Athina Lazaridou

Structural characteristics and rheological properties of locust bean galactomannans: a comparison of samples from different carob tree populations

Water-soluble galactomannans were isolated from the seeds of 12 carob tree populations grown in different regions of southern Greece. Their structures, molecular weight distributions and rheological properties were examined. The intrinsic viscosity values and estimated average molecular weights varied in the ranges 8.15–13.02 dl g−1 and (2.3–3.9) × 106 respectively. Molecular sieve chromatography showed large variations in the molecular size distributions. The Manp/Galp ratio varied between 3.08 and 3.82, as determined by GC analysis of the alditol acetate derivatives of the monomeric constituents. There were also differences in the relative distribution of the free (Manp-Manp), monosubstituted (Manp-Manp(Galp)) and disubstituted (Manp(Galp)-Manp(Galp)) dyads of β-(14)-mannose, as revealed by 13C NMR spectroscopy of the native polysaccharides. The pseudoplastic behaviour of galactomannan solutions (10–20 g l−1) was confirmed by steady shear and dynamic rheological tests. Aqueous galactomannan (5 g l−1)–xanthan gum (5 g l−1) mixed systems gave gels on cooling (G′ ≫ G″). Galactomannans with high limiting viscosities, high Manp/Galp ratios and a low proportion of the Manp(Galp)-Manp(Galp) dyad yielded the strongest mixed gel network structures with xanthan, implying that interchain associations between the two polymers occur via the unsubstituted segments (‘smooth regions’) of the carob galactomannan chains. © 2000 Society of Chemical Industry

Production and characterization of pullulan from beet molasses using a nonpigmented strain of Aureobasidium pullulans in batch culture

The production of pullulan from beet molasses by a pigment-free strain of Aureobasidium pullulans on shake-flask culture was investigated. Combined pretreatment of molasses with sulfuric acid and activated carbon to remove potential fermentation inhibitors present in molasses resulted in a maximum pullulan concentration of 24 g/L, a biomass dry wt of 14 g/L, a pullulan yield of 52.5%, and a sugar utilization of 92% with optimum fermentation conditions (initial sugar concentration of 50 g/L and initial pH of 7.0). The addition of other nutrients as carbon and nitrogen supplements (olive oil, ammonium sulfate, yeast extract) did not further improve the production of the exopolysaccharides. Structural characterization of the isolated polysaccharides from the fermentation broths by 13C-nuclear magnetic resonance spectroscopy and pullulanase digestion combined with size-exclusion chromatography confirmed the identity of pullulan and the homogeneity (>93% dry basis) of the elaborated polysaccharides by the microorganism. Using multiangle laser light scattering and refractive index detectors in conjunction with high-performance size-exclusion chromatography molecular size distributions and estimates of the molecular weight (Mw=2.1−4.1×105), root mean square of the radius of gyration (Rg=30−38 nm), and polydispersity index (Mw/Mn=1.4−2.4) were obtained. The fermentation products of molasses pretreated with sulfuric acid and/or activated carbon were more homogeneous and free of contaminating proteins. In the concentration range of 2.8−10.0 (w/v), the solution’s rheologic behavior of the isolated pullulans was almost Newtonian (within 1 and 1200 s−1 at 20°C); a slight shear thinning was observed at 10.0 (w/v) for the high molecular weight samples. Overall, beet molasses pretreated with sulfuric acid and activated carbon appears as an attractive fermentation medium for the production of pullulan by A. pullulans.

Sequential solvent extraction and structural characterization of polysaccharides from the endosperm cell walls of barley grown in different environments.

The objective of this study was to examine the composition and molecular structure of the endosperm cell walls (CW) derived from barley grain grown in three environments in Canada, and differing in grain hardness, protein, and total β-glucan contents. The endosperm CW were isolated from barley, cv. Metcalfe, grown in Davidson, SK (Sample A), Hythe, AB (sample B), and Hamiota, MB (sample C). The CW were sequentially extracted with water at 65(o)C, saturated Ba(OH)2, again with water at 25(o)C, and 1M NaOH, resulting in fractions designated WE65, BaE, Ba/WE, and NaE, respectively. The monosaccharide analysis indicated the presence of β-glucans, arabinoxylans, and small amounts of arabinogalactans, glucomannans, and xyloglucans. Cellulose was detected in the CW remnants. The CW of sample A, exhibiting a lower grain hardness than sample B, contained the lowest amount of β-glucans, but the highest amount of arabinoxylans and the mannose-containing polysaccharides. The CW of sample C, characterized by very high protein content in the grain, contained the highest amount of β-glucans and the lowest amount of other polysaccharides. Polysaccharides in the CW of sample B, exhibiting the highest grain hardness, were characterized by the highest weight average molecular weights (Mw). β-Glucans in the CW of Sample B showed the highest ratio of DP3/DP4 and the longest cellulosic fragments in the polymeric chains. Of the three barley samples, arabinoxylans in the endosperm CW of sample A exhibited the lowest degree of branching, the highest amount of unsubstituted Xyl residues, and the highest ratio of singly to doubly substituted Xylp. The highest water solubility of the CW of sample C was associated with the highest concentration of β-glucans, the lowest DP3/DP4 ratio, and the lowest Mw of the polymeric constituents. Arabinoxylans with the lowest amount of doubly substituted but the highest amount of unsubstituted xylose residues and long sequences of unsubstituted xylan regions were found in the NaE fractions. The NaE fractions showed a high ratio of →4)-Glcp-(1→ to →3)-Glcp-(1→ linkages and some →4)-Manp-(1→ linkages, indicating a high level of long cellulosic regions in β-glucan chains and the presence of glucomannans.

Using particle tracking to probe the local dynamics of barley β-glucan solutions upon gelation.

The sol-gel transition of aqueous barley β-glucan solutions which undergo gelation with ageing has been studied by conventional bulk rheology, phase contrast microscopy and particle tracking microrheology. Characterisation of the primary structure of the β-glucan isolate was carried out by enzymic methods and HPLC. The Brownian diffusion of fluorescent microspheres (0.75 μm diameter, carboxylate-coated particles) was used to probe the spatial mechanical properties of the gelling systems at the scale of microns; the potential use of passive particle tracking to study biopolymer gelling systems that present spatial heterogeneities is thus explored. For the β-glucan gels cured at 25°C both microrheology and bulk rheology revealed that with increasing the polysaccharide concentration the gelation time decreased, while the gelation rate and gel strength of the barley β-glucan gels increased. The particle tracking method had higher sensitivity and could map molecular ordering and structural heterogeneities in the evolving polysaccharide network at a micro-level. That is, different size pores were generated upon ageing with regions of depleted or less amount of β-glucan molecules. Furthermore, this method could detect changes in the fine structure of the system before such events can be registered by bulk rheological measurements; i.e. microheterogeneity and aggregation of β-glucan chains were revealed by particle tracking at earlier temporal stages of the experiment.

1H NMR Metabolic Fingerprinting to Probe Temporal Postharvest Changes on Qualitative Attributes and Phytochemical Profile of Sweet Cherry Fruit

Sweet cherry fruits (Prunus avium cvs. ‘Canada Giant’, ‘Ferrovia’) were harvested at commercial maturity stage and analyzed at harvest and after maintenance at room temperature (storage at ∼20°C, shelf life) for 1, 2, 4, 6, and 8 days, respectively. Fruit were initially analyzed for respiration rate, qualitative attributes and textural properties: ‘Canada Giant’ fruit were characterized by higher weight losses and stem browning index, being more intense over the late stages of shelf life period; meanwhile ‘Ferrovia’ possessed appreciably better performance even after extended shelf life period. A gradual decrease of respiration rate was monitored in both cultivars, culminated after 8 days at 20°C. The sweet cherry fruit nutraceutical profile was monitored using an array of instrumental techniques (spectrophotometric assays, HPLC, 1H-NMR). Fruit antioxidant capacity was enhanced with the progress of shelf life period, concomitant with the increased levels of total anthocyanin and of phenolic compounds. ‘Ferrovia’ fruit presented higher contents of neochlorogenic acid and p-coumaroylquinic acid throughout the shelf life period. We further developed an 1H-NMR method that allows the study of primary and secondary metabolites in a single running, without previous separation and isolation procedures. Diagnostic peaks were located in the aliphatic region for sugars and organic acids, in the aromatic region for phenolic compounds and at 8.2–8.6 ppm for anthocyanins. This NMR-based methodology provides a unifying tool for quantitative and qualitative characterization of metabolite changes of sweet cherry fruits; it is also expected to be further exploited for monitoring temporal changes in other fleshy fruits.

Preservation of pears in water in the presence of Sinapis arvensis seeds: A Greek tradition

In this research, the microbiological and physicochemical changes during preservation of pears in water in the presence of Sinapis arvensis seeds (PWS FL) according to the traditional Greek home food manufacture were studied. Pears preserved in water served as control (PW FL). The growth of lactic acid bacteria (LAB) coming from the pear surface was enhanced in the presence of Sinapis seeds, while Enterobacteriaceae and Gram-negative bacteria declined coincidently with the lower (P<0.05) pH of the PWS FL. LAB predominated over the other microbial groups in the fermentation liquids (FLs) of both systems. All the 49 LAB isolates from one fermentation experiment were identified as Leuconostoc mesenteroides subsp. cremoris by the SDS-PAGE of whole-cell proteins, while RAPD-PCR fingerprinting and partial 16S rRNA sequence determination of selected isolates did not discriminate them at the subspecies level. Fruit preserved in PWS FL had higher titratable or volatile acidity, phenolic compounds or antioxidant capacity as well as lower pH and firmness than the control fruit. All physicochemical parameters of the FLs increased except of the pH which decreased. Coincidently with higher population of LAB in PWS FL the levels of citric, lactic and acetic acid were higher than in control. Oxalic acid and related unknown substances were found at higher levels in PWS FL than the control and may be the agent(s) enhancing the growth of LAB and/or contributing partially to the decline of Enterobacteriaceae. The organoleptic test showed that fruit preserved in PWS FL had better overall acceptance than the control, and that it retained most of the positive traits.

Postharvest responses of sweet cherry fruit and stem tissues revealed by metabolomic profiling

Sweet cherry, a non-climacteric and highly perishable fruit, is usually cold-stored during post-harvest period to prevent senescence; therefore, metabolic profiling in response to cold storage in sweet cherry is of economic and scientific interest. In the present work, metabolic analysis was performed in fruit and stem tissues to determine the metabolic dynamics associated with cold storage in response to 1-methylcyclopropene (1-MCP), an ethylene-action inhibitor, and modified atmosphere packaging (MAP). Fruit (cv. Regina) following harvest were treated with 1-MCP and then cold-stored (0 °C, relative humidity 95%) for 1 month in the presence or in the absence of MAP and subsequently maintained at 20 °C for up to 2 days. Physiological analysis suggested that cold storage stimulated anthocyanin production, respiration rate and stem browning. Cherry stem exposed to 1-MCP displayed senescence symptoms as demonstrated by the higher stem browning and the lower stem traction force while MAP treatment considerably altered these features. The metabolic profile of fruits and stems just following cold storage was distinctly different from those analyzed at harvest. Marked tissue-specific differences were also detected among sweet cherries exposed to individual and to combined 1-MCP and MAP treatments, notably for amino acid biosynthesis. The significance of some of these metabolites as cold storage hallmarks is discussed in the context of the limited knowledge on the 1-MCP and MAP response mechanisms at the level of cherry fruit and stem tissues. Overall, this study provides the first steps toward understanding tissue-specific postharvest behavior in sweet cherry under various conditions.

Determination of Free and Total Underivatized Amino Acids Including L-Canavanine in Bitter Vetch Seeds Using Hydrophilic Interaction Liquid Chromatography

ABSTRACT A new hydrophilic interaction liquid chromatography method coupled with diode-array detector was developed for the determination of 17 underivatized amino acids including L-canavanine in bitter vetch [Vicia ervilia (L.) Willd.] seeds. Amino acids were extracted as free as well as total extracts after acid hydrolysis, followed by chromatographic separation on a Zorbax Rx-SIL column with a mobile phase of acetonitrile/potassium phosphate buffer (12.5 mM; pH 3.0) using gradient elution and detection at 190 nm. The method is characterized by a wide linear range (0.01–200 µg/mL, r > 0.9987), sufficient accuracy (relative error 86.3–109.1%), and suitable precision for the results (relative standard deviation <4.9% in the case of intra-day and <9.8% in the case of inter-day precision). The limits of detection and quantification for free amino acids ranged from 0.01 to 0.24 mg/g and 0.03 to 0.72 mg/g, respectively, whereas the total amino acids ranged from 0.02 to 0.47 mg/g and 0.07 to 1.43 mg/g, respectively. The mean recoveries of free and total amino acids in spiked samples exceeded 70.3% for most amino acids. The mean total content of free and total amino acids in bitter vetch seeds was 1.71 and 14.88 g/100 g seed, whereas the corresponding values for canavanine were 0.07 and 0.19 g/100 g seed, respectively.