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.     

Interaction of β‐casein with (−)‐epigallocatechin‐3‐gallate assayed by fluorescence quenching: effect of thermal processing temperature

The interactions between the flavan‐3‐ol (?)‐epigallocatechin‐3‐gallate (EGCG) and bovine β‐casein in phosphate‐buffered saline (PBS) of pH 6.5 subjected to thermal processing at various temperatures (25–100 °C) were investigated using fluorescence quenching. The results indicated that different temperatures had different effects on the structural changes and EGCG‐binding ability of β‐casein. At temperatures below 60 °C, the β‐casein–EGCG interaction changed little (P > 0.05) with increasing temperature. At temperatures above 80 °C, native assemblies of β‐casein in solution dissociated into individual β‐casein molecules and unfolded, as demonstrated by a red shift of the maximum fluorescence emission wavelength (λ_max) of up to 8.8 nm. The highest quenching constant (K_q) and the number of binding sites (n) were 0.92 (±0.01) × 10¹³ m ^?1 s^?1 and 0.73 (±0.02) (100 °C), respectively. These results provide insight into the potential of interactions between β‐casein–EGCG that may modulate bioactivity or bioavailability to be altered during thermal process.     

Porosity and Water Activity Effects on Stability of Crystalline β‐Carotene in Freeze‐Dried Solids

Abstract: Stability of entrapped crystalline β‐carotene as affected by water activity, solids microstructure, and composition of freeze‐dried systems was investigated. Aliquots (1000 mm³, 20% w/w solids) of solutions of maltodextrins of various dextrose equivalents (M040: DE6, M100: DE11, and M250: DE25.5), M100‐sugars (1:1 glucose, fructose and sucrose), and agar for gelation with dispersed β‐carotene were frozen at ?20, ?40, or ?80 °C and freeze‐dried. Glass transition and α‐relaxation temperatures were determined with differential scanning calorimetry and dynamic mechanical analysis, respectively. β‐Carotene contents were monitored spectrophotometrically. In the glassy solids, pore microstructure had a major effect on β‐carotene stability. Small pores with thin walls and large surface area allowed β‐carotene exposure to oxygen which led to a higher loss, whereas structural collapse enhanced stability of β‐carotene by decreasing exposure to oxygen. As water plasticized matrices, an increase in molecular mobility in the matrix enhanced β‐carotene degradation. Stability of dispersed β‐carotene was highest at around 0.2 a_w, but decreasing structural relaxation times above the glass transition correlated well with the rate of β‐carotene degradation at higher a_w. Microstructure, a_w, and component mobility are important factors in the control of stability of β‐carotene in freeze‐dried solids Practical Application: β‐Carotene expresses various nutritional benefits; however, it is sensitive to oxygen and the degradation contributes to loss of nutritional values as well as product color. To increase stability of β‐carotene in freeze‐dried foods, the amount of oxygen penetration need to be limited. The modification of freeze‐dried food structures, for example, porosity and structural collapse, components, and humidity effectively enhance the stability of dispersed β‐carotene in freeze‐dried solids.     

Reduction efficiency of the neurotoxin β‐ODAP in low‐toxin varieties of Lathyrus sativus seeds by solid state fermentation with Aspergillus oryzae and Rhizopus microsporus var chinensis

Solid state fermentation of several low‐toxin varieties of grass pea (Lathyrus sativus L) seeds with Aspergillus oryzae and Rhizopus microsporus var chinensis removed the neurotoxin β‐ODAP (3‐N‐oxalyl‐L ‐2,3‐diaminopropanoic acid) to a considerable degree from the seed meal. The detoxification efficiency was statistically significant and ranged from 52.4% (p < 0.01) to 82.2% (p < 0.001), which was lower than for a high‐toxin variety processed by the same fermentation procedure (94.8%, p < 0.001). While the content of β‐ODAP decreased, those of other free protein amino acids, especially glutamic acid, histidine, threonine, tyrosine, valine and lysine, increased dramatically in the fermented seeds. Efforts to remove the neurotoxin from Lathyrus sativus either by breeding or by food processing to obtain toxin‐free grass pea seeds have been made worldwide for several decades. The efficiencies of various reported processing methods are summarised and compared. © 2000 Society of Chemical Industry     

Electrospray MS‐based characterization of β‐carbolines – mutagenic constituents of thermally processed meat

The β‐carbolines 1‐methyl‐9H‐pyrido [3,4‐b]indole and 9H‐pyrido[3,4b]indole have been implicated as having causative roles in a number of human diseases, such as Parkinson's disease and cancer. As they can be formed during the heating of protein‐rich food, a number of analytical methodologies have been proposed for their detection and quantification in foodstuff. For this purpose, LC‐MS and LC‐MS/MS have emerged as the most specific analytical methods, and the quantification is based on the occurrence of unusual ions, such as [M+H‐(H^?)]⁺ and [M+H‐2H]⁺. In this study, we have investigated the formation of these ions by accurate‐mass electrospray MS/MS and demonstrated that these ions are formed from gas‐phase ion‐molecule reactions between water vapor present in the collision cell and the protonated molecule of 1‐methyl‐9H‐pyrido [3,4‐b]indole and 9H‐pyrido[3,4b]indole. Although this reaction has been previously described for heterocyclic amine ions, it has been overlooked in the most of recent LC‐MS and LC‐MS/MS studies, and no complete data of the fragmentation are reported. Our results demonstrate that additional attention should be given with respect to eliminating water vapor residues in the mass spectrometer when analysis of β‐carbolines is performed, as this residue may affect the reliability in the results of quantification.     

Prevalence of β‐Lactamase Producing Escherichia coli from Retail Meat in Turkey

Extended spectrum β‐lactamase (ESBL) and plasmid‐mediated AmpC β‐lactamase (pAmpC) producing Escherichia coli have been shown to be present in humans and animals representing a significant problem worldwide. This study aimed to search the presence of ESBL and/or AmpC‐producing E. coli in retail meats (chicken and beef) in Turkey. A total of 88 β‐lactamase‐producing E. coli were isolated from chicken (n = 81/100) and beef meat (n = 7/100) samples and their susceptibility to several antimicrobials were tested using disc diffusion method. E. coli isolates were further characterized for their phylogenetic groups. β‐Lactamase encoding (bla_TEM, bla_SHV, bla_OXA, bla_CTX‐M, and bla_AmpC) and quinolone resistance genes (qnrA, qnrB, qnrS, qepA, and acc(6′)‐Ib‐cr) were also secreened by polymerase chain reaction (PCR). However, in regard to β‐lactamase genes, 84 of 88 isolates were positive for bla_CTX‐M‐1 (n = 39), bla_CTX‐M‐3 (n = 5), bla_CTX‐M‐15 (n = 4), bla_TEM‐1b (n = 2), bla_SHV‐12 (n = 1), bla_CTX‐M‐1/bla_TEM‐1b (n = 10), bla_CTX‐M‐1/bla_TEM‐1b/bla_SHV‐5 (n = 1), bla_CTX‐M‐1/bla_CMY‐2 (n = 1) and bla_TEM‐1b/bla_CMY‐2 (n = 6), bla_CTX‐M‐15/bla_SHV‐12 (n = 1), bla_CTX‐M‐15/bla_TEM‐1b (n = 1), bla_TEM‐1b/bla_SHV‐12 (n = 1)_, and bla_CMY‐2 (n = 12) genes. Resistance to cefuroxime (75.6% and 85.7%), nalidixic acid (89% and 85.7%), tetracycline (91.4% and 100%), streptomycin (40.2% and 100%), and trimethoprim‐sulfamethoxazole (36.6% and 85.7%) was observed among strains isolated from chicken and beef, respectively. However, all isolates were found to be susceptible to amikacin, imipenem, and cefepime. Resistance to ampicillin and cefoxitin was significantly linked to bla_CMY‐2 gene, while there was a significant correlation between CTX‐M type ESBL and antimicrobial resistance to cefuroxime and streptomycin (P < 0.05). The results of this study suggest that raw chicken retail meats are highly contaminated with ESBL‐producing E. coli implementing a great risk to human health in Turkey.     

Multiple forms of β‐galactosidase from mango (Mangifera indica L Alphonso) fruit pulp

Mango (Mangifera indica L cv Alphonso) was found to contain three isoforms (I, II and III) of β‐galactosidase which, upon purification on Sephadex G‐200, had relative abundances of 44, 38 and 18%, respectively. The total specific activity increased from 20 to 727 µmol l^?1 upon purification, representing a ～36‐fold increase with a recovery of 0.28 U U^?1. The optimal pH for activity and stability were in the ranges 3.6–4.3 and 4–6.2, respectively. The optimal temperature for β‐galactosidase activity was between 42 and 47 °C with T_m in the range 45–51 °C. The K_m for pNP‐β‐galactopyranoside was 0.98, 1.11 and 0.95 mM , and V_max was 0.56, 0.53 and 0.35 µmol pNP min^?1, respectively for isoforms I, II and III. Hg²⁺ caused strong inhibition, whereas galacturonic acid, galactose, xylose, fucose and mannose slightly inhibited the activity of β‐galactosidase isoforms. The apparent molecular weights by GPC were 78, 58 and 91 kDa for isoforms I, II and III, respectively. The ability of these isoforms to degrade the endogenous substrate (arabinogalactan) possibly suggests a role in pectin dissolution during tissue softening/fruit ripening. Copyright © 2004 Society of Chemical Industry     

Partial characterization of β‐ d‐xylosidase from wheat malts

Arabinoxylans (AXs) from wheat malts potentially affect beer quality and production. β‐ d ‐Xylosidase is a key enzyme that degrades the main chains of AXs to produce xylose. This study performed a partial characterization of β‐ d ‐xylosidase from wheat malts. The optimal temperature was 70 °C and the enzyme exhibited excellent thermostability, that is, residual activities were 92.6% at 60 °C for 1 h. The enzyme was stable over a pH range of 3.0–6.0 and showed optimum activity at pH 3.5 and 4.5. Kinetic parameters K_m and V_max of wheat malt β‐ d ‐xylosidase against p‐nitrophenyl‐xyloside were 1.74 mmol L⁻¹ and 0.76 m m min⁻¹, respectively. The enzyme activity was severely inhibited by Cu²⁺, moderately inhibited by Mn²⁺, Mg²⁺, Al³⁺, Ca²⁺, Ba²⁺ and Na⁺ and mildly inhibited by Fe³⁺ and Fe²⁺. The partial enzymatic characterization achieved in this study can be used as a theoretical basis for purifying β‐ d ‐xylosidase from wheat malts. Copyright © 2015 The Institute of Brewing & Distilling     

Characterization of an extracellular β‐d‐fructofuranosidase produced by Aspergillus niveus during solid‐state fermentation (SSF) of cassava husk

β‐d ‐Fructofuranosidases are biotechnologically important enzymes produced by various organisms. Here, Aspergillus niveus produced an extracellular β‐d ‐fructofuranosidase during SSF of cassava husk. This enzyme was purified 8.5‐fold (recovery of 5.2%). A 37‐kDa protein band was observed after 8% SDS‐PAGE. Native molecular mass is 91.2 kDa. Optimal temperature and pH of activity were 55°C and 4.5, respectively. The enzyme was stable at 50°C for 1 hr, and 80% of its activity was retained after 1 hr at pH 8.0. The enzymatic activity was improved by Mn²⁺, was resistant to most solvents, and was inhibited by Triton X‐100 and Tween 20. K_m and V_max with sucrose were 22.98 mM and 120.48 U/mg of protein, respectively. With Mn²⁺, these values were 16.31 mM and 0.30 U/mg of protein. The enzyme did not hydrolyze inulin and for this reason can be considered a true invertase. Thus, A. niveus β‐d ‐fructofuranosidase holds promise for invert sugar production.

Practical applications

β‐d ‐Fructofuranosidase is an enzyme that can be applied to different industrial sectors, especially food and beverage industries. It is responsible for the hydrolysis of sucrose and yields an equimolar mixture of D‐glucose and D‐fructose, named as inverted sugar syrup, with broad applications in the confectionery industry. The Aspergillus niveus enzyme hydrolyzed only sucrose here and can be considered a true invertase, showing its potential for application to invert sugar production. Besides, the use of cassava husk for enzyme production means an interesting utilization route of this agroindustrial residue. Thus, characterization of this enzyme is an important step for identification of its potential for practical applications.     

Vitamin E levels,thiobarbituric acid test and sensory evaluation of breast muscles from broilers fed α‐tocopheryl acetate‐ and β‐carotene‐supplemented diets

The objective of this study was to investigate the effect of dietary α‐tocopheryl acetate and β‐carotene supplementation on lipid oxidation of breast meat from broilers fed lard as the fat source. Supplementation of broilers with 100 mg kg^?1 α‐tocopheryl acetate increased the vitamin E levels in raw breast samples significantly (p < 0.05), whereas the presence of 1.5 mg kg^?1 dietary β‐carotene tended to decrease vitamin E deposition. The presence of vitamin E delayed lipid oxidation significantly, but thiobarbituric acid values of samples from broilers fed the β‐carotene‐supplemented diet did not differ from those of control samples. Vitamin E reduced sensory meat rancidity, whilst vitamin E, β‐carotene and their combination modified meat texture. The results show the effectiveness of dietary α‐tocopheryl acetate supplementation in protecting broiler meat against lipid oxidation. Copyright © 2004 Society of Chemical Industry     

Phytosterols in banana (Musa spp.) flower inhibit α‐glucosidase and α‐amylase hydrolysations and glycation reaction

Three phytosterols were isolated from Musa spp. flowers for evaluating their capabilities in inhibiting glucosidase and amylase activities and glycation of protein and sugar. The three phytosterols were identified as β‐sitosterol (PS1), 31‐norcyclolaudenone (PS2) and (24R)‐4α, 14α, 4‐trimethyl‐5α‐cholesta‐8, 25(27)‐dien‐3β‐ol (PS3). IC₅₀ values (the concentration of inhibiting 50% of enzyme activity) of PS1, PS2 and PS3 against α‐glucosidase were 283.67, 11.33 and 43.10 μg mL^?1, respectively. For inhibition of α‐amylase, the IC₅₀ values of PS1, PS2 and PS3 were 52.55, 76.25 and 532.02 μg mL^?1, respectively. PS1 was an uncompetitive inhibitor against α‐amylase with K_m at 5.51 μg mL^?1, while PS2 and PS3 exhibited a mixed‐type inhibition with K_m at 52.36 and 2.49 μg mL^?1, respectively. PS1 and PS2 also significantly inhibited the formation of advanced glycation end products (AGEs) in a BSA–fructose model. The results suggest that banana flower could possess the capability in prevention of the diseases associated with abnormal blood sugar and AGEs levels, such as diabetes.     

Detection of Extended‐Spectrum β‐Lactamase and Plasmid‐Mediated Quinolone Resistance Determinants in Escherichia coli Isolates from Retail Meat in China

The aim of this study was to investigate the presence of extended‐spectrum β‐lactamase (ESBL) and plasmid‐mediated quinolone resistance (PMQR) genes in Escherichia coli isolated from retail meat samples in Henan Province, China. E. coli isolates were detected in 179 of 645 (27.7%) retail meat samples. Resistance of these isolates to antimicrobials was commonly observed, with 78.2% of isolates resistant to streptomycin, 74.3% resistant to tetracycline and 54.2% resistant to trimethoprim/sulfamethoxazole. Of the 179 isolates, 30 (16.7%) expressed ESBL, with bla_TEM‐1 (n = 17) and bla_CTX‐M‐14 (n = 9) most commonly mediating the ESBL phenotype. PMQR genes were present in 14 isolates (7.8%), with qnr and aac(6′)‐Ib‐cr detected alone or in combination in nine (5.0%) and seven isolates (3.9%), respectively. The qnr genes detected included qnrS1 (n = 5), qnrA1 (n = 3), and qnrB4 (n = 1). The qepA gene was absent among these isolates. CTX‐M‐14 was the most prevalent ESBL type among the PMQR‐positive isolates. The qnr and aac(6′)‐Ib‐cr genes were found to co‐reside and be co‐transferred with bla_CTX‐M‐14 or bla_TEM‐1 in five isolates. Our data suggest that retail meat may act as a reservoir for multi‐resistant E. coli and may facilitate the dissemination of resistance genes.     

Chaperone‐like activity of β‐casein and its effect on residual in vitro activity of horseradish peroxidase

In this study, the residual activity horseradish peroxidase was used as a novel marker of chaperone‐like activity of β‐casein under elevated temperature. It was shown that β‐casein does affect residual activity of horseradish peroxidase (HRP) depending on the concentration and molar ratio between proteins. Incubating HRP (0.1 mg mL^?1) for 10 min at 72 °C resulted in residual activity of 59 ± 5%, while addition of 1 mg mL^?1 β‐casein resulted in increase in residual activity up to 85 ± 1%. Increased residual activity is not merely attributed to an effect of higher total protein concentration, as similar experiment with bovine serum albumin resulted in residual activity of horseradish peroxidase that was significantly lower than without any addition. The effect of β‐casein on HRP disappears when pH is below the isoelectric point of β‐casein. It was also proven by light scattering studies that β‐casein interacts with horseradish peroxidase when the temperature was increased from 25 to 70 °C whereas interactions seem to cease when temperature was lowered back to 25 °C. This study highlights how specific proteins can influence enzyme activity, which is of potential importance for various industries such as enzyme manufacturers and food industry.     

Effect of Different Indigenous Yeast β‐Glucosidases on the Liberation of Bound Aroma Compounds

This study investigated β‐D‐glucosidase activity in the indigenous wine yeast present on grape berries in Yantai in Shandong Province, China. Yeast population profiles from the Yantai production area in China were examined. Among the ten species identified by RFLP analysis of the 5.8S rRNA gene, four exhibited higher β‐glucosidase activity, namely, Hanseniaspora uvarum, Trichosporon asahii, Pichia fermentans and Saccharomyces cerevisiae. The β‐glucosidases from the four representative strains were chosen to hydrolyse the glycosidic precursors of Cabernet Sauvignon. After enzymatic hydrolysis, 31 compounds were identified and quantified, including terpenes, C₁₃‐noriso‐prenoid, C₆ compounds, alcohols, aldehydes and volatile phenols. Results showed that different strains exhibited different hydrolytic abilities on the bound aroma precursors. The main variables included C₆ compounds, terpenes and alcohols. The concentration of the 14 compounds showed significant differences between enzymatic treatments, with 11 treated using the β‐glucosidase of the F6 strain (T. asahii). These findings may have some applicative value for utilizing the strains or their β‐glucosidases, which are able to complement and optimize wine quality.     

Preparation and characteristics of squid pen β‐chitin prepared under optimal deproteinisation and demineralisation condition

Squid (Todarodes pacifica) pen was an excellent source of β‐chitin with 25.5% yield. The optimal condition to prepare squid pen β‐chitin was established: deproteinisation with 3% NaOH for 30 min at 15 psi/121 °C and a solid/solvent ratio of 1:10 (w/v) and a subsequent demineralisation with 1 N HCl for 30 min at room temperature and a solid/solvent ratio of 1:10 (w/v). Squid pen β‐chitin contained 6.29% nitrogen, 0.25% ash, and negligible fat with degree of acetylation of 94.02%, residual amino acid of 0.499 g/100 g and bulk density of 0.28 g mL^?1. Depending on its particle size, squid pen β‐chitin visually looked white (L* = 82.82, a* = ?0.67, b* = 6.31; particle size of 0.15–0.18 mm) or light grey (L* = 62.88, a* = 0.33, b* = 10.66; particle size of 0.425–0.841 mm). Water, fat and dye‐binding capacity of squid pen β‐chitin was 694.67%, 194.03% and 79.81%, respectively.     

Preparation and Use of Poly(hydroxyethyl methacrylate) Cryogels Containing L‐Histidine for β‐Casein Adsorption

The objective of this study was to determine β‐casein adsorption by using supermacroporous poly(2‐hydroxyethyl methacrylate‐N‐methacryloyl‐(l) ‐histidine methyl ester) [p(HEMA‐MAH)] cryogel. β‐Casein adsorption properties of p(HEMA‐MAH) cryogel were studied for the application of β‐casein purification. The cryogel was produced by free radical polymerization initiated by N,N,N’,N’‐tetramethylene diamine and ammonium persulfate pairs in an ice bath. P(HEMA‐MAH) cryogel was characterized by swelling tests, Fourier transform infrared spectroscopy, and scanning electron microscopy. The effects of the flow rate, pH, temperature, initial β‐casein concentration, and ionic strength on the adsorption efficiency of cryogel were studied. The equilibrium swelling degree of the p(HEMA‐MAH) cryogel was 6.73 g H₂O/g cryogel. β‐Casein adsorption capacity of p(HEMA‐MAH) cryogel from aqueous solution was estimated as 31.17 mg/g cryogel. It was also observed that β‐casein could be repeatedly adsorbed and desorbed with p(HEMA‐MAH) cryogel without significant loss in the adsorption capacity.     

Structural characterisation of β‐cyclodextrin crosslinked by adipic acid

This study was conducted to investigate the structural characterisation of β‐cyclodextrin (β‐CD) crosslinked by adipic acid. β‐CD was treated with different concentrations (0%, 5%, 10% and 15%, w/v) of adipic acid. Different instruments, such as scanning electron microsope (SEM), Fourier‐transform infrared (FT‐IR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) spectra were used to find out chemical structure in the crosslinked β‐CD. SEM analysis suggested that crosslinking β‐CD with 15% adipic acid changed the original morphology and considerably increased the particle size of the raw material. FT‐IR spectroscopy data showed that an intensive absorption band at 1706 cm^?1 was present in the β‐CD samples treated with 10% and 15% adipic acid, indicating a crosslinking between hydroxyl groups of β‐CD and carboxyl groups of adipic acid. NMR spectra revealed that the ester linkages between hydroxyl groups of β‐CD and carboxyl groups of adipic acid were formed after crosslinking of β‐CD with adipic acid.     

A predictive model of the effects of genotypic,pre‐ and postharvest stages on barley β‐glucan levels

BACKGROUND: β‐Glucan is a bioactive component of cereal grains that has many potential uses and health‐promoting benefits. Recent research has focused on improving the nutritional value of food by increasing human exposure to β‐glucan. This study looks at the development of a farm‐level baseline model (including scenario analysis) to evaluate the impact of pre‐ and postharvest stages (including genotypic factors, environmental conditions, agronomic factors and storage) on β‐glucan levels in barley. Monte Carlo simulation techniques were employed to model various stages in pre‐ and postharvest processes and to simulate the factors influencing the level of β‐glucan content in both hulled barley (H_B) and hull‐less barley (H_LB) genotypes. RESULTS: The baseline model found that the mean simulated level of β‐glucan was 40.99 and 56.77 g kg^?1 for H_B and H_LB genotypes respectively. A sensitivity analysis highlighted that genotype was the most important parameter in determining the final β‐glucan content (correlation coefficients of 0.66 and 0.78 for H_B and H_LB respectively), more so than any of the agronomic factors analysed. The scenario analysis highlighted the importance of harvest date (scenario 2) and storage conditions (scenario 3), with a potential 32.6 and 32.7% decrease in β‐glucan (compared with the baseline model) if harvesting is carried out early during physiological maturity (i.e. at growth stage 92) and a potential 20.1 and 19.5% increase in β‐glucan for H_B and H_LB respectively if storage time is minimised. CONCLUSION: This study predicted the influence of genotypic, pre‐ and postharvest operations on β‐glucan content and thus allows strategies to be identified to influence β‐glucan content in barley products. Copyright © 2008 Society of Chemical Industry     

Characteristics of immobilised β‐glucosidase and its effect on bound volatile compounds in orange juice

In this study, bound volatile compounds were isolated and extracted with Amberlite XAD‐2 resin and then hydrolysed by free or immobilised β‐glucosidase. The released bound volatiles were analysed by GC‐MS. In addition, the optimisation of immobilisation method on sodium alginate and the characteristics of immobilised β‐glucosidase were studied. The results showed that crosslinking‐entrapment was the best method. The optimal conditions of this method were as follows: sodium alginate concentration 3.5%, glutaraldehyde concentration 1%, crosslinking time 3 h, immobilisation time 2 h and CaCl₂ concentration 3%. The optimum temperature for β‐glucosidase (65 °C) was decreased by 10 °C after immobilisation, while the optimum pH values for free and immobilised β‐glucosidase were both at pH 5.0. The K_m values of free and immobilised β‐glucosidase were 14.89 and 0.59 m , respectively. In total, thirteen and six bound volatile compounds were detected in orange juice hydrolysed by free and immobilised β‐glucosidase, including benzenic compounds, terpenic compounds, hydroxy esters, C₁₃‐norisoprenoids and alcohols.