Improved keeping quality of minimally fresh processed celery sticks by modified atmosphere packaging

Recommended storage conditions of green celery sticks are 4 °C for 10 days, but there are no reports about optimal modified atmosphere packaging (MAP) conditions to preserve them longer. The objective of this research was to describe the gas composition of MAP generated by two polymeric films and its effects on chemical, sensorial and microbial quality, and physiological disorders of celery sticks stored at 4 °C for 15 days. Green sticks of 15-cm length of ‘Trinova’ cv. were placed in hermetically sealed plastic bags: low-density polyethylene, oriented polypropylene (OPP) and polyethylene-perforated bags as control (air). The O₂ and CO₂ concentrations, soluble solid content, pH, titratable acidity, colour, sensorial quality and sugar and organic acids contents were monitored. Compared to the control, both MAP treatments improved the sensory quality, avoided the loss of green colour, decreased the development of pithiness and retarded the growth of microorganisms. In any treatment neither off-odours nor off-flavours were detected. After 15 days at 4 °C within the OPP bags a steady-state atmosphere of 6 kPa O₂+7 kPa CO₂ was reached and celery sticks stored under these bags showed the best quality.     

Listeria monocytogenes Inactivation in Turkey Rolls and Battered Chicken Nuggets Subjected to Simulated Commercial Cooking

Cured and uncured turkey rolls inoculted with 10⁷Listeria monocytogenes CFU/g were vacuum packaged and cooked to internal temperatures of 68°C and 74°C, respectively, in a steam-injected chamber. Samples were stored up to 15 wk at 4°C. Battered chicken nuggets were also inoculated internally with about 10⁷L. monocytogenes CFU/ g. Nuggets enclosed in bags were cooked under moist heating conditions in a convection oven to an internal temperature of 71°C. Nuggets were flushed with 30% CO₂, 70% N₂ atmosphere and sealed. Chicken nuggets were stored at 4°C up to 30 days. No Listeria monocytogenes were recovered from the cooked products suggesting that similar commercial processes are adequate to reduce populations of L. monocytogenes below detection limits.     

Effect of Storage Conditions and Chemical Treatments on Firmness, in Vitro Protein Digestibility, Condensed Tannins, Phytic Acid and Divalent Cations of Cooked Black Beans (Phaseolus vulgaris)

Black beans stored at 30° or 40°C and 80% relative humidity showed marked increases in firmness and decreases in in vitro digestibility of proteins. Changes in these properties were small when beans were stored at 5°C and 50% relative humidity. The adverse effects of poor storage conditions could be practically eliminated by soaking beans in salt solutions instead of water. The changes in firmness and digestibility were accompanied by changes in the detectable concentrations of tannins and phytates. Protein digestibility appears to be reduced by interactions between protein and tannins, especially high molecular weight tannins. Concentration of these tannins is affected by poly-phenol oxidase activity. Firmness increased and protein digestibility decreased as the phytic acid content decreased.     

Calcium Treatment to Maintain Quality of Zucchini Squash Slices

Zucchini squash slices dipped in solutions of CaCl₂ alone or with chlorine were stored at 0°C, 5°C, and 10°C. Slices developed water soaked areas (chilling injury) at 0°C and brown discoloration at 5°C and 10°C, which increased with storage. The amount and severity of chilling injury/browning/decay of water-dipped controls were least at 5°C. Calcium treatments helped in reducing development of decay, rate of total microbial growth, ascorbic acid loss, and shear force decrease of slices stored at 0°C and 10°C but not at 5°C. Addition of chlorine to CaCl₂ seemed to have some benefits at 0°C or 10°C.     

Residual peroxidase activity as influenced by blanching,SO2 treatment and freezing of cauliflowers

The influence of blanching time and SO₂ treatment on the residual peroxidase activity and its implication for the sensory quality of frozen cauliflowers were assessed after storage for up to one year at ?18°C. The treated cauliflowers, sealed in polythene bags, were placed in waxed paperboard cartons and frozen in a contact plate freezer at ?35°C. The sensory quality of frozen stored cauliflowers related well to their residual peroxidase activity, which was sensitive to the SO₂ treatment. Blanched cauliflowers following a brief dip in a metabisulphite solution prior to freezing gave a significantly (P<0.05) superior product even when stored for one year. The residual peroxidase activity, which ranged from 1 to 5.5% in the blanched samples, was below 1 % in the SO ₂-treated samples, and the SO₂ content of50 ppm found in these stored samples disappeared after 3 min cooking in boiling water.     

Microwave Processing to Destroy Salmonellae in Corn-Soy-Milk Blends and Effect on Product Quality

Enriched corn-soy-milk (CSM) blends were inoculated with Salmonella senftenberg and packed in 50-lb (22.7 kg) bags. The inoculated product and CSM bags containing natural salmonellae contamination were heated from 21° to 56.7°C through 82.2°C in 3.9 – 10 min, respectively, using a 60 Kw (2450 MHz) continuous microwave tunnel, and then palletized with and without 4-cm spacers between rows. Spacer palletized bags cooled to 43°C after 9.7 hr with moving air and after 23.3 hr without moving air, but 60 hr was required with no spacers. Initial most probable numbers (MPN) of 4 × 10² cells/g for S. senftenberg were reduced 10²-fold to 10⁵-fold after processing at 56.7° through 82.2°C, respectively. Nutritional damage occurred at process temperatures of 77.8° and 82.2°C. At 61.1° and 67.2°C, MPN were reduced 2 × 10³-fold with no significant change in rheology, moisture, color, vitamins A and B₁, available lysine, and protein efficiency ratios.     

Physiology and Microbiological Quality of Fresh-cut Mango Cubes as Affected by High-O2 Controlled Atmospheres

Preliminary study showed that among 40‐ to 100‐kPa O₂ atmospheres, 60‐kPa O₂ reduced the respiration of fresh‐cut ‘Carabao’ mango cubes the most when held at 5 °C or 13 °C for 42 h. Therefore, the effects of 60‐kPa O₂ on the physiology and microbial quality of fresh‐cut ‘Carabao’ and ‘Nam Dokmai’ mango cubes were determined and compared with those held in air. The high‐O₂ atmosphere reduced the respiration rate of ‘Carabao’ mango cubes stored at 5 °C but stimulated the rate after 2 d of storage at 13 °C. Browning of ‘Carabao’ cubes was accelerated by 60‐kPa O₂ at 13 °C. With ‘Nam Dokmai’ cubes, the high O₂ had no effect on respiration rate, browning, and incidence of water‐soaked appearance at 5 °C and 13 °C. The high O₂ did not affect texture or ascorbic acid content of ‘Carabao’ and ‘Nam Dokmai’ mango cubes at either temperature. Counts of lactic acid bacteria and molds were below the detection level (2.4 log colony‐forming units [CFU]/g) during storage at both temperatures. However, 60‐kPa O₂ stimulated the growth of mesophilic aerobic bacteria on ‘Carabao’ cubes and yeasts of ‘Nam Dokmai’ cubes at 13 °C. The increased microbial count may have been due to the higher pH of cubes stored in 60‐kPa O₂ at 13 °C than at 5 °C or in air. Within ‘Nam Dokmai’ mango cubes, the predominant genera in mesophilic aerobic bacteria were Enterobacter, Klebsiella, and Pantoea and in the yeasts were Candida, Cryptococcus, and Rhodotorula. These results indicate that 60‐kPa O₂ is not desirable for mango cubes when held at 13 °C.     

Changes in appearance and natural microflora on iceberg lettuce treated in warm,chlorinated water and then stored at refrigeration temperature

The objective of this study was to determine the effect of warm, chlorinated water on the survival and subsequent growth of naturally occurring microorganisms and visual quality of fresh-cut iceberg lettuce. After dipping cut lettuce leaves in water containing 20 mg l⁻¹free chlorine for 90 s at 50°C, samples were stored at 5 or 15°C for up to 18 or 7 days, respectively. Populations of aerobic mesophiles, psychrotrophs, Enterobacteriaceae, lactic acid bacteria, and yeasts and molds were determined. The visual appearance and development of brown discoloration were monitored. Treatment of lettuce in warm (50°C) chlorinated water delayed browning of lettuce. Shelf life of lettuce stored at 5°C, as determined by subjective evaluation of color and general appearance, was about 5 days longer than that of lettuce stored at 15°C. Treatment in warm (50°) water, with or without 20 mg l⁻¹chlorine, and in chlorinated water at 20°C significantly (α= 0·05) reduced the initial population of mesophilic aerobic microflora by 1·73–1·96 log₁₀cfu g⁻¹. Populations increased, regardless of treatment, as storage time at 5°C and 15°C increased. The same trends were observed in populations of psychrotrophs and Enterobacteriaceae. Yeast populations increased slightly in lettuce stored at 5°C but were consistently about 3 logs lower than mesophilic aerobes. Populations of molds and lactic acid bacteria were less than 2 log₁₀cfu g⁻¹throughout storage at 5 or 15°C. Results suggest that heat (50°C) treatment may have delayed browning and reduced initial populations of some groups of micro-organisms naturally occurring on iceberg lettuce, but enhanced microbial growth during subsequent storage.     

Chemical and microbial stability of high moisture dried apricots during storage

BACKGROUND: This study was conducted to determine the chemical and microbial stability of high moisture (HM) dried apricots during storage at 5, 20 and 30 °C for a period of 8 months. HM dried apricots were obtained by rehydrating dried apricots in ‘water’ and ‘water + H₂O₂’. RESULTS: Analysis of kinetic data suggested first‐order models for loss of SO₂ and non‐enzymatic browning reactions. Higher storage temperatures increased the rate of SO₂ loss and formation of brown colour in HM dried apricots. Results from extensive colour measurements (non‐enzymatic browning, reflectance colour and β‐carotene) revealed that the colour of HM dried apricots stored at 5 °C was almost unchanged during 8 months of storage. The colour of samples stored at 30 °C was unacceptable starting from 2 months of storage. Total mesophilic aerobic bacteria counts decreased 0.7, 1.1 and 1.5 log cycles after 8 months of storage at 5, 20 and 30 °C, respectively. For the same storage period, the decrease in mesophilic bacteria was 0.62 log cycle in samples rehydrated in ‘water + H₂O₂’ and stored at 20 °C. CONCLUSION: These results suggest that HM dried apricots should be stored at temperatures lower than 20 °C to preserve the characteristic golden yellow colour. A relatively low level of SO₂ (1458 mg kg^?1 at 200 g kg^?1 moisture level) was sufficient to prevent the growth of spoilage organisms in HM dried apricots at all three storage temperatures. Copyright © 2008 Society of Chemical Industry     

Influence of storage temperature on the quality of salted mackerel (Rastrelliger kangurta) and pink perch (Nemipterus japonicus)

Dry-salted mackerel and pink perch were stored at two temperatures: ambient (26·8 ± 3·3°C) and 2·5 ± 1°C. Changes in moisture content, salt content, water activity (a_w), peroxide value (PV), free fatty acid content (FFA), total volatile base nitrogen (TVBN) content, halophilic bacterial count and sensory scores for overall acceptability were studied. Loss of moisture and absorption of salt were considerably higher in the products stored at ambient temperature. The decrease in a_w was more pronounced at ambient temperature than at the lower temperature. Although the chemical indices of freshness (PV, FFA and TVBN) and the halophilic counts showed increasing trends, they were considerably lower in the products stored at the lower temperature. Sensory evaluation for overall acceptability indicated that storage at the lower temperature could considerably extend the shelf-life of salted fish.     

Clostridium botulinum Growth and Toxigenesis in Shelf-Stable Noodles

Unacidified and acidified noodles were inoculated with a composite of C. botulinum types A and B spores. Noodles were cooked, packaged in oxygen-permeable polypropylene bags, steamed, cooled, then stored aerobically at 7 or 23°C, or anaerobically at 30°C. Toxin did not develop in any aerobically stored samples at pH ±4.5. Toxin developed in samples with pH >5.0, stored aerobically and anaerobically. In addition, toxin was detected in one anaerobically incubated acidified unit where pH had been increased by microbial growth. Proper acidification of product prevented toxic growth of C. botulinum.     

EFFECT OF BLANCHING AND SULFITE TREATMENT ON THE QUALITY OF FROZEN CAULIFLOWER

The influence of blanching time and post-blanching sulfite treatment on the sensory quality and texture of frozen cauliflower were assessed after storage at -18°C for up to one year. The treated cauliflower florets, sealed in polyethylene bags, were placed in waxed paperboard cartons and frozen in a contact plate freezer at -35°C. Samples blanched for 3 min and dipped in a solution containing 1000ppm of SO₂ for 5 min gave a significantly (p<0.05) superior product even when stored for one year. The residual SO₂ content of 50 ppm found in these stored samples disappeared after a 3 min cooking in boiling water. Cauliflower texture was influenced by blanching time but the textural differences of blanched samples diminished following freezing and storage. After a 3 min cooking, the texture of all thawed samples were comparable to that of fresh cauliflower cooked for 10–12 min.     

Changes in Mitochondrial Properties During Low Temperature Storage of Apples

Mitochondria were isolated from ‘Cortland’ and ‘Winesap’ apples stored at 90% RH and either 1° or 5°C. Respiratory control ratios of mitochondria isolated from ‘Nured Winesap’ apples stored at 5°C were consistently lower than from those stored at 1°C. Succinoxidase and Ca ⁺² ATPase activity was higher in mitochondria of ‘Cortland’ apples stored at 1°C. Large increases were observed in mitochondrial Ca ⁺² uptake after 4 wk storage of ‘Nured Winesap’ apples at 5°C and after 1 wk storage of ‘Cortland’ apples at 1°C. Although no symptoms of chilling injury were observed in the tissue of either cultivar, the mitochondrial response suggested chilling resistance in ‘Nured Winesap’ apples and chilling sensitivity in ‘Cortland’ apples.     

Development of Staphylococcal Toxin and Sensory Deterioration During Storage of Nitrogen and Vacuum Packaged Nitrite-Free Bacon-Like Product

Toxin production by S. aureus was studied in nitrite-free bacon-like product packaged in air permeable film, vacuum packages, and packages flushed with N₂ during storage at 8°C, 12°C or 26°C. Product wrapped in air permeable film deteriorated rapidly at 26°C and was rejected by sensory evaluation prior to staphylococcal enterotoxin detection. Enterotoxin was not detected in vacuum or N₂-flushed packages stored at 26°C. Samples stored at 12°C supported S. aureus growth although enterotoxin was not detected at 12°C or 8°C in any packaging environment. The potential for staphylococcal food poisoning resulting from the production of a nitrite-free bacon-like product was limited under the conditions studied.     

Effects of water stress on the post-harvest quality of two leafy vegetables,telfairia occidentalis and pterocarpus soyauxii during storage

The effect of water stress (excessive water loss) on the post-harvest quality of two leafy vegetables, Telfairia occidentalis and Pterocarpus soyauxii, at ambient (30–35°C) and low temperature (10°C) was investigated in south-eastern Nigeria. The effect of seal-packaging the vegetables in polyethylene and paper bags on quality decline of the leafy vegetables was also monitored. Unsealed leaves of T occidentalis and P soyauxii rapidly lost water during storage at either ambient or low temperature. There were decreases in the chlorophyll, protein and ascorbic acid contents in the stressed leaves. Packaging of the leaves in polyethylene bags alleviated these losses. Sealing of the leaves in polyethylene bags also alleviated water stress.     

Survival and Growth of Salmonella hadar on Minimally Processed Cabbage as Influenced by Storage Abuse Conditions

Shredded, washed and centrifuged cabbage was packaged in monooriented polypropylene (OPP) bags, inoculated with Salmonella hadar and stored 10 days at 4°C, 12°C and 20°C. Microbiological, appearance, odor and headspace gas analysis were evaluated throughout storage. S. hadar and mesophilic aerobic and psychrotrophic microorganism growth was affected by storage time and temperature. S. hadar counts were lower (p<0.05) at 4°C than at 12°C and 20°C. The score ratings for general appearance, wilting, browning and off-odor showed that all samples were commercially acceptable. Results indicated that S. hadar could survive and proliferate on minimally processed cabbage, thereby posing a potential hazard to consumers.     

Bacteria Associated with Spoilage of Braunschweiger

Refrigerated braunschweiger was spoiled mainly by Gram positive, catalase negative coçci identified as Streptococcus faecalis and Pediococcus pentosaceus. P. pentosaceus was isolated from sausage without nitrite held at refrigeration for 12 wk and from sausages made with 156 ppm nitrite stored at 22°C for 21 days. It produced souring and a low pH in the sausage. S. faecalis was isolated from refrigerated sausages and produced a perfumy or scented odor under anaerobic conditions. S. faecalis survived 65°C for 5 min and 60°C for 60 min. P. pentosaceus at levels of 10⁸ cells/ml of broth survived 65°C for 5 min but did not survive when the number of cells was 10³/ml.     

Growth and Enterotoxin A Production by Staphylococcus aureus in Precooked Bacon in the Intermediate Moisture Range

Different water activities were obtained in precooked bacon by varying the frying time. Water activity (a_w) correlated best to the moisture, salt and protein content. When stored aerobically at 37°C, S. aureus A100 was capable of rapid growth in precooked bacon at a a_w of 0.84 or above, whereas at 20°C a a_w of 0.88 or higher was required. Under anaerobic storage at 37°C, growth was observed at a a_w of 0.90, and at 20°C slight growth was noted at a a_w of 0.91. The increase in the minimal a_w required for aerobic growth at the lower temperature was reflected in the differences between the isotherms obtained at 37°C and 20°C. The maximum populations achieved were higher for samples stored aerobically. Enterotoxin A (19–821 ng/g) was found in all aerobically stored samples where growth occurred. Enterotoxin A (38–109 ng/g) was also found in all anaerobically incubated samples where the population of S. aureus increased more than one logarithmic cycle.     

Irradiation and Packaging Affect the Nitrate-Nitrogen Concentrations of Potatoes

Russet Burbank and Kennebec potato cultivars were irradiated with dosages of 0.1 and 1.0 KGy and stored in polyethylene or paper bags for 1 or 3 mo at 5°C or 20°C. Tubers receiving irradiation showed a significant (p<0.01) increase in nitrate-nitrogen concentration as compared to controls. Those receiving the 1.0 KGy dose had the highest nitrate-nitrogen concentration. Tubers stored in polyethylene bags were significantly (p<0.01) higher in nitrate-nitrogen concentration than those stored in paper bags. Tubers stored at 20°C were significantly (p<0.01) higher in nitrate-nitrogen than those stored at 5°C. These trends were consistent for both cultivars. The cortex region was significantly (p<0.01) higher in nitrate-nitrogen concentration than the pith region. Kennebec tubers were significantly (p<0.01) higher in nitrate-nitrogen than the Russet Burbank tubers for all irradiation doses and storage temperatures.     

Growth or Survival of Listeria monocytogenes in Ready-to-Eat Meat Products and Combination Deli Salads During Refrigerated Storage

Growth or survival of Listeria monocytogenes in cold‐smoked salmon; sliced, cooked ham; sliced, roasted turkey; shrimp salad; and coleslaw obtained at retail supermarkets stored at 5 °C, 7 °C, or 10 °C (41 °F, 45 °F, or 50 °F, respectively) for up to 14 d was evaluated. Cold‐smoked salmon, ham, and turkey were obtained in case‐ready, vacuum packages. All food products were stored aerobically to reflect additional handling within the retail supermarket. Cold‐smoked salmon, ham, and turkey supported the growth of L. monocytogenes at all 3 storage temperatures. Fitted growth curves of initial populations (about 3 log₁₀ colony‐forming units [CFU]/g) in cold‐smoked salmon, ham, and turkey stored at 5 °C achieved maximal growth rates of 0.29, 0.45, and 0.42 log₁₀ CFU/g growth per day, respectively. Storage at 10 °C increased the estimated maximal growth rate of the pathogen by 0.56 to 1.08 log₁₀ CFU/ g growth per day compared with storage at 5 °C. A decline in populations of L. monocytogenes was observed in shrimp salad and coleslaw, and the rate of decline was influenced by storage temperature. Retention of viability was higher in shrimp salad than in coleslaw, where populations fell 1.2, 1.8, and 2.5 log₁₀ CFU/g at 5 °C, 7 °C, and 10 °C, respectively, after 14 d of storage. Inability of shrimp salad and coleslaw to support the growth of L. monocytogenes may be attributed to the acidic pH (4.8 and 4.5, respectively) of the formulations used in this study. Results show that the behavior of L. monocytogenes in potentially hazardous ready‐to‐eat foods is dependent upon the composition of individual food products as well as storage temperature.