Quality and shelf life evaluation of fermented sausages of buffalo meat with different levels of heart and fat

Investigations were carried to study the effect of heart incorporation (0%, 15% and 20%) and increasing levels of fat (20% and 25%) on physicochemical (pH, moisture content and thiobarbituric acid, TBA number) and microbiological (total plate count and yeast and mold count) quality and shelf life of semi dry sausages of buffalo meat during refrigerated storage (4 °C). Different levels of fat significantly (p < 0.05) increased the pH of the sausage samples. However different levels of heart incorporation did not significantly (p < 0.05) affect pH, moisture content and TBA number of sausage samples. Fresh samples had pH, moisture content and TBA number in the range of 5.15–5.28, 42.4–47.4% and 0.073–0.134 respectively. Refrigerated storage significantly (p < 0.05) increased TBA number of control samples while storage did not significantly (p < 0.05) increase the TBA number of sodium ascorbate (SA) treated samples. Total plate counts of twelve sausage samples were f under the TFTC (too few to count) limit at the initial stage. Incorporation of different levels of heart and also increasing levels of fat did not significantly (p < 0.05) increase the log TPC/g values. Yeast and molds were not detected in twelve samples of semi dry fermented sausages in their fresh condition. Storage revealed that there was a consistent decrease in pH, and moisture content. Refrigerated storage significantly (p < 0.05) reduced both pH and moisture contents. TBA number and total plate counts and yeast and mold counts of controls were found to increase significantly (p < 0.05) during refrigerated storage. However, in SA treated sausage, only TPC and yeast and mold count significantly (p < 0.05) increased during refrigerated storage. Shelf life of the sausages was found to be 60 days under refrigerated storage (4 °C).     

Contribution of hydrogen peroxide to the inhibition of Staphylococcus aureus by Lactococcus garvieae in interaction with raw milk microbial community

The response of Staphylococcus aureus growth inhibition by Lactococcus garvieae to catalase and milk lactoperoxidase, and its efficiency in raw milk cheese were evaluated. S. aureus and L. garvieae were co-cultivated in broth buffered at pH 6.8, and in raw, pasteurized and microfiltered milk, in presence and absence of catalase. Although H₂O₂ production by L. garvieae was detected only in agitated broth, the inhibition of S. aureus by L. garvieae was reduced by catalase both in static and shaking cultures by 2.7 log, pasteurized milk (∼0.7 log), microfiltered milk (∼0.6 log) and raw milk (∼0.2 log). The growth of S. aureus alone in microfiltered milk was delayed compared with that in pasteurized milk and inhibition of S. aureus by L. garvieae was stronger in microfiltered milk. The inhibition of coagulase-positive staphylococci (CPS) by L. garvieae in raw milk cheese was similar to that in raw milk (∼0.8 log), but weaker than that in pasteurized and microfiltered milks. L. garvieae also had an early antagonistic effect on the growth of several other microbial groups, which lastingly affected populations levels and balance during cheese ripening.     

Effects of X-ray radiation on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri inoculated on shredded iceberg lettuce

The main goal of this investigation was to study the efficacy of X-ray doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) on inoculated Escherichia coli O157: H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on shredded iceberg lettuce. The second goal was to study the effect of X-ray on the inherent microflora counts and visual color of shredded iceberg lettuce during storage at 4 °C for 30 days. Treatment with 1.0 kGy X-ray significantly reduced the population of E. coli O157: H7, L. monocytogenes, Salmonella enterica and S. flexneri on shredded iceberg lettuce by 4.4, 4.1, 4.8 and 4.4-log CFU 5 cm⁻², respectively. Furthermore, more than a 5 log CFU reduction of E. coli O157: H7, L. monocytogenes, S. enterica and S. flexneri was achieved with 2.0 kGy X-ray. Treatment with X-ray reduced the initial microflora on iceberg lettuce and kept them significantly (p < 0.05) lower than the control during storage at 4 °C and 90% RH for 30 days. Treatment with X-ray did not significantly (p > 0.05) change the green color of iceberg lettuce leaves. Treatment with X-ray significantly reduced selected pathogens and inherent microorganisms on shredded iceberg lettuce leaves, which could be a good alternative to other technologies for produce (lettuce) industry.     

Development and application of a predictive model of Aspergillus candidus growth as a tool to improve shelf life of bakery products

Molds are responsible for spoilage of bakery products during storage. A modeling approach to predict the effect of water activity (a_w) and temperature on the appearance time of Aspergillus candidus was developed and validated on cakes. The gamma concept of Zwietering was adapted to model fungal growth, taking into account the impact of temperature and a_w. We hypothesized that the same model could be used to calculate the time for mycelium to become visible (t_v), by substituting the matrix parameter by t_v. Cardinal values of A. candidus were determined on potato dextrose agar, and predicted t_v were further validated by challenge-tests run on 51 pastries. Taking into account the a_w dynamics recorded in pastries during reasonable conditions of storage, high correlation was shown between predicted and observed t_v when the a_w at equilibrium (after 14 days of storage) was used for modeling (A_f = 1.072, B_f = 0.979). Validation studies on industrial cakes confirmed the experimental results and demonstrated the suitability of the model to predict t_v in food as a function of a_w and temperature.     

Enhancement of the nitrogen fixation efficiency of genetically-engineered Rhizobium with high catalase activity

The vktA catalase gene, which had been cloned from Vibrio rumoiensis S-1^T having extraordinarily high catalase activity, was introduced into the root nodule bacterium, Rhizobium leguminosarum bv. phaseoli USDA 2676. The catalase activity of the vktA-transformed R. leguminosarum cells (free-living) was three orders in magnitude higher than that of the parent cells and this transformant could grow in a higher concentration of exogenous hydrogen peroxide (H₂O₂). The vktA-transformant was inoculated to the host plant (Phaseolus vulgaris L.) and the nodulation efficiency was evaluated. The results showed that the nitrogen-fixing activity of nodules was increased 1.7 to 2.3 times as compared to the parent. The levels of H₂O₂ in nodules formed by the vktA-transformant were decreased by around 73%, while those of leghemoglobins (Lba and Lbb) were increased by 1.2 (Lba) and 2.1 (Lbb) times compared with the parent. These results indicated that the increase of catalase activity in rhizobia could be useful to improve the nitrogen-fixing efficiency of nodules by the reduction of H₂O₂ content concomitantly with the enhancement of leghemoglobins contents.     

Effects of electron-beam irradiation on the shelf life, microbial populations and sensory characteristics of summer truffles (Tuber aestivum) packaged under modified atmospheres

The effects of two doses of electron-beam irradiation (1.5 kGy and 2.5 kGy) on the microbial populations (total mesophilic aerobes, Pseudomonas genus, Enterobacteriaceae family, molds and yeasts) and sensory characteristics of Tuber aestivum packaged under modified atmospheres were monitored immediately after treatment, and weekly during 42 days of storage at 4 °C. Treatment with 1.5 and 2.5 kGy reduced the pseudomonads populations by 4.3 and 5.5 logs, respectively. Enterobacteriaceae counts decreased by 5.4 logs with the 1.5 kGy dose and counts below the detection limit (<1.0 log cfu/g) were obtained with the 2.5 kGy dose. Lactic acid bacteria and yeasts were less affected by the ionizing radiation treatments and they became the dominant microbial populations throughout storage with microbial counts up to 7.1 log cfu/g. The carbon dioxide levels inside the packages containing irradiated truffles were lower than those of the non-irradiated ones, suggesting a decrease in the respiration rate of the treated ascocarps. The treatments with 1.5 and 2.5 kGy e-beam did not negatively affect the sensory characteristics of truffles, but a visible superficial yeast growth was detected in truffles irradiated with 1.5 kGy at the end of their shelf life (day 28). Treatment with 2.5 kGy e-beam has prolonged the shelf life to 42 days, compared with 21 days for the untreated samples.     

Combination of high-intensity pulsed electric fields with natural antimicrobials to inactivate pathogenic microorganisms and extend the shelf-life of melon and watermelon juices

The effect of high-intensity pulsed electric field (HIPEF) combined with citric acid (0.5-2.0%, w/v) or cinnamon bark oil (0.05-0.30%, w/v) against populations of Escherichia coli O157:H7, Salmonella Enteritidis and Listeria monocytogenes in melon and watermelon juices were evaluated. Microbiological shelf-life and sensory attributes were also determined. Populations of E. coli O157:H7, S. Enteritidis and L. monocytogenes were reduced by more than 5.0log(10)CFU/ml in HIPEF-processed melon (35kV/cm for 1709 micros at 193Hz and 4 micros pulse duration) and watermelon (35kV/cm for 1682 micros at 193Hz and 4 micros pulse duration) juices containing 2.0% and 1.5% of citric acid, respectively, or 0.2% of cinnamon bark oil. In addition, these treatments were also able to inactivate mesophilic, psychrophilic and, molds and yeasts populations, leading to a shelf-life of more than 91 days in both juices stored at 5 degrees C. Hence, the microbiological quality and safety of these fruit juices by combining HIPEF and citric acid or cinnamon bark oil were ensured. However, the taste and odor in those HIPEF-treated melon and watermelon juices containing antimicrobials were significantly affected. Therefore, further studies are needed to decrease the impact on the sensory attributes by using antimicrobials.     

Application of Classification and Regression Tree (CART) analysis on the microflora of minced meat for classification according to Reg. (EC) 2073/2005

In a retrospective study on the microbiology of minced meat from small food businesses supplying directly to the consumer, the relative contribution of meat supplier, meat species and outlet where meat was minced was assessed by "Classification and Regression Tree" (CART) analysis. Samples (n=888) originated from 129 outlets of a single supermarket chain. Sampling units were 4-5 packs (pork, beef, and mixed pork-beef). Total aerobic counts (TACs) were 5.3±1.0 log CFU/g. In 75.6% of samples, E. coli were <1 log CFU/g. The proportion of "unsatisfactory" sample sets [as defined in Reg. (EC) 2073/2005] were 31.3 and 4.5% for TAC and E. coli, respectively. For classification according to TACs, the outlet where meat was minced and the "meat supplier" were the most important predictors. For E. coli, "outlet" was the most important predictor, but the limit of detection of 1 log CFU/g was not discriminative enough to allow further conclusions.     

Contribution of the NADH-oxidase (Nox) to the aerobic life of Lactobacillus sanfranciscensis DSM20451T

Lactobacillus sanfranciscensis is the key bacterium in traditional sourdough fermentation. The molecular background of its oxygen tolerance was investigated by comparison of wild type and NADH-oxidase (Nox) knock out mutants. The nox gene of L. sanfranciscensis DSM20451^T coding for a NADH-oxidase (Nox) was inactivated by single crossover integration to yield strain L. sanfranciscensis DSM20451Δnox. By inactivation of the native NADH-oxidase gene, it was ensured that besides fructose, O₂ can react as an electron acceptor. In aerated cultures the mutant strain was only able to grow in MRS media supplemented with fructose as electron acceptor, whereas the wild type strain showed a fructose independent growth response. The use of oxygen as an external electron acceptor enables L. sanfranciscensis to shift from acetyl-phosphate into the acetate branch and gain an additionally ATP, while the reduced cofactors were regenerated by Nox-activity. In aerated cultures the wild type strain formed a fermentation ratio of lactate to acetate of 1.09 in MRS supplemented with fructose after 24 h of fermentation, while the mutant strain formed a fermentation ratio of 3.05. Additionally, L. sanfranciscensis showed manganese-dependent growth response in aerated cultures, the final OD and growth velocity was increased in media supplemented with manganese. The expression of two predicted Mn²⁺/Fe²⁺ transporters MntH1 and MntH2 in L. sanfranciscensis DSM20451^T was verified by amplification of a 318 bp fragment of MntH1 and a 239 bp fragment of MntH2 from cDNA library obtained from aerobically, exponentially growing cells of L. sanfranciscensis DSM20451^T in MRS. Moreover, the mutant strain DSM20451Δnox was more sensitive to the superoxide generating agent paraquat and showed inhibition of growth on diamide-treated MRS-plates without fructose supplementation.     

Lachancea thermotolerans and Saccharomyces cerevisiae in simultaneous and sequential co-fermentation: A strategy to enhance acidity and improve the overall quality of wine

In the last few years there is an increasing interest on the use of mixed fermentation of Saccharomyces and non-Saccharomyces wine yeasts for inoculation of wine fermentations to enhance the quality and improve complexity of wines. In the present work Lachancea (Kluyveromyces) thermotolerans and Saccharomyces cerevisiae were evaluated in simultaneous and sequential fermentation with the aim to enhance acidity and improve the quality of wine.     

Kinetic study of the effect of the osmotic dehydration pre-treatment to the shelf life of frozen cucumber

Quality of frozen cucumber can significantly be improved by means of osmotic dehydration as a pre-freezing treatment. The objective of this work was to study the effect of osmotic pre-treatment with alternative osmotic solutes – oligofructose and a high DE maltodextrin – on the quality and functional properties of frozen cucumber tissue. Colour, texture and sensory characteristics of pre-treated and conventionally frozen samples were comparatively measured at 3 months time, during storage at four different temperatures, − 5, − 8, − 12, − 15 °C. Colour change was kinetically studied, and its temperature dependence was modelled by the Arrhenius equation. Dehydrofrozen samples exhibited significantly improved stability, with the rates of colour change being reduced up to 36.7% for osmotically pre-treated cucumbers, compared to the untreated samples. The results indicate that osmodehydrofrozen compared to conventionally frozen sliced cucumbers show improved firmness for prolonged storage period. Sensory evaluation also showed good organoleptic quality in osmodehydrofrozen cucumber slices.

Industrial relevance

The poor quality of frozen cucumber can significantly be improved by means of the cryoprotection accomplished by a pre-freezing osmotic dehydration step. Osmotic dehydration at mild temperatures can preserve product texture, and enhance flavour and other sensory properties (colour). In this paper, the effect of osmotic pre-treatment on the quality and shelf life of frozen cucumber tissue was investigated. The aim was to develop a method of processing cucumber that maintains palatable product while optimizing quality at the beginning and during frozen storage.     

Probabilistic representation of the exposure of consumers to Clostridium botulinum neurotoxin in a minimally processed potato product

We have examined the potential of a well-specified, minimally processed potato product as a vehicle for the exposure of consumers to Clostridium botulinum neurotoxin. The product is a relatively simple combination of raw potato flakes, flour, starch and other minor ingredients and has an extended lifetime under refrigeration conditions. A combination of information and data, from a variety of sources that includes the manufacturer, has shown that the product is particularly safe with respect to non-proteolytic C. botulinum hazards. The model concentrates on a simple end point, the toxicity of an individual retail unit of the product at the point of consumer preparation, which is related to an individual risk. The probabilistic analysis was built using Bayesian Belief Network (BBN) techniques.     

The effects of thyme (Thymus vulgaris) and rosemary (Rosmarinus officinalis) essential oils on Brochothrix thermosphacta and on the shelf life of beef packaged in high-oxygen modified atmosphere

The objective of the study was to determine the Minimal Inhibitory Concentration (MIC) of thyme (29.4% thymol, 21.6% p-cymene) and rosemary essential oils (27.6% 1,8-cineole, 13.5% limonene, 13.0% β-pinene) against Brochothrix thermosphacta and to establish the feasibility of their use as components of modified atmosphere during beef refrigerated storage. The minimum inhibitory concentration (MIC) of thyme oil against B. thermosphacta is 0.05% and that of rosemary oil 0.5%. The MIC values are independent on strain and temperature of growth, however the bactericidal effects are strain dependent. The addition of any of oil at a concentration equal to 2MIC to the modified atmosphere (80% O₂/20% CO₂) does not significantly influence the microbial quality of meat. At the same time, such a concentration of the essential oils was considerably detrimental to the organoleptic factors.     

Assessing the cross contamination and transfer rates of Salmonella enterica from chicken to lettuce under different food-handling scenarios

Cross contamination of foodborne pathogens from raw meats to ready-to-eat foods has caused a number of foodborne outbreaks. The cross contamination and transfer rates of Salmonella enterica from chicken to lettuce under various food-handling scenarios were determined. The following scenarios were tested: in scenario 1, cutting board and knife used to cut chicken (10⁶ CFU/g) were also used for cutting lettuce, without washing; in scenario 2, cutting board and knife were washed with water separately after cutting chicken, and subsequently used for cutting lettuce; and in scenario 3, cutting board and knife were thoroughly washed with soap and hot water after cutting chicken, and before cutting lettuce. In each scenario, cutting board, knife, chicken and lettuce were sampled for population of S. enterica. For scenario 1, both before and after cutting lettuce, the cutting board and knife each had about 2 logs CFU/cm² of S. enterica, respectively. The cut lettuce had about 3 logs CFU/g of S. enterica. In scenario 2, fewer organisms (0.5–2.4 logs CFU/g or cm²) were transferred. The transfer rates in both scenarios ranged from 0.02 to 75%. However, in scenario 3, <1 log CFU/g or cm² organisms were detected on lettuce, cutting board or knife, after washing and cutting lettuce. This shows that the FDA recommended practice for cleaning cutting boards is effective in removing S. enterica and preventing cross contamination.     

Antioxidant action of ganghwayakssuk (Artemisia princeps Pamp.) in combination with ascorbic acid to increase the shelf life in raw and deep fried chicken nuggets

Raw and deep fried chicken nuggets containing various levels of ganghwayakssuk ethanolic extract (GE) in combination with ascorbic acid (Aa) were evaluated for shelf-life during refrigerated storage (4 °C). The pH and color (lightness, redness, and yellowness) values of raw and deep fried samples were significantly affected by the addition of GE (P < 0.05). All antioxidant combinations except for Aa + GE 0.01 were effective at delaying lipid oxidation (CD, POV, and TBARS) when compared to the control or Aa. Raw samples with GE 0.2 and Aa + GE 0.1 exhibited lower bacterial populations during storage. The sensory characteristics (color, juiciness, flavor, tenderness, and overall acceptability) did not differ significantly in all deep fried chicken nugget samples, except color, whereas storage time had a significant effect (P < 0.05). The results suggest the possibility of utilizing raw and deep fried chicken nuggets with a mixture of ganghwayakssuk and ascorbic acid for the increase of shelf-life and quality.     

Combination of warm water and hydrogen peroxide to reduce the numbers of Salmonella Typhimurium and Listeria innocua on field salad (Valerianella locusta)

The optimal conditions of decontamination of field salad by treatment with warm water containing hydrogen peroxide were determined with the aid of a central composite design. It was the aim to improve the hygienic status while keeping the sensory quality at the highest level possible. Two series of experiments were performed to study the effects of the following parameters: temperature (45–50 °C), H₂O₂ (1–4%) and treatment time (60–210 s). In series 1 the effect on sensory properties and reduction of total aerobic counts was investigated. To determine sensory quality, treated samples stored at 4 °C for 7 days were subjected to evaluation by 15 panelists. Overall visual quality (OVQ), color, texture and odor correlated well with product acceptability (R²=0.934, 0.946, 0.945 and 0.956, respectively), and OVQ was the most sensitive criterion. An acceptability of 75% in OVQ was chosen as the limit and an acceptance area was defined to deduce permitted conditions for decontamination. Within that area a reduction of total counts by 2.64–3.22 and 1.9–3.48 log₁₀ cfu/g was achieved after treatment and storage at 4 °C for 7 days, respectively. In series 2 field salad was inoculated with Listeria innocua and Salmonella Typhimurium and it was observed that within the area of acceptability a reduction of the numbers of the challenge organisms by 1.27–3.26 and 0.79–3.05 log₁₀ cfu/g, respectively, was achieved immediately after treatment, and by 1.64–3.09 (L. innocua) and 1.1–2.63 log₁₀ cfu/g (S. Typhimurium) after storage. The initial decontaminating effect on L. innocua and S. Typhimurium was sustained or even increased after storage, when the salad was treated below 48.9 °C for more than 68 s. Three independent experiments confirmed the reliability of the models of the count reduction of L. innocua and S. Typhimurium.     

Effectiveness of commercial household steam cleaning systems in reducing the populations of Listeria monocytogenes and spoilage bacteria on inoculated pork skin surfaces

In a previous study conducted in our laboratory, a commercial household steam cleaner was found to be effective in reducing the naturally occurring bacterial populations on 72 beef and 72 hog carcasses processed by four small and very small meat processing plants. The goals of this study were to determine the maximum levels of bacterial reduction caused by treatments using the steam cleaner, and to compare the efficacy of this cleaner with the efficacies of two other commercial household steam cleaning systems in reducing bacterial populations on the surface of pork skin artificially inoculated with ca. 7.61 or of Listeria monocytogenes. The contaminated pork skin samples were treated with the three stream cleaners for 30-180 s in 30 s intervals, and assayed for the populations of L. monocytogenes as well as total aerobic and thermoduric bacteria. The application of steam significantly reduced the population of L. monocytogenes (7.61-), as well as total aerobic (5.68-) and thermoduric (6.12-) bacteria on the surface of pork skin (P?0.05). Significant differences in microbial reductions were observed between different inoculation levels, treatment times, and types of cleaning systems used in the study (P?0.05).     

Assessment of the ability of seaweed extracts to protect against hydrogen peroxide and tert-butyl hydroperoxide induced cellular damage in Caco-2 cells

The ability of brown seaweed extracts, Ascophyllum nodosum, Laminaria hyperborea, Pelvetia canaliculata, Fucus vesiculosus and Fucus serratus to protect against tert-butyl hydroperoxide (tert-BOOH) induced stress in Caco-2 cells was investigated. Oxidative stress was determined by measuring alteration in the enzymatic activity of catalase (CAT) and superoxide dismutases (SOD) and cellular levels of glutathione (GSH). L. hyperborea, P. canaliculata and F. serratus significantly protected against tert-BOOH induced SOD reduction but did not protect against the reduction in CAT activity or the increased cellular levels of GSH. The ability of F. serratus and F. vesiculosus to protect against H₂O₂ and tert-BOOH induced DNA damage was also assessed. The DNA protective effects of the two seaweed extracts was compared to those of three metal chelators; deferoxamine mesylate (DFO), 1,10-phenanthroline (o-phen) and 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetrakis (BAPTA-AM). F. serratus and F. vesiculosus significantly protected (P < 0.05) against H₂O₂ (50 μM) induced DNA damage but not tert-BOOH induced damage.     

A case for the standardization of protocols used in screening cowpea, Vigna unguiculata for resistance to Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae)

Cowpea cultivars Ife Brown, Maiduguri-A, Maiduguri-B and TVu 2027, were screened for resistance to Callosobruchus maculatus (F.) attack using different seed and insect densities. The number of eggs laid on the seeds and most other demographic variables increased with increase in insect density (number of females per 40 seeds). Although the same trend was observed with increase in seed density (seeds per 8 females), this was less predictable. However, the number of eggs per seed decreased significantly as seed density increased, but increased with increase in female density. Adult emergence increased significantly with increase in both insect and seed density while the growth index did not vary. Significantly more eggs were laid on the seeds of TVu 2027 (the resistant control) than on all the other cultivars when 20 or 40 seeds were available to 8 females, or at the lowest insect density (2 females per 40 seeds). However, percentage adult emergence and growth were higher on Ife Brown (susceptible control) than on TVu 2027 and the two Maiduguri cultivars. Measurements of percentage adult emergence and growth index indicated clear cultivar differences at all seed and insect densities. Also, although the loss in weight of seed increased with increase in insect density and decreased significantly with increase in seed density, meaningful differences in resistance among test cultivars were not always apparent at all densities. Based on these findings, we propose using 40 seeds and 2 pairs of adult beetles in screening cowpea for resistance. In addition, we conclude that % adult emergence, growth index and % weight loss are the most reliable indicators for resistance of cowpea to damage by this insect. The need to standardize experimental procedures used for host plant resistance work on storage pests of cowpea is emphasized.