Pack Atmosphere Research Articles

Gamma radiation processing under modified atmosphere packaging effects on microbial quality and antioxidant activity of fresh leafy vegetables during storage

Fresh leafy vegetables are great source of vital nutrients, to promote health and prevent diseases but they can transmit pathogenic microorganisms to human beings. Shelf life of these products is very limited post harvest and after three days at refrigeration temperature, they will spoil. Radiation processing combined with modified atmosphere packaging and refrigeration temperature is a practical treatment to ensure safety and enhance vegetables shelf life even to be used in international trades. The effects of irradiation doses at 0, 0.25, 0.5 and 1 kGy on fresh leafy vegetables packed under air, N2 and vacuum atmospheres up to10 days of storage at 4 °C were studied. According to the results of microbial tests, and antioxidant activity of DPPH°, gamma radiation at dose of 0.5 kGy under N2 packing atmosphere are recommended as optimal storage conditions up to 10 days at 4 °C for fresh garlic chives, basil, mint and parsley.

Improving Transport Properties of Bi-2223 Superconducting Tapes With the Optimization of Packing Atmosphere

Multifilamentary Bi2Sr2Ca2Cu3O10+δ (Bi-2223) high temperature superconducting tapes were fabricated by powder-in-tube process. During the precursor powder packing process, environment atmosphere was changed from pure oxygen to dry air and 7.5% O2 balanced with N2, with the oxygen partial pressure decreasing from 100% to 25% and 7.5%, respectively. The change of packing atmosphere obviously influenced the phase assemblage in the early stage of Bi-2223 phase formation process. Therefore, the chemical composition of obtained Bi-2223 phase as well as the content and distribution of secondary phases changed accordingly. Meanwhile, the changes of intergrain connections and the flux pinning properties were investigated based on the in-field critical current, $I_{c}$ – B measurements. Finally, attributed to the decreased oxygen partial pressure in packing atmosphere, the $I_{c}$ improvements of 25% at self-field and 0.6 T were obtained comparing with the tapes packed under pure oxygen. With further optimization of sintering process, the final $I_{c}$ of 116 A was achieved, which corresponded to the critical current density, $J_{c}$ of ∼21 kAcm−2.

Influence of Packing Atmosphere on the Microstructures and Transport Properties of Bi-2223/AgAu Tapes

Oxygen partial pressure was the key factor to tune the phase evolution mechanism of Bi-2223 system. In order to investigate the influence of packing atmosphere on the phase formation rate of Bi-2223, microstructures‚ and the current capacity of final tapes‚ 37-filamentary Bi-2223/AgAu tapes were fabricated by powder-in-tube (PIT) process, and the powder packing process operated in the glove box under different atmosphere of pure O2‚ air, and N2–7.5%O2, with the oxygen partial pressure of 100%‚ 25%, and 7.5%, respectively. With different packing atmosphere, the phase formation rate of Bi-2223 increased obviously during the first heat treatment process (HT1). While, based on the same HT1 process, the maximum Bi-2223 phase content was obtained in the tapes with packing atmosphere of N2–7.5%O2‚ which should be attributed to the suitable Bi-2223 content and distribution. Due to the improvement of superconducting phase content and better texture structure, the critical current density increased with decreasing oxygen partial pressure of packing atmosphere and the maximum value of 19.9 kA/cm2 was reached. Moreover‚ the in-field current capacities of these Bi-2223/AgAu tapes have also been enhanced with low oxygen partial pressure in packing atmosphere, attributed to the improvements of intergrain connectivity.

Quality changes of Atlantic horse mackerel fillets (Trachurus trachurus) packed in a modified atmosphere at different storage temperatures

Atlantic horse mackerel (Trachurus trachurus) is an important commercial fish in Europe. Changes in microbial growth, sensory quality and chemical evolution of modified atmosphere packed (MAP) horse mackerel fillets (48% CO₂/50% N₂/2% O₂) were monitored at different storage temperatures (2, 4, 6 and 10 °C). The observed sensory shelf life of MAP fish fillets was found to be approximately 7 days at 2 °C, 6 days at 4 °C, 5 at 6 °C and 3 days at 10 °C. A significant correlation was observed between all sensory attributes and two groups of bacteria [total viable count (TVC) and psychrotrophic bacteria], with sensorial rejection when the bacteria approached 10⁶ CFU g⁻¹ at 4, 6 and 10 °C. A level of 30-50 mg total volatile basic nitrogen 100 g⁻¹ of mackerel muscle was well correlated with sensory shelf life determination at all temperatures, except for 2 °C. During the storage time, lipid oxidation did not increase at any temperature and could not be related to quality decay. The presence of acetaldehyde and butyraldehyde in the packing atmosphere was only found in fillets stored at the highest temperature studied (10 °C). In this study, key quality parameters were established to monitor the spoilage and shelf life of MAP Trachurus trachurus stored at different temperatures. In addition, these results confirm the use of modified atmosphere packaging as a mild preservation method for fillets of Atlantic horse mackerel.

An amendment to the classical model of internal oxidation: Model-inherent transition characteristics

An analytical method based on the flux balance at the inter-region boundary is explored for the evolution of a binary alloy in the corresponding Rhines pack atmosphere where the solute forms only one type of oxide. This alloy may undergo an exclusive external oxidation, an exclusive internal oxidation or a mixed oxidation. The assumption of zero solubility-product is very restrictive for a complete analysis of the mixed oxidation. Nevertheless, an analysis of the exclusive internal oxidation, improved upon the classical theory, gives the transition characteristics and hence a domain of the existence of this possibility.

CONSERVAÇÃO PÓS-COLHEITA DE MANGABA SOB REFRIGERAÇÃO E MODIFICAÇÃO DA ATMOSFERA DE ARMAZENAMENTO

The objective of this study was to evaluate the effects of packing atmosphere alteration on the mangaba fruits quality (Hancornia speciosa Gomes), stored under refrigeration (11 ± 1°C), using polyvinyl chloride or low density polyethylene films, with or without potassium permanganate. Regardless the kind of film, the titratable acidity and soluble solids content increased, while the pH decreased, along the storage period. During that time, under modified atmosphere and refrigeration, fruits showed higher values for the soluble solids/titrable acidity ratio than other fruits. A significant loss of fresh matter occurred for the fruits packed with polyvinyl chloride, in relation to those packed with low density polyethylene. The fruits under atmosphere modified by polyvinyl chloride film, with or without potassium permanganate, and by low density polyethylene, with potassium permanganate, maintained good general features, until the eighth storage day. However, the fruits packed with low density polyethylene, without potassium permanganate, maintained their good features only until the fourth storage day. During ten storage days, none of the samples were visibly attacked by microorganisms. KEY-WORDS: Hancornia speciosa; packaging; shelf life.

Effect of Lactic Acid Bacteria on Beef Steak Microbial Flora Stored Under Modified Atmosphere and on Listeria Monocytogenes in Broth Cultures

Beef steaks were inoculated with one or other of two protective strains of lactic acid bacteria, the bacteriocinogenic Lactobacillus sakei CTC 372 or the uncharacterised Lactobacillus CTC 711. They were stored under modified atmospheres (20–40% CO2). Inoculation of meat with both strains inhibited the growth of the spoilage bacteria. Neither CO2 in the pack atmosphere, inoculation with protective strains, nor a combination of both, affected formation of metmyoglobin or the development of off-odours. The formation of metmyoglobin in meat pigments and the sensory odour scores were compatible to those of fresh meat which had not undergone either oxidative deterioration or microbial spoilage. Listeria monocytogenes were inhibited in broth by meat surface microbiota containing either of the protective strains. With an initial population of 5.6 log cfu/mL, after 7 days incubation at 3°C, Listeria monocytogenes were recovered at log mean population of 2.8 log cfu/mL when neither protective strain was present. At 8°C, the population of Listeria monocytogenes recovered were reduced by about 2.5 or 1.5 log cfu/mL in the presence of Lactobacillus sakei CTC 372 or Lactobacillus CTC 711, respectively. At 25°C, the population of Listeria monocytogenes recovered from broth containing either protective strain were about 5 log cfu/mL less than the population recovered from broth containing Listeria monocytogenes only.

NUGGETS FORMULADOS CON CARNE DE AVE MECÁNICAMENTE RECUPERADA Y LAVADA: ESTABILIDAD DURANTE EL ALMACENAMIENTO EN CONGELACIÓNNUGGETS WITH WASHED MECHANICALLY DEBONED CHICKEN MEAT: FROZEN STORAGE STABILITY

The effect of 20 % washed mechanically deboned chicken meat (WM) as a substitute of breast meat (HDCM) on chicken nuggets characteristics during frozen storage was investigated. Two different formulations were made, one with 100 % HDCM, the other with 20 % WM as a substitute for HDCM. WM was produced by washing mechanically deboned chicken meat, 3 steps of 20 min each. Nuggets were packed in air or under vacuum and kept frozen (−22 ± 2°C). Thiobarbituric acid reactive substances (TBARS), sensory evaluation, mesophilic aerobic count, psychrotrophic count and detection of Salmonella were determined during six months. TBARS and sensory evaluation showed that oxidative phenomena in nuggets with 20 % WM is similar to the 100 % HDCM formulation. This conclusion is valid for both, air or vacuum packed nuggets. No difference was found in microbiological counts between formulations or packing atmosphere. Resumen Se estudió el efecto de la incorporación de 20 % de carne de ave mecánicamente recuperada y lavada (WM) sobre la conservación de nuggets de pollo. Se elaboraron 2 formulaciones, una con 100 % de carne de pechuga (HDCM), la otra reemplazando 20 % de HDCM por WM. La WM se obtuvo a partir de carne de ave mecánicamente recuperada tras realizar 3 lavados de 20 min. Ambas formulaciones se conservaron a −22 ± 2°C, envasadas con aire y a vacío. Durante 6 meses se determinó el contenido de sustancias que reaccionan con el ácido tiobarbitúrico (TBARS), evaluación sensorial, microorganismos aerobios mesófilos, psicrótrofos y Salmonella. Según los resultados de las TBARS y de la evaluación sensorial, los nuggets con 20 % de WM no presentaron cambios con respecto a los elaborados íntegramente con HDCM. Esta conclusión es válida para los productos envasados con aire y a vacío. Tampoco se observaron diferencias en los recuentos microbiológicos entre ambas formulaciones o atmósferas. Palabras clave: Nuggets, conservación, carne de ave, carne mecánicamente recuperada y lavada

Effect of lactic acid bacteria on extention of shelf life and growth of Listeria monocytogenes in beef steaks stored in CO2- rich atmosphere

Beef steaks were inoculated with one or other of two protective strains of lactic acid bacteria (bacteriocinogenic Lactobacillus sakei CTC 372 or the uncharacterized Lactobacillus CTC 711), and stored under modified atmospheres (20-40% CO2). Inoculation of meat with LAB inhibited growth of the spoilage bacteria. Neither CO2 in the pack atmosphere or inoculation with protective strains, nor a combination of both, affected formation of metmyoglobin or the development of off-odours. The formation of metmyoglobin in meat pigments and the sensory odour scores were compatible to those of fresh meat which had not undergone either oxidative deterioration or microbial spoilage. Listeria monocytogenes was inhibited in broth by meat surface microbiota containing the protective strains. With initial numbers of 5.6 log cfu mL-1, after 7 days incubation at 3oC, L. monocytogenes were recovered at log mean numbers of 2.8 log cfu mL-1 when no protective strain was present. At 8oC, the numbers of L. monocytogenes were reduced by about 2.5 or 1.5 log mL-1 in the presence of Lb. sakei CTC 372 or Lb. CTC 711, respectively. At 25oC, the numbers of L. monocytogenes recovered from broth containing either protective strain were about 5 log lower than the numbers recovered from broth containing L. monocytogenes only.

The shelf-life of beef steaks treated with dl-lactic acid and antioxidants and stored under modified atmospheres

Beef steaks were treated with 1.5% lactic acid alone or supplemented with antioxidants (0.1% rosemary extract and 0.05% ascorbic acid). The steaks were stored under modified atmospheres containing either 60% O 2/40% CO 2 or 70% O 2/20% CO 2/10% N 2. Both the 40% CO 2 atmosphere and the lactic acid treatment significantly ( P<0.05) inhibited growth of lactic acid bacteria, Brochothrix thermosphacta and Pseudomonas spp. Neither CO 2 in the pack atmosphere, treatment with lactic acid, nor a combination of both, affected formation of thiobarbituric acid reactive substances, myoglobin oxidation, or CIE a * values. However, treatment with antioxidants significantly ( P<0.05) delayed oxidation of both myoglobin and lipids, and so extended the storage-life.

Absorption kinetics of oxygen scavengers

The oxygen (O2) absorption kinetics of six commercial O2 scavengers were studied. The scavengers were placed in bags which were filled with 240 mL of air, 4.5 L N2 + 15 mL of air, or 3.5 L CO2 + 9 mL of air. The O2 concentration in each bag was measured at hourly intervals for 8 h. The effects of variability among individual scavengers, initial O2 concentrations of 20% or 500 ppm (0.05%), temperatures of 25, 12, 2 or −1.5 °C, and scavenger capacity on the O2 absorption rate were determined. In addition, the effect of placing scavengers within over‐wrapped trays within bags, was examined. Rates of O2 absorption varied by factors of up to 2 between individual O2 scavengers of the same type, but rates of absorption by groups of four scavengers of the same type were similar. Low temperatures gave longer O2 half‐life when compared with those at higher temperatures, e.g. O2 half‐lives of 7.1 and 1.0 h at −1.5 and 25 °C, respectively, were obtained for one scavenger type. Shorter O2 half‐lives were obtained in air than in N2 atmospheres at the same temperature, e.g. O2 half‐lives of 1.0 and 3.3 h in air and N2 at 25 °C, respectively, were obtained for one scavenger type. The O2 absorption reactions were of first order for both high and low initial O2 concentrations. However, O2 concentration was the primary limiting factor for O2 absorption in atmospheres having O2 concentration of 500 ppm because of the dominance of diffusion. Scavengers, when placed within over‐wrapped trays within bags had up to 12 times longer O2 half‐lives, indicating that the O2 permeable film acts as an O2 barrier when pack atmosphere has low O2 concentrations. To obtain consistent and reproducible results, it is recommended that multiple scavengers be used in a packaging system. The appropriate number should be based on scavenger type, desired O2 absorption rate, storage temperature, and pack atmosphere (air/N2/CO2).

Improved use of oxygen scavengers to stabilize the colour of retail‐ready meat cuts stored in modified atmospheres

A series of three experiments were conducted to develop a retail packaging system suitable for use in centralized meat processing and packaging operations using modified atmosphere master packaging (MAP) of display‐ready beef and pork cuts. It was shown that oxygen (O2) scavengers were needed inside retail trays, lidded or over‐wrapped trays could be used with equal success but inclusion of a grid inside the retail tray was not required. It was established that a minimum of eight O2 scavengers with an O2 absorption rate high enough to achieve an O2 half‐life of 0.6–0.7 h in the pack atmosphere were needed where the O2 concentration could otherwise remain ≤500 ppm at any time during storage. Composite results from these experiments clearly showed that the best performance resulted from use of hard plastic retail trays containing eight O2 scavengers, with high O2 absorption rate, when placed underneath an absorbent pad and over‐wrapped with an O2 permeable film. Small holes in two corners of the O2 permeable film to permit free exchange of atmospheres within the retail packages facilitated O2 reduction during MAP storage.

Physical characteristics of lamb primals packaged under vacuum or modified atmospheres

Lamb primals (shoulders) were packaged under vacuum, 80% O 2/20% CO 2, 50% CO 2/50% N 2 or 100% CO 2 and stored at 5 or 0 °C. Pack contents were examined at 7 day intervals to determine the composition of the pack atmosphere, drip loss, colour (muscle and fat) and pH (surface and internal). The composition of the gas atmospheres changed very little during storage. The only significant differences between developed head space compositions above primals stored at the two different temperatures (5 and 0 °C) were noted in packs stored for 28 days under 80% O 2/20% CO 2. Low levels of drip loss (<0.5%) were noted in all packs stored under the modified gas atmospheres. In contrast, significantly higher levels of drip loss (0.5–1.1%) were noted in vacuum packaged lamb stored at 5 and 0 °C. Acceptable muscle colour was observed 2 hr after opening of all packs. The only significant differences between atmospheres for lean muscle colour were noted after 28 days storage. Fat colour did not generally change during storage in any of the atmospheres, apart from a slight bleaching effect at 7 days. There were no significant differences between the surface or internal pH values noted after storage under any of the atmosphere/temperature combinations. In general, higher pH values were observed at the surface of the meat than in the interior. This pattern was noted before and after storage.

Effects of modified atmospheres on textural and cell wall changes of asparagus during shelf‐life

SummarySpears of asparagus cultivator (cv) Regal harvested from a commercial crop on 16 May, 30 May, and 6 June, 1989 were packaged in rigid PVC trays (300g per pack) over‐wrapped with non‐perforated 15 μ stretch PVC (Auto RMF‐A), a similar micro‐perforated film or with a highly perforated control film. Packs were held at 8°C for 1 d, then transferred to 20°C to simulate commercial cool chain distribution and ambient display. Respiration rates as mg CO2 production kg‐1h‐1 were determined for each harvest, and changes in the pack atmosphere composition and weight losses were monitored during shelf‐life. On the day of harvest, and after 3 and 6d shelf‐life, shear force's required to cut through spears and visual quality were determined, and cooked samples were assessed for tenderness, stringiness, flavour, and bitterness by a trained sensory panel. At these intervals, samples of asparagus from each treatment were also extracted for alcohol‐insoluble residues (AIR's), from which the composition of sugars and cell wall phenolics were also determined.Rates of respiration and the extent of pack atmosphere modification were similar for each harvest; in non‐perforated packs, CO2 increased to &gt; 11% and O2 fell to &lt; 2% and in microperforated packs, CO2 equilibrated to ca 5–6% and O2 decreased to a minimum of ca 6–7%. The shear forces needed to cut stems increased during 6 d shelf‐life; this increase was greatest for control‐packed spears and least for those from non‐perforated packs. Regrowth (elongation of the stem and opening of bracts) was almost eliminated in non‐perforated packs, and much reduced in micro‐perforated packs. Asparagus in micro‐perforated packs became slightly less tender and more stringy, whereas control‐packed spears became much tougher and stringier during shelf‐life; changes in flavour and bitterness were slight. Levels of most cell wallsugars changed little, although some obvious changes were detected during shelf‐life; galactose decreased in all treatments, arabinose decreased and xylose content increased considerably (67%) in control‐packed spears. Similarly, the lignin content of asparagus increased by &gt;400% in control, by 200% in micro‐perforated and by &lt; 100% in non‐perforated packs.The relationships between instrumental and sensory methods for assessing textural changes in asparagus and the changes in cell wall composition, and the effects of modified pack atmospheres on these changes are discussed. The possible benefits and limitations of modified atmosphere (MA) packaging to retard post‐harvest deterioration, particularly textural changes in asparagus are also discussed.

The response of unripe Conference pears to modified atmosphere retail packaging

SummaryUnripe green Conference pears with initial firmness values of 46–55 N were sealed in modified atmosphere (MA) low density polyethylene (LDPE, 30μ) pillow packs and in perforated control packs on three dates during 1985–1986. Changes in pack atmosphere composition, skin chlorophyll content, flesh firmness and sensory quality were monitored during 14–20 days simulated shelf‐life at 20°C. In MA packs, equilibrated atmospheres containing 5–9% CO2 and &lt; 5% O2 developed within c. 3 days. Chlorophyll degradation was completely inhibited by MA and resumed when packs were perforated, but MA only partially retarded the rate of flesh softening. Variations in the rate of ripening changes in duplicate MA packs could not be explained simply by differences in pack atmospheres. Furthermore, pears retarded by MA packaging failed to develop the normal sweet, aromatic flavour and succulent, juicy texture of ‘eating‐ripe’ fruit, even when the packs were perforated after 4 days.The differences in the responses of pears and apples to MA packaging, and the limitations of using this technique for the commercial marketing of English pears are discussed.