phase extraction using silica Cartridge column chromatography. The structure of the new compound was established as a deoxyloganic acid lauryl ester by spectroscopic data including one- and two-dimensional NMR, electrospray ionization mass spectrometry, infrared analysis and UV spectra. The antioxidant activity of the purified compound was evaluated by measuring the radical-scavenging effect on 2,2-diphenyl-1-picrylhydrazyl and by using the ferric reducing antioxidant power assays. The pure compound has not been previously identified in the genus Olea and could be used as for studying the biosynthetic pathway of oleuropein aglycon.     

Utilization of protein concentrates from ungerminated and germinated fluted pumpkin (Telfairia occidentalis Hook) seeds in cookie formulations

Cookies (soft type biscuits) were produced from blends of wheat flour containing graded levels (0–25%) of protein concentrates prepared from ungerminated and germinated fluted pumpkin (Telfairia occidentalis Hook) seeds and evaluated for nutritional, baking and sensory properties. Protein quality was investigated using weanling albino rats fed diets that were formulated to supply 10% protein using cookie samples, with casein as a control. Cookies produced from blends containing protein concentrates from germinated seeds had higher contents of crude protein and lower levels of polyphenol and phytic acid, compared with cookies supplemented with concentrates from ungerminated seeds. The use of up to 15% concentrate from ungerminated seeds in the blends produced cookies with spread ratio, hardness, colour and flavour similar to the 100% wheat flour (control) cookies. Cookies supplemented with concentrates from germinated seeds at 15–25% levels were nutritionally comparable to diets based on casein, but at the expense of acceptability. Copyright © 2004 Society of Chemical Industry     

Ethephon‐induced fractional changes of pectic polysaccharides in developing cape gooseberry (Physalis peruviana L) fruits

Pectic polysaccharides extracted from fruit tissue of cape gooseberry (Physalis peruviana L) at different maturity levels were fractionated and analyzed for galacturonic acid backbone molecules. Preharvest spray of the fruits at 7 days old with ethephon resulted in a higher accumulation of water‐soluble and oxalate‐soluble pectic fractions than non‐treated fruits, while this treatment effectively enhanced the polygalacturonase enzyme activity necessary for maintenance of pectin degradation. Treatment with ethephon not only enhanced the solubilization rate but also resulted in a net increase in total pectic polymer content in developing cape gooseberry fruits. Copyright © 2005 Society of Chemical Industry     

Variations of polyphenols,sugars, carotenoids,and volatile constituents in pumpkin (Cucurbita moschata) during high pressure processing: A kinetic study

High pressure processing (HPP) is an attractive technology for the preservation of vegetables with health promoting properties such as pumpkins. In this study pumpkin cubes were treated at six different pressures (100 to 600 MPa) at 20 °C for 3 min. Polyphenols (extracted both with solvent and by squeezing the residual material), carotenoids, sugars, and volatiles were evaluated. HPP at medium pressures (200–400 MPa) resulted in higher number of extractable polyphenols. Total sugars in HPP-treated samples were overall declining with increasing pressure. The total amount of carotenoids was higher in samples treated at lower pressures (100–300 MPa) and in the one at 600 MPa compared to untreated ones. Regarding volatile compounds, significant changes were observed for some aldehydes that increase after HPP application. This study revealed that treatment with intermediate pressure could ensure a higher amount of “availability” of polyphenols, carotenoids, volatiles, and total sugars in pumpkin samples.     

Lipid classes,fatty acid composition and triacylglycerol molecular species in the kernels of pumpkin (Cucurbita spp) seeds

The lipids extracted from the kernels of pumpkin (Cucurbita spp) seeds of three cultivars were classified by thin layer chromatography into six fractions: steryl esters (SEs, 0.5–1.2%), triacylglycerols (TAGs, 92.7–93.4%), free fatty acids (FFAs, 2.9–3.5%), sn‐1,3‐diacylglycerols (1,3‐DAGs, 0.4–0.9%), sn‐1,2‐diacylglycerols (1,2‐DAGs, 0.7–0.9%) and phospholipids (PLs, 1.5%). Fatty acids derivatised as methyl esters were analysed by gas chromatography with flame ionisation detection. Molecular species and fatty acid distributions of TAGs, isolated from the total lipids in the kernels, were analysed by a combination of argentation thin layer chromatography (TLC) and gas chromatography. A modified argentation TLC procedure, developed to optimise the separation of the complex mixture of total TAGs, provided 11 different groups of TAGs, based on both the degree of unsaturation and the total chain length of fatty acid groups. With a few exceptions, SM₂ (5.8–20.1%), S₂D (8.8–11.2%), M₃ (6.7–24.8%), SMD (6.8–16.7%), M₂D (16.7–23.6%), SD₂ (4.6–15.1%) and MD₂ (4.9–18.6%) were the main TAG components. These results suggest that there are significant differences (P < 0.05) not only in fatty acid distributions of acyl lipids but also in molecular species of TAGs among the three cultivars. The differences in pumpkin cultivars could be appreciable, based on the distribution of molecular species in TAGs. However, pumpkin seed kernels could be utilised successfully as a source of edible oils for human consumption. Copyright © 2004 Society of Chemical Industry     

Analysis of factors affecting volatile compound formation in roasted pumpkin seeds with selected ion flow tube-mass spectrometry (SIFT-MS) and sensory analysis

Pumpkin (Cucurbita pepo and maxima) seeds are uniquely flavored and commonly consumed as a healthy roasted snack. The objective was to determine dominant volatiles in raw and roasted pumpkin seeds, and the effect of seed coat, moisture content, fatty acid ratio, total lipids, reducing sugars, and harvest year on volatile formation. Sensory was conducted to evaluate overall liking of seed variety and texture. Seed processing included extraction from the fruit, dehydration, and roasting (150 °C). Oil extraction was done using soxhlet, fatty acid profile using Gas Chromatography Flame Ionization Detector, and reducing sugars using 3,5-dinitrosalicylic acid and UV-spectroscopy. Headspace analysis of seeds was performed by selected ion flow tube-mass spectrometry (SIFT-MS). Volatiles dominating in raw pumpkin seeds were lipid aldehydes, ethyl acetate, 2,3-butandione, and dimethylsulfide. Compounds contributing to roasted aroma include alkylpyrazines and Strecker and lipid aldehydes. Overall, hull-less seeds had higher volatile lipid aldehydes and Strecker aldehydes. Seeds dehydrated to a moisture content of 6.5% before roasting had higher initial and final volatile concentrations than seeds starting at 50% moisture. Higher oil content resulted in higher lipid aldehyde formation during roasting with a moderate correlation between free fatty acid ratio and corresponding lipid aldehyde. Harvest year (2009 compared with 2010) had a significant impact on volatile formation in hull-less seeds, but not as much as variety differences. No significant correlation was found between reducing sugars and volatile formation. Sensory showed that hull-less seeds were liked significantly more than hulled seeds. PRACTICAL APPLICATION: Elucidation of aromatic flavor development during roasting with SIFT-MS provides information on flavor release and offers better control during processing. Knowledge of volatiles in raw and roasted pumpkin seeds and effects of seed coat, moisture content, seed composition, and harvest date will allow for better control over the production/storage/transportation process and a more educated decision during selection of a variety for production of pumpkin seeds in the snack food industry.     

Physicochemical and functional properties of whole and defatted meals from Mexican (Cucurbita pepo) pumpkin seeds

Chemical composition and some functional and thermal properties in whole pumpkin seed meal (WPSM) and defatted pumpkin seed meal (DPSM) were determined. The DPSM exhibited higher water absorption capacity (3 g H₂O per g sample), water solubility capacity (8.75%), oil absorption capacity (2.73 g oil per g sample), emulsifying capacity (61.71%), foaming capacity (51.92%) and gelling capacity (12% w/v) than the WPSM. The DPSM also had better swelling power (3.33% at 60 °C, rising to 4.31% at 90 °C), higher phase transition temperatures (T₀ = 80.04 °C, T_p = 86.50 °C and T_f = 93.20 °C) and a higher phase transition energy (0.93 J g^?1). However, the WPSM had higher bulk density (0.57 g cm^?3) and better foam stability (from 30 to 120 min). Micrographs showed defatting to cause microstructural changes in meal starch granules and proteins. Its high protein content makes the DPSM a potential alternative input in the food industry.