Development of a microbial Time Temperature Indicator for monitoring the shelf life of meat

Time Temperature Indicators (TTIs) constitute smart devices through which the full history of the time-temperature profile of a food is monitored. The objective of the current study was to develop a versatile microbial TTI based on the violacein formation, a violet pigment produced by the microorganism Janthinobacterium sp. during early growth, depending on temperature and intrinsic properties of the growth medium. The TTI system consisted of Tryptic Soy Agar enriched with 1% glycerol, spot-inoculated with the bacterium. Input parameters were the storage temperature, the pH of the medium, the initial concentration of the microorganism and the volume of the spot. Image analysis was used to estimate the color change of the spots. Luminosity (L^⁎) parameter described the color change adequately. The Baranyi model was used to fit the violacein kinetics data (L^⁎ curve) estimating the TTI's endpoint, i.e., the time at which the violet color occurred. Survival analysis was used to analyze the endpoint data assessing the activation energy, E_a^TTI, and the TTI's endpoint at a reference temperature (t^TTI,ref_endpoint). The E_a^TTI and t^TTI,ref_endpoint (T_ref = 0 °C) parameters ranged between 65.1–110.3 kJ/mol and 10.1–107.6, respectively. Based on the estimated E_a^TTI and t^TTI,ref_endpoint parameters, a decision can be made on the most suitable combination of pH, initial concentration and spot quantity for monitoring the impact of time-temperature profile of different foods on the occurrence of spoilage. The TTI was validated for spoilage of minced beef meat under isothermal and dynamic storage conditions using data generated in this study. The applicability of the TTI was also evaluated to other meat products, including vacuum packaged cooked meat products, using literature data.     

Advances in the study of the kinetics of color and fluorescence development in concentrated milk systems

The kinetics of color and fluorescence development in systems containing whole milk powder (WMP), sucrose (S) and water were studied; the influence of three design variables: pH (6, 7 and 8), temperature (105, 122.5 and 140 °C) and WMP/S ratio (R = 0.3, 0.68 and 1.06) being particularly investigated. The Kubelka-Munk index (K/S), luminance or lightness (L), optical density (OD) and fluorescence (F), were measured at different reaction times. Reaction pseudo-order (n) varied between 0 and 1 and reaction rate constants for the development of fluorescence and the color parameters were found to be more dependent on temperature than on R at all measured pH values. Temperature dependence of CP was analyzed through the activation energy (E_a) values. The variables F and OD, which are related to the molecular aspects of the systems, showed the extreme values of E_a, while than K/S and 100/L, related to the macroscopic appearance or reflectance, showed intermediate E_a values and lower dependence with R and pH. When compared to the variables related to brown pigment development, fluorescence development showed a higher relative change, which shows its higher sensitivity as a reaction marker. The variables that most affected color and F development were temperature and protein concentration, respectively.     

Development and characterization of a prototype of a lactic acid–based time–temperature indicator for monitoring food product quality

Temperature is a crucial factor affecting the quality and safety of food products during both distribution and storage. The difficulty in controlling and monitoring the temperature history of food products makes it difficult to precisely predict shelf life. Time–temperature indicators (TTIs) provide a visual summary of a product’s accumulated chill-chain history, recording the effects of both time and temperature. Attempts have been made to develop a prototype of a time–temperature indicator based on the diffusion of lactic acid, which is temperature-dependent. Four lactic acid-based TTIs were made in different substrate concentrations. Color changes associated with the diffusion of lactic acid were monitored. In the vapor diffusion of lactic acid, an irreversible color change of a chemical chromatic indicator (from green to red) clearly and progressively occurred due to the pH reduction. The temperature dependence of these TTIs kinetics was characterized isothermally in the range of 4–45 °C, yielding activation energy (E_a) of, approximately, 50 kJ mol⁻¹. The mathematical models of each TTI were established according to the relationships between color changes and time and temperature. The differences between the E_a values of the TTIs and the E_a associated with food quality losses – including enzymatic loss, hydrolysis, lipid oxidation, nutrient loss and microbial growth – were less than 40 kJ mol⁻¹, and therefore these TTIs could be considered as good candidates to monitor food quality losses. Although these TTIs do not cover the whole range of food quality losses, they could be applied to show the time–temperature history of some foods, especially fruits and vegetables, and to indicate food quality associated with time–temperature exposure.     

A century of gray: A genomic locus found in 2 distinct Pseudomonas spp. is associated with historical and contemporary color defects in dairy products worldwide

Some gram-negative bacteria, including Pseudomonas spp., can grow at refrigeration temperatures and cause flavor, odor, and texture defects in fluid milk. Historical and modern cases exist of gray and blue color defects in fluid milk due to Pseudomonas, and several recent reports have detailed fresh cheese spoilage associated with blue-pigment-forming Pseudomonas. Our goal was to investigate the genomes of pigmented Pseudomonas isolates responsible for historical and modern pigmented spoilage of dairy products in the United States to determine the genetic basis of pigment-forming phenotypes. We performed whole genome sequencing of 9 Pseudomonas isolates: 3 from recent incidents of gray-pigmented fluid milk (Pseudomonas fluorescens group), 1 from blue-pigmented cheese (P. fluorescens group), 2 from a historical blue milk spoilage incident (Pseudomonas putida group), and 3 with no evidence for blue or gray pigment formation (2 from P. fluorescens group and 1 from Pseudomonas chlororaphis group). All 6 isolates collected from products with a gray or blue pigment defect were confirmed to produce pigment using potato dextrose agar or pasteurized milk. A subset of 2 isolates was selected for inoculation into milk and onto the surface of a model cheese for subsequent color measurement. These isolates produced different colors on potato dextrose agar, but produced nearly identical color defects in milk and on model cheese. For the same subset of 2 isolates, the gray color defect in milk was produced only in containers with ample headspace and not in full containers, suggesting that oxygen is vital for pigment formation. This work also demonstrated that a Pseudomonas isolate from cheese can produce a pigment defect in milk, and vice versa. Comparative genomics identified an accessory locus encoding tryptophan biosynthesis genes that was present in all isolates that produced gray or blue pigment under laboratory conditions and was only previously reported in 2 P. fluorescens isolates responsible for blue mozzarella in Italy. Because this locus was found in genetically distant isolates belonging to different Pseudomonas species groups, it may have been acquired via horizontal gene transfer. These data suggest that several past and present gray- or blue-pigmented dairy spoilage events share a common genetic etiology that transcends species-level identification and merits further investigation to determine mechanistic details and modes of prevention.     

Development of a microbial time-temperature integrator system using lactic acid bacteria

A microbial time-temperature integrator (TTI) system was developed using lactic acid bacteria (Weissella koreensis) obtained from baechukimchi. Activation energy (Ea), which represents the temperature dependence of the TTI response, was calculated using the Arrhenius equation. Ea values for the color change (ΔE value), maximum specific growth rate (μ_max), and pH change of the TTI measured under different isothermal conditions (5, 10, 15 and 20°C) were 99.88, 95.91, and 93.38 kJ/mol, respectively. According to the time taken to reach the TTI endpoint by the initial inoculum level of W. koreensis (6.2, 5.5, 4.5, and 3.4 log CFU/mL), a negative correlation was observed in 63.5, 101.8, 115.1 and 166.6 h. In addition, initial bacterial counts decreased significantly up to almost 4% at 20°C in 3 months when W. koreensis viability was measured at the freezing point of the microbial TTI system (20 and ?80°C) for 1 week, 1 month, 2 months, and 3 months. However, viability was about 95% at 80°C. This microbial TTI system would be useful to monitor the quality of food with similar Ea values during storage or distribution.     

Effects of packaging atmospheres on shelf-life quality of ground ostrich meat

Fresh ground ostrich meat was packaged under high oxygen (O2), high nitrogen (N2), vacuum (VAC) and ambient air (AIR) atmospheres, stored at 4 ± 1 °C and displayed under 1700 ± 100 lux of fluorescent lighting for 9 days. The meat was evaluated for changes in typical shelf-life characteristics consisting of pH, color properties (CIE L^∗, a^∗, b^∗, and total color difference, ΔE), oxidative changes (thiobarbituric acid value and hexanal content) and bacterial counts (total viable cell, coliform, lactic acid bacteria, Enterobacteriaceae, Pseudomonas spp.) Initial meat pH was 6.16 and declined slightly during storage. TBA values and hexanal content were highest in O2 and lowest (P ? 0.05) in VAC and N2 atmospheres. Surface lightness (L^∗) and redness (a^∗) were highest in O2 packaging initially, decreasing (P ? 0.05) by day 9. ΔE of the ground ostrich increased during storage in only O₂ and AIR packaging. All packaging methods had generally similar effects on microbial outgrowth. Total aerobic bacteria attained >10⁶ CFU/g meat between day 3 and day 6. Ground ostrich meat was below saleable quality in less than 6 days based on all of the meat attributes. For O2 packaging however, quality based on lipid oxidation and color properties indicated a shelf-life of less than 3 days. Oxidation is likely the limiting factor for shelf-life of ground ostrich meat.     

Freshness assessment of gilthead sea bream (Sparus aurata) by machine vision based on gill and eye color changes

The fish freshness was evaluated using machine vision technique through color changes of eyes and gills of farmed and wild gilthead sea bream (Sparus aurata), being employed lightness (L^*), redness (a^*), yellowness (b^*), chroma (c^*), and total color difference (ΔE) parameters during fish ice storage. A digital color imaging system, calibrated to provide accurate CIELAB color measurements, was employed to record the visual characteristics of eyes and gills. The region of interest was automatically selected using a computer program developed in MATLAB software. L^*, b^*, and ΔE of eyes increased with storage time, while c^* decreased. The a^* parameter of fish eyes did not show clear a trend with storage time. The L^*, b^*, and ΔE of fish gills increased with storage time, but a^* and c^* decreased. Regression analysis and artificial neural networks approaches were used to correlate the eyes and gills color parameters with the time of storage and a strong correlation was found between color parameters and storage day. Gills color changes were more precise than those found for eyes in order to evaluate the fish freshness. However, the gills cover should be removed for taking the images and thus, the method is destructive and time-consuming. Therefore, the color parameters of fish eyes can be used as a green, low cost and easy method for fast and on-line assessing of fish freshness in food industry.     

Color degradation kinetics of pineapple puree during thermal processing

Improvement of color, as a quality attribute of processed pineapple puree, has been made possible by the increase in knowledge of kinetic of color change. The kinetics of color degradation of pineapple puree were investigated during heat treatment at 70-110 °C in order to cover the temperature range that used in preheat and sterilization of commercial aseptic pineapple puree. Color changes associated with heat-treated puree were monitored using Hunter colorimeter (L, a, b, total color difference—ΔE) and Browning index (A₄₂₀). The changes in L and b values fitted well to the first-order kinetic model while ΔE, a value, and Browning index followed the zero-order kinetic. The dependence of the rate constant on temperature was represented by an Arrhenius equation. The results suggested that ΔE and lightness, based on activation energy, were the most sensitive measures of color change at temperature range 70-90 and 95-110 °C, respectively.     

Effect of freeze-thaw cycles on physicochemical properties and color stability of beef semimembranosus muscle

The effects of freeze-thaw cycle on the physicochemical properties and color stability of beef semimembranosus muscle during cold storage were investigated. Meat was tested for effects on color (CIE L^?, a^?, b^?), myoglobin content (%), metmyoglobin reducing ability (MRA), thiobarbituric acid reactive substances (TBARS), heme pigment content (ppm), SDS-PAGE profile, and tissue microstructure. Fresh meat showed significantly (p < 0.05) higher values of CIE a^?, CIE b^?, and oxymyoglobin content (%) compared to freeze-thawed meat during cold storage. However, metmyoglobin content (%) was higher in freeze-thawed meat than in fresh meat during 7 days of cold storage. There were no significant differences (p > 0.05) in MRA among the treatments during cold storage. The TBARS value (0.387 mg/kg) of fresh meat was significantly (p < 0.05) higher than those of freeze-thawed meats after 5 days of cold storage. These results suggest that the freeze-thaw process could accelerate the deterioration of meat color.     

High pressure effect on the color of minced cured restructured ham at different levels of drying, pH, and NaCl

Color changes of minced cured restructured ham was studied considering the effects of high pressure (HP) treatment (600 MPa, 13 °C, 5 min), raw meat pH₂₄ (low, normal, high), salt content (15, 30 g/kg), and drying (20%, 50% weight loss). Raw hams were selected based on pH₂₄ in Semimembranosus, mixed with additives, frozen, sliced, and dried using the Quick-Dry-Slice® process. Meat color (CIE 1976 L*a*b*) and reflectance spectra were measured before and after HP treatment. HP significantly increased L*, decreased a*, and decreased b* for restructured ham dried to 20% weight loss, regardless of salt content and pH₂₄. L* and a* were best preserved in high pH/high salt restructured ham. HP had no effect on the color of restructured ham dried to 50% weight loss. HP had no effect on the shape of reflectance curves, indicating that the pigment responsible for minced cured restructured ham color did not change due to HP.     

Isolation and characterization of melanin from Osmanthus fragrans’ seeds

Melanin derived from Osmanthus fragrans’ seeds was isolated from O. fragrans’ seeds by alkaline extraction, acid hydrolysis, and repeated precipitation with a yield of 0.34 g/100 g (wet weight basis). Physical and chemical properties of the melanin revealed that the melanin derived directly from O. fragrans’ seeds were similar to typical melanin. The melanin was stable under ultraviolet light or room-light, stable in the range of 25-100 °C, relatively stable in alkaline solution, reducer and salt, but was bleached by strong oxidants (KMnO₄, K₂Cr₂O₇ and NaOCl). The metal-ion of Ca²⁺, Cu²⁺, Fe³⁺ and Zn²⁺ had the function of color increase or color preservation to the melanin. Although Mg²⁺, Al³⁺ and Na⁺ reduce pigment color, it was not obvious. Amino acid and organic acid did not affect the melanin, while sugar, starch, and glucose affected it slightly.     

Pressure Degradation Kinetics of Anthocyanin Pigment and Visual Color of Chinese Bayberry Juice

Pressure degradation kinetics of the anthocyanin pigment content and visual color (L, a, and b values) of Chinese bayberry juice were evaluated at selected pressures (400, 500, and 600 MPa) and holding times (5–10 min). Results indicated that the degradation of anthocyanin content after high pressure processing and during storage followed the first-order models, as well as the change of a and L × a × b values after high pressure processing. The activation energies (V_a) for anthocyanin content, a and L × a × b changes after high pressure processing were –19.845, –14.915, and –12.908 cm³ mol^–1, respectively. V_a analysis indicated that anthocyanin was more pressure sensitive than visual color parameters.     

Isolation and characterization of pigment from Cinnamomum burmannii' peel

Cinnamomum burmannii is cultivated for use as a spice, and as an ornamental tree. With the aim to develop a natural colorant for use in cosmetics and food additives from a new source, in the present study, pigment derived from C. burmannii' peel (CBP) was isolated by alkaline extraction, acid hydrolysis, repeated precipitation and purification by Sephadex G-75 with a total yield of 0.06 g/100 g (wet weight basis). The color values of the pigment was E_1 cm^1% 278 nm = 65.21. Physical and chemical properties revealed that CBP presses similar properties as most natural pigment. It was scarcely soluble in both water and all common organic solvents, and was soluble only in alkaline aqueous and DMSO. It was stable under ultraviolet light or room-light, stable in the range of 25-100 °C, relatively stable in alkaline aqueous and reducer, but was bleached by strong oxidants (KMnO₄, H₂O₂ and NaOCl). Sodium benzoic acid, tartaric acid, table salt and cane sugar affected it slightly. Spectroscopic analysis of CBP in relation with its structure was also discussed. This is the first report on the characterization of pigment obtained from C. burmannii 'peel.     

Effects of brine concentration and temperature on color of vacuum pulse osmotically dehydrated sardine sheets

The effects of brine concentration (0.15-0.27 g NaCl/g) and temperature (30-38 °C) on the color parameters (L, a, b, ΔE) of vacuum pulse osmotically dehydrated sardine sheets were investigated. The results showed that osmotic dehydration has a significant effect on color of sardine sheets. Redness (a-value) and yellowness (b-value) decreased through dehydration time while lightness (L-value) and total color difference (ΔE) increased. The decreases in redness and yellowness were lesser with increasing temperature and brine concentration while increases in lightness and ΔE were higher. These changes would be predicted by simple models as a function of the temperature, brine concentration, and dehydration time.     

Prediction of beef quality attributes using VIS/NIR hyperspectral scattering imaging technique

Hyperspectral imaging images were used to predict fresh beef tenderness (WBSF: Warner-Bratzler Shear Force) and color parameters (L^∗, a^∗, b^∗). Sixty-five fresh strip loin cuts were collected from 33 carcass after 2 days postmortem. After acquiring hyperspectral images, the samples were vacuum packaged and aged for 7 days, and then the color parameters and WBSF of the samples were measured as references. The optical scattering profiles were extracted from the images and fitted to the Lorentzian distribution (LD) function with three parameters. LD parameters, such as the scattering asymptotic vale, the peak height, and full scattering width were determined at each wavelength. Stepwise discrimination was used to identify optimal wavelengths. The LD parameters’ combinations with optimal wavelengths were used to establish multi-linear regression (MLR) models to predict the beef attributes. The models were able to predict beef WBSF with R_cv = 0.91, and color parameters (L^∗, a^∗, b^∗) with R_cv of 0.96, 0.96 and 0.97, respectively.     

Immobilization of β-galactosidase from Cicer arietinum (gram chicken bean) and its catalytic actions

β-Galactosidase (β-d-galactosidase galactohydrolase EC 3.2.1.23) isolated and purified from Cicer arietinum (gram chicken bean) was immobilized on two kinds of modified resin D202 with glutaraldehyde. Both the immobilized enzymes had high protein-binding capacity and high yield of enzyme activity. Kinetics results showed that the enzyme activity attained its maximum at 57°C, pH 6 for the immobilized β-galactosidase I and 52°C, pH 6 for the immobilized β-galactosidase II, respectively. The operational pH range was increased. Kinetic constants (K_m, V_max and E_a) for the free and bound enzymes, with ONPG as substrate, were studied. Results showed that K_m and V_max of immobilized enzymes were decreased while E_a of them was increased. The effects of some compounds and organic solvents for the free and immobilized enzymes were discussed. Inhibitory constants for raffinose, lactose and d-galactose, which were all reversible inhibitors of the enzymes, were also obtained.     

Pigment composition and color parameters of commercial Spanish red wine samples: linkage to quality perception

Anthocyanins play a crucial role in wine color. Thus, their analysis results essential for evaluating their contribution to perceived color in wines, attribute directly linked to quality judgements. In this context, this study was aimed at: (1) defining the color space of a relative large number of commercial oaked Spanish red wines and (2) establishing a linkage between wine coloring, anthocyanic composition, and quality perception of this set of wines. Therefore, CIELab parameters (a ₁₀*, b ₁₀*, L ₁₀*), monomeric anthocyanin contents analyzed by HPLC with ultraviolet and mass detection, and polymeric pigment content estimated by a protein precipitation assay combined with bisulfite bleaching were evaluated in a total of 58 wine samples. Principal component analysis was performed on color variables, and their correlations were discussed. The results have evidenced the important role played by the pyranoanthocyanic compounds since they seem to be the main contributors to the red color of these aged wines, and they have been demonstrated not to increase their yellow nuances. On the other hand, results highlight that, regardless of the time of aging, wines presenting more red (higher values for a ₁₀* and for low molecular weighted anthocyanins) and lower yellow nuances (lower values for b ₁₀* and T) as well as a darker color (lower in L ₁₀* and higher in CI) are in general evaluated with higher quality scores by wine experts.     

On-line color monitoring of solid foods during supercritical CO2 pasteurization

An on-line color monitoring system for solid foods to be used during supercritical carbon dioxide (SC-CO₂) pasteurization was designed and tested. The experimental apparatus described here allowed for the measurement of reflectance spectra and color parameters (L^∗, a^∗, b^∗) during (on-line) as well as before and after treatments (off-line).The results demonstrated that SC-CO₂ pasteurization applied at 12.0 MPa, 40 °C slightly affected the color of freshly cut pieces of coconut and carrot during the process performed at different treatment times (10, 20, and 30 min). Reflectance spectra of coconut, acquired on-line, showed that CO₂ influenced the color immediately upon treatment: lightness (L^∗) changed from 86.10 ± 2.80 at 1 min to 79.57 ± 0.74 at 30 min. The decompression was demonstrated to be the critical parameter affecting the color of carrot. The off-line measurements showed that 30 min of treatment induced 38% and 22% decrease of redness (a^∗) and yellowness (b^∗), respectively.The proposed apparatus allowed for a non-invasive, immediate and direct monitoring of food color before, during and after SC-CO₂ pasteurization.     

Phytochemical stability in dried apple and green tea functional products as related to moisture properties

In this study, apple products made with and without added green tea extract were freeze-dried and stored for up to 45 days at 30 °C in low and intermediate moisture environments (water activity, a_w, 0.11, 0.22, 0.32, 0.57, and 0.75). Kinetic models were developed for the changes in color and decreases in contents of selected green tea and apple monomeric and polymeric flavanols and ascorbic acid. Moisture isotherms were developed for each product. At various moisture levels, the glass transition temperature (T_g) was measured by DSC and water mobility by ¹H NMR. Chemical changes were related to T_g, a_w, and water mobility in the products.Phytochemical degradation occurred more rapidly at higher moisture contents, except for caffeine which was stable. In the product containing apple with green tea, the content of monomeric flavan-3-ols decreased by 34% and 39% after 45 days of storage at a_w of 0.56 and 0.75, respectively. Phytochemical degradation correlated with increasing a_w, T_g, and water mobility. This study showed that, in general, storage at a_w 0.75 most affected phytochemical stability and color.     

Influence of vacuum-aging period on bloom development of the beef gluteus medius from top sirloin butts

The gluteus medius (GM) from USDA Select beef carcasses was used to test the effect of aging period on bloom development. Top sirloin butts (IMPS #184) were randomly allocated to 0, 7, 14, 21, 28, and 35 d vacuum-aging at 2 °C (n = 10/aging period). Each week, aged top sirloin butts were faced before two 2.5-cm-thick, non-adjacent steaks were cut and instrumental color (L^∗, a^∗, and b^∗) of the GM was measured at 10-min intervals for 2 h after cutting. Steaks aged for 7 and 14 d were a more vivid (greater chroma values; P < 0.05), redder (greater a^∗ values; P < 0.05), and more yellow (greater b^∗ values; P < 0.05) color than steaks from the other aging periods. Change in total color (ΔE) was greater (P < 0.05) for steaks from top sirloin butts aged 7, 14, and 21 d than steaks from top butts aged 28 and 35 d, whereas oxymyoglobin percentages for steaks from top butts aged 7 and 14 days were greater (P < 0.05) than those from top sirloin butts aged 28 and 35 d. As much as 90% of the total increase (P < 0.05) in a^∗, b^∗, and chroma values, as well as hue angles and oxymyoglobin percentages, was achieved during the first 60 min after cutting.