The effects of electrical stimulation, thawing, ageing and packaging on the colour and display life of lamb chops

Electrical stimulation, freezing and thawing, ageing and type of packaging used during ageing are factors which could influence the final colour of meat. The experiment reported here determined the individual and additive effects of these factors in displayed lamb. Initial panel scores for colour of chops were increased by electrical stimulation and decreased by thawing and by ageing for up to six weeks. Chops from loins which had been aged in vacuum pack had higher initial scores than those aged in oxygen-permeable film. Hunter colour values for chops from stimulated carcasses were much less variable than those for chops from unstimulated carcasses. Stimulation, therefore, produced a more uniform product. Hunter L, a and b values all declined during display, the greatest decline being in a (redness). Hunter values were not good predictors of initial panel scores but Hunter a and hue (a b ) both declined with panel scores. With no ageing, the display life of stimulated chilled lamb was longer than that of unstimulated lamb, but this advantage disappeared after ageing for 2 weeks in a vacuum pack. The display life of thawed unstimulated lamb was only slightly inferior to that of chilled unstimulated lamb when both were vacuum-packed, but thawed stimulated lamb resulted in a much reduced display life. Ageing of loins in oxygen-permeable film adversely affected display life of chops. Total drip loss from rigor to the end of display was significantly affected by all treatments except stimulation. The dominant cause of drip loss was the freeze-thaw treatment. In chilled and thawed lamb, ageing increased drip. Packaging had a lesser effect on drip.     

Colour stability of thawed lamb chops. I. Effect of short-term frozen storage

The colour stability of thawed lamb chops was examined, by colour panel and colorimeter, under simulated retail display conditions. Chops held frozen at –20°C for 1 week had a display life of 3 days when thawed, compared with 2 days for fresh chops. When the frozen storage was increased to 8 weeks the display life was reduced to 1 day. When the whole loin was stored frozen for 8 weeks, chops cut from it and thawed had a 2-day display life. By comparison, vacuum-packed chops stored at –1.5°C for 8 weeks had a 3-day display life. The relationship between Hunter colour values and panel scores is discussed.     

Colour stability of thawed lamb chops. II. Chops from loins frozen for long periods

Colour stability was examined during simulated retail display of thawed chops cut from loins after frozen storage. When loins had been stored for 30 weeks at –20°C, the thawed chops had a 2-day display life. If chops were stored at –20°C for an additional 8 weeks before thawing, display life decreased to 1 day. When loins were thawed, then cut into chops, a display life of 4 days was obtained. Thawed chops from loins stored for 60 weeks behaved similarly. The experiment showed no adverse trend with increased frozen storage, except for increased drip, and indicates definite commercial possibilities for chops cut from loins stored frozen.     

Effect of tray liners on the drip loss of lamb chops during retail display

The amount of drip lost by lamb chops during display was affected by the type of tray liner used. In one study involving chilled and frozen/thawed meat, the use of an absorbent paper liner increased the drip loss and influenced whether or not the quantity of drip was affected by freezing/thawing. In another study, thawed chops held for 24 h on plastic coated trays without liner or on a plastic coated liner had less than 2% drip loss, whereas adjacent chops from the same loin processed and held in the same way but displayed on liners of absorbent paper or paper pouches of diatomaceous earth lost 4·3% and 5·6% drip, respectively. This effect of the material in contact with the meat should be considered when reporting drip loss data and when comparing results with those of other researchers.     

Increase in retail display of frozen lamb chops with increased loin storage time before cutting into chops

There is a steady deterioration of the colour of lamb chops during frozen storage. Storing meat in carcass form or as primals before cutting and packaging minimizes the exposure of the meat surfaces to deteriorating environmental effects. This experiment examines the effects of storage conditions (form, time and temperature) on the display life of frozen chops. Loins were removed from recently frozen carcasses and stored for 0, 10, 20 or 30 weeks at temperatures of -5°C, -10°C and -20°C. Chops were cut from the stored loins, packaged in oxygen permeable film, stored in the dark at -20°C for 0,4,8 or 12 weeks and then displayed at -20°C under continuous lighting. The retail display life of the chops was assessed by an experienced colour panel. The most rapid colour deterioration occurred in chops cut from unstored frozen loins and held for 12 weeks prior to display (display life of less than 1 day). Chops cut from loins stored for 30 weeks at -20°C, and then held for 12 weeks prior to display had a display life of 23 days. Both increased loin storage temperature and an increased duration of chop storage before display decreased the retial display life. This study indicates that frozen storage of cut chops for as little as 4 weeks reduces the display life by almost 80% so that whole carcasses or loins rather than cut chops should be shipped to distant markets. unstored frozen loins and held for 12 weeks prior to display (display life of less.     

Factors influencing frozen display life of lamb chops and steaks: Effect of packaging and temperature

Frozen lamb loin and rib chops and leg steaks were wrapped in film of high oxygen permeability or vacuum packaged in film of low oxygen permeability and stored in the dark at -10, -20 or -35°C for periods from 0-20 weeks. After storage, the wrapped cuts were displayed in an open-top cabinet operating at -20°C under continuous fluorescent lighting (Philips Deluxe 32°). Cuts were evaluated by a trained colour panel to determine acceptable display life, and chop lean colour was evaluated using a Hunter colorimeter. Cuts wrapped in oxygen permeable film had better colour retention during storage and display. Storage of the frozen chops reduced the display life, with the largest effect occurring during the first 4-5 weeks' storage. Cuts stored at -10°C had no display life after 10 weeks' storage, whereas cuts stored at -20 and -35°C had some acceptable display life even after the longest storage period tested. Rib chops in general had better colour stability than loin chops.     

Influence of different gas compositions on the short-term storage stability of mother-packaged retail-ready lamb packs

Longissmus dorsi muscles were removed from Suffolk cross-breed lambs (aged 4-9 months) and cut into steaks. Lamb steaks were over-wrapped on trays and placed in vacuum pack bags. Bags were divided into 3 groups and flushed with gas mixtures containing 100:0, 90:10 or 80:20/CO(2):N(2). Mother packed lamb bags were stored for 4 days (T2) and 7 days (T3), respectively, in darkness at 4 °C, prior to retail display. The effect of aerobic packaging alone on lamb meat quality was used as the control (T1). Under retail display, all over-wrapped trays were held under refrigerated conditions (4 °C, 616 lx) for up to 8 days. Steaks were assessed for microbial growth, oxidative and colour stability as well as pH every 2 days. Mother-packing in 100:0/CO(2):N(2) was the most effective way of extending the storage life of retail ready lamb prior to display, particularly over longer storage periods. TVCs for T3 lamb meat using all gas compositions remained below 2.0×10(6) CFUs/g meat up until day 6 compared to day 4 in both T1 and T2 lamb. Lipid oxidation in lamb mother-packed for 7 days occurred at a faster comparative rate than discolouration and microbial growth and was the major determinant of shelf-life. However, under simulated retail display in aerobic packages, TBARS values did not increase significantly. There was no significant difference between Hunter 'a' values for T3 lamb meat and the control, but T3 meat mother-packed in 100:0/CO(2):N(2) had higher 'a' values than those of the control and T3 meat packed in other gas compositions. Lamb steaks in T3 previously mother-packed in 100:0/CO(2):N(2) were also significantly (p<0.05) higher than those of T2 on day 0. T3 meat also maintained initial colour values over those of the control.     

Meat quality comparison between fresh and frozen/thawed ostrich M. iliofibularis

A pairwise comparison of the meat quality between fresh and frozen/thawed Musculus iliofibularis was conducted. Thirty-two (16 left; 16 right) muscles were collected and allocated to two treatments: fresh and frozen/thawed. Frozen vacuum-packed samples were stored for 1 month at -20°C before thawing. The fresh samples had higher pH (P<0.05), water binding capacity (P<0.05), CIE L* (P<0.0001), CIE a* (P<0.05) and Chroma values (P<0.05) than the frozen/thawed samples, indicating the fresh samples were bright red in appearance and had minimal exudate. The frozen/thawed samples lost 5.09±0.21% moisture during thawing and had a greater drip loss (P<0.0001) and shear force (P<0.001). No differences were obtained with regard to cooking loss, CIE b*, hue and TBARS. Protein oxidation (mM carbonyls/mg protein) was lower (P<0.05) in the frozen/thawed samples, which was attributed to the higher (P<0.0001) protein concentration negating the higher (P<0.001) carbonyl content. Industrial freezing and thawing regimes negatively affected the quality of ostrich meat.     

Combined effect of freeze chilling and MAP on quality parameters of raw chicken fillets

The effect of short-term frozen storage prior to thawing on the quality of freeze-chilled chicken fillets was investigated, as was the effect of modified atmosphere packaging (MAP). Four process treatments were used: (1) fresh chicken chilled at 4 degrees C without previous freezing, (2) freeze-chilled for 7 days and thawed at 4 degrees C, (3) chilled at 4 degrees C packaged under MAP (70% N(2)-30%CO(2)), and (4) packaged under MAP, freeze-chilled for 7 days and thawed at 4 degrees C. Microbiological, chemical and sensory analyses were conducted on samples for a period up to 15 days. Freeze-chilled fillets gave a lower total viable count (TVC) at a given sampling day than chilled fillets. MAP, as expected, delayed microbial growth. The Pseudomonads were the dominant microbial species in fillets under aerobic conditions. MAP reduced the populations of Pseudomonads by 2-4 log cfu/g. Lactic acid bacteria (LAB) and Enterobacteriaceae increased progressively for all treatments throughout storage. Yeasts and molds were inhibited by MAP and by freeze chilling. Total volatile basic nitrogen (TVB-N) values increased rapidly for the chilled fillets but remained significantly lower for the freeze-chilled and the MA-packaged samples. MAP and especially freeze chilling enhanced drip loss. MAP did not affect redness or yellowness of product while freeze chilling decreased product redness. Lightness was not affected by either MAP or freeze chilling. Based on taste, which proved to be the most sensitive sensory attribute, shelf life of product ranged from 6 to 7 days for all treatments leading to the conclusion that freeze chilling is a suitable technology for fresh chicken fillets enabling their distribution as a frozen product and upon subsequent thawing at their final destination, their retail display as chilled products. MAP in combination with freeze chilling had a negligible effect on product quality.     

Effect of freezing method and frozen storage duration on instrumental quality of lamb throughout display

This study evaluated the effect of freezing method (FM) (air blast freezer, freezing tunnel, or nitrogen chamber) and frozen storage duration (FSD) (1, 3, or 6 months) on the instrumental measurements of quality of thawed lamb, aged for a total of 72 h, throughout a 10-d display period, compared to the quality of fresh meat. pH, colour, lipid oxidation, thawing, and cooking losses in Longissimus thoracis and lumborum muscle, were determined following standard methods. FM affected yellowness, FSD redness and thawing losses, and both affected oxidation (increased as freezing rate decreased and/or as storage duration increased). When compared with fresh meat, the main differences appeared on oxidation (where a significant interaction between treatment (3FM × 3FSD + fresh meat) with display duration was detected), and on total losses (thaw + cook losses). Oxidation was lower in fresh meat, but values were not significantly different from those stored frozen for 1 month. Fresh meat had smaller total losses than did thawed meat, but losses were not significantly different from meat frozen in the freezing tunnel and stored frozen for 1 month. Display duration had a greater effect on instrumental quality parameters than did FM or FSD. pH, b*, and oxidation increased, and L* and a* decreased with an increase in the number of days on display. In conclusion, neither freezing method nor frozen storage up to 6 months influenced extensively the properties of lamb when instrumental measurements of quality were measured in meat that had been displayed for 1 d after thawing. The small deterioration shown in this study should not give consumers concerns about frozen meat.     

Effect of rigor temperature and frozen storage on functional properties of hot-boned manufacturing beef

Within 45 min post-mortem, 10mm thick strips of semitendinosus muscle from both unstimulated and high voltage stimulated heifer sides were held at 0, 5, 10, 25 and 35 °C for 24 hr, during which they entered rigor. Half the samples were frozen and stored at -20 °C for one month. The pH, sarcomere length, drip, total (TPS), myofibrillar (MPS) and sarcoplasmic (SPS) protein solubilities, and Hunter L (?), a (?) and b (?) values were determined at 24 hr and on thawed samples. Electrical stimulation did not significantly affect any of the parameters measured. The ultimate pH of samples entering rigor at 10 and 25 °C was lower (p < 0.001) than that of samples held at the other temperatures. Rather surprisingly, there was no significant difference in sarcomere length due to rigor temperature. Samples entering rigor at 35 °C had lower TPS, MPS and SPS values than samples held at 0 to 25 °C (p < 0.001). The MPS increased with rigor temperature up to 25 °C (p < 0.001). Drip and total moisture losses, and Hunter L (?), a (?) and b (?) values also increased with rigor temperature (p < 0.001) whereas SPS decreased and NMR meat water spin-lattice relaxation time (T1) shortened with increasing rigor temperature (p < 0.001). Hue angle and cook loss decreased with rigor temperature in 24 hr samples but increased with rigor temperature in frozen samples. After frozen storage, SPS, T1, cook loss and Hunter L (?), a (?), b (?) values decreased, but TPS, MPS, drip losses and hue angle increased. There were significant (p < 0.05) correlations between SPS, hue angle, drip losses and T1.     

Lipolytic and proteolytic properties of dry-cured boneless hams ripened in modified atmospheres

We studied proteolytic and lipolytic properties of dry-cured boneless ham (porcine quadriceps femoris) made with chilled (10°C, 48 h) or frozen/thawed meat (frozen at -20°C frozen for 90 days and followed by thawing at 10°C for 48 h) were determined. Dry-cured meats were stored in modified atmosphere packages (100% N(2) and a mixture of 75% N(2)+25% CO(2)) at 15°C with the intention of reducing ripening space. Results showed that dry-cured hams made with frozen/thawed raw meat had more salt, volatile fatty acids and free fatty acid content after salting and smoking. Whereas, samples prepared with chilled meats contained more nitrogenous compounds (water-soluble nitrogen, non-protein nitrogen, and free amino acids). Volatile and free fatty acid contents in all samples significantly increased with storage. Acetic acid was the predominant volatile fatty acid. To confirm lipolytic activity in dry-cured ham stored in modified atmospheres, we calculated the lipolytic coefficient. The lipolytic coefficients of all samples were positive values and significantly (P<0.05) increased with storage indicating lipolysis in samples were still active. Furthermore, nitrogenous compounds in dry-cured ham significantly (P<0.05) increased with storage indicating proteolysis in samples were not affected by modified atmosphere storage. Aerobic, anaerobic and lactic acid bacteria counts in dry-cured meats were stable to modified atmospheres storage for 20 weeks at 15°C. Flavor, texture and color score in sensory evaluation for dry-cured ham made with chilled meat were significantly higher than that made with frozen/thawed meat. All samples had high overall acceptance scores in sensory evaluation. Results in this study suggested that dry-cured boneless ham stored in modified atmospheres for 20 weeks at 15°C was another feasibility to ripen the meat without affecting lipolysis, proteolysis, microbiology and sensory quality.     

Meat and storage effects on processing characteristics of beef roasts

Two experiments were done to determine the effect of storage conditions and meat cut on the processing characteristics of beef roasts. The first experiment examined the effect of storage condition (fresh/frozen), cap on/off, thawing regime and holding time post thawing on purge, brine uptake, cook yield and colour of raw and cooked roasts. The second experiment examined the effect of meat cut (insides/flats) and chilled storage for up to 8 weeks on processing characteristics of roast beef. Purge was greater for insides stored frozen without cap and air thawed. Frozen thawed cuts had increased brine retention after injection, after tumbling and after cooking. Flats had less purge and higher cook yields when manufactured into roast beef. Raw and cooked colour was not significantly affected by most factors investigated. Raw meat was more red than meat that had been frozen.     

Effect of oxidized dietary lipid and vitamin E on the colour stability of pork chops

The effect of oxidized corn oil and vitamin E (α-tocopheryl acetate) in pig diets on the oxidative stability of muscle lipids and on the surface colour characteristics of fresh and previously frozen pork chops in refrigerated storage was investigated. Lipid oxidation (TBARS values) and surface redness (Hunter 'a' values) were significantly influenced (P < 0·01) by dietary α-tocopheryl acetate levels but not by degree of oxidation of dietary corn oil. Lipid oxidation and colour deterioration during refrigerated storage were greater in previously frozen chops compared to fresh chops. TBARS values were lower and Hunter 'a' values higher in pork chops from pigs fed 100 and 200 mg α-tocopheryl acetate/kg diet compared to pigs fed 10 mg/kg diet after 2, 4, 6 and 8 days of refrigerated storage. Hunter 'a' values were significantly correlated (P < 0·01) with the logarithm of TBARS values. The results suggest that oxidation of myoglobin precedes oxidation of muscle lipids in pork chops stored at 4°C.     

CRANBEFCRY JUICE MARINADE IMPROVES SENSORY AND MICROBIOLOGICAL PROPERTIES OF VACUUM-PACKAGED LAMB CHOPS

Marination was investigated as a means to add value and improve the palatability of lamb chops. Vacuum-packaged whole lamb loins (n = 24) were assigned randomly to a 14 or 20-day aging period. Loins were split and right and left sides were designated to receive one of two treatments: control or marinade with spice rub. Loins were cut into chops and chops were vacuum-packaged and displayed for 0–, 7– or 14-days in a retail display case. Chops from both aging periods assigned to the 0 day retail display period were evaluated for both raw and cooked characteristics by consumers. Consumers indicated that cooked appearance. odor, juiciness, flavor, tenderness, and overall-like were higher for treated chops than for controls (P < 0.05). However, consumers preferred the appearance of raw control chops over the appearance of raw treated chops (P < 0.05). Treated lamb chops had lower aerobic plate counts at 7 and 14 days of retail display for both aging periods (P < 0.05), and lower 2-thiobarbituric acid (TBARS) values than control chops (P < 0.05). A treatment × retail display day interaction (P < 0.05) was observed for TBARS values as treated chops had lower TBARS values than control chops as days of retail display increased. Marinating lamb chops improved palatability traits of cooked lamb chops and extended the shelf-life characteristics of raw lamb chops.     

THE EFFECTS OF FROZEN STORAGE AND PROTECTIVE STORAGE WRAP ON THE RETAIL CASE-LIFE OF PORK LOIN CHOPS

Loin chops from 60 pork carcass sides were utilized to evaluate the influences of frozen storage and protective storage wrap upon factors contributing to the retail case-life of thawed chops. The composite results of this study indicated that pork loin chops could be frozen and stored for 168 days or less at ?30° C and have a retail case-life of at least 6 days, under the conditions employed in the present study. The possible exception is an amount of drip in the packages of chops stored in certain protective wraps which may be unacceptable when displayed for prolonged periods.     

Electrical Stimulation, Hot-Boning and Prerigor Cookery Effects on Lamb Longissimus Tenderness

Paired halves of 32 lamb carcasses were either electrically stimulated (ES) or not (NES), then assigned to one of the following treatments: (1) hot-boned, cooked prerigor, frozen and reheated (HEPRC); (2) conventionally chilled and boned, cooked, frozen and reheated (CB-ARC); (3) hot-boned, frozen and cooked (HB); and (4) cold- boned, frozen and cooked (CB). Electrical stimulation lowered (P < 0.05) peak force (PF) of chops from CB-ARC, HB and CB treatments. Nonstimulated HB-PRC chops had a lower (P < 0.05) PF than ES, HB-PRC chops. Lower (P < 0.05) compression values were noted for HEPRC and CB-ARC chops than for HB and CB chops. Electrical stimulation reduced (P < 0.05) PF regardless of cooking method. Chops cooked in the microwave had lower (P < 0.05) work values than chops cooked in the convection oven.     

Effect of freezing on sensory quality, shear force and water loss in beef M. longissimus dorsi

The objective of this study was to determine how sensory quality, shear force and water loss differ between beef stored either chilled or frozen before cooking. Meat tenderness was analysed instrumentally and sensorially using both a consumer panel and a semi-trained panel. Both M. longissimus dorsi (LD) from eight young Holstein bulls were cut into eight samples, weighed, vacuum packed and aged at 4 °C for 2, 7 or 14 days. After ageing, the frozen samples were kept at −20 °C prior to heat treatment. Water holding capacity was recorded as purge or thawing loss and cooking loss or as combined loss. Sensory analyses were performed on samples aged 7 days. Peak force values declined with ageing time and freezing. Frozen meat aged 2 days had the same peak force values as chilled meat aged 7 days. Total energy was the same for both treatments at day 2 and 7, whereas at day 14 frozen samples showed significantly higher values than chilled samples. The sensory panel experienced the chilled meat to be more tender, juicier and having a more intense meat taste than the frozen meat, whereas the consumers could not find any significant difference in degree of liking. Water holding capacity was lower for the frozen samples. The results indicate that conclusions from studies concerning sensory quality of beef will depend on whether the meat has been kept chilled or frozen before testing.     

Effect of different storage conditions on E. coli O157:H7 and the indigenous bacterial microflora on lamb meat

Lamb chops inoculated with 2.23-2.83 log cfu/g of E. coli O157:H7 strain NCTC 12900 were packed in air (AP), vacuum (VP), and two modified atmospheres (MAP) consisting of 100% CO2 and a commercial mixture of 35% CO2/35% O2/30% N2. All samples (initial total counts <3.5 log cfu/g) were stored in a commercial cold storage facility set at 4 degrees C and one AP trial also at 12+/-1 degrees C in a temperature controlled incubator. Pathogen and indigenous flora evolution, physicochemical and sensory changes, surface packages temperature and MAP gas composition were monitored throughout the lamb meat shelf life. Temperature monitoring revealed that during chilled storage packed chops exceeded 7 degrees C about 3% of the time for periods of 10-20 min at 6 h intervals corresponding to defrosting cycles. In AP samples under these conditions, the E. coli O157:H7 strain had an overall increase of 0.48 log cfu/g by day 12. This increase, which may be regarded as an artefact of the sampling procedure, might also be a response to fluctuating temperatures. Regardless of rapid proliferation of the background microflora on AP lamb meat kept at 12+/-1 degrees C, the pathogen significantly increased by 2.35 log cfu/g after nine days. There was a slight decrease (0.20 log cfu/g) of the pathogen numbers after four weeks cold storage in VP despite a significant increase in lactic acid bacteria (LAB). With a relatively small outgrowth of LAB, chilled storage in 100% and 35% CO2 resulted in significant differences compared to similar conditions in air (decrease from initial numbers of 0.80 and 0.45 log cfu/g, respectively). Our data confirm the importance of effective temperature control to prevent pathogen growth on raw meat and also that contaminated meat remains hazardous regardless of refrigeration and protective packaging. Further studies are needed to determine the behaviour of E. coli O157:H7 at temperatures that fluctuate around the minimum for growth.     

Effects of thawing temperature on the physicochemical properties of pre-rigor frozen chicken breast and leg muscles

The objective of this study was to evaluate effects of thawing temperature on the biochemical and physicochemical properties of pre-rigor frozen chicken breast and leg muscles. Breast and leg muscles from 24 broiler chickens were excised within 10min postmortem. Pre-rigor muscles were frozen at -20°C and thawed at 0 and 18°C, and pH, R-value, sarcomere length, muscle shortening, thaw and cook loss, shear force and myofibrillar fragmentation index (MFI) compared with those in pre-rigor or 2°C chilled muscles. The ultimate pH of 18°C thawed muscle was lower than that of 0°C thawed and 2°C chilled muscles. As expected, the shortening of sarcomere length and muscle length of thaw rigor muscles were more than those of chilled muscle, but there were no significant differences between chilled muscle and 0°C thawed muscle. Also, there were no significant differences in R-value (Abs 250/Abs 260) and cook loss due to thawing temperature. Samples thawed at 0°C had higher MFI and lower shear value than samples thawed at 18°C. Shear force value and MFI were not significantly different between chilled muscle and 0°C thawed muscle. By thawing at 0°C, thaw shortening was prevented, and tender meat comparable to the chilled meat was obtained.