The storage life of chilled pork packaged under carbon dioxide

Pork cuts of longissimus dorsi muscle with overlaying fat and skin were packed under vacuum in film of low oxygen transmission rate, or under CO₂ in gas impermeable aluminium foil laminate. Cuts were stored at +3 or −1·5°C. Vacuum packaged cuts were grossly spoiled by Brochothrix thermosphacta after 2 weeks' storage at 3°C and after 5 weeks at −1·5°C. Cuts packaged under CO₂ were grossly spoiled by B. thermosphacta after 5·5 weeks' storage at 3°C. Growth of B. thermosphacta was suppressed when CO₂ packaged cuts were stored at −1·5°C. At that temperature, slow growth of enterobacteria was detected after a lag of about 18 weeks. The enterobacteria caused gross spoilage of an increasing proportion of cuts between 18 and 26 weeks. Muscle tissue with pale, soft, exudative (PSE) characteristics tended to lose colour after long storage periods, apparently because of loss of myogglobin with exudate. Until spoilage, the eating qualities of pork appeared little affected by prolonged storage.     

The effects of residual oxygen concentration and temperature on the degradation of the colour of beef packaged under oxygen-depleted atmospheres

Samples of beef longissimus dorsi (LD), approximately 5 × 5 × 1 cm, were packaged in pairs under 10 litre volumes of N₂ or CO₂ containing O₂ at concentrations between 100 and 1000 ppm. The packaged samples were stored at temperatures of 5, 1, 0 or −1·5°C, for times between 4 and 48 h. Samples of beef psoas major (PM) were packaged under N₂ or CO₂ containing O₂ at between 100 and 600 ppm, and stored at −1·5°C for 24 or 48 h. After storage, each sample was assessed for colour deterioration and discoloration, and for the fraction of metmyoglobin in the surface pigment.

The results obtained with N₂ and CO₂ atmospheres were similar. The colours of all LD samples had deteriorated after 4 h storage at 5 or 1°C, although the degree of deterioration increased with increasing O₂ concentration. All LD samples stored for 12 h at 5 or 1°C were extensively discoloured, with metmyoglobin fractions generally exceeding 60%, but those stored at −1·5°C for 48 h or less, under O₂ concentrations ≤ 400 ppm had undergraded colours. The colours of some LD samples stored at −1·5°C under about 600 ppm of O₂ were also undergraded, but the colours of samples stored under 800 or 1000 ppm had deteriorated by 24 h. The colours of LD samples stored at 0°C under > 200 ppm had deteriorated after 24 h storage, and the colours of samples stored under 100 ppm O₂ had deteriorated after 48 h storage. All PM samples were wholly discoloured after storage at −1·5°C. Evidently, the colour of beef muscle of high colour stability is resistant to degradation by atmospheres containing < 600 ppm of O₂ when the meat is stored at sub-zero temperatures, but not when the storage temperature is at or above 0°C. Beef muscle of low colour stability, such as the PM, will discolour at all low concentrations of O₂ irrespective of the storage temperature.     

Effect of the dietary supplementation with vitamin E on colour stability and lipid oxidation in packaged, minced pork

The effect of supplementation of vitamin E (200 W kg⁻¹ feed) in the diet of pigs on colour stability and lipid oxidation in minced pork was studied. Control and enriched diets were provided for the last 12 weeks before slaughter. Half of the samples of minced shoulder meat from control and supplemented pigs were packaged on trays with oxygen-permeable overwraps and half in modified atmosphere packs (initial gas mixture: O₂/CO₂/N₂ = 66/ 27/7). Meats were stored for 10 days at 7 °C in an illuminated retail display cabinet. The meat from vitamin E-supplemented pigs was more resistant to lipid oxidation than was the control meat. Gas packaging appeared to increase lipid oxidation in control meat, whereas lipid oxidation was stable in meat from vitamin E-supplemented pigs. Colour stability for gaspacked meat was comparable for both dietary groups. However, oxygen-permeable overwraps had a negative effect on colour stability in vitamin E-enriched meat. The reason for this is not known. The shelf-life of enriched and control meat was similar. Thus supplementation of pig feeds with vitamin E is recommended if an improved stability against lipid oxidation of (minced) pork is required.     

Effect of gas barrier characteristics of films on aflatoxin production by Aspergillus flavus in peanuts packaged under modified atmosphere packaging (MAP) conditions

The effects of the gas barrier characteristics of three films (ASI, ASII and ASIII) and storage temperature on the growth of, and aflatoxin production by, Aspergillus flavus in peanuts packaged in air and under a modified gas atmosphere of CO₂:N₂ (65:35) were investigated. Mold growth was barely visible in air packaged peanuts using high-medium barrier films (ASI and ASII) and stored at 20°C with more extensive growth occurring in air packaged peanuts stored at 25 and 30°C. Extensive mycelial growth and sporulation occurred in all air packaged peanuts in a low barrier film (ASIII), especially at 30°C. Gas packaging inhibited mold growth in peanuts packaged in a high gas barrier film at 20°C. However, mold growth occurred in gas packaged peanuts packaged in film ASII at higher storage temperatures while extensive mycelial growth was observed in all peanuts packaged in film ASIII irrespective of storage temperature. Levels of aflatoxin greater than the regulatory limit of 20 ng/g were detected in all air packaged peanuts with the highest level of aflatoxin (76 ng/g) being detected in peanuts packaged in a high gas barrier film ASI. Aflatoxin production was inhibited in gas packaged peanuts using a high barrier film. However, higher levels of aflatoxin were detected in all gas packaged peanuts in medium-low gas barrier films (ASII and ASIII), particularly at higher storage temperatures. This study has shown that MAP using a CO₂:N₂ (65:35) gas mixture was effective in controlling aflatoxin production by A. flavus in peanuts to levels less than the regulatory limit of 20 ng/g. However, the antimycotic effect of low O₂-high CO₂ atmospheres is dependent on the gas barrier characteristics of the packaging films, especially at higher storage temperatures.     

Combined effect of modified atmosphere bulk packaging, dietary vitamin E supplementation and microbiological contamination on colour stability of Musculus gluteus medius

Five Simmentaler type calves were fed diets supplemented with 500 mg vitamin E per day and five fed control diets. Rump steaks from each carcass were PVC-overwrapped and bulk packaged in 100% CO, or 20% CO₂:80% O₂. Bulk packs were stored up to 42 days at 4°C and steaks displayed up to 7 days at 4°C. Bacterial counts of rump steaks from either packaging treatment were not significantly influenced during bulk storage or retail display by supplementation with dietary vitamin E. Both packaging treatments delayed bacterial growth during bulk storage. Aerobic plate counts of rump steaks stored in 100% CO₂ were lower than those of rump steaks stored in 20% CO₂: 80%: O₂. This study showed that rump steaks supplemented with dietary vitamin E can be bulk packaged in 20% CO₂: 80% O₂ or 100% CO₂ and stored for up to 42 days with shelf life of 4–7 days.     

The effect of vacuum packaging and gaseous atmosphere on microbial growth in tripe

Changes in bacterial flora of tripe samples, stored at 4°C in air, vacuum packaged or in a CO₂-enriched atmosphere were studied. Aerobic plate counts showed a rapid increase in samples stored in air reaching a level of 1·6 × 10⁹/g from an initial level of 9·0 × 10³/g. The aerobic bacterial population inhibited in both vacuum packed and CO₂-enriched atmosphere storage. The shelf lives of samples stored in air, under vacuum packaging or in gas mixtures, were 4, 8 and 9 days, respectively. Enterobacteriaceae and anaerobic counts tended to be higher under vacuum storage than in a CO₂-enriched atmosphere. The numbers of lactic acid-producing bacteria were generally found to be lower under vacuum storage than in gas mixtures.     

The effect of wholesale vacuum and 100% CO2 storage on the subsequent microbiological, colour and acceptability attributes of PVC-overwrapped pork loin chops

The shelf life of chops cut from pork loins, after either vacuum or 100% CO₂ storage (0, 7 or 14 days), was determined. The PVC-overwrapped chops were assessed, following a shelf life study of 0, 2, 5 or 7 days at 0 or 5°C, regarding quality attributes such as microbiological contamination levels, colour and acceptability. The study indicated that according to the psychrotrophic counts, the PVC-overwrapped retail chops, from the vacuum as well as the 100% CO₂ stored pork loins (0, 7 or 14 days), still attained a conventional shelf life of 3 days.

Lactic acid bacteria and pseudomonads largely represented the psychrotrophic counts. No clear pattern could be detected regarding the colour scores except that the samples displayed at 0°C tended to retain colour longer. These samples were also judged to be more acceptable, although the determination of acceptability was subjective.     

Addition of tea catechins and vitamin C on sensory evaluation, colour and lipid stability during chilled storage in cooked or raw beef and chicken patties

The effects of addition of tea catechins (TC) and vitamin C (VC) on sensory evaluation, colour and lipid stability in cooked or raw beef and chicken meat patties during refrigerated storage were studied. Fresh beef striploin and chicken breast muscles were minced, following removal of external fat and connective tissue. Following mincing, beef and chicken were assigned to one of the following five treatments: control (meat treated with no antioxidant); TC200, meat plus 200 mg TC/kg muscle; TC400, meat plus 400 mg TC/kg muscle; VC200, meat plus 200 mg VC/kg muscle, VC400, meat plus 400 mg VC/kg muscle. Sodium chloride (1%) was added to all samples. Patties (125 g portions), formed from the above-treated minced meat, were oven cooked, cooled, and packaged in 30% CO₂:70% N₂. Fresh raw beef and chicken patties were packaged in 80% O₂:20% CO₂. All samples were stored for up to 7 days under fluorescent lighting at 4 °C. Sensory parameters (colour, flavour, taste, tenderness and overall acceptability) were evaluated on cooked beef and chicken patties after 1, 3 and 6 days of storage. Surface colour (Hunter L, a and b values), and lipid oxidation (2-thiobarbituric acid reactive substances) were measured on days 1, 3 and 6 of storage for cooked meats and on days 2 and 7 for raw beef and chicken. Tea catechins addition (200 or 400 mg/kg) to minced meat caused (P < 0.05) discolouration in cooked beef and chicken meat patties and significantly reduced (P < 0.001) lipid oxidation in cooked or raw beef patties compared to the control. Beef, either raw or cooked, was more susceptible (P < 0.01) to oxidation compared to chicken. Raw meat stored in high oxygen conditions was more susceptible to lipid oxidation than cooked meat stored in anaerobic conditions. Tea catechins treatments (TC200 and TC400) inhibited (P < 0.05) lipid oxidation in raw beef to a greater extent than vitamin C treatments (VC200 and VC400). These results indicate that tea catechins are potent natural antioxidants and exhibit greater antioxidant efficacy compared to vitamin C.     

Influence of storage period and packaging method on sliced dry cured beef "Cecina de Leon": Effects on microbiological, physicochemical and sensory quality

Quality aspects of sliced dry-cured beef “Cecina de León” preserved in vacuum and gas mixtures (20%/80% CO₂/N₂ and 80%/20% CO₂/N₂) were studied. The evolution of microbiological, physicochemical and sensory parameters were analysed during storage (210 days) at 6 °C. Although microbial counts at 60 days of the gas-packaged samples were lower than the vacuum-packed ones, they were never higher than the spoilage limit (7 log ufc/g). A slight increase (p < 0.05) in pH was observed throughout storage of “Cecina de León” packaged under vacuum and in gas mixtures. However, a decrease (p < 0.05) in a_w was observed during storage of “Cecina de León” packaged under vacuum but a_w did not vary (p > 0.05) during storage in the gas-packaged samples. No changes were observed (p > 0.05) in lightness (L^*), redness (a^*) and yellowness (b^*) in vacuum and gas packaged samples during storage. However, sensorially evaluated colour showed lower values in gas packaged samples during 30 days storage. This difference was decisive in establishing the shelf-life of “Cecina de León” slices preserved in gas mixtures (20%/80% CO₂/N₂ and 80%/20% CO₂/N₂). Therefore, from a microbiological point of view, gas mixtures are more effective in extending the shelf-life of “Cecina de León” slices. It is concluded that vacuum packaging allows longer storage than gas-packaging as it maintains a good visual appearance of “Cecina de León”, the main parameter in consumers’ perception of meat quality.     

Display life of sheep meats retail packaged under atmospheres of various volumes and compositions

Longissmus dorsi loins were removed from Suffolk cross-breed lambs (4–9 months) and hoggets (15–20 months). The effect of package gas composition was investigated by packaging loins with gas mixtures containing 80:20:0, 60:20:20 and 60:40:0/O₂:CO₂:N₂ with a 2:1 headspace to meat volume ratio. The most effective gas mixture for prolonging shelf-life was used to study the effect of different headspace to meat volume ratios. Loins were packaged with a headspace to meat volume ratio of 2:1, 1.5:1 or 1:1. All modified atmosphere (MA) packs were held under refrigerated display conditions (4 °C, 616 lx) for 12 days. Loins were assessed for microbial, oxidative and colour stability and headspace composition every 3 days. The 80:20:0/O₂:CO₂:N₂ gas composition and the 2:1 headspace to meat volume ratio was the most effective packaging combination at maintaining and prolonging the attractive red colour of MA packaged lamb and hogget meat. 80:20:0/O₂:CO₂:N₂ resulted in significantly (p<0.01) higher Hunter a values in lamb. The 2:1 ratio gave higher visual assessment values in lamb and higher Hunter ‘a' values for hogget meat throughout the trial. The 2:1 ratio was the most effective at decreasing Pseudomonas and increasing the numbers of lactic acid bacteria in the total microbial load in both lamb and hogget meat. Lipid oxidation in lamb and hogget meat occurred at a slower comparative rate than discolouration or microbial growth and was not the major determinant of shelf-life. The 2:1 headspace to meat volume ratio was most effective at maintaining the initial gas mix in both lamb and hogget MA packs.     

Effect of modified atmospheres on microbiological, color and sensory properties of refrigerated pork

Pork loin samples were stored (4 °C) in nylon polyethylene plastic bags using different modified atmospheres packaging (MAP): vacuum, 100% CO₂ 99% CO₂ + 1% CO, 100% O₂ or 100% CO followed by vacuum. Throughout the storage period Pseudomonas growth was limited in loins packaged in all MAPs evaluated, except for 100% O₂. Psychrotrophs reached 10⁷ CFU g⁻¹ after 20 days of storage except for the loin samples in 100% O₂ MAP that present count above 10⁸ CFU g⁻¹. The 1% CO/99% CO₂ atmosphere was best for preserving the desirable pork loin color and the L* and a* values remained similar to the fresh meat values using this MAP. Pork loins in 99% CO₂/1% CO MAP obtained the highest consumer acceptance scores after 24 h of storage. These samples and those treated with CO and then vacuum packaged received the greatest acceptance scores even after 20 days of storage.     

The display life of retail-packaged beef steaks after their storage in master packs under various atmospheres

Beef strip loins were divided into four portions. One portion of each loin was vacuum-packaged and then stored at −1·5°C. The other portions were each divided into three steaks, which were retail-packaged. The retail packs were master-packaged under atmospheres of N₂, CO₂, or O₂ + CO₂ (2 : 1, v/v) and then stored at 2°C. Product was assessed after storage times of up to 60 days. At each assessment, a vacuum pack and a master pack of each type, each containing product from the same loin, were withdrawn from storage. The vacuum-packaged product was cut into three steaks, which were retail-packaged. The newly prepared retail packs and those from the master packs were displayed in a retail cabinet, at air temperatures that averaged between 3 and 5·7°C, and were assessed twice daily until the product was judged to be unacceptable. When first assessed, steaks cut from vacuum-packaged product were generally considered desirable, with little metmyoglobin in the surface pigment, although the edges of same steaks were discoloured. Steaks stored under N₂ or CO₂ for 4 days or less were only slightly desirable at best, with metmyoglobin forming relatively large fractions of the surface pigment. However, after storage under N₂ or CO₂ for 6 days or more, metmyoglobin fractions were low, and the steaks bloomed to a desirable red colour. Steaks stored under O₂ + CO₂ had lower metmyoglobin fractions, and were desirable after storage for up to 8 days. However, the fractions of metmyoglobin increased, and steaks were judged to be less desirable after longer storage times. Steaks stored under O₂ + CO₂ for 20 days were unacceptable. After storage, the numbers of bacteria on steaks from vacuum packs and N₂, CO₂, and O₂ + CO₂ atmospheres were, respectively, <10⁴, <10⁶, <10⁵, and <10⁴ CFU/cm². The flora from steaks stored under CO₂ were composed wholly of lactic acid bacteria. Other flora were dominated by lactic acid bacteria, but contained fractions of enterobacteria and/or Brochothrix thermosphacta.

The appearance of product from vacuum packs generally was unacceptable after 72 h of display. The display life of steaks stored under N₂ or CO₂ was shorter than that of the product from vacuum packs when product was stored for 2 days or less, or 46 days or more. After other storage times, the product from vacuum packs or master packs with N₂ or CO₂ atmospheres had a similar display life. The display life of product stored under O₂ + CO₂ was similar to that of product from vacuum packs or CO₂ or O₂ + CO₂ was similar to that of product from vacuum packs after storage times of 8 days or less but was shorter after storage times of 12 or 16 days. The flora on displayed product from vacuum packs or CO₂ or O₂ + CO₂. atmospheres did not attain the maximum number of 10⁷ CFU/cm². and the product did not develop off-odours of microbial origin. However, numbers of 10⁷ CFU/cm² were approached or attained during display of product stored under N₂ for 28 days or longer, and some of that product developed moderate off-odours. It then appears that, under temperature regimes that are common in commercial practice, retail-packaged strip-loin steaks with a display life of 2 days or longer can be obtained from master packs after storage periods of up to about 2, 4, or 7 weeks, respectively, with master-pack atmospheres of O₂ + COPin2 (2 : 1, v/v), N₂, or CO₂.     

Colour stability of beef from different Spanish native cattle breeds stored under vacuum and modified atmosphere

Beef steaks from five Spanish cattle breeds were submitted to three packaging conditions: (a) 15 days under vacuum, (b) 15 days under modified atmosphere (MAP) (60% O₂, 30% CO₂ and 10% N₂), and (c) 10 days under vacuum plus 5 days more under MAP. CIE L^*a^*b^* coordinates, chroma (C^*) and hue (H^*), relative concentration of myoglobin, oxymyoglobin and metmyoglobin at the meat surface and sensory evaluation of colour were determined 0, 5, 10 and 15 days after packaging. Beef under MAP showed higher lightness (L^*) and hue (H^*) and lower redness (a^*) and chroma (C^*) than beef under vacuum. Colour of beef under MAP was not acceptable after 15 days of storage, due to the high metmyoglobin concentration. Yellowness (b^*) was the indicator of differences due to ageing and differences in colour between breeds were related to L^*, a^* and H^* values. Packaging conditions had a greater effect on beef colour than breed, but breed differences might change with packaging atmosphere. Both packaging and breed are major factors in packaged beef quality.     

Effect of dietary supplementation of vitamin E on characteristics of lamb meat packed under modified atmosphere

The effect of dietary vitamin E supplementation on modified-atmosphere packed lamb meat during storage was studied. Thirty-six weaned male Manchego breed lambs were fed diets supplemented with three different vitamin E concentrations (0, 250, 500 and 1000 mg/kg feed) for an average of 37 days, in the 13–26 kg live weight growth range. Slices of m. longissimus dorsi were packaged under modified atmosphere (70% O₂ and 30% CO₂), stored at 2 ± 1 °C in darkness for 14 and 28 days. Meat quality parameters after both storage periods were assessed. Dietary vitamin E supplementation significantly increased -tocopherol concentration in muscle. Initially, lipid oxidation (TBARS), meat colour and bacterial load were similar in all groups. Lipid and colour oxidation of meat increased significantly (P < 0.001) throughout storage. The increase was greater in non-supplemented lambs than in supplemented ones. The bacterial counts after 28 days of storage reached the limit for microbiological shelf life (7 log₁₀cfu/cm²). Dietary vitamin E supplementation increased the shelf life of meat packaged under modified atmosphere to 14 days. TBARS, pigment oxidation and bacterial load were inside the acceptable limit. The meat maintained its quality for 28 days of storage only when lambs were fed with the 1000 mg/kg dietary supplement, though the bacterial load was at the limit of acceptability.     

Quality Changes of Prerigor Filleted Atlantic Salmon (Salmo salar L.) Packaged in Modified Atmosphere Using CO2 Emitter, Traditional MAP, and Vacuum

ABSTRACT:  Pieces of prerigor salmon fillets were packaged in modified atmosphere (60% CO₂ and 40% N₂) and in vacuum. The MA packages had a gas to product volume ratio (g/p ratio) of 3/1 (traditional MAP) and 1/1 (packaged with a CO₂ emitter). All the samples were stored at 1.2 °C for 25 d. The MA packages had lower bacterial growth during storage compared to vacuum packages. The analyses of 16S rRNA at day 22 indicated a similar bacterial diversity, independent of packaging methods, dominated by  Photobacterium phosphoreum . The results therefore suggest that CO₂ inhibited total bacterial count, including,  P. phosphoreum . Negative odors and liquid losses were detected earlier for the vacuum-packaged samples (8 d) compared to the MA samples (15 d) and higher levels were detected at the end of the storage period. The breaking strength (firmness) tended to be lower for the MA packaged samples compared with the vacuum samples after 15 d of storage, whereas the redness ( a * value) and the yellowness ( b * value) were significantly higher for the MA samples. In conclusion, MA packaging preserved the quality better during storage than vacuum packaging. MA packaging with a CO₂ emitter and reduced g/p ratio gave similar or better results compared with traditional MAP, thus CO₂ emitters are well suited for reduction of volume of MA packaged farmed salmon fillet pieces.     

Colour changes and consumer acceptability of bulk packaged pork retail cuts stored under O(2), CO(2) and N(2)

A centralised bulk packaging technique, utilising various gas mixtures, c. 100% CO₂ + oxygen scavenger, c. 80% O₂:20% CO₂ and c. 25% CO₂:50% N₂:25% O₂, was evaluated in terms of consumer acceptability and colour. The inclusion of an oxygen scavenger ensured that pork retail chops bulk packaged in a 100% CO₂ were as acceptable after 0, and 14 days bulk storage and subsequent retail display than chops stored in oxygen-enriched atmospheres. The study also indicated that a saturation level of 10 and higher indicated that the appearance of the pork chop was acceptable to the consumer panel. From the results of this study it is apparent that consumers find pork retail packs, bulk packaged in oxygen depleted atmospheres, as acceptable as pork chops stored in oxygen enriched atmospheres.     

Centralised bulk pre-packaging of fresh pork retail cuts in various gas atmospheres

A centralised bulk pre-packaging technique (laboratory method), utilising various gas mixtures (c. 100% CO₂; c. 75% CO₂:25% N₂; c. 80% O₂: 20% CO₂ and c. 25% CO₂:50% N₂:25% O₂), was evaluated in terms of quality attributes such as microbiology, colour, odour and consumer acceptability. According to the bacterial counts recorded, all four packaging treatments were successful in prolonging the storage life (21 days c. 0°C) of centralised bulk pre-packaged pork retail cuts, while still ensuring a subsequent shelf life of at least 3 days (c. 0°C). The gas mixture comprising c. 25% CO₂:50% N₂:25% O₂ was the most successful treatment in terms of acceptability and colour scores.     

Microbiological and sensory characteristics of beef loin steaks: Role of subcutaneous fat

Beef loin steaks with the subcutaneous fat attached, without subcutaneous fat and the subcutaneous fat that was removed from steaks were packaged and stored at 4°C ± 1°C in polyvinyl chloride (PVC) film for 0–6 days and in high-oxygen barrier (HOB) film for 0–28 days. Aerobic plate counts (APCs) of subcutaneous fat of intact steaks and of subcutaneous fat that was packaged and stored separately in PVC and HOB films were greater (P < 0·05) than those of comparable lean samples. The APCs of lean of steaks without subcutaneous fat that were packaged and stored in HOB film were lower (P < 0·05) than those of the lean of intact steaks. APCs of the lean of these two types of steaks packaged and stored in PVC film did not differ (P > 0·05). Mean surface discoloration and mean overall appearance scores of intact steaks packaged and stored in HOB film were greater than those of steaks packaged and stored without subcutaneous fat; differences were significant (P < 0·05) after 21 and 14 days, respectively. This difference in surface discoloration was attributed to metmyoglobin formation due to possibly higher levels of oxygen remaining in the packages of steaks without subcutaneous fat than in packages containing steaks with the fat attached.     

气调包装协同高功率脉冲微波对河蟹肉储藏期品质影响研究

为研究气调包装协同高功率脉冲微波对河蟹肉的保质效果,设置不同气体类型和组成比例(100％CO2、80％CO2+20％N2、50％CO2+50％N2、20％CO2+80％N2)以及协同高功率脉冲微波(作用频率200 Hz、时间6 min)处理,测定处理后河蟹肉在25℃贮藏期间菌落总数、挥发性盐基氮(total volat...