Purification and physicochemical characterization of ovine β‐lactoglobulin and α‐lactalbumin

Ovine whey proteins were fractionated and studied by using different analytical techniques. Anion‐exchange chromatography and reversed‐phase high‐performance liquid chromatography (HPLC) showed the presence of two fractions of β‐lactoglobulin but only one of α‐lactalbumin. Gel permeation and sodium dodecyl sulfate (SDS)‐polyacrylamide gel electrophoresis allowed the calculation of the apparent molecular mass of each component, while HPLC coupled to electrospray ionisation‐mass spectrometry (ESI‐MS) technique, giving the exact molecular masses, demonstrated the presence of two variants A and B of ovine β‐lactoglobulin. Amino acid compositions of the two variants of β‐lactoglobulin differed only in their His and Tyr contents. Circular dichroism spectroscopy profiles showed pH conformation changes of each component. The thermograms of the different whey protein components showed a higher heat resistance of β‐lactoglobulin A compared to β‐lactoglobulin B at pH 2, and indicated high instability of ovine α‐lactalbumin at this pH.     

Chemical characteristics of Śliwowica Łącka and other plum brandies

BACKGROUND: ?liwowica ??cka is a strong, distilled, home‐made plum brandy produced in a submontane region of Poland. The aim of the present study was to determine the chemical composition of this alcoholic beverage (samples from the years 2001–2004) and compare it with that of other plum brandies. Gas chromatography and spectrophotometry methods were used to detect major volatile components. RESULTS: Home‐made Polish plum brandies generally contained more ethanol (64.7–72.5% v/v), methanol (5.59–8.74 g L^?1100°) and butanol (32–335 mg L^?1100°) and less isobutanol (406–491 mg L^?1100°), pentanol (4.3–14.9 mg L^?1100°) and 2‐phenylethanol (61–68 mg L^?1100°) than other samples. The amyl alcohols/1‐propanol and isobutanol/1‐propanol ratios might be used as indices to distinguish spontaneously fermented plum brandies from those produced by monoculture. Statistically significant differences (P < 0.01) were found in the plum brandy sensory characteristics examined. Total sensory scores of Polish plum brandies ranged between 12.0 and 14.3, while Slovakian Slivovica received the highest score (16.7). CONCLUSION: The results showed that plum brandies produced in the ??cko area are characterised by a similar and original chemical composition that results mainly from spontaneous fermentation as well as traditional production technology. Copyright © 2007 Society of Chemical Industry     

Investigation of the interaction between (−)‐epigallocatechin‐3‐gallate with trypsin and α‐chymotrypsin

Tea polyphenol (TP) inhibits digestive enzymes and reduces food digestibility. To explore the interaction between TP with digestive enzymes, bindings of ‐epigallocatechin‐3‐gallate (EGCG) to trypsin and α‐chymotrypsin were studied in detail using fluorescence, resonance light‐scattering, circular dichroism, fourier transform infrared spectroscopy methods and protein‐ligand docking. The binding parameters were calculated according to Stern–Volmer equation, and the thermodynamic parameters were determined by the van't Hoff equation. The results indicated that EGCG was capable of binding trypsin and α‐chymotrypsin with high affinity, resulting in a change of native conformation of these enzymes. EGCG had a greater influence on the structure of α‐chymotrypsin than trypsin. This study can be used to explain the binding interaction mechanism between TP and digestive enzymes.     

Bioequivalence of β‐carotene and retinol

For many years it was accepted that 6 mg of β‐carotene were required to produce 1 mg of vitamin A in the form of retinol. The equivalence was based on the assumptions that two‐thirds of dietary β‐carotene are not absorbed, while in the metabolism of the remaining third 1 mol of β‐carotene is converted to 1 mol retinol. Recently, the bioequivalence was raised to 12 mg β‐carotene and 1 mg retinol. The objective of this review was to re‐examine the data that were used to support the new equivalence ratio, especially since some of these data were obtained in developing countries where infestation with gut parasites and exposure to other infections is common, yet the influence of inflammation on plasma carotenoid and retinol concentrations is frequently ignored. Bioequivalence studies examined in this review include those done in developing and developed countries, depletion and repletion studies, feeding with vegetable sources of β‐carotene or pure supplements, influence of helminths, carotenoid interactions and matrix effects and studies using stable isotopes (SI). SI studies show the bioefficacy of β‐carotene conversion to retinol is generally poor even for pure β‐carotene unless the dose is small and fed regularly until equilibration is reached. Retinol formation appears to be inversely influenced by previous vitamin A intake, the amount of material given and current vitamin A status. In spite of technical complexities, more SI studies where liver reserves of vitamin A are determined pre and post intervention are needed to evaluate β‐carotene bioefficacy of different vegetable sources. Copyright © 2006 Society of Chemical Industry     

Chilling injury development of ‘Tahitian’ lime, ‘Emperor’ mandarin, ‘Marsh’ grapefruit and ‘Valencia’ orange

The effect of varying levels of ethylene on the chilling injury (CI) development and the changes in the levels of putrescine, squalene and α-farnesene of ‘Tahitian’ lime (Citrus latifolia Tanaka), ‘Emperor’ mandarin (Citrus reticulata Blanco), ‘Marsh’ grapefruit (Citrus paradisi Macf) and ‘Valencia’ orange (Citrus sinensis L Osbeck) stored at 0°C was investigated. It was found that different citrus fruits stored at 0°C had varying sensitivity to CI, and that low levels of exogenous ethyiene induced earlier and more severe CI in all citrus fiuits. The levels of endogenous putrescine, squalene and α-farnesene varied between fruit, and was affected by the time of exposure at 0°C and the presence of ethylene. The patterns of change indicate that loss of squalene coupled with loss of α-farnesene could be involved in induction of CI.     

Influence of whey peptides on the surface activity of κ‐casein and β‐lactoglobulin A

Whey protein hydrolysate (WPH) was fractionated by reverse‐phase chromatography to obtain fractions of varying surface‐hydrophobicities. A model oil–water interface (MI) was pre‐coated with the WPH or fractions thereof. Contact angle (θ) of sessile drops of κ‐casein (κ‐CN) or β‐lactoglobulin A (β‐LGA) were measured on the MI. Pre‐coating of MI with un‐fractionated WPH decreased θ, that is, increased surface activity, of both κ‐CN (35–8.3°) and β‐LGA (38–21.3°). Conversely, pre‐coating of MI with the fractions significantly increased θ of both proteins as a function of hydrophobicity. Data provide insight into variability of whey protein functionality in food applications.     

Screening of β‐Glucosidase and β‐Xylosidase Activities in Four Non‐Saccharomyces Yeast Isolates

The finding of new isolates of non‐Saccharomyces yeasts, showing beneficial enzymes (such as β‐glucosidase and β‐xylosidase), can contribute to the production of quality wines. In a selection and characterization program, we have studied 114 isolates of non‐Saccharomyces yeasts. Four isolates were selected because of their both high β‐glucosidase and β‐xylosidase activities. The ribosomal D1/D2 regions were sequenced to identify them as Pichia membranifaciens Pm7, Hanseniaspora vineae Hv3, H. uvarum Hu8, and Wickerhamomyces anomalus Wa1. The induction process was optimized to be carried on YNB‐medium supplemented with 4% xylan, inoculated with 106 cfu/mL and incubated 48 h at 28 °C without agitation. Most of the strains had a pH optimum of 5.0 to 6.0 for both the β‐glucosidase and β‐xylosidase activities. The effect of sugars was different for each isolate and activity. Each isolate showed a characteristic set of inhibition, enhancement or null effect for β‐glucosidase and β‐xylosidase. The volatile compounds liberated from wine incubated with each of the 4 yeasts were also studied, showing an overall terpene increase (1.1 to 1.3‐folds) when wines were treated with non‐Saccharomyces isolates. In detail, terpineol, 4‐vinyl‐phenol and 2‐methoxy‐4‐vinylphenol increased after the addition of Hanseniaspora isolates. Wines treated with Hanseniaspora, Wickerhamomyces, or Pichia produced more 2‐phenyl ethanol than those inoculated with other yeasts.     

Thermal modifications of structure and codenaturation of α‐lactalbumin and β‐lactoglobulin induce changes of solubility and susceptibility to proteases

Study of heat denaturation of major whey proteins (β‐lactoglobulin or α‐lactalbumin) either in separated purified forms, or in forms present in fresh industrial whey or in recomposed mixture respecting whey proportions, indicated significant differences in their denaturation depending on pH, temperature of heating, presence or absence of other co‐denaturation partner, and of existence of a previous thermal pretreatment (industrial whey). α‐Lactalbumin, usually resistant to tryptic hydrolysis, aggregated after heating at ⪈85°C. After its denaturation, α‐lactalbumin was susceptible to tryptic hydrolysis probably because of exposure of its previously hidden tryptic cleavage sites (Lys‐X and Arg‐X bonds). Heating over 85°C of β‐lactoglobulin increased its aggregation and exposure of its peptic cleavage sites. The co‐denaturation of α‐lactalbumin with β‐lactoglobulin increased their aggregation and resulted in complete exposure of β‐lactoglobulin peptic cleavage sites and partial unveiling of α‐lactalbumin tryptic cleavage sites. The exposure of α‐lactalbumin tryptic cleavage sites was slightly enhanced when the α‐lactalbumin/β‐lactoglobulin mixture was heated at pH 7.5. Co‐denaturation of fresh whey by heating at 95°C and pH 4.5 and above produced aggregates stabilized mostly by covalent disulfide bonds easily reduced by β‐mercaptoethanol. The aggregates stabilized by covalent bonds other than disulfide arose from a same thermal treatment but performed at pH 3.5. Thermal treatment of whey at pH 7.5 considerably enhanced tryptic and peptic hydrolysis of both major proteins.     

Characterization of the Supermolecular Structure of Polydatin/6‐O‐α‐Maltosyl‐β‐cyclodextrin Inclusion Complex

Polydatin is the main bioactive ingredient in many medicinal plants, such as Hu‐zhang (Polygonum cuspidatum), with many bioactivities. However, its poor aqueous solubility restricts its application in functional food. In this work, 6‐O‐α‐Maltosyl‐β‐cyclodextrin (Malt‐β‐CD), a new kind of β‐CD derivative was used to enhance the aqueous solubility and stability of polydatin by forming the inclusion complex. The phase solubility study showed that polydatin and Malt‐β‐CD could form the complex with the stoichiometric ratio of 1:1. The supermolecular structure of the polydatin/Malt‐β‐CD complex was characterized by ultraviolet–visible spectroscopy (UV), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffractometry (XRD), thermogravimetric/differential scanning calorimetry (TG/DSC), and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy. The changes of the characteristic spectral and thermal properties of polydatin suggested that polydatin could entrap inside the cavity of Malt‐β‐CD. Furthermore, to reasonably understand the complexation mode, the supermolecular structure of polydatin/Malt‐β‐CD inclusion complex was postulated by a molecular docking method based on Autodock 4.2.3. It was clearly observed that the ring B of polydatin oriented toward the narrow rim of Malt‐β‐CD with ring A and glucosyl group practically exposed to the wide rim by hydrogen bonding, which was in a good agreement with the spectral data.     

Synthesis of β‐Galactooligosaccharides from Lactose Using Microbial β‐Galactosidases

Abstract: Galactooligosaccharides (GOSs) are nondigestible oligosaccharides and are comprised of 2 to 20 molecules of galactose and 1 molecule of glucose. They are recognized as important prebiotics for their stimulation of the proliferation of intestinal lactic acid bacteria and bifidobacteria. Therefore, they beneficially affect the host by selectively stimulating the growth and/or activity of a limited number of gastrointestinal microbes (probiotics) that confer health benefits. Prebiotics and probiotics have only recently been recognized as contributors to human health. A GOS can be produced by a series of enzymatic reactions catalyzed by β‐galactosidase, where the glycosyl group of one or more D‐galactosyl units is transferred onto the D‐galactose moiety of lactose, in a process known as transgalactosylation. Microbes can be used as a source for the β‐galactosidase enzyme or as agents to produce GOS molecules. Commercial β‐galactosidase enzymes also do have a great potential for their use in GOS synthesis. These transgalactosyl reactions, which could find useful application in the dairy as well as the larger food industry, have not been fully exploited. A better understanding of the enzyme reaction as well as improved analytical techniques for GOS measurements are important in achieving this worthwhile objective.     

The (1–3, 1–4)‐β‐Glucanases in Malting Barley: Enzyme Survival and Genetic and Environmental Effects

Eighteen barley genotypes used in Brazilian malting barley breeding programs were characterized in relation to (1–3, 1–4)‐β‐glucanase activity in green and kilned malt. They were tested to determine the loss of enzyme activity during kilning in the malting process and the environmental effects on enzyme activity were measured. The genotypes analyzed showed great variation regarding the enzyme activity in both kinds of malt, in a range from 531.94 to 934.31 U/kg in green malt, and from 187.02 to 518.40 U/kg in dry malt. The mean enzyme activity loss during kilning was close to 60%, very similar to the results obtained in other studies. The loss among genotypes varied from 8.04% to 71.54%. The enzyme activity varied significantly under the different environments tested, showing existence of environmental effects on the genotypes analyzed. Embrapa 127 was the genotype that exhibited the highest enzyme activity in finished malt although it had shown a low activity in green malt, reflecting a negligible loss of activity during kilning. The data indicate promising results to malting barley breeding due to the wide variability exhibited by genotypes as to enzyme activity and levels of isoenzyme with high thermostability.