Furan formation in starch-based model systems containing carbohydrates in combination with proteins,ascorbic acid and lipids

Formation of the “possibly carcinogenic” furan during thermal treatment of a starch-based model food system containing selected sugars alone and in the presence of proteins, ascorbic acid and lipids, respectively, was investigated. The results showed that in starch gels containing various sugars significantly more furan was formed at pH 6 than at pH 4. Moreover, addition of whey proteins enhanced the generation of furan considerably at both pH values tested. In acidic conditions, no significant difference was observed between the amounts of furan found in a starch–carbohydrate–ascorbic acid model system and those formed in a starch-based samples containing only ascorbic acid. Addition of fresh lipids did not affect furan formation. However, when oxidised soybean oil was applied, the generated amounts of furan were higher than expected from the sum of furan found in the separate starch–carbohydrate and starch–lipid samples. Interestingly, the most efficient carbohydrate in furan generation, among the sugars tested, at pH 6, was lactose, especially when heated in the presence of proteins. This is the first report on the generation of furan from lactose.     

Concurrent dyeing and finishing of cotton with natural colour and citric acid in the presence of NaH2PO4 as catalyst under thermal treatment

Cotton fabric was simultaneously modified and dyed with citric acid and Camellia sinensis, and citric acid and Punica granatum in the presence of sodium di‐hydrogen phosphate (NaH₂PO₄) as the catalyst using a pad–dry–cure technique. Treatment with 10% citric acid, 15% NaH₂PO₄ and any of the above‐mentioned dyes at 100% wet pick‐up, followed by drying at 95°C for 5 min and curing of the dried fabric at 140°C for 5 min produced most balanced improvements in respect of the depth of shade, wrinkle recovery and colour fastness to light, wash and rubbing with retention of more than 70% of the original strength. Infrared analysis of the dyed cotton fabric indicated that the treatment of cotton with citric acid and either Camellia sinensis or Punica granatum under the influence of an esterification catalyst led to the esterification of carboxyl groups of citric acid and of hydroxyl groups of cotton cellulose and with that of both the dyes. The said process also led to some degree of cross‐linking of polymeric chains of cotton.     

Lactulose production from lactose by recombinant cellobiose 2‐epimerase in permeabilised Escherichia coli cells

Caldicellulosiruptor saccharolyticus cellobiose 2‐epimerase (CsCE) catalyses the single substrate lactose into lactulose and is the most efficient enzyme ever found for the enzymatic synthesis of lactulose. Ethanol‐permeabilised Escherichia coli cells containing CsCE were used as biocatalysts for lactulose production. The reaction conditions for maximum lactulose production were optimised to be 600 g L^?1 lactose, pH 7.5, 80 °C and 12.5 U mL^?1 of whole‐cell biocatalyst. After incubated at Na₂HPO₄–NaH₂PO₄ buffer for 2 h, approximately 390.59 g L^?1 lactulose was obtained with a conversion yield of 65.1%. The lowest production and conversion yield of epilactose were also found in Na₂HPO₄–NaH₂PO₄ buffer with a final concentration of 11.7 g L^?1 and a conversion yield <2%. The results represent a promising technology to attain high production and conversion yield of lactulose with a high purity on industrial scale.     

Formation of glucose and fructose acetates during maturation and ageing of balsamic vinegars

We report for the first time the detection of glucose acetates in balsamic vinegars. It is well known that during traditional balsamic vinegar (TBV) ageing several modifications occur. In this paper it was experimentally determined that some modifications take also place during the short maturation time of balsamic vinegar of Modena (BVM), with an increase of the esters content due to the reaction between acetic acid and sugars, in particular glucose. The formation of esters was observed both on reference solutions containing glucose and acetic acid, subjected to an accelerated ageing by heating at 50 °C, and on real balsamic vinegar samples. Glucose esters were mainly detected as α- and β-glucopyranose acetates. The formation of fructose acetates in reference solutions, was also studied, recording a more complex pattern of products. The structures of the esters were determined by GC/MS analyses and NMR spectroscopy.     

Factors influencing quantities of sugars and organic acids in blackcurrant concentrates

 Use of endogenous non-volatile flavour components, i. e. sugars and organic acids, in fruit juice products is desirable. A study of 133 blackcurrant concentrates from three seasons examined variation in sugars and acids arising from storage of fruit at freezing or sub-ambient temperature, seasonal differences, geographical origin and choice of conventional thermal-evaporative or freeze concentration technology. Compared with freeze concentrates, conventional concentrates had significantly higher contents of total sugars and acids, notably malic acid, and higher fructose/glucose, lower malic/citric acid and similar sugar/acid ratios. Concentrates from frozen fruit generally had smaller amounts of fructose, total sugars and fructose/glucose ratios than those from fresh fruit, as well as less citric, ascorbic and total acids and lower sugar/acid ratios. Principal component analysis of 40 randomly chosen concentrates showed that variance is dominated by differences in fructose, total sugars and ascorbic acid contents and sugar/acid ratios. Geographical origin and concentration technology were major sources of variance but changes in post-production sub-ambient storage could not be excluded. Received: 4 July 1997 /  Revised version: 14 October 1997     

Effect of ionizing radiation on furan formation in fresh-cut fruits and vegetables

ABSTRACT:  Furan, a possible carcinogen, is commonly induced by thermal processing in a wide variety of foods. The possible formation of furan from fresh-cut fruits and vegetables due to irradiation was studied. Nineteen fresh-cut fruits and vegetables were irradiated by 5 kGy gamma rays at 4 °C. Furan was analyzed from the irradiated samples using a number of preparation methods. The results showed that almost all tested fruits and vegetables, upon irradiation, produced nondetectable levels, or less than 1 ng/g of furan. Irradiation induced low ng/g levels of furan only in grape and pineapple. Dipping apple slices into calcium ascorbate before irradiation did not increase furan formation. The pH and the amount of simple sugars in fresh fruits and vegetables had a role in furan formation. Low levels of furan were induced by irradiation only in those fruits that had a high amount of simple sugars and low pH.     

Quantifying the spoilage and shelf-life of yoghurt with fruits

The aim of the present study was to develop a predictive model to quantify the spoilage of yoghurt with fruits. Product samples were stored at various temperatures (5-20 °C). Samples were subjected to microbiological (total viable counts, lactic acid bacteria-LAB, yeasts and moulds) and physico-chemical analysis (pH, titratable acidity and sugars). LAB was the dominant micro-flora. Yeasts population increased at all temperatures but a delay was observed during the first days of storage. Titratable acidity and pH remained almost constant at low temperatures (5 and 10 °C). However, at higher temperatures (>10 °C), an increase in titratable acidity and reduction in pH was observed. Sugar concentration (fructose, lactose and glucose) decreased during storage. A mathematical model was developed for shelf-life determination of the product. It was successfully validated at a temperature (17 °C) not used during model development. The results showed that shelf-life of this product could not be established based only on microbiological data and use of other parameters such as sensory or/and physico-chemical analysis is required. Shelf-life determination by spoilage tests is time-consuming and the need for new rapid techniques has been raised. The developed model could help dairy industries to establish shelf-life predictions on yoghurt with fruits stored under constant temperature conditions.     

The use of malolactic Oenococcus oeni (ATCC 39401) for deacidification of media containing glucose, malic acid and citric acid

 Malolactic fermentation is widely used to reduce the acidity of grape juices in wine production. However, application of the same technology to the production of wine from berries of the northern regions is not straightforward. Unlike grapes, these berries are rich in citric and malic acid while the sugar content is low. An ideal deacidification process for the northern berries would be the microbial degradation of these acids with minimal loss of sugars. Therefore, the co-metabolism of citric acid and glucose was studied under different conditions of malic acid degradation by Oenococcus oeni. At low pH values (pH <4.5) degradation of malic acid always proceeded first to completion with practically no consumption of glucose or citric acid. After the exhaustion of malic acid the degradation of both citric acid and glucose were initiated simultaneously. Following the exhaustion of malic acid and citric acid the remaining glucose remained nonfermentable. Thus, it is concluded that, by maintaining the culture in a resting state by the control of pH, selective degradation of acids can be achieved without subsequent loss of glucose. Received: 20 January 2000     

Production and stability of chlorine dioxide in organic acid solutions as affected by pH, type of acid, and concentration of sodium chlorite, and its effectiveness in inactivating Bacillus cereus spores

We studied the production and stability of chlorine dioxide (ClO₂) in organic acid solutions and its effectiveness in killing Bacillus cereus spores. Sodium chlorite (5000, 10,000, or 50,000 μg/ml) was added to 5% acetic, citric, or lactic acid solution, adjusted to pH 3.0, 4.0, 5.0, or 6.0, and held at 21 °C for up to 14 days. The amount of ClO₂ produced was higher as the concentration of sodium chlorite was increased and as the pH of the acid solutions was decreased. However, the stability in production of ClO₂ was enhanced by increasing the pH of the organic acid solutions. To evaluate the lethal activity of ClO₂ produced in various acid solutions as affected by acidulant and pH, suspensions of B. cereus spores were treated at 21 °C for 1, 3, 5, or 10 min in hydrochloric acid or organic acid solutions (pH 3.0, 4.0, 5.0, or 6.0) containing ClO₂ at concentrations of 100, 50, or 25 μg/ml. Populations of viable spores treated with ClO₂ at concentrations of 100 or 50 μg/ml in organic acid solutions decreased more rapidly than populations treated with the same concentrations of ClO₂ in HCl. Rates of inactivation tended to increase with higher pH of ClO₂ solutions. Results show that ClO₂ formed in organic acid solutions has higher stability and is more lethal to B. cereus spores than ClO₂ formed at the same concentration in HCl solution. This finding emphasizes the benefits of using organic acid solutions to prepare ClO₂ intended for use as an antimicrobial.     

Effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers and formation of melanoidins as result of the Maillard reaction

This study investigates the effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers, can influence the formation of melanoidins as result of the Maillard reaction. Remarkable enolization reaction of sugars was observed in the course of the Maillard reaction. Especially, the degree of sugar enolization was increased as the pH levels increased, which was higher in fructose than glucose systems. Otherwise, enolization of sugars on heating with amino acid was higher in glucose than fructose systems. Formation of isomer in Glc/d-Lys, Fru/d-Asn and Fru/d-Lys were increased upon increase of pH levels. The relative amounts of isomers in Glc/l-Asn and Glc/d-Asn were decreased upon increase of pH levels. Browning development was dependent on the pH levels, being more significant for model systems apart from heated glucose solution alone. Browning development of fructose systems was higher than glucose-amino acid systems. The l- and d-isomers both showed different absorption in the UV–vis spectra and that these occur at similar shape. Every peak has a stable absorbance appeared in the range between 260 and 320 nm, characteristic of melanoidins.     

Effect of heat treatment,pH, sugar concentration,and metal ion addition on green color retention in homogenized puree of Thompson seedless grape

Homogenized puree of Thompson seedless (Vitis vinifera ‘Thompson Seedless’) grape was treated under different conditions, including heating time (5–30 min), temperature (20–80 °C) and pH (2–10). Treatments with separate additions of glucose, fructose, and sucrose at concentrations of 100–600 g/L and salts of MgCl₂, ZnCl₂, GuSO₄, and KCl at concentration of 1 g/L were also tested at 20 °C up to 30 min. Relative chlorophyll pigment retention (CR) was measured at 664 nm. The chlorophyll pigments were the most stable at 20 °C and the nature pH of grape puree (pH 3.4). Increasing temperature and changing pH reduced CR. After 30 min treatment at 80 °C, CR decreased to lower than 20% and 50% at pH 2 and 5, separately. Increasing fructose and sucrose concentrations reduced CR at pH 3, but increased it at most levels at pH 4. Increasing glucose concentration protected chlorophyll pigment from reduction in some cases at pH 3 and 4. CR increased with addition of metal ions increased at pH 4, but decreased at pH 3. Conditions of 23.3 °C, pH 4.5, and 120 g/kg fructose and 210 g/kg glucose produced the highest CR value.     

Influence of calcium and phosphorus, lactose, and salt-to-moisture ratio on Cheddar cheese quality: changes in residual sugars and water-soluble organic acids during ripening

Cheddar cheese ripening involves the conversion of lactose to glucose and galactose or galactose-6-phosphate by starter and nonstarter lactic acid bacteria. Under ideal conditions (i.e., where bacteria grow under no stress of pH, water activity, and salt), these sugars are mainly converted to lactic acid. However, during ripening of cheese, survival and growth of bacteria occurs under the stressed condition of low pH, low water activity, and high salt content. This forces bacteria to use alternate biochemical pathways resulting in production of other organic acids. The objective of this study was to determine if the level and type of organic acids produced during ripening was influenced by calcium (Ca) and phosphorus (P), residual lactose, and salt-to-moisture ratio (S/M) of cheese. Eight cheeses with 2 levels of Ca and P (0.67 and 0.47% vs. 0.53 and 0.39%, respectively), lactose at pressing (2.4 vs. 0.78%), and S/M (6.4 vs. 4.8%) were manufactured. The cheeses were analyzed for organic acids (citric, orotic, pyruvic, lactic, formic, uric, acetic, propanoic, and butyric acids) and residual sugars (lactose, galactose) during 48 wk of ripening using an HPLC-based method. Different factors influenced changes in concentration of residual sugars and organic acids during ripening and are discussed in detail. Our results indicated that the largest decrease in lactose and the largest increase in lactic acid occurred between salting and d 1 of ripening. It was interesting to observe that although the lactose content in cheese was influenced by several factors (Ca and P, residual lactose, and S/M), the concentration of lactic acid was influenced only by S/M. More lactic acid was produced in low S/M treatments compared with high S/M treatments. Although surprising for Cheddar cheese, a substantial amount (0.2 to 0.4%) of galactose was observed throughout ripening in all treatments. Minor changes in the levels of citric, uric, butyric, and propanoic acids were observed during early ripening, whereas during later ripening, a substantial increase was observed. A gradual decrease in orotic acid and a gradual increase in pyruvic acid content of the cheeses were observed during 12 mo of ripening. In contrast, acetic acid did not show a particular trend, indicating its role as an intermediate in a biochemical pathway, rather than a final product.     

Furan formation during UV-treatment of fruit juices

Furan is a suspected human carcinogen and reported to be produced by thermal or ultraviolet light (UV-C) treatment of various foods, such as fruit juices and sugar solutions. This study explores the formation of furan during UV-treatment of high fructose corn syrup (HFCS) solution and simulated juices containing it and validates the results with two real juices, apple juice and apple cider. Studies performed on individual components of fruit juices revealed fructose to be the main constituent in fruit juices that is responsible for furan formation during UV-treatment. Furan formation was promoted at acidic pH, yet was suppressed in the presence of ascorbic acid. Furan synthesis is strongly influenced by absorbance of the treated solution, with increasing absorption coefficient leading to reduced furan formation. Formation of furan in fruit juices sweetened with HFCS when subjected to UV-treatment has been firmly established.     

Model studies for wheat sourdough systems using gluten,lactate buffer and sodium chloride

Model studies were conducted in order to study the influence of acid and NaCl, as occurring in wheat sourdough bread, on fundamental rheological properties of wheat gluten. Gluten was divided into pieces and subjected to a swelling period in lactate buffer of pH 3.9, with or without added NaCl (3 g/100 ml). The respective controls were unbuffered NaCl solution and pure water. The microstructure of the gluten pieces was studied by laser-scanning confocal microscopy and the recombined pieces were examined using fundamental rheology. The combination of buffer (pH 3.9) and NaCl in comparison to unbuffered NaCl solution caused a denser, but partially dissolved fibrillar microstructure. Further to this, swelling of the gluten was reduced (62.0% versus 65.9% moisture) and an increase in firmness and elasticity was observed: in comparison with unbuffered NaCl solution, the absolute value of the complex dynamic modulus (|G*|) was higher, while the phase angle was lower in dynamic oscillatory measurements at 30 °C and dynamic temperature sweeps (30–95 °C), while in creep tests at 30 °C and 95 °C strain values were lower and relative recovery higher. In contrast, pH 3.9 buffer without added NaCl caused softer rheological behaviour than water and a film-like microstructure.     

Effects of high hydrostatic pressure and high-temperature short-time on mango nectars: Changes in microorganisms,acid invertase, 5-hydroxymethylfurfural,sugars, viscosity,and cloud

High hydrostatic pressure (HHP, 600 MPa/1 min) and high-temperature short-time (HTST, 110 °C/8.6 s) treatments of mango nectars were comparatively evaluated by examining their effects on natural microorganisms, acid invertase, 5-hydroxymethylfurfural (HMF), sugars, pH, titratable acid (TA), viscosity, and cloud, immediately after treatments and during 16-week storage at 4 and 25 °C. At both stages of the experiment, the counts of yeast and mold in treated mango nectars were less than 1.00 log₁₀CFU/mL, while total aerobic bacteria were less than 1.70 log₁₀CFU/mL. Both HHP and HTST treatments caused a significant decrease in fructose, glucose and total sugar, as well as a significant increase in HMF and cloud of mango nectars, while changes in sucrose, pH, and TA were insignificant. During the 16-week storage, however, fructose, glucose, TA and HMF increased, while sucrose, total sugar, pH and cloud decreased significantly. The kinetic data of changes in sucrose, fructose and glucose fitted well into a combined model. The activity of acid invertase was reduced by 91.4% in HTST-treated mango nectars and, increased by 8.57% after HHP treatment. In both cases, these levels remained stable during storage. There was no significant change in the viscosity of mango nectars after HHP treatment, while a significant increase after HTST treatment. Both HHP- and HTST-treated mango nectars showed a gradual decrease in the viscosity during storage.Industrial relevanceMango (Mangifera indica L.) is one of the important tropical fruits, and its processed products are of high commercial and economic importance. This work presents a comparison on HHP- and HTST-treated mango nectars after processing and during storage, on natural microorganisms, acid invertase, 5-hydroxymethylfurfural, sugars, pH, titratable acid, viscosity, and cloud. The available data would provide technical support for the evaluation and application of HHP or HTST in the mango nectar industry, and also for the establishment of criteria for commercial production of high quality mango nectars with safety requirements.     

The use of buffered acidulant systems to improve the microbiological stability of acid foods

The inhibition of the growth of micro-organisms depends not only on the pH of the substrate but also on the kind of acidulant used to adjust the pH, its dissociation constant pKa and its concentration. Yarrowia lipolytica, isolated from a spoiled shrimp salad, is killed by 1% acetic acid in brain heart infusion broth (BHI) buffered to pH 4·5 with NaOH, while growth is observed in unbuffered BHI adjusted to pH 4·5. Lactobacillus brevis, isolated from a tartar sauce, on the contrary, is only slightly inhibited in 1% buffered acetic acid (pH 4·5) compared with the growth in the unbuffered medium (pH 4·5). There is no inhibitory effect of 1% buffered citric acid (pH 4·5) on the growth of Y. lipolytica and L. brevis. Compared with the growth in unbuffered lactic acid containing BHI, 1% buffered lactic acid (pH 4·5) clearly has an inhibitory, but not a lethal effect on L. brevis; it has, however, no inhibitory effect on Y. lipolytica.Industrial salads containing approximately 1% acetic acid and 1% lactic acid in the aqueous phase and buffered to pH 4·85–4·95 showed to have a greater microbiological stability than the unbuffered salads.     

Acid tolerance in Salmonella typhimurium induced by culturing in the presence of organic acids at different growth temperatures

The influence of growth temperature and acidification of the culture medium up to pH 4.25 with acetic, citric, lactic and hydrochloric acids on the growth and subsequent acid resistance at pH 3.0 of Salmonella typhimurium CECT 443 was studied. The minimum pH value which allowed for S. typhimurium growth within the temperature range of 25–37 °C was 4.5 when the pH was reduced using citric and hydrochloric acids, and 5.4 and 6.4 when lactic acid and acetic acid were used, respectively. At high (45 °C) or low (10 °C) temperatures, the growth pH boundary was increased about 1 pH unit. The growth temperature markedly modified the acid resistance of the resulting cells. In all cases, D-values were lower for cells grown at 10 °C and significantly increased with increasing growth temperature up to 37 °C, at which D-values obtained were up to 10 times higher. Cells grown at 45 °C showed D-values similar to those found for cells grown at 25 °C. The growth of cells in acidified media, regardless of the pH value, caused an increase in their acid resistance at the four incubation temperatures, although the magnitude of the Acid Tolerance Response (ATR) observed depended on the growth temperature. Acid adapted cultures at 10 °C showed D-values ranging from 5.75 to 6.91 min, which turned out to be about 2 times higher than those corresponding to non-acid adapted cultures, while higher temperatures induced an increase in D-values of at least 3.5 times. Another finding was that, while at 10 and 45 °C no significant differences among the effect of the different acids tested in inducing an ATR were observed, when cells were grown at 25 and 37 °C citric acid generally turned out to be the acid which induced the strongest ATR. Results obtained in this study show that growth temperature is an important factor affecting S. typhimurium acid resistance and could contribute to find new strategies based on intelligent combinations of hurdles, which could prevent the development or survival of Salmonella spp. in foods. The fact that moderately low temperatures (10 °C) markedly decrease the acid resistance and increase the growth pH boundary of S. typhimurium suggests the convenience to control the temperature during food processing as a strategy to prevent the growth and survival of this pathogenic microorganism.     

Comparison of NIR and MIR spectroscopic methods for determination of individual sugars,organic acids and carotenoids in passion fruit

In this work, NIR and MIR spectroscopy was investigated and compared for predicting passion fruit ripening parameters as sugars, organic acids and carotenoids. Spectra of 56 samples of the lyophilized passion fruit were collected using an integrating sphere in NIR range and attenuated total reflectance accessory in MIR range. Individual sugars (sucrose, glucose and fructose), organic acids (malic and citric acids) and carotenoids (β-carotene) contents were determined by reference methods. Spectral and reference data were analyzed by principal component analysis. Partial least square regression (PLSR) was used to establish calibration models. MIR technique was better than the NIR technique for glucose (R²_v = 0.942), fructose (R²_v = 0.855), sucrose (R²_v = 0.818), total sugar (R²_v = 0.914) and citric acid (R²_v = 0.913) content determination. On the other hand, NIR was superior for total acids (R²_v = 0.903) content determination. For malic acid and β-carotene contents both methods were unsatisfactory due to low concentrations of these constituents in the passion fruits.     

Influences of Operating Parameters on the Formation of Furan During Heating Based on Models of Polyunsaturated Fatty Acids

Furan, a possible carcinogen, is commonly produced by thermal processing in a number of heated foods. The existence of furan levels in foods has attracted considerable attention worldwide. Recent research of furan in food has focused on the possible influences of operating parameters on the furan formation during heat processing. The aim of our study was to investigate the impacts of multiple factors (pH, temperature, heating time, ferric, and glutamic acid) on furan formation using linolenic and linoleic acids‐based model systems in which furan was analyzed by headspace gas chromatography–mass spectrometry (HS‐GC–MS). The results revealed that the content of furan increased rapidly when the heating temperature was elevated, with the highest levels of furan in neutral buffer solutions, the furan levels were also found to be related to heating time in all model systems. Ferric promoted furan formation from polyunsaturated fatty acids, conversely glutamic acid with an optimum concentration suppressed the furan formation. The minimal level of furan in foods during thermal treatment could be achieved via adding furan formation suppressors, and/or avoidance of furan forming promoter.     

Nonenzymatic Browning in Liquid Model Systems of High Water Activity: Kinetics of Color Changes due to Maillard's Reaction Between Different Single Sugars and Glycine and Comparison with Caramelization Browning

Sugar- (fructose, xylose, glucose, lactose, maltose, sucrose) glycine solutions of water activity adjusted to 0.90 (by adding NaCI) were heated at 45–65°C. The behavior of fructose-glycine solutions was well described by a zero-order reaction model, but for the other sugars a fractional-order (～ 0.5) kinetic model was necessary. Activation energies for glucose, fructose and sucrose systems were 25.7, 29.3 and 36.6 kcah/mole, respectively. At pH 6 the descending order for color development was xylose > glucose > fructose > lactose > maltose > sucrose; at pH lower than 6 fructose browned faster than glucose. The role of hydrolysis of sucrose as related to Maillard's browning of heated sucrose-glycine solutions was studied. Caramelization browning seemed to contribute noticeably to total color development only in fructose-glycine solutions.