Purification and characterization of a dipeptidase from Lactobacillus delbrueckii subsp. bulgaricus

A metal-dependent dipeptidase has been purified from a cell-free extract of Lactobacillus delbrueckii subsp. bulgaricus B14 by ammonium sulphate precipitation, anion exchange chromatography, metal chelating affinity chromatography with immobilized Cu²⁺, and repeated FPLC anion exchange chromatography. The molecular mass of the purified enzyme was estimated to be 51 kD by SDS-polyacrylamide gel electrophoresis as well as by gel filtration, which indicates that it does not consist of subunits. The enzyme was most active at pH 7 and 50°C. Reducing agents, like dithiothreitol and β-mercaptoethanol, increased enzyme activity while metal chelating agents had an inhibitory effect. Enzyme activity, inhibited by EDTA and EGTA, could be partially restored by Co²⁺ and Mn²⁺. The enzyme was most active on dipeptides containing an aminoterminal hydrophobic amino acid such as Leu-Leu and Leu-Gly. Kinetic studies indicated that the dipeptidase had a higher affinity for the first substrate mentioned. The K_m-values for both substrates were about 0·56 and 1·23 mM, with turnover numbers of 870 and 480 s⁻¹, respectively.     

Trypsin-like enzyme from intestine and pyloric caeca of spotted goatfish (Pseudupeneus maculatus)

Trypsin-like enzyme was partially purified from the intestine and pyloric caeca of spotted goatfish (Pseudupeneus maculatus) by a simple three steps procedure: heat treatment, ammonium sulphate precipitation and Sephadex G-75 filtration. The enzymes from the intestine and pyloric caeca were 96- and 57.7-fold purified with yield values of 68.1% and 26.1%, respectively. The pyloric caeca enzyme collected from the Sephadex G-75 filtration showed a single band in SDS–PAGE (24.5 kDa). Both enzymes presented identical optima pH (9.0) and temperature (55 °C). After incubation at 45 °C for 30 min, enzymes obtained from intestine remained fully activity while a loss of activity (10%) of enzyme extracted from pyloric caeca was registered. Michaelis constant was not significantly different for trypsin-like enzyme from pyloric caeca (1.82 ± 0.19 mM) and that from the intestine (1.94 ± 0.45 mM) acting on benzoyl-dl-arginine-p-nitroanilide (BAPNA). Finally, their activities were inhibited by the following ions in decreasing order: Al³⁺ > Zn²⁺ > Hg²⁺ = Cu²⁺ > Cd²⁺. The effects of Ca²⁺, Mg²⁺, Mn²⁺, Ba²⁺, K¹⁺, Li¹⁺ and Co²⁺ showed to be less intensive. The similarities between them provide basis for the proposition of obtaining an attractive protease preparation from the tons of intestine and pyloric caeca, that are usually discarded, from this fish which is an important species exported by North-eastern Brazilian fishery industry.     

Purification and characterization of a glucoamylase from Rhizopus oryzae

Glucoamylase (EC 3.2.1.3) of Rhizopus oryzae NRRL 395 was purified approximately sevenfold by sequential ammonium sulfate fractionation, Biogel P-100 gel filtration, Q-Sepharose anion exchange and S-Sepharose cation exchange. The pH and temperature optima were 4·8 and 60°C, respectively. Enzyme was stable at temperatures up to 40°C and pH values between 3 and 8. The molecular weight was 67 000 daltons as determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and the pI was 8·7 as determined by chromatofocusing. The K_m for amylopectin and soluble starch were 0·98 and 1·34 mg/ml, respectively. The V_max for amylopectin and soluble starch were 782 and 136 μmoles of glucose produced per mg of protein per min, respectively. The enzyme activity was inhibited by Hg²⁺, Pb²⁺ and Cd²⁺, but not by EDTA.     

Thermal inactivation of lectins (PHA) isolated from Phaseolus vulgaris

The influence of the thermal process on the loss of ability to bind a carbohydrate target was studied on lectins (PHA) purified from Phaseolus vulgaris seeds. Thermal inactivation of aqueous solutions of pure PHA occurred according to a biphasic first-order mechanism, the thermodynamic parameters, at pH 7·3, being as follows: ΔH*₁ = ΔH*₂ = 86·2 kcal mole⁻¹, ΔS*₁ = − 54·04 cal deg⁻¹ and ΔS*₂ = − 56·71 cal deg⁻¹. The first-order rate constants appeared to be dependent on pH (minimal around 7) and divalent cations. All different subunits constituting the whole PHA were inactivated at the same rate. The biphasic nature of this process is independent of the presence of 10 m Ca⁺⁺ or Mg⁺⁺ and appeared to indicate a discrete aggregation of PHA molecules.     

Effect of pretreatment and temperature on air-drying of Dioscorea alata and Dioscorea rotundata slices

Effects of pretreatment and drying conditions on yam varieties, namely Dioscorea alata and Dioscorea rotundata, in a fabricated laboratory scale hot air drier at temperature range of 50–80 °C and constant air velocity of 1.5 m²/s were investigated. Mass transfer during air-drying of yam slices was described using Fick’s diffusion model. Drying took place entirely in the falling rate period. Temperature dependency of moisture on diffusivity was illustrated by the Arrhenius relationship. Over the range of temperature, moisture diffusivities varied from 9.92 × 10⁻⁸ to 1.02 × 10⁻⁷ and 0.829 × 10⁻⁶ to 1.298 × 10⁻⁵ m²/s for D. alata and D. rotundata, respectively. Activation energy for drying of D. alata and D. rotundata varied from 25.25 to 46.46 and 41.75 to 72.47 kJ/mol, respectively.     

Identification of halothane genotypes by calcium accumulation and their meat quality using live pigs

The three halothane genotypes (NN, Nn, and nm) were identified by measuring the capacity for Ca²⁺ accumulation by sarcoplasmic reticulum in whole muscle homogenate preparations of M. longissimus dorsi with a Ca²⁺ specific electrode at 35°C. Significant differences (P < 0·001) in deterioration (%) of Ca²⁺ accumulation, 12% for NN, 35% for Nn, and 81% for nn pigs, were observed after ageing the whole muscle homogenate preparations for 24 h in ice.

Predictions of meat quality in live pigs (n = 34) based on the values for water-holding capacity, assessed as fluid (g/0·5 g wet wt LD), and pH (fluid) by using small biopsy LD samples (Cheah et al. 1993) were performed on all the halothane genotypes. The halothane genotype NN (n = 11) showed a fluid value of 0·37 ± 0·01 and a pH (fluid) value of 6·62 ± 0·03 as compared with 0·61 ± 0·02 and 5·84 ± 0·04, respectively, for the halothane genotype nn (n = 13). The Nn pigs (n = 10) showed fluid (0·49 ± 0·03) and pH (fluid) (6·19 ± 0·11) values between those values observed for the two homozygotes (NN and nn). Predictions of meat quality in live pigs from biopsy LD muscles were confirmed from assessments on post-mortem LD muscles based on pH₁ and fibre optic probe (FOP) measurements.

The extent of deterioration (%) in Ca²⁺ accumulation showed high correlations with fluid (r = −0·861) and pH (fluid) (r = −0·831) in the biopsy LD samples, and with pH₁ (r = 0·663), FOP (r = −0·812), and drip (%) loss (r = −0·777) in the post-mortem LD samples.     

Diflubenzuron as a grain protectant for control of Sitophilus species

Diflubenzuron, applied to wheat at low doses (0.2–0.6 mg kg⁻¹), prevents development of first generation (F1) progeny of Sitophilus oryzae and S. granarius species except those developing from a short period of oviposition (1–2 weeks) immediately after application. These F1 progeny fail to produce F2 progeny when transferred to wheat dosed with diflubenzuron, and produce very few progeny when transferred to untreated wheat suggesting an effect on fertility in the adult insect. At 30°C, a dose of 0.4 mg kg⁻¹ is adequate to control S. oryzae and S. granarius, although a dose of 0.6 mg kg⁻¹ is required at 20°C. Strategies for use of diflubenzuron are discussed.     

Physiological properties of Lactobacillus paracasei, L. danicus and L. curvatus strains isolated from Estonian semi-hard cheese

Growth and survival of Lactobacillus paracasei (six strains), L. danicus sp. nov. (four isolates, two strains) and L. curvatus (two strains) from semi-hard Estonian cheeses were comparatively studied in different environmental conditions of relevance for their growth in cheese and survival in gastric environment. Maximum specific growth rates for L. paracasei strains varied between 0.40 and 0.57 h⁻¹, and all strains were tolerant to low water activities, heating at 60 °C for 30 min and pH 3. The newly discovered genetically distinct species L. danicus was characterized by low maximum growth rates (0.26–0.38 h⁻¹) and low temperature optimum (<30 °C). It was acid and heat sensitive and inhibited at salt concentrations from 4% and water activities below 0.93. L. curvatus was characterized by the highest growth rates (0.65–0.70 h⁻¹), tolerance to high NaCl concentrations, but sensitivity to heating, bile salts and low pH. The study showed that genetically different LAB species isolated from cheese could be distinguished by simple cultivation experiments.     

Purification and properties of an acid phosphatase from Lactobacillus curvatus DPC2024

An acid phosphatase was purified to homogeneity from a cell-free extract of Lactobacillus curvatus DPC2024 by chromatography on diethylaminoethyl-Sephacel, Phenyl Sepharose, chelating Sepharose Fast Flow and MonoQ. The purified enzyme was a tetramer with a subunit molecular mass of 26 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis and gel filtration chromatography. Its optimum activity was at pH 4.5 and 70°C, with more than 65% of its activity retained after pre-heating for 30 min at 70°C. The enzyme was strongly inhibited by NaF (0.1 m ) and ZnCl₂ (1.0 m ); slightly inhibited by hexametaphosphate, tripolyphosphate or pyrophosphate at 1.0 m concentrations; but unaffected by 10 m ascorbic acid. The acid phosphatase hydrolysed a number of phosphate esters but not bis(p-nitrophenyl)phosphate nor uridine-5′-monophosphate. The N-terminal amino acid sequence of the first 20 residues of this enzyme showed 65% homology with an acid phosphatase from Lactobacillus plantarum DPC2739 and some homology with other phosphatases from mammals, yeasts and Escherichia coli.     

Purification and characterisation of trypsins from the spleen of skipjack tuna (Katsuwonus pelamis)

Three trypsin isoforms, trypsins A, B and C, from the spleen of skipjack tuna (Katsuwonus pelamis) were purified by a series of chromatographies including Sephacryl S-200, Sephadex G-50 and diethylaminoethyl-cellulose to obtain a single band on native-PAGE and SDS–PAGE. The molecular mass of all the trypsin isoforms was estimated to be 24 kDa by size exclusion chromatography and SDS–PAGE. The optimum pH and temperature of the three isoforms for the hydrolysis of N-p-tosyl-l-arginine methyl ester hydrochloride were 8.5 and 60 °C, respectively. Trypsins were stable to heat treatment up to 50 °C, and over a pH range of 6.0–11.0. All isoforms were stabilised by calcium ions. The trypsin activities were effectively inhibited by soybean trypsin inhibitor, TLCK and partially inhibited by ethylenediaminetetraacetic acid, while E-64, N-ethylmaleimide, iodoacetic acid, TPCK and pepstatin A showed no inhibitory effect. Activities decreased continuously as NaCl concentration (0–30%) increased. Trypsins A, B and C showed K_m of 0.11–0.29 mM and K_cat of 57.1–114 s⁻¹. The N-terminal amino acid sequence of 20 residues of three trypsin isoforms was IVGGYECQAHSQPHQVSLNS and had high homology to those of other fish trypsins.     

Changes in histamine and microbiological analyses in fresh and frozen tuna muscle during temperature abuse

Temperature abuse of tuna (Thunnus alalunga) was carried out in order to assess the histamine buildup in fish-processing facilities where fish can be exposed to high temperatures for short periods of time. Histamine production was studied in tuna loins under different storage and abuse conditions. Tuna was stored at 0-2°C, 3-4°C, and 6-7°C, and abused for 2 h daily at 20°C and 30°C for 7-12 days. Loins abused at 30°C for 2 h daily contained potentially toxic histamine concentrations (67-382 mg kg^-1) when stored at a low refrigeration temperature (0-2°C), whereas when stored at 6-7°C, the loins contained highly toxic histamine concentrations (544.5-4156.6 mg kg^-1). Lower histamine concentrations (23-48 mg kg^-1 in loins stored at 0-2°C and 124.7-2435.8 mg kg^-1 in loins stored at 6-7°C) were observed in temperature-abused loins that were initially frozen. An increase over time was observed in most microbial counts tested. Bacteria isolated from the temperature-abused loins showed a varied ability of histamine production, with Morganella morganii, Klebsiella oxytoca, Staphylococcus hominis, and Enterococcus hirae being the most active histamine-producing bacteria.     

The efficacy of linalool, a major component of freshly-milled Ocimum canum Sims (Lamiaceae), for protection against postharvest damage by certain stored product Coleoptera

Linalool was present at 8.6 ± 0.9 mg/g in the dried leaves of Ocimum canum Sims, an annual mint used in Rwanda to protect against postharvest insect damage. Direct exposure of adults of Zabrotes subfasciatus (Bohem.) to milled, dried O. canum leaves resulted in 100% mortality of males and 50% mortality of females after 48 hr. Dose-response curves for linalool were completed with adult Z. subfasciatus, Acanthoscelides obtectus (Say), Rhyzopertha dominica (F.), and Sitophilus oryzae (L.) using a filter paper bioassay. The LC₅₀ values were: 428 μg/cm² for Z. subfasciatus; 405 μg/cm² for A. obtectus; 428 μg/cm² for R. dominica; 427 μg/cm² for S. oryzae. Knockdown was occasionally followed by recovery at doses less than the LC₅₀ for all species. There are significant differences in the LC₅₀ and LT₅₀ values for male and female Z. subfasciatus. At the lower dosages hyperactivity rarely preceded moribundity and mortality where these occurred, while at higher dosages hyperactivity occurred soon after initial exposure and preceded imminent death. A concentration increase from 250 to 750 μg/cm², representing a tripling of dosage, spanned th 10–100% response mortality for all species at 24 hr. Air-exposure of linalool-treated papers (500 μg/cm²) for up to 24 hr significantly decreased toxicity to both sexes of Z. subfasciatus. Quantitative analysis showed the only significant decrease in the amount of linalool to occur after 0.25 hr, and this did not fully correlate with the resulting decrease in efficacy against both sexes of Z. subfasciatus. The results are discussed in terms of the efficacy of using O. canum for the protection against loss due to insects in the traditional food storage systems of Rwanda.     

The influence of oxygen on the differentiation of temperature-sensitive and temperature-insensitive Lactococcus lactis subsp. cremoris starter strains

The differentiation of temperature-insensitive and temperature-sensitive strains of Lactococcus lactis subsp. cremoris by using a modified sodium-β-glycerophosphate/milk medium is described (temperature-insensitive strains are defined as those that continue to grow at 38°C and temperature-sensitive strains as those that do not grow, or grow poorly, at 38°C). The physiological basis for the differentiation assay was examined by using L. lactis subsp. cremoris strains 2146 (temperature-insensitive) and 2182 (temperature-sensitive) as test strains. After aerobic incubation on the medium, strain 2146 formed uniform colonies, 0·5 mm in diameter, while strain 2182 formed larger colonies, 1·0–1·5 mm in diameter. The differential was dependent on the medium constituents, on an aerobic gas phase, and on the effects of H₂O₂ generated within the colonies. The addition of 0·5% (w/v) pyruvate to the medium facilitated the growth of colonies of strain 2146 to 3-mm diameter, while the colony size of strain 2182 remained at 1-mm diameter, and thus the colony-size differential between strains was reversed. The growth of both strains was inhibited at 0·4–0·8% air saturation during suspension culture in sodium-β-glycerophosphate/milk medium. The inclusion of catalase in the cultures overcame the growth inhibition. There was no observable difference between the two strains in their oxygen sensitivity or NADH oxidase/peroxidase enzymology.     

Prediction of moisture transfer parameters for microwave drying of lactose powder using Bi–G drying correlation

The mass transport properties characterising the drying of lactose powder were determined using a correlation proposed by Dincer and Hussain [Dincer, I. & Hussain, M. M. (2004). Development of a new Bi–Di correlation for solids drying. International Journal of Heat and Mass Transfer, 47, 653–658]. Experimental moisture content data for lactose samples dried under convective, microwave, combined convective-microwave and combined vacuum-microwave conditions were collected. The drying coefficients and lag factors were calculated from the experimental data and incorporated into the model. The Bi numbers were in the range 0.185–439, and moisture diffusivities and diffusion coefficients in the range from 0.135 × 10⁻⁹ to 102 × 10⁻⁹ and from 0.194 × 10⁻⁶ to 118 × 10⁻⁶ m/s, respectively. The predicted moisture profiles showed adequate agreement with the experimental observations, with the average error between experimental and predicted results being ±13.7%.     

Clostridium perfringens and its toxins in minced meat from Kars, Turkey

The aim of this study was to determine the prevalence of Clostridium perfringens and its toxins in minced meat. A total of 96 minced meat samples were collected from local markets (16) and small butcher's shops (80) in Kars (Turkey). Samples were analysed for the presence of C. perfringens and its toxins using a commercially available ELISA kit. A total of 31 (32%) Clostridium spp. strains were isolated and 17 (55%) of these isolates were identified as C. perfringens. Four (25%) of the samples from local markets and 27 (34%) from small butcher's shops were contaminated with Clostridium spp. Furthermore, C. perfringens was isolated from two (12%) and 15 (19%) samples from local markets and small butcher's shops, respectively. Mean counts of Clostridium spp. were 2.2 ± 0.83 × 10² CFU g^-1 for local markets and 4.35 ± 8.53 × 10² CFU g^-1 for small butcher's shops; mean counts for C. porringers were 2.75 ± 0.21 × 10² and 6.82 ± 10.96 × 10² CFU g^-1 from markets and butcher's shops, respectively. The number of samples contaminated with both Clostridium spp. and C. perfringens was higher in small butcher's shops than in local markets. Moreover, higher numbers of Clostridium spp. and C. perfringens were isolated in samples from small butcher's shops than from local markets. A total of 13 (13%) samples were also positive for toxins produced by the organism, as detected by ELISA. Eleven samples from small butcher's shops and two samples from local markets were positive for the C. perfringens toxins tested. Moreover, two (12%), one (1%), four (4%) and two (2%) samples were contaminated with C. perfringens types A, B, C and D, respectively. In conclusion, some meat samples collected from local markets and small butcher's shops contained C. perfringens and its toxins and, therefore, present a potential risk of food poisoning.     

Some properties of the polygalacturonase from four Zimbabwean wild fruits (Uapaca kirkiana, Zizphus mauritiana, Tamarindus indica and Berchemia discolor fruits)

Polygalacturonase was extracted from ripe Uapaca kirkiana, Zizphus mauritiana, Tamarindus indica and Berchemia discolor fruits of Zimbabwe. Protein concentrations and activities of the enzymes in the extracts were determined in the four fruit extracts. The protein concentrations in the enzyme extracts ranged from 0.82 ± 0.17 to 1.97 ± 0.13 mg/ml and enzyme activities from 1.99 ± 0.13 to 6.64 ± 0.38 mmol min⁻¹ mg⁻¹ in the four fruit extracts. Optimum pH of the enzyme ranged from 4.5 to 5 and optimum temperature from 25 to 37 °C. The enzyme extracts reduced the viscosity of 1% pectin solutions in an experiment which was done together with assay for reducing sugars to prove the activities of the enzyme extracts in the four wild fruits. The K_m and V_max ranged from 0.115 to 0.252 mg/ml and 0.0057 to 0.0119 mmol reducing groups/min/mg protein, respectively, in the four polygalacturonase extracts. Calcium chloride and sodium chloride activated the PG from all sources to a greater extend than magnesium chloride and barium chloride. PG from the other three fruits had very little effect on the polysaccharide from U. kirkiana.     

A practical trial of pyrethrins-in-oil surface sprays for the protection of bagged grain against infestation by Cadra cautella (Wlk.) (Lepidoptera, Phycitidae) in Kenya

Two formulations of synergized pyrethrins in technical white oil were tested as monthly protective sprays on stacks of fumigated bagged wheat, primarily against Cadra cautella (Wlk.) but also against Sitophilus oryzae (L) and Tribolium castaneum (Hbst.), under warm-temperate storage conditions in up-country Kenya. The formulations were: 0·4% pyrethrins with 2·0% piperonyl butoxide, applied at 50 ml/m², and 0·4% pyrethrins with 0·4% piperonyl butoxide at 20 ml/m².

Results were assessed by recording infestation in samples taken from each stack after 18 weeks storage and five spray applications.

Both treatments gave reasonably good protection against C. cautella but were not satisfactory against S. oryzae or T. castaneum. There was no evidence of any taint in bread made from the treated grain, but the higher application rate caused excessive staining of the bags.

It is concluded that satisfactory control of reinfestation by C. cautella can be expected in practice using 0·4% pyrethrins in oil with only a minimal quantity of added piperonyl butoxide, and that 20 ml/m² is a suitable rate for application to bagged produce.     

Evaluation of culture media for enrichment and isolation of Shigella sonnei and S. flexneri

The performance of Gram-negative (GN) broth with (10 μg/ml) and without novobiocin, Shigella broth (SB) with 0.5 and 3.0 μg/ml novobiocin, all incubated at 37 °C (SB with 3.0 μg/ml novobiocin also at 42 °C) and buffered brilliant green bile glucose (EE) broth with 1.0 μg/ml novobiocin incubated at 37 and 42 °C were evaluated for resuscitation and growth of Shigella sonnei and S. flexneri (eight strains; unstressed, chill-stressed and acid-stressed) and non-shigellae (11 strains). GN broth with or without novobiocin supported significantly less growth of Shigella sp. No significant differences in growth of shigellae were obtained between the other culture media. Performance depended more on the Shigella strain used. None of the tested media were significantly superior for suppressing the competitive flora.

Electivity and selectivity of MacConkey agar (MAC), tergitol-7 agar (T7), desoxycholate citrate agar (DCA), xylose lysine desoxycholate agar (XLD), Salmonella Shigella agar and Hektoen enteric agar (HEA) were determined by ecometric testing. HEA confirmed to be a high selective medium for both non-shigellae and stressed Shigella sp. Klebsiella sp., Enterobacter sp., Citrobacter sp., Salmonella sp. and the Escherichia strains can mask the presence of shigellae.

In vitro competition experiments and experiments with artificially contaminated foods showed higher resistance of S. sonnei than S. flexneri towards the stress imposed by the food matrix and its indigenous flora. Reliable detection, however, of shigellae in foods with the current enrichment and isolation media was not achieved.     

Comparison of various assays used for detection of beta-lactam antibiotics in poultry meat

In this study, microbiological tests for the detection of beta-lactam antibiotics in meat and meat products were evaluated. The traditional FPT (four plate test, containing Bacillus subtilis and Kocuria rhizophila), BsDA (Bacillus stearothermophilus disc assay) and a newly developed microbiological test, Premi®Test (containing Bacillus stearothermophilus) were included in the study. The limit of detection (LOD) of the Premi®Test was compared with the LOD of the traditional methods. The detection limits of the tests were determined by using beta-lactam antibiotic standards dissolved in meat juice, as well as meat tissue obtained from laying hens after experimental administration of amoxicillin. Positive samples, based on inhibition of growth of the organism in the test, were confirmed by high performance liquid chromatography (HPLC). Growth inhibition in the traditional tests is visible as a clear zone on the plate, whereas for Premi®Test, this is based on the absence of a colour change of the test. The LODs of antibiotics tested were as follows: Penicillin G (PENG) 5 µg kg^-1, amoxicillin (AMOX) 10 µg kg^-1, ampicillin (AMP) 25 µg kg^-1, oxacillin (OXA) 30 µg kg^-1, and cloxacillin (CLOX) 30 µg kg^-1 on the plate with Bacillus stearothermophilus. Beta-lactam antibiotics can be detected also on one plate seeded with Kocuria rhizophila, although the LODs are higher: PENG 10 µg kg^-1, AMOX 25 µg kg^-1, AMP 30 µg kg^-1, OXA 50 µg kg^-1, and CLOX 50 µg kg^-1. Premi®Test was performed according to the Standard Operating Procedure intended for detection of beta-lactam antibiotics in poultry tissues with following LODs: PENG 4 µg kg^-1, AMOX 5 µg kg^-1, AMP 5 µg kg^-1, OXA 40 µg kg^-1, CLOX 50 µg kg^-1. All tests are able to detect beta-lactam antibiotics such as penicillin G, ampicillin, amoxicillin, oxacillin and cloxacillin below the maximum residue level (MRL). However, the detection limits of the Premi®Test for PENG, AMOX and AMP were below the limits of BsDA and the plate containing Kocuria rhizophila.     

The effects of spray and blast-chilling on carcass shrinkage and pork muscle quality

Combinations of blast- and spray-chilling of pork carcasses were compared to spray-chilling at conventional chilling temperatures with regard to carcass shrinkage during chilling and pork muscle quality. In experiment 1, pork sides were spray-chilled at 1°C for the first 10 h (40 spray cycles of 60-s duration every 15 min) of cooling or blast-chilled at −20°C for 1, 2 or 3 h followed by spray-chilling for 9, 8 or 7 h duration, respectively. All pork sides were then chilled to 24 h post mortem at 1°C. Experiment 2 followed the same procedures as experiment 1, except that −40°C was used as the blast-chill temperature.

Carcass shrinkage was similar for all treatments in experiment 1 at 24 h ranging from 0·5–0·7 g 100 g⁻¹. Blast/spray-chilling increased the rate of chilling and reduced the rate of post-mortem pH decline in two muscles (longissimus thoracis, LT and semimembranosus, SM) compared to the combined conventional/spray-chill treatment. Carcasses that were blast-chilled for 3 h had LT muscles that were darker with a higher protein solubility, less drip loss, shorter lengths and higher shear values compared to those from carcasses in the conventional/spray-chill treatment. In experiment 2, carcasses blast-chilled for 3 h at −40°C recorded a weight gain at 24 h of 0·4 g 100 g⁻¹, compared to a weight loss in all other treatments (0·2–0·4 g 100 g⁻¹). Muscle colour was darker in both the LT and SM of carcasses blast-chilled for 3 h at −40°C compared to carcasses from the conventional/spray-chill treatment, but most other measurements of muscle quality showed an inconsistent response to chilling treatment.