Impact of Mixtures of Different Fresh‐Cut Fruits on Respiration and Ethylene Production Rates

Packaging and storage of fresh‐cut fruits and vegetables are a challenging task, since fresh produce continue to respire and senesce after harvest and processing accelerates the physiological processes. The response on respiration and ethylene production rates of fresh produce to changes in O₂ and CO₂ concentrations and temperature has been extensively studied for whole fruits but literature is limited on processed and mixed fresh‐cut fruits. This study aimed to investigate the effects of mixing various proportions of fresh‐cut fruits (melon chunks, apple slices, and pineapples cubes) on respiration and ethylene production rates and to develop predictive models for modified atmosphere packaging. The experiment was designed according to a simplex lattice method and respiration and ethylene production rates were measured at 10 °C. Results showed that single component pineapple cubes, apple slices, and melon chunks, in this order, had significant constant coefficients (P = 0.05) and the greatest impact on respiration rate while the interactive binary and tertiary coefficients were insignificant. For ethylene production rates, single component apple slices, melon chunks, and pineapple cubes, and their 3‐component mixtures, in this order, had significant constant coefficients (P = 0.05) while binary coefficients were insignificant. Mathematical models were developed and validated; the cubical model was the best to describe the influence of proportion of fruit on respiration and ethylene production rates, however, considering simplicity the linear part of the model is recommended to quantify respiration and ethylene production rates of mixed fresh‐cut fruits.     

Predictive Modeling for Growth of Non‐ and Cold‐adapted Listeria monocytogenes on Fresh‐cut Cantaloupe at Different Storage Temperatures

The aim of this study was to determine the growth kinetics of Listeria monocytogenes, with and without cold‐adaption, on fresh‐cut cantaloupe under different storage temperatures. Fresh‐cut samples, spot inoculated with a 4‐strain cocktail of L. monocytogenes (～3.2 log CFU/g), were exposed to constant storage temperatures held at 10, 15, 20, 25, or 30 °C. All growth curves of L. monocytogenes were fitted to the Baranyi, modified Gompertz, and Huang models. Regardless of conditions under which cells grew, the time needed to reach 5 log CFU/g decreased with the elevated storage temperature. Experimental results showed that there were no significant differences (P > 0.05) in the maximum growth rate k (log CFU/g h^?1) and lag phase duration λ (h) between the cultures of L. monocytogenes with or without previous cold‐adaption treatments. No distinct difference was observed in the growth pattern among 3 primary models at various storage temperatures. The growth curves of secondary modeling were fitted on an Arrhenius‐type model for describing the relationship between k and temperature of the L. monocytogenes on fresh‐cut cantaloupe from 10 to 30 °C. The root mean square error values of secondary models for non‐ and cold‐adapted cells were 0.018, 0.021, and 0.024, and 0.039, 0.026, and 0.017 at the modified Gompertz, Baranyi, and Huang model, respectively, indicating that these 3 models presented the good statistical fit. This study may provide valuable information to predict the growth of L. monocytogenes on fresh‐cut cantaloupes at different storage conditions.     

Detection of Listeria monocytogenes in Fresh Produce Using Molecular Beacon—Real‐time PCR Technology

ABSTRACT: The capability of an assay to detect Listeria monocytogenes from artificially inoculated fresh‐cut produce such as cantaloupe and mixed salad was demonstrated. An oligonucleotide probe that becomes fluorescent upon hybridization to the target DNA (Molecular Beacon, MB) was used in a real‐time polymerase chain reaction (PCR) assay. As few as 4 to 7 colony‐forming units (CFU) of L. monocytogenes per 25 g of artificially contaminated produce could be detected. A comparison of 2 commercially available kits using MB‐PCR (iQ‐Check, Bio‐Rad Laboratories) and conventional PCR (BAX, Dupont Qualicon) was performed on artificially inoculated produce. The time required to detect L. monocytogenes (from produce to PCR) was considerably shorter for the iQ‐Check protocol (approximately 26 h) compared with the BAX‐PCR (approximately 52 h). The iQ‐Check protocol was also used to confirm the identity of the L. monocytogenes isolates obtained during a microbiological screen of conventional and organic leaf lettuce and alfalfa sprout samples from local supermarkets. The iQ check protocol was successful in differentiating L. monocytogenes isolates from other Listeria spp. such as L. welshimeri, L. innocua, and L. ivanovii. This is the 1st report of the application of the MB probe being used for real‐time detection of L. monocytogenes in whole and fresh‐cut produce.     

Effectiveness of Hydrothermal‐Calcium Chloride Treatment and Chitosan on Quality Retention and Microbial Growth during Storage of Fresh‐Cut Papaya

Rapid degradation of fresh‐cut papaya limits its marketability. Hydrothermal treatments in combination with a calcium dip, applied to whole fruit before slicing, and also the application of chitosan as a coating film, have been found to have very good results in maintaining the quality of fresh‐cut fruits. Based on these considerations, the aim of this study was to evaluate the effect of hydrothermal treatment (HT; 49 °C, 25 min) containing calcium chloride (Ca; 1%, w/v) followed by dipping in chitosan (Chit; 1%, w/v, 3 min) on the physical, chemical, and microbial qualities of papaya slices stored at 5 °C for 10 d. Pulp color, firmness, ascorbic acid, total phenolics, β‐carotene, and lycopene were evaluated every 2 d while the microbial quality (mesophilics, psychrophilics, molds, and yeasts) was evaluated every 5 d. Fruit treated with HT‐Ca and HT‐Ca + Chit showed better color and firmness retention than Control and Chit. Papaya slices treated with HT‐Ca + Chit had higher nutritional content and lower microbial growth at the end of storage. The application of the HT‐Ca + Chit could be used to reduce deterioration processes, maintaining physical, chemical, and microbial qualities and increasing the shelf life of fresh‐cut papaya stored at 5 °C.     

A Comparative Study of Natural Antimicrobial Delivery Systems for Microbial Safety and Quality of Fresh‐Cut Lettuce

Nanoencapsulation can provide a means to effectively deliver antimicrobial compounds and enhance the safety of fresh produce. However, to date there are no studies which directly compares how different nanoencapsulation systems affect fresh produce safety and quality. This study compared the effects on quality and safety of fresh‐cut lettuce treated with free and nanoencapsulated natural antimicrobial, cinnamon bark extract (CBE). A challenge study compared antimicrobial efficacy of 3 different nanoencapsulated CBE systems. The most effective antimicrobial treatment against Listeria monocytogenes was chitosan‐co‐poly‐N‐isopropylacrylamide (chitosan‐PNIPAAM) encapsulated CBE, with a reduction on bacterial load up to 2 log₁₀ CFU/g (P < 0.05) compared to the other encapsulation systems when fresh‐cut lettuce was stored at 5 °C and 10 °C for 15 d. Subsequently, chitosan‐PNIPAAM‐CBE nanoparticles (20, 40, and 80 mg/mL) were compared to a control and free CBE (400, 800, and 1600 μg/mL) for its effects on fresh‐cut lettuce quality over 15 d at 5 °C. By the 10th day, the most effective antimicrobial concentration was 80 mg/mL for chitosan‐PNIPAAM‐CBE, up to 2 log₁₀ CFU/g reduction (P < 0.05), compared with the other treatments. There was no significant difference between control and treated samples up to day 10 for the quality attributes evaluated. Chitosan‐PNIPAAM‐CBE nanoparticles effectively inhibited spoilage microorganisms’ growth and extended fresh‐cut lettuce shelf‐life. Overall, nanoencapsulation provided a method to effectively deliver essential oil and enhanced produce safety, while creating little to no detrimental quality changes on the fresh‐cut lettuce.     

Selected Quality Characteristics of Fresh‐Cut Sweet Potatoes Coated with Chitosan during 17‐Day Refrigerated Storage

ABSTRACT: Selected quality characteristics of fresh‐cut sweet potatoes (FCSP) coated with chitosan were evaluated during 17‐d refrigerated storage. The FCSP cubes were coated with a solution (1%, w/v) of chitosan having 470 or 1110 kDa. Color (L*, a*, b*) values of uncoated and chitosan‐coated FCSP during storage were generally affected by storage time as well as coating treatments (P < 0.05). No significant changes in color lightness (L*) of 470 kDa‐coated FCSP were observed during the 17‐d storage. During days 3 to 17, 470 kDa‐coated FCSP had significantly higher redness (a*) and yellowness (b*) values than did uncoated and 1110 kDa‐coated FCSP. Texture firmness of uncoated and chitosan‐coated FCSP exhibited minimal changes during the 17‐d storage. Although actual weight loss values (%) of uncoated and chitosan‐coated FCSP were not significantly different at day 17, the weight loss difference (%) between day 3 and day 17 for uncoated FCSP (3.02%) was slightly higher compared to those (2.24% to 2.26%) of chitosan‐coated FCSP. The initial total aerobic count was 4.7 log₁₀ CFU/g which then gradually increased to 8.54 and 9.67 log₁₀ CFU/g after 17 d of storage for 470 kDa‐coated and uncoated FCSP, respectively. After day 6, the total aerobic counts of uncoated FCSP were higher than those of 470 kDa‐coated FCSP. The yeast and mold count of chitosan‐coated FCSP was about 2.5 log₁₀ CFU/g at day 17. Overall, consumers could not differentiate between 470 kDa‐coated FCSP at day 17 and uncoated FCSP at day 0.     

Production of Volatiles in Fresh‐Cut Apple: Effect of Applying Alginate Coatings Containing Linoleic Acid or Isoleucine

One of the main quality parameters in apples is aroma, its main precursors are fatty acids (FA) and amino acids (AA). In this study, alginate edible coatings were used as carriers of linoleic acid or isoleucine to serve as precursors for the production of aroma in cut apples. Apple wedges were immersed in a CaCl₂ solution and coated with one of the following formulations: alginate solution (Alg‐Ca), Alg‐Ca‐low‐level linoleic acid (0.61 g/Lt), (LFA), Alg‐Ca‐high‐level linoleic acid (2.44 g/L; HFA), Alg‐Ca‐low‐level isoleucine (0.61 g/L; LAA), and Alg‐Ca‐high‐level isoleucine (2.44 g/L; HAA). Apple wedges were stored at 3 °C and 85% relative humidity for 21 d and key volatiles were studied during storage. Addition of precursors, mainly isoleucine, showed to increase the production of some key volatiles on coated fresh‐cut apples during storage. The concentration of 2‐methyl‐1‐butanol was 4 times higher from day 12 to day 21 in HAA, while 2‐methyl butyl acetate increased from day 12 to day 21 in HAA. After 21 d, HAA‐apples presented a 40‐fold value of 2‐methyl‐butyl acetate, compared to Alg‐Ca cut apples. Values of hexanal increased during cut apple storage when the coating carried linoleic acid, mainly on HFA, from 3 to 12 d. The ability of apples to metabolize AA and FA depends on the concentration of precursors, but also depends on key enzymes, previous apple storage, among others. Further studies should be done to better clarify the behavior of fresh‐cut apples as living tissue to metabolize precursors contained in edible coatings for the production of volatiles.     

Combined Application of Antibrowning,Heat Treatment and Modified‐Atmosphere Packaging to Extend the Shelf Life of Fresh‐Cut Lotus Root

This work aimed to determine the effects of different concentrations of antibrowning treatments (that is, distilled water [DW], 1% ascorbic acid [AA], 0.5% chamomile [CM], and 1% AA + 0.5% CM) and heat‐treatment (55 °C for 45 s) combined with packaging under 4 different modified‐atmosphere gas compositions (that is, air, vacuum, 100% CO₂, 50% CO₂/50% N₂) on the quality and microbiological characteristics of fresh‐cut lotus root. The quality characteristics (that is, color, weight loss, texture, pH, polyphenoloxidase activity, and total phenolic content) of the AA + CM‐dipped sample in 100% CO₂ packaging were maintained significantly better than those of the other samples (P < 0.05). The microbiological counts observed in the DW‐dipped sample during storage were higher than those of the AA, CM, and AA + CM samples, and heat‐treatment retarded the microbiological deterioration of fresh‐cut lotus root. Therefore, the results revealed that dipping in an antibrowning treatment (AA + CM), and 100% CO₂ MAP with heat treatment effectively extend the shelf life of fresh‐cut lotus root to 21 d at 5 °C.     

E: Food Engineering & Physical Properties. Effect of Supercritical Carbon Dioxide Pasteurization on Natural Microbiota,Texture, and Microstructure of Fresh‐Cut Coconut

Abstract: The objective of the present study was the evaluation of the effectiveness of supercritical carbon dioxide (SC‐CO₂) as a nonthermal technology for the pasteurization of fresh‐cut coconut, as an example of ready‐to‐eat and minimally processed food. First, the inactivation kinetics of microbiota on coconut were determined using SC‐CO₂ treatments (pressures at 8 and 12 MPa, temperatures from 24 to 45 °C, treatment times from 5 to 60 min). Second, the effects of SC‐CO₂ on the hardness and microstructure of fresh‐cut coconut processed at the optimal conditions for microbial reduction were investigated. SC‐CO₂ treatment of 15 min at 45 °C and 12 MPa induced 4 log CFU/g reductions of mesophilic microorganisms, lactic acid bacteria, total coliforms, and yeasts and molds. The hardness of coconut was not affected by the treatment but the samples developed an irregular and disorderly microstructure. Results suggested the potential of SC‐CO₂ in preserving fresh‐cut fruits and ready‐to‐eat products. Practical Application: The effectiveness of SC‐CO₂ as a nonthermal technology for the pasteurization of fresh‐cut coconut was studied. The results demonstrated the possibility to apply the treatment as a method to induce the inactivation of the natural microorganisms, preventing the microbial spoilage and, at the same time, preserving the hardness of the product. The available data will give a valuable input to the fresh‐cut fruits industry.     

Prevalence,Antimicrobial Resistance,and Virulence Characteristics of mecA‐Encoding Coagulase‐Negative Staphylococci Isolated from Soft Cheese in Brazil

Coagulase‐negative staphylococci (CoNS), which are generally neglected as foodborne bacteria, are emerging as significant opportunistic pathogens that may be highly resistant to available antimicrobial drugs. In this study, antimicrobial susceptibility patterns, mecA gene occurrence, and virulence‐associated characteristics were evaluated in CoNS isolated from soft cheese in Brazil. A total of 227 bacterial isolates were recovered from 35 cheese samples belonging to 5 batches with 7 different trademarks. The CoNS counts ranged from 10⁶ to 10⁷ CFU/g. High antimicrobial resistance percentages were observed for oxacillin (76.2%), penicillin (78.5%), erythromycin (67.8%), gentamicin (47.2%), clindamycin (35.7%), rifampicin (26.8%), azithromycin (14.7%), tetracycline (14.7%), levofloxacin (14.2%), and sulfamethoxazole‐trimethoprim (11.9%). A low antimicrobial resistance percentage was observed for chloramphenicol (2.3%), and all of the tested bacteria were susceptible to vancomycin and linezolid. In total, a multiple antibiotic resistance (MAR) index of >0.2 was observed for 80.6% of the isolated CoNS. However, the MAR index ranged from 50% to 92.6% when only bacterial cheese isolates belonging to the same trademark were considered. Regarding to the prevalence of CoNS carrying mecA gene, 81.5% of the isolated strains were mecA⁺, and 76.2% of these were phenotypically resistant to oxacillin. Three isolates carried the enterotoxin A gene (sea), 29.5% produced biofilm in a laboratory test, and α‐ or ß‐hemolysis were observed for 3% and 5.2%, respectively. This study highlights the extent of the antimicrobial resistance phenomenon in neglected foodborne microorganisms and the potential public health risks that are related to the consumption of CoNS‐contaminated soft cheese.     

食源性金黄色葡萄球菌肠毒素基因型分布研究

目的 采用PCR法扩增食源性金黄色葡萄球菌中肠毒素基因以了解该菌肠毒素基因携带情况,比较食物中毒和食品监测来源菌株中肠毒素基因检出率差异.方法 合成sea、seb、sec、sed和see五种肠毒素基因特异性引物,用常规PCR方法扩增食物中毒和食品监测来源菌株中各自肠毒素基因,同时采用mini-VIDAS检测食物中毒来源菌株中肠毒素.结果 110株菌株中有30株检出肠毒素基因,检出率为27.3％,肠毒素基因阳性菌株均只检出1种肠毒素基因.其中来自2起食物中毒的14株菌株均检出seb型肠毒素和相关基因,检出率为100％.来源于食品监测样本的96株菌株中有16株检出肠毒素基因,检出率为16.7％,包括sea型4株、seb型2株、sec型4株、sed型6株.结论 在宁波市食品监测中所分离的金黄色葡萄球菌所携带的肠毒素基因主要有sea、seb、sec和sed四型,而seb型肠毒素是引起金黄色葡萄球菌肠毒素所致食物中毒的主要因素.     

The Cost and Benefit of Listeria Monocytogenes Food Safety Measures

The objectives of this study were to evaluate economic techniques used to determine the cost and benefit of Listeria monocyto-genes control and to estimate the economic optimum of L. monocytogenes food safety measures. The level of food safety measures is optimal if marginal benefit and marginal cost equate. Estimates of benefit and cost of L. monocytogenes food safety measures, from available published literature, are derived from different methods of economic analysis (willingness to pay, cost of illness, cost function, and event study methods). The estimated annual benefit and cost of L. monocytogenes food safety measures range from $2.3 billion to $22 billion and from $.01 billion to $2.4 billion, respectively. The estimated marginal benefit exceeds the estimated marginal cost, which implies that more food safety measures are warranted before the optimal level of L. monocytogenes food safety can be reached. However, due to considerable lack of data, the optimal level of L. monocytogenes food safety measures could not be estimated. When better data become available, this study can serve as a template for estimating the optimal level of food safety. The understanding of the economic optimum of food safety level will contribute to designing a control program that is economical and acceptable for US society.     

Culture‐Independent Rapid Detection Methods for Bacterial Pathogens and Toxins in Food Matrices

Rapid detection of bacterial pathogens and toxins in foods is necessary to provide real‐time results to mitigate foodborne illness outbreaks. Cultural enrichment methods, although the most widely used, are time‐consuming and therefore inadequate for rapid pathogen detection from food samples. The development of novel “rapid” detection methods has decreased detection time dramatically. This review presents an overview of detection methods for various foodborne pathogens, including Listeria monocytogenes, Salmonella enterica, and shiga toxin‐producing Escherichia coli, and bacterial toxins in food matrices, with emphasis on those methods which do not require cultural enrichment. Discussed methods include nucleic acid‐, immunological‐, and biosensor‐based techniques. A summary of each type of detection method is given, including referenced methods from the literature. Since these discussed methods do not require cultural enrichment, there is a higher probability of interference from the food matrices. Therefore, the review also discusses the potential interference of food components on detection methods and addresses preprocessing strategies to overcome matrix associated inhibition and to concentrate low quantities of pathogens and toxins in food. Development of rapid and sensitive detection technologies advances and ensures public health safety and security.     

Interactions of Foodborne Pathogens with Free‐living Protozoa: Potential Consequences for Food Safety

Free‐living protozoa (FLP) are ubiquitous in natural ecosystems where they play an important role in the reduction of bacterial biomass and the regeneration of nutrients. However, it has been shown that some species such as Acanthamoeba castellanii, Acanthamoeba polyphaga, and Tetrahymena pyriformis can act as hosts of pathogenic bacteria. There is a growing concern that FLP might contribute to the maintenance of bacterial pathogens in the environment. In addition to survival and/or replication of bacterial pathogens in FLP, resistance to antimicrobial agents and increased virulence of bacteria after passage through protozoa have been reported. This review presents an overview of FLP in food‐associated environments and on foods, and discusses bacterial interactions with FLP, with focus on the foodborne pathogens Campylobacter jejuni, Salmonella spp., Escherichia coli O157:H7, and Listeria monocytogenes. The consequences of these microbial interactions to food safety are evaluated.     

Efficacy of bovicin HC5 and nisin combination against Listeria monocytogenes and Staphylococcus aureus in fresh cheese

Fresh and soft cheeses provide a suitable medium for the growth of many microorganisms and have been frequently associated with foodborne diseases. This study aimed to evaluate the effects of the bacteriocins bovicin HC5 and nisin on Listeria monocytogenes and Staphylococcus aureus in Minas Frescal cheese, a traditional Brazilian fresh product. The cheese was inoculated with 10⁴ CFU g^?1 of both pathogens, and the bacteriocins were added at 600 AU g^?1 of each one. After 9 days of storage at 4 °C, L. monocytogenes Scott A were not detected in 25 g samples. Although the bacteriocins reduced the population of S. aureus ATCC 6538, increasing numbers were detected after 15 days of storage at 4 °C. Staphylococcal enterotoxin C was detected in cheeses added of bacteriocins and stored under abusive temperature of 15 °C. The results demonstrate the potential application of combination of bovicin HC5 and nisin in controlling the pathogens growth assessed in Minas Frescal cheese.     

北京五城区零售鲜切果蔬中重要食源性致病菌污染与耐药性研究

目的 为探究鲜切果蔬中食源性致病菌污染及耐药现状,采集北京五城区零售鲜切果蔬样品进行重要食源性致病菌检测及耐药性研究.方法 本研究采用食品微生物检验国家标准方法,分别检测金黄色葡萄球菌、沙门氏菌、单核细胞增生李斯特氏菌和大肠埃希氏菌,对目标菌分离株进行耐药性测定,并通过荧光定量聚合酶链式反应(PCR)方法筛查致泻大肠埃...     

Quality aspects of fresh‐cut ‘long‐storage tomato’ as affected by package,calcium chloride and storage time

In this research, some quality changes during storage at 4 °C were assessed in fresh‐cut fruits of a ‘long‐storage tomato’ landrace, packaged in biocompostable materials (PLA Ingeo tray/NatureFlex? film) or in conventional plastics (PET tray + polypropylene film). The effects of dipping in CaCl₂ on the shelf‐life extension were also assessed. Plants were cultivated both off‐season (greenhouse) and in‐season (open field). CO₂ and O₂ concentration, fruit weight loss, firmness, colour, microbial load were measured at 0, 4, 7, 12 days of storage. Headspace gas changes and fruit weight loss were minimised in conventional package. BIO package prevented water condensation, led to max 5% weight loss and made fruits less susceptible to spoilage. Dipping in CaCl₂ induced better firmness, especially in biopackage. Off‐season fruits had overall lower quality than in‐season fruits; however, these may contribute to extend the production season, with interesting marketing implications for the agri‐food industry.     

Optimisation of the peracetic acid washing disinfection of fresh‐cut strawberries based on microbial load reduction and bioactive compounds retention

Total microbial count reduction (TMR), total anthocyanins (TAR), and ascorbic acid retention (AAR) after the operation at different PAA concentrations (0–100 mg L^?1), contact times (10–120 s), and temperatures (4–40°C) were used for multiple optimisation using Derringer′s desirability function. Two optimization scenarios (OP 1 and OP 2) were studied. OP 1 was proposed with the goal to maximize TMR with 90% TAR and AAR; and OP 2 maximizing TAR and AAR with TMR of 2 log UFC g^?1. The optimized variable levels obtained were the following: 100 mg L^?1 PAA, 24 °C and 50 s for OP 1 and 20 mg L^?1 PAA, 18 °C and 52 s for OP 2. Additional validation experiments showed agreement between predicted and experimental results. OP 2 conditions are recommended to fresh‐cut strawberries washing disinfection because of an acceptable TMR, higher TAR and AAR, better sensory attributes, and the economic convenience of lesser PAA consumption.