Growth of Clostridium perfringens from spore inocula in cooked cured beef: development of a predictive model

The objective of this study was to develop a model to predict the growth of C. perfringens from spores at temperatures applicable to the cooling of cooked cured meat products. C. perfringens growth from spores was not observed at a temperature of 12 °C for up to 3 weeks. The two parameters: germination, outgrowth, and lag (GOL) time and exponential growth rate, EGR, were determined using a function derived from mechanistic and stochastic considerations and the observed relative growths at specified times. A general model to predict the amount of relative growth for arbitrary temperature was determined by fitting the exponential growth rates to a square root Ratkowsky function, and assuming a constant ratio of GOL and generation times. The predicted relative growth is sensitive to the value of this ratio. A closed form equation was developed that can be used to estimate the relative growth for a general cooling scenario and determine a standard error of the estimate. The equation depends upon microbiological assumptions of the effect of history of the GOL times for gradual changes in temperature. Applying multivariate statistical procedures, a confidence interval was computed on the prediction of the amount of growth for a given temperature. The model predicts, for example, a relative growth of 3.17 with an upper 95% confidence limit of 8.50 when cooling the product from 51 to 11 °C in 8 h, assuming a log linear decline in temperature with time.     

Survival kinetics of Ephestia kuehniella eggs during 46–75 °C heat treatment

The effect of heat treatment on the survival of Ephestia kuehniella eggs was examined. Samples of 60 eggs were immersed in hot water at constant temperature in the 46–75 °C range for 5–1200 s. Following heat treatment and cooling, the eggs were stored at 24 ± 1 °C in a growth chamber for 7 days before survival evaluation. Statistical analysis of the data demonstrated that the thermal survival kinetics were best represented by a first-order reaction. The rate constant had an Arrhenius-type dependence over the 54–75 °C temperature range. Kinetic parameters were estimated by non-linear regression. The activation energy (E_a) and rate constant (k_ref) at the reference temperature (T_ref = 64.8 °C), were determined as 102.2 ± 6.2 kJ mol⁻¹ and 0.061 ± 0.003 s⁻¹, respectively, over the 54–75 °C temperature range. A 0.01% survival rate was obtained after 50 s at 75 °C. The data at temperatures below 50 °C were not in accordance with those at higher temperatures. Above this temperature, mortality was likely due to physiological disorders, as noted on a DSC thermogram.     

Shelf life of modified atmosphere packed cooked meat products: a predictive model

The effect of temperature, concentration of dissolved CO2 and water activity on the growth of Lactobacillus sake was investigated by developing predictive models for the lag phase and the maximum specific growth rate of this specific spoilage organism for gas-packed cooked meat products. Two types of predictive model were compared: an extended Ratkowsky model and a response surface model. In general, response surface models showed a slightly better correlation, but the response surface model for the maximum specific growth rate showed illogical predictions at low water activities. The concentration of dissolved CO2 proved to be a significant independent variable for the maximum specific growth rate as well as for the lag phase of L. sake. Synergistic actions on the shelf life-extending effect were noticed between temperature and dissolved CO2, as well as between water activity and dissolved CO2. The developed models were validated by comparison with the existing model of Kant-Muermans et al. (1997) and by means of experiments in gas-packed cooked meat products. Both developed models proved to be useful in the prediction of the microbial shelf life of gas-packed cooked meat products.     

Survival of salmonellae in skimmilk powder during storage at 20–35°C

Effect of 1-, 2-, 3-, 7- and 14-day storage of skimmilk powder at 20, 25, 30 and 35°C on the survival of S. typhimurium, S. anatum and S. dublin was examined. Salmonellae were always recovered in all experimental variants when the samples were inoculated with high numbers of these bacteria. When small inoculum was applied it was found that the rates of salmonellae destruction increased as the temperature and the time of storage was increased. It is concluded that storage of skimmilk powder at ambient temperature may, depending on the level of contamination, considerably or completely eliminate these bacteria from the product.     

Behaviour of Listeria monocytogenes in the presence of Listeria innocua during storage of minced beef under vacuum or in air at 0°C and 10°C

Minced beef was inoculated with low levels (1·2–1·7 log₁₀cfu g⁻¹) of Listeria monocytogenes or Listeria innocua, or a combination of the two strains. Inoculated samples were stored at 0 or 10°C under two packaging atmospheres (aerobic and vacuum) for up to 28 days and surviving organisms recovered on Palcam Agar. The only significant increases in numbers of Listeria spp. occurred in samples held at 10°C under aerobic conditions. In vacuum packs, growth of both strains was inhibited. Under aerobic conditions meat pH increased from an initial value of pH 5·85 to c. 8·85 within 28 days. The pH of vacuum packaged meat declined to c. 4·95 during the same period. These differences in pH may be related to differences in the nature and effects of different background microflora that were observed to develop under each of these packaging conditions.Pseudomonas spp. predominated in aerobically stored beef, whereas in vacuum packed beef lactic acid bacteria predominated. No significant differences were observed between the growth rates of Listeria spp. inoculated into beef mince in pure and mixed culture. This suggests that the more frequent prevalence of Listeria innocua than Listeria monocytogenes in meat and meat products is not due to overgrowth or inhibition of the pathogen (Listeria monocytogenes) by the non-pathogen(Listeria innocua) during low-temperature storage.     

Phospholipid changes in the course of beef meat storing at 4 °C

The mean molecular weight of beef meat phospholipids (738) and the recalculating factor (23.8), making possible to determine the total phospholipid content from lipid phosphorus, were estimated experimentally. The total amount of phospholipids decreases from 569 to 486 mg per 100 g of meat during 14 days of meat storing at 4 °C. The content of phosphatidylcholine, sphingomyelin, phosphatidylserine and phosphatidylinositol decreases, too. In contrast to this the content of lyso-phosphatides and temporarily also phosphatidylethanolamine is increasing. This temporary increase of phosphatidyiethanolamine (PE) concentration is due to enzymatic demethylation of phosphatidylcholine (PC). The course of this conversion has been followed by PE PC ratio changes in the course of meat storing.     

Growth of Bacillus cereus in natural and acidified carrot substrates over the temperature range 5–30°C

Minimally processed refrigerated foods have a relevant potential in the food market, although the potential risk posed by sporulated emerging psycrotrophs pathogens has to be evaluated. Bacillus cereus is one of these pathogenic micro-organisms. In this paper, the ability to grow of several strains of B. cereus in nutrient broth and in a carrot-based substrate (broth) was evaluated. All the strains tested grew at 12°C or higher temperatures both in nutrient broth and in carrot substrate. One of the strains was able to grow rapidly even at 5°C. Acidification of the carrot substrate proved to be efficient inhibiting B. cereus. For the two strains tested, growth was not observed at pH below 4·75 acidifiying with citric acid or with lemon juice. When the effect of pH was combined with refrigeration, acidification at pH 5·0 was sufficient to inhibit B. cereus at 12°C or lower temperatures. Therefore, the combination of these two factors could have a great potential to control B. cereus growth in minimally processed foods, such as carrot based products. Additionally, lemon juice can be considered as a more natural alternative to citric acid.     

Effect of freezing storage at −20 °C and cooking methods on some lipid fractions of lamb meat

Freezing storage and cooking methods might affect the lipid fractions of lamb meat. Some fractions of meat lipids are very sensitive to freezing storage and several cooking methods. Among the different fractions of lipids that might be liable to changes during storage and subsequent cooking and in the same time affect meat flavour are: phospholipids and cholesterol together with its esters. Frozen storage of lamb meat is not the best keeping acceptability scores. Moist heat proved to be the best cooking method for palatability characteristics and not the dry heat.     

Mathematical modelling of the heat inactivation of trypsin inhibitors in soymilk at 121–154 °C

Response surface methodology (RSM) was used to investigate the effects of processing temperature and time on the inactivation of trypsin inhibitors (TI) in soymilk. The factorial experimental design consisted of four levels of temperature and six levels of time in a temperature range of 121–154 °C and a time interval of 10–90 s. A quadratic polynomial equation, relating log(% TI retained) as a function of heating time and temperature, was satisfactorily fitted to the experimental data by least squares regression with r² (correlationcoefficient) = 0.959. Within the range of heating times investigated, TI in soymilk was satisfactorily destroyed to 10% retained at 143 and 154 °C with 62 and 29 s heating time respectively. © 2002 Society of Chemical Industry     

Comparison of changes occurring in rheological properties of gelled tissue and model sausage prepared from duck breast muscles stored at −2°C and −18°C

The changes of rheological parameters of gelled tissue and model sausage prepared from duck breast muscles stored at ?2°C and ?18°C were compared. The changes of conventional elasticity and flowability and the sum of reciprocal immediate elasticity modulus and reciprocal elasticity modulus of gelled tissue, and conventional plasticity and Newtonian viscosity of model sausage are comparable for both temperatures and are higher at ?2°C than ?18°C. At both temperatures the changes occurring in rheological parameters of model sausage can not be predicted according to the changes in rheological parameters of gelled muscle tissue.     

Gelatinisation Characteristics and Enzyme Susceptibility of Different Types of Barley Starch in the Temperature Range 48–72°C1

The gelatinisation temperatures, pasting characteristics and enzymic susceptibilities in the temperature range 48–72°C of normal, high amylose, low amylose and zero amylose barley starches were determined. Normal starches had the lowest gelatinisation temperatures, but low and zero amylose starches had the lowest pasting temperatures. Normal starches were the most readily soluble in water at 48–60°C in the presence of a mixture of α‐amylase, β‐amylase and limit dextrinase and were most readily broken down to reducing sugars by these enzymes. High amylose starch was the most resistant to enzymic hydrolysis in the temperature range 48–72°C and, hence, produced the lowest level of reducing sugars.     

Changes in the flesh of cooked farmed salmon (Oncorhynchus kisutch) with previous storage in slurry ice (−1.5 °C)

Whole, farmed Coho salmon (Oncorhynchus kisutch) were sacrificed in slurry ice (−1.5 °C) then stored in this medium for further processing after 0, 5 and 9 days. They were cooked whole and the flesh was evaluated by sensory, physical and chemical techniques to establish if significant changes had occurred as a result of the storage period. Initial samples from harvest were also evaluated for comparison. There was evidence of increases in trimethylamine, lipid hydrolysis, lipid oxidation (anisidine and thiobarbituric acid values) and interaction compound formation (fluorescence and browning measurements). The fish structure became more breakable with longer storage but there were no changes in sensory assessments for rancid and putrid odours, so that scores were less than 0.5 on a 11-point scale. From the present results, primary and secondary lipid oxidation development and further interaction compound formation appear to be the main measurable indicators of quality changes in cooked Coho salmon. However, and according to sensory appreciation, slurry ice has shown to be a suitable medium for previous storage of Coho salmon for periods of up to 9 days.     

Shelf life extension of ground meat stored at 4 °C using chitosan and an oxygen absorber

The combined effect of chitosan (1%) and an oxygen absorber on shelf life extension of fresh ground meat stored at 4 °C was investigated. Parameters monitored over a 10‐day storage period were Total Viable Count (TVC), Pseudomonas spp., Brochothrix thermosphacta, lactic acid bacteria, Enterobacteriaceae, pH, thiobarbituric acid (TBA), colour, odour and taste. Microbial populations were reduced by 0.4–2.0 log CFU g^?1 for a given sampling day using either chitosan or the oxygen absorber, with the more pronounced effect being achieved by the combination of two. Thiobarbituric acid values for all samples increased during storage with the exception of samples treated with both chitosan and the oxygen absorber in which Thiobarbituric acid values decreased. Changes in pH values with time/different treatments were statistically insignificant. Colour parameters were affected by most treatments. On the basis of microbiological and sensory evaluation, a shelf life extension of 5–6 days was obtained for samples treated with the chitosan and the oxygen absorber combination.     

Kinetics of mould growth in the stored barley ecosystem contaminated with Aspergillus westerdijkiae,Penicillium viridicatum and Fusarium poae at 23–30 °C

BACKGROUND: Owing to the lack of a rapid method for determining fungi on cereals, the best way to enhance the safety and nutritive value of stored grain is to develop prognostic tools based on the relationship between easily measurable online parameters, e.g. water activity (a_w) and temperature (t) of grain, and fungal growth. This study examined the effect of unfavourable temperature (23 and 30 °C) and humidity (0.80–0.94 a_w) storage conditions on mould growth in the stored barley ecosystem with its adverse microbiological state provided by contamination with Aspergillus westerdijkiae, Penicillium viridicatum and Fusarium poae. RESULTS: Among the applied storage parameters, a_w turned out to be the main factor affecting mould development. The longest lag phase and period of fungal activation were observed for grain with 0.80 a_w, which was not threatened with fungal development for at least 30 days. However, in grain with 0.92 and 0.94 a_w, fungal activation occurred within 24–48 h. CONCLUSION: The obtained data and the identification of critical points in mould growth may be used to develop a control system for the postharvest preservation of barley based on a_w and temperature of grain, which are easy to measure in practice. © 2012 Society of Chemical Industry     

Moisture adsorption isotherms of Tarhana at 25 °C and 35 °C and the investigation of fitness of various isotherm equations to moisture sorption data of Tarhana

Moisture adsorption isotherms of Tarhana were determined at 25 °C and 35 °C. As the temperature increased, the adsorbed moisture content decreased at water activities between 0.2 and 0.9. The experimental sorption data obtained were applied to the Halsey, Harkins‐Jura, Smith, BET and Freundlich isotherm equations to test fitness of these equations to Tarhana. The order of best fit or sorption data obtained for Tarhana was Halsey > Harkins‐Jura > Smith > Henderson > BET > Freundlich. The obtained sorption data fitted the Halsey, Harkins‐Jura and Smith isotherm equations quite well in the 0.2–0.9 water activity range; However, the best fit was obtained in the Freundlich, BET and Henderson isotherm equations in this water activity range. © 2000 Society of Chemical Industry     

Original article: The effect of freezing at −18 °C and −70 °C with and without ascorbic acid on the stability of antioxidant in extracts of apple and orange fruits

The influence of low temperature and storage time on the antioxidant capacity of standard solutions and apple and orange extracts was evaluated. In addition, the effects of ascorbic acid (AA) addition to the fruit extracts in terms of antioxidant capacity, AA content and soluble and hydrolyzable polyphenol contents were also analysed. Polyphenol contents in both apple and orange extracts were stable during storage period, which reflected also in the antioxidant capacity stability. Freezing at ?18 °C did not result in different retention rates for polyphenols, AA and antioxidant capacity when compared to freezing at ?70 °C. However, vitamin C content in orange juice, without AA addition, slightly increased along the experimental period (10 days). Thus, this study shows that it may not be necessary to measure the antioxidant capacity immediately after the preparation of fruit extracts or antioxidant standard solutions.     

Influence of a combined hot air and UV‐C treatment on quality parameters of fresh‐cut broccoli florets at 0 °C

Broccoli is a horticultural product with a high nutritional value that can be consumed fresh but also minimally processed. However, broccoli is highly perishable since it develops a senescence quickly that deteriorates commercial and nutritional quality of the product. In this work we analysed the effect of a combination of UV‐C and heat treatment on quality and senescence of fresh‐cut broccoli florets stored at 0 °C. Combined treatment delayed yellowing as evidenced by higher Hue values and lower chlorophyll degradation. The treatment diminished respiratory activity indicating higher tissue integrity. Treated samples showed higher phenolic content and antioxidant capacity. On day 21 of storage, treated samples had higher levels of total sugars, and total proteins. The results suggest that a combined treatment with heat and UV‐C may reduce senescence, tissue damage and helps to maintain a better quality of the product during storage at 0 °C.     

Kinetics of ascorbic acid degradation and colour change in ground cashew apples treated at high temperatures (100–180 °C)

Ascorbic acid (AA) degradation and colour changes, measured by the lightness index (L*), were determined in cashew apples (at low dissolved O₂ concentrations) heated at high temperature (100–180 °C) in a hermetically sealed cell. A nonisothermal method was developed to estimate thermal degradation kinetics. The results showed that reaction kinetics during heat treatments were well represented by first‐order reactions. The temperature dependence of the kinetic constants was described by an Arrhenius type equation. The activation energy (E_a) for AA degradation and lightness index were 94 ± 3 and 98 ± 3 kJ mol^?1, respectively. The reaction rate constant at 140 °C for AA degradation (64 × 10^?5 ± 3 × 10^?5 s^?1) was twice that for the lightness index change (33 × 10^?5 ± 2 × 10^?5 s^?1). Results allow generating temperature profiles of heat processes that would help preserve the AA of cashew apples as well as control the colour formation during high‐temperature processes.     

The oxidative stability of lard at −20°C: Evidence for a synergistic prooxidant effect of copper and curing salts

In connection with an interest in the problem of rancidity development in cold-stored cured meat products (particularly bacon), the effect of certain trace components and permitted food additives on the oxidative stability of model systems containing lard was examined. Lard, to which additions of various single additives or combination of additives had been made, was stored for periods of up to 16 weeks at ?20°C. Samples were removed during this time to assess the extent of their oxidation by chemical analysis (peroxide value determination) and sensory evaluation (odour). The additives studied included water, sodium chloride, sodium nitrate, sodium nitrite and copper (as palmitate, acetate and sulphate). It was observed that there was progressive oxidative deterioration of the lard with noticeable rancidity developing after 8 to 16 weeks' storage at ?20°C when water, sodium chloride, sodium nitrate, sodium nitrite and copper were present in combination.