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.     

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.     

Study on microwave‐accelerated casein protein grafted with glucose and β‐cyclodextrin to improve the gel properties

The effect of glycosylation treatment coupled with microwave heating (MH) on gel properties and structure change of casein were investigated. Conjugation was confirmed by electrophoresis. Protein disulphide bonds were broken by microwave irradiation to create an increase first and a decrease later in free sulfhydryl contents with time, thereby inducing subunit disaggregation. Also, the exposure of hydrophobic core residues was increased in MH‐treated casein, which brings about protein disaggregation and unfolding. It showed that graft reactions by MH had much faster than those by water bath heating (WH). The content of disulphide bonds is 7.2% and 6.0% in the casein–glucose and casein–β‐cyclodextrin, respectively, treated by MH which was reduced significantly than that of treated by WH. Moreover, MH can increase the hardness of the gel. Consequently, MH could improve the efficiency of the reaction and gel properties.     

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.     

Variety and germination time effect on total β‐glucan,water‐insoluble β‐glucan,water‐soluble β‐glucan components and β‐glucanase levels in improved sorghum varieties SK5912, KSV8 and ICSV400 before and after malting and their relationships to wort viscosity

The effects of variety and germination time on β‐glucan components – total β‐glucan (TBG), water insoluble β‐glucan (WIBG) and water soluble β‐glucan (WSBG) and β‐glucanase (BG) levels – before and after malting in improved sorghum varieties SK5912, KSV8 and ICSV400 and their relationships to wort specific viscosity (SV) were studied. This study was part of efforts to aid local malting and brewing industries in the application of sorghum varieties that are abundantly available to reduce costs. At the fifth day of germination, variety ICSV400 had the lowest TBG, WIBG and WSBG levels in its raw and malt samples. Variety SK5912 had the highest TBG, WIBG and WSBG levels in its raw samples, while variety KSV8 had the highest levels of TBG, WIBG and WSBG in its malt samples. Similarly, variety ICSV400 malts developed the highest BG levels, while the KSV8 malts gave the lowest level. The effect of variety, germination time and variety × germination time interaction was significant (p < 0.05) on the TBG, WIBG and BG levels and was not significant on the WSBG levels. Weak and significant correlation of TBG levels with SV (0.25, p < 0.05 for SK5912; 0.24, p < 0.05 for KSV8; and 0.31, p < 0.05 for ICSV400) was observed in all the samples, suggesting that the low β‐glucan levels may not be primarily and solely responsible for any viscosity impediments associated with sorghum worts during run‐off. With improvement in the effective utilization of sorghum, ICSV400 appeared the most suitable variety for malting and brewing in Nigeria.Copyright © 2016 The Institute of Brewing & Distilling     

Enzymatic Properties of β‐1,3‐Glucanase from Streptomyces sp Mo.

Streptomyces sp Mo endo‐β‐1,3‐glucanase was found to have hydrolyzing activity toward curdlan and released laminarioligosaccharides selectively. The molecular weight was estimated to be 36000 Da and its N‐terminal amino acid sequence was VTPPDISVTN. The optimal pH was 6 and the enzyme was found to be stable from pH 5 to 8. The optimal temperature was 60 °C and the activity was stable below 50 °C. The enzyme hydrolyzed selectively curdlan containing only β‐1,3 linkages. The enzyme had 89% relative activity toward Laminaria digitata laminarin, which contains a small amount of β‐1,6 linkages compared with curdlan, while Eisenia bicyclis laminarin with a higher amount of β‐1,6‐linkages, was not hydrolyzed. Mo enzyme adsorbed completely on curdlan powder. The enzymatic hydrolysis of curdlan powder resulted in the accumulation of laminaribiose (yield 81.7%). Trisaccharide was inevitably released from the hydrolysis of laminarioligosaccharides with 5 to 7 degrees of polymerization (DP). Although the enzyme cleaved off disaccharide (DP 2) from tetrasaccharide (DP 4), the reaction rate was lower than those of DP 5 to 7. The results indicated that the active site of Mo endo‐β‐1,3‐glucanase can efficiently recognize glucosyl residue chain of greater than DP 5 and hydrolyzes the β‐1,3 linkage between the 3rd and 4th glucosyl residue.     

In vivo effect of oat cereal β‐glucan on metabolic indexes and satiety‐related hormones in diet‐induced obesity C57‐Bl mice

This study explored the dose‐dependent effect of oat cereal β‐glucan on improving metabolic indexes of obesity mice. C57‐Bl mice were randomized to chow diet (N) group and high fat diet group and other three doses of oat β‐glucan groups (low β‐glucan, medium β‐glucan, and high β‐glucan). Energy intake, glucose, lipids, and appetite related hormones were tested. Dose‐dependent relation was observed on oat β‐glucan doses and body weight change, average energy intake, total cholesterol, HDL cholesterol, plasma neural peptide Y, arcuate neural peptide Y mRNA, and arcuate neural peptide Y receptor 2 mRNA level. Oat β‐glucan helped to increase plasma peptide Y‐Y and intestine peptide Y‐Y expression in obesity mice.     

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.