Rheological behavior and stability of d-limonene emulsions made by a novel hydrocolloid (Angum gum) compared with Arabic gum

Our goal was to evaluate emulsion stability, droplet size analysis and rheological behavior of the emulsions prepared by a native biopolymer namely Angum gum (An) compared with Arabic gum (Ar) stabilized emulsions. After gum extraction, gum dispersions with maltodextrin were prepared in water (in 1-5% concentrations) and emulsified with 5% and 10% d-limonene using high pressure homogenization. Statistical analysis revealed a significant influence of gum type and gum concentration on emulsion stability at α = 0.05. Flavor level was not important statistically in emulsion stability but it was the only factor with a significant influence (P < 0.05) on surface tension of the emulsions. The results showed that Angum gum was superior to Arabic gum in stabilizing emulsions during storage. Also, rheological data revealed that Angum gum-emulsions’ behavior was following the Herschel-Bulkley model with higher viscosities compared to Arabic gum emulsions, which could be the main reason of higher emulsion stabilities with this novel hydrocolloid.     

Determination of l- and d-amino acids in smokeless tobacco products and tobacco

Quantities of free l- and d-amino acids were determined by GC-SIM-MS in 25 European snuff tobaccos (from Germany, England and Sweden) and eight chewing tobaccos (from the Philippines, Africa and Denmark) and compared to those of cigar, cigarillo, and freshly harvested tobacco leaves of cultivars of Nicotiana tabacum L. Amino acids were isolated from tobacco samples by treatment with 70% aqueous methanol and purified by a cation exchanger. Next they were converted into their N(O)-pentafluoropropionylamino acid-(2)-propyl esters, and enantiomers separated and quantified by GC-SIM-MS on a Chirasil^®-l-Val capillary column. Among l-amino acids the most abundant were Pro, Asx and Glx in the low milligram range (about 2–6 mg/g) whereas the other l-amino acids were in the submilligram range. Though native tobacco leaves contained low amounts of few d-AAs (0.2–1.9%), all processed tobacco samples had d-amino acids in varying amounts and patterns.     

Screening of d-amino acid oxidase inhibitor by a new multi-assay method

This paper describes an investigation of the inhibition of a d-amino acid oxidase (DAAO) activity in several kinds of food additives and fruit. To screen for an inhibitor of DAAO, the method employed checked for two kinds of indicators, namely, pyruvic acid (indicator-1) and hydrogen peroxide (indicator-2), both of which are formed by digestion by DAAO of d-alanine (the standard d-amino acid used in this study). For measurement of pyruvic acid, a reliable and authenticated method was employed: the presence of pyruvic acid was determined by converting it into a chromophore derivative by tagging with 2,4-dinitro phenylhydrazine (DNP), followed by measurement of absorbance at 445 nm. The pyruvic acid thus determined is referred to as “(colorimetric) indicator-1”. To measure hydrogen peroxide, a highly sensitive fluorogenic substrate, 3-(p-hydroxyphenyl)propionic acid (HPPA), was employed in the present study. Hydrogen peroxide was detected by measuring fluorescence intensity (Ex. = 320 nm, Em. = 405 nm) of 2,2′-dihydroxybiphenyl-5,5′-dipropionic acid (oxidize-HPPA), which is produced by horseradish peroxidase (HRP)-catalyzed oxidation of HPPA with hydrogen peroxide. The hydrogen peroxide thus determined is referred to as “(flourometric) indicator-2” After optimizing the multi-assay procedures, the inhibition of DAAO activity against d-alanine (used as the standard d-amino acid) in 11 kinds of food additives and five kinds of fruit was evaluated, first in terms of indicator-1. Then, two substrates, potassium sorbate and apple juice, that were screened by indicator-1, were further evaluated by indicator-2 to conform the inhibition of DAAO activity. This is the first demonstration of the inhibition of DAAO activity by potassium sorbate, which is widely used as a synthetic preservative in food and apple juice.     

Optimization of natural fermentative medium for selenium-enriched yeast by d-optimal mixture design

Natural fermentative medium for selenium-enriched yeast (Saccharomyces cerevisiae) culture was investigated using response surface methodology (RSM). The medium with a concentration of 15 μg/mL Na₂SeO₃, contained various ratios of juices from germinated brown rice (0.40 ∼ 0.80, 12 Brix), beerwort (0.10 ∼ 0.50, 12 Brix) and soybean sprout (0.10 ∼ 0.50, 12 Brix), which were optimized by applying d-optimal mixture design (DMD). The effects of their ratios on biomass yield and total selenium (Se) yield were analyzed. The results showed that when the mixed ratio of the components was 4:4:2 (v:v:v), the maximum value of biomass yield and total Se yield were 8.5 g/L and 3.53 mg/L, respectively. Verification experimental trials were performed for validating the models, and it indicated that the above mixture of these natural materials can be used as proper medium for the growth of selenium-enriched yeast and accumulation of Se.     

Optical resolution of n-butyl d- and l-lactates using immobilized lipase catalyst

n-Butyl d- and l-lactates (BuDLa and BuLLa) were incubated with immobilized lipase. ¹H-NMR showed that BuDLa reacted to oligomers, while BuLLa did not react. A mixture containing 90.4% of BuLLa and 9.6% of BuDLa was incubated with the enzyme for 72 h, then distilled. The purity of BuLLa increased to 98.6%.     

Aroma compounds generated from thermal reaction of l-ascorbic acid with l-cysteine

The reaction of l-ascorbic acid with l-cysteine in heated aqueous solution (141 ± 1 °C) at five different pH values (5.00, 6.00, 7.00, 8.00, or 9.00) for 2 h, resulted in the formation of a complex mixture of aroma volatiles. The volatile compounds generated were analysed by SPME–GC–MS. The results gave 43 aroma compounds. The reaction between l-ascorbic acid and l-cysteine led mainly to the formation of alicyclic sulphur compounds, thiophenes, thienothiophenes, thiophenones, thiazoles and pyrazines, most of which contain sulphur. Many of these volatiles had meaty flavour. The origin of many of the compounds was explained. The studies showed that thienothiophenes and thienones were formed mainly at acidic pH. In contrast, higher pH values could promote the production of thiophenes, thiazoles and pyrazines.     

Rapid and accurate determination of d- and l-lactate,lactose and galactose by enzymatic reactions coupled to formation of a fluorochromophore: Applications in food quality control

A fluorometric-coupled reaction for the accurate and rapid determination d- and l-lactate and lactose, galactose in foods is presented. The method was found useful for an accurate determination of these metabolites in heterogeneous, opaque and colourful foods without pretreatments. Example for the determination of lactose, galactose, d- and l-lactate in milk, and yogurts and d- and l-lactate in milk, wine and beer is provided. Unexpectedly, we found that the composition of some commercial bio-yogurts produced in Israel is not consistent with the classical definition of yogurts. Thus, this method offers rapid and accurate methodology, which should be particularly valuable in food quality control.     

Substrate specificity of a recombinant d-lyxose isomerase from Providencia stuartii for monosaccharides

The specific activity and catalytic efficiency (k_cat/K_m) of the recombinant putative protein from Providencia stuartii was the highest for d-lyxose among the aldose substrates, indicating that it is a d-lyxose isomerase. Gel filtration analysis suggested that the native enzyme is a dimer with a molecular mass of 44 kDa. The maximal activity for d-lyxose isomerization was observed at pH 7.5 and 45 °C in the presence of 1 mM Mn²⁺. The enzyme exhibited high isomerization activity for aldose substrates with the C2 and C3 hydroxyl groups in the left-hand configuration, such as d-lyxose, d-mannose, l-ribose, d-talose, and l-allose (listed in decreasing order of activity). The enzyme exhibited the highest activity for d-xylulose among all pentoses and hexoses. Thus, d-lyxose was produced at 288 g/l from 500 g/l d-xylulose by d-lyxose isomerase at pH 7.5 and 45 °C for 2 h, with a conversion yield of 58 % and a volumetric productivity of 144 g l^− 1 h^− 1. The observed k_cat/K_m (920 mM^− 1 s^− 1) of P. stuartiid-lyxose isomerase for d-xylulose is higher than any of the k_cat/K_m values previously reported for sugar and sugar phosphate isomerases with monosaccharide substrates. These results suggest that the enzyme will be useful as an industrial producer of d-lyxose.     

Myogenic induction of human mesenchymal stem cells by culture on dendrimer-immobilized surface with d-glucose display

Culture surfaces were designed by immobilizing dendrimer with d-glucose display, that is, 1st-generation (G1) and 3rd-generation (G3) dendrimer surfaces. In the cultures of human mesenchymal stem cells (hMSCs), the effect of the prepared culture surfaces was examined in terms of regulating cell morphology and differentiation. The time-lapse observation revealed that the cells on the G3 surface showed more dynamic behaviors of temporal stretching and contracting associated with stimulated migration, as compared with the cells on the G1 and plain surfaces. On the G3 surface, moreover, a frequency of round-shaped cells increased, and spreading of the cells was appreciably suppressed. From the cytoskeletal staining of F-actin, it was found that the immature stress fibers were of significance in the cells on the G3 surface. In addition, the cells on the G3 surface expressed RhoA inactivation and Rac1 activation during the culture, indicating that the G3 surface permits the regulation of RhoA and Rac1 expression associated with altering in cellular morphology and migratory behaviors. It was also found that desmin expression was, in particular, promoted on the G3 surface, thus supporting the consideration that a balance of Rho family GTPases activation induces myogenesis in hMSCs. The current results suggest that the dendrimer surface can be a potential tool for the guided differentiation of hMSCs directing to myocyte-like cells in the absence of an aqueous myogenesis-inducing factor.     

Mechanism of formation of sulphur aroma compounds from l-ascorbic acid and l-cysteine during the Maillard reaction

The sulphur aroma compounds produced from a phosphate-buffered solution (pH 8) of l-cysteine and l-, l-[1-¹³C] or l-[4-¹³C] ascorbic acid, heated at 140 ± 2 °C for 2 h, were examined by headspace SPME in combination with GC-MS. MS data indicated that C-1 of l-ascorbic acid was not involved in the formation of sulphur aroma compounds. The sulphur aroma compounds formed by reaction of l-ascorbic acid with l-cysteine mainly contained thiophenes, thiazoles and sulphur-containing alicyclic compounds. Among these compounds, 1-butanethiol, diethyl disulphide, 5-ethyl-2-methylthiazole, cis and trans-3,5-dimethyl-1,2,4-trithiolane, thieno[2,3-b]thiophene, thieno[3,2-b]thiophene, cis and trans-3,5-diethyl-1,2,4-trithiolane, 1,2,5,6-tetrathiocane, 2-ethylthieno[2,3-b]thiophene, 2,4,6-trimethyl-1,3,5-trithiane and cyclic octaatomic sulphur (S₈) were formed solely by l-cysteine degradation, and the rest by reaction of l-ascorbic acid degradation products, such as hydroxybutanedione, butanedione, acetaldehyde, acetol, pyruvaldehyde and formaldehyde with l-cysteine or its degradation products, such as H₂S and NH₃. A new reaction pathway from l-ascorbic acid via its degradation products was proposed.     

Characterization of d-succinylase from Cupriavidus sp. P4-10-C and its application in d-amino acid synthesis

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Alterations in d-amino acid concentrations and microbial community structures during the fermentation of red and white wines

Alterations in d-amino acid concentrations and microbial community structures during the fermentation of red and white wines were analyzed to clarify the relationship between the occurrence of d-amino acids and the actions of fermentative microorganisms. Relatives of Saccharomyces cerevisiae and Oenococcus oeni were detected in red wine samples, and relatives of S. cerevisiae, O. oeni, and Gluconacetobacter saccharivorans were detected in white wine samples. The S. cerevisiae relatives were detected throughout the fermentation process, whereas the O. oeni relatives were detected at the late stage of fermentation in both the red and white wine samples. The G. saccharivorans relative was detected in the early stage of fermentation. The amino acid analysis showed that d-alanine, d-glutamic acid, and d-lysine were present in both the red and white wine samples. The concentrations of these d-amino acids increased as the fermentation continued, especially from the malolactic fermentation stage to the end of the fermentation processes. These increases seem to be linked to the presence of O. oeni relatives.     

Reaction of Nα-acetyl-dl-tryptophan amide with d-xylose or d-glucose in acidic solution

The reaction of $\text{N}{}^{\mathrm{\alpha }}\text{-}\text{acetyl}\text{-}\text{dl}\text{)-}\text{tryptophan}$ amide (a model for proteinbound tryptophan) with either $\text{d}\text{-}\text{xylose}$ or $\text{d}\text{-}\text{glucose}$ in acidic solution at 75 or 100°C gave the respective $\text{N}{}^{\mathrm{\alpha }}\text{-}\text{acetyl}\text{-1-(β-}\text{d}\text{-}\text{glycopyranosyl}\text{)-}\text{dl}\text{-}\text{tryptophan}$ amides as the main products in 10–20% yield. These results indicate that the indole nitrogen of protein-bound tryptophan may react with reducing carbohydrates during acid hydrolysis of proteins or, to a lesser extent, during food processing in acidic conditions.     

Studies on the retention of microencapsulated l-5-methyltetrahydrofolic acid in baked bread using skim milk powder

Our aim was to protect l-5-methyltetrahydrofolic acid (L-5-MTHF) from degradation throughout the baking and storage of a fortified white bread using microencapsulation. L-5-MTHF, with or without sodium ascorbate (ASC), was microencapsulated using skim milk powder (SMP) as the coating agent. Recoveries of L-5-MTHF in spray-dried materials were greater than 95 ± 5%. Microencapsulated L-5-MTHF was completely released from the skim milk coating material in simulated gastric fluid within the first 10 min at 37 °C. Incorporation of SMP-L-5-MTHF or SMP-L-5-MTHF + ASC into bread gave recoveries of 81.3 ± 1.3% and 87.1 ± 1.2% (n = 3), respectively, for L-5-MTHF immediately after bread baking. These treatments also showed significantly (p < 0.05) greater L-5-MTHF stability during room temperature storage, compared to the free L-5-MTHF. This study has shown that SMP is an effective microencapsulating agent and in the presence of ASC will produce excellent conditions for stabilising L-5-MTHF in baked bread.     

The determination of l-carnitine in several food samples

We designed this study to re-validate some methodological parameters of the radio-enzymatic assay, including phenomena of residual, non-carnitine radioactivity present in some assay mixtures of food samples. The second part of the paper presents l-carnitine concentrations (total-, free- and acyl-carnitine) in a wide range of food samples of animal and plant origin.     

In vivo investigation on the potential of galangin,kaempferol and myricetin for protection of d-galactose-induced cognitive impairment

The potential of three natural flavonols (galangin, kaempferol and myricetin) to protect against d-galactose-induced cognitive impairment in mice was investigated. After 8 weeks treatment, the mice were assessed by behavioural tests. The levels of oxidative stress, the amount of Na⁺,K⁺-ATPase and extracellular signal-regulated kinases (ERK)-cyclic AMP response element binding protein (CREB) signaling pathway in hippocampus were also analysed. It was found that all the three dietary flavonols could ameliorate the oxidative stress, enhance the activity of Na⁺,K⁺-ATPase and regulate the expression of ERK-CREB pathway in mice. However, only kaempferol and myricetin could significantly improve the learning and memory capability when compared with d-galactose model. Our results suggest that the presence of hydroxyl groups in the B ring of flavonols may have contribution to the neuroprotective activity.