Monitoring of ATP and viable cells on meat surface by UV-Vis reflectance spectrum analysis

Cleanliness monitoring at slaughterhouses depend on traditional methods, e.g., visual inspection or swabbing. The visual inspection is not always accurate. Swabbing requires skilled workers and further plate count or ATP bioluminescence technique. To solve these problems, a rapid technique based on non-destructive UV-Vis reflectance was developed to monitor the ATP and viable cells. Samples were lean part of pork loin. The samples stored at 15 °C were analyzed at 0, 24, 48, 72, 84 and 96 h for ATP, plate count and UV-Vis reflectance. The reflectance spectra were measured from 240 to 540 nm at 20 °C, and then the area of 40 × 40 mm² of the sample surface was swabbed for the determination of plate count and ATP amount. The plate count on the sample surface increased from the initial count of 29 to 3.2 × 10⁷ CFU/cm² after 84 h. The ATP amount also increased with time from the initial amount of 9.2 × 10⁻¹⁵ to 2.8 × 10⁻¹⁰ mol/cm² after 84 h. The linear relationship was observed between the ATP amount and plate count with the determination coefficient of 0.95. The 2nd derivative of raw spectra gave a high correlation for the first 48 h with both ATP amount and viable cell count showing the determination coefficient of 0.89 and 0.83, respectively at 318 nm. The results strongly suggested that the UV-Vis reflectance spectrum analysis could be used as the real-time monitoring of ATP and/or plate count on meat surface with the optimal wavelength.     

Non-destructive evaluation of ATP content and plate count on pork meat surface by fluorescence spectroscopy

The potential of fluorescence spectroscopy was investigated for the non-destructive evaluation of ATP content and plate count on pork meat surface stored aerobically at 15 °C during three days. Excitation (Ex) Emission (Em) Matrix of fluorescence intensity was obtained and fluorescence from tryptophan (Ex = 295 nm and Em = 335 nm) and NADPH (Ex = 335 nm and Em = 450 nm) was detected. Because tryptophan and NADPH fluorescence changed along with the growth of microorganisms, microbial spoilage on meat could be detected from fluorescence. By applying PLSR (Partial Least Squares Regression) analysis, ATP content and plate count were predicted with good determination coefficient (0.94–0.97 in calibration and 0.84–0.88 in validation).     

Microbiological quality and potential public health risks of export meat from springbok (Antidorcas marsupialis) in Namibia

To assess the microbiological quality and safety of export game meat; i) a total of 80 pooled meat samples for aerobic plate count (APC) and Enterobacteriaceae ii) water used in harvesting and processing for microbiological quality and iii) meat and rectal contents for Salmonella spp. and Shiga toxin Escherichia coli (STEC) were evaluated in 2009 and 2010. No differences (p > 0.05) in the APCs were observed between the years, but the mean Enterobacteriaceae count for 2009 was 1.33 ± 0.69 log₁₀ cfu/cm² compared to 2.93 ± 1.50 log₁₀ cfu/cm² for 2010. Insignificant Heterotrophic Plate Count (HPC) levels were detected in 9/23 field water samples, while fecal bacterial (coliforms, Clostridium perfringens and enterococci) were absent in all samples. No Salmonella spp. was isolated and all E. coli isolates from meat were negative for STEC virulence genes (stx1, stx2, eae and hlyA), suggesting a negligible role by springbok in the epidemiology of STEC and Salmonella.     

Nondestructive Hygiene Monitoring on Pork Meat Surface Using Excitation–Emission Matrices with Two-Dimensional Savitzky–Golay Second-Order Differentiation

To develop a rapid and nondestructive hygiene-monitoring system in meat-processing plants, plate count and ATP content on pork meat surfaces were quantitatively determined with particular attention to NAD(P)H fluorescence produced by microorganisms. An excitation (Ex)–emission (Em) matrix (EEM) was obtained, and the five fluorescence peaks of tryptophan, NAD(P)H, zinc protoporphyrin IX, protoporphyrin IX, and riboflavin were observed. Plate count and ATP content were predicted with good accuracy [r _p?=?0.90–0.94 and root mean square error of prediction (RMSEP)?=?log₁₀ (0.68–0.79 CFU cm^?2) for plate count and r _p?=?0.84–0.89 and RMSEP?=?log₁₀ (0.61–0.71, mol cm^?2) for ATP content]. Two-dimensional Savitzky–Golay second-order differentiation was found to be a powerful preprocessing tool of EEMs to improve prediction accuracy. Better prediction accuracy was obtained when the sensitivity of the fluorescence spectrophotometer was set to focus on fluorescence from NAD(P)H than that from both tryptophan and NAD(P)H. However, little linear relationship was observed between plate count and fluorescence intensity from NAD(P)H (R ²?=?0.31). The absolute value of regression coefficient (RC) of partial least-squares regression (PLSR) at the wavelength assigned to NAD(P)H, zinc protoporphyrin IX, protoporphyrin IX, and riboflavin was high. It can be concluded that a good prediction model was developed in which four fluorescence compounds of NAD(P)H, zinc protoporphyrin IX, protoporphyrin IX, and riboflavin contribute to the prediction model, and these compounds are probably produced by microorganisms.     

Predictive model for growth of Clostridium perfringens during cooling of cooked uncured meat and poultry

Comparison of Clostridium perfringens spore germination and outgrowth in cooked uncured products during cooling for different meat species is presented. Cooked, uncured product was inoculated with C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated in a water bath stabilized at selected temperatures between 10 and 51 °C and sampled periodically. For dynamic experiments, the samples were cooled from 54.4 to 27 °C and subsequently from 27 to 4 °C for different time periods, designated as x and y hours, respectively. The growth models used were based on a model developed by Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int. J. Food Micro. 23, 277-294), which incorporates a constant, referred to as the physiological state constant, q₀. The value of this constant captures the cells’ history before the cooling begins. To estimate specific growth rates, data from isothermal experiments were used, from which a secondary model was developed, based on a form of Ratkowsky’s 4-parameter equation. The estimated growth kinetics associated with pork and chicken were similar, but growth appeared to be slightly greater in beef; for beef, the maximum specific growth rates estimated from the Ratkowsky curve was about 2.7 log₁₀ cfu/h, while for the other two species, chicken and pork, the estimate was about 2.2 log₁₀ cfu/h. Physiological state constants were estimated by minimizing the mean square error of predictions of the log₁₀ of the relative increase versus the corresponding observed quantities for the dynamic experiments: for beef the estimate was 0.007, while those for pork and chicken the estimates were about 0.014 and 0.011, respectively. For a hypothetical 1.5 h cooling from 54 °C to 27° and 5 h to 4 °C, corresponding to USDA-FSIS cooling compliance guidelines, the predicted growth (log₁₀ of the relative increase) for each species was: 1.29 for beef; 1.07 for chicken and 0.95 log₁₀ for pork. However, it was noticed that for pork in particular, the model using the derived q₀ had a tendency to over-predict relative growth when the observed amount of relative growth was small, and under-predict the relative growth when the observed amount of relative growth was large. To provide more fail-safe estimate, rather than using the derived value of q₀, a value of 0.04 is recommended for pork.     

Influence of meat exudates on the quality characteristics of fresh and freeze-thawed pork

The influence of the accumulated exudates released from pork loin of itself on the quality characteristics of fresh and freeze-thawed pork during cold storage was investigated. Pork loins were divided into four groups (fresh pork with exudates, fresh pork without exudates, freeze-thawed pork with exudates and freeze-thawed pork without exudates) and stored at 1.0 °C for 7 days. Exudate amount increased due to freeze-thawing and with storage, and most quality traits such as drip loss, cooking loss, tenderness, lightness, redness, and moisture content were affected by freeze-thawing (p < 0.05). Freeze–thaw increased drip loss but decreased moisture content, cooking loss, tenderness, lightness and redness of meat (p < 0.05). Microbial growth was solely affected by exudate removal and the removal of initial exudates decreased microbial growth (p < 0.05). Exudates were positively correlated with total protein content and total plate count but negatively correlated with pH and cooking loss. Therefore, removing meat exudates and avoiding freeze can slow down the quality deterioration of pork during cold storage.     

Theoretical analysis on pulsed microwave heating of pork meat supported on ceramic plate

Theoretical analysis has been carried out to study the role of ceramic plates (alumina and SiC) and pulsed microwave heating of pork meat (Pork Luncheon Roll (PLR) and White Pudding (WP)) samples. Spatial hot spots occur either at the center of the sample or at the outer face or at the face attached with alumina plate and application of pulsing minimizes formation of hot spots within meat samples. Pulsing of microwave is characterized by set point for temperature difference (ΔT_S) and on–off constraints for temperature (T′). It is found that alumina plate with higher ΔT_S and lower T′ may be recommended for thick meat samples (both WP and PLR) whereas for thin meat samples, lower ΔT_S with alumina plate/without plate may be preferred. It is also observed that SiC plate may be selectively used with ΔT_S = 20 K for both the pork meats. The distributed microwave incidence is found to be effective due to lesser degree of thermal runaway in absence of pulsing for both meat samples.     

Technical note: Determination of corn hardness in diverse corn germplasm using near-infrared reflectance baseline shift as a measure of grinding resistance

Vitreousness and Stenvert kernel hardness characteristics in corn germplasm have been related to in situ and in vivo starch digestibility in lactating dairy cows. Because of the tedious nature of determining vitreousness by manual dissection or conducting Stenvert hardness measurements, it is challenging to screen corn germplasm for animal performance potential. The resistance of corn to grinding is typically measured in a Stenvert mill and quantified by grinding time and column height. The baseline shift (BLS) of near-infrared reflectance spectroscopy, which is a normal artifact of grinding-induced particle size differentiation, was calculated and evaluated as an alternative measure of grinding resistance. Stenvert grind time, column height, BLS, and ruminal DM degradability (RDMD) of 31 diverse corn germplasm harvested in triplicate at 2 maturities were made. After grinding, total and 6 partial (100 nm) BLS were calculated [Σ x_i + x_j…, where x_i = log₁₀(1/R) at the ith nanometer and R = reflectance] and compared with vitreousness, Stenvert grinding time, column height, or RDMD of corns using correlation and regression procedures. Total and all partial BLS were correlated with vitreousness, Stenvert measures, and RDMD. Relationships between BLS and vitreousness, Stenvert measures, or RDMD were stronger for partial BLS at shorter near-infrared wavelengths (1,080-1,180 nm) than at longer wavelengths (i.e., 2,280-2,380 nm) or total near-infrared BLS (1,000-2,498 nm). The partial BLS from 1,080 to 1,180 nm and vitreousness were better related to RDMD of corn germplasm than Stenvert grind time or column height.     

Potential prediction of the microbial spoilage of beef using spatially resolved hyperspectral scattering profiles

Spoilage in beef is the result of decomposition and the formation of metabolites caused by the growth and enzymatic activity of microorganisms. There is still no technology for the rapid, accurate and non-destructive detection of bacterially spoiled or contaminated beef. In this study, hyperspectral imaging technique was exploited to measure biochemical changes within the fresh beef. Fresh beef rump steaks were purchased from a commercial plant, and left to spoil in refrigerator at 8 °C. Every 12 h, hyperspectral scattering profiles over the spectral region between 400 and 1100 nm were collected directly from the sample surface in reflection pattern in order to develop an optimal model for prediction of the beef spoilage, in parallel the total viable count (TVC) per gram of beef were obtained by classical microbiological plating methods. The spectral scattering profiles at individual wavelengths were fitted accurately by a two-parameter Lorentzian distribution function. TVC prediction models were developed, using multi-linear regression, on relating individual Lorentzian parameters and their combinations at different wavelengths to log₁₀(TVC) value. The best predictions were obtained with r² = 0.95 and SEP = 0.30 for log₁₀(TVC). The research demonstrated that hyperspectral imaging technique showed potential for real-time and non-destructive detection of bacterial spoilage in beef.     

Effects of different storage conditions on quality related porphyrin fluorescence signatures of pork slices

This study evaluated the potential of fluorescence as an indicator of pork quality by determining the effects of various conditions on fluorescence signatures (excitation at 420 nm, emission at 550-750 nm).Storage of porcine musculus longissimus dorsi in PE bags led to a clear increase in porphyrin fluorescence intensity after approx. 10 d post mortem. Modified gas atmosphere (70% O₂, 30% CO₂) inhibited the fluorescence emission of zinc protoporphyrin and protoporphyrin IX due to quenching by oxygen. Bleaching processes caused similar effects by halogen light exposure during meat storage. However, already formed signals could not be manipulated by oxygen or halogen light. Storage under vacuum reduced the quenching effects and resulted in increased fluorescence intensities. Freezing and thawing of meat samples delayed and reduced the increase in fluorescence intensity. Only minor effects could be detected at long-term frozen storage for two months.Consequently porphyrin fluorescence analysis is a potential means to indicate changes of pork quality and remaining shelf life.     

Monitoring quality loss of pasteurized skim milk using visible and short wavelength near-infrared spectroscopy and multivariate analysis

Visible and short wavelength near-infrared diffuse reflectance spectroscopy (600 to 1,100 nm) was evaluated as a technique for detecting and monitoring spoilage of pasteurized skim milk at 3 storage temperatures (6, 21, and 37°C) over 3 to 30 h (control, t = 0 h; n = 3). Spectra, total aerobic plate count, and pH were obtained, with a total of 60 spectra acquired per sample. Multivariate statistical procedures, including principal component analysis, soft independent modeling of class analogy, and partial least squares calibration models were developed for predicting the degree of milk spoilage. Principal component analysis showed apparent clustering and segregation of milk samples that were stored at different time intervals. Milk samples that were stored for 30 h or less at different temperatures were noticeably separated from control and distinctly clustered. Soft independent modeling of class analogy analysis could correctly classify 88 to 93% of spectra of incubated samples from control at 30 h. A partial least squares model with 5 latent variables correlating spectral features with bacterial counts and pH yielded a correlation coefficient (R = 0.99 and 0.99) and a standard error of prediction (0.34 log₁₀ cfu/mL and 0.031 pH unit), respectively. It may be feasible to use short wavelength near-infrared spectroscopy to detect and monitor milk spoilage rapidly and noninvasively by correlating changes in spectral features with the level of bacterial proliferation and milk spoilage.     

The effect of pH on shelf-life of pork during aging and simulated retail display

The pork industry uses pH to differentiate product of varying quality; thus, the effect of pH on shelf-life is important as time during transport is extended. The objective was to develop regression equations to predict shelf-life over a range of ultimate pH (5.42–6.26). Shelf-life was evaluated after vacuum aging pork loin sections 0, 7, 14, 21, or 28 d and during 3 d of simulated retail display (4.5 °C) for pork loin chops. Correlation coefficients indicated a strong relationship between pH and quality measurements. Regression analysis with Aging Day and pH was able to explain 87% of the variation in aerobic plate counts for pork. After 28 d of vacuum aging, loin sections from the upper end of the pH distribution had about a 3 log(1000X) greater aerobic plate count than did the lower end pH product. An increase in pH resulted in pork with lower L*, a*, b* and R₆₃₀ − R₅₈₀ values and as Aging Day increased, instrumental measurements of color increased slightly. Although higher pH is associated with improved pork quality, higher pH and longer aging periods will result in increased microbial proliferation and decreased shelf-life. Thus, an intermediate pH may provide the most desirable combination of quality and shelf-life when extensive aging is used.     

Wavelength selection in vis/NIR spectra for detection of bruises on apples by ROC analysis

Selection of informative wavelengths is a crucial step for online spectral imaging applications. In this paper, four cultivars of apples were utilized to select effective wavelengths for bruise detection within 380-1000 nm. Each of the wavelength variables was considered as an independent classifier for bruised/normal classification, and all classifiers were evaluated and compared by receiver operating characteristic (ROC) analysis. According to the area under the ROC curve (AUC), the reflectance difference between two wavelengths (R(λ₁) − R(λ₂)), was determined as the best wavelength pair for the Fuji, Jonagold, Orin and Sinano Gold cultivars as follows: R(808 nm) − R(760 nm), R(832 nm) − R(772 nm), R(834 nm) − R(762 nm) and R(788 nm) − R(742 nm), respectively. The performance of the wavelengths selected in this paper was measured by comparing the predicted sensitivity, predicted specificity and predicted classification accuracy with those of the model proposed by partial least squares discriminant analysis (PLSDA), which used all of the wavelength variables. The results showed that the predictive ability of both methods was generally on the same level.     

The suitability of plasma powder for cold-set binding of pork and restructured dry ham

To determine the ability of cold-set binder plasma powder (PP) for manufacturing restructured deboned dry ham, the effect of meat pre-treatment and PP preparation on the binding rate (k) and maximum binding force (BF_max) of pork model systems and deboned ham were evaluated. In pork model systems, the highest values for k (about 0.4 Ncm^− 2 h^− 1) and BF_max (about 2.5 Ncm^− 2) were obtained when powder or rehydrated plasma [in water or in NaCl aqueous solution at 0.5%] was applied onto the meat surface without additional pre-treatment or prior immersion in saline aqueous solution. Similar meat pre-treatment and PP preparation were used to restructure fresh deboned leg resulting in stable meat binding performances during salting and drying. An important increase in the binding force (BF_max > 10 Ncm^− 2) occurred over the drying period (after 4 weeks). Scanning electron microscopy showed different morphologies of the binding area, mainly depending on whether powder or rehydrated plasma was used.     

Oxidation in HiOx-packaged pork Longissimus muscle predisposes myofibrillar and sarcoplasmic proteins to N-nitrosamine formation in nitrite-curing solution

The effect of meat protein in situ oxidation on the formation of N-nitrosodiethylamine (NDEA) was investigated. Fresh minced pork was untreated (Con) or treated with 700 mg/kg α-tocopherol (Toc) or 300 mg/kg tea polyphenols (PPE), packaged in a HiOx atmosphere (78.8% O₂, 18.8% CO₂, 2.4% N₂), then stored at 2 ± 1 °C for up to 10 days. Crude myofibrillar (MP) or sarcoplasmic (SP) protein (20 mg/mL) extracted from stored meat was reacted with 43 μM sodium nitrite at 80 °C for 1 h. Lipid oxidation was totally inhibited in PPE pork but increased in Con and Toc samples after 10 days. There was significant protein oxidation (losses of sulfhydryls, formation of protein carbonyls) in both MP and SP in all samples during storage. However, the Con group suffered more extensive protein oxidation than Toc and PPE and produced more NDEA (P < 0.05), indicating that protein oxidation promoted nitrosation.     

Growth potential of Listeria monocytogenes strains in mixed ready-to-eat salads

In this study, a microbiological challenge test in three artificially contaminated retail mixed mayonnaise-based ready-to-eat salads stored at refrigerator temperatures (3 °C and 7 °C) for 48 h was carried out. Shrimp-tomato salad, smoked ham salad and garlic cheese salad were separately contaminated by a suspension of particular Listeria monocytogenes strains. The number of L. monocytogenes, Enterobacteriaceae, staphylococci and total plate count (CFU/g) was determined. Listeria monocytogenes growth potential in the salads was calculated and evaluated.A significant increase in total plate count and L. monocytogenes count throughout storage of all three investigated salads was found. Enterobacteriaceae levels were high at the beginning in all salads but significantly (p < 0.05) decreased throughout the experiment depending on the temperature.All investigated L. monocytogenes strains demonstrated growth at both temperatures but expressed different growth potential. Especially garlic cheese salad and smoked ham salad were able to support the growth of Listeria. Shrimp-tomato salad supported growth the least. The growth potential increased with the increasing temperature and exceeded 0.5 log₁₀ CFU/g in many cases. If the potential for growth is > 0.5 log₁₀ CFU/g, food products can potentially endanger human health. Reference strain (ATCC 7644) showed the least growth potential almost in all cases in comparison with strains isolated from frozen pollock loins and from thermally treated specialty sausage containing preservatives. To eliminate the occurrence of microbiological risks, the shelf-life of the studied salads was estimated.     

TBARS predictive models of pork sausages stored at different temperatures

2-Thiobarbituric acid reactive substances (TBARS) is an important quality index for pork sausages. To study this in pork sausages during storage, kinetic models were developed to predict TBARS content changes of pork sausages at different temperatures. The predictive models of TBARS content with respect to storage time and temperature were developed based on primary and Arrhenius equations. The regression coefficients (R² > 0.95) indicated the acceptability of the primary reaction and Arrhenius model for predicting TBARS content changes of pork sausages. The activation energy (E_A) of TBARS is 14.12 kJ mol^− 1, and the corresponding rate constant (k₀) is 9.262 × 10¹⁰. Relative errors between predicted and measured values of TBARS content are all within ± 8%. Thus, the established model could effectively predict the TBARS content of pork sausages between 5 and 35 °C during storage.     

Evaluating Previous Thermal Treatment of Chicken Patties by Visible/Near-Infrared Spectroscopy

Cooking history at the center point in chicken patties was quantified in terms of both time-temperature integrated indices (C and F) and endpoint temperature (T_max). Intact cooked patties were scanned for reflectance and transmittance spectroscopy. Reflectance resulted in better calibrations for the indices of thermal history than did transmittance. Three reflectance wavelength ranges, visible (400 to 700 nm), near-infrared (1100 to 2500 nm), and visible/near-infrared (400 to 2500 nm), were evaluated, and visible/near-infrared yielded the highest accuracy. The best calibration resulted in a standard error of prediction (SEP) of 0.11 log₁₀(min) for log₁₀C, 0.25 log₁₀(min) for log₁₀F, and 2.54°C for T_max on an independent validation sample set.     

Imaging optical diffuse reflectance in beef muscles for tenderness prediction

The objective of this study was to investigate the potential of a novel optical reflectance imaging method to predict beef tenderness. Two-dimensional (2D) optical reflectance in beef muscles induced by a point incident light was acquired. A set of five parameters were extracted from each reflectance image to describe quantitatively the reflectance profiles. Two parameters, q and B, were derived by numerically fitting the equi-intensity contours of the reflectance pattern. Two spatial gradients were calculated along the directions parallel and perpendicular to muscle fibers and total scattering intensity was obtained by excluding the specular reflectance. This method was applied to analyze 2D images of optical diffuse reflectance in 336 beef samples obtained from 14 steers in which large variations in tenderness were generated by altering animal genetics, suspension method and aging time as well as utilizing muscles varying in their inherent tenderness. Tenderness was evaluated using Warner–Bratzler shear force (WBSF). The effects of animal breed, muscle, types of suspension, and aging were investigated and results indicate that the scattering intensity measured at 1-d was correlated (R² = 0.50 at λ = 720 nm) with 10-d WBSF in M. longissimus dorsi muscles; and the q parameters measured at 1-d was correlated (R² = 0.46 at λ = 720 nm) with 10-d WBSF in M. psoas major muscles. These results show analyzing 2D reflectance images of meat surfaces provides valuable information regarding the physical characteristics of meat that are responsible for beef tenderness.     

Identification of animal meat muscles by visible and near infrared reflectance spectroscopy

Visible (VIS) and near infrared reflectance spectroscopy (NIRS) was used to identify and authenticate different meat muscle species. Samples from beef (n: 100), lamb (n: 140), pork (n: 44) and chicken (n: 48) muscles were homogenised and scanned in the visible (VIS) and near infrared (NIR) region (400-2500 nm) in a monochromator instrument in reflectance. Both Principal Component Analysis (PCA) and dummy partial least-squares regression (PLS) models were developed to identify different meat species. The models correctly classified more than 80% of the meat sample muscles according with the muscle specie. The results showed the potential of VIS and NIR spectra as an objective and rapid method for authentication and identification of meat muscle species.