Process–Structure–Function Relations of Pectin in Food

Pectin, a complex polysaccharide rich in galacturonic acid, has been identified as a critical structural component of plant cell walls. The functionality of this intricate macromolecule in fruit- and vegetable-based–derived products and ingredients is strongly determined by the nanostructure of its most abundant polymer, homogalacturonan. During food processing, pectic homogalacturonan is susceptible to various enzymatic as well as nonenzymatic conversion reactions modifying its structural and, hence, its functional properties. Consequently, a profound understanding of the various process–structure–function relations of pectin aids food scientists to tailor the functional properties of plant-based derived products and ingredients. This review describes the current knowledge on process–structure–function relations of pectin in foods with special focus on pectin's functionality with regard to textural attributes of solid plant-based foods and rheological properties of particulated fruit- and vegetable-derived products. In this context, both pectin research performed via traditional, ex situ physicochemical analyses of fractionated walls and isolated polymers and pectin investigation through in situ pectin localization are considered.     

Time-dependent flow properties of starch–milk–sugar pastes

The time-dependent flow properties of starch–milk–sugar (SMS) pastes have been studied. The flow properties were assessed from the measurement of the shear stress versus time of shearing at constant shear rate. Corn and wheat starches were used in this study, while the sugars were glucose, sucrose, and fructose. The Weltman model was used to evaluate the flow properties of SMS pastes prepared under different conditions. SMS pastes heated at 95 and 85 °C exhibited a thixotropic behavior, while pastes heated at 75 °C behaved like a rheopectic fluid. It was noted that the thixotropy occurred at high shear stress (above 50 Pa), and the rheopexy occurred at low shear stress (below 45 Pa). The degree of thixotropy, as assessed by the Weltman model parameters, increased significantly with starch concentration, and with less pronounced effect with sugar concentration. The effect of sugar type on the degree of thixotropy of SMS pastes heated at 95 °C decreased in the following order: fructose>sucrose>glucose. The type of starch played a role in the time-dependent flow properties of the SMS paste, with a general conclusion that wheat starch had a greater degree of thixotropy than corn starch.     

Improving characteristics of melamine–urea–formaldehyde resin by addition of blocked polyurethane prepolymer

In this paper, the effect of blocked polyurethane prepolymer (BPUP) with four R values (the ratio of –NCO to –OH) and different blending proportions on the characteristics of melamine–urea–formaldehyde (MUF) resin were first investigated. The properties of the modified adhesive systems were examined by dynamic wettability and shear strength. The results indicated that the bonding performance and the wettability of high R value blending modification were superior to that of low R value case. In addition, the optimal bonding performance came from the MUF resin modified by 15% BPUP (R = 5) addition. Besides, the K value on wood substrates with different moisture contents (MC) was calculated by wetting model to interpret the wetting kinetics. The polymer blending adhesive has a potential capacity for making wood-based panels from high-moisture raw materials.     

Characterization of protein–polyphenol interactions

Dietary polyphenols have received attention for their biologically significant functions as antioxidants, anticarcinogens or antimutagens, which have led to their recognition as potential nutraceuticals. Polyphenols also characteristically possess a significant binding affinity for proteins, which can lead to the formation of soluble and insoluble protein–polyphenol complexes. Questions remain concerning whether and to what extent the protein–polyphenol interaction influences functionality. For example, is the formation of protein–polyphenol complexes an obstacle to the nutritional bioavailability of either species? This article discusses the development of suitable methodologies to investigate the physicochemical basis of protein–polyphenol interactions and the influence of structure–activity relationships on binding affinities.     

Effect of ionizing radiation on quality characteristics of vacuum-packaged normal,pale–soft–exudative,and dark–firm–dry pork

Normal, pale–soft–exudative (PSE), and dark–firm–dry (DFD) pork Longissimus dorsi muscles were vacuum-packaged, irradiated at 0, 2.5 or 4.5 kGy, and stored at 4 °C for 10 days. The pH, color and lipid oxidation of pork were determined at 0, 5 and 10 days of storage. Volatile production from pork loins was determined at Day 0 and Day 10, and sensory characteristics at Day 7 of storage. Irradiation increased the redness of vacuum-packaged normal, PSE and DFD pork. However, the 2-thiobarbituric acid reactive substances (TBARS) values of three types of pork were not influenced by irradiation and storage time. Irradiation increased the production of sulfur (S)-containing volatile compounds, such as mercaptomethane, dimethyl sulfide, carbon disulfide, methyl thioacetate, and dimethyl disulfide, as well as total volatiles in all three types of pork. Normal pork produced higher levels of total and S-containing volatile compounds than the PSE and DFD pork did. The volatiles produced by irradiation were retained in the vacuum packaging bag during storage. Although the odor preference for the three meat types of pork was not different, the panelists could distinguish irradiated meat from the non-irradiated. Industrial relevance: Several US meat companies have already started test-marketing irradiated meat products. Irradiation and the subsequent storage of pork improved the color of PSE and DFD pork, and showed generally similar effects on the production of volatiles, except that there appeared to be a lower level of S-volatiles in the PSE than in the other two samples. This indicated that irradiation can increase the utilization of low-quality pork (PSE and DFD). DFD pork, in particular, which has shorter shelf-life than the others, could benefit the most from irradiation because the shelf-life of DFD meat can be extended significantly by both the methods of vacuum packaging and irradiation.     

Microstructure of acid–induced skim milk–locust bean gum–xanthan gels

The microstructure of acid skim milk gels (14% w/w milk protein low heat powder) with or without addition of locust bean gum (LBG), xanthan gum (XG) and LBG/XG blends was determined by transmission electron microscopy (TEM), phase-contrast light microscopy (PCLM) and scanning electron microscopy (SEM). Three polysaccharide concentrations (0.001%, 0.02% and 0.1%, w/w) were used for binary mixtures. In the case of ternary mixtures, three LBG/XG weight ratios were used (4/16, 11/9 and 16/4) at 0.02% total polysaccharide concentration. Control acid skim milk gels were structured by a homogeneous network of casein particles (0.1–0.7 μm in diameter) and clusters immobilizing whey in small pores (1–5 μm in diameter). Filamentous structures and small aggregates were observed at the surface of casein particles. Low concentration of LBG or XG (0.001% w/w) did not affect markedly the microstructure of acid skim milk gels. Conversely, LBG or XG at 0.02 or 0.1% concentration and LBG/XG blends at the three ratios selected had a great influence on the gel microstructure. Although the size and surface structure of the casein particles were not modified by the presence of polysaccharides, the primary casein network appeared very compact with a decrease of pore size and a large increase in the porosity of the network at the supramolecular level (sponge-like morphology). The effect is stronger for gels containing LBG and XG used at higher concentration and less apparent for gels containing LBG/XG blends. Skim milk/XG gels were highly organized into fibrous structures whereas skim milk/LBG gels were more heterogeneous. These structures were discussed in the light of volume-exclusion effects (demixing) and specific interactions between casein micelles and polysaccharides. At the three weight ratios, skim milk/LBG/XG gels displayed both jagged “coral-like”, “veil-like” and filamentous structures. These structures could originate from a secondary network constituted by the known LBG/XG synergistic interactions.     

Evaluation of Dispersive Liquid–Liquid Microextraction–HPLC–UV for Determination of Deoxynivalenol (DON) in Wheat Flour

A fast and simple method for the extraction of deoxynivalenol (DON) from wheat flour using dispersive liquid–liquid microextraction (DLLME) followed by high-performance liquid chromatography–UV detection has been developed and compared with immunoaffinity column cleanup (IAC) process. The influence of several important parameters on the extraction efficacy was studied. Under optimized conditions, a linear calibration curve was obtained in the range of 50–1,000 μg/L. Average recoveries of DON from spiked wheat samples at levels of 500 μg/kg for DLLME and IAC ranged from 72.9?±?1.6 and 85.5?±?3.1, respectively. A good correlation was found for spiked samples between DLLME and IAC methods. The limit of detection was 125 and 50 μg/kg for DLLME and IAC method, respectively. Advantages of DLLME method with respect to the IAC have been pointed out.     

Estimation of the free volume of starch–water barriers

The permeation of volatiles through amorphous barrier materials is affected by their size and geometry as well as by their physical–chemical affinity for the barrier. The gas barrier property of an amorphous polymer is generally a function of density, cohesive energy density and stiffness as well as of the free volume available for the diffusion of volatiles in the microstructure of polymers. The barrier property of amorphous starch is investigated by measuring the density and the cohesive energy density as a function of water contents in an extended temperature range in which the material is either a brittle to rubbery solid or a viscoelastic liquid melt. Free volumes available for the diffusion of volatiles in starch barriers are deduced numerically from a mean field equation of state providing molecular scaling parameters for starch–water mixtures from a least squares fit of experimental data. The consistency of the mean field scaling parameters is reflected in their ability to predict accurate surface tension for these systems. The adsorption of small amounts of water is found to increase the density and to reduce the free volume of starch glasses by a phenomenon called antiplasticization as it results in an increase of Young's moduli of materials whereas the opposite is true for plasticization. At higher moisture contents, an overwhelming plasticization leads to a weakening of gas barrier properties as the free volume of starch is increased during swelling by water.     

Addition of gelatin enhanced gelation of corn–milk yogurt

Corn–milk yogurt set by a combination of sodium caseinate plus gelatin at concentrations of 0, 0.2, 0.4 and 0.6% (w/v) were studied. The quality of the gels was determined by measurement of acidity, syneresis, texture profile analysis, viscoelasticity, structure scanning electron microscope and microbiology. Texture profile analysis (TPA) showed that increasing levels of gelatin increased hardness, adhesiveness and springiness as well as the acidity of the products. Viscoelastic behaviour displayed similar trends to the TPA characteristics, the storage modulus was less frequency dependent than the loss modulus giving a loss tangent of 0.2 in the high gelatin systems, which might indicate a true gel system. The microstructure was dense and spongy-like with small air cells, in particular, those having a high concentration of gelatin (0.6%, w/v) gave a very firm structure which might impair palatability. The addition of a commercial gelatin at 0.4% (w/v) gave good acceptability for the product (little syneresis of the gels produced). While the gelatin used for this study had a bloom value of 246 g the authors acknowledge that a different commercial gelatin may well result in a different concentration being required.     

Fabrication and characterization of exfoliated chitosan–gelatin–montmorillonite nanocomposite nanofibers

Polymeric nanofibers as one of the most known nanotechnology products have huge potential applications in many fields due to their high aspect ratio and porosity, being capable of formation of three-dimensional structures and having great mechanical and biological properties. Chitosan is a natural abundant polymer which has attracted huge interests in biomedical and biological industries due to its biocompatible, biodegradable, and non-toxicity properties. However, electrospinning of chitosan is found to be a great challenge, blending it with other polymers such as gelatin was explored as means to improve the morphological deficiencies of chitosan nanofibers and facilitate its electrospinnability. On the other hand, montmorillonite (MMT) has been attracted great attention due to its remarkable improvement in properties of polymeric composites nanofibers. The main objective of this work was on effect of concretion of gelatin–chitosan blends and MMT on morphology of resulted nanocomposite nanofibers. The x-ray diffraction data demonstrated the exfoliation of MMT layers. The morphology of electrospun chiosan–gelatin–MMT composite nanofibers was characterized using scanning electron microscope (SEM). The miscibility of blend was determined using SEM and Fourier transform infrared spectrometer/attenuated total reflectance.     

Time–intensity studies of astringent taste

The intensity of astringent taste was studied in wine, vermouth and other beverages during ingestion and for up to 100 s after swallowing, and the reproducibilities determined. Better reproducibility was observed of the same assessor on different days than between different assessors on the same day. Preprinted forms and mouse operated or touch-sensitive computer recording gave similar results. The residence time in the mouth influenced the maximum intensity and the rate of its decrease, which followed exponential relation. Solutions of tannic acid and catechin tasted more astringent in water than in wine or orange juice. Natural astringent substances in red wine or in tea infusion gave similar time dependence as model solutions. Sugar decreased the astringency in red wine, but quinine hydrochloride or additional ethanol had no pronounced effect.     

Structure–property relationship of different types of polyester industrial yarns

Four major types of polyester industrial yarns (1000 Denier) which are used commercially were studied for their key structural parameters. An attempt has been made to establish a relationship between morphology and properties of these yarns. High tenacity (HT) polyester yarn has the highest birefringence, amorphous orientation, and long period but is relatively less crystalline. High shrinkage characteristic of HT polyester yarn can be accounted for its higher amorphous orientation. High modulus low shrinkage (HMLS) polyester yarn has higher crystallinity and crystal size compared to HT yarn. Fraction of tie molecules of these yarns has been calculated and found that low shrinkage (LS) and super low shrinkage (SLS) yarns have lesser tie molecules. These LS and SLS yarns are tailor-made to achieve lower shrinkage and at the same time maintaining a good level of tenacity. This is achieved with lower amorphous orientation in the final drawn yarn structure. Amorphous orientation was found to have stronger influence than any other structural parameter on the key yarn properties like modulus, tenacity, elongation, and shrinkage.     

Influence of pectin structure on texture of pectin–calcium gels

A library of pectins with varying degree and pattern of methoxylation was produced by demethoxylating a parent pectin by use of NaOH or pectinmethylesterase from plant or fungal origin. Additionally, pectin was chemically depolymerised by a heat treatment. The resulting pectins were characterised in terms of degree and pattern of methoxylation (“(absolute) degree of blockiness”) and the extent of depolymerisation. Pectin–calcium gels were prepared and their texture was studied by performing compression tests. From the resulting force vs. distance curves, the modulus of elasticity under low strain and the fracture stress and strain were determined. The modulus of elasticity under low strain increased with decreasing degree of methoxylation. At very low degree of methoxylation, gels were brittle, resulting in low fracture stress. Both modulus of elasticity and fracture stress correlated more with degree of blockiness and absolute degree of blockiness as compared to degree of methoxylation. Gel strength increased with increasing Ca²⁺ or pectin concentration. Depolymerisation of pectin resulted in formation of brittle gels.Industrial relevancePectin with low degree of methoxylation can form a gel in presence of calcium. Therefore, it is widely used in the food industry. In addition, pectin-calcium interactions are of importance for the texture of fruits and vegetables, since crosslinked pectin in the cell wall provides cell-cell adhesion and mechanical strength of tissues. This research is focused on textural characteristics of pectin-calcium gels. It is shown that pectin structural properties influence texture of gels. As a result, control of pectin structure allows fine-tuning of functional properties.     

Protein–polysaccharide interactions: Phase behaviour of pectin–soy flour mixture

Biopolymers mixed systems have been widely studied in the past two decades, resulting in advances in knowledge of the key parameters involved in macromolecules–macromolecules interactions. Sound understanding and control of these parameters should enable food scientists to design coating or film with desired functional properties. In this study the phase behaviour of high methoxyl pectin and soy flour at pH 4.6 was investigated. The aim was to investigate the effect of different concentrations of pectin (P) and soy flour (SF) solution and different P/SF ratios on mixture phase behaviour. Pectin suspensions at 16 mg ml⁻¹ and 8 mg ml⁻¹ concentrations and soy flour suspensions at 13 mg ml⁻¹ and 6.5 mg ml⁻¹ concentrations were prepared and mixed together in different ratios (10/90, 25/75, 50/50, 75/25, 90/10). Turbidity and rheological measurements were performed to obtain information on pectin–soy flour interaction in electrostatic compatibility conditions. The experimental data show that soy flour solution is a non-stable system in which complexes may be formed during aging. It becomes insoluble and settles to the bottom of the suspension. By blending charged soy flour, at high concentration, with anionic pectin an associative interaction between biopolymers occurs which stabilizes the protein in solution. The best pectin and soy flour suspension for forming film with a continuous network was at concentrations of 16 mg ml⁻¹ and 13 mg ml⁻¹.     

Selenium speciation analysis of Misgurnus anguillicaudatus selenoprotein by HPLC–ICP–MS and HPLC–ESI–MS/MS

Analytical methods for selenium (Se) speciation were developed using high-performance liquid chromatography (HPLC) coupled to either inductively coupled plasma mass spectrometry (ICP?CMS) or electrospray ionization tandem mass spectrometry (ESI?CMS/MS). Separations of selenomethionine (Se-Met) and selenocysteine (Se-(Cys)₂) with favorable peak shape and resolution were obtained by both HPLC-ICP-MS and HPLC?CESI?CMS/MS. Both methods achieved low limits of detection, high sensitivity and favorable stability. With HPLC?CESI?CMS/MS, signal suppression was observed when complex matrix was co-eluted, but excellent structural characterization was still achieved. Thus, HPLC-ICP-MS is better for the detection of Se species, and HPLC?CESI?CMS/MS is essential for molecular identification and confirmation. A water-soluble selenoprotein from purified M. anguillicaudatus muscle tissue was analyzed by the two complementary systems (HPLC-ICP-MS and HPLC?CESI?CMS/MS) with high sensitivity and accuracy. The results demonstrated that Se-Met was the predominant selenoamino acid in the purified selenoprotein from M. anguillicaudatus muscle tissue, and the concentration of Se-Met in the selenoprotein was 6.280?mg/kg (dry mass). In addition, in HPLC-ICP-MS, an unknown Se-containing compound with similar polarity to Se-(Cys)₂ was discovered. Using complementary data from HPLC?CESI?CMS/MS, it was determined that this unknown Se-containing compound was not Se(Cys)_2.     

Formation of the aroma of a raw goat milk cheese during maturation analysed by SPME–GC–MS

The volatile profile of the Spanish goat raw milk cheese of the protected designation of origin (PDO) “Queso Ibores” was studied at four stages of maturation (day 1, 30, 60, and 90) by the method of solid-phase micro-extraction–gas chromatography–mass spectrometry (SPME–GC–MS) to determinate the characteristic volatile compounds of this cheese and to know the changes in the volatile profile of this cheese during maturation. According to the PDO, Ibores cheese aroma varies between sweet and mild and it has a strong taste, slightly tart. A total of 64 compounds were detected: 14 acids, 18 alcohols, 13 esters, 6 ketones and 13 compounds which could not be classified in these groups. Carboxylic acids were the most abundant volatile compounds in the headspace of Ibores cheese. Content of volatile compounds was significantly modified (P < 0.05) during ripening. The relative total amounts of acids, esters and ketones increased during the first 60 days of maturation. The most characteristic compounds of Ibores cheese aroma were butanoic, hexanoic and octanoic acids, some alcohols (2-butanol and 2-heptanol), ethyl esters of hexanoic and butanoic acids, some methyl ketones (2-butanone, 2-pentanone and 2-heptanone) and δ-decalactone.     

An overview of binary taste–taste interactions

The human gustatory system is capable of identifying five major taste qualities: sweet, sour, bitter, salty and savory (umami), and perhaps several sub-qualities. This is a relatively small number of qualities given the vast number and structural diversity of chemical compounds that elicit taste. When we consume a food, our taste receptor cells are activated by numerous stimuli via several transduction pathways. An important food-related taste question which remains largely unanswered is: How do taste perceptions change when multiple taste stimuli are presented together in a food or beverage rather than when presented alone? The interactions among taste compounds is a large research area that has interested electrophysiologists, psychophysicists, biochemists, and food scientists alike. On a practical level, taste interactions are important in the development and modification of foods, beverages or oral care products. Is there enhancement or suppression of intensity when adding stimuli of the same or different qualities together? Relevant psychophysical literature on taste–taste interactions along with selected psychophysical theory is reviewed. We suggest that the position of the individual taste stimuli on the concentration-intensity psychophysical curve (expansive, linear, or compressive phase of the curve) predicts important interactions when reporting enhancement or suppression of taste mixtures.     

The UPLC–ESI–QqQLIT–MS/MS method for quantitative determination of phytochemicals in ethanolic extracts of different parts of eight Ficus species: Development and validation

Ficus and validation of the ultra performance liquid chromatography–electrospray ionization hybrid triple quadrupole–linear ion trap–tandem mass spectrometry (UPLC–ESI–QqQ_LIT–MS/MS) method in a multiple-reaction monitoring (MRM) mode for the quantitative determination of 19 phytochemicals. The chromatographic separation of targeted phytochemicals was performed using the Waters ACQUITY UPLC BEH? C18 column (1.7 μm, 2.1 mm × 50 mm) with 0.1% formic acid with water and acetonitrile as a mobile phase at a flow rate of 0.25 mL/min. The validation parameters showed the overall recoveries from 95.78?101.44% (RSD ≤ 3.25%), precision (intra-day: RSD ≤ 2.96%; inter-day: RSD ≤ 2.89%), linearity (R² ≥ 0.9982), limit of detection (8.60 × 10^–10?2.18 × 10^–6 mg/mL), and the limit of quantitation (2.60 × 10^–9–6.63 × 10^–6 mg/mL) in the concentration range from 0.5 to 1000 × 10^–6 mg/mL. This method was successfully applied in ethanolic extracts of different parts (fruits, leaves, and barks) of selected eight Ficus species. Quinic acid was predominant followed by rutin and chlorogenic acid among the studied nineteen phytochemicals. Ficus benjamina showed the maximum total content in fruits and leaves. The UPLC–ESI–QqQ_LIT–MS/MS method combined with principal component analysis (PCA) was successfully used for Ficus species discrimination on the basis of the contents of 15 compounds. The UPLC–ESI–QqQ_LIT–MS/MS method combined with PCA could be used for quality control.