Optimisation of drying conditions for the extraction of β‐carotene,phenolic and ascorbic acid content from yellow‐fleshed sweet potato using response surface methodology

The objective of this study was to optimise drying conditions for the extractions of β‐carotene, phenolic and ascorbic content from yellow‐fleshed sweet potato using response surface methodology. A face‐centred cubic was used to investigate the effects of three independent variables namely drying temperature 55–65 °C, citric acid concentration 1–3%w/v and soaking time 1–3 min. The optimal conditions for parameters were 55–62 °C, citric acid concentration 1.08–2.19% and soaking time 1.53–2.00 min. Under the above mentioned conditions, the experimental β‐carotene content was 14.61 mg g^?1, total phenolic and ascorbic acid content were 4.0 and 17.53 mg g^?1, respectively, which were close to the predicted values. Therefore, the results showed that optimise conditions could be used to enhance the antioxidant activities of functional foods.     

Effect of gums on viability and β‐galactosidase activity of Lactobacillus spp. in milk drink during refrigerated storage

The viability and β‐galactosidase activity of four Lactobacillus strains in milk drink containing gums during 28 days of refrigerated storage at 4 °C were assessed. The population of Lactobacillus rhamnosus GGB101 and Lactobacillus rhamnosus GGB103 were maintained, whereas the population of Lactobacillus reuteri DSM20016 and Lactobacillus reuteri SD2112 significantly decreased. The recommended level of 6 log CFU g^?1 was exceeded for all tested trains throughout storage. The highest viable number of Lactobacillus rhamnosus GGB103 (8.76 ± 0.03 log CFU mL^?1) was obtained in the product containing carrageenan–maltodextrin. The addition of guar–locust bean–carrageenan led to 20‐fold increase in the level of β‐galactosidase activity for L. rhamnosus GGB101 (1208 ± 2.12 Miller units mL^?1) compared to the control (61 ± 2.83 Miller units mL^?1). Our results suggested that gums could be added to milk to improve viability and enhance β‐galactosidase activity of Lactobacillus.     

Production of soya milk containing low flatulence‐causing oligosaccharides in a packed bed reactor using immobilised α‐galactosidase

Peanut α‐galactosidase was immobilised in calcium alginate beads and used to hydrolyse the flatulence‐causing oligosaccharides, raffinose and stachyose, in soya milk in batch and in packed bed reactor with recycle. The immobilised enzyme exhibited a slightly lower activity than the free enzyme. The activity yield of immobilised α‐galactosidase was 75.1% and the immobilisation yield was 82.6%. Batch hydrolysis using immobilised enzyme at 55 °C resulted in 96% reduction in the oligosaccharides after 12 h. For the continuous process, a packed bed reactor with recycle was used. More than 98% of the oligosaccharides were hydrolysed after 6 h of reaction at 55 °C. The immobilised enzyme also proved to be stable up to three repeated hydrolysis reactions.     

Properties and applications of β‐glycosidase from Bacteroides thetaiotaomicron that specifically hydrolyses isoflavone glycosides

To modify the glycan part of glycosides, the gene encoding β‐glycosidase was cloned from Bacteroides thetaiotaomicron VPI‐5482. The cloned gene, bt_1780, was expressed in Escherichia coli MC1061 and the expressed enzyme was purified using Ni‐NTA affinity chromatography. The purified enzyme, BTBG, showed optimal activity at 50 °C and pH 5.5. Interestingly, this enzyme did not have any hydrolysing activity on ordinary β‐linkage–containing substrates such as xylobiose, lactose and cello‐oligosaccharide, but specifically hydrolysed isoflavone glycosides such as daidzin, genistin and glycitin. Compared to a commercial beta glucosidase, BTBG selectively hydrolysed isoflavone glycosides in soybean extract mixture solution. These results suggest that BTBG may be a specialized enzyme for the hydrolysis of glycosides and that the substrate specificity of BTBG is applicable for the bioconversion of isoflavone glycosides in the food industry.     

Optimisation of cross‐linking β‐cyclodextrin and its recycling efficiency for cholesterol removal in milk and cream

This study was carried out to investigate the optimum conditions of cross‐linking β‐cyclodextrin (β‐CD) and recycling for cholesterol removal in milk and cream. The cross‐linked β‐CD was prepared with a 15% adipic acid solution, and the water solubility of the β‐CD was measured for the optimum conditions based on mixing temperature, mixing time, cross‐linking temperature, cross‐linking reaction time and cooling time. In the results of this study, optimum conditions were 80 °C mixing temperature, 2 h mixing time, 60 °C cross‐linking temperature, 24 h cross‐linking reaction time and 48 h cooling time. After determining the optimum conditions, the recyclable yields of the cross‐linked β‐CD ranged from 90.01% to 55.17% in six recyclings and the percentage of cholesterol removal by 15% cross‐linked β‐CD was over 90% until eighth recycling. On the basis of the results, this study suggests that 15% adipic acid‐added cross‐linked β‐CD maximised recyclable yield and that cholesterol removal was improved during recycling.     

γ‐Glu‐Met synthesised using a bacterial glutaminase as a potential inhibitor of dipeptidyl peptidase IV

This study describes γ‐glutamyl dipeptides as competitive inhibitors of dipeptidyl peptidase‐IV (DPP‐IV), and the feasible synthesis of γ‐Glu‐Met through transpeptidation catalysed by a commercial glutaminase of Bacillus amyloliquefaciens. γ‐Glu‐Met, γ‐Glu‐Leu, γ‐Glu‐Phe, γ‐Glu‐Trp or γ‐Glu‐Tyr exhibited a competitive inhibitory effect on DPP‐IV. The yield of γ‐Glu‐Met was 26.16% under optimised conditions: 200 mm Gln, 20 mm Met, 0.1 U mL^?1 enzyme, pH 9.0, 37 °C and reaction time 3 h. For the first time, the side products containing characteristic sequences, that is poly‐γ‐glutamyl short chains with a terminal Met residue (γ‐Glu‐γ‐Glu‐Met and γ‐Glu‐γ‐Glu‐γ‐Glu‐Met) were identified. The superiority of the commercial glutaminase in the synthesis of DPP‐IV‐inhibitory peptides can enable the application of this novel process for manufacturing γ‐glutamyl‐peptides as potential functional ingredients in the type 2 diabetic diet.     

Limited hydrolysis of β‐casein by cell wall proteinase and its effect on hydrolysates's conformational and structural properties

Optimisation of enzymatic hydrolysis of β‐casein with cell envelope proteinase (CEP) from Lactobacillus acidophilus JQ‐1 to produce the angiotensin‐I‐converting enzyme (ACE) inhibitory peptides using response surface methodology (RSM). Under optimal conditions (enzyme‐to‐substrate ([E]/[S]) ratio (w/w) of 0.132 and pH of 8.00 at 38.8 °C), the ACE inhibitory activity of hydrolysates was 72.06% and the total peptides was 11.75 mg mL^?1. Scanning electron microscopy (SEM) micrographs indicated that the tightness of the β‐casein surface structure was gradually weakened and small holes appeared after enzymatic treatment, while Fourier transform infrared spectroscopy (FTIR) spectra indicated remarkable changes in the chemical composition and macromolecular conformation of β‐casein after enzymatic hydrolysis. Differential scanning calorimetry (DSC) analysis indicated that the corresponding hydrolysates had higher thermal stability. The enzymatic hydrolysis also led to an increase in the free sulfhydryl content of β‐casein hydrolysates compared with raw β‐casein, which led to the increase in the antioxidant activity of β‐casein hydrolysates.     

Antipathogenic activity and preservative effect of levan (β‐2,6‐fructan), a multifunctional polysaccharide

The objective of this study was to investigate the antibacterial activity of levan compounds, including high‐molecular‐weight levan, low‐molecular‐weight levan and difructose dianhydride IV (DFA IV). The levans exhibited broad antibacterial spectra against foodborne pathogenic bacteria, in a concentration‐dependent manner. From comparison with simple saccharides, often regarded as by‐products of levan production, it turned out that the antibacterial activity of levans was primarily caused by themselves. The strongest effect was observed with low‐molecular‐weight levan as compared to the others, and oligosaccharides as well. The low‐molecular‐weight levan was therefore applied to bread making. The bread samples inoculated with pathogenic bacteria were divided into two groups: bread with sugar alone (control) and bread with both sugar and levan (treatment). It was found from the in situ test that the viability of pathogenic bacteria in bread was reduced by the addition of low‐molecular‐weight levan. Therefore, levan compounds have potential as alternative sweeteners for reduction in pathogenic contamination.     

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.     

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.     

Bioactive action of β‐glucosidase enzyme of Bifidobacterium longum upon isoflavone glucosides present in soymilk

Bioconversion of isoflavone glucosides and antioxidant activity by probiotic strain (Bifidobacterium longum) during soymilk fermentation was investigated, as well as partial characterisation of the produced enzyme β‐glucosidase. The enzyme has higher affinity for genistin than for other substrates assayed. Maximum activity occurred at 42 °C and at pH 6.0; keeping 70–80% of activity for 60 days stored at low temperatures. Bifidobacterium longum grew well in soymilk (8.26 log CFU mL^?1 and pH of 3.9 at 24 h) and were produced in good quantities of organic acids. High hydrolysis degree of isoflavone glucosides (81.2%) was observed at 24 h. Enhancements in bioactivity were assessed in fermented soymilk by monitoring the radical‐scavenging activity, antioxidant activity and DNA protective action. The use of probiotic Bifidobacterium strain as β‐glucosidase producer increased bioactive isoflavone content and demonstrated that this enzyme plays a key role in the bioavailability of soymilk isoflavones, reducing the bioconversion time compared to other studies.     

Effects of malting on β‐glucanase and phytase activity in barley grain

The effects of malting on β‐glucan and phytate were investigated in one naked and one covered barley by a full factorial experiment with three factors (steeping temperature, moisture content and germination temperature) each with two levels. Analysis of total content of β‐glucan in the malted samples showed small changes after steeping at the high temperature (48 °C), while steeping at the lower temperature (15 °C) gave a significantly lower content. This trend was even stronger for β‐glucan unextractable at 38 °C. Analysis of the activity of β‐glucanase for the samples steeped at 15 °C showed a strong increase over the time of germination, while those steeped at 48 °C had a much slower development. The other two factors influenced the outcome to a small extent, mainly because the steeping temperature was the most important factor overall where any changes in β‐glucan and β‐glucanase were observed. When β‐glucan was extracted at 100 °C, a larger yield was obtained, and this was influenced by the steeping temperature in a much stronger way than for β‐glucan extracted at 38 °C. Determination of average molecular weight for β‐glucan extracted at 100 °C gave a lower value for samples steeped at 15 than at 48 °C. The design did not have any large effects on phytate degradation and phytase activity. However, it indicated that selective control of the enzymes might be possible, since phytase activity was barely affected by the parameters studied, while β‐glucanase was heavily affected. © 2002 Society of Chemical Industry     

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.     

Optimisation of Novozym‐435‐catalysed esterification of fatty acid mixture for the preparation of medium‐ and long‐chain triglycerides (MLCT) in solvent‐free medium

Novozym‐435‐catalysed esterification of caprylic acid, capric acid and oleic acid with glycerol for the synthesis of medium‐ and long‐chain triglycerides (MLCT) in vacuum and solvent‐free system was investigated in this study. Response surface methodology with a three‐level, four‐factorial design was applied to optimise the enzymatic esterification for the synthesis of MLCT. The optimum conditions were as follows: reaction temperature 90 °C, 4.80 wt% enzyme load (relative to the weight of total substrates) and substrate molar ratio (fatty acids/glycerol) of 3:1 and 12.37 h. Under above‐mentioned conditions, Triglycerides (TG) yield, MLCT and the residual free fatty acids (FFA) content in the product were 93.54%, 72.19% and 4.21%, respectively. The content of caprylic acid, capric acid and long‐chain fatty acids of TG was 24%, 10% and 66%, respectively. Novozym 435 in the study showed no selectivity for the different fatty acids and also could be used 14 times without obvious loss of enzyme activity.     

Enhanced bioaccessibility of β‐carotene from yellow‐orange vegetables and green leafy vegetables by domestic heat processing

Effect of heat treatment involved in domestic cooking on the bioaccessibility of β‐carotene from yellow‐orange as well as green leafy vegetables was evaluated. Heat treatment of these vegetables by pressure‐cooking, stir‐frying and open‐pan boiling had a beneficial influence on the bioaccessibility of β‐carotene. The extent of increase in the per cent bioaccessibility of β‐carotene as a result of pressure‐cooking was 21–84%. Stir‐frying in presence of a small quantity of oil brought about an enormous increase in the bioaccessibility of β‐carotene from these vegetables, the extent of increase being 67–191%. Open‐pan boiling of vegetables increased the bioaccessibility of β‐carotene in the range 23–36%. Thus, among the three domestic heat processing methods, stir‐frying results in maximum bioaccessibility of this provitamin. The use of suitably heat‐processed vegetable sources of β‐carotene could form a dietary strategy to derive this micronutrient maximally by the population dependent on plant foods.     

Isolation of a gene encoding a G protein α subunit involved in the regulation of cAMP levels in the yeast Kluyveromyces lactis

Using chromosomal DNA from Kluyveromyces lactis as template and oligodeoxynucleotides designed from conserved regions of various G protein alpha subunits we were able to amplify by the polymerase chain reaction two products of approximately 0·5 kb (P-1) and 0·8 kb (P-2). Sequencing showed that these two fragments share high homology with genes coding for the Gα subunits from different sources. Using the P-1 fragment as a probe we screened a genomic library from K. lactis and we cloned a gene (KlGPA2) whose deduced amino acid sequence showed, depending on the exact alignment, 62% similarity and 38% identity with Gpa1p and 76% similarity and 63% identity with Gpa2p, the G protein α subunits from Saccharomyces cerevisiae. KlGPA2 is a single-copy gene and its disruption rendered viable cells with significantly reduced cAMP level, indicating that this Gα subunit may be involved in regulating the adenylyl cyclase activity, rather than participating in the mating pheromone response pathway. KlGpa2p shares some structural similarities with members of the mammalian Gαs family (stimulatory of adenylyl cyclase) including the absence in its N-terminus of a myristoyl-modification sequence. The sequence reported in this paper has been deposited in the GenBank data base (Accession No. L45105).     

Mechanisms of the Release of Bound β‐Amylase

The aim was to identify the mechanism(s) responsible for the release of bound β‐amylase in soluble forms in vitro and during the germination of barley. Preparations of bound β‐amylase, from barley, were treated with different agents including papain, thiols, starchy endosperm extract and reagents with amphipathic characteristics. The time courses of the release of the bound enzyme were compared using the different releasing agents. All the reagents tested caused some release of bound β‐amylase. Probably a very complex combination of mechanisms is involved in the release of bound β‐amylase as barley germinates. Initial release may be by cleavage of disulphide bonds which bind β‐amylase to insoluble protein. Material having amphipathic characteristics may break hydrophobic associations between β‐amylase and insoluble protein(s). The larger molecular weight isoforms are proteolysed to form the lower molecular weight materials present in malt. Limited proteolysis may also occur before the release of bound enzyme. Whether or not proteolysis is directly responsible for the release of bound enzyme remains uncertain.     

Mango wine aroma enhancement by pulp contact and β‐glucosidase

This study determined the influence of pulp maceration and β‐glucosidase on mango wine physico‐chemical properties and volatile profiles. The distinction in pH, sugars and organic acids among different treatments was not statistically significant. All wine samples reached around 8% (v/v) ethanol from about 16% (w/v) of sugars. The wine with pulp contact contained about ten times higher α‐terpinolene and up to three times higher acetate esters than the wine without pulp contact, but mitigated the production of medium‐chain fatty acids and relative ethyl esters by up to six times. β‐glucosidase enhanced terpenols by up to ten times and acetate esters by up to three times. Furthermore, enzyme treatment mitigated, by up to five times, the formation of medium‐chain fatty acids and ethyl esters to moderate levels. Sensory evaluation showed pulp contact, and β‐glucosidase not only improved the intensity and complexity of wine aroma but balanced odour attributes.     

Microencapsulation of β‐carotene using native pinhão starch,modified pinhão starch and gelatin by freeze‐drying

Beta‐carotene was microencapsulated by freeze‐drying using native pinhão starch, hydrolysed pinhão starch 6 dextrose equivalent (DE), hydrolysed pinhão starch 12 DE and the mixture of these materials with gelatin as coating material. The purpose of this research was to produce and characterize these microcapsules. The capsules’ efficiency, surface content, moisture, morphology, solubility, particle size and glass transition temperature were analysed. The hydrolysed pinhão starch 12 DE showed the highest total β‐carotene content and the lowest surface β‐carotene content, unlike the native starch. Using scanning electron microscopy, it was observed that all microcapsules presented undefined shapes. The samples with gelatin had wider particle size distribution, higher diameters, lower solubility and higher glass transition temperature when compared with other the samples. Results obtained suggest that the modified pinhão starch can be considered as potential wall material for encapsulation of β‐carotene.     

Alterations of the Profiles of Iso‐α‐Acids During Beer Ageing,Marked Instability of Trans‐Iso‐α‐Acids and Implications for Beer Bitterness Consistency in Relation to Tetrahydroiso‐α‐Acids

Age‐induced decomposition of iso‐α‐acids, the main bittering principles of beer, determines the consistency of the beer bitter taste. In this study, the profiles of iso‐α‐acids in selected high‐quality top‐fermented and lager beers were monitored by quantitative high‐performance liquid chromatography at various time intervals during ageing. The degradation of the iso‐α‐acids as a function of time is represented by the ratio, in percentage, of the sum of the concentrations of trans‐isocohumulone and trans‐isohumulone to the sum of the concentrations of cis‐isocohumulone and cis‐isohumulone. This parameter is relevant with respect to the evaluation of bitterness deterioration in aged beers. Trans‐iso‐α‐acids having a shelf half‐life of less than one year proved to be significantly less stable than cis‐iso‐α‐acids, but it appears feasible to counteract degradation if a suitable beer matrix is available. The fate of the trans‐iso‐α‐acids in particular adversely affects beer bitterness consistency. In addition to using hop products containing low amounts of trans‐iso‐α‐acids, brewers may profit of the remarkable stability of tetrahydroiso‐α‐acids, even on prolonged storage, for the production of consistently bitter beers.