Effect of film and temperature on the sensory, microbiological and nutritional quality of minimally processed cauliflower

The effect of atmosphere modification, generated using three different packaging films, on the quality of cauliflower minimally processed when stored at 4 or 8 °C for up 20 days was evaluated. The colour, texture, weight loss, sensory attributes, as well as microbial counts and sugars and ascorbic acid content were determined. The atmosphere generated with the perforated polyvinylchloride (PVC) film was hardly modified, whereas the other two films (non-perforated PVC and polypropylene films) originated changes in CO₂ and O₂ levels during storage. The different packaging conditions and storage temperature influenced yellowing. An increase in shear force was observed. Weight losses were below 5%. Mesophiles and Pseudomonas counts were below 7 log CFU g⁻¹, the populations being lower with film B and film C than with film A. Cauliflower maintained an acceptable appearance in all the films studied. Total sugars decreased about 27% after 20 days of storage, whereas ascorbic acid did not change.     

Effect of nisin and high temperature pasteurization on the shelf-life of whole milk

Two experiments were conducted to assess the effectiveness of nisin on the keeping quality of pasteurized whole milk. After pasteurization, milk samples were stored at 10°C and samples were analysed at intervals for total plate count (TPC), Lactobacillus count, calcium ion concentration, pH and total acidity (TA). In the first experiment nisin was added to milk samples in the range 0 to 50 IU ml^-1 prior to pasteurization at 72°C for 15 s. AH concentrations of nisin used were effective in controlling microbial growth. Milk containing 40 and 50 IU ml^-1 nisin had not spoiled after 41 days' storage compared to spoilage time of 14 days for the control milk. In the second experiment 40 IU ml^-1 of nisin was combined with three 'pasteurization' processes: 72°C for 15 s, 90°C for 15 s and 115°C for 2 s. The milk processed at 72°C for 15 s with nisin showed an increased keeping quality of about 7 days compared with the control and showed a significantly lower count for Lactobacillus. In contrast, nisin had a much greater effect on TPC counts in the milk pasteurized at 90°C for 15 s, and after 28 days' storage at 10°C the milk was still acceptable. Milks treated both with and without nisin at 115°C for 2 s were microbiologically acceptable after 28 days, with counts less than 10 ml^-1. However, the milk with nisin was superior in flavour, as no noticeable off-flavours were apparent after 32 days. All these results are consistent, as shown by the microbiological and chemical analyses. Addition of nisin to milk prior to pasteurization provides an opportunity to achieve extended shelf-life in regions with poor refrigeration.     

Quality characteristics of minimally processed leek packaged using different films and stored in lighting conditions

Since minimal processing of vegetables does not impede their capacity to react to external stimuli, this work sought to study the effect of lighting on minimally processed leek during storage. White and green cuts were processed separately and packaged using films with different permeability: a totally permeable PVC film and two P-Plus films: P-Plus 120 and P-Plus 90, with O₂ permeability of 8000 and 5000 cm³ m⁻² 24 h⁻¹ atm⁻¹ at 25 °C, respectively. All the packaged leek was stored at 4 °C for more than 26 days in two different conditions: in complete darkness and in light. Lighting caused an increase in stomatal aperture and respiratory rate. Thus, the white cut achieved atmospheres with higher CO₂ (10%) and lower O₂ (12%) content than samples packed in the same film kept in the dark. The green cut saw respiratory activity compensated by photosynthesis, and the atmosphere composition remained similar to atmospheric conditions until day 18. Lighting also affected the colour, accelerating the changes in appearance. Exposure to light had a negative effect on the quality parameters.     

Influence of Maturity at Processing on Quality Attributes of Fresh-cut Conference Pears

ABSTRACT: Influence of ripeness state of Conference pears on the respiration and quality changes of the minimally processed fruit was studied. The fruits processed at partially ripe maturity were the most suitable to obtain fresh-cut products. Slightly under-ripe pears exhibited less browning and firmness degradation. Treatments consisting of dips in 10 g/L ascorbic acid and 5 g/L calcium chloride and packaging in 15 cm^-2× m^-2× 24 day^-1× bar^-1 preserved the initial appearance of pear cubes for at least 14 d. Because of a significant inhibition of ethylene production, 0 kPa O₂ initial atmosphere was effective in preventing quality changes. Presence of ethanol, as a result of fermentative anaerobic processes, increased with ripeness, especially beyond the 1st 21 d of storage at 4 °C. On the contrary, acetaldehyde was less affected than ethanol by processing and storage conditions.     

The effects of different incubation temperatures on the acetaldehyde content and viable bacteria counts of bio-yogurt made from ewe's milk

Yogurt and bio-yogurt were manufactured from ewe's milk using a starter culture and a probiotic culture. Incubation was carried out at 37°C and 42°C until pH 4.6 was reached and the yogurts were stored at 4 +1°C for 14 days. Analysis after 1, 7 and 14 days showed that incubation temperature and storage time significantly influenced overall properties of the samples. During the storage, whey separation and pH decreased, but titratable acidity, lactic acid and volatile fatty acid contents increased. Viable bacterial counts in all bio-yogurts were above 10⁷ cfu g⁻¹ at the end of storage.     

Changes in the Quality of Fresh-cut Jicama in Relation to Storage Temperatures and Controlled Atmospheres

ABSTRACT: Intact jicama (Pachyrhizus erosus) roots are chilling sensitive, but quality of fresh-cut pieces (1.8 × 4.5 cm cylinders) was best maintained at low storage temperatures (0 to 5 °C). Respiration rates of different piece sizes were similar, and averaged 2, 7 and 10 μL CO₂-g ⁻¹h⁻¹ at 0 °C, 5 °C and 10 °C, respectively. Storage in air at 5 °C to 10 °C resulted in surface browning and was associated with increases in phenolics and phenylalanine ammonia lyase and polyphenol oxidase activities. High CO₂ atmospheres (5 to 10%) at 5 °C were very effective in retarding microbial growth and discoloration. The source of jicama root notably affected the quality and shelf-life of the fresh-cut pieces. Fresh-cut pieces from stored roots (2 wk at 19 to 22 °C) had lower visual quality and crispness during subsequent storage than did pieces from recently harvested roots.     

Microbial flora of technological interest in raw ovine milk during 6°C storage

Changes in the microbial flora of ovine milk of medium hygienic quality (initial mean total plate count 3.3  ×  10⁵ cfu/mL) were studied throughout refrigerated storage at 6°C. Total plate counts after 48 h of refrigerated storage (mean count 4.6  ×  10⁵ cfu/mL) were under the current standards in the European Union (EU) for raw ovine milk to be used for cheesemaking after heat treatment. However, after 96 h, mean total plate counts (1.6  ×  10⁷ cfu/mL) were above the standards. Lactococci were found at levels higher than Pseudomonas spp. in milk freshly drawn (54.5% and 3.5% of total plate count, respectively) and after 96 h at 6°C (47.9% and 33.9% of total plate count, respectively). Lactobacilli, enterococci, coliforms and thermodurics were found at values lower than lactococci and Pseudomonas spp., before and after refrigerated storage ( ≤  0.08% of the total plate count). A significant growth ( P  < 0.001) was detected for mesophiles, Pseudomonas spp. and lactococci after 96 h of refrigeration at 6°C; however, thermodurics, coliforms, lactobacilli and enterococci, showed no significant increase ( P  > 0.05). Presumptive Escherichia coli (β-glucuronidase-positive) underwent a decrease throughout storage at 6°C.     

牦牛肉品质特性研究进展

为了研究食用菌对贮藏过程中牦牛肉丸食用品质的影响。本研究以添加不同种类食用菌粉（香菇、猴头菇、牛肝菌、茶树菇）的牦牛肉丸为研究对象,测定分析不同处理组牦牛肉丸制品在贮藏期间的色泽、pH、保水性、硫代巴比妥酸值（TBARS）、质构特性、流变特性、乳化活性（Emulsifying activity index,EAI）和乳化稳定性（Emulsifying stability index,ESI）等品质指标的变化与差异。结果表明：与空白对照组相比,在0~15 d的贮藏期内,添加香菇能够显著改善冷藏条件下牦牛肉丸的b^*值（15 d的b^*值较空白组低4.52）,添加牛肝菌、茶树菇可提高牛肉丸的pH（第15 d两组均为6.64）,添加香菇使牛肉丸保水性改善,香菇、猴头菇的添加显著提高牦牛肉丸的弹性和咀嚼性（P<0.05）,茶树菇的添加减缓了肉丸的EAI和ESI下降,添加食用菌对牦牛肉丸的凝胶能力有显著改善（P<0.05）,并一定程度抑制脂质氧化,其中香菇组TBARS最低;0~2 d贮藏期内,添加食用菌粉的牦牛肉丸感官评分更好。综上,香菇对于牦牛肉丸贮藏期间的各食用品质能够产生较好影响,其他食用菌能一定程度提高牦牛肉丸贮藏期内的部分食用品质,具有一定开发应用价值。     

Microwave Oven Heating for Inactivation of Listeria Monocytogenes on Frankfurters before Consumption

ABSTRACT:  Microwave oven heating was evaluated for inactivation of  Listeria monocytogenes  on inoculated and stored frankfurters. Frankfurters formulated without/with 1.5% potassium lactate and 0.1% sodium diacetate were inoculated with  L. monocytogenes  (1.9 ± 0.2 log CFU/cm²), vacuum-packaged, and stored (4 °C) to simulate conditions prior to purchase by consumers. At storage days 18, 36, and 54, packages were opened and placed at 7 °C, simulating aerobic storage in a household refrigerator. At 0, 3, and 7 d of aerobic storage, 2 frankfurters were placed in a bowl with water (250 mL) and treated in a household microwave oven at high (1100 W) power for 30, 45, 60, or 75 s, or medium (550 W) power for 60 or 75 s. Frankfurters and the heating water were analyzed for total microbial counts and  L. monocytogenes  populations. Exposure to high power for 75 s reduced pathogen levels (0.7 ± 0.0 to 1.0 ± 0.1 log CFU/cm²) to below the detection limit (<−0.4 log CFU/cm²) on frankfurters with lactate/diacetate, even after 54 d of vacuum-packaged storage followed by 7 d of aerobic storage. For frankfurters without lactate/diacetate, high power for 75 s caused reductions between > 1.5 and 5.9 log CFU/cm² from control levels of 1.5 ± 0.1 to 7.2 ± 0.5 log CFU/cm². Depending on treatment and storage time, the water used to reheat the frankfurters had viable  L. monocytogenes  counts of <−2.4 to 5.5 ± 0.5 log CFU/mL. The results indicated that frankfurters should be reheated in a microwave oven at high power for 75 s to inactivate up to 3.7 log CFU/cm² of  L. monocytogenes  contamination.     

Influence of exposure to light on the sensorial quality of minimally processed cauliflower

ABSTRACT:  The impact of lighting on minimally processed cauliflower packaged in 4 different film types (PVC and 3 P-Plus) has been measured and quantified. The effect on the sensorial quality of storage at 4 °C in darkness and partial or continuous lighting was evaluated. The gas concentrations in the packages and the weight losses were also determined. Atmosphere composition inside the packages depended on both the permeability of the film used for the packaging and exposure to light. Samples stored with lighting maintained the gaseous exchange between plant tissue and the atmosphere inside the packages for longer periods than in samples kept in darkness. This prompted a greater loss of water vapor as well as the development of atmospheres with low levels of O₂ and high levels of CO₂ in the samples packed with less permeable films. The most important aspect in sensory evaluation was color. In instrumental color evaluation, coordinates h * and L * were the main means for estimating color evolution. The presence of light accelerated browning in the cut zones. The development of abnormal coloring in these areas marked the end of shelf life for minimally processed cauliflower. Among the sensory attributes studied, color was the most affected by exposure to light. Samples packed in P-Plus 120 film displayed the lowest level of color deterioration in the cut zones. However, under lit conditions, the low permeability of this film caused atmospheres with very low O₂ contents and high CO₂ contents. These atmospheres produced a loss of texture and the development of off-odors.     

Microbiological, physicochemical and organoleptic changes in dry-salted olives of Thassos variety stored under different modified atmospheres at 4 and 20 °C

Microbiological, physico-chemical and organoleptic changes were studied in dry-salted olives, cv. Thassos, stored under different atmospheres (100% carbon dioxide and nitrogen, 40% CO₂/30%O₂/30%N₂ and air) at 4 and 20 °C for 180 days. The initial microbial flora comprised of yeasts, no lactic acid bacteria, enterobacteria, pseudomonads or Staphylococcus aureus were detected, as the low water activity/high salt content does not favour their growth. At 4 °C, the population of yeasts declined steadily throughout storage but to a different extent depending on the gaseous atmospheres. At 20 °C, there was an initial decline in yeast counts in all samples followed by a steady increase until the end of the storage period. The CO₂ atmosphere was most effective at keeping the number of yeasts low at both storage temperatures. All gas atmospheres prevented fungal growth at both temperatures apart from the samples stored in air. The pH, a_w and salt content of the olives did not change significantly throughout the storage period. The prevailing yeast species was the salt tolerant Candida famata . The organoleptic characteristics did not differ significantly among differently treated olives. However, increased rancidity and reduced fruit colour was observed in the samples stored at 20 °C.     

Cooked and brined shrimps packed in a modified atmosphere have a shelf-life of >7 months at 0 °C, but spoil in 4–6 days at 25 °C

Summary Spoilage and safety of cooked, brined and modified atmosphere packed shrimps were studied at 0, 5, 8, 15 and 25 °C. Shrimps from two sources, cold and warm waters, were brined in a sodium–chloride brine containing benzoic, citric and sorbic acids. Shelf-life was above 7 months at 0 °C but only 4–6 days at 25 °C. Apparent activation energy for the effect of temperature on shelf-life was > 100 kJ mol^-1. This pronounced effect of temperature was explained by changes in spoilage microflora at different storage temperatures. Simple and empirical mathematical models for rates of spoilage were developed for the prediction of shelf-life at different temperatures. To evaluate safety, products were challenged with Listeria monocytogenes and spores of Clostridium botulinum . Above 5 °C growth responses of L. monocytogenes followed the square root model with a T_min-value of +0.2 °C. Cl. botulinum produced toxin at the time of spoilage at 25 °C but only in shrimps with < 3% water-phase salt.     

Effects of gas atmosphere and temperature on the respiration rates of whole and sliced mushrooms (Agaricus bisporus)--implications for film permeability in modified atmosphere packages

ABSTRACT:  An open flowthrough respirometer was used to determine the respiration rates of whole and sliced mushrooms as a function of O₂, CO₂, and storage temperature. Respiration rates were measured under the following O₂ concentrations: 20, 15, 10, 5, and 2% at 5 temperatures (4, 8, 10, 13, and 16 °C). The effects of 5 CO₂ concentrations (0, 2, 5, 10, 15%) at two O₂ levels (2 and 20%) were also examined at these temperatures. Mushroom respiration increased with temperature following an Arrhenius-type relationship; activation energies and corresponding Q₁₀ values were calculated. Lowering the oxygen concentration significantly decreased the respiration rate. The effects of reducing O₂ levels were greater at higher storage temperatures. Both activation energies and Q₁₀ values were lower under reduced O₂ atmospheres compared with those in air. A Michaelis–Menten enzyme kinetics model was evaluated for describing the influence of gas concentrations on respiration rate. The effects of O₂ fitted the O₂ enzyme kinetics model well. CO₂ exhibited small inhibitory effects on respiration of whole and sliced mushrooms, especially at low O₂ concentrations and low temperatures. The enzyme model was used to predict respiration under an optimal modified atmosphere for mushrooms, and the required film O₂ and CO₂ permeabilities were defined for key pack design parameters.     

The yeast flora of stored ready-to-use carrots and their role in spoilage

Spoilage of ready-to-use grated raw carrots packaged in polymeric films and stored at 10°C was investigated for involvement of yeasts. Cryptococcus albidus was only isolated during the first 3 days of storage, increasing to levels of 10⁵–10⁶g^-1. Candida lambica was more commonly isolated after 3–7 days of storage, and reached 10⁷–10⁸g^-1 after 12 days. Candida sake was present throughout storage, increasing from 10⁵–10⁶ after 3 days to 10⁷–10⁸ after 12 days. In some samples, Candida parapsilosis and Candida tropicalis were also isolated at levels similars to C. sake . All the yeasts isolated at the end of storage were fermentative species and their metabolism was characterized with a Warburg apparatus. Neither the number of yeasts nor the composition of the yeast flora were related to the deterioration of the product. Although Candida lambica inoculated on grated carrots caused spoilage after 12 days at 10°C, the high O₂ permeable film was most effective in reducing exudate.     

Storage characteristics of sous vide cooked roast beef

The technological, microbiological, and sensory storage characteristics of low temperature sous vide cooked roast beef were investigated. the effect of two heat treatments, 59°C (P₇₀¹⁰in core 8.4) and 62°C (P₇₀¹⁰ in core 15.9) on the stability of spiced roast beef made from Musculus semitendinosus with a high initial microbial load were compared as well as storage temperatures of 2 and 10°C. Although chilling baths with circulating water were used, recommended chilling rates for sous vide products could not be attained. Yield was significantly higher at 59°C and at a storage temperature of 2°C but decreased during storage. At 62°C the meat became significantly more tender than at 59°C as measured by shear force. No differences in microbiology were observed between heating regimes. At low storage temperature products were microbiologically stable over a 35-day period. At 10°C, however, a rise in psychrotrophic aerobic counts and occasional pack swelling was observed. In a commercial scale experiment conducted with sous vide cooked (62°C) beef with low initial counts, no increase in aerobic counts was observed at 2, 5 and 10°C while swelling occurred in 28% of the packages stored at 10°C and in none at 2 and 5°C. the swelling was due to different types of gas-producing clostridia. Warmed-over flavour (as TBARS) showed no development during storage in intact packages, while slicing and serving the roast beef under commercial conditions resulted in a marked increase to < 100 μmole kg⁻¹. In spiced roast beef only minor changes in off-odour and off-flavour of the product were observed during 23 days of storage at 2°C.     

Shelf-Life Extension of Fresh Mushrooms (Agaricus bisporus) By Application of Hydrogen Peroxide and Browning Inhibitors

ABSTRACT: An experimental washing process for fresh mushrooms entailing immersion in 5% H₂O₂, followed by application of a sodium erythorbate-based browning inhibitor, was optimized, scaled up, and made continuous. The laboratory process described previously was modified by adding a pre-wash step using 0.5% to 1% H₂O₂, increasing the wash solution H₂O₂ concentration from 3% to 5%, and substituting 4% sodium erythorbate + 0.1% NaCl for the more complex browning inhibitor formulation used previously. A continuous, commercial-scale washing facility was built to test the new process. Mushrooms washed by this process were free of adhering soil, less subject to brown blotch than conventionally washed mushrooms, and at least as resistant to enzymatic browning as unwashed mushrooms during storage at 4 °C. Storage at 10 °C accelerated development of brown blotch and browning.     

Effects of gas atmosphere, antimicrobial dip and temperature on the fate of Listeria innocua and Listeria monocytogenes on minimally processed lettuce

The growth and survival of inoculated strains of Listeria innocua and L. monocytogenes on minimally processed lettuce were studied. The effects of package atmospheres (lettuce sealed within packages after flushing with 100% N₂ or without flushing with N₂, lettuce sealed within perforated packages), antimicrobial dips (100 p.p.m. chlorine solution for 5 min, 1% citric acid solution for 5 min) and storage temperatures (3°C and 8°C) were investigated. Populations of L. innocua and L. monocytogenes on undipped lettuce stored at 3°C gradually decreased (by 1–1.5 log cycles) during a 14 day storage period. By contrast counts on lettuce stored at 8°C did not change significantly ( P > 0.05). Flushing packages of lettuce with 100% N₂ followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2–3 log cycles) in L. innocua and L. monocytogenes counts during storage. L. innocua , strain NCTC 11288, behaviour was similar to that of L. monocytogenes (strains ATCC, 19114 and NCTC 11994) under these storage temperatures and atmospheres. Using L. innocua as a model for L. monocytogenes , it was found that dipping lettuce in a chlorine or citric acid solution followed by storage at 8°C resulted in a significant increase ( P < 0.05, by 2 log cycles) in L. innocua populations compared with undipped samples. It is concluded that N₂ flushing or use of antimicrobial dips combined with storage at 8°C, both enhanced the survival and growth of Listeria populations on shredded lettuce.     

Effect of Time, Temperature, and Slicing on Respiration Rate of Mushrooms

ABSTRACT:  Respiration rate measurement considering the effects of cutting, temperature, and storage time are important for the shelf life study and modified atmosphere-packaging design of fresh-cut produce. This study investigates in the respiration rate of fresh whole and sliced mushrooms at 0, 4, 8, 12, 16, and 20 °C under ambient atmosphere and different storage times. The O₂ consumption rate increased with temperature and ranged from 22.13 to 102.41 mL/(kg.h) and 28.87 to 143.22 mL/(kg.h) for whole and sliced mushrooms, respectively, in the temperature range tested. Similar trend was observed for CO₂ production rate. Slicing of mushrooms increased the respiration rate by 30% at 0 °C and 40% at 20 °C indicating that the mushrooms are not as sensitive to the stress caused by cutting as other fresh produce. Storage time affected both respiration rate of whole and sliced mushrooms and this effect was prominent at higher temperatures. The respiration rates increased initially for some time, then decreased and reached steady state value at 12, 16, and 20 °C. A 2nd-order polynomial equation was used to fit the respiration rate data as a function of time at each temperature tested.     

Mathematical modelling of O2 consumption and CO2 production rates of whole mushrooms accounting for the effect of temperature and gas composition

Investigation of respiration rate of fresh produce, under different gas composition and temperatures, and respective mathematical modelling is central for the modified atmosphere packaging design. This work investigates the effect of temperature (4, 8, 12, 16, 20 °C) and gas composition (O₂ between 3 to 21% and CO₂ between 0 to 15%) on respiration rate of whole mushrooms. Oxygen and carbon dioxide respiration rates increased significantly (3–4 fold) as the temperature elevated from 4 to 20 °C and were in the range of 13.23 ± 3.12 to 102.41 ± 2.132 mL kg⁻¹ h⁻¹) and 14.33 ± 1.56 to 97.02 ± 2.51 mL kg⁻¹ h⁻¹) respectively. Low O₂ and high CO₂ levels reduced O₂ consumption and CO₂ production rates of whole mushrooms on average by a circa 47–60% at all temperatures as compared to the respiration rate at ambient air. Mathematical models were developed for RO₂ and RCO₂, by combining the Arrhenius and Michaelis–Menten uncompetitive equations. These models predicted well, O₂ consumption and CO₂ production rates of whole mushrooms as a function of both temperature and gas composition.     

Comparison of high pressure treatment and thermal pasteurization effects on the quality and shelf life of guava puree

The effects of high pressures and thermal pasteurization on the survival of microorganisms, enzyme inactivation and quality changes of guava puree during storage at 4°C were investigated and compared with untreated samples. After treatment at a pressure of 600MPa and 25°C for 15 min, the microorganisms in guava puree were inactivated to less than 10 cfu mL⁻¹ and the product exhibited no change in colour, pectin, cloud and ascorbic acid content as compared with fresh samples. The inactivation of enzymes in guava puree by thermal pasteurization was greater than by high pressures. The microbial count in guava puree reduced to 200 cfu mL⁻¹ and the product showed marked changes in viscosity, turbidity and colour when heated at 88–90°C for 24s. The content of pectin, cloud and ascorbic acid as well as colour in untreated and high pressurized (400MPa) guava puree gradually decreased, whereas these changes were not observed in pasteurized (88–90°C) and high pressurized (6000MPa) puree during storage at 4°C for 60 days. The guava puree treated at 600MPa and 25°C for 15 min retained good quality similar to the freshly extracted puree after storage at 4°C for 40 days.