Commercial application of high-pressure processing for increasing starter-free fresh cheese shelf-life

Different non-thermal technologies have been proposed to extend the shelf-life of solid food products, high-pressure processing (HPP) being one of the emerging technologies which has been most extensively studied. In this study, one of the first commercial industrial-scale applications of HPP on a starter-free fresh cheese, with the aim of increasing its shelf-life, is presented. The effect of 500 MPa (5 min, 16 °C) on physico-chemical, microbial, colour, microstructure, texture and sensorial characteristics of starter-free fresh cheeses during cold storage of 21 days was studied. The results showed that pressurised cheeses presented a shelf-life of about 19–21 days when stored at 4 °C, whereas control cheese became unsuitable for consumption on day 7–8. On the other hand, cheese treated at 500 MPa was firmer and more yellow than the untreated one. However, these changes, which were detected by instrumental and sensory analysis, did not affect the preference for pressurised cheese. These results may lead to practical applications of HPP in the food industry to produce microbiologically safe cheese with extended shelf-life and sensory quality.     

延长鲜粉条保存期的研究

利用脱氢乙酸(DHA)、二丁基羟基甲酚、对羟基苯甲酸丙酯、山梨酸、乙醇、过氧化氢、鹿蹄草、双乙酸钠、丙酸钙9种防腐剂在常温下对鲜粉条保存期进行了研究,得出了有效延长鲜粉条保存期的复合防腐剂组合是脱氢乙酸0.04%、山梨酸0.04%(均以淀粉添加量计)、乙醇5%。鲜粉条在常温下能存放4d。     

Effect of high pressure on fresh cheese shelf-life

The effect of high pressure (HP; 300 and 400 MPa for 5 min at 6 °C) on physico-chemical, microbial, color, texture and sensorial characteristics of starter-free fresh cheeses stored at 4 and 8 °C was studied. Physico-chemical parameters considered were total solids, fat, total protein, pH, whey loss and water activity. The microbiological quality was studied, on cheeses stored at 4 and 8 °C, by enumerating aerobic mesophilic bacteria, lactococci, psychrotrophic bacteria, Enterobacteriaceae, Escherichia coli, molds and yeasts. Cheeses treated at 300 and 400 MPa, stored at 4 °C, presented a shelf-life of 14 and 21 days, respectively, compared to untreated control cheese, which presented a shelf life of 7 days. On the other hand, HP treatments modified the texture (more firm) and color (more yellow) compared to control cheeses. These changes were detected by instrumental and sensory analysis.     

The shelf-life of dairy products: 2. Raw milk and fresh products

In the second of this series of articles, the specific factors controlling the shelf-life of raw milk, pasteurized milk and cream, cottage cheese and yogurt are considered. The shelf-life of raw milk depends on the quality of the milk ex-farm and on subsequent transport and storage conditions. Shelf-life may be enhanced by deep cooling or thermization. Post heat treatment contamination by Gram negative psychrotrophic bacteria is the major determinant of shelf-life of pasteurized products. In cultured dairy products, yeast and mould contamination is the most usual cause of spoilage.     

Effect of packaging conditions on shelf-life of fresh foal meat

The objective was to determine the shelf life of foal meat (Longissimus dorsi) stored in four different packages: (i) vacuum, (ii) overwrap and (iii) two modified atmospheres (MAP): high O(2) MAP (80% O(2)+20% CO(2)) and low O(2) MAP (30% O(2)+70% CO(2)) stored at 2 °C during 14 days. Shelf life evaluation was based on pH, colour, lipid and protein oxidation, microbial counts and sensory assessment of odour, colour and appearance. Based on aerobic bacterial counts, the shelf life of foal meat samples in overwrap and high O(2) MAP packages would be 10 days at most, almost 14 days in low O(2) MAP and more than 14 days in vacuum packaging. Scores for sensorial evaluation were unacceptable after 10 days of storage in samples in overwrap and MAP packs, but they were still acceptable in vacuum ones. Moreover, for all packaging conditions except vacuum, which remained constant, a decrease in redness (a*) and an increase in carbonyl content and TBAR'S values was observed with storage time. High O(2) levels negatively affected foal meat quality, while anaerobic conditions extended shelf life to 14 days.     

Low-level heat-treatment to extend shelf-life of fresh fish

The application of heat to reduce the microbial load and extend the lag phase was studied on whole fish and with bacterial isolates from fresh fish in mixed culture. Bacterial isolates obtained from fresh horse-mackerel ( Trachurus trachurus ) were heat treated at 60°C for 20s and stored in nutrient broth on ice. the flora were shown to be heat sensitive and the initial numbers were reduced by over 2.0 log₁₀ cycles. Heating at 60°C extended the lag phase but subsequent growth rates were increased, giving a shelf-life extension of a day and a half. There were no significant effects on visual EC grades of whole fish or on the flavour of cooked fillets.     

The influence of different centralised pre-packaging systems on the shelf-life of fresh pork

The influence of different centralised pre-packaging systems (PVC, modified atmosphere packaging (MAP), 25% CO(2) and 75% O(2), vacuum skin packaging (VSP) and the mother bag concept, 100% CO(2)) on the shelf-life (0, 7, 14 and 21 days at 0°C) of fresh pork was determined using microbiological, colour, odour and acceptability characteristics. All the packaging treatments were equally efficient for the first 4 days of retail display. In the extended shelf-life study (7, 14 and 21 days) the mother bag centralised packaging system gave the most promising shelf-life results (21 days) and was also judged superior in terms of odour. Modified atmosphere packaging (14 days) and VSP (7 days) may be considered as other possible options.     

生鲜鲩鱼片货架期预测模型的建立与评价

以生鲜鲩鱼片为对象,研究在15.0、10.0、5.0、-0.7℃贮藏的鲩鱼片在贮藏期间其细菌总数、挥发性盐基氮(TVB-N)和感官评定变化,以探讨鲩鱼片贮藏过程中的品质变化并建立其剩余货架期的预测模型。结果表明,随着贮藏时间的延长,鱼片肌肉的感官指标呈下降趋势,而细菌总数和TVB-N值呈上升趋势。用修正的Gompertz模型描述各温度下细菌总数的增长规律,优于一级化学反应动力学模型和Logistic模型。贮藏温度对细菌最大比生长速率μm和延滞时间λ的影响,采用Arrhennius方程描述,呈现良好线性关系,R2分别为0.956和0.990。在-0.7～15.0℃贮藏时,以细菌总数为标准建立货架期预测模型,所预测货架期分别为1.0、1.9、4.6、17.5d,与实测值的相对误差均小于12.5%,表明该模型可以快速可靠地预测-0.7～15℃贮藏生鲜鲩鱼片的剩余货架期。     

生湿面制品中丙二醇添加量对其货架期水分含量变化规律研究

研究选取了面条、饺子皮等两种在我国较为常见且消费量较大的生湿面制品,并模拟现在市场上生湿面制品的物流和销售环境,进行了生湿面制品中丙二醇添加量对其货架期水分含量变化规律研究。研究采用了0%、0.15%、0.5%、1%、1.5%、2%、2.5%、3%8个丙二醇浓度序列,作为实验的变化因素,检测了饺子皮样品和面条样品在两种不同环境下的水分含量,并研究了其变化规律。研究结果表明,无论是湿面条还是饺子皮样品,未添加丙二醇的空白样品水分含量下降速率最快,随着丙二醇添加量的增加,样品水分含量下降速率减慢,丙二醇添加量在2%以上能够显著延缓样品中的水分下降速率,水分保持作用较为显著,而添加2%丙二醇时水分保持效果最佳。      

Effect of modified atmosphere and active packaging on the shelf-life of fresh bluefin tuna fillets

The aim of this work was to study the influence of the combined use of MAP and antioxidant-based active packaging on the shelf-life of fresh bluefin tuna fillets stored at 3 °C. Active packaging films were produced by embedding α-tocopherol into an unstabilized low density polyethylene (LDPE) matrix at three concentrations (0.1%, 0.5%, 1%). α-Tocopherol release kinetics, in vitro antioxidant activity, oxygen permeability and crystallinity degree were determined to characterize the film. Preliminary shelf-life tests were performed to select critical quality indices, the best gas composition and the best α-tocopherol concentrations in the active film. Then, the effectiveness of the chosen active packaging film in combination with MAP was assessed by monitoring critical quality indices of fresh bluefin tuna fillet during storage at 3 °C for 18 days. Obtained results showed that (i) 100% N₂ atmosphere has a protective effect on haemoglobin and lipid oxidation processes monitored, (ii) active film is able to reduce fat oxidation, (iii) the combined effect of MAP and active packaging can be considered a valuable tool to increase the shelf-life of raw fish products.     

高密度CO2对生鲜调理鸡肉杀菌动力学模型构建

研究不同压力、温度和时间的高密度CO2对生鲜调理鸡肉中细菌的杀菌效果,并采用Weibull、Modified Gompertz、Logistic模型来拟合高密度CO2杀菌的动力学过程,以精确因子(Af),偏差因子(Bf),根平方和(SS),根平方方差(RMSE)和决定系数(R2)作为模型拟合度优劣的评判指标,旨在找出最能拟合高密度CO2处理下微生物失活曲线的数学模型,为高密度CO2杀菌的实际应用提供理论依据.结果表明:随着处理压力、温度、时间的增加,高密度CO2杀菌效果逐渐增强;预测值和实测值的相关决定系数R2表明三种模型都能较好的拟合生鲜调理鸡肉中细菌的失活曲线,其中Logistic模型较拟合度最好,Modified Gompertz其次,Weibull最差.本结果可为高密度CO2新型非热力杀菌技术在肉品上的实际应用提供理论依据.     

Effect of water activity (aw) and irradiation on the shelf-life of fresh noodles

In this work, the effect of water activity (a_w), irradiation and their combination on the preservation of fresh noodles was studied. Microbial growth, pH and sensory characteristics were investigated during 16 days' storage time under 37 °C. The combination of glycerol (3%), propylene glycol (2%), compound phosphate (0.4%) and salt (3%) was proved to be the most effective group which could reduce a_w from 0.979 (control) to 0.900. Under this condition, the shelf-life of fresh noodles could be extended for more than 7 times. Moreover, a synergism between humectants and irradiation treatment was observed in relation to microorganism inhibition and shelf-life extension. For all the irradiated noodles, TPC (total plate count) did never exceed the selected deterioration threshold limit (10⁶ CFU/g) during the entire observation period. When the irradiation dose was 4 kGy or higher, scarcely any bacteria proliferation was observed. Noodle samples irradiated at 4 kGy showed the best pH and sensory stability as the storage time increased.

Industrial relevance

This paper presents an effective and low-cost method to prolong the shelf-life of fresh noodles, which can largely extend the store time of fresh noodles at room temperature, and does not produce any negative changes in sensory attributes. This method will be a new system for food preservation with lots of possible industrial applications. The results of this research also have implications for dumpling skins and other noodle types.     

比萨专用粉制备研究

该文报道以加麦、国优小麦为原料制备比萨专用粉工艺,通过以必胜客比萨、棒约翰比萨为对照的应用效果比较,运用感官评定和质构分析等方法加以分析,结果表明,所制备比萨专用粉既适于作为薄底比萨、又适于作为厚底比萨原料,更具适用性。     

A dissolving CO2 headspace combined with organic acids prolongs the shelf-life of fresh pork

The aim of this paper was to evaluate the effect of a novel CO₂ packaging method in combination with organic acids on the microbial growth in fresh pork meat. Fresh pork fillet was packed with a small amount of 100% CO₂ (initial gas/product ratio 0.2/1.0) and a brine solution containing citric acid (3% w/w, pH 5), acetic acid (1% w/w, pH 5) or a combination of both. Microbial counts and composition in the product were determined. CO₂, citric acid and acetic acid each reduced total growth after four weeks of storage and delayed the onset of microbial growth. Combinations of treatments increased the effects and microbial growth in samples packed with a combination of CO₂ and both acids was negligible even after 35 days. However, the addition of citric acid to the packages led to significant precipitation in the brine. Analysis of the bacterial flora showed that lactic-acid bacteria dominated the flora in samples packed with CO₂ while vacuum-packed samples contained high numbers of Pseudomonas sp. and yeast. As all CO₂ dissolved in the product within hours after packaging, the outer appearance of the package was that of a vacuum-package. As a result, this novel packaging method combined the advantages of modified atmosphere packaging (antimicrobial effect of CO₂) and vacuum packaging (low space requirement).     

Development of shelf-life kinetic model for modified atmosphere packaging of fresh sliced mushrooms

Mushrooms are highly perishable and their shelf-life depends on processing, package properties and environmental conditions during storage and distribution. The aims of this work were to evaluate the effect of temperature and number of film perforations on quality and develop shelf-life kinetic model for a modified atmosphere packaging (MAP) for sliced button mushrooms. Sliced mushrooms were packed in a tray, covered with cellophane film, and stored for 7 days at four levels of temperature (0, 5, 10, and 15 °C) and three levels of perforations at each temperature ranging the number of perforations from 1 (58 perforations per m²) to 6 (349 perforations per m²). Headspace gas composition and quality parameters (weight loss, pH, firmness and colour) were measured throughout the storage period. Increasing the storage temperature required an increase of the number of perforations in order to obtain the optimum MAP conditions. Temperature had a significant effect (p < 0.05) on quality of sliced mushrooms. Firmness was identified as a critical quality parameter; therefore, a kinetic model was developed to describe the influence of temperature on firmness and predict shelf-life of sliced mushrooms. Fresh sliced mushrooms had a shelf-life of 1, 2, 4, and 7.5 days at 15, 10, 5, and 0 °C, respectively, under optimum MAP conditions.     

Understanding critical factors for the quality and shelf-life of MAP fresh meat: a review

Due to increased demands for greater stringency in relation to hygiene and safety issues associated with fresh food products, coupled with ever-increasing demands by retailers for cost-effective extensions to product shelf-lives and the requirement to meet consumer expectations in relation to convenience and quality, the food packaging industry has rapidly developed to meet and satisfy expectations. One of the areas of research that has shown promise, and had success, is modified atmosphere packaging (MAP). The success of MAP-fresh meat depends on many factors including good initial product quality, good hygiene from the source plants, correct packaging material selection, the appropriate gas mix for the product, reliable packaging equipment, and maintenance of controlled temperatures and humidity levels. Advances in plastic materials and equipment have propelled advances in MAP, but other technological and logistical considerations are needed for successful MAP systems for raw chilled meat. Although several parameters critical for the quality of MA packed meat have been studied and each found to be crucial, understanding of the interactions between the parameters is needed. This review was undertaken to present the most comprehensive and current overview of the widely available, scattered information about the various integrated critical factors responsible for the quality and shelf life of MA packed meat with an interest to stimulate further research to optimize different quality parameters.     

China's growing CO2 emissions--a race between increasing consumption and efficiency gains

China's rapidly growing economy and energy consumption are creating serious environmental problems on both local and global scales. Understanding the key drivers behind China's growing energy consumption and the associated CO2 emissions is critical for the development of global climate policies and provides insight into how other emerging economies may develop a low emissions future. Using recently released Chinese economic input-output data and structural decomposition analysis we analyze how changes in China's technology, economic structure, urbanization, and lifestyles affect CO2 emissions. We find that infrastructure construction and urban household consumption, both in turn driven by urbanization and lifestyle changes, have outpaced efficiency improvements in the growth of CO2 emissions. Net trade had a small effect on total emissions due to equal, but significant, growth in emissions from the production of exports and emissions avoided by imports. Technology and efficiency improvements have only partially offset consumption growth, but there remains considerable untapped potential to reduce emissions by improving both production and consumption systems. As China continues to rapidly develop there is an opportunity to further implement and extend policies, such as the Circular Economy, that will help China avoid the high emissions path taken by today's developed countries.     

Effect of varying oxygen concentrations on the shelf-life of fresh pork sausages packaged in modified atmosphere

A total of 105 fresh pork sausages were packaged in atmospheres varying in oxygen concentration, using the following mixtures (%O₂/%CO₂/%N₂): 0/20/80, 0/20/80 + O₂ scavenger, 20/20/60, 40/20/40, 60/20/20, and 80/20/0. In addition, two batches were subjected to vacuum packaging or over-wrap with O₂-permeable film. They were stored for 20 days at 2 ± 1 °C in the dark. Values of pH, CIE L*, a* and b* color parameters, surface metmyoglobin percentage, TBA-reactive substances, psychrotroph aerobe bacterial numbers and sensory discoloration and off-odor were assessed throughout storage. Packaging in the absence of O₂, either under vacuum or in atmosphere with O₂ scavenger, led to extension of shelf-life in terms of both color and odor stability due to low oxidation rates. Increase of O₂ caused a significant enhancement of oxidation, decrease of shelf-life due to discoloration and off-odor development. The highest O₂ concentration gave rise to a significant color improvement, though only for a limited period of 8 days.     

The shelf-life of dairy products: 1. Factors influencing raw milk and fresh products

This review forms the first part of a series of four articles which will consider factors affecting the shelf-life of dairy products. In this report factors influencing the shelf-life of raw milk and fresh products are highlighted. Potential methods of controlling bacterial growth are discussed in detail.