Structural changes in squid (Loligo japonica) collagen after modification by formaldehyde

BACKGROUND: Formaldehyde (FA) has been suggested to cause changes in texture and functional properties in some marine species. It was therefore hypothesised that FA may affect collagen, a fundamental constituent of the extracellular matrix in squid. RESULTS: Two types of collagen, I and V, were isolated by pepsin digestion and differential salt precipitation. Type V collagen contained higher proportions of isoleucine, leucine, and lysine and lower proportions of alanine and hydroxyproline. The effects of FA on pepsin‐solubilised squid collagen were examined by differential scanning calorimetry and Raman spectroscopy. The squid collagen showed a transition temperature (T_m1) of 37.2 ± 0.2 °C, which was significantly reduced in the presence of 2 and 10 mmol L^?1 FA. In the presence of 1, 2 and 10 mmol L^?1 FA an additional peak (T_m2) was also observed at 77.7 ± 0.1, 78.4 ± 0.1 and 62.7 ± 0.2 °C respectively, suggesting FA–collagen interactions. Treatment with 2 mmol L^?1 FA increased the I₉₄₀/I₁₀₀₅ ratio from 1.09 to 1.66 and shifted the 990 and 1245 cm^?1 bands. The tyrosine doublet ratio (I₈₅₀/I₈₃₀) was also increased about threefold, suggesting that α helix, β sheet type and random coil structures were changed by FA. CONCLUSION: The secondary structure of squid collagen can be affected by FA through hydrophobic interactions. Copyright © 2008 Society of Chemical Industry     

Pectin methyl esterase treatment on high‐methoxy pectin for making fruit jam with reduced sugar content

BACKGROUND: Pectin methyl esterase (PME) has been postulated to catalyse the transacylation reaction between pectin molecules. The present study aimed to prove the occurrence of this reaction. The feasibility of applying PME‐catalysed transacylation between high‐methoxy pectin molecules in making fruit jam with reduced sugar content was also investigated. RESULTS: PME treatment increased the turbidity and particle size in pectin solution and the molecular weight of pectin, while it decreased the number of methoxy ester linkages and the intensity of the CH₃ absorption peak in the Fourier transform infrared spectrum without changes in the number of total ester linkages in pectin molecules. These findings support the occurrence of PME‐catalysed transacylation between pectin molecules. Higher values of hardness, gumminess and chewiness were found in a jam containing PME‐treated citrus pectin (10 g L^?1) and sugar (350 g L^?1) as compared with either a jam containing untreated citrus pectin (10 g L^?1) and sugar (350 g L^?1) or strawberry jam containing pectin (10 g L^?1) from the fruit and sugar (650 g L^?1). CONCLUSION: The demand for sugar in jam making can be greatly reduced by the use of PME‐treated high‐methoxy pectin. Copyright © 2012 Society of Chemical Industry     

Physicochemical properties and thermal stability of Lep w 1, the major allergen of whiff

Whiff (Lepidorhombus whiffiagonis) is a fish frequently consumed in Spain. Lep w 1, its major allergen, is a calcium‐binding β‐parvalbumin. The resistance of Lep w 1 to heat denaturation and to digestion were studied by circular dichroism spectroscopy and by in vitro gastric digestion systems. Purified Lep w 1 was thermally stable up to 65°C at neutral pH. Calcium depletion resulted in a change of its structure as determined by circular dichroism spectroscopy. A partial loss of structure was also observed at acidic pH; however, the allergen retained its full IgE‐binding ability. The partially denatured Lep w 1 was easily digested by pepsin within 2 min. Further, the IgE reactivity of proteins extracted from cooked fish and their stability to proteolysis were analyzed. The extract revealed a higher number of IgE reactive bands than an extract from uncooked fish. IgE binding to these proteins could not be inhibited by an extract from uncooked fish. In contrast to a raw fish extract, the cooked extract showed higher resistance to pepsinolysis. The stability of Lep w 1 to thermal denaturation and digestion explains the high allergenicity of whiff.     

Constitutive expression,purification and characterisation of pectin methylesterase from Aspergillus niger in Pichia pastoris for potential application in the fruit juice industry

BACKGROUND: Pectin methylesterase (PME) catalyses the hydrolysis of the methyl ester of pectin, yielding free carboxyl groups and methanol. PME is widely used in the food, cosmetic and pharmaceutical industries. RESULTS: PME from Aspergillus niger was constitutively expressed to a high level in the yeast Pichia pastoris. The recombinant PME was purified by a combination of ammonium sulfate fractionation and ion exchange chromatography, giving an overall yield of 28.0%. It appeared as a single band in sodium dodecyl sulfate polyacrylamide gel electrophoresis, with a molecular mass of about 45 kDa. Optimal activity of the enzyme occurred at a temperature of 50 °C and a pH of 4.7. The K_m, V_max and k_cat values of the enzyme with respect to pectin were 8.6 mmol L^?1 [ ], 1.376 mmol min^?1 mg^?1 and 8.26 × 10² s^?1 respectively. Cations such as K⁺, Mg²⁺, Ni²⁺, Mn²⁺ and Co²⁺ slightly inhibited its activity, whereas Na⁺ had no effect. CONCLUSION: PME from A. niger was constitutively expressed to a high level in P. pastoris without methanol induction. The recombinant PME was purified and characterised and shown to be a good candidate for potential application in the fruit juice industry. Copyright © 2012 Society of Chemical Industry     

Effects of two contrasting dietary fibres on starch digestion,short‐chain fatty acid production and transit time in rats

Dietary fibres may cause dietary starch to escape digestion in the small intestine and enter the large intestine. If this results from the dietary fibres reducing the gastrointestinal transit time, those dietary fibres that reduce this the most would be expected to cause the most starch to escape digestion. We tested in rats the relative abilities of two contrasting dietary fibres, apple pectin (a soluble dietary fibre) and wheat straw (an insoluble, lignified dietary fibre), to reduce the whole gut transit time and to cause dietary starch to escape digestion. We provided male Wistar rats with a control, modified AIN‐76™ diet containing 20% fat but no dietary fibre, and with this diet containing 10% dietary fibre; the dietary fibre replaced the equivalent weight of starch in the control diet. Both dietary fibres, but particularly wheat straw, reduced the transit time compared with the fibre‐free control diet. Pectin, but not wheat straw, resulted in substantial amounts of starch in the caecal contents. This effect may result from the pectin increasing the viscosity of the digesta or causing it to gel. Large amounts of short‐chain fatty acids were found only in the caeca of rats provided with pectin. © 2000 Society of Chemical Industry     

Influence of harvest time on citrus pectin and its in vitro inhibition of fibroblast growth factor signal transduction

Seasonal changes in pectin content and chemical composition were studied in three anatomical layers of ‘Rio Red’ grapefruit (Citrus paradisi Macf), a currently popular cultivar in the Rio Grande Valley in Texas, USA. Fruits were harvested at intervals between August 1998 and May 1999. Pectin content in flavedo decreased throughout the season, while in albedo and segment membrane the pectin content was lowest in mid‐season (November and January). In all three layers the anhydrogalacturonic acid (AGA) content of pectin was highest in mid‐season. While the methoxyl content (MC) of pectin increased, the total neutral sugar (TNS) content of pectin decreased in all three layers throughout the season. The in vitro effect of grapefruit pectin on fibroblast growth factor (FGF)–FGF receptor (FGFR) interaction was also investigated. The strong interdependence of heparin on factor–receptor interaction provides means for identifying new antagonists of growth factor activity and thus for treatment of various diseases. Our results showed that grapefruit pectin significantly inhibited the binding of FGF‐1 to FGFR1 in the presence of 0.1 µg ml^?1 heparin. Pectin of albedo from grapefruits harvested in January was the most potent inhibitor. The in vitro inhibitory activity was significantly correlated with the percentage of rhamnose. Kinetic studies revealed a competitive nature of pectin on FGF signal transduction with heparin. The observation that the biological activity of heparin can be antagonised by citrus pectin suggests that pectins should be investigated further as anti‐growth factor agents for potential health benefits. © 2002 Society of Chemical Industry     

Solvent extraction and in vitro simulated gastrointestinal digestion of phenolic compounds from purple sweet potato

The total content of phenolic compounds in purple sweet potato (PSP) was determined and the release of such compounds from PSP in gastrointestinal digestion was studied in vitro. The extraction conditions for the maximum recovery of free phenol (FP) and bound phenol (BP) from PSP were determined by response surface methodology (RSM). The maximum recovery of FPPSP was 14.16 ± 0.87 mg GAE per g short for dry weight (DW), which was obtained using 60% (v/v) ethanol maceration with a liquid–solid ratio of 57.21:1 (mL g⁻¹) at 51.93 °C for 2.12 h. The maximum recovery for BPPSP was 7.54 mg GAE per g DW, which was obtained upon hydrolysis with 1.87 mol L⁻¹ NaOH at a liquid–solid ratio of 35.93:1 (mL g⁻¹) for 4.74 h. The maximum phenolic content was released after 1 and 2 h for the in vitro gastric and intestinal digestion respectively. The release of the phenolics was promoted by pepsin and gastric acid during gastric digestion, while it was further promoted by trypsin during intestinal digestion.     

Interactions of digestive enzymes and milk proteins with tea catechins at gastric and intestinal pH

The interactions of digestive enzymes (pepsin, pancreatin) and milk proteins (β‐casein, β‐lactoglobulin (β‐Lg)) with (?)‐epigallocatechin gallate (EGCG), (?)‐epigallocatechin (EGC) and (?)‐epicatechin (EC) at gastric and intestinal pH were investigated by fluorescence spectroscopy. The results indicated that in the gastric environment, all three tea catechins showed binding affinities in descending order of strength with β‐casein first, followed by β‐Lg and then pepsin. The highest affinity was observed for EGCG–β‐casein, with a binding constant (K_A) of 2.502(±0.201) × 10⁵ m ^?1. In the intestinal environment, the binding strengths of the proteins with EGCG and EGC were in the order β‐Lg > pancreatin > β‐casein; for binding with EC, the strength order was β‐casein > β‐Lg > pancreatin. The combination EGCG–β‐Lg had the strongest binding affinity, with a K_A of 14.300(±0.997) × 10⁵ m ^?1. Thermodynamic analysis revealed that tea catechins complexed with milk proteins and digestive enzymes via different hydrophilic and hydrophobic interactions depending on the different digestion environments and types of catechins, proteins and enzymes.     

Identification of physicochemical properties of Scylla paramamosain allergen,arginin kinase

BACKGROUND: Arginine kinase (AK) is expressed in a wide variety of species, including human food sources (seafood) and pests (cockroaches and moths), and has been reported as a novel allergen. However, there has been little research on the allergenicity of AK in crustaceans. In this study the physicochemical properties of AK from mud crab (Scylla paramamosain) were investigated. RESULTS: Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis, immunoblotting and inhibition enzyme‐linked immunosorbent assay revealed that purified AK was unstable in thermal processing and in acid buffer. Under simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) conditions, purified AK was much more readily degraded by pepsin than by trypsin or chymotrypsin. The unpurified AK in crab myogen degraded more markedly than purified AK. In addition, in two‐phase gastrointestinal digestion, AK was rapidly degraded by pepsin but resistant to trypsin and chymotrypsin digestion, while tropomyosin derived from mud crab was resistant to pepsin digestion but digested readily by trypsin or chymotrypsin. Further study of serum samples obtained from crab‐allergic human patients indicated that the allergenicity of AK was markedly reduced by digestion with SGF but not SIF. CONCLUSION: AK is an important food allergen despite its unstable physicochemical properties of digestibility. Copyright © 2012 Society of Chemical Industry     

Characterisation of gold kiwifruit pectin isolated by enzymatic treatment

Pectin was extracted from gold kiwifruit by four commercial enzyme preparations (Celluclast 1.5 L, Cytolase CL, Cellulyve TR 400 and NS33048). The chosen enzymes were used either in single or in combination, with and without protease addition. The recovered pectin was characterised and compared for the yield, total nonstarch polysaccharide and neutral sugar composition, protein and ash, pectin, molecular weight distribution and the viscosity. Results indicated that enzyme‐extracted gold kiwifruit pectin was rich in galacturonic acid. Purified pectin yield, and their physicochemical composition and rheological property (viscosity), was significantly affected by the type of enzyme used. The pectin extracted by Celluclast 1.5 L demonstrated to be the most viscous and recorded the highest in molecular weight (M_w) (1.65 × 10⁶ g mol^–1) compared with the other extracts. The extract M_w and their distribution were discussed and related to their viscosity behaviour.     

Characteristics of enzymatically-deesterified pectin gels produced in the presence of monovalent ionic salts

Pectin methylesterases (PMEs) from Valencia orange (p-PME) and Aspergillus aculeatus (f-PME) were used to produce pectin gels in the presence of 0.2 M monovalent ionic salts. At pH 5.0, pectin gels were induced following enzymatic deesterification of high methoxy pectin, with greater deesterification observed using p-PME compared to f-PME. Under these conditions, the deesterification limit of f-PME ended up with a pectin of DE 30.5–31.9 which did not gel at the PME reaction completion, while p-PME reduced the pectin's DE to 16.0–17.2, resulting in gel formation. The pectin gel induced by KCl was significantly stronger than the NaCl-induced gel, but LiCl did not induce pectin gelation. The gel strength was influenced by both DE and species of monovalent cation. The KCl-induced gels released less water than NaCl-induced gels. A synergistic effect on gel strength was observed from the pectin treated with a combination of (p + f)-PMEs, producing even more stable gels. These results indicated that the pectin gelation of our system would be enhanced both by using larger monovalent cation and by lowering the DE value, which would presumably be attributed to the different action patterns recognized for p- and f-PMEs. This pectin gelation system could provide a useful alternative to acid-sugar or calcium cross-linked gels in food and other industrial applications.     

Determination of kinetic parameters of pectolytic enzymes at low pectin concentrations by a simple method

A simple and sensitive method for determination of the pectolytic enzyme activity was improved for soluble and immobilized forms of the enzyme. During enzymatic hydrolyzation of pectin, samples were collected from substrate solution at certain time intervals. Pectin in the samples was precipitated by alcohol and then pectin concentration was determined by measuring the refractive index of a prepared aqueous solution of these precipitates. The validity of this technique was evaluated using the kinetic behavior of soluble and immobilized enzymes. The kinetics of free and Duolite A568-immobilized pectinase was investigated. Michaelis-Menten constants and maximal reaction rates were found as K _m=20.71 g l ^-1 and V _max=81.30 g l ^-1s ^-1 for free enzyme and K _m=1.02 g l ^-1 and V _max=0.035 g s ^-1 g ^-1 particles for immobilized pectinase at 20 °C.     

果胶功能性质新进展

果胶是一种来源于植物细胞壁的酸性无毒杂多糖。作为一种天然的食品添加剂,果胶在食品和医药工业得到了广泛的应用。本文综述了果胶控制脂质消化、降低胆固醇以及抑制肿瘤的作用,介绍了果胶益生元的潜力,阐述了果胶作为益生菌运载体以及在食品活性包装的应用,最后对果胶部分功能性质存在的问题和解决方法进行展望,以期为果胶进一步开发和应用提供理论支持。     

The effect of in vitro gastrointestinal simulation on bioactivities of kefir

Kefir is a fermented milk beverage and known to have positive effects on gut microbial diversity and human health. In this study, digested and undigested kefir samples were compared for changes in their antihypertensive, antidiabetic, antioxidant and antimicrobial activities. Results showed that the amount of total phenolic substances, 2,2-diphenyl-1-picrylhydrazyl radical scavenging (DPPH) activity, and the angiotensin-converting enzyme inhibitor (ACE-I) activity increased from 43.76 ± 0.005 mg gallic acid equivalents (GAE)/L, 4.20 ± 0.55%, and 9.91 ± 3.90% in undigested kefir to 668.16 ± 3.332 mg GAE/L, 63.06 ± 0.64%, and 98.88 ± 0.42% in digested kefir, respectively. While the dipeptidyl peptidase IV-inhibitory (DPPIV-I) activity of undigested kefir increased by 19.11 ± 7.35% after digestion, the optical density of the ferric-reducing antioxidant power (FRAP) decreased from 1.188 ± 0.05 to 0.278 ± 0.009, and the protein amount decreased from 101.4 mg L⁻¹ to 12.42 mg L⁻¹ in digested kefir. No antimicrobial effect was observed in undigested kefir, whereas, digested kefir samples were active, but only against Escherichia coli. These results show that the gastrointestinal digestion processes of kefir generally increase the number of bioactive molecules, and the digestion process must be taken into account to determine the biological capability of foods.     

Development of a method to measure dietary fibre in oranges

A method to measure dietary fibre in oranges has been developed. Pectin was extracted from the food sample using heat, acid and a cation-exchange resin. This was followed by enzymic digestions, using pepsin and pancreatin, of the remaining residue. Optimal levels of resin, pH, time and temperature for maximum pectin extraction were found. Optimal levels of enzymes and pH for maximal enzyme digestion was also found. Other food products tested for dietary fibre content were: cauliflower, oranges, pole beans, carrots and whole wheat flour. Values found were greater than those for other fibre analyses; however, most other methods fail to measure the water-soluble indigestible components, such as pectin.     

INFLUENCE OF TRANSGLUTAMINASE-INDUCED CROSS-LINKING ON IN VITRO DIGESTIBILITY OF SOY PROTEIN ISOLATE

The influence of covalent cross‐linking by microbial transglutaminase (MTGase) on the sequential in vitro pepsin and trypsin digestion process and the digestibility of soy protein isolate (SPI), was investigated by sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and nitrogen release analyses. Various subunits of β‐conglycinin and acidic subunits of glycinin were cross‐linked by MTGase to form high molecular weight (MW) biopolymers, while basic subunits of glycinin were unaffected. SDS‐PAGE analysis indicated that the cross‐linking mainly affected in vitro pepsin digestion pattern of various subunits of β‐conglycinin, while the trypsin digestion pattern of native SPI was nearly unaffected. Nitrogen release analysis showed that the in vitro pepsin or/and trypsin digestibility of native SPI (at the end of pepsin or trypsin ingestion) was significantly decreased (P ≤ 0.01) by the MTGase treatment (for more than 2 h). The cross‐linking by MTGase also significantly decreased the in vitro digestibility of preheated SPI. These results suggest that the cross‐linking by means of transglutaminase may negatively affect the nutritional properties of food proteins.     

In vitro digestion of major allergen in salmon roe and its peptide portion with proteolytic resistance

A fish yolk protein, β′-component (β′-c), is the major allergen in chum salmon roe. The effect of proteolysis on the allergenicity of β′-c was estimated. Changes in the IgE-binding ability of β′-c upon pepsin and trypsin digestion were investigated by monitoring the proteolytic cleavage. In the pepsin–trypsin digestion of chum salmon yolk protein, the β′-c contained therein was degraded in a manner similar to that of other yolk proteins, but digestion fragments with a molecular mass of >10 kDa remained throughout the digestion process. Specifically, the peptide sequence between 31-Y and 119-Q (10 kDa) was stable to pepsin–trypsin digestion and the portion showed high IgE-binding ability. As a result, pepsin–trypsin digestion had little effect on the IgE-binding ability of β′-c. These results suggest that β′-c reaches the small intestine in the form of high-molecular-mass components with IgE-binding ability in vivo.     

Optimisation of hydrolysis of purple sea urchin (Strongylocentrotus nudus) gonad by response surface methodology and evaluation of in vitro antioxidant activity of the hydrolysate

BACKGROUND: Hydrolysates prepared from sea urchin (Strongylocentrotus nudus) gonad by enzymatic treatment showed strong 1,1‐diphenyl‐2‐picrylhydrazyl radical scavenging activity and reducing power. RESULTS: Hydrolysis of S. nudus gonad by the commercial protease papain was optimised for maximum degree of hydrolysis (DH) and trichloroacetic acid‐soluble peptide index (TCA‐SPI) using response surface methodology. Results showed that the optimal conditions were the following: temperature of 48.83 °C, pH of 6.92, enzyme‐to‐substrate ratio of 3143 U g^?1, and substrate concentration of 83.5 g L^?1. Under these conditions, a DH of 27.96 ± 0.54% and a TCA‐SPI of 57.32 ± 0.63% were obtained. The hydrolysate prepared in the optimal conditions was fractionated by an ultra‐filtration system and the resultant fraction below 10 kDa was found to effectively scavenge hydroxyl radical (EC₅₀ = 13.29 ± 0.33 mg mL^?1) and hydrogen peroxide (EC₅₀ = 16.40 ± 0.37 mg mL^?1), inhibit lipid peroxidation (EC₅₀ = 11.05 ± 0.62 mg mL^?1), chelate Fe²⁺ (EC₅₀ = 7.26 ± 0.44 mg mL^?1), and protect mice macrophages against death induced by tert‐butyl hydroperoxide. CONCLUSION: Hydrolysates prepared from S. nudus gonad have the potential to be applied as natural antioxidant agents. Copyright © 2012 Society of Chemical Industry     

Effect of debranching on the rheological properties of Ca-pectin gels

Water-soluble pectin (WSP) extract was subjected to controlled carrot pectin methylesterase treatment, thereby producing de-esterified pectin (DEP). Both WSP and DEP were incubated with a mixture of endo-arabinanase and α-L-arabinofuranosidase to yield partially debranched pectins (WSP_DBr and DEP_DBr respectively). Pectin samples were characterised in terms of degree of methylesterification (DM), neutral sugar content, and degree of branching (DBr). The characterised pectins were used for the preparation of pectin gels with high and low calcium ion (Ca²⁺) concentrations. The rheological characteristics of the produced gels were evaluated by means of small-amplitude oscillatory tests. These characteristics include network development of the gel, gel strength (G′), gel elastic character and gel type. Partial debranching of pectin resulted in a reduction of the arabinose content (by approximately 50%) and caused a slight decrease in polymer DBr. Gels produced from semi-dilute solutions of partially debranched pectins showed network development profiles similar to those prepared from semi-dilute solutions of the corresponding non-debranched polymers. Yet, the former gels showed lower G′ values, poor gel elastic character and a “weaker” nature as compared to the latter. Next to Ca²⁺ cross-links, the presence of long arabinose-containing side chains is suggested to play an important role in the rheological characteristics of Ca²⁺-pectin gels.     

Effect of garlic consumption on total antioxidant status and some biochemical and haematological parameters in blood of rats

BACKGROUND: The effect of diet garlic supplementation on total antioxidant status (TAS), nitric oxide (NO) and routine biochemical and haematological parameters was investigated in blood of rats. A total of 30 male rats were divided equally into two groups. Each of 15 rats of treatment group was fed 600 mg kg^?1 garlic solution in distilled water by gavage and controls only received distilled water. After garlic consumption for 1 month, blood serum total antioxidant, nitrate and some biochemical and haematological tests including serum lipids parameters, blood sugar, complete blood count (CBC), and haemoglobin were measured. RESULTS: The garlic treatment group showed significantly increase in the mean level of TAS from 0.77 ± 0.10 mol L^?1 to 1.18 ± 0.11 mol L^?1 (P < 0.01) and nitrate (a NO metabolite) from 0.78 ± 0.06 µmol L^?1 to 1.44 ± 0.27 µmol L^?1 (P < 0.05) in the blood sera of rats compared with the controls. There were no significant differences between the routine biochemical and haematological parameters. CONCLUSION: Garlic consumption should have antioxidant properties and may not affect the lipids profile and total blood cell counts. Copyright © 2009 Society of Chemical Industry