塑料包装袋透气性对保鲜蔬菜颜色的影响

塑料包装具有一定的气体阻隔性,使包装内环境气体组成因蔬菜呼吸作用的进行而达到低氧、高二氧化碳状态,抑制了呼吸作用的进行,减缓蔬菜衰老变质,从而达到保鲜目的;但二氧化碳浓度过高、氧气浓度过低又会造成无氧呼吸并积累有毒物质,因此在保鲜包装中应使用具有一定透气性的包装材料,以保证包装袋内外可发生一定程度的气体交换。本文测试了四种塑料包装材料的气体透过率,利用自制计算机视觉系统跟踪测试了经过其包装后蔬菜在6d内的颜色变化情况,初步分析了塑料包装袋透气性对蔬菜颜色的影响,从护色角度得出了聚酯/聚乙烯较适宜作为蔬菜包装材料的结论。     

Naringinase Immobilization in Packaging Films for Reducing Naringin Concentration in Grapefruit Juice

Naringin, a bitter compound in citrus, may be converted to a nonbitter form by enzymic hydrolysis. Our objective was to determine the feasibility of immobilizing naringinase in a food contact approved packaging film. Naringinase from Penicillium sp. was immobilized in cellulose acetate films with up to 23% efficiency at 7°C. Kinetic studies showed that the free enzyme had an optimum pH=3.5 and the immobilized enzyme pH=4.0. Activation energy decreased upon immobilization (from 14.2 to 11.0 Kcal/mol), thus providing an increased catalytic efficiency for immobilized naringinase. The Michaelis constant for immobilized naringinase (K_m=2.1 mM) was lower than for free enzyme (K_mm=3.6 mM). Keeping films under dry storage for 1 mo at room temperature did not cause decreased enzyme activity. A film area/volume ratio (cm²/mL of 10° Brix grapefruit juice) of 7.2 hydrolyzed 60% of the naringin in 15 days at 7°C.     

塑料食品包装材料的卫生安全性分析

食品包装材料中有毒有害化学物质的迁移是引起食品污染的重要途径之一。本文主要根据近年来发表的有关食品包装材料领域的相关文献为基础,针对塑料食品包装材料中的加工助剂、油墨和树脂自身中的有毒有害物质等迁移物产生的危害进行了分析,为塑料食品包装材料的质量控制提供参考。     

The effects of modified atmosphere gas composition on microbiological criteria, color and oxidation values of minced beef meat

This paper reports the effects of modified atmosphere gas compositions with different concentrations of CO(2)/O(2)/N(2) on color properties (L*, a* and b* values), oxidation stability (TBARS value) and microbiological properties of minced beef meat stored at +4 °C. Sampling was carried out on the 1st, 3rd, 5th, 7th, 9th, 11th and 14th day of storage. The gas mixtures used were as follows: (i) %30O(2) + %70CO(2) (MAP1), (ii) %50O(2) + %50CO(2) (MAP2), (iii) %70O(2) + %30CO(2) (MAP3), (iv) %50O(2) + %30CO(2) + %20N(2) (MAP4), and (v) %30O(2) + %30CO(2) + %40N(2) (MAP5). Control samples (AP) were packaged under atmospheric air. Pseudomonas, lactic acid bacteria, Brochothrix thermosphacta, and Enterobacteriaceae members were monitored. Among these five modified atmosphere gas compositions, the best preservation for minced beef meat was in MAP4 gas combination maintaining acceptable color together with oxidation stability and acceptable microbial loads until the end of storage period of fourteen days.     

Chitosan biobased and intelligent films: Monitoring pH variations

Many factors can influence the shelf-life product, such as pH, water activity, nutrient levels available oxygen, etc. Variations in food pH could occur due to microorganism growth and chemical reactions that may impact flavour, consistency and shelf-life. The objective of this paper was to obtain and characterize the fast pH-colourimetric indicator device, applying a simple manufacturing technique, using food grade and biodegradable materials. The intelligent film was based on natural compounds as chitosan and anthocyanin (pH-colourimetric indicator). Chitosan intelligent films (C-ATH, 2.0 g/100 g) were obtained incorporating anthocyanin (1.0 g/100 g) in matrix films. Initially, a dark violet colour was observed in chitosan films dried. When immersed in different pH buffers, the colour range of the films varied from pink (in acid pH) to bluish-green (in neutral pH) and to violet (in basic pH). The water solubility and water vapour transmission rate of C-ATH were decreased to 60% and 48%, respectively, as compared to control film (CF, without indicator). The mechanical properties such as tensile strength and rigidity were maintained, and the elongation at break was reduced to 47% compared to CF. The advantages of this system were the simple manufacturing process, biodegradability and usage of natural and safe compounds.     

Involvement of Clostridium gasigenes and C. algidicarnis in 'blown pack' spoilage of Brazilian vacuum-packed beef

The objectives of this study were to isolate psychrotrophic clostridia from Brazilian vacuum-packed beef cuts (spoiled or not) and to identify the isolates by using 16S rRNA gene sequencing. Anaerobic psychrotrophic microorganisms were also enumerated and samples were collected to verify the incidence of psychrotrophic clostridia in the abattoir environment. Vacuum-packed beef cuts (n = 8 grossly distended and n = 5 non-spoiled) and environmental samples were obtained from a beef packing plant located in the state of São Paulo, Brazil. Each sample was divided in three subsamples (exudate, beef surface and beef core) that were analyzed for vegetative forms, total spore-forming, and sulfide reducing spore-forming, both activated by alcohol and heat. Biochemical profiles of the isolates were obtained using API20A, with further identification using 16S rRNA gene sequencing. The growth temperature and the pH range were also assessed. Populations of psychrotrophic anaerobic vegetative microorganisms of up to 10¹⁰ CFU/(g, mL or 100 cm²) were found in ‘blown pack’ samples, while in non-spoiled samples populations of 10⁵ CFU/(g, CFU/mL or CFU/100cm²) was found. Overall, a higher population of total spores and sulfide reducing spores activated by heat in spoiled samples was found. Clostridium gasigenes (n = 10) and C. algidicarnis (n = 2) were identified using 16S rRNA gene sequencing. Among the ten C. gasigenes isolates, six were from spoiled samples (C1, C2 and C9), two were isolated from non-spoiled samples (C4 and C5) and two were isolated from the hide and the abattoir corridor/beef cut conveyor belt. C. algidicarnis was recovered from spoiled beef packs (C2). Although some samples (C3, C7, C10 and C14) presented signs of ‘blown pack’ spoilage, Clostridium was not recovered. C. algidicarnis (n = 1) and C. gasigenes (n = 9) isolates have shown a psychrotrophic behavior, grew in the range 6.2-8.2. This is the first report on the isolation of psychrotrophic Clostridium (C. gasigenes and C. algidicarnis) in Brazil. This study shows that psychrotrophic Clostridium may pose a risk for the stability of vacuum-packed beef produced in tropical countries during shelf-life and highlights the need of adopting control measures to reduce their incidence in abattoir and the occurrence of ‘blown pack’ spoilage.     

Lipid Oxidation in Cooked Pork as Affected by Vitamin E, Cooking and Storage Conditions

The individual and combined effects of muscle vitamin E level, cooking conditions (duration, temperature and rate) and packaging on lipid oxidation in refrigerated cooked pork were examined. Oxidative stability following cooking was higher in pork with a higher vitamin E level (p<0.01), cooked at a lower cooking temperature (p<0.01), cooked for a shorter time (p<0.01), cooked at a faster cooking rate (p<0.05) or stored in vacuum packs (p<0.01). Significant two-way and three-way interactions were observed between the effects of muscle vitamin E level, cooking conditions and packaging on lipid oxidation. Adopting more than one of these approaches to minimize lipid oxidation was more effective than adopting a single approach.     

Influence of Injection, Packaging, and Storage Conditions on the Quality of Beef and Bison Steaks

The combined effects of injection, packaging (modified atmosphere packaging [MAP] with 70% O₂/ 30% CO₂ and vacuum packaging [VP]), storage temperature (‐1 °C and +4 °C), and storage time on the color, microbial and oxidative stability of beef and bison longissimus lumborum (LL) steaks were investigated. Beef LL steaks in MAP retained their bright red color longer than bison steaks. Bison steaks developed higher 2‐Thiobarbituric acid reactive substances (TBARS) during storage, and this might have influenced the resulting rapid loss of redness from the bloomed meat. Storage at ‐1 °C in MAP provided greater color stability and a longer storage life for both meat species studied. Injection of salt/phosphate had a beneficial effect on the color stability of steaks during retail display; however, this positive effect was more pronounced for bison steaks compared with those of beef. Steaks stored overnight under MAP before retail display maintained the highest a* values for up to 5 d compared with those stored under vacuum. MAP‐OV steaks generally maintained the highest OMB content for up to 5 d during retail display compared with those stored under vacuum. Nevertheless, OMB levels were significantly (P < 0.05) lower in bison steaks compared with those of beef irrespective of packaging treatments. Injected steaks and those stored at ‐1 °C had significantly (P < 0.05) higher OMB levels compared with non‐injected counterparts and those stored at +4 °C, respectively. MAP is an excellent option for short‐term storage due to its positive effects on meat color, but for longer storage, VP may be necessary. Storing meat under vacuum and then placing it under MAP just before retail display might be another option to increase shelf life.     

国内外纸塑复合食品包装材料安全法规的现状

纸塑复合食品包装材料因其便利性而得到广泛应用,但纸、塑料以及印刷油墨、胶粘剂中的小分子化学残留物通常会迁移到食品中,造成食品污染并威胁到消费者的健康。本文论述了美国FDA、欧盟EC及中国的纸塑复合食品包装材料的相关法律法规,重点对法规中规定的需检测的有害物质进行了论述,介绍了FDA规定的间接食品添加剂、"阀值管理"方式、EC规定的重金属迁移量指标以及中国针对塑料、纸和具体产品的相应规定。     

托盘和真空包装对冷却猪肉中MetMb还原活性的影响

在冷却肉的贮藏过程中,其肌红蛋白(Mb)被氧化为高铁肌红蛋白(MetMb),导致了冷却肉的褐变。研究了托盘包装和真空包装条件下,冷却肉自身的还原系统活性变化规律及其对肉色稳定性的影响。在2周的贮藏期内,真空与托盘包装冷却肉糜肌浆蛋白粗提液的还原活性持续下降;但真空包装组MetMb还原酶粗提液还原活力第1天到第14天活性差异不显著,托盘包装组前后差异显著。真空包装组在贮藏期间MetMb含量持续下降,但托盘包装组MetMb含量则持续上升,说明无氧条件有利于MetMb的还原。托盘包装组TBA在贮藏期间持续上生,但真空包装组TBA变化不明显。结果表明,托盘包装不利于冷却肉自身MetMb还原能力的维持,而真空包装的无氧环境,有利于MetMb的还原和肉色的保持。