Microbiological Status and Quality Traits of Ready-to-Eat Minimally Processed Vegetables Sold in Córdoba, Argentina

Background: The changes and the availability of processed foods have increased the demand for ready-to-eat foods, such as Minimally Processed Vegetables (MPVs). The purpose of this work was to evaluate the microbiological status and quality traits of the MPVs obtained from retail outlets of Córdoba, Argentina. Methods: Totally, 60 MPVs of 12 brands (30 single-ingredient salads and 30 mixed salad trays) were randomly sampled from different retail outlets of Córdoba, Argentina. The samples were analyzed according to international standards for Total Coliforms (TC), Fecal Coliforms (FC), Escherichia coli, Salmonella spp., Staphylococcus aureus, and Yeast and Molds (YM). The quality traits (respect to physical and sensory properties) of the MPVs were evaluated. Statistical analyses were performed with InfoStat. Results: All 60 MPV samples were positive for TC, ranging from 1.32 to 3.38 log Most Probable Number (MPN)/g. FC counts ranged from 0.30 to 1.95 log MPN/g. Out of 60 samples, 15 (25%) were positive for E. coli. Three brands of mixed trays were positive for S. aureus. Regarding sensory characteristics, the parameters such as freshness, turgid, normal color, decay, and dehydration were compliance in 42 out of 60 (70%) samples. Conclusion: Some MPVs sampled from Córdoba, Argentina showed low microbiological quality and imperfect quality traits.

Prevalence and Characterization of Food-Borne Vibrio parahaemolyticus From African Salad in Southern Nigeria

The demand for minimally processed vegetables (African salad) has increased partly due to its inclusion in ready-to-eat foods. Nevertheless, the associated risk of the presence of emergent foodborne pathogens, such as Vibrio parahaemolyticus might be underestimated. The present study was designed to isolate and characterize foodborne V. parahaemolyticus from minimally processed vegetables using culture-based methods and molecular approach. A total of 300 samples were examined from retail outlets between November 2018 and August 2019 from Southern Nigeria. The prevalence of vibrios from the overall samples based on the colonial proliferation of yellow, blue-green and/or green colonies on thiosulfate citrate bile salts sucrose agar was 74/300 (24.6%). An average of two green or blue-green colonies from respective plates was screened for V. parahaemolyticus using analytical profile index (API) 20 NE. Polymerase chain reaction further confirmed the identity of positive V. parahaemolyticus. The counts of V. parahaemolyticus ranged from 1.5 to 1,000 MPN/g. A total of 63 recovered V. parahaemolyticus were characterized further. The resistance profile of the isolates include ampicillin 57/63 (90.5%), cefotaxime 41/63 (65.1%), ceftazidime 30/63 (47.6%), amikacin 32/63 (50.8%), kanamycin 15/63 (23.8%), and oxytetracycline 16/63 (25.4%). The multiple antibiotic index ranged from 0–0.81. The formation of biofilm by the isolates revealed the following: strong formation 15/63 (23.8%), moderate formation 31/63 (49.2%), weak formation 12/63 (19.1%), and no formation 5/63 (7.9%). A total of 63/63 (100%), 9/63 (14.3%), and 20/63 (31.8%) of the isolates harbored the tox R gene, TDH-related hemolysin (trh) and thermostable direct hemolysin (tdh) determinants respectively. The isolates with O2 serogroup were most prevalent via PCR. Isolates that were resistant to tetracycline, kanamycin, and chloramphenicol possessed resistant genes. The presence of multidrug-resistant vibrios in the minimally processed vegetables constitutes a public health risk and thus necessitates continued surveillance.

Comparison of peracetic acid and chlorine effectiveness during fresh-cut vegetables processing at industrial scale

This study was conducted to compare the efficacy of two sanitizing agents (chlorine and PAA) in reducing (both spoilage and pathogenic) microorganisms and in reducing disinfection by-products ( DBPs) in the washing stage of three types of minimally processed vegetables: Iceberg lettuce, carrots and baby leaves. These fresh-cut products are consumed uncooked and, hence, a proper sanitation is essential in preventing food-borne illness outbreaks. The comparison was done at industrial scale, using equipment already present in the fresh-cut industry and washers designed and manufatured for this purpose. Results showed that, regarding washing water hygiene and final product microbial quality, the use of PAA had a similar efficacy than chlorine. Different scenarios (SCN) combining PAA, chlorine and water have been tested simulating the current industrial processes for each one of the tested vegetables. Overall, results confirmed that the use of a sanitizer, PAA or chlorine, in the washing water of the three tested vegetables is effective for the prevention of cross-contamination during the washing process and hence, to guarantee produce food safety. Regarding final product microbiological quality and shelf life, the use of chlorine or PAA showed no significant differences in lettuces neither in baby leaves. Regarging the potential formation of chlorinated DBPs in processing water, they were found not in significant amounts when washing water was treated with PAA in all scenarios and vegetables tested. Washing with 80 mg/L chlorine generated important amounts of THMs, chlorates and chlorites. While chlorates and chlorites were always below the recommended levels or legal limits established for drinking water, THMs exceeded these legal limits . With respect to perchlorates, values were below the quantification limit in all SCNs. Results obtained in the present study show that PAA is a reliable alternative to chlorine disinfection strategies in the fresh-cut industry.

Expiration Date of Ready-to-Eat Salads: Effects on Microbial Load and Biochemical Attributes

When minimally processed vegetables reach their expiration date, expose an increased microbial load. This includes mainly spoilage microorganisms but also foodborne pathogens, thus affecting the quality and safety of highly consumed ready-to-eat salads. A total of 144 ready-to-eat salads from the Cypriot market were analyzed in an attempt to determine the effects of the expiration date on the microbial load and plant metabolic variables of the salads. Possible correlations between them were also investigated for the first time. Furthermore, the impacts of the season (winter, summer), salad producing companies and type of salad and/or their interactions with the tested parameters were investigated. Results revealed that the microbial load (mainly spoilage microorganisms, such as Pseudomonas spp., yeasts and molds) increased towards the end of the shelf life. The microbial load was differentiated among the five salad producers and/or the salad types, highlighting the importance of a common and safe sanitation-processing chain in the preparation of ready-to-eat salads. Summer was the season in which Escherichia coli counts were found to be higher for plain lettuce, while Staphylococcus spp. was increased numbers for the lettuce+endive/radicchio, lettuce+rocket and lettuce+chives type of salads. Additionally, an increased Staphylococcus spp. was observed for plain rocket salads in winter. All samples examined were found negative for Salmonella enterica and Listeria monocytogenes. Moreover, carbon dioxide production and damage indexes (hydrogen peroxide and lipid peroxidation) increased on expiration date on both winter and summer seasons, indicating plant tissue stress at the end of shelf life. These findings indicate that the expiration date and relevant shelf life of processed vegetables are important parameters to be considered when postharvest management is applied to these products, ensuring safety and quality.

Emulsions Incorporated in Polysaccharide-Based Active Coatings for Fresh and Minimally Processed Vegetables

The consumption of minimally processed fresh vegetables has increased by the consumer’s demand of natural products without synthetic preservatives and colorants. These new consumption behaviors have prompted research on the combination of emulsion techniques and coatings that have traditionally been used by the food industries. This combination brings great potential for improving the quality of fresh-cut fruits and vegetables by allowing the incorporation of natural and multifunctional additives directly into food formulations. These antioxidant, antibacterial, and/or antifungal additives are usually encapsulated at the nano- or micro-scale for their stabilization and protection to make them available by food through the coating. These nano- or micro-emulsions are responsible for the release of the active agents to bring them into direct contact with food to protect it from possible organoleptic degradation. Keeping in mind the widespread applications of micro and nanoemulsions for preserving the quality and safety of fresh vegetables, this review reports the latest works based on emulsion techniques and polysaccharide-based coatings as carriers of active compounds. The technical challenges of micro and nanoemulsion techniques, the potential benefits and drawbacks of their use, the development of polysaccharide-based coatings with natural active additives are considered, since these systems can be used as alternatives to conventional coatings in food formulations.

The Influence of Two-Component Mixtures from Spanish Origanum Oil with Spanish Marjoram Oil or Coriander Oil on Antilisterial Activity and Sensory Quality of a Fresh Cut Vegetable Mixture

The aim of this study was to evaluate two-component mixtures of essential oils (EOs) in sub-inhibitory concentrations for antilisterial protection of minimally processed vegetables. Spanish origanum oil (SOO), Spanish marjoram oil (SMO) and coriander oil (CO) and a mixture of fresh leafy vegetables with red beet were used. The chemical compositions of selected EOs were analyzed by gas chromatography. Carvacrol was the major component of SOO. The dominant active component of SMO was 1,8-cineole, while the major constituent in CO was linalool. The study shows that essential oils in combination, namely SOO + SMO and SOO + CO in a ¼ MIC + ¼ MIC (Minimal Inhibitory Concentration), have a synergistic effect against L. monocytogenes. The reduction of L. monocytogenes in vegetable mixtures treated by EOs in these selected combinations after 24 h of storage was approximately equal to the limit of detection. Furthermore, it was found that the vegetable mixture treated with SOO + SMO had the highest-rated sensorial quality and could therefore meet consumer expectations.

Antioxidant profile of Canada lettuce (Lactuca canadensis) and madeira vine (Anredera cordifolia) minimally processed

This study aimed to evaluate the stability of natural antioxidants in minimally processed Anredera cordifoliaand Lactuca canadensisand their physical-chemical and antioxidant characteristics at time zero of storage (T0) and after 3, 6, 9 and 12 days, at a temperature of 7 °C. For the attribute color, L. canadensisdid not show significant differences between the parameters, whereas A. cordifoliashowed variation in its lightness from the third day of storage. Both vegetables had significant increments of pH, which ranged from 5.77 to 6.16 in A. cordifoliaand from 6.23 to 6.43 in L. canadensis. The contents of soluble solids also increased significantly, from 2.28 to 4.17 °Brix and from 4.89 to 6.30 °Brix in A. cordifoliaand L. canadensis, respectively. No significant difference was observed in total titratable acidity at any of the times evaluated (p>0.05). Among the bioactive compounds of the minimally processed vegetables, the contents of carotenoids, tannins, and total phenolic compounds were affected by storage, demonstrating that this process has an influence on the concentrations of the natural antioxidants studied.

Edible coatings used for conservation of minimally processed vegetables: a review

The minimally processed vegetable (MPV) market has been growing in recent decades. This growth is related to the change in lifestyle and eating habits of consumers who seek practical and healthy food for consumption. Maintaining the characteristics and quality of MPVs is a significant challenge for producers and traders. Minimal processing steps increase the perishability of these MPVs, thus increasing oxidative reactions and their metabolic rate. The research focused on the development of technologies that reduce these reactions gained prominence. Edible films and coatings produced from natural sources have emerged as alternative packaging for food applications and have received attention due to their advantages, such as their biodegradable and renewable nature, availability, and cost. The use of edible coatings for the preservation of vegetables in the postharvest condition, whether intact or minimally processed, has been identified as an emerging technology of great potential as they can control the internal atmosphere of MPVs. Biopolymers such as polysaccharides, lipids, and proteins have been evaluated in the formulation of these coatings. The choice of appropriate material will depend on the characteristics of the plant, the biopolymer, and the intended objectives of the film. This review aims to present some application examples, the main types of edible coatings, and the application techniques used in MPVs based on the literature, to assist a choice that can generate greater coating efficiency.