Application of high pressure processing for extending the shelf-life of sliced raw squid

This study was designed to evaluate the effect of high pressure processing (HPP) on the microbiological safety and quality of sliced raw squid during refrigerated storage. The sliced and vacuum-packed raw squid samples were treated at 200, 300, and 400 MPa for 20 min by using a custom-made high pressure processor. The numbers of psychrotrophic bacteria in the sliced raw squids treated at 200, 300, and 400 MPa were reduced by 0.5, 2.5, and >4.7 log CFU/g, respectively. The amounts of trimethylamine (TMA) produced in the sliced raw squids were reduced by 20, 33, and 51% at 200, 300, and 400 MPa, respectively, as compared to the control. The amount of total biogenic amines (BAs) in the control significantly increased up to 1.70 mg/g after 10 days of refrigerated storage, while that in the 400 MPa-treated squid sample gradually increased up to 1.33 mg/g. The autolytic activity values in the control, 200, 300, and 400 MPa-treated squid samples were 4.70, 2.28, 2.18, and 1.55 nkat/g, respectively, after 20 days of refrigerated storage. The HPP effectively retarded the microbial growth, TMA formation, autolytic activity in the sliced raw squids. Therefore, the HPP could be used as an effective processing tool for improving microbiological safety and quality of seafood.     

Effect of thermal and high-pressure processing on the nutritional value and quality attributes of a nectarine purée with industrial origin during the refrigerated storage

The application of hydrostatic high pressure on an industrial line of nectarine (Prunus persica L.) purées was assessed in comparison with the traditional thermal treatment of pasteurization. Changes after thermal processing (85 °C, 5 min) and after high-pressure processing (HPP: 450 or 600 MPa for 5 or 10 min) and during the refrigerated storage (60 d) of an industrially produced nectarine purée were evaluated. Conventional heat pasteurization as well as HPP showed similar microorganisms' inactivation and maintained the microbial stability of purées until the end of the refrigerated storage (60 d). In general, thermally treated purée and HP-treated purée at 600 MPa showed more intense color changes after processing than the other treatment. In addition, thermally treated purée showed more intense color changes during storage than HPP. The highest carotenoids extractability was found in those purées treated at the lowest high-pressure-treatment intensity and holding time (450 MPa/5 min), but at the end of the storage (day 60), no differences in individual or total carotenoid levels were found between the purées. HPP at 600 MPa/10 min showed the highest polyphenols content after the treatment and during the storage. At day 0, significantly higher values were found of total antioxidant activity in purée HP-treated at 450 MPa/10 min than in untreated purée; while at the end of the storage, HP-treated purée at 600 MPa/10 min had the highest antioxidant activity. Hydrostatic high-pressure application in the industrial line of nectarine purée presented some advantages compared to the thermal treatment; however, some of the changes found were lessen during the storage period. In addition, more studies need to be carried out for HP-treatment intensity optimization.     

Effect of high pressure processing on the quality of squid (Todarodes pacificus) during refrigerated storage

The influence of high pressure processing (HPP) on the inhibition of trimethylamine-N-oxide demethylase (TMAOase) activity and off-odour production in squid treated at 300 MPa for 20 min was investigated during 12 days of refrigerated storage. TMAOase activity of raw squid (21.5 nkat/g) was significantly decreased to approximately 5 nkat/g after 20 min of HPP. The production of dimethylamine (DMA) in HPP-treated squid for 20 min was significantly decreased to 0.31 μmol/g after 12 days of storage. The decrease in DMA was correlated with the decrease in TMAOase activity. At 300 MPa, the number of total aerobic bacteria in squid was reduced by 1.26 log units after 20 min of HPP. The HPP-treated samples effectively reduced the amount of trimethylamine (TMA). Therefore, the HPP could be used as a promising alternative technology to retard the quality deterioration of squid by inhibiting TMAOase activity and microbial growth.     

Effects of ultrafiltration combined with high-pressure processing,ultrasound and heat treatments on the quality of a blueberry–grape–pineapple–cantaloupe juice blend

This study investigated the effect of ultrafiltration (UF) combined with high-pressure processing (HPP) at 550 MPa, 25 °C for 5 min, ultrasound (US) at 520 W, 40 °C for 10 min and heat treatment (HT) at 90 °C for 3 min on the microbial, physicochemical and sensory properties of a blueberry–grape–pineapple–cantaloupe juice blend during 104 days of storage at 4 °C. After UF, the shelf life of the HPP- and US-treated clear juice blends were 104 and 72 days during the storage at 4 °C respectively. HPP, US and HT treatment minimally affected the anthocyanin and total phenol contents, while HPP better maintained the ascorbic acid levels and sensory properties in the clear juice blend during the storage. Therefore, HPP combined with UF was identified as a prospective processing technique in the fruit juice industry.     

High-pressure processing decelerates lipolysis and formation of volatile compounds in ovine milk blue-veined cheese

Enzyme-rich cheeses are prone to over-ripening during refrigerated storage. Blue-veined cheeses fall within this category because of the profuse growth of Penicillium roqueforti in their interior, which results in the production of highly active proteinases, lipases, and other enzymes responsible for the formation of a great number of flavor compounds. To control the excessive formation of free fatty acids (FFA) and volatile compounds, blue-veined cheeses were submitted to high-pressure processing (HPP) at 400 or 600 MPa on d 21, 42, or 63 after manufacture. Cheeses were ripened for 30 d at 10°C and 93% relative humidity, followed by 60 d at 5°C, and then held at 3°C until d 360. High-pressure processing influenced the concentrations of acetic acid and short-chain, medium-chain, and long-chain FFA. The effect was dependent on treatment conditions (pressure level and cheese age at the time of treatment). The lowest concentrations of acetic acid and FFA were recorded for cheeses treated at 600 MPa on d 21; these cheeses showed the lowest esterase activity values. Acetic acid and all FFA groups increased during ripening and refrigerated storage. The 102 volatile compounds detected in cheese belonged to 10 chemical groups (5 aldehydes, 12 ketones, 17 alcohols, 12 acids, 35 esters, 9 hydrocarbons, 5 aromatic compounds, 3 nitrogen compounds, 3 terpenes, and 1 sulfur compound). High-pressure processing influenced the levels of 97 individual compounds, whereas 68 individual compounds varied during refrigerated storage. Total concentrations of all groups of volatile compounds were influenced by HPP, but only ketones, acids, esters, and sulfur compounds varied during refrigerated storage. The lowest total concentrations for most groups of volatile compounds were recorded for the cheese pressurized at 600 MPa on d 21. A principal component analysis combining total concentrations of groups of FFA and volatile compounds discriminated cheeses by age and by the pressure level applied to HPP cheeses.     

Quality of Banana Puree During Storage: a Comparison of High Pressure Processing and Thermal Pasteurization Methods

The quality features of banana puree after high pressure processing (HPP) at 500 MPa for 10 min and thermal pasteurization (TP) at 90 °C for 2 min during 30 days of refrigerated storage were compared in this study. Initial counts in banana puree of greater than 3.80 log colony-forming units (CFU)/g of total aerobic bacteria (TAB) and 3.10 log CFU/g of molds and yeasts (M&Y) were reduced by HPP and TP. TAB were approximately 1.0 CFU/g, and M&Y were less than 0.3 log CFU/g in HPP- and TP-processed puree during storage. HPP and TP did not change pH, titratable acidity (TA), total soluble solids (TSS), lightness (L), and yellowness (b), total phenolic content (TPC), and antioxidant capacity (AC), but HPP raised redness (a) and TP reduced a and ascorbic acid (AA). During storage, L, a, and b in HPP- and TP-processed purees did not change but HPP-processed puree increased pH and decreased TA. After storage, the percentage of TPC and AA was 75.85 and 55.09 % in the HPP group and 96.30 and 68.09 % in the TP group, indicating a significant loss of TPC and a greater loss of AA in HPP-processed puree. The loss of AC agreed with the loss of AA and TPC. HPP preserved particle size distribution and viscosity of purees, whereas TP increased the number of smaller particles and viscosity after processing and in storage. Twenty-six volatiles (18 esters) and 22 volatiles (15 esters) were detected in HPP- and TP-processed purees, and the ester fraction was 69.79 and 52.36 %, respectively. HPP was found to be an effective alternative pasteurization method for preserving the quality of fresh banana puree.     

Effects of Thermal and High-pressure Treatments on the Microbiological,Nutritional and Sensory Quality of a Multi-fruit Smoothie

Fruit juices have become an important product for the healthy food world. In the last 5 years, the sales of industrial juices treated by non-thermal preservation technologies such as high-pressure processing (HPP) have strongly increased. In the present study, the effect of the application of two stabilization treatments, mild heating (MH; 80 °C for 7 min) and high-pressure processing (HPP; 350 MPa for 5 min), on multi-fruit smoothies was compared on a wide range of quality parameters immediately after treatment and during a refrigerated storage of 21 days. From the physico-chemical and instrumental colour point of view, immediately after treatment, HPP smoothies were more similar to the fresh product than those treated by MH. During storage, the colour of MH smoothies was more stable although HPP ones showed lower browning index and viscosity more similar to the untreated product. Additionally, HPP provided smoothies with better sensory properties and higher nutritional quality than MH. In general, HPP smoothies were more similar to the untreated product. However, HPP smoothies kept a residual enzyme activity which is likely to limit the shelf life of this multi-fruit smoothie.     

Use of mild-heat treatment following high-pressure processing to prevent recovery of pressure-injured Listeria monocytogenes in milk

This study examined the inactivation of Listeria monocytogenes in milk by high-pressure processing (HPP) and bacterial recovery during storage after HPP. We developed a technique to inhibit the bacterial recovery during storage after HPP (550 MPa for 5 min) using a mild-heat treatment (30-50 degrees C). Various mild-heat treatments were conducted following HPP to investigate the condition on which the bacterial recovery was prevented. Immediately after HPP of 550 MPa at 25 degrees C for 5 min, no L. monocytogenes cells were detected in milk regardless of the inoculum levels (3, 5, and 7 log(10)CFU/ml). However, the number of L. monocytogenes cells increased by >8 log(10)CFU/ml regardless of the inoculum levels after 28 days of storage at 4 degrees C. Significant recovery was observed during storage at 25 degrees C; the bacterial number increased by >8 log(10)CFU/ml after 3 days of storage in the case of an initial inoculum level of 7 and 5 log(10)CFU/ml. Even in the case of an initial inoculum level of 3 log(10)CFU/ml, the bacterial number reached the level of 8 log(10)CFU/ml after 7 days of storage. No bacterial recovery was observed with storage at 37 degrees C for 28 days. Milk samples were treated by various mild-heat treatments (30-50 degrees C for 5-240 min) following HPP of 550 MPa at 25 degrees C for 5 min, and then stored at 25 degrees C for 70 days. The mild-heat treatment (e.g., 37 degrees C for 240 min or 50 degrees C for 10 min) inhibited the recovery of L. monocytogenes in milk after HPP. No recovery of L. monocytogenes in milk was observed during 70-day storage at 25 degrees C in samples that received mild-heat treatments such as mentioned above following HPP (550 MPa for 5 min). Moreover, the mild-heat treatment conditions (temperature and holding time) required to inhibit the recovery of L. monocytogenes in milk was modelled using a logistic regression procedure. The predicted interface of recovery/no recovery can be used to calculate the mild-heat treatment condition to control bacterial recovery during storage at 25 degrees C after HPP (550 MPa for 5 min). The results in this study would contribute to enhance the safety of high-pressure-processed milk.     

Effect of high pressure treatment on microbial populations of sliced vacuum-packed cooked ham

In this study, culture-dependent and culture-independent approaches were used to reveal the microbial diversity and dynamic changes occurring in sliced vacuum-packed cooked ham after high pressure processing (HPP, 400MPa or 600MPa for 10min at 22°C) during refrigerated storage over 90days. Direct extraction of genome DNA and total RNA from meat samples, followed by PCR-denaturing gradient gel electrophoresis (DGGE) and RT-PCR-DGGE on 16S rDNA V3 region, was performed to define the structure of the bacterial populations and active species in pressurized cooked ham. Results showed that HPP affected differently the various species detected. The predominant spoilage organisms of cooked ham, such as Lactobacillus sakei and Lactobacillus curvatus, were found to be very sensitive to pressure as they were unable to be detected in HPP samples at any time during refrigerated storage. Weissella viridescens and Leuconostoc mesenteroides survived HPP at 600MPa for 10min at 22°C and were responsible for the final spoilage. An RNA-based DGGE approach clearly has potential for the analysis of active species that have survived in pressurized cooked ham. High pressure processing at 400 or 600MPa for 10min at room temperature (22°C) has a powerful inhibitory effect on the major spoilage bacteria of sliced vacuum-packed cooked ham. High pressure treatment may lead to reduced microbial diversity and improve the products' safety.     

超高压处理抑制低温烟熏火腿中的优势腐败菌

研究尝试应用微生物菌体总RNA提取代替DNA提取,进而通过反转录-PCR( RT-PCR),结合变性梯度凝胶电泳(denaturing gradient gel electrophoresis,DGGE)技术,以期揭示超高压处理后低温烟熏火腿中腐败微生物的存活情况,探索RNA-DGGE手段判定超高压处理后微生物存活状态的可行性.分别以400 MPa和600 MPa的压力在室温(22℃)条件下,对包装后的烟熏火腿进行10 min超高压处理,未经高压处理样品作对照,于4℃冷藏条件下,贮藏1、15、30、60、90 d,直接提取样品中微生物的总RNA,对其进行RT-PCR和DGGE指纹图谱分析.DGGE指纹图谱显示,超高压处理对烟熏火腿中的优势腐败菌具有较强的抑制作用,且随压力的升高抑菌效应增强;超高压处理后烟熏火腿微生物种群结构变得单一,Weissella viridescens和Leuconostoc mesenteroides是超高压处理后烟熏火腿中的优势腐败菌.基于菌体总RNA提取的DGGE手段能够有效检测超高压处理后微生物的存活状况,揭示超高压对低温烟熏火腿中优势腐败微生物的抑菌效果.     

Effects of high-pressure processing on the safety, quality, and shelf life of ready-to-eat meats

Ready-to-eat (RTE) meats (low-fat pastrami, Strassburg beef, export sausage, and Cajun beef) were pressure treated at 600 MPa, 20 degrees C, for 180 s to evaluate the feasibility of using high-pressure processing (HPP) for the safe shelf-life extension of these products. After processing, samples were stored at 4 degrees C for 98 days during which time microbiological enumeration and enrichments were performed. Additionally, sensory analyses were undertaken to determine consumer acceptability and purchase intent over the duration of storage. Counts of aerobic and anaerobic mesophiles, lactic acid bacteria, Listeria spp., staphylococci, Brochothrix thermosphacta, coliforms, and yeasts and molds revealed that there were undetectable or low levels for all types of microorganisms throughout storage. Comparison of consumer hedonic ratings for unprocessed and processed meats revealed no difference in consumer acceptability, and no deterioration in the sensory quality was evident for any of the products tested during the study. Additionally, inoculated pack studies were conducted to determine if HPP could be used as a postlethality treatment to reduce or eliminate Listeria monocytogenes and thus assess the potential use of HPP in a hazard analysis critical control point plan for production of RTE meats. Inoculated samples (initial level of 10(4) CFU/g) were pressure treated (600 MPa, 20 degrees C, for 180 s) and stored at 4 degrees C, and survival of L. monocytogenes was monitored for 91 days. L. monocytogenes was not detected by plating methods until day 91, but selective enrichments showed sporadic recovery in three of the four products examined. The results show that HPP at 600 MPa, 20 degrees C, for 180 s can extend the refrigerated shelf life of RTE meats and reduce L. monocytogenes numbers by more than 4 log CFU/g in inoculated product.     

Structure and shelf stability of milk protein gels created by pressure-assisted enzymatic gelation

In this work, pressure-assisted enzymatic gelation was applied to milk proteins, with the goal of enhancing the structure and stability of pressure-created milk protein gels. High-pressure processing (HPP) at 600 MPa, 3 min, and 5°C was applied to milk protein concentrate (MPC) samples of 12.5% protein concentration, both in the absence and in the presence of calf chymosin [up to 60 IMCU (international milk-clotting units)/kg of milk] or camel chymosin (up to 45 IMCU/kg of milk). Gel hardness, water-holding capacity, and degree of proteolysis were used to assess network strength and shelf stability. The processing trials and all measurements were conducted in triplicate. Statistical analyses of the data were performed by ANOVA, at a 95% confidence level. After HPP treatment, we observed significant structural changes for all samples. Pressurization of MPC, with or without chymosin addition, led to extensive protein aggregation and network formation. The strength of HPP-created milk protein gels without chymosin addition, as measured by the elastic modulus (G′), had a value of 2,242 Pa. The value of G′ increased with increasing chymosin concentration, reaching as high as 4,800 Pa for samples with 45 IMCU/kg of camel chymosin. During 4 wk of refrigerated storage, the HPP and chymosin MPC gels maintained higher gel hardness and better structural stability compared with HPP only (no chymosin) MPC gels. The water-holding capacity of the gels without chymosin remained at 100% during 28 d of refrigerated storage. The HPP and chymosin MPC gels had a lower water-holding capacity (91–94%) than the HPP-only counterparts, but their water-holding capacity did not decrease during storage. Overall, these findings demonstrate that controlled, fast structural modification of high-concentration protein systems can be obtained by HPP-assisted enzymatic treatment, and the created gels have a strong, stable network. This study provides insights into the possibility of using HPP for the development of milk-protein-based products with novel structures and textures and long refrigerated shelf life, along with the built-in safety imparted by the HPP treatment.     

Effects of high-pressure processing on the volatile compounds of sliced cooked pork shoulder during refrigerated storage

The effect of high-pressure processing (pressure levels of 400, 500 and 600 MPa, and exposure times of 5 and 10 min) on the volatile profile of vacuum-packaged sliced cooked pork shoulder held for 28 days at 4 °C was assessed. The volatile fraction of pressurized samples scarcely changed immediately after treatment and remained stable for 14 days, regardless the pressure and time of exposure. After 21 days of storage, significant differences were observed in the profile of volatile compounds in pressurized samples as compared with control samples, these differences being treatment dependent. At the end of the storage period, control and 400 MPa samples showed higher levels of acetic and fatty acids, ethanol and ethyl esters, whereas 500 and 600 MPa samples contained higher levels of ethanal, branched-chain aldehydes, diacetyl, acetoin, and 2,3-butanediol among other compounds. These results suggest that the high-pressure treatment had a discriminant effect on the microbiota of cooked pork shoulder, which led to the accumulation of different volatile compounds during the refrigerated storage of control and pressurized samples.     

Effect of moderate pressure treatments on microstructure, texture, and sensory properties of stirred-curd cheddar shreds

A moderate high-pressure processing (HPP) treatment is proposed to accelerate the shredability of Cheddar cheese. High pressure processing (345 and 483 MPa for 3 and 7 min) applied to unripened (1 d old) stirred-curd Cheddar cheese yielded microstructure changes that differed with pressure level and processing time. Untreated and pressure-treated cheese shredded at d 27 and 1, respectively, shared similar visual and tactile sensory properties. The moderate (345 MPa) and the higher (483 MPa) pressure treatments reduced the presence of crumbles, increased mean shred particle length, improved length uniformity, and enhanced surface smoothness in shreds produced from unripened cheese. High-pressure processing treatments did not affect the mechanical properties of ripened cheese or the proteolytic susceptibility of milk protein. It was concluded that a moderate HPP treatment could allow processors to shred Cheddar cheese immediately after block cooling, reducing refrigerated storage costs, with expected savings of over 15 US dollars/1000 lb cheese, and allowing fewer steps in the handling of cheese blocks produced for shredding.     

不同加工方式对熟制克氏原螯虾冷藏期间品质的影响

本文研究了不同加工方式对熟制克氏原螯虾冷藏期间品质的影响，对克氏原螯虾分别进行熟制后杀菌（100 ℃、5 min后121 ℃、5 min，0.18 MPa）和同时熟化杀菌（110 ℃、10 min，0.13 MPa）处理，以熟制后无杀菌（100 ℃、5 min）样品为对照组。随后将三组样品分别置于4 ℃冰箱中冷藏，期间测定各组样品的pH、质构分析（texture profile analysis，TPA）、总挥发性盐基氮（total volatile base nitrogen，TVB-N）、硫代巴比妥酸反应物（thiobarbituric acid reactive substances，TBARS）、离心损失率、肌原纤维蛋白特性、菌落总数等指标变化，并结合微观结构观察，来评价不同加工方式处理后熟制克氏原螯虾冷藏期间的品质变化。结果得出，先熟制后杀菌的加工方式下克氏原螯虾的肌肉发生严重断裂，硬度和弹性显著低于其他组（P<0.05）。熟制杀菌同时完成的加工方式下虾肉硬度和弹性值显著优于其他组（P<0.05）。其中，熟制无杀菌工艺下的克氏原螯虾冷藏货架期为7 d，显著低于其他组（P<0.05）。而熟制杀菌一步到位加工方式能使熟制克氏原螯虾保持较好品质，使其冷藏货架期延长28 d。     

Effect of hydrostatic high-pressure processing on the chemical,functional, and rheological properties of starter-free Queso Fresco

Queso Fresco (QF), a popular high-moisture, high-pH Hispanic-style cheese sold in the United States, underwent high-pressure processing (HPP), which has the potential to improve the safety of cheese, to determine the effects of this process on quality traits of the cheese. Starter-free, rennet-set QF (manufactured from pasteurized, homogenized milk, milled before hooping, and not pressed) was cut into 4.5- × 4.5- × 15-cm blocks and double vacuum packaged. Phase 1 of the research examined the effects of hydrostatic HPP on the quality traits of fresh QF that had been warmed to a core temperature of 20 or 40°C; processed at 200, 400, or 600 MPa for 5, 10, or 20 min; and stored at 4°C for 6 to 8 d. Phase 2 examined the long-term effects of HPP on quality traits when QF was treated at 600 MPa for 3 or 10 min, and stored at 4 or 10°C for up to 12 wk. Warming the QF to 40°C before packaging and exposure to high pressure resulted in loss of free whey from the cheese into the package, lower moisture content, and harder cheese. In phase 2, the control QF, regardless of aging temperature, was significantly softer than HPP cheeses over the 12 wk of storage. Hardness, fracture stress, and fracture rigidity increased with length of exposure time and storage temperature, with minor changes in the other properties. Queso Fresco remained a bright white, weak-bodied cheese that crumbled and did not melt upon heating. Although high pressures or long processing times may be required for the elimination of pathogens, cheese producers must be aware that HPP altered the rheological properties of QF and caused wheying-off in cheeses not pressed before packaging.     

Impact of Thermal and Pressure-Based Technologies on Carotenoid Retention and Quality Attributes in Tomato Juice

The aim of this study was to investigate the impact of thermal processing (TP) (90 °C, 90 s), high-pressure processing (HPP) (600 MPa, 46 °C, 5 min), and high-pressure homogenization (HPH) (246 MPa, 99 °C, <1 s) on product quality parameters, specifically carotenoid content, and physicochemical attributes of particle size, color, viscosity, total soluble solids, and pH in tomato juice. Unprocessed tomato juice was used as control. The four major species of carotenoids (lycopene, β-carotene, phytoene, and phytofluene) in tomato juice were analyzed by HPLC. The content of total lycopene, all-trans-lycopene, cis-lycopene isomers,  phytoene, and phytofluene, in TP-, HPP-, and HPH-treated tomato juice did not significantly differ from that in unprocessed (control) juice. Significant reduction in β-carotene content was observed after TP treatment but not after HPP and HPH treatments. HPH significantly reduced tomato juice particle volume mean diameter from ～330 μm in control, HPP-, and TP-treated tomato juices to ～17 μm. A concomitant increase in apparent viscosity was observed in HPH-treated juice versus control. HPH-treated juice had increased redness (a*) and yellowness (b*) than that in control and HPP-treated tomato juices. These results indicate that high-pressure-based technologies (HPP and HPH) can preserve carotenoids as well as improve physicochemical properties.     

Volatile compounds in low-acid fermented sausage “espetec” and sliced cooked pork shoulder subjected to high pressure processing. A comparison of dynamic headspace and solid-phase microextraction

Two extraction techniques, dynamic headspace extraction (DHE) and solid-phase microextraction (SPME), were compared to assess the effect of high-pressure treatment (400 MPa, 10 min, 12 °C) on the volatile compounds of low-acid fermented sausage “espetec” and sliced cooked pork shoulder stored at 4 °C. DHE was more efficient at extracting low-boiling compounds such as ethanal, 2,3-butanedione and alcohols, while SPME extracted more efficiently a higher number of chemical families, especially fatty acids. The effect of pressurisation on the volatile fraction of “espetec” was better categorized by DHE, whereas SPME was more appropriate for cooked pork shoulder. The volatile fraction of “espetec” changed slightly after pressurisation, mainly showing a decrease in the levels of lipid-derived compounds, like linear alkanes, aldehydes, or 1-alcohols in pressurised samples. The volatile profile of cooked pork shoulder underwent substantial changes during refrigerated storage, mainly due to microbial metabolism, most of these changes being limited by HPP.     

超高压处理对LDPE、PA6食品包装材料包装性能可逆性的研究

本文在不同条件下对LDPE、PA6进行超高压(HPP)处理,测定不同压力、保压时间及存储时间对材料拉伸强度、热封性能、阻隔性能、热性能以及包装性能可逆性的影响。实验表明:处理压力、保压时间及存储时间对2种材料的热封性均未产生显著影响,但LDPE、PA6试样的拉伸强度随压力升高明显增大;当压力300 MPa时LDPE的透湿性逐渐上升,当压力300 MPa时LDPE的透湿性又逐渐降低,对PA6来说,当压力100 MPa时,材料的透湿性明显下降由10.13 g/(m2·d)(0.1 MPa/10 min)降低到6.79 g/(m2·d)(200 MPa/10 min),但随压力增大透湿性下降的幅度并不明显;两种材料的熔融焓在HPP下均有升高,当存储24 h后,两种材料的ΔH又有所恢复;与0.1 MPa下相比,经过HPP后对异丙基甲苯在LDPE(500 MPa)和PA6(100 MPa)薄膜中的渗透率分别降低约50%和58%,但随着存储时间的延长又逐渐恢复至常压下的渗透率。研究发现实验中采用的LDPE和PA6 2种薄膜的包装性能均有可逆现象出现。