Biochemical,sensory and microbiological attributes of wild turbot (Scophthalmus maximus), from the Black Sea,during chilled storage

Freshness of wild turbot (Scophtalmus maximus) stored in ice was assessed by chemical, sensory and microbiological methods. The limit for sensory acceptability of wild turbot stored in ice was ∼12–15 days. The quality of turbot decreased on day 15 (B) and they were no longer acceptable on day 19 (C). The TVB-N level showed fluctuations during storage, indicating that TVB-N could not be a good indicator of turbot quality. The release of FFA increased from an initial value of 6.33 (expressed as % of oleic acid) to a final value of 20.6 during the storage period. The initial PV value was 5.60 meq/kg for turbot stored in ice and it started to increase to 21.6 meq/kg on day 12 and then started to decrease to 13.6 meq/kg at the end of storage period. The level of TMA in wild turbot increased sharply from an initial value of 9.36 mg/kg to a final value of 38.9 mg/kg. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.92, 0.89, 0.99, 0.89, 0.96 and 0.89, respectively, for the wild turbot stored in ice. Turbot maintained high (E) and good quality (A) during the first 12 days of chilled storage when the average K, K_i and P values were ∼78–85%, and H, F_r and G values were ∼45%, 15% and 149%, respectively. Eight biogenic amines were investigated, namely, histamine, putrescine, cadaverine, spermidine, spermine, tryptamine, tyramine, and 2-phenylethylamine, three amines (histamine, tyramine, and tryptamine) were not detected in any of the fish samples during the storage period. As storage time progressed, putrescine and cadaverine became the dominant amines, reaching 22.7, and 16.9 mg/kg, respectively, at 19 days of storage in ice. Total viable counts of whole gutted turbot increased from the initial value of 3.3 log cfu g⁻¹ (day 0) to 7.87 log cfu g⁻¹ (day 19) over the period of storage. If 10⁶ microorganisms/g are considered to be the TVC limit of acceptability, the shelf life of turbot was approximately ∼13–14 days.     

Characterisation of thermostable trypsin and determination of trypsin isozymes from intestine of Nile tilapia (Oreochromis niloticus L.)

Trypsin from intestinal extracts of Nile tilapia (Oreochromis niloticus L.) was characterised. Three-step purification – by ammonium sulphate precipitation, Sephadex G-100, and Q Sepharose – was applied to isolate trypsin, and resulted in 3.77% recovery with a 5.34-fold increase in specific activity. At least 6 isoforms of trypsin were found in different ages. Only one major trypsin isozyme was isolated with high purity, as assessed by SDS-PAGE and native-PAGE zymogram, appearing as a single band of approximately 22.39 kDa protein. The purified trypsin was stable, with activity over a wide pH range of 6.0–11.0 and an optimal temperature of approximately 55–60 °C. The relative activity of the purified enzyme was dramatically increased in the presence of commercially used detergents, alkylbenzene sulphonate or alcohol ethoxylate, at 1% (v/v). The observed Michaelis–Menten constant (K_m) and catalytic constant (K_cat) of the purified trypsin for BAPNA were 0.16 mM and 23.8 s⁻¹, respectively. The catalytic efficiency (K_cat/K_m) was 238 s⁻¹ mM⁻¹.     

Freshness assessment of ray fish stored in ice by biochemical,chemical and physical methods

Ray fish were caught, filleted, and stored in ice. Fillets were analysed for 18 days to determine the chemical, biochemical and physical changes and their relation to the muscle eating quality. Trimethylamine (TMA-N), total volatile bases (TVB-N), ATP content and breakdown products, K value, pH, texture, water-holding capacity (WHC) and colour changes were monitored. At the beginning of the study, the ray fish muscle showed a low concentration of ATP and a high value of inosine 5′-monophosphate (IMP). Regarding to the signs of freshness and deterioration, K value presented an exponential increase (r2 = 0.95) with an initial value of 4.7% and a final value of 47.5%. Furthermore, the TBV-N and TMA-N significantly increased (P < 0.05) during the storage in ice. As for the physical analysis whereas the texture changed (P < 0.05); pH and the WHC were not affected (P < 0.05). The overall results of this study indicated that the edible quality of ray fish muscle was maintained during at least 15 days of ice storage.     

The effects of gamma-irradiation on the nucleotide degradation compounds in sea bass (Dicentrarchus labrax) stored in ice

The effects of two irradiation doses (2.5 and 5 kGy) on nucleotide breakdown compounds in sea bass stored in ice were investigated. Nucleotide degradation was slower in sea bass irradiated at 2.5 and 5 kGy than untreated samples. Irradiated samples had lower hypoxanthine and inosine content than the control group. Significant differences (p < 0.05) in K and related values were found between control groups and irradiated samples (2.5 and 5 kGy). H and G values showed a good correlation with storage time (r² ? 0.98) while linear regressions of K and Ki ranged from 0.95 and 0.93 to 0.98 and 0.97, respectively. A dose of 5 kGy seemed to be more effective than that of 2.5 kGy to reduce nucleotide breakdown in sea bass. The best linear correlation was obtained from G and H values; thus, they might be used as freshness indicators for non-irradiated and irradiated sea bass.     

Molecular characteristics of partially hydrolyzed fucoidans from sporophyll of Undaria Pinnatifida and their in vitro anticancer activity

The effects of molecular characteristics on the anticancer activity of fucoidans were investigated after hydrolysis by copper acetate and then fractionation with 30 and 5 kDa membranes, which produced three fucoidan fractions: F_>30 K, F_5–30 K and F_<5 K. The F_>30 K and F_5–30 K consisted of mostly carbohydrate (58.2–61.3%) and sulphate (31.7–35.5%) with small amounts of proteins (1.2–6.4%). However, the major constituents of F_<5 K were sulphate (31.8%) and ash (37.5%) with smaller amounts of carbohydrate (15.5%) and protein (1.2%). The molecular weights (M_w) of F_>30 K, F_5–30 K and F_<5 K, obtained by a light scattering technique, were 262, 5.6 and 1.6 kDa, respectively. The observed anticancer activities were 18.0–28.5% for F_>30 K, 19.2–57.5% for F_5–30 K and 26.5–36.5% for F_<5 K, respectively, in the concentration range of 0.2–0.8 mg/mL. The results suggest that the anticancer activity of fucoidans could be considerably improved by lowering their M_w and by improving the binding properties of sulphate groups possibly through changing the molecular conformation.     

Nucleotide degradation and biogenic amine formation of wild white grouper (Epinephelus aeneus) stored in ice and at chill temperature (4 °C)

Sensory (cooked and uncooked), chemical (proximate composition, TVB-N, nucleotide degradation products and biogenic amines) and microbiological quality (TVC and total coliform) changes were investigated during storage of ungutted white grouper kept in ice and at chill temperature (4 °C). According to the sensory assessment, the shelf life of white grouper was 16 days in ice and 4 days for fish stored at chill temperature. TVB-N values increased with storage time. Amines found in white grouper stored in ice were TMA, putrescine, cadaverine, 2-phenylethylamine, dopamine, agmatine, tryptamine and serotonin. Histamine, spermine, spermidine were never detected with either storage condition. The acceptability limit in terms of microbial count was exceeded at 8 days in ice and at 4 days for fish stored at chill temperature. Total coliform count was 2.8 log₁₀ cfu/ml at 1 day and reached 10⁵ cfu/ml for both storage conditions.     

Characterisation of a β-N-acetylhexosaminidase from a commercial papaya latex preparation

A β-N-acetylhexosaminidase (β-NAHA) (EC 3.2.1.52) with molecular mass of 64.1 kDa and isoelectric point of 5.5 was purified from a commercial papaya latex preparation. The optimum pH for p-nitrophenyl-N-acetyl-β-d-glucosaminide (pNP-β-GlcNAc) hydrolysis was five; the optimum temperature was 50 °C; the K_m was 0.18 mM, V_max was 37.6 μmol min⁻¹ mg⁻¹ and activation energy (E_a) was 10.3 kcal/mol. The enzyme was thermally stable after holding at 30–45 °C for 40 min, but its activity decreased significantly when the temperature exceeded 50 °C. Heavy metal ions, Ag⁺ and Hg²⁺, at a concentration of 0.25 mM and Zn²⁺ and Cu²⁺, at a concentration of 0.5 mM, significantly inhibited enzyme activity. The β-NAHA had only one active site for binding both pNP-β-GlcNAc and p-nitrophenyl-N-acetyl-β-d-galactosaminide (pNP-β-GalNAc). A prototropic group with pKa value of about five on the enzyme may be involved in substrate binding and transformation, as examined by Dixon–Webb plots.     

Postmortem changes in cazon fish muscle stored on ice

The biochemical, chemical and physical postmortem changes and their relation to the cazon muscle eating quality were studied during an 18 day storage period at 0 °C (ice). Content of ATP and breakdown products, K value, pH, trimethylamine (TMA-N), total volatile bases (TVB-N), water-holding capacity (WHC), colour and texture changes were examined. At the beginning of the study, the cazon muscle showed a low concentration of ATP and a high value of IMP. Regarding to the signs of freshness and deterioration, K value presented a linear increase (r² = 0.97) with an initial value of 1.05% and a final value of 58.9%. The TBV-N and TMA-N significantly increased (P < 0.05). As for the physical analysis whereas the pH and the WHC changed (P < 0.05); texture was not affected (P < 0.05). The overall results of this study indicated that the edible quality of cazon fish muscle was maintained during at least 18 days of ice storage.     

Chemical and microbiological quality of grass carp (Ctenopharyngodon idella) slaughtered by different methods

The effect of two slaughter methods (immersion in ice-water slurry and electrical stunning followed by ice slurry asphyxiation) on chemical and microbiological parameters of grass carp (Ctenopharyngodon idella) stored in ice for 20 days was evaluated. No differences in total volatile basic nitrogen (TVB-N), pH, carbohydrate or protein content of mucus were observed between the slaughter methods. Ice-slaughtered fish had lower bacteria counts at the beginning of storage, but higher counts than fish slaughtered by electricity at the end of storage (p < 0.05). However, no significant differences in the shelf life were observed between the slaughter methods evaluated (limit of acceptability – counts > 3 × 10⁶ CFU g⁻¹ – attained after 13–16 days). Results indicated that the chemical parameters evaluated have a limited applicability to assess the shelf life of grass carp stored in ice, since pH limit (6.8) was exceeded after 4 days, while TVB-N limit (30 mg%) was not attained after 20 days of storage.     

Rapid,simple and sensitive determination of the apparent formation constants of trans-resveratrol complexes with natural cyclodextrins in aqueous medium using HPLC

The study of the complexation of trans-resveratrol with natural cyclodextrins (CDs) in aqueous medium under different physico-chemical conditions of pH or temperature is essential if this antioxidant compound is to be used successfully in the food industry as ingredient of functional foods, due its poor stability, bioavailability and solubility. In this paper, a rapid, simple and sensitive determination of the apparent formation constant of trans-resveratrol/CD complexes by HPLC in aqueous medium has been investigated for first time. It can be observed that trans-resveratrol forms a 1:1 complex with α-, β- and γ-CD. The highest value of the apparent formation constant (K_F = 1922 ± 89 M⁻¹) was found for β-CD and a strong dependence of K_F on pH can be seen in the region where the trans-resveratrol begins the deprotonation of their hydroxyl groups. Moreover, an increase in the system’s temperature produced a decrease in the values of K_F. Finally, to gain information on the mechanism of the trans-resveratrol affinity for CD, the thermodynamic parameters of the complexation were obtained.     

Characterisation of a thermostable xylanase from Chaetomium sp. and its application in Chinese steamed bread

A novel thermophilic xylanase-producing fungus, Chaetomium sp. CQ31 produced 131 U ml⁻¹ of xylanase when grown on a medium containing corncob (3.5%, w/v) at 37 °C for 6 days. A low molecular xylanase was purified 6.5-fold to homogeneity with a recovery yield of 17.5%. Its molecular mass was estimated to be 25.1 kDa by SDS–PAGE. The xylanase had an optimum pH of 7.5, and its optimal temperature was 65 °C. Apparent K_m values of the xylanase for birchwood, beechwood and oat-spelt xylan were 1.3, 0.86 and 4.4 mg/ml, respectively. The influence of this xylanase on the quality of Chinese steamed bread (CSB) was further studied. Addition of xylanase in the range 2.5–5.0 ppm caused a 20–24.5% increase in specific volume over the control and remarkable decrease (8.9–24.2%) in firmness was also noticed. This is the first report on the purification, characterisation and application of a xylanase from Chaetomium sp. CQ31.     

Effect on lamb meat quality of including thyme (Thymus zygis ssp. gracilis) leaves in ewes’ diet

The aim of this study was to investigate the effect of including thyme leaves (TL) in the diet of pregnant sheep on the sensorial characteristics, bacterial spoilage and oxidative stability of lamb meat stored in modified atmosphere (70% O₂:30% CO₂). For this, thirty-six sheep were randomly assigned to three groups: control (basal diet), T₁ (3.7% thyme leaves), T₂ (7.5% thyme leaves). Meat spoilage (TV, PSY, MY, ENT, and LA), TBARS, CIELAB coordinates, metmyoglobin and the sensory characteristics of fresh lamb meat were analyzed on days 0, 7, 14 and 21. The presence of antioxidant compounds in the diet containing TL delayed (P < 0.05) colour deterioration, lipid oxidation and bacterial counts, while at the same time imparting a better appearance to the fresh lamb meat. In general, this effect was more pronounced at the higher level of TL (7.5%). High Pearson’s correlation coefficients were found between the sensory attributes, CIELAB coordinates and TBARS.     

Evaluation of the performance of osmotic dehydration sheets on freshness parameters in cold-stored beef biceps femoris muscle

This study aimed to evaluate the effects of osmotic dehydration sheet (ODS) packaging on the quality parameters of beef biceps femoris muscle samples stored at 4 °C for 0, 1, 3 and 7 days. Quality indices such as Hunter color values (L^∗, a^∗ and b^∗, the percentage of metmyoglobin (Met-Mb%), K value (freshness index), and the contents of adenosine triphosphate (ATP)-related compounds (ARCs), thiobarbituric acid reactive substances (TBA-RS) and volatile basic nitrogen (VBN) were measured. ODS gave lower a^∗ and b^∗ values and lower Met-Mb% compared with control samples wrapped in polyvinylidene chloride film (PVDCF) (P < 0.01), but had no effect on L^∗ (P < 0.01). As a result, with higher levels of osmotic dehydration produced by the ODS, the percentage of weight loss and the total contents of ARCs and inosine monophosphate of the samples also increased (P < 0.05). The K values of ODS samples were also significantly lower than PVDCF-wrapped samples (P < 0.05). Low performance ODS wrapping reduced the TBA-RS values below those found with PVDCF and high performance ODS processing (P < 0.01). Moreover, the use of ODS had no effect on VBN values. Thus, although the bright red of beef samples changed to a dark purple color and the weights of samples decreased, the ODS approach has potential as a tool for decreasing the deterioration of other quality indices such as Met-Mb%, TBA-RS, ARCs, K values and the VBN content of cold-stored beef.     

Sensory,physical, chemical and microbiological changes in aquacultured meagre (Argyrosomus regius) fillets during ice storage

Commercial-sized meagre fillets were stored on ice at 4 °C for 18 days, in order to evaluate the loss of quality and freshness that occurs over this period of time. Physicochemical (pH, thiobarbituric acid (TBA), total volatile basic nitrogen (TVBN), trimethylamine (TMA), water activity, water-holding capacity, colour, texture and fatty acid profile), sensory and microbiological analyses were carried out at 0, 4, 7, 11, 14 and 18 days of storage. As part of the sensory analysis, attributes associated with fillet appearance, odour and texture were examined. Variations in pH, TBA, TVBN and TMA were observed throughout the storage period, although only TBA displayed a significant correlation with time (r = 0.96). L^∗ and b^∗ values increased, and the chroma and hue values decreased, reflecting the colour changes experienced by the fillets over time. With regards to the texture profile, hardness was significantly correlated with time (−0.68). All the sensory analysis attributes exhibited significant variations and correlations close to 1.00 with storage time, which is a reflection of the fillets’ loss of freshness. The correlation coefficients between aerobic mesophilic and psychrophilic bacteria, enterobacteria and coliform counts on the one hand and storage time on the other were also very high (0.99–1.00). A regression analysis using the acceptability limit set by the ICMSF standard (1986) for total aerobic mesophilic counts (7 log cfu/g) yielded a shelf-life for meagre fillets of 9 days. The TBA, sensory and microbiological analyses displayed very strong correlations with storage time, and they may be considered suitable indicators for evaluating meagre fillet spoilage during refrigerated storage.     

Sensory,microbiological and chemical assessment of the freshness of red mullet (Mullus barbatus) and goldband goatfish (Upeneus moluccensis) during storage in ice

The shelf life of red mullet and goldband goatfish during ice storage were studied in terms of sensory, microbiological and chemical changes. The sensory acceptability limit was 8 days for goldband goatfish (Upeneus moluccensis) and 11 days for red mullet (Mullus barbatus) stored in ice. The TVC level was correlated with sensory assessment. The TVC exceeded 7 log cfu g⁻¹ after 8 days for goldband goatfish, and 11 days for red mullet. At the end of storage period, pH, TVB-N, TBA, FFA and PV for red mullet were 7.84, 47.19 mg/100 g, 0.69 mg MA kg⁻¹, 1.17% oleic acid and 1.58 meq O₂/kg and for goldband goatfish they were 7.53, 43.97 mg/100 g, 0.74 mg MA kg⁻¹, 1.62% oleic acid and 1.68 meq O₂/kg, respectively. In red mullet, agmatine, serotonin, histamine and dopamine became the dominant amines, reaching 7.30, 5.97, 2.52 and 2.31 mg/100 g, respectively. Also the dominant amines for goldband goatfish were 4.37, 3.88, 3.38 and 2.00 mg/100 g for histamine, agmatine, dopamine and putrescine, respectively.     

Pasteurization of grapefruit juice using a centrifugal ultraviolet light irradiator

Studies are lacking on the nonthermal pasteurization of liquid foods using UV irradiators that centrifugally form very thin films to overcome the problem of limited penetration depth of UV. Grapefruit juice inoculated with Escherichia coli or Saccharomyces cerevisiae was processed at the following conditions: UV dose 4.8–24 mJ/cm²; treatment time 3.2 s, cylinder rotational speed 450–750 rpm, cylinder inclination angle 15–45°, outlet temperature 11 °C, and flow rate 300 ml/min, and was stored for 35 days. Appropriate dilutions of the samples were pour plated with TSA and TSA + 3% NaCl for E. coli and Sabouraud dextrose agar (SDA) and SDA + 5% NaCl for S. cerevisiae. Nonthermal UV processing at 19 mJ/cm², 450 rpm and 15° reduced E. coli in grapefruit juice by 5.1 log₁₀. A dose of 14 mJ/cm² reduced S. cerevisiae by 6.0 log₁₀. Inactivation increased linearly with increasing UV dose. The inactivations at 600 and 750 rpm were similar, and were better than at 450 rpm. The results at 30° and 45° were similar, and were better than at 15°. The occurrence of sublethal injury in either microorganism was not detected. Storing UV processed grapefruit juice at 4 and 10 °C reduced the surviving E. coli to below 1 log₁₀ cfu/ml in 14 days. Processing UV juice reduced the population of S. cerevisiae to less than 1 log₁₀ cfu/ml where it remained for 35 days during refrigerated storage. These results suggest that grapefruit juice may be pasteurized using a nonthermal UV irradiator that centrifugally forms a thin film.     

Biochemical and thermal properties of β-galactosidase enzymes produced by artisanal yoghurt cultures

β-Galactosidases, produced by pure and mixed cultures of Streptococcus thermophilus 95/2 (St 95/2) and Lactobacillus delbrueckii ssp bulgaricus 77 (Lb 77) isolated from the Toros mountain region of Turkey, were characterised with respect to their biochemical and thermal properties. Optimum pH and temperature for maximum activity were determined and these enzymes were stable in the pH range 7–9 and in the temperature range 20–37 °C, retaining 80–90% of their initial activities. The inactivation energies of β-galactosidase from Lb 77, St 95/2 and mixed culture (Lb 77 and St 95/2) were 51.3, 44.0 and 48.3 kcal mol⁻¹, respectively. Moreover, thermodynamic (ΔG, ΔS, ΔH) and kinetic constants (K_m and V_max) were determined and effects of metal ions were investigated. As a result, these enzymes could be considered as potential candidates for lactose hydrolysis of milk and milk products.     

Modelling starch digestion in sweetpotato with biphasic digestograms

The kinetics of starch digestion in 20 sweetpotato samples obtained from Papua New Guinea were investigated using an in vitro procedure based on glucometry. Irrespective of the cultivars (3-mun, Carot kaukau, Wahgi besta, Nillgai, Baiyer kaukau, and 1-mun), provinces, farmers and locations, the samples exhibited biphasic digestograms, possibly due to initial impediments to amylolysis and/or transport of digestion products by non-starch components (e.g. plant cell walls). The biphasic digestograms were segmented into two monophasic digestograms using a second-order polynomial (average r² = 0.723; p < 0.001), and a modified first-order kinetic model adequately described the digestograms (average r² = 0.984, p < 0.001; mean relative deviation modulus, MRDM, =8). Generally, the digestion rate constants (initial, K_i = 3.2-5.2 × 10⁻³ min⁻¹; final, K_f = 3.8-18.4 × 10⁻³ min⁻¹) indicated faster digestion during the final segment after the initial impediments to digestion had possibly been overcome. K_i was significantly (p < 0.05) different among the samples, which did not significantly (p < 0.05) differ in K_f. A logistic model, which treated each digestogram as a single process, also adequately described the biphasic behaviours (average r² = 0.994, p < 0.001; mean relative deviation modulus, MRDM, =15). The digestion parameters from the segment and logistic approaches significantly (p < 0.05) differed among the sweetpotato samples. The rate of digestion from the logistic model was significantly (p < 0.05) related to the initial and final rates of digestion from the segment approach (K = 3.99 K_i + 0.65 K_f; r² = 0.456; p < 0.001). Irrespective of the approach, maximum starch digestion was less than 100% in some samples to indicate the presence of resistant starch type 1, 2 or both. The present study is the first to model biphasic starch digestograms.     

Trypsin from viscera of vermiculated sailfin catfish, Pterygoplichthys disjunctivus, Weber, 1991: Its purification and characterization

Pterygoplichthys disjunctivus viscera trypsin was purified by fractionation with ammonium sulphate, gel filtration, affinity and ion exchange chromatography (DEAE-Sepharose). Trypsin molecular weight was approximately 27.5 kDa according to SDS–PAGE, shown a single band in zymography. It exhibited maximal activity at pH 9.5 and 40 °C, using N-benzoyl-dl-arginine-p-nitroanilide (BAPNA) as substrate. Enzyme was effectively inhibited by phenyl methyl sulphonyl fluoride (PMSF) (100%), N-α-p-tosyl-l-lysine chloromethyl ketone (TLCK) (85.4%), benzamidine (80.2%), and soybean trypsin inhibitor (75.6%) and partially inhibited by N-tosyl-l-phenylalanine chloromethyl ketone (TPCK) (10.3%), ethylendiaminetetraacetic acid (EDTA) (8.7%) and pepstatin A (1.2%). Enzyme activity was slightly affected by metal ions (Fe²⁺ > Hg²⁺ > Mn²⁺ > K⁺ > Mg²⁺ > Li⁺ > Cu²⁺). Trypsin activity decreased continuously as NaCl concentration increased (0–30%). K_m and k_cat values were 0.13 mM and 1.46 s⁻¹, respectively. Results suggest the enzyme have a potential application where room processing temperatures (25–35 °C) or high salt (30%) concentration are needed, such as in fish sauce production.     

Antioxidant properties of different cultivars of Portulaca oleracea

Methanolic extracts of six cultivars of Portulaca oleracea were analyzed for their total phenol content (TPC) using the Folin–Ciocalteu method. The antioxidant activity was measured using the 1,1-diphenyl-2-picrylhydrazyl, ferric-reducing antioxidant power (FRAP) and β-carotene bleaching (BCB) assays. The iodine titration method was used to determine the ascorbic acid content (AAC). The TPC of the cultivars of P. oleracea ranged from 127 ± 13 to 478 ± 45 mg GAE/100 g of fresh weight of plant. There was good correlation between the TPC value and its AEAC, IC₅₀ and FRAP values (r² > 0.9) for all the cultivars. The AAC for the cultivars ranged from 38.5 ± 0.6 to 73.0 ± 17.5 mg/100 g. The TPC value of the common variety PO1, was the lowest compared to the ornamental cultivars (PO2–PO6). The BCB assay showed that all cultivars were capable of inhibiting lipid peroxidation and the inhibition power did not correlate with TPC value.