Survivability and β‐galactosidase activity of bifidobacteria stored at low temperatures

Abstract

This work evaluated the ability of strains representing six species of Bifidobacterium with probiotic potential to survive and maintain β‐galactosidase activity through a two‐step, low‐temperature storage period. Cultures were also evaluated for their ability to ferment skim milk and retain viability during storage at 4°C. Bifidobacterium longum ATCC 15707, B. breve 15700, and B. bifidum 29521 maintained the greatest viabilities at > 1 x 10⁷ CFU/mL, and B. infantis 15702 maintained the highest β‐galactosidase activity at > 1 U/ml (with < 1 × 10⁵ CFU/mL) after ‐60 to 4°C storage. In fermented skim milk, B. breve 15700, B. bifidum 29521, and B. animalis 25527 tolerated a final product pH of 4.75 with > 1 × 10⁸ CFU/mL remaining after 14 days of storage at 4°C. Overall, it was found that highest levels of β‐galactosidase activities did not necessarily correlate to the highest plate‐count populations.     

Influence of low dose irradiation on the quality of fresh buffalo meat stored at 0-3°C

The effect of low dose irradiation on the microbiological, chemical and sensory qualities of fresh buffalo meat stored at 0-3°C was studied. Meat slices packed in polyethylene bags subjected to 2·5 kGy dose had a shelf-life of 4 weeks with acceptable sensory score, low total volatile basic nitrogen values and remarkable improvement in microbiological quality. Irradiated meat was completely free of Pseudomonas spp. and Enterobacteriaceae throughout storage. In contrast, the unirradiated control meat spoiled within 2 weeks.     

Changes in quality of rainbow trout (Oncorhynchus mykiss) fillets preserved with salt and sugar at low concentrations and stored at 4°C

The effects of dry-curing with low concentrations of salt and sugar on the quality of rainbow trout (Oncorhynchus mykiss) fillets were studied over a 16-day storage period at 4°C. Physicochemical characteristics (total volatile base nitrogen (TVB-N), biogenic amines (BAs), ATP-related compounds and K value), microbial populations (total aerobic counts (TAC), H₂S-producing bacteria, Pseudomonas, Aeromonas, and lactic acid bacteria) and sensory (SA) indicators were analyzed. Fish samples were subjected to the following treatments: untreated (control), dry-cured with 1.3% salt (T1), and dry-cured with 1.3% salt that also contained 0.9% sugar (T2). SA indicated that the sensory quality of the control, T1, and T2 was unacceptable after 8, 12, and 12 days of storage, respectively. Moreover, the cadaverine concentration of treated samples was significantly lower (P < 0.05) than the control after storing for 8 days. T1 and T2 were significantly higher (P < 0.05) than the control in inosine 5-monophosphate (IMP) content from the 2th to 10th day. Cadaverine, putrescine, hypoxanthine, and TAC were correlated significantly (P < 0.01) with SA, and these seemed to be reliable indicators of fish quality. The results indicated that curing treatments extended the shelf life of rainbow trout fillets, which could be exploited by processors.     

Crystallization of Honey at −20°C

Honeys from different regions of the province of Buenos Aires were stored at ?20°C, and factors that affect crystallization were analyzed. Crystals were observed by light microscopy. Firmness, adhesivity and viscosity of the samples were measured. Honey was characterized by determining the water activity, turbidity, moisture, fructose, and glucose contents. Results show that the viscous characteristics of the samples depend on the number, size, and disposition of crystals. Various honey samples exhibited Newtonian, pseudoplastic, and thixotropic behaviors. Crystallization was favored at higher moisture contents, suggesting that the parameters that affect honey crystallization at room temperature have a different effect at freezing temperatures. Honey that presented higher values of firmness had a moisture content lower than 17%, and a linear inverse relationship was observed between the adhesivity and firmness of honey samples.     

Accumulation of stimulants of Toll-like receptor (TLR)-2 and TLR4 in meat products stored at 5 °C

Recent evidence suggests that exposure to stimulants of the innate immune receptors Toll-like receptor (TLR)-2 and TLR4 may contribute to the development of atherosclerosis and insulin resistance. We showed recently that common foodsuffs can contain TLR-stimulants, and that the greatest concentrations were present in meat-based products. Using a recently developed quantitative bioassay, we here examined the kinetics of accumulation of TLR2- and TLR4-stimulants in a variety of meat products held at 5 °C in air or under a modified atmosphere for up to 8 d. Meat content of TLR-stimulants increased with time in each meat examined and was paralleled by growth of pseudomonads and Enterobacteriaceae, suggesting that bacterial lipopeptides and lipopolysaccharides are the likely sources of TLR2- and TLR4-stimulants, respectively. TLR-stimulants reached the highest levels (approximately 80 μg lipopeptide-equivalents per gramme and approximately 7 μg lipopolysaccharide-equivalents per gram) in meat that was minced rather than intact, and when stored in air rather than under a modified atmosphere. TLR2- and TLR4-stimulants in meat products cooked for 1 h retained approximately 20% and approximately 40% of their bioactivity, respectively. In summary, storage conditions and microbial flora critically regulate the kinetics of TLR2- and TLR4-stimulant accumulation in meat products and these may retain biological activity after cooking. PRACTICAL APPLICATION: The novel assays presented in this work could be used to predict the potential of foodstuffs to promote inflammatory signaling in human subjects, which may be deleterious to health. These assays may also be used to monitor the historical microbial flora in food products after cooking or other forms of food processing may have rendered the original microflora nonviable.     

Effect of low temperatures (-18 to +5°C) on the texture of beef lean

The textural properties of beef over the temperature range −18 to +5 °C were measured using Warner Bratzler (WB) and tensile techniques. In addition, the effects of rapid radio frequency (RF) tempering and slower conventional air tempering on texture were compared. Temperature showed a significant effect (P < 0.05) on WB and tensile shear force, with higher values obtained at temperatures on or below −5 °C. Work to fracture values showed two peaks at −15 and −3 °C. Sample thickness and muscle fibre direction were also important factors affecting shear force, with samples cut across fibres showing higher values. Tempering method showed no effect (P ? 0.05) on the textural properties measured. In light of the rapid nature of RF tempering, these findings will be of interest to the meat industry.     

Effects of combining of smoking and marinating on the shelf life of anchovy stored at 4°C

The quality of smoked and marinated anchovy was investigated in terms of sensory, chemical [total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA), peroxide value (PV), fatty acids, free fatty acids (FFA), and pH] and microbiological parameters (total aerobic count (TVC), coliform, Escherichia coli, Salmonella, Staphylococcus aureus) during 7 months of storage. The results of sensory analyses showed that the total appearance, odor-taste, and texture scores decreased gradually during storage period. The results of the chemical analyses also correlated well with the sensory analyses apart from TVBN value. TBA significantly increased (p<0.05) from 1.9 to 4.25 MA/kg after the storage of 6 month. Peroxide value (POV) showed significant fluctuations (p<0.05) during the storage period. Initial TVC of 3.8 log CFU/g increased to 6.2 log CFU/g at the end of storage period. According to results obtained from sensory, chemical, and microbiological analyses, shelf life of this product was about 6 month.     

Physicochemical,microbiological, and sensory attributes of chitosan-coated grass carp (Ctenopharyngodon idellus) fillets stored at 4°C

This study investigated the effect of chitosan coating (1 and 2%) on the quality of grass carp fillets stored at 4°C for 20 days. During storage, the physicochemical properties (pH, thiobarbituric acid value, total volatile basic nitrogen value, trimethylamine nitrogen value, K-value, water loss, and instrumental texture), microbiology (total viable count and psychrotrophic count), and sensory properties were evaluated. The results showed that chitosan coating could effectively inhibit bacterial growth, improve physicochemical and sensory qualities, and it reduced the deterioration of the quality of grass carp fillets. Compared with fillets without chitosan coating, the shelf life of fillets with 1 and 2% chitosan coating was extended by ~3 and 6–7 days, respectively.     

Effects of three preservative agents on the shelf life of vacuum packaged Chinese-style sausage stored at 20°C

The influence of 3% sorbitol, 3% sodium lactate and 100 mg/kg nisin on the shelf life of vacuum packaged Chinese-style sausage stored at 20°C was studied. Growth of microbiological populations (aerobe, anaerobe, lactic acid bacteria, leuconostocs) and slime formation on the sausage were not retarded during storage by addition of nisin. Sorbitol lowered the initial water activity of the sausage, however, microbiological spoilage accompanied with pH decline, increase in volatile basic nitrogen compounds and a sour odour defect were observed after 10 days storage. Sodium lactate was bacteriostatic as it inhibited microbial as well as chemical changes during storage so that the shelf life was 25 days at 20°C. The dextran content of the vacuum packaged Chinese-style sausage indicated the spoilage 2-3 days earlier than that seen by other chemical assays or sensory evaluation.     

Quality deterioration in frozen Nile perch (Lates niloticus) stored at −13 and −27°C

Nile perch fillets stored at −13 and −27°C were monitored to determine changes in protein functionality [expressible moisture (EM), water uptake ability (WUA), soluble protein (SP) and emulsion capacity (EC)], changes in lipids [free fatty acids (FFA) and malonaldehyde accumulation] and changes in sensory properties. For samples stored at both temperatures, WUA, EC and SP decreased with time of storage while EM, FFA, malonaldehyde and off-flavors increased. Texture, taste and overall acceptability changed only for the samples stored at −13°.     

Selective effect of the product type and the packaging conditions on the species of lactic acid bacteria dominating the spoilage microbial association of cooked meats at 4°C

The product type was shown to strongly affect the growth rate and the composition of the spoilage lactic flora during refrigerated (4°C) storage of cooked, cured meats, sharing their processing plant environment, day of production and film packaging conditions. Growth of lactic acid bacteria (LAB) under vacuum was more prolific on the product in the order: ham>turkey breast fillet>smoked pork loin>pariza>mortadella>bacon, and ham>frankfurters, manufactured in two industrial meat plants A and B, respectively. The Lactobacillus sakei/curvatus group prevailed in all products, except the non-smoked, boiled whole-meats, i.e. cooked ham and turkey breast fillet, where Leuconostoc mesenteroides subsp.mesenteroides predominated. Lactobacillus sakei was by far the most prevalent species in smoked whole-meats, i.e. pork loin and bacon. Emulsion sausages, i.e. pariza, mortadella and frankfurters, contained a more diverse lactic flora.Leuconostoc carnosum and Lc. citreum occurred in boiled, whole-meats and emulsion sausages, respectively.Weissella viridescens was isolated from smoked meat products only. A very good correlation between the LAB growth and types and important intrinsic factors, such as the product pH, moisture, salt (brine) concentration and cooking method could be observed. When ham and frankfurters from plant B were stored in air, yeasts and mainly Brochothrix thermosphacta became important members of the spoilage association. Growth of LAB was faster in air. The presence of oxygen resulted in a replacement ofLc. mesenteroides subsp. mesenteroides by other Leuconostoc spp. in ham, and in a shift of the spoilage flora from homo- to heterofermentative LAB species in frankfurters.     

Effect of packaging atmosphere and pH on the virulence and growth ofYersinia enterocoliticaon pork stored at 4°C

Growth and virulence of pathogenicYersinia enterocoliticawere investigated on high (pH>6.0) and normal (pH<5.8) pH pork packaged in modified atmospheres and stored at 4°C. Modified atmospheres used in the study were vacuum packaging and saturated CO₂. Pork was packaged in a high gas barrier packaging film and examined over a 30-day period. Phenotypic characteristics were used to detect the presence of the virulence plasmid ofY. enterocoliticaafter exposure to the pork packaging and storage regimen. Phenotypic characteristics ofY. enterocoliticaisolates from pork loin stored at 4°C for 30 days that were studied included Congo red uptake, calcium dependence and autoagglutination in methyl red Voges–Proskauer broth and tissue culture medium. Numbers ofY. enterocoliticaon the lean surface of high pH pork slices increased approximately 2.7logcfucm⁻²when vacuum packaged and stored at 4°C for 30 days. Storage of inoculated normal pH pork in 100% CO₂resulted inY. enterocoliticaremaining in the lag phase over the storage period. Virulence ofY. enterocoliticawas maintained in 25 to 35% of isolates following storage for 30 days at 4°C in vacuum- and CO₂-packaged meats and was not affected by pH of the pork loin.     

Formation of acrylamide at temperatures lower than 100°C: the case of prunes and a model study

Acrylamide concentrations in prune products--baby strained prunes (range = 75-265 μg kg(-1)), baby apple/prune juice (33-61 μg kg(-1)), prune juice (186-916 μg kg(-1)) and prunes (58-332 μg kg(-1))--on the Canadian market were determined. The formation of acrylamide in a simulated plum juice was also investigated under 'drying conditions' in an open vessel at temperatures <100°C for 24 h and under 'wet conditions' in a closed vessel at a temperature of 120°C for 1 h. Acrylamide was produced in a simulated plum juice under 'drying conditions' in amounts comparable with those found in prunes and prune juices. Acrylamide was not produced in simulated plum juice under 'wet conditions' in a closed vessel at temperature of 120°C for 1 h, but under the same condition an authentic prune juice doubled its acrylamide concentration. Formation of acrylamide in prune products was attributed to the presence of asparagine and sugars in the starting materials.     

Development and validation of a predictive microbiology model for survival and growth of Salmonella on chicken stored at 4 to 12 °C

Salmonella spp. are a leading cause of foodborne illness. Mathematical models that predict Salmonella survival and growth on food from a low initial dose, in response to storage and handling conditions, are valuable tools for helping assess and manage this public health risk. The objective of this study was to develop and to validate the first predictive microbiology model for survival and growth of a low initial dose of Salmonella on chicken during refrigerated storage. Chicken skin was inoculated with a low initial dose (0.9 log) of a multiple antibiotic-resistant strain of Salmonella Typhimurium DT104 (ATCC 700408) and then stored at 4 to 12 °C for 0 to 10 days. A general regression neural network (GRNN) model that predicted log change of Salmonella Typhimurium DT104 as a function of time and temperature was developed. Percentage of residuals in an acceptable prediction zone, from -1 (fail-safe) to 0.5 (fail-dangerous) log, was used to validate the GRNN model by using a criterion of 70% acceptable predictions. Survival but not growth of Salmonella Typhimurium DT104 was observed at 4 to 8 °C. Maximum growth of Salmonella Typhimurium DT104 during 10 days of storage was 0.7 log at 9 °C, 1.1 log at 10 °C, 1.8 log at 11 °C, and 2.9 log at 12 °C. Performance of the GRNN model for predicting dependent data (n=163) was 85% acceptable predictions, for predicting independent data for interpolation (n=77) was 84% acceptable predictions, and for predicting independent data for extrapolation (n=70) to Salmonella Kentucky was 87% acceptable predictions. Thus, the GRNN model provided valid predictions for survival and growth of Salmonella on chicken during refrigerated storage, and therefore the model can be used with confidence to help assess and manage this public health risk.     

Effects of ozonation on microbiological,chemical and sensory attributes of vacuum-packaged rainbow trout stored at 4±0.5°C

The effects of ozone in aqueous solution on the shelf life of whole, vacuum-packaged rainbow trout, stored under refrigeration (4±0.5°C) were studied by monitoring the microbiological, chemical and sensory changes for a period of 15 days. Vacuum-packaged non-ozonated trout served as the control sample. Ozonation affected populations of bacteria namely, mesophilic aerobic bacteria, Pseudomonas spp. and H₂S-producing bacteria until day 11 of storage, Brochothrix thermosphacta, lactic acid bacteria and Enterobacteriaceae until day 8 of storage. Trimethylamine (TMA) values of all rainbow trout samples remained low (<3 mg N/100 g) until day 11 of storage, and then increased to 12.2, 8.9 and 4.7 mg N/100 g for the control and the samples ozonated for 60 and 90 min, respectively on day 15 of storage. Total volatile basic nitrogen (TVB-N) values remained relatively constant (20–25 mg N/100 g) until day 11 of storage, but increased to 61.1, 37.6 and 39.4 mg N/100 g flesh for the control and ozonated specimen for 60 and 90 min, respectively on day 15 of storage. Thiobarbituric acid (TBA) values remained relatively constant (1–3 mg MA/kg flesh) until day 12 of storage but increased to 8.4, 6.4 and 3.8 mg MA/kg flesh on day 15 of storage for the control and the ozonated trout for 60 and 90 min, respectively. Sensory evaluation (odor, taste and texture) of cooked rainbow trout showed a very good correlation with bacterial populations. On the basis of both sensory and microbiological data, a shelf life of 10 and 12 days was obtained for ozonated, vacuum-packaged and refrigerated rainbow trout at 60 and 90 min, respectively.