Effect of pre rigor stretching on beef tenderness development

The objective of this study was to determine effects of pre rigor stretching on beef tenderness development. Beef loins (M. longissimus dorsi; n=24) were assigned to either stretching or non-stretching treatments and aged for 14days at -1.5°C. Sarcomere length, shear force, water-holding capacity and proteolysis were determined for the loins at 1, 7 and 14days of ageing. Stretching increased the length of the loins by 33% resulting in a trend of increasing sarcomere length (P=0.19). However, no significant differences for shear force values, purge, drip and cooking losses between treatments were found. Shear force values decreased with ageing times (P<0.05). Western blot assay found that stretching did not affect the extent of desmin degradation. The findings from the present study suggest that pre rigor stretching with the current increase in length will not contribute to tenderness improvement of the beef loins.     

The protective effect of electrical stimulation and wrapping on beef tenderness at high pre rigor temperatures

A three factorial experimental design involving electrical stimulation (ES/NES), wrapping (wrapped/unwrapped) and pre rigor temperature (15 °C or 35 °C) was applied to 70 beef M. longissimus lumborum muscles to obtain a wide variation in shear force and drip loss. The shear force of all treatment groups decreased during ageing. As anticipated, wrapping and electrical stimulation had positive effects on shear force. However, high pre rigor temperature (35 °C) did not result in higher shear force values if the muscles were electrically stimulated, wrapped or both. The results suggested that electrical stimulation protects against the negative effects of high pre rigor temperatures. The drip loss of all treatment groups increased during ageing in a manner that was unrelated to treatment but was correlated to tenderness (r² = 0.70; p < 0.0001). It was concluded that the application of electrical stimulation, whatever the pre rigor temperature, protects beef from toughening through the prevention of rigor shortening and the avoidance of inhibition of ageing enzymes.     

Tenderness enhancement of beef from Bos indicus and Bos taurus cattle following electrical stimulation

High voltage electrical stimulation (1130 V peak, 14.28 bidirectional half sinusoidal pulses/s) or low voltage stimulation (45 V peak, 36 alternating square wave pulses/s) was used on cattle: (1) low voltage stimulation applied for 10 or 40 s with fast and slow chilling or high voltage stimulation for 60 s with normal chilling, applied to 100% Bos taurus cattle, (2) low voltage stimulation (40 s) and high voltage stimulation (60 s) with normal chilling applied to mixed Bos indicus and B.taurus cattle, (3) high voltage stimulation (54 s) with normal chilling applied to B. taurus and B. indicus cattle of 0–100% B. indicus composition, and (4) high voltage stimulation (60 s) applied to 100% B. taurus and 100% B. indicus cattle. All stimulation parameters enhanced the tenderness of steaks from M. longissimus thoracis et lumborum (LTL) aged at 1 °C up to 28 days compared with non stimulated LTL. Short low voltage stimulation of 10 s was marginally more effective than no stimulation and longer durations of 40 s were very effective and high voltage stimulation was most effective.     

Effects of rigor temperature and electrical stimulation on venison quality

The effects of rigor temperature and electrical stimulation on venison quality were assessed using venison longissimus dorsi muscle. In the first trial, effect of rigor temperature (0, 15, 25, 30, 35 and 42 °C) and time post-mortem (at rigor, 3, 7 and 14 days) on drip and cooking losses, % expressible water (water holding capacity, WHC), sarcomere length, protein solubility, meat tenderness and colour were investigated. In the second trial, the effects of rigor temperature (15 and 35 °C), electric stimulation (stimulated or not stimulated) and time (at rigor, 3 and 6 weeks post-mortem) on tenderness and colour were further investigated. Results of the first trial showed no clearly established trends of the effect of rigor temperature and time on the cooking and drip losses and protein solubility except venison muscles that went into rigor at 42 °C tended to have higher drip loss and lower protein solubilities compared to muscles that went into rigor at the other temperatures. Venison water holding capacity (WHC) decreased with the increase in rigor temperature (P < 0.001) and venison became more tender with time post-mortem. Venison colour improved with increasing rigor temperature. During display, samples that went into rigor at 15, 25 and 35 °C had the lowest and those at 0 and 42 °C had the highest rate of change of redness (a^*) value with time. In the second trial, tenderness was improved by stimulation (P = 0.01). Redness (a^*) values were affected by rigor temperature (P < 0.01) and post-mortem time (P < 0.001) but not by electrical stimulation. It is concluded that venison tenderness can be improved via the manipulation of rigor temperature to obtain acceptable level of tenderness early post-mortem with less damaging effect on colour stability.     

Effects of electrical stimulation, chilling temperature and hot-boning on the tenderness of bovine muscles

The objective of this study was to determine the effects of hot-boning, low voltage electrical stimulation (ES) and chilling temperature on the tenderness of bovine M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles. LD (n=32) and SM (n=32) muscles were subjected to different post-mortem treatments; hot-boning (before 90min post-mortem), cold-boning (at 48h post-mortem), low voltage ES and rapid or slow chilling. Hot-boned muscles which were not electrically stimulated (NES) had higher Warner Bratzler shear force (WBSF) values (P<0.001) and shorter sarcomeres (P<0.001) than cold-boned muscles. Hot-boned muscles subjected to ES had lower pH values (P<0.001) post-stimulation and up to 8h post-mortem than NES muscles. At both chilling temperatures WBSF values were lower in ES hot-boned LD and SM muscles at days 2, 7 and 14 post-mortem than NES muscles. Hot-boned muscles subjected to slow chilling had longer sarcomeres (P<0.001) than those subjected to fast chilling. In hot-boned SM muscles, ES resulted in longer sarcomere lengths (P<0.001). However, ES did not have a significant effect on the sarcomere length of LD muscles. As indicated by WBSF values all muscles tenderised during ageing, including muscles which were 'cold shortened'. Proteolysis was not the main reason for differences in WBSF values between ES and NES muscles as judged by qualitative sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). A combination of slow chilling and ES had a positive effect on hot-boned muscles with respect to WBSF values.     

Variation in the response to manipulation of post-mortem glycolysis in beef muscles by low-voltage electrical stimulation and conditioning temperature

The aim of this study was to investigate how manipulation of glycolytic rate by post-mortem processing conditions influences quality of aged beef of two bovine muscles of different physiological character, longissimus dorsi (LD) and adductor (AD). Post-mortem glycolysis was manipulated by low-voltage electrical stimulation (LV-ES) of half carcasses and by chilling rate of the muscles. Multivariate statistical analysis was used to visualise the data, while ANOVA was used to identify significant effects and interactions. As expected there was a significant effect of LV-ES on the pH decline in the first hours post-mortem in both muscles. Moreover, significant effects of LV-ES on WB shear force measured 2 and 8 days after slaughter were observed for LD at both chilling temperatures, while for AD no effect on WB shear force was observed. Furthermore, the results revealed a large individual variation in the response of LV-ES on both pH decline and WB shear force, and this variation did not always correlate for the two responses. Some animals showed no response of LV-ES on pH decline, but still had an improved WB shear force, and vice versa. The results from this study indicate that there probably are other mechanisms than accelerated pH decline and prevention of cold-shortening, by which LV-ES can affect meat tenderness.     

The influence of high temperature, type of muscle and electrical stimulation on the course of rigor, ageing and tenderness of beef muscles

The course of rigor mortis (rigor), ageing and tenderness has been evaluated for three beef muscles; M. biceps femoris (BF), M. semimembranosus (SM) and M. semitendinosus (ST), when entering rigor at constant temperatures of 15 and 37°C respectively, with and without electrical stimulation (ES/NS) (85 V, 14 Hz and 32 s). The course of post-mortem changes has been registered by isometric tension, by shortening of unrestrained muscle strips and by following the pH decline and the changes in metabolites, such as ATP and CP. Ageing at +4°C was recorded by measuring Warner-Bratzler (W-B) shear values 2, 8 and 15 days post mortem. On the last occasion, the sensory properties of the cooked meat were also evaluated. Maximum shortening and isometric tension were higher at 37°C as compared to 15°C, whereas ES did not reduce rigor shortening. A high correlation between maximum shortening and the ATP-level at the onset of the shortening rapid phase was found (r = 0·77(???)), which could explain the greater shortening obtained at 37°C compared to 15°C. Rigor shortening is an important phenomenon governing meat tenderness as tenderness is highly affected by rigor temperature but not by ES. This was the case for muscles SM and ST but not for BF muscle. Even though tenderness was measured after ageing (15 days post mortem), shortening during rigor seems to be more important for toughness when rigor mortis occurs at 37°C than any suggested tenderizing effect due to increased proteolysis in this temperature region.     

The influence of low temperature, type of muscle and electrical stimulation on the course of rigor mortis, ageing and tenderness of beef muscles

The course of rigor mortis, ageing and tenderness have been evaluated for two beef muscles, M. semimembranosus (SM) and M. longissimus dorsi (LD), when entering rigor at constant temperatures in the cold-shortening region (1, 4, 7 and 10°C). The influence of electrical stimulation (ES) was also examined. Post-mortem changes were registered by shortening and isometric tension and by following the decline of pH, ATP and creatine phosphate. The effect of ageing on tenderness was recorded by measuring shear-force (2, 8 and 15 days post mortem) and the sensory properties were assessed 15 days post mortem. It was found that shortening increased with decreasing temperature, resulting in decreased tenderness. Tenderness for LD, but not for SM, was improved by ES at 1 and 4°C, whereas ES did not give rise to any decrease in the degree of shortening during rigor mortis development. This suggests that ES influences tenderization more than it prevents cold-shortening. The samples with a pre-rigor mortis temperature of 1°C could not be tenderized, when stored up to 15 days, whereas this was the case for the muscles entering rigor mortis at the other higher temperatures. The results show that under the conditions used in this study, the course of rigor mortis is more important for the ultimate tenderness than the course of ageing.     

Effect of low voltage electrical stimulation on biochemical and quality characteristics of Longissimus thoracis muscle from one-humped Camel (Camelus dromedaries)

The effects of electrical stimulation (90 V) 20 min post mortem on meat quality and muscle fibre types of four age group camels (1–3, 4–6, 7–9, 10–12 years) camels were assessed. Quality of the Longissimus thoracis at 1 and 7 days post mortem ageing was evaluated using shear force, pH, sarcomere length, myofibrillar fragmentation index, expressed juice, cooking loss and L^∗, a^∗, b^∗ colour values. Age of camel and electrical stimulation had a significant effect on meat quality of L. thoracis. Electrical stimulation resulted in a significantly (P < 0.05) more rapid pH fall in muscle during the first 24 h after slaughter. Muscles from electrically-stimulated carcasses had significantly (P < 0.05) lower pH values, longer sarcomeres, lower shear force value, higher expressed juice and myofibrillar fragmentation index than those from non-stimulated ones. Electrically-stimulated meat was significantly (P < 0.05) lighter in colour than non-stimulated based on L^∗ value. Muscles of 1–3 year camels had a significantly (P < 0.05) lower shear force value, and pH, but longer sarcomere, and higher myofibrillar fragmentation index, expressed juice, and lightness colour (L^∗) than those of the 10–12 years camels. The proportions of Type I, Type IIA and Type IIB were 25.0, 41.1 and 33.6%, respectively were found in camel meat. Muscle samples from 1–3 year camels had significantly (P < 0.05) higher Type I and lower Type IIB fibres compared to those from 10–12 year camel samples. These results indicated that age and ES had a significant effect on camel meat quality.     

Effect of muscle and post-mortem rate of pH and temperature fall on antioxidant enzyme activities in beef

The aim of this study was to investigate the effect of muscle, inner and outer Musculus biceps femoris (IBF and OBF respectively) and Musculus longissimus dorsi (LD), on the post-mortem rate of pH and temperature fall, and the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) during simulated retail display. At day 0 of display (2 days post-mortem), the CAT and GSH-Px activities were lower in IBF than in OBF and LD (P < 0.001), and the SOD activity was lower in OBF compared to IBF and LD (P < 0.001). At day 10 of display, SOD and CAT activities had decreased in all three muscles compared to day 0 (P < 0.001), whereas the GSH-Px activity did increase with time of display. Across muscles, there were significant relationships between temperature fall, colour, lipid and colour stability and antioxidant enzyme activities.     

Fingerprint of lactic acid bacteria population in beef carpaccio is influenced by storage process and seasonal changes

We have investigated the population structure of lactic acid bacteria (LAB) for several beef carpaccio available on the market with the purpose of comparing the effect of storage process (modified-atmosphere packaging and vacuum-packaging) and of seasonal changes on this microbial population. Out of 60 samples we have characterised 214 isolates accounting for 10 LAB species and 35 isolates accounting for 11 non-LAB species. Lactobacillus sakei, Leuconostoc carnosum and Leuconostoc mesenteroides were the most prevailing LAB species with a frequency of identification within 66%, 62% and 52% of the samples respectively. These 3 species were also characterised by a phenotypic intra-species diversity of isolates based on colony morphology. We showed that the prevalence was increased 1.5 fold for L. sakei and L. mesenteroides during the summer sampling in comparison to the spring or the fall sampling suggesting an environmental origin of these two species. Seasonal variations were also observed for the prevalence of Lactobacillus fuchuensis and L. carnosum in spring (2- and 1.5-fold increase, respectively) and of Brochothrix thermosphacta in fall (6-fold increase). Finally, we demonstrated that the growth potential after the sell-by-date was favourable of 1.25 log₁₀ cfu g⁻¹ to Leuconostoc spp. in modified-atmosphere packaging and of 1.38 log₁₀ cfu g⁻¹ to Lactobacillus spp. in vacuum-packaging. In conclusion, we show that important and unsuspected traits in bacterial population dynamics can be unravelled by large sampling strategies. We discuss about the need to take this assessment into account for further studies on bacterial ecosystems of meat.     

The effects of a beta-agonist treatment, vitamin D3 supplementation and electrical stimulation on meat quality of feedlot steers

In this study, 20 young steers received no beta-agonist (C), 100 animals all received zilpaterol hydrochloride (Z), with 1 group only receiving Z while the other 4 groups received zilpaterol and vitamin D3 at the following levels (IU/animal/day) and durations before slaughter: 7 million for 3 days (3D7M); 7 million for 6 days (6D7M); 7 million for 6 days with 7 days no supplementation (6D7M7N) and 1 million for 9 days (9D1M). Left carcass sides were electrically stimulated (ES) and the right side not stimulated (NES). Samples were aged for 3 or 14 days post mortem. Parameters included Warner-Bratzler shear force (WBSF), myofibril filament length, sarcomere length and calpastatin and calpain enzyme activity. Both ES and prolonged aging reduced WBSF (P<0.001). 6D7M, 6D7M7N and Z remained significantly tougher than C (P<0.001), while 3D7M and 9D1M improved WBSF under NES conditions. ES is more effective to alleviate beta-agonist induced toughness than high vitamin D3 supplements.     

Legume type and temperature effects on the toxicity of insecticide to the genus Callosobruchus (Coleoptera: Bruchidae)

Three bruchid pest species, Callosobruchus maculatus, Callosobruchus chinensis and Callosobruchus rhodesianus, were studied for their response to insecticide toxicity taking into account the separate and interactive effects of temperature and pre-adult food. The food types used were cowpea (Vigna unguiculata) and mungbean (Vigna radiata). Callosobruchus maculatus was the most tolerant to malathion and the least affected by temperature change while C. rhodesianus was the least tolerant. Over a 4 °C range (23°, 25°, 27 °C), there was generally a significant impact of temperature on the tolerance of the three species to the insecticide. The food type on which the insects developed influenced considerably the degree of insecticide tolerance. Callosobruchus maculatus and C. chinensis populations reared on mungbean had higher tolerance to malathion than their counterparts reared on cowpea, but the opposite was observed in C. rhodesianus populations. The food influence in this study suggested an ancestral cause or fitness cost depending on the species. The interaction of food-by-temperature had no significant effect on malathion toxicity to this genus. Correlation analysis showed C. chinensis to be relatively less sensitive to insecticide concentration over the range studied compared with the other two species.     

Effect of dietary beta-agonist treatment, vitamin D3 supplementation and electrical stimulation of carcasses on colour and drip loss of steaks from feedlot steers

In this study, 20 young steers received no beta-agonist (C) and 100 animals all received zilpaterol hydrochloride (Z), with 1 group receiving Z while the other 4 groups receiving Z and vitamin D₃ at the following levels (IU/animal/day) and durations before slaughter: 7 million for 3 days (3D7M) or 6 days (6D7M), 7 million for 6 days with 7 days no supplementation (6D7M7N) and 1 million for 9 days (9D1M). Left carcass sides were electrically stimulated (ES) and right sides not (NES). Samples were analysed fresh or vacuum-aged for 14 days post mortem. Parameters included drip loss and instrumental colour measurements. In general, zilpaterol showed increased drip loss, lighter meat, and reduced redness. Vitamin D₃ supplementation could not consistently overcome these negative effects. All vitamin D₃ treatments reduced drip loss of stimulated aged steaks.     

Modelling the effect of temperature and water activity in the growth boundaries of Aspergillus ochraceus and Aspergillus parasiticus

The aim of this work was to model the growth of Aspergillus parasiticus and Aspergillus ochraceus, both mycotoxin producers, near to the growth/no growth boundaries and validate those models in sterile maize grain, peanuts and coffee beans. Malt extract agar was adjusted to six different water activities: 0.93, 0.91, 0.89, 0.87, 0.85 and 0.80. Plates were incubated at 10, 15, 20, 25, 30, 37 and 42 °C. For each of the 42 conditions, 10 Petri dishes were inoculated. Both kinetic and probability models were applied to colony growth data. The results of the present study indicate that the developed probability modelling approach could be satisfactorily employed to quantify the combined effect of temperature and water activity on the growth responses of A. ochraceus and A. parasiticus. However, validation of kinetic results led to poor goodness of prediction. In this study, the validation samples were placed near to the expected boundaries of the models in order to test them under the worst situation. Probability of growth prediction under extreme growth conditions was somewhat compromised, but it can be considered acceptable.     

Quantifying the individual effects of ethanol and temperature on the fitness advantage of Saccharomyces cerevisiae

The presence of Saccharomyces cerevisiae in grape berries and fresh musts is usually very low. However, as fermentation progresses, the population levels of this species considerably increase. In this study, we use the concept of fitness advantage to measure how increasing ethanol concentrations (0-25%) and temperature values (4-46 °C) in wine fermentations affects competition between S. cerevisiae and several non-Saccharomyces yeasts (Hanseniaspora uvarum, Torulaspora delbrueckii, Candida zemplinina, Pichia fermentans and Kluyveromyces marxianus). We used a mathematical approach to model the hypothetical time needed for S. cerevisiae to impose itself on a mixed population of the non-Saccharomyces species described above. This approach also took into consideration the influence of environmental factors and the initial population levels of S. cerevisiae (0.1, 1.0 and 10.0%). Our results suggest that Saccharomyces niche construction via ethanol production does not provide a clear ecological advantage (at least not until the ethanol concentration exceeds 9%), whereas a temperature rise (above 15 °C) does give S. cerevisiae a considerable advantage. The initial frequency of S. cerevisiae considerably influences the time it needs to impose itself (until it reaches a final frequency of 99% in the mixed culture), the lowest time values being found at the highest initial frequency. In light of these results, the application of low temperatures in the wine industry could favor the growth and survival of non-Saccharomyces species for a longer period of time.     

Effect of water activity, temperature and incubation time on growth and ochratoxin A production by Aspergillus niger and Aspergillus carbonarius on maize kernels

The aim of this study was to determine the effects of water activity (a_w) (0.92-0.98), temperature (5-45 °C) and incubation time (5-60 days) on growth and ochratoxin A (OTA) production by Aspergillus niger and Aspergillus carbonarius on maize kernels using a simple method. Colony diameters of both strains at 0.92 a_w were significantly lower than those at 0.96 and 0.98 a_w levels. The optimum growth temperature range for A. niger was 25-40 °C and for A. carbonarius 20-35 °C. A. niger produced OTA from 15 to 40 °C, and the highest OTA level was recorded at 15 °C. The concentration of OTA produced at 0.92 a_w was significantly lower than those at 0.96 and 0.98 a_w. A. carbonarius produced OTA from 15 to 35 °C and the maximum concentration was achieved at 15 °C, although not differing statistically from the concentration detected at 20 °C. At 0.98 a_w the OTA concentration was significantly higher than at 0.96 and 0.92 a_w. Our results show that maize supports both growth and OTA production by A. niger and A. carbonarius. The studied strains were able to produce OTA in maize kernels from the fifth day of incubation over a wide range of temperatures and water availabilities. Although the limit of quantification of our method was higher than that required for the analysis of OTA in food commodities, it has proved to be a useful and rapid way to detect OTA production by fungi inoculated onto natural substrates, in a similar way as for pure culture. Both species could be a source of OTA in this cereal in temperate and tropical zones of the world.     

The application of staphylococci with flavour-generating potential is affected by acidification in fermented dry sausages

Differences in the production of bacterial metabolites with potential impact on fermented sausage flavour were found in meat simulation medium when comparing different strains of Staphylococcus xylosus and Staphylococcus carnosus as starter cultures. Overall, higher levels of 3-methyl-1-butanol and acetoin were found for S. xylosus, with some intraspecies variability. In addition, sausage fermentation parameters affected staphylococcal growth and metabolism. Strong acidification, as in Northern-European types of fermented dry sausage, inhibited S. xylosus 3PA6 but not S. carnosus 833. During a milder, Southern-European type of acidification, both strains displayed survival over time. During in situ sausage trials, variations in the degree of acidification and the choice of starter microorganisms were of importance, whereas modifications in fat and salt contents had no effects. Staphylococcus sciuri αSg2, Staphylococcus succinus 4PB1, and S. xylosus 3PA6 were unable to survive the fermentation of a Northern-European type of fermented dry sausage, characterized by low or no 3-methyl-1-butanol and acetoin production. Inoculation with S. sciuri αSg2, S. succinus 4PB1, or S. xylosus 3PA6 led to 3-methyl-1-butanol and acetoin production in Southern-European type of fermented dry sausages, which was not observed with S. carnosus 833.     

A model of the effect of temperature on the growth of pathogenic and nonpathogenic Vibrio parahaemolyticus isolated from oysters in Korea

Vibrio parahaemolyticus is recognized as the leading cause of human gastroenteritis associated with the consumption of seafood. The objective of this study was to model the growth kinetics of pathogenic and nonpathogenic V. parahaemolyticus in broth and oyster slurry. Primary growth models of V. parahaemolyticus in broth and oyster slurry fit well to a modified Gomperz equation (broth R(2)=0.99; oyster slurry R(2)=0.96). The lag time (LT), specific growth rate (SGR), and maximum population density (MPD) of each primary model were compared. The growth of nonpathogenic V. parahaemolyticus was found to be more rapid than that of pathogenic V. parahaemolyticus, regardless of the model medium. In addition, significant (P<0.05) differences in the growth kinetics between pathogenic and nonpathogenic V. parahaemolyticus in broth were observed at 10 degrees C. When compared to growth in broth, the growth of V. parahaemolyticus was delayed in oyster slurry, and growth was not observed at 10 or 15 degrees C. The Davey and square root models were identified as appropriate secondary models for predicting the LT and SGR, respectively. For the broth model, the average B(f) and A(f) values for LT were found to be 0.97 and 1.3, respectively, whereas the average B(f) and A(f) values for SGR were 1.05 and 1.11, respectively. The model generated in this study predicted an LT that was shorter and an SGR that was similar to those that were actually observed, which indicates that these models provide a reliable and safe prediction of V. parahaemolyticus growth.     

Influence of the sporulation temperature on the impact of the nutrients inosine and l-alanine on Bacillus cereus spore germination

The effect of sporulation temperature on Bacillus cereus spore germination triggered by the nutrient germinants inosine and l-alanine was investigated. The germination (expressed as % A(600nm) fall) of heat-activated spores of B. cereus strain ATCC14579 produced at 20 and 37 degrees C, and of psychrotrophic strains LM9 and D15 produced at 15 and 37 degrees C was followed in a germination buffer containing inosine at concentrations between 0.01 and 10mmoll(-1), or l-alanine between 1 and 100mmoll(-1). Spores wet-heat resistance at 90 degrees C was also determined. Spores of the three strains produced at the lowest temperatures generally showed a higher germination capacity in response to both inosine and in l-alanine than those produced at 37 degrees C, and were also more susceptible to heat. Low sporulation temperature is confirmed as a detrimental factor to B. cereus spore wet-heat resistance, and conversely gave spores with a sensitivity to the nutrient germinants inosine and l-alanine higher than that of spores formed close to the maximal sporulation temperature.