Proof-of-concept study of a whey protein isolate based carbon dioxide indicator to measure the shelf-life of packaged foods

A whey protein isolate (WPI) based carbon dioxide (CO₂) indicator was studied under different CO₂ conditions. WPI based CO₂ indicators were prepared and incubated in a CO₂ filled chamber in order to investigate the CO₂ dependent transition behavior in visual appearance. Transparency of the WPI based CO₂ indicator with 0.1% WPI changed from 91.8% to 24.6%. An indicator with 0.3% WPI changed from 73.7% to 7.7%. The change in visual appearance at the transition point was definite. The indicator showed an irreversible visual change due to the hysteresis behavior of the indicator. Desorption of CO₂ did not restore the transparency. The CO₂ dependent visual transition point was controlled by adding different concentrations of NaCl to the indicators. A WPI based CO₂ indicator has potential for application as a CO₂ dependent spoilage and over-ripeness indicator for a variety of foods.     

Kinetic Study of the Radical Scavenging of Capsaicin in Homogeneous Solutions and Aqueous Triton X‐100 Micellar Suspensions

A kinetic study of capsaicin (CAP) toward radicals has been performed using stopped‐flow spectrophotometry in detail. The second‐order rate constants (k₂) for the reaction of CAP toward 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and galvinoxyl have been measured in methanol, ethanol, 2‐propanol/water (5:1, v/v), and aqueous micellar suspensions containing 5% Triton X‐100 (pH 4.0 to 10.0), respectively. The decay rates of DPPH and galvinoxyl for the reaction with CAP increased linearly in a concentration‐dependent manner in homogeneous solutions and aqueous micellar suspensions. However, the k₂ for CAP obtained in an aqueous micellar suspension showed notable pH dependence; that is, the reactivity of CAP increased with an increasing pH value from 4 to 10. In addition, a good correlation between the k₂ value and the molar fraction of CAP (phenolate anion (CAP‐O^?)/undeprotonated form (CAP‐OH)) was observed. These properties are associated with the pKa of CAP. Furthermore, it was found that the CAP‐O^? reacts with galvinoxyl about 6 times as fast as the CAP‐OH. These results indicate that sequential proton loss electron transfer from the phenolic hydrogen of CAP may be responsible for the scavenging of radicals in an aqueous micellar suspensions.     

A dissolving CO2 headspace combined with organic acids prolongs the shelf-life of fresh pork

The aim of this paper was to evaluate the effect of a novel CO₂ packaging method in combination with organic acids on the microbial growth in fresh pork meat. Fresh pork fillet was packed with a small amount of 100% CO₂ (initial gas/product ratio 0.2/1.0) and a brine solution containing citric acid (3% w/w, pH 5), acetic acid (1% w/w, pH 5) or a combination of both. Microbial counts and composition in the product were determined. CO₂, citric acid and acetic acid each reduced total growth after four weeks of storage and delayed the onset of microbial growth. Combinations of treatments increased the effects and microbial growth in samples packed with a combination of CO₂ and both acids was negligible even after 35 days. However, the addition of citric acid to the packages led to significant precipitation in the brine. Analysis of the bacterial flora showed that lactic-acid bacteria dominated the flora in samples packed with CO₂ while vacuum-packed samples contained high numbers of Pseudomonas sp. and yeast. As all CO₂ dissolved in the product within hours after packaging, the outer appearance of the package was that of a vacuum-package. As a result, this novel packaging method combined the advantages of modified atmosphere packaging (antimicrobial effect of CO₂) and vacuum packaging (low space requirement).     

Chitosan-limonene coating in combination with modified atmosphere packaging preserve postharvest quality of cucumber during storage

Since cucumbers suffer from a short postharvest life, applying different technologies is increasingly used as effective ways to increase their shelf life and quality. In this study a combination of chitosan-limonene coating and MAP storage has been used as a postharvest treatment to maintain cucumber quality. Samples were stored in three different packages: A (21% O₂, macro-perforated package to be in equilibrium with air); package B (active MAP, starting concentrations 10% O₂?+?5% CO₂); package C (passive MAP starting concentrations 21% O₂?+?0.1% CO₂); they were stored at three temperatures (20, 10, and 4 °C). Quality parameters of cucumber such as weight loss, firmness, color, pH, fungal growth, T_g, organoleptic properties were determined. Interactive effects of coating, package, temperature, and storage time showed that coating and MAP in general had positive effects on several quality aspects. Coating combined with active MAP had the most positive effect on most postharvest attributes. However, using active MAP at higher temperature led to quality problems and is only useful if storage time is short. The combined usage of active MAP and chitosan-based coating on cucumber represents an innovative and interesting method for commercial application.     

Monitoring Technology for Gamma‐Aminobutyric acid Production in Polished Mochi Barley Grains using a Carbon Dioxide Sensor

Gamma‐aminobutyric acid (GABA) has many biological functions, including the inhibition of blood pressure increases and acceleration of growth hormone secretion. In this study, we discovered the utility of measuring the concentration of carbon dioxide (CO₂) dissolved in the reaction solution, for development of a real‐time and convenient technique to estimate GABA production. In addition to mochi barley bran, we examined the polished grains of three species: mochi barley (a variant of hulless barley), barley, and Japanese millet, all soaked in l ‐glutamic acid (l ‐Glu) solution at pH 4.5. We found a positive correlation between GABA and CO₂ concentrations, and the production of CO₂ was suppressed in the absence of l ‐Glu at pH 4.5. These results suggest that GABA content can be easily predicted by measuring the aqueous CO₂ content using a CO₂ sensor, during the process of GABA production in polished mochi barley grains and bran.     

The influence of oxygen and organic hydrogen acceotors on glycolytic dioxide production in Brettanomyces anomalus

The yeast Brettanomyces anomalus showed the Custers effect in that under strictly anaerobic conditions, in the presence of glucose, CO₂ production was negligble. CO₂ production was stimulated by mixing anaerobic cell suspensions with an aerated glucose solution in astopped-flow cell. Glycolytic CO₂ production continued even after oxygen exhaustion. Studies using an open reaction vessel showed that the rate of glycolytic CO₂ production could be increased to a maximum level by exposing the anaerobic cell suspension to brief pulses of O₂. A cell suspension CO₂ at a maximal rate demonstrated the Pasteur effect on switching the mobile gas to a mixture conatining oxygen (5.05 KPa). In contrast to glycolytic CO₂ production in vivo nicotinamide pool responded rapidly to changes in oxygen concentration. The addition of acetaldehyde, acetone, or 3-hydroxy-butan-2-one led to a temprorary production of CO₂ at an initial rate depending on the concentration of substance added according to the Michaelis–Menten equation. The maximal rates were equal with all three substances, whereas tha apparent K_m values were different. The total amount of CO₂ produced was 22-fold greater than the amount of acetaldehyde added. Added organic hydrogen acceptors modulated the intracellular reedox balance of B. anomalus under conditions. These results are discussed in relation to the current hypothesis of the Custers effect.     

The effect of hydrogen peroxide bleaching of canola meal on product colour,dry matter and protein extractability and molecular weight profile

The aim of this study was to bleach canola meal by hydrogen peroxide to understand the treatment effect on product colour, dry matter and nitrogen extractability. Meal suspensions at 2.5%, 5% and 10% (w/v) were treated in 3, 6 and 10% H₂O₂ at pH 3, 7 and 10. The bleached meal was extracted under acidic and alkaline conditions. The results showed a high bleaching effectiveness of canola meal by H₂O₂. The L* parameter was increased from 47.18 ± 0.56 up to 86.80 ± 1.05. Effect of pH was significant and the highly bleached meal was obtained at pH 10. Extractability of dry matter was increased when the meal was treated with H₂O₂, from 26.87 ± 0.10% for the control meal up to 83.20 ± 0.59% for the meal treated in 10% H₂O₂ in a 2.5% (w/v) suspension. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis showed a depolymerisation effect of H₂O₂ on the high molecular weight proteins.     

Calcium and chitosan-mediated clustering of whey protein particles for tuning their colloidal stability and flow behaviour

Whey protein microgel (WPM) particles were prepared by heating whey protein dispersions (40 mg mL⁻¹) at pH 5.8 and 80 °C for 15 min. Supplementation with 5 mm CaCl₂ at pH 6.0 increased the hydrodynamic diameter of WPMs, but did not influence the ζ-potential of the particles. The latter was attributed to clustering of WPMs by Ca²⁺ bridges. Supplementing WPM suspension with chitosan (0.5 mg mL⁻¹) at pH 5.0 caused formation of micron-sized clusters and a progressive increase in suspension viscosity over the subsequent 48 h. The latter was ascribed to development of a complexed lattice that inhibited sedimentation of WPMs. Immediately after chitosan supplementation, the WPM suspension changed from Newtonian to shear-thinning fluid. Fourier transform infra-red spectroscopy results suggested that microgelation proceeded by formation of inter-molecular β-sheets and loss of α-helix structure. It also indicated that chitosan may interact with WPMs at pH 6.0 through its acetyl groups.     

An attempt to minimize potassium sorbate concentration in sponge cakes by modified atmosphere packaging combination to prevent fungal spoilage

The combined effect of modified atmosphere packaging (MAP) and potassium sorbate (PS) on the preservation of a typical Spanish cake (sponge cake) was studied. A full factorial experiment design including other factors, such as water activity (a_w) (0.80, 0.85 and 0.90) and pH (6 and 7.5) was applied. Eurotium amstelodami, E. herbariorum, E. repens and E. rubrum colony radii were measured daily for 28 days. All different combinations of PS concentration and MAP were more effective at pH 6 than at 7.5. As a_w increased, the amount of PS or carbon dioxide (CO₂) necessary to prevent or delay fungal growth increased. The antifungal activity of PS could be improved by packaging in a suitable modified atmosphere (MA). At pH 6, 0.1% of PS effectively prevented mould spoilage upto 28 days in the entire a_w range, by combining with 50–70% CO₂ level. On the other hand, 0.2% of PS in 30% N₂:70% CO₂ MA packages prevented spoilage of neutral cake analogues at all a_w levels. Control air-packaged bags with 0.2% of PS showed visible growth after 6 days, at pH 6 and 0.90 a_w. If no MAP was used, low a_w was the main preservation factor.     

Modified atmosphere packaging of filleted rainbow trout

Shelf‐lives of filleted rainbow trout (Oncorhynchus mykiss) packaged in over‐wrap, vacuum and gas mixture conditions and stored at 1 ± 1 °C were compared by measurement of pH, total volatile bases (TVB), hypoxanthine content, lipid oxidation (TBARS value), superficial counts of aerobic psychrotrophic flora and sensory analysis (colour, odour and flavour). The gas mixtures evaluated were 10% O₂ + 50% CO₂ + 40% N₂, 10% O₂ + 50% CO₂ + 40% Ar, 20% O₂ + 50% CO₂ + 30% N₂, 20% O₂ + 50% CO₂ + 30% Ar, 30% O₂ + 50% CO₂ + 20% N₂ and 30% O₂ + 50% CO₂ + 20% Ar. Sensory quality deterioration was delayed and bacterial growth as well as increases in pH, TVB and hypoxanthine levels were reduced by modified atmosphere packaging (MAP). Lipid oxidation was higher in gas packages with 20 and 30% O₂ than in those with 10% O₂. Vacuum‐packed fillets presented the lowest TBARS values. In summary, MAP gave rise to a significant extension of shelf‐life when compared with vacuum and over‐wrap packaging. No significant differences were found between the packages containing either N₂ or Ar. The best evaluated atmosphere consisted of 10% O₂ + 50%CO₂ + 40% N₂/Ar. © 2002 Society of Chemical Industry     

Elucidation of the formation of CO2 in culinary dry products

 The formation of CO₂ in tomato powder, chosen as an example of a dry culinary product, was investigated at room temperature and at low values of water activity (a _w). CO₂ formation correlated well with parameters that represent the beginning and progression of the Maillard reaction. In the absence of O₂, CO₂ formation decreased. Pectin and depolymerized pectin did not influence CO₂ formation while galacturonic acid (GalA) had a large effect. Determination of ¹³CO₂ in low-moisture model systems revealed that CO₂ was not formed by decarboxylation of GalA alone. Only a small proportion of [1-¹³C]glycine and GalA was degraded by the Strecker pathway; however, glucose reacted with the labelled amino acid forming ¹³CO₂ which amounted to over 90% of the total CO₂ formed. Therefore, CO₂ could be used as an early indicator for the beginning of the Maillard reaction in dry culinary products. Received: 28 October 1996     

Effects of supercritical carbon dioxide on volatile formation from Maillard reaction between ribose and cysteine

BACKGROUND: Supercritical carbon dioxide (SC‐CO₂) technology is being used in an increasing number of food‐manufacturing applications; however, its effect on the Maillard reaction is not well studied. The objective of this study was to investigate the effect of SC‐CO₂ treatment (140 °C, 40 MPa) on the Maillard reaction of an aqueous ribose–cysteine model system under varying pH conditions (5.6, 7.0 and 8.0), with emphasis on the formation of volatile compounds. RESULTS: SC‐CO₂ had a suppressing effect on the browning stages of the reaction under acidic and neutral pH conditions, while it appeared to have an accelerating effect at pH 8.0. Over 70 volatile compounds were positively identified from the headspace of the model system by gas chromatography–mass spectrometry. The volatiles were dominated by sulfur‐containing compounds including thiophenes and fused bicyclic sulfur‐containing compounds under all experimental conditions. Several compounds, including 2‐methyl‐3‐furanthiol, 2‐furanmethanethiol, 3‐thiophenethiol, and 2‐methyl‐3‐thiophenethiol, and one of the intermediates, furfural, were generated in much higher amounts in the SC‐CO₂‐treated samples, especially at alkaline and neutral pH values. CONCLUSION: SC‐CO₂ treatment was inhibitory to the formation of most volatiles in the Maillard reaction, but enhanced the formation of some intermediates and well‐known meaty flavoured compounds. Copyright © 2007 Society of Chemical Industry     

Elucidation of the formation of CO2 in culinary dry products

 The formation of CO₂ in tomato powder, chosen as an example of a dry culinary product, was investigated at room temperature and at low values of water activity (a _w). CO₂ formation correlated well with parameters that represent the beginning and progression of the Maillard reaction. In the absence of O₂, CO₂ formation decreased. Pectin and depolymerized pectin did not influence CO₂ formation while galacturonic acid (GalA) had a large effect. Determination of ¹³CO₂ in low-moisture model systems revealed that CO₂ was not formed by decarboxylation of GalA alone. Only a small proportion of [1-¹³C]glycine and GalA was degraded by the Strecker pathway; however, glucose reacted with the labelled amino acid forming ¹³CO₂ which amounted to over 90% of the total CO₂ formed. Therefore, CO₂ could be used as an early indicator for the beginning of the Maillard reaction in dry culinary products. Received: 28 October 1996     

Browning Inhibition and Textural Changes of Pre-Peeled Potatoes Caused by Anaerobic Conditions

Sulphite treatment is often used for inhibition of enzymatic browning of pre-peeled potatoes. Introduction of CO₂ or N₂ gases in the immersion water was investigated as an alternative to sulphite. The samples were stored at 4 °C. Daily introduction of the gases reduced the O₂ content from approx. 8.8 mg/L (measured at 20 °C) to 0.2-1.9 mg/L during the immersion period. The CO₂ treatment inhibited the browning completely and N₂ treatment did not. It is assumed that this is due to the lower pH in the CO₂ water. When CO₂ was added only one time at the start of the experiment, it also inhibited discoloration, but the immersion water developed a weak brown colour. Both the CO₂ and the N₂ treatment induced hardening in the outer potato tuber tissue after cooking after 4-7 d of storage, as did Na₂SO₃ solutions.     

Pasting properties of Angelica dahurica starches in the presence of NaCl,Na2CO3, NaOH,glucose, fructose and sucrose

The pasting viscosities of starches from Angelica dahurica (three cultivars named Chuan Baizhi, Yu Baizhi and Qi Baizhi in Chinese, respectively), in the presence of NaCl, Na₂CO₃, NaOH, glucose, fructose and sucrose were determined with a rapid visco analyser. The pasting peak, trough or final viscosities and the pasting temperatures (Pt) of Baizhi starches increased with NaCl concentration increased from 0 to 3.0%. The peak viscosities of Baizhi starches increased at 0.2% Na₂CO₃ concentration and then decreased with Na₂CO₃ concentration up to 0.8%. The trough and final viscosities and the Pt decreased with Na₂CO₃ concentration up to 0.8%. The peak viscosities increased in 0.1%, but decreased in 0.2% NaOH concentration. The trough and final viscosities and the Pt decreased in the presence of NaOH. With the concentration of sugar (glucose, fructose and sucrose) increased from 0 to 20%, the pasting peak, trough and final viscosities of these starches increased significantly. For the same Baizhi starch, the elevation of peak viscosity was the most significant when fructose was added, and the elevation of final viscosity was the greatest when sucrose was added.     

Physical and oxidative stability of pre-emulsified oil bodies extracted from soybeans

Soybeans contain oil bodies that are coated by a layer of oleosin proteins. In nature, this protein coating protects the oil bodies from environmental stresses and might be utilised by food manufacturers for the same purpose. In this study, an aqueous extraction method was developed to increase the yield of oil bodies extracted from soybean. This method involved a two-step procedure: (i) blending, dispersion, and filtration of soybeans; (ii) homogenisation, suspension, and centrifugation of the filter cake. Using this extraction method about 65% of the oil bodies could be obtained. The mean particle diameter (d₄₃) and sedimentation of the resulting oil bodies increased during storage, suggesting they were prone to aggregation. Heat treatment (90 °C, 30 min) of the oil body suspensions immediately after extraction improved their storage stability, which was attributed to deactivation of endogenous enzymes such as lipase and lipoxygenase. Heat treatment did not adversely affect the oxidative stability of the oil body suspensions at pH 3 or 7 during storage at 37 °C. These results suggest that this aqueous extraction method can be used to prepare oil body suspensions with improved long-term stability.     

Cellulose Nanocrystal Reinforced Chitosan Coatings for Improving the Storability of Postharvest Pears Under Both Ambient and Cold Storages

Cellulose nanocrystal (CNC, 0%, 5%, and 10% w/w, in chitosan, dry basis) reinforced 2% chitosan aqueous coatings were evaluated for delaying the ripening and quality deterioration of postharvest green D'Anjou (Pyrus communis L.) and Bartlett (Pyrus communis L.) pears during 3 wk of ambient storage (20 ± 2 °C and 30 ± 2% RH) or 5 mo of cold storage (–1.1 °C and 90% RH), respectively. Ethylene and CO₂ production, color, firmness, and internal fruit quality were monitored during both storage conditions. Moisture and gas barrier, antibacterial activity, and surface morphology of the derived films were also evaluated to investigate the mechanisms of delayed fruit ripening and quality deterioration. In the ambient storage study, the 5% CNC reinforced chitosan coating significantly (P < 0.05) delayed green chlorophyll degradation of pear peels, prevented internal browning, reduced senescence scalding, and improved retained fruit firmness. During cold storage, the 5% CNC reinforced chitosan coating showed a competitive effect on delaying fruit postharvest quality deterioration compared to a commercial product (Semperfresh?, Pace International, Wapato, Wash., U.S.A.). The 5% CNC coating strongly adhered to the pear surface, provided a superior gas barrier and a more homogenous matrix in comparison with the other coatings tested. Hence, it was effective in delaying ripening and improving the storability of postharvest pears during both ambient and cold storage.     

壳聚糖基复合光催化剂及光催化纸的制备与性能研究

本研究将壳聚糖与光催化剂(实验室自制硅藻土基-N-掺杂TiO_2)复合制备壳聚糖基复合光催化剂,然后将其以一定比例与纸浆混合抄造光催化纸;采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和傅里叶变换红外光谱仪(FT-IR)等对复合光催化剂的形貌、结构及组成成分等进行了表征;利用SEM对光催化纸形态结构、催化剂分布状态等情况进行了分析,并分别对亚甲基蓝(MB)和甲醛进行了光催化降解实验。结果表明,复合光催化剂对MB和甲醛都有较好的光催化降解效果。在250 W高压汞灯照射7 h、检测波长分别为664 nm和630 nm条件下,复合光催化剂对MB的降解率达80%以上、对甲醛的降解率达49%以上;壳聚糖用量10%的复合光催化剂在纸张中的添加量20%时,光催化纸对甲醛的降解率为44%,其抗张指数从空白样的32. 4 N·m/g提升到34. 7 N·m/g,耐破指数从空白样的1. 68 kPa·m~2/g提升到2. 36 kPa·m~2/g。     

Inactivation Kinetics of Lactobacillus plantarum by High Pressure Carbon Dioxide

Inactivation kinetics of Lactobacillus plantarum by high pressure CO₂ was investigated to understand the mechanism of microbial inactivation. The inactivation rates increased with pressure, temperature and exposure time, and with decreasing pH of media. Microbial inactivation was governed essentially by penetration of CO₂ into cells and its effectiveness could be improved by the enhanced transfer rate. Microbial reduction of 8 log cycles was observed within 120 min under CO₂ pressure of 70 kg/cm² at 30°C. We hypothesized that the cell death resulted from the lowered intracellular pH and damage to the cell membrane due to penetration of CO₂. Pressurized CO₂ treatment is a potential nonthermal technology for food preservation.     

Influence of Na2CO3 on the quality of dough with rice wine sourdough and steamed bread

The potential use of Na₂CO₃ in the dough with rice wine sourdough and steamed bread was studied in the processing steamed bread, by looking at the effects of Na₂CO₃ addition on the dough and steamed bread quality. The relationship between Na₂CO₃ concentration and pH was linear. Increasing the added Na₂CO₃ levels from 0.10% to 0.30% resulted initially in a lower content of free sulfhydryl groups (SH), but this eventually increased. Na₂CO₃ addition resulted in increased glutenin macropolymer (GMP) content in the dough and reduced the softness of the dough. Dough with 0.20% Na₂CO₃ had significantly lower Jmax and a values compared to the other Na₂CO₃ concentrations tested, indicating this concentration to be ideal for reduced dough softness and appropriate interaction between molecules in dough structure. The addition of 0.20% and 0.25% Na₂CO₃ was also beneficial to the extension of gluten and the formation of a proper and uniform gluten network, making the dough more fine and smooth. Additionally, significant correlations were found between the creep–recovery of dough and the specific volume and hardness of steamed bread. Finally, the addition of 0.20% Na₂CO₃ in dough resulted in improved specific volume, whiteness and the sensory score of rice wine sourdough steamed bread.