The effects of irradiation on quality of injected fresh pork loins

A comparison of irradiation effects on injected and uninjected fresh pork loin quality was conducted. Sixty pork loins from pigs of similar genetics were obtained from a pork harvesting facility immediately prior to processing. Thirty loins were injected with a brine composed of 2.17% salt/3.04% phosphate/20.8% lactate brine while thirty were not injected. Injected loins were pumped to 13% added weight. Ten loins of each group of thirty were not irradiated while an additional 10 loins were irradiated at 2.2 kGy and the final ten loins were irradiated at 4.4 kGy. Lipid oxidation, color, purge, volatiles, and tenderness were measured on sections of the treated loins after 0, 7, 21, and 35 days of refrigerated storage. Lipid oxidation was minimal for the 0 and the 2.2 kGy-treated loins, but was significantly greater (P<0.05) at day 35 for the loins treated with 4.4 kGy. Warner-Bratzler shear (WBS) force measurements were significantly lower (P<0.05) for the injected loins, but irradiation did not have an effect on shear force. Purge was significantly lower for the uninjected loins irradiated at 2.2 kGy than for those irradiated at 0 and 4.4 kGy. The injection treatment did not alter the effects of irradiation on the quality characteristics measured.     

Bacteriology and storage life of moisture-enhanced pork

This study was undertaken to determine the impact of the moisture enhancement process on the bacterial contamination and storage life of vacuum-packaged pork loins. Bone-in and boneless pork loins injected with brine (sodium chloride, sodium phosphate, lemon juice) were obtained from a commercial processing facility and stored for 5 weeks in vacuum packaging at 2 and 5 degrees C. At weekly intervals, samples were excised to determine numbers of spoilage bacteria and pathogens. The loins were subjectively evaluated by a sensory panel to quantify appearance and odor acceptability. Moisture-enhanced loins were initially contaminated with a population of psychrotrophic bacteria that was approximately 2 log units higher than that for noninjected boneless loins. This difference was largely due to contamination by larger numbers of pseudomonads in the brine-injected loins. There were no significant differences in the initial numbers of lactic acid bacteria, Enterobacteriaceae, or Brochothrix thermosphacta. Similar trends in spoilage bacterial populations were observed for moisture-enhanced loins with bones, but Enterobacteriaceae counts were also found to be approximately 1 log unit higher for the injected product. Brine-injected loins generally had larger bacterial numbers at each storage time, but there were no consistent injection treatment effects on bacterial growth. Brine injection did not affect color or odor deterioration, and the storage life for vacuum-packaged loins was the same as that for noninjected controls. The incidence of Listeria monocytogenes was 21% for control loins and 27% for moisture-enhanced loins. Although the brine injection process resulted in an increase in bacterial contamination, there was no evidence that this contamination would affect the storage life of vacuum-packaged loins, and further research is necessary to determine the significance of the increased incidence of L. monocytogenes.     

The effects of RN genotype and tumbling on processing yield in cured-smoked pork loins

The objective was to investigate the effects of RN genotype and tumbling treatment on yields throughout the processing of cured-smoked loins. Furthermore, the economic outcome was calculated for the different treatments because the technological yield is important for the meat industry. The study comprised two separate trials, T1 and T2, and included loins from 62 and 32 female pigs crossbreed with Hampshire, respectively. All loins in T1 were tumbled, whereas half of the loins in T2 were tumbled and the remainder was non-tumbled. Glucose and glucose-6-phosphate concentrations in meat juice and drip loss were higher, and ultimate pH and technological yield lower in loins of the RN(-) carriers than those of non-carriers. Water loss during processing was largest at heating, when yield between RN genotypes differed the most for T2. Yield between genotypes differed the most at curing for T1. When tumbling was included in the processing the technological yield increased, but the RN allele was still negatively affected. Salt content in cured-smoked loins was higher in non-carriers than RN(-) carriers in T1, whereas salt content in non-tumbled non-carriers was significantly lower than in the other cured-smoked loins in T2. Tumbled cured-smoked loins contained more water than non-tumbled loins. There were moderate to high correlations between ultimate pH and processing yields except for curing yield. Water content in the cured-smoked loins was positively related to technological yield. The differences between the two trials suggest that the process design greatly influences the final product.     

Predicting cutability of packer-trimmed pork loins

This study explored the possibility of determining retail yields of packer-trimmed pork loins by the use of either a swine backfat probe or the Hennessy and Chong Fat Depth Indicator. The standard deviation for retail yield in this study was 3·82. Regression equations developed to predict percentages of retail yield from pork loins produced residual standard deviations that ranged from 4·20 to 2·94. Low to intermediate relationships were found between fatness measurements and percentages of fat-free lean from packer-trimmed pork loins. Prediction equations utilising the Fat Depth Indicator predicted retail yield percentages with greater precision than did a swine backfat probe (2·94 versus 3·33, respectively).     

Microbiological conditions of moisture-enhanced pork before and after cooking

Substantial numbers of aerobic bacteria but few coliforms or Listeria spp. and no Escherichia coli were recovered from both swab samples and brines circulated in cleaned equipment used for injecting pork loins. After meat was processed for 30 or 60 min, the numbers of aerobic bacteria in brines had increased by >1 log unit, to about 4.5 log cfu ml⁻¹, but coliforms were <2 and E. coli and Listeria spp. were <1 log cfu ml⁻¹. The numbers of bacteria on the surfaces of pork loins before and after injection of the meat were similar. No bacteria were recovered from the deep tissues of the uninjected meat, but aerobic bacteria were recovered at log-mean numbers of 2.1 log cfu g⁻¹ and coliforms at log-total numbers of 1.2 log cfu 25 g⁻¹ from 25 samples of deep tissues of injected meat. Aerobic bacteria were recovered at log total numbers of 1.0 log cfu 25 g⁻¹ from 25 samples of injected pork cooked to a central temperature of 61 °C, but no bacteria were recovered from the deep tissues of meat cooked to 70 °C. The findings suggest that moisture-enhanced pork cooked to a medium rare condition can be microbiologically safe.     

Characterization of striping in fresh, enhanced pork loins

To investigate the striping phenomenon in fresh, enhanced pork, a series of experiments were undertaken to identify possible causes of the problem. No one factor (individual brine components, brine pH, ingredient concentration, enhancement pressure, meat and brine pH, or enhancement level) was specifically identified, which could be used to reduce the severity of the striping problem. Furthermore, tumbling the product for 2h, did not reduce the amount of striping, indicating once striping has occurred, it is permanent. Evaluation of the striping pattern indicates that the stripes are formed not only at the needle injection site, but also follow the muscle fiber orientation. The use of darker pork provided more of a contrast when evaluating striping, thus exacerbating the perceived level of striping.     

Temperature abuse affects the quality of irradiated pork loins

The influence of temperature abuse on the quality of irradiated pork loins was investigated. Pork loins were obtained directly from a local packing plant, sliced and vacuum-packaged. Pork loins were randomly separated into 3 groups, sliced, and assigned to receive 0, 1.5, or 2.5 kGy electron-beam irradiation. Then, each chop was further cut into three equal pieces and assigned to three temperature treatments: Trt I was placed in a refrigerator directly after irradiation; Trt II was left at room temperature for 3 h before refrigeration; and Trt III was exposed at room temperature for 1 h three consecutive days with intermittent storage at 4 °C between exposures. Before irradiation, each loin pieces were vacuum-packaged. Color, 2-thiobarbituric acid reactive substances (TBARS), and volatiles were measured after 0, 14, 28 and 42 days of storage, and water-holding capacity and sensory characteristics of the loins were measured after 0, 14 and 28 days of storage. Temperature abuse had no significant effect on color, oxidation, and volatiles of irradiated pork loins. However, temperature abuse improved water-holding capacity of meat, which could be caused by the accelerated hydrolysis of muscle proteins at higher temperature. Irradiation increased redness, sulfur contents in volatiles and off-odor of pork loin. Off-odor and redness induced by irradiation sustained during storage. Among sulfur compounds, the content of dimethyl disulfide decreased gradually while the level of thiourea remained relatively constant. Irradiation also increased water loss, which might be related to the structural damage in membrane during irradiation. This study shows that temperature abuse has little effect on the quality of irradiated pork.     

Physicochemical and microbiological changes in irradiated fresh pork loins

The effect of γ-irradiation on the physicochemical and microbiological properties of fresh pork was studied. Radiation treatments were carried out under air on fresh pork loins at doses of 2, 4 and 8 kGy and the loins were evaluated for deamidation, solubility, sulphydryl content and surface hydrophobicity. Deamidation was significantly (p0.05) affected by the treatment with 98% deamidation at a dose of 8 kGy. No significant changes (p > 0.05) were noted in sulphydryl content under the same conditions. The increase in deamidation resulted in a decrease in hydrophobicity and an increase in protein solubility. γ-irradiation also reduced the number of microorganisms in the meat. Mesophiles were more resistant to the irradiation treatment than psychrotrophs and Pseudomonas. All irradiated pork samples (1 or 3 kGy) had a bacterial count lower that 10⁷ CFU/g after 15 days of storage. A minimal dose of 1 kGy was sufficient to increase the shelf life of fresh pork loins although variations in initial pork contamination was found to be the determining factor accounting for the effectiveness of the treatment.     

Prediction of color and pH measurement throughout boneless center-cut pork loins

Boneless pork loins (N=95) divided into three groupings based on National Pork Producers Council color standards were utilized to characterize changes in color and pH throughout the loin. CIE L(?), CIE a(?), CIE b(?), saturation, and hue angle differed (P<0.05) for color category and chop position. A color category by position interaction (P<0.05) existed only for pH values. These differences in color and pH measures throughout the loin indicate that one measurement may not characterize the entire boneless loin. For all color and pH measures significant orthogonal and polynomial contrasts existed, therefore, separate regression equations were developed for each color category to predict position response. Multiple regression equations were significant for most objective measures of color and pH, but the low R(2) values indicate that these models provide little information as to changes in color and pH throughout the boneless pork loin.     

Bacterial contamination of recirculating brine used in the commercial production of moisture-enhanced pork

In a commercial process for the production of moisture-enhanced pork, boneless pork loins were conveyed through a recirculating injection apparatus, and brine (sodium phosphate, sodium chloride, and lemon juice solids) was pumped into the meat through banks of needles inserted automatically into the upper surfaces of cuts. Brine samples were collected at intervals during the production process and analyzed to determine the total plate count and the numbers of lactic acid bacteria, pseudomonads, Brochothrix thermosphacta, and Enterobacteriaceae. Listeria monocytogenes numbers in the brine were determined using a PCR with primers for the hemolysin gene in combination with a most probable numbers determination. Maximum numbers of bacteria (log CFU/ml) recovered from the brine after 2.5 h of recirculation were as follows: total plate count, 4.50; lactic acid bacteria, 2.99; pseudomonads, 3.95; B. thermosphacta, 2.79; and enterics, 3.01. There was an increase in the number of L. monocytogenes in the recirculating brine with time, reaching a maximum of 2.34 log CFU/100 ml after 2.5 h of moisture-enhanced pork production. Thus, recirculating brines can harbor large populations of spoilage bacteria and L. monocytogenes and are an important source of contamination for moisture-enhanced pork.     

Survival of Campylobacter jejuni and Salmonella enterica Typhimurium in vacuum-packed, moisture-enhanced pork

The abilities of Campylobacter jejuni and Salmonella enterica Typhimurium to survive in vacuum-packaged, moisture-enhanced pork stored at 4 or 10°C were examined. Pork loins were surface inoculated with either C. jejuni or Salmonella Typhimurium and then moisture enhanced to a target of 10 or 20%. The enhanced pork loins were sliced 1 cm thick and vacuum packaged. A pork loin without moisture enhancement was sliced and vacuum packaged as a control. Samples were collected, plated, and the numbers of surviving organisms were determined periodically during storage at 4 and 10°C. The numbers of C. jejuni or Salmonella Typhimurium in samples with different moisture enhancement levels were similar (P > 0.05). No significant differences (P > 0.05) in C. jejuni counts were observed between samples at 10°C and those at 4°C. In contrast, the numbers of Salmonella Typhimurium in samples at 10°C had significantly (P < 0.05) increased (0.41 log CFU/g) from those at the refrigerated temperature of 4°C. Vacuum storage at 4 and 10°C for 28 days did not result in dramatic reductions in the mean numbers of C. jejuni and Salmonella Typhimurium. Our findings indicate that vacuum packaging under chilled conditions will not add substantially to safety for moisture-enhanced pork. Strict hygienic practices or the implementation of decontamination technologies is recommended.     

Survey of conditioning indicators for pork loins: changes in myofibrils, proteins and peptides during postmortem conditioning of vacuum-packed pork loins for 30 days

This study was performed to examine the changes in myofibrils, proteins and peptides during postmortem conditioning of vacuum-packed pork loins at 4 °C for 30 days. The fragmentation of myofibrils has been observed during postmortem aging for 20 days and its ratio increased until 20 days. The 32 kDa component derived from troponin T increased during storage for 20 days, while a glyceraldehyde 3-phosphate dehydrogenase (GAPDH) among sarcoplasmic proteins was significantly degraded during storage for 15 days. Some oligopeptides increased during such storage, two peptides (peptides P1 and P2) significantly increasing during storage for 20 days. Their sequences were APPPPAEVHVHEEVH (P1) and VPTPNVSVVDLT (P2). Homology analysis showed that peptides P1 and P2 were derived from troponin T and GAPDH, respectively. It was concluded that the fragmentation of myofibrils, the increases in the 32 kDa component and peptides P1 and P2, and the decrease in GAPDH were useful as conditioning indicators of progressive degree during the storage of pork loins stored at 4 °C.     

Biogenic amines content during extended ageing of dry-cured pork loins inoculated with probiotics

The study determined the content of biogenic amines in dry-cured pork loins inoculated with Lactobacillus casei ?OCK 0900 probiotic strain, in 4, 8 and 16 month-old samples. Cadaverine, putrescine and tryptamine levels showed a time-dependent increase during ageing. Histamine and spermidine were not detected. Spermine which was present at very low concentrations, tended to decrease. Cadaverine and tryptamine were the main biogenic amines at the end of the ageing period with average values of 39.6 mg/kg and 49.2 mg/kg respectively. The results were within the values reported for other dry-cured meat products and below the suggested toxic levels. The pH of samples increased significantly (p < 0.05) with ageing time. The a_w values decreased significantly (p < 0.05) during ageing, with a mean value of 0.953 ± 0.007 for samples aged for 4 months, and 0.852 ± 0.007 for samples aged for 16-months.     

Effect of enhancement on the formation of heterocyclic amines in cooked pork loins: Preliminary studies

Heterocyclic amines (HCAs) which are produced in meats cooked at high temperature a risk factor for certain human cancers. This study evaluated the effect of enhancement on HCA formation in cooked pork loins. Three samples of pork loin were prepared including non-injected loin, 12% water-injected loin, and 12% salt/phosphate injected loin. The HCAs were identified in all samples: PhIP (2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine), MeIQx (2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline), and DiMeIQx (2-amino-3,4,8-trimethylimidazo [4,5-f]quinoxaline). Injection of salt/phosphate significantly reduced the level of PhIP by 42.7%, MeIQx by 79.0%, and DiMeIQx by 75.0%. Enhancement with water alone did not reduce HCA formation.     

Effects of dry aging of bone-in and boneless strip loins using two aging processes for two aging times

This experiment investigated the combined effects of two dry-aging methods (unpackaged and in a bag), two loin-cut styles (bone-in shell loins and boneless strip loins), and two aging times (21 and 28 days) on the physical, chemical, sensory, and microbial properties of dry-aged beef. Sections from shell and strip loin were assigned randomly to be aged unpackaged or aged packaged in a bag with high moisture permeability. Weight losses increased with aging time. Shell loins lost more (P < 0.05) weight during aging compared with strip loins; dry aging in a bag had less (P < 0.05) weight loss than unpackaged aging. There were no differences (P > 0.05) in any of the sensory traits between shell and strip loins or dry aging using a traditional method or in a bag. Dry aging in a bag creates positive effects on yields, no negative effects on product quality, and adds flexibility and control of the aging environment.     

Effects of dry aging of bone-in and boneless strip loins using two aging processes for two aging times

This experiment investigated the combined effects of two dry-aging methods (unpackaged and in a bag), two loin-cut styles (bone-in shell loins and boneless strip loins), and two aging times (21 and 28 days) on the physical, chemical, sensory, and microbial properties of dry-aged beef. Sections from shell and strip loin were assigned randomly to be aged unpackaged or aged packaged in a bag with high moisture permeability. Weight losses increased with aging time. Shell loins lost more (P < 0.05) weight during aging compared with strip loins; dry aging in a bag had less (P < 0.05) weight loss than unpackaged aging. There were no differences (P > 0.05) in any of the sensory traits between shell and strip loins or dry aging using a traditional method or in a bag. Dry aging in a bag creates positive effects on yields, no negative effects on product quality, and adds flexibility and control of the aging environment.     

Effects of cooked temperature on pork tenderness and relationships among muscle physiology and pork quality traits in loins from Landrace and Berkshire swine

The effect of, and associations between, loin muscle morphology and pork quality indicator traits were assessed at three cooked temperatures in loin chops from 38 purebred Berkshire and 52 purebred Landrace swine. Three loin chops from each pig were randomly assigned to cooked temperature treatments of 62, 71, or 79 °C and loin tenderness was assessed as Warner–Bratzler shear force (WBSF). Cooked temperature (P < 0.001), breed (P < 0.001) and breed × cooked temperature (P < 0.001) effects influenced loin chop WBSF, whereby WBSF increased as cooked temperature increased. Chops from Landrace pigs had greater WBSF at each cooked temperature compared with chops from Berkshire pigs. Chops from Landrace pigs became less tender with increasing cooked temperature, whereas chops from Berkshire pigs became less tender only when cooked to 79 °C. In loins from Landrace pigs, Minolta a1 at 62 °C (R² = 0.07), and average muscle fiber diameter at 71 °C and 79 °C (R² = 0.07 and 0.24, respectively), contributed to WBSF variation. In contrast, for loins from Berkshire pigs, loin ultimate pH and intramuscular fat percentage accounted for 27% and 30% of the variation in WBSF at 62 °C and 71 °C, respectively, and loin ultimate pH accounted for 7% of variation in WBSF at 79 °C. Results suggest that loins from Berkshire pigs have properties that resist toughening at greater cooked temperatures and that associations between quality measures and loin tenderness differ between Landrace and Berkshire pigs.     

Proteolytic activity of Penicillium chrysogenum and Debaryomyces hansenii during controlled ripening of pork loins

The role of micro-organisms on the ripening process of dry-cured ham, particularly with respect to proteolysis, is not clear. This is partially due to the lack of an adequate system to study changes on a sterile control meat product for long ripening times. Using a meat system based on sterile pork loins ripened under aseptic conditions for 106 days, the contribution to the proteolysis of two micro-organisms isolated from dry-cured ham has been established. Changes were studied by SDS-PAGE of sarcoplasmic and myofibrillar proteins, capillary zone electrophoresis (CZE) of low ionic strength-soluble nitrogen compounds, and HPLC of free amino acids. Debaryomyces hansenii Dh345 did not show any significant proteolytic activity. However, Penicillium chrysogenum Pg222 showed high proteolytic activity on myofibrillar proteins resulting in an increase in soluble nitrogen compounds. For this, P. chrysogenum Pg222 should be considered to be used as starter culture in meat products made using long ripening times.     

Effects of micro-perforated film on the quality and shelf life improvements of pork loins during chilled storage

The effects of micro-perforated film (MPF) packaging method on the quality and shelf life of pork loin during chilled storage were investigated, compared with non-packaging (control) and non-perforated film (PPF) packaging. Loins were removed from five hogs after slaughter and chilling, and each loin was portioned into four parts. These samples (40 sections) were allocated to each of five intervals (0, 1, 4, 7 and 14 days) to minimize variation among treatments and stored for 14 days under 55±10% relative humidity and 0±1?°C. Total aerobic counts of control sample were significantly lower than those from MPF or PPF loins after 14 days of storage. At 14 days, the counts of Pseudomonas and Enterobacteriaceae in the samples from MPF were significantly lower than those from PPF. At 7 days, 'L' value for the control and 'a' value for PPF were significantly lower, and ΔE values for the control were significantly higher than other samples. During storage time, percentage weight loss was the most in the control samples with MPF following and PPF the least. Accordingly, water contents decreased highest in the control samples followed by those from MPF and PPF. TBA values increased with storage time, however no significant differences were observed among treatments. Sensory evaluation analyses showed that MPF samples were generally better evaluated in all parameters over the storage time. Therefore, it has been concluded that MPF could be used as an effective packaging technology since it extends the shelf life of fresh meat by controlling the microbial growth and evaporation at a moderate level.     

Protein quality and microbiological changes in aerobically- or vacuum-packaged, irradiated fresh pork loins

The effect of gamma-irradiation on the physicochemical, organoleptic and microbiological properties of pork was studied, during 43 days of storage at 4±1°C. Irradiation treatments were carried out under air or vacuum packaging on fresh pork loins at a dose of 6 kGy, at two different dose rates: 2 kGy/h and 20 kGy/h. The loins were evaluated for protein sulphydryl content and emulsifying capacity, surface hydrophobicity of proteins and sensorial evaluation. Regardless of the type of packaging and dose rate of irradiation, all irradiated pork samples were effectively prevented from bacterial spoilage for at least 43 days. Meat redness and texture of irradiated loins were relatively well preserved during the storage period, especially when samples were stored under vacuum. Overall, the physicochemical and organoleptic changes in pork loins appeared to be relatively little affected by the 6 kGy dose. No marked changes in emulsifying capacity and protein sulphydryl content of proteins were noted throughout the storage period. However, the hydrophobicity was reduced (P?0.05) by the faster dose rate of irradiation and by longer storage.