THE INFLUENCE OF pH AND OF SELECTED CATIONS ON THE FERMENTATION OF MALTOSE AND MALTOTRIOSE

The fermentation of maltose and maltotriose in metal-free buffer solutions strongly depends on the pH value; the optimum pH is close to 5·0 and activity diminishes to zero above pH 7·2. Potassium stimulates utilization of these sugars at pH values of 5·0 and below, but in contrast to the situation with glucose, pH still influences fermentation markedly in the presence of potassium. Both pH and potassium influence sugar uptake rather than internal metabolism. Zinc, magnesium and ammonium ions stimulate utilization of both sugars by stimulating uptake mechanisms.     

A preliminary investigation of caramelisation and isomerisation of allulose at medium temperatures and alkaline pHs: a comparison study with other monosaccharides

Allulose, also known as rare sugar, is a very reactive monosaccharide in browning reactions. In this study, the caramelisation of allulose was investigated for the first time. To study caramelisation, sugar solutions (glucose, fructose and allulose) were prepared with distilled water and buffer solutions at pH 7, 10, 12 and were freeze-dried afterwards. To let caramelisation occur, samples were incubated at 55% relative humidity (RH) and 50 °C. Results showed that samples prepared with pH 10 and pH 12 buffer solutions resulted in a higher browning rate than samples prepared with distilled water (DW) and pH 7 buffer solution. Moreover, according to HPLC and total reducing sugar content results, allulose (Allu) samples had the lowest remaining reducing sugar (RRS) amount, indicating that Allu samples depleted more in the reaction. Overall, the approach followed in this study can be considered as a novel strategy to obtain allulose-containing caramel-like products more efficiently than conventional methods.     

Chemical and physico-chemical characterisation of fibres from Laminaria digitata (kombu breton): A physiological approach

The content and chemical composition of soluble and insoluble dietary fibres from the brown marine alga Laminaria digitata (kombu breton) were determined. Two enzymic-gravimetric methods were used to determine (1) the content of soluble and insoluble fibres according to a modification of the AOAC procedure, and (2) the distribution of the soluble fibres in saline buffer at 37°C and at pH 2·0 and 7·5 used to simulate the gastric and intestinal phases of digestion, respectively. The total dietary fibre contents obtained by the two methods were similar (37·3 and 40·0%) and of these 84·8–87·4% was soluble. A partitioning of soluble fibres may occur during digestion since 49·3% was recovered in saline buffer at pH 2·0 whereas 50·7% was recovered in saline buffer at pH 7·5. Solubility of dietary fibres was related to the chemistry of brown algal polysaccharides. Fucans and laminarans were essentially soluble at pH 2·0 and alginate at pH 7·5, and insoluble fibres consisted primarily of cellulose. Oil adsorption and hydration properties (uptake, retention and swelling) in water, 154 mM NaCl, and 38 mM CaCl₂ at 20 and 37°C of three particle sizes of L digitata were measured. Oil adsorption was low (0·16–0·41 g g^?1) and was related to the particle size of the fibres. Hydration properties were more important with small particles except in CaCl₂ solution and followed the order water > NaCl > CaCl₂. Water uptake and swelling were greater at 37°C than at 20°C. The overall decrease in hydration properties observed with solutions of ionic strength ～0·15 was interpreted as reflecting the decrease in the electrostatic repulsion between charged polysaccharides. The lowest water uptake, water retention and swelling were obtained with solutions of CaCl₂, and were related to the known selective afinity of alginate for calcium. Thus, L digitata is especially rich in soluble dietaryfibres, and these have physico-chemical properties characteristic of the polysaccharides present. Water absorption and uptake and swelling can be modulated according lovarious physical and chemical parameters.     

Physico-chemical changes in Cavendish banana (Musa cavendishiiL var Montel) at different positions within a bunch during development and maturation

Studies on the physico-chemical changes between different hand positions (top, middle and bottom) within a bunch and different finger positions (upper and lower) within a hand at different maturity stages (between 3 and 15 weeks from the flower emergence) were carried out on ‘Montel’ banana (Musa cavendishii L). The suitable harvesting stage was found to be between 12 and 15 weeks after flower emergence. The size, weight, volume and peel colour of fruits increased significantly (P < 0·01) for fruits from all positions (hands and fingers within a hand) of the bunch until the end of maturity stage. On the other hand, texture values of the fruit decreased significantly (P < 0·01). The total soluble solids (TSS), ascorbic acid (AA) and sugar contents increased slowly during development, but the increase was rapid during ripening. The starch composition accumulated gradually (P < 0·05) at the early stages and decreased thereafter. The pH and titratable acidity (TA) values showed an irregular pattern in all the fruits from all positions during the maturity stage. However, significant differences were also detected in size, weight, volume, peel colour, texture, TSS, AA, pH, TA, starch and sugar contents between different hands and different fingers portions from the same bunch. © 1998 Society of Chemical Industry     

Effect of heating,pH and thermoradiation on inactivation of Vibrio vulnificus

The effects of heating, thermoradiation and pH (5·5 to 7·0) on inactivation of V. vulnificus cells in buffers, oyster and fish homogenates were studied. Cells were more sensitive to thermoradiation than heating or radiation alone. Synergistic effects were observed during thermoradiation of V. vulnificus (10⁷ cells ml^-1) at 40°C in buffer (pH 5·5), in fresh oyster (pH 6·2) and in fresh fish (pH 6·7). This synergistic effect was also noted when the same number of cells in fresh fish homogenates were irradiated at 45°C. Inactivation of cells varied depending on the environment and were more pronounced in buffers than in oyster or fish homogenates. The D₁₀ (dose in kGy inactivating 90% of cells) at 25·C was 0·078 in buffer (pH 7·0), 0·125 in oyster (pH 6·2) and 0·187 in fish (pH 6·7), but at 35°C, the D₁₀ values were 0·054, 0·093 and 0·125 kGy, respectively. Low initial numbers of cells (10 ml^-1) in pH 7·0 buffer were rapidly inactivated by thermoradiation (40·C) compared to high cell number (10⁷ ml^-1) and the D₁₀ (kGy) was 0·024 for the former and 0·047 latter. These D₁₀ values (kGy) were 0·046 and 0·093 in fresh oysters (pH 6·2), 0·093 and 0·109 kGy in fresh fish (pH 6·7), for the low and the high cell numbers, respectively following thermoradiation at 40°C.     

The effect of postharvest handling and processing on sea urchin (Evechinus chloroticus) gonad quality

Sea urchin gonads also known as roe or uni are a high‐valued food, considered a delicacy in many parts of the world. To determine the impact of stress caused by exposure of live urchins to air on the subsequent shelf‐life of recovered gonads, urchins (Evechinus chloroticus) were held in air at either 4 °C for 144 h or 15 °C for 72h. The coelomic fluid of urchins held in air showed a decrease in pH and increase in lactic acid concentration, percentage solid, turbidity level, colour and coelomocyte numbers. Gonads recovered from urchins held in air exhibited enhanced rates of deterioration over time, as assessed by a loss of surface definition and a decrease in their water‐holding capacity and height‐to‐surface ratio (melting). Gonad deterioration was minimised by implementing a brine + alum wash upon immediate removal of gonads from live urchins. This research has shown that the manner in which live urchins are held and processed has a dramatic impact on the subsequent shelf‐life and quality of the recovered gonads.     

The effect of added L-ascorbic acid,and sodium chloride on the change in concentration of some volatiles in pressurised peach homogenate during storage

White peach (Prunus persica L cv Yamane) homogenates with sugar (20%), or with sugar (20%) and/or L -ascorbic acid (0·1%) and/or sodium chloride (0·5%), were packed in plastic bottles, pressurised (400 MPa, 20°C, 10 min), and then stored at 0 and 25°C for various periods. The headspace volatiles which were absorbed on Tenax TA using dynamic headspace sampling were heat desorbed and analysed by capillary gas chromatography mass spectrometry. Enzymatic formation of benzaldehyde during storage was observed in all samples. The homogenate with L -ascorbic acid showed the highest level of benzaldehyde formation. The flavour quality and colour of the pressurised homogenates with ascorbic acid stored at lower temperature were excellent. © 1997 SCI.     

Development of caramel colour with improved colour stability and reduced 4-methylimidazole

ABSTRACT

This study investigated the effect of chemical substances, such as Mg²⁺ (as magnesium sulphate), Zn²⁺ (as zinc sulphate), Fe²⁺ (as iron sulphate), ascorbic acid, and citric acid, on the formation of 4-methylimidazole (4-MI) and colour stability of caramel colour. The 4-MI concentration in the caramel colour without chemical substances was 963.10 μg/g, and this decreased the most (67.7%) with the addition of 0.1 molar ratio of citric acid. Colour stability was evaluated by measuring the total colour change (ΔE) after storage, and heating in pH 2, 4, and 7 solutions and 50% solution in ethyl alcohol. Among the chemical substances added to reduce 4-MI in the caramel colour, Mg²⁺ (0.1 molar ratio) and ascorbic acid improved the colour stability more than the others.     

Modelling the effect of pH on the colour degradation of blanched broccoli

In ready-to-eat salads, a low pH is often applied in the salad dressing. The effect of pH on the colour change of blanched-frozen-and-thawed broccoli was studied. Different acids were used to achieve the pH values in buffer solutions. A model on chlorophyll degradation in fruits and vegetables was developed based on a simplification of existing knowledge. From integral non-linear regression analysis, it was concluded that the pH gradient at the boundary between product and buffer solution had a marked effect at low pH values. Furthermore, based on the analyses and the obtained residuals, another colour degrading process was revealed that gradually increases in relative importance at higher pH values. The effect of the five acids applied could be attributed to a single proportionality factor, probably related to the hydrophilic nature of the acid applied. The statistical analysis showed a percentage variance accounted for (R²_adj) of more than 99.6%. The apparent rate of colour degradation was found to be linearly related to the concentration of hydrogen ions.     

Varietal Classification of Young Red Wines in Terms of Chemical and Colour Parameters

Six varietal red wines produced in Murcia (Spain) were analysed for selected enological and colour parameters (31 variables in total). As regards acid content there were no important differences among the vinifications studied. The initial content of glucose and fructose was quite high in all the wines, which resulted in very high ethanol content (between 14·1% in Cinsault Noir wine and 16·4% in Tempranillo wine). The colour of the wines was determined by means of the Yxy coordinates and CIELAB parameters, but not one of them could significantly differentiate among vinifications. Principal component analysis and discriminant analysis were used to identify and to explain differences among samples. Discriminant analysis allowed a clear separation of the 80·7% of the cases analysed by a selection of only three variables ( L *, a *, C *). With a selection of 10 variables including x coordinate, colour intensity 1 and 2, pH, ionised anthocyanins, total phenolics, percentage of yellow pigments, total anthocyanins, hue and L * was possible to characterise the 95% of the cases analysed, but 100% in Monastrell-1, Tempranillo Graciano and Cinsault Noir wines.     

Influence of System Composition on Ascorbic Acid Destruction at Processing Temperatures

The anaerobic L -ascorbic acid (AAs) destruction in glucose aqueous model systems (water activity, a_w, 0·94) of pH 3·5, 4·1 and 5·0 was studied. The AAs degraded as a function of time and temperature (70, 80 and 90°C) with a behaviour that, in general, could be described by first order kinetics except for AAs in the system containing L -lysine, in which the results adjusted to zero order. The increment of pH from 3·5 to 5·0 accelerated AAs destruction and browning reactions. The addition of tin(II) or lysine to the glucose medium, increased AAs loss and browning. No difference was observed in AAs degradation and colour intensity when sorbic or propionic acid were used as antimycotics, at pH 3·5. Packaging the glucose system of acid pH with an air chamber, produced a faster destruction of AAs and browning of the solution than the one observed for the same system in anaerobic condition. In aerobic condition, the presence of glucose produced a lesser degradation of AAs than the one observed in the system without humectants. © 1997 SCI     

Faecal Composition and Nitrogen Excretion of Rats Fed on Diets Containing Sweet Lupin (Lupinus angustifoliusL) or its Fractions

Five N balance studies were conducted to determine the faecal composition and N excretion of feeding raw Lupinus angustifolius seed meal and its fractions for growing rats using a semi-synthetic lactalbumin-based diet as control. Diets were formulated to have equal amounts of energy. The protein was incorporated at the level of 10% bulk and contained unsupplemented lupin seed meal (LMU) and fully supplemented lupin seed meal (LMFS) at 360 g kg⁻¹ diet, aqueous extract non-dialysed (LPAND) at 196 g kg⁻¹ aqueous extract dialysed soluble at pH 7·0 (LPAD) at 148 g kg⁻¹ aqueous extract dialysed insoluble at pH 7·0 (LPADI) at 124 g kg⁻¹, buffer dialysed soluble at pH 7·0 (BUSOL) at 136 g kg⁻¹, buffer dialysed insoluble at pH 7·0 (BUDI) at 119 g kg⁻¹ and lupin meal residue after aqueous and buffer extraction (LMR) at 170 g kg⁻¹ diet. Rats were pair-fed for 10 days with all the above diets which had been supplemented with essential amino acids up to the target requirements for rats. Faecal wet and dry weight were increased in rats fed on LMU, LMPS and LMR diets compared to those obtained from the control diet based on lactalbumin (milk protein) LACT. The higher faecal weight was largely due to water content. The higher faecal N excretion observed in LMU, LMFS, LPAND, LPAD, BUSOL, BUDI and LMR compared to that of LACT diet was significantly lower and thus which was assumed not to be due to a decrease in the digestibility of the dietary protein, which was over 90% as compared to that in the control group. Analysis suggested that an increase in endogenous N excretion is involved in the rise of its excretion in the faeces, and indicates a long-term effect of this seed as a protein and or fibre source in monogastrics.     

Chemical Composition,Amino Acid Content and Protein Quality of the Little-Known Legume Bauhinia purpurea L

Some nutritional and antinutritional characteristics and biological value of Bauhinia purpurea L seeds were studied. The mature seeds contained (g kg^-1 as is) 271·7 crude protein, 58·7 crude fibre, 124·5 crude fat, 29·3 ash and 515·3 carbohydrates. Potassium, phosphorus and iron occurred in higher concentrations when compared with commonly consumed legumes. The globulins and albumins together constituted major storage proteins (82% total protein). The essential amino acid profile of total seed proteins compared well with the FAO/WHO reference pattern except for a deficiency of sulphur-containing amino acids and tryptophan. When compared with the globulins, the albumins appeared to be a rich source of cystine, methionine, threonine, lysine and tryptophan. Seed lipids contained high levels of the unsaturated fatty acids, oleic and linoleic, which accounted for 62·6% of total fatty acids recovered. Both dry heating and autoclaving significantly reduced the antinutritional compounds. The in vitro protein digestibilities of raw, dry-heated and autoclaved seeds were 59·5, 72·3 and 78·7%, respectively. True digestibility and net protein utilisation were significantly higher in processed seed samples compared with raw seeds. Regarding utilisable protein, autoclaved samples exhibited relatively higher values than raw seeds. © 1997 SCI.     

Isolation and characterisation of four trypsin-chymotrypsin inhibitors from lentil seeds

Twenty-three proteinase inhibitors were isolated from Syrian local small lentils (Lens culinaris) by ammonium sulphate fractionation of the acidic extract followed by affinity chromatography on anhydrotrypsin-Sepharose. They all inhibited human and bovine trypsin and chymotrypsin. Three inhibitors (LCI-11·7, -3·3 and -4·6) were separated and purified to homogeneity by anion exchange chromatography and preparative isoelectric focusing (IEF) with immobilised pH gradients; a fourth (LCI-2·2) required additional reversed-phase high-pressure liquid chromatography. The four inhibitors were similar in their amino acid composition, with high cystine and aspartic acid/asparagine content, and lack of free sulphydryl groups, methionine and tryptophan. The calculated minimum number of amino acid residues per molecule, the calculated molecular masses confirmed by gel liquid chromatography, gel-permeation high-pressure liquid chromatography and sodium-dodecylsulphate polyacrylamide gel electrophoresis, and the isoelectric points determined by IEF (immobilised pH gradients and carrier ampholytes) were 84, 77, 68 and 60 residues per molecule, 9200, 8500, 7200 and 6750, and 5·26, 5·88, 6·80 and 7·80 for LCI-1·7, -2·2, -3·3 and -4·6, respectively. All four inhibitors inhibited human trypsin less than bovine trypsin, and human chymotrypsin more than the bovine enzyme. All these properties are in accordance with the classification of the four lentil inhibitors as members of the Bowman-Birk proteinase inhibitor family. © 1998 Society of Chemical Industry.     

电位法测定罐头食品中的氯化钠

<正> 氯化钠是食品加工中最常用的辅助材料,也是人体生理过程中不可缺少的物质。在出口罐头食品中,常常需要测定某些肉类、禽蛋类和蔬菜类的氯化钠含量。最常用的测定方法有Mohr法和volhard法,电位滴定法和盐分测定仪法。下表列出几种测定方法的优缺点比较:     

Effect of pH and Ionic Strength on the Heat Stability of Rapeseed 12S Globulin (Cruciferin) by the ANS Fluorescence Method

The heat stability of rapeseed 12S globulin (cruciferin) was examined using 8-anilinonaphthalene-1-sulphonic acid (ANS) as a fluorescence probe. Heating cruciferin (0·06–0·3 mg ml⁻¹ in 10 mM glycyl–glycyl piperizine buffer, pH 7·0, with 0·1–1·0 M NaCl) for 20 min increased its hydrophobicity as monitored by ANS fluorescence measurements. The mid-point temperature for the heat effect (T_m) increased linearly with increasing solvent pH (T_m (°C)=4·16 pH+41 (μ=0.1)) or sodium chloride concentration (T_m (°C)=14·7 [NaCl]+71 (pH=7·0)). The range of T_m values for cruciferin was 45–96°C. At 20°C cruciferin was unstable at pH<3·0 but relatively stable under alkaline conditions (pH 8–10). Though possessing an oligomeric structure, cruciferin appears to heat denature in accordance with the two-stage deactivation model for simple globular proteins.     

Chitosan inhibits growth of spoilage micro-organisms in chilled pork products

The aim of this study was to develop novel preservation systems for chilled, comminuted pork products that are sold raw using the natural compound chitosan (polymeric ß -1,4- N -acetylglucosamine). In vitro testing showed that viable numbers of Saccharomycodes ludwigii were reduced by up to 4 log cfu ml⁻¹ on exposure to 0·05% chitosan in 0·9% saline at pH 6·2. Higher concentrations of chitosan (0·25 and 0·5%) were required to achieve similar levels of inactivation withLactobacillus viridescens, Lac. sake and Listeria innocua. Torulaspora delbrueckii and Salmonella enteritidis PT4 were resistant to chitosan at the concentrations tested in this study (up to 0·5%). Trials in real foods showed that dipping of standard and skinless pork sausages in chitosan solutions (1·0%) reduced the native microflora (total viable counts, yeasts and moulds, and lactic acid bacteria) by approximately 1–3 log cfu g⁻¹ for 18 days at 7°C. Chitosan treatment increased the shelf-life of chilled skinless sausages from 7 to 15 days. Addition of 0·3 and 0·6% chitosan to an unseasoned minced pork mixture reduced total viable counts, yeasts and moulds, and lactic acid bacteria by up to 3 log cfu g⁻¹ for 18 days at 4°C compared with the untreated control. The results indicated that chitosan was an effective inhibitor of microbial growth in chilled comminuted pork products.     

Decomposition of betacyanins and betaxanthins by heat and pH changes

Authors investigated the decomposition of the main beetroot colourings betanin and vulgaxanthin I as a function of temperature and pH value in acetate and citrate buffer solutions, in a temperature-range between 60 °C and 80 °C and pH range of 3.3–6.2. The temperature dependence of betain decomposition is characterized by a Q₁₀ value of 2.23 ± 0.45, and the reaction rate was doubled by reducing the pH value from 6.2 to 3.3 independent from the type of acid used. Also the interaction between temperature and pH value on colour decomposition was verified. Investigations were carried out at low oxygen content, and under this conditions the reaction was exactly described - considering the time interval of 20 min - by a linear function at 60 °C, pH value 3.3–6.2 and by an exponential function at 70 °C and 80 °C and pH 3.3–4.65. Activation energy for betain degradation is 77.5 ± 6.76 kJ/mol.     

Effect of pH and temperature on the thermostability of prickly pear (Opuntia ficus‐indica) yellow‐orange pigments

The colour stability of the yellow‐orange pigment (λ_max = 476 nm) of prickly pear (Opuntia ficus‐indica) fruit was determined as a function of temperature and pH. The experiments were carried out at three different temperatures (50, 70 and 90°C) with pigment solutions at pH values ranging from 2–7. The degree of pigment retention decreased with increasing temperature as a function of increasing thermal exposure time with least pigment degradation at pH 5. The reaction rate constants were determined as 0.0062, 0.0383 and 0.1102 min^–1 for a thermal degradation reaction rate of pseudo‐first order. The activation energy was calculated as 65.1 kJ·mol^–1.     

Stability of fructooligosaccharides,sugars and colour of yacon (Smallanthus sonchifolius) roots during blanching and drying

Yacon (Smallanthus sonchifolius) root is an important source of fructooligosaccharides (FOS). This study evaluated the influence of the blanching and drying processes on the sugars, FOS and colour of the obtained flour. Blanching in boiling water of 5 mm slices for 6 min allowed to inactivate 95% of polyphenol oxidase and peroxidase activity. Blanching solutions containing ascorbic, citric and lactic acid were detrimental in terms of FOS retention (68.2–87.4%) due to hydrolysis mainly of GF3, GF4 and GF5 FOS, and also important losses of reducing sugars (RS) were observed (69.5–87.4% retention). Blanching treatments that included ascorbic acid/CaCl₂ prevented RS and FOS losses and improved colour of the obtained flour. The drying tested temperatures of 50–80 °C did not affect the RS retention and FOS losses associated to hydrolysis and the use of 80 °C rapidly reduced the water content and minimised browning reactions yielding flours with excellent colour characteristics with high FOS content that can be derived to the elaboration of prebiotic containing functional foods or for the extraction and purification of FOS.