research paper on ready to eat food products

• Search Menu
• Advance articles
• Editor's Choice
• Supplement Archive
• Article Collection Archive
• Author Guidelines
• Submission Site
• Open Access
• Call for Papers
• Why Publish?
• About Nutrition Reviews
• About International Life Sciences Institute
• Editorial Board
• Early Career Editorial Board
• Advertising and Corporate Services
• Journals Career Network
• Self-Archiving Policy
• Journals on Oxford Academic
• Books on Oxford Academic

Article Contents

Introduction, suggestions.

• < Previous

Current situation and perspectives of ready-to-eat food/meal suppliers

Working Group 2 Members: Takashi Sakata (Leader, Ishinomaki Senshu University), Takeaki Akabane (ADEKA Corp.), Chikako Akagaki (SEVEN-ELEVEN JAPAN Co., Ltd.), Rie Akamatsu (Ochanomizu University and The Japanese Society of Nutrition and Dietetics), Toshihiko Hagiwara (NICHIREI Corp.), Naoki Hayashi (Ajinomoto Co., Inc.), Li Han (Nippon Suisan Kaisha, Ltd.), Hajime Kato (Yano Research Institute Ltd.), Kayo Kurotani and Kazuko Ishikawa-Takata (the National Institutes of Biomedical Innovation, Health and Nutrition), Shunsuke Omoto (Kirin Holdings Company, Ltd.), Takashi Tanaka (YAMAZAKI BAKING Co. Ltd.), and Yoshiko Yokomukai (International Life Science Institute JAPAN)

• Article contents
• Figures & tables
• Supplementary Data

Takashi Sakata, for Working Group 2 of the Healthy Diet Research Committee of International Life Sciences Institute, Japan, Current situation and perspectives of ready-to-eat food/meal suppliers, Nutrition Reviews , Volume 78, Issue Supplement_3, December 2020, Pages 27–30, https://doi.org/10.1093/nutrit/nuaa089

• Permissions Icon Permissions

Working Group 2 of the Healthy Diet Research Committee of International Life Sciences Institute Japan (WG2) assessed the concept and practice of healthy eating in the ready-to-eat food/meal industry in Japan. WG2 interviewed 14 arbitrarily selected member companies that included “health” or “nutrition” in their management policy, and sent a questionnaire to 338 member companies of the Japan Ready-Made Meal Association. Ready-to-eat food/meal suppliers mainly referred to Dietary Reference Intakes for Japanese, the Japanese Food Guide, and/or Healthy Japan 21 for their menu construction. They increased dietary fiber, variety, vegetables, whole-grain cereals, millet rice, and soy bean products; and reduced energy, carbohydrates, and salt in “healthy” food. They tended to avoid making direct appeals to health. Many companies reduced the salt content without drawing attention to the practice. They continually strive to improve flavor as the single most important factor for selling healthy food. The cycling of menus is used to increase diversity in food consumption. These industries require both academia and the government to define priorities for increasing and decreasing particular nutrients as the main targets and to establish the maximum time for balancing each nutrient.

Ready-to-eat food or meals in Japan is defined as “food or a meal that can be eaten without cooking or heating at home, workplace, school, etc., such as lunch boxes and daily dishes with a short shelf life.” 1 The sales of ready-to-eat food/meals is growing and, in 2017, they exceeded JPY 10 trillion. 1 The expected increase in the number of elderly people and the results of women’s empowerment in Japan should favor this sector of the food industry.

The main products of these ready-to-eat food/meal suppliers are cooked rice (50%) and daily dishes (34%), namely lunch boxes, rice balls, sandwiches, croquettes, and vegetable salads in the Tokyo metropolitan area. 1 These products are sold mainly via convenience stores (32%), specialty stores (29%), and food supermarkets (26%). 1

We conducted a survey to evaluate the concept of “healthy eating” among ready-to-eat food companies that are expected to grow in Japan, and we summarized the findings for academic research and governmental policy and regulation needed to achieve healthy eating.

Working Group 2 of the Healthy Diet Research Committee of International Life Sciences Institute (ILSI) Japan (WG2) conducted a round-table discussion with the Japan Ready-Made Meal Association (JRMA) to clarify the general business structure, and then performed semistructured interviews to arbitrarily select 14 (of 24 approached) JRMA member companies stating “health” or “nutrition” in their management policy. We administered a nationwide online questionnaire via Google forms to only the 14 selected JRMA member companies via the JRMA. JRMA is a national association comprising 338 regular member companies, 216 supporting member companies, and 40 cooperating companies.

Findings from interviews

Of 24 member companies of JRMA that publish statements on healthy or nutritious food in their policies and were selected for visits by WG2, 14 companies accepted the visit. Annual sales of these 14 companies exceeded JPY 40 billion; the average annual sales of JRMA regular member companies in 2019 totaled JPY 12.6 billion ( Table 1 ).

Characteristics of interviewed companies

Abbreviations: Dept., department; JPY, Japanese yen.

Interviewed companies generally based their meals and menus on Dietary Reference Intakes for Japanese, 2 the Japanese Food Guide, 3 or Healthy Japan 21. 4 These companies intended to increase or improve ingredient variety (n = 5 companies), vegetables (n = 4), dietary fiber (n = 3), lactic acid bacteria (n = 2), green and yellow vegetables, millet rice, organic ingredients, quinoa, ω3-fatty acids, iron, lycopene, calcium, protein, and nutrient balance. They intended to reduce or omit salt (n = 8 companies), energy (n = 5), additives (n = 4), chemical seasoning (n = 3), carbohydrates (n = 2), and lipids.

It was a general tendency of all interviewed companies to avoid direct health appeals such as “reduced salt,” although many of them actually reduced the salt content in their products gradually but continuously. These companies considered direct health appeals to be unpopular and to reduce sales. They emphasized a healthy atmosphere as a whole. It was also noted that some positive wording such as “rice bowl with lots of vegetables” increased sales.

All companies considered good flavor to be the single most important sales factor. Therefore, they regularly worked to improve the flavor of their products and tested the customers’ opinions of the improvements often via face-to-face tastings as points of sale, which resulted in an increase or recovery of the sales.

One company selling warm lunchboxes developed 2 series of cycling menus for 1 week, one with large portions and another relatively fit with respect to energy and salt content. The main customers of the company are busy people who do not pay much attention to nutrition or health. The company intended to increase the variety of ingredients and tried to balance the nutrient intake if the customer purchases the same cycling menu, even without considering the contents of the lunch box. Interestingly, most of these customers purchased the large-portion meals and the fit meals alternately, that is, there was approximately a 50% improvement. This can be an important tactic for improving the nutritional status of laymen without pressing them to behave healthily.

Findings from nationwide questionnaire

JRMA distributed the questionnaire to 338 member companies online in July 2019. In total, 88 companies responded the questionnaire (response rate, 26.0%). Just 50 of the 88 responding companies had annual sales of more than JPY 1 billion. Considering the average annual sales of JRMA regular member companies of JPY 12.6 billion, response rate should have been higher in smaller companies than in large companies. The proportion of responding companies selling via supermarket was approximately twice that of the JRMA regular member companies. Therefore, the results may have sampling bias and, accordingly, may not represent the overall tendency of JRMA members.

Distributions of their main product and route of sales indicated that the composition of these companies approximately, but not entirely, reflected the composition of the JRMA ( Figure 1 ). Therefore, the results may not represent the status quo of all JRMA member companies.

Main products and routes of sales of responding Japan Ready-Made Meal Association member companies (multiple answers, n = 88). Abbreviation: EC, electronic commerce.

Approximately 60% of the responding companies had health- or nutrition-oriented wording in their management policies or on their homepage. Approximately 75% of the responding companies produced health- or nutrition-oriented products ( Figure 2 ). The responding companies most often cited Dietary Reference Intakes for Japanese 2 and Japanese Food Guide Spinning Top as the resources on which they based their the menu design ( Figure 3 ).

Health or nutrient orientation of responding companies (n = 88).

Governmental guidelines or policies on which responding companies based their menu construction (multiple answers, n = 88). *Ministry of Health, Labour and Welfare; **Ministry of Health, Labour and Welfare, and Ministry of Agriculture, Forestry and Fisheries; ***Ministry of Health, Labour and Welfare, Ministry of Agriculture, Forestry and Fisheries, and Ministry of Education, Culture, Sports, Science and Technology.

Nutrients focused on in successful health- or nutrition-oriented products were energy, carbohydrate, dietary fiber, sodium, protein, and lipid. Ingredients in successful health- or nutrition-oriented products were vegetables, whole-grain cereals, soy products, miscellaneous grains, seasoning, animal meat, seafood, fermented products, and oil ( Figure 4 ). There was no marked tendency with regard to focused nutrient or ingredient in failed health- or nutrition-oriented products.

Nutrients and ingredients focused in successful health or nutrition-oriented products (multiple answers, n = 88). Abbreviation: Na, sodium.

The challenges for responding companies in the development and sales of health- or nutrition-oriented products were to produce good-tasting products at a low cost that appeal to the consumer via an efficient production process with stabilization of the food content.

On the basis of the surveys findings, WG2 wants to highlight the importance of developing and disseminating simple and easily understandable guidelines and labeling policies for the production of healthy and nutritious ready-to-eat food/meals. In this regard, WG2 proposes to define priorities for which nutrients to increase or decrease, to prioritize target population (eg, those who are establishing food habits or those who eat without consideration of what they eat), and to indicate the maximum time to balance each nutrient.

Acknowledgments

The WG2 members sincerely express their gratitude for the generous cooperation of Japan Ready-Made Meal Association and its member companies, which was essential for conducting this study. The study plan of the survey was reviewed by the Ethics Committee for Human Studies of Ishinomaki Senshu University (application no. 2018–001) and determined to be a study not requiring the permission of the committee. Although, many authors belong to private companies, all authors wrote a pledge stating that all information gathered during this survey belongs to ILSI Japan and will not be used otherwise without the consent of ILSI Japan.

Author contributions . T.S. supervised the study. All authors equally contributed to develop the research design, conduct the survey, analyze the data, and prepare the manuscript, and all approved the final manuscript.

Funding . This research was conducted as a part of the activities of the International Life Sciences Institute Japan Research Committee, which are not compensated except for travel expenses for academia members, as required.

Declaration of interest . T.S. is a vice president and a member of the Board of Trustees for International Life Sciences Institute (ILSI) Japan. He is also a member of the organizing committee and the program committee for the 8th International Conference on Nutrition and Aging held October 1-2, 2019. R.A. is a member of the program committee for the 8th International Conference on Nutrition and Aging. Companies to which authors belong are members of ILSI Japan and support the organization’s activities.

White Paper of Japan Ready-Made Meal Association (2018) (Digest on-line edition). Japan Ready-Made Meal Association.   http://www.nsouzai-kyoukai.or.jp/wp-content/uploads/hpb-media/hakusho2018_digest1.pdf .

Ministry of Health, Labour and Welfare. Overview of Dietary Reference Intakes for Japanese (2015). Available at: https://www.mhlw.go.jp/file/06-Seisakujouhou-10900000-Kenkoukyoku/Overview.pdf . Accessed April 18, 2020.

Ministry of Health, Labour and Welfare; Ministry of Agriculture, Forestry, and Fisheries. Japanese Food Guide Spinning Top. Do you have a well-balanced diet? https://www.maff.go.jp/j/balance_guide/b_use/pdf/eng_reiari.pdf . Accessed April 18, 2020.

Ministry of Health, Labour and Welfare. A basic direction for comprehensive implementation of national health promotion. Ministerial Notification No. 430 of the Ministry of Health, Labour and Welfare. Available at: https://www.mhlw.go.jp/file/06-Seisakujouhou-10900000-Kenkoukyoku/0000047330.pdf . Accessed April 28, 2020.

Author notes

• dietary fiber
• carbohydrates
• biological sciences
• science of nutrition
• whole grains
• healthy diet
• academia (organization)

Email alerts

Citing articles via.

• Recommend to your Library

Affiliations

• Online ISSN 1753-4887
• Print ISSN 0029-6643
• Copyright © 2024 International Life Sciences Institute
• About Oxford Academic
• Publish journals with us
• University press partners
• What we publish
• New features  
• Open access
• Institutional account management
• Rights and permissions
• Get help with access
• Accessibility
• Advertising
• Media enquiries
• Oxford University Press
• Oxford Languages
• University of Oxford

Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide

• Copyright © 2024 Oxford University Press
• Cookie settings
• Cookie policy
• Privacy policy
• Legal notice

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• Int J Environ Res Public Health

Assessment of the Microbiological Quality of Ready-to-Eat Salads—Are There Any Reasons for Concern about Public Health?

Anna Łepecka.

1 Department of Meat and Fat Technology, Prof. Waclaw Dabrowski Institute of Agriculture and Food Biotechnology—State Research Institute, 02-532 Warsaw, Poland; [email protected]

Dorota Zielińska

2 Department of Food Gastronomy and Food Hygiene, Institute of Human Nutrition Sciences, Warsaw University of Life Sciences-SGGW, 02-776 Warsaw, Poland; lp.ude.wggs@aksnileiz_atorod (D.Z.); moc.liamg@49sarubalebazi (I.B.); lp.ude.wggs@akswejark_nyzolok_atunad (D.K.-K.)

Piotr Szymański

Izabela buras, danuta kołożyn-krajewska.

Ready-to-eat food products can be readily consumed without further preparation and are convenient for busy on-the-go consumers. The objective of the study was to assess the microbiological quality of ready-to-eat salads. Thirty RTE salads were tested for the presence of bacteria, yeasts, and molds using the TEMPO and agar plate method. The study demonstrated that most of the tested products were characterized by varying microbiological quality. The total number of mesophilic microbiotas was about 6 log CFU g −1 . The high number of microorganisms was due to yeast and molds or Enterobacteriaceae . Half of the salads were contaminated with E. coli and three salads were contaminated with S. aureus . LAB were also found, which can be explained mainly by a dairy ingredient. In some salads, Salmonella spp. and L. monocytogenes were detected (26.7% and 33.3% of the samples, respectively). Based on the conducted tests, it was found that the microbiological quality was not satisfactory. The results presented in this study indicate that there is a significant problem of the presence of pathogens. Manufacturers should strive to reduce the possibility of microbial contamination through the use of widely understood hygiene of the production process, using hurdle technology, including the modified atmosphere and refrigerated storage.

1. Introduction

Convenience food has become an alternative to traditionally prepared food. Convenience food can be defined as: food, typically a complete meal, that has been pre-prepared commercially and so requires minimum further preparation by the consumer. The market offers more and more new high-quality food products, produced using new recipes, modern production and packaging technologies [ 1 , 2 ].

Currently, the demand for ready-to-eat (RTE) products, including salads, is increasing. RTE salads are minimally processed products. By definition, minimally processed food has the appearance of fresh food, is characterized by the least changed characteristics, and is safe to eat. RTE food products can be readily consumed without further preparation and are convenient for busy consumers. The production of ready-to-eat salads is constantly growing and they are currently produced on an industrial scale [ 3 ]. The availability of both RTE fruit and vegetables on the market may contribute to increasing the consumption of fruit and vegetables in the general population and thus contribute to efforts to achieve a daily consumption of 400 g of vegetables and fruit per capita, as recommended by the World Health Organization [ 4 ]. It was estimated that in Europe in 2021, the average amount of ready-to-eat meals consumed per person was about 15 kg [ 5 ].

In addition to providing the necessary ingredients, food items should be characterized by health quality, including appropriate microbiological quality, guaranteeing safety to health. Healthy food quality depends on the conditions and ways of obtaining the raw materials, pre-treatment and thermal processing, storage, transport, and conditions of sale [ 3 ]. All these operations can result in damage to the natural barrier of the epidermis and disrupt the internal compartmentalization, which in turn separates enzymes from substrates, thus, promoting microbial proliferation and inducing increased respiration in the plant. This, in turn, results in an increase in metabolism and the aging of tissues [ 4 ]. Due to numerous cases of food poisoning caused by microorganisms and toxins found in food, research and the control of food products are important. There are legal regulations regarding food, defining microbiological criteria and limits for the occurrence of microorganisms in food. These criteria, however, apply to selected food groups and regulate the selected acceptable limits of microorganisms [ 6 , 7 ].

According to the WHO [ 8 ], 550 million people suffer from Salmonella poisoning every year, and about 220 million of them are children under 5 years of age. Salmonella is one of the four key global causes of diarrheal diseases. Currently, in the European Union, salmonellosis is the second most deadly disease, after campylobacteriosis, causing food poisoning [ 9 ] with a notification rate of 20.0 cases per 100,000 population [ 10 ]. The trend towards human salmonellosis has been stable over the past five years after a long period of a downward trend. Additionally, Salmonella Enteritidis caused the vast majority (72.4%) of food-borne salmonellosis outbreaks [ 10 ].

Subsequently, 1 million people suffer from listeriosis per year [ 11 ]. Unfortunately, most cases require hospitalization. According to EFSA and ECDC [ 9 ], the number of poisonings by Listeria monocytogenes in the European Union is constantly increasing. The listeriosis notification rate is 0.47 cases per 100,000 people [ 12 ]. One of the reasons for this increase is the interest in ready-to-eat products. Based on the EFSA and ECDC study [ 9 ], L. monocytogenes was found in RTE foods in the largest number of samples of fish and fish products (6.0% of samples), salads (4.2% of samples), meat and meat products (1.8% of samples), soft and semi-soft cheeses (0.9% of samples), fruit and vegetables (0.6% of samples), and hard cheeses (0.1% of samples). According to the EFSA BIOHAZ Report [ 13 ] ready-to-eat salads were found to be the main source of poisoning by L. monocytogenes . In 2013, in Germany, three human cases of listeriosis were found after eating ready-to-eat vegetables, juices, and mixed salads (one death was reported). In the same country, in 2014, two cases were observed after eating mixed food (iceberg lettuce with yogurt dressing, and gouda cheese). In Switzerland, thirty-one human listeriosis cases were found in 2014 (four deaths were reported). L. monocytogenes were found in ready-to-eat vegetables, juices and pre-cut salads.

Ready-to-eat salads could show the presence of various microbial pathogens including Escherichia coli , Staphylococcus aureus , Salmonella spp., Listeria monocytogenes , Campylobacter jejuni , Clostridium perfringens , total aerobic and spoilage bacteria, yeasts, and molds, which are concerned with serious threats [ 14 , 15 ]. In addition, a high number of microorganisms are also becoming a reservoir of antibiotic resistance genes, which has now become a global problem [ 16 , 17 ].

Although the European Commission Regulation No. 852/2004 [ 18 ] on the hygiene of foodstuffs requires businesses to implement Good Hygiene Practice and a food safety management system based on hazard analysis and critical control point (HACCP) principles, many authors indicated that RTE food causes high microbiological risk [ 19 ]. However, the knowledge of factors affecting the quality of RTE foods is still inconclusive.

The main objective of this study was to assess the microbiological quality of ready-to-eat salads from the Polish market and to evaluate whether the composition, time, and method of packaging had an impact on the shelf life of these salads.

2. Materials and Methods

2.1. materials.

Thirty salads were purchased in autumn at several discount stores from the Polish market (Warsaw) and retail chains. The products were fresh, before the expiry date, transported in thermal bags, and then refrigerated (4–8 °C) until the beginning of the study. The samples were tested on the day of purchase. All of the products were tightly packed in plastic boxes like ‘lunch boxes’. Three salads of each type were purchased from the same production batch and tested. Table 1 and Table 2 present information about the tested salads according to the manufacturers’ declarations.

Ingredients of the tested salads according to the producer’s declaration.

Nutritional value and other information about the salads.

Explanatory: (+)—modified atmosphere/preservatives presence; (−)—modified atmosphere/preservatives absence.

The mixed ingredients of the ready-to-eat salads included raw and cooked ingredients, e.g., vegetables (leafy vegetables, cherry tomatoes, and carrots), meat (ham, smoked chicken, and grilled chicken), fish (salmon and tuna), cheeses, and carbohydrate sources (pasta, and buckwheat). The tested salads differed in composition, shelf-life, the way they were packed and storage temperature. The recommended maximum storage temperature as indicated on the label was 10 °C. The shelf life was 1–7 days. Some of the salads had dressings/sauces in sachets and some of the salads were mixed and ready to eat. In most cases, the producers did not give the composition of the dressings/sauces. Some of the dressings/sauces in the salads were with the addition of preservatives.

2.2. Methods

2.2.1. samples preparation.

Three salads were prepared from each production batch. First, 25 g of the salad product was weighed by taking different ingredients to obtain a representative sample. Then, 225 mL of peptone water (BioMaxima, Lublin, Poland) was added and homogenized in a stomacher (Stomacher 80 Biomaster, Seward Limited, London, UK) for 5 min. Filtered stomacher bags (BagFilter ® 400 P, Interscience, Paris, France) were used to eliminate any solid particles. Decimal dilutions were made, and the prepared samples were used for further testing.

2.2.2. Microbiological Analysis

Microbiological tests (count of aerobic mesophilic total flora, Staphylococcus aureus , Enterobacteriaceae , Escherichia coli , lactic acid bacteria, yeasts, and molds) were carried out using the TEMPO ® system (bioMérieux, Marcy-l’Étoile, France). The dehydrated culture media in the bottles were prepared by adding 3.9 mL of sterile distilled water. Then, 0.1 mL of the sample solution was added to them in a suitable dilution and vortexed (5–10 s; Heidolph, Schwabach, Germany). The samples were incubated in INE 400 Incubator (Memmert GmbH + Co.KG, Buechenbach, Germany) according to the manufacturer’s manual. The results are presented on a logarithmic scale (log CFU g −1 ) and standard deviation.

The samples were analyzed for the presence of microorganisms commonly isolated from RTE vegetables, i.e., Salmonella spp. and L. monocytogenes . The plate method was used according to ISO standards [ 20 , 21 ].

The samples of the salads (25 g) were mixed with peptone water (BioMaxima, Lublin, Poland) and incubated at 37 °C for 24 h to pre-incubation. For selective propagation, nutrient broth (BioMaxima, Lublin, Poland) was used. An aliquot of 1 mL was withdrawn and transferred to 9 mL of broth and incubated again at 37 °C for 24 h. Sterile Petri dishes were poured into 15–20 mL of BGA (Brilliant Green Agar; Oxoid, Waltham, MA, USA) and, after setting with an automatic pipette, surface culture was performed. Subsequently, 0.1 mL of the sample was applied to the surface of the substrate and spread over the substrate with a sterile paddle. The cultures were incubated at 35 °C for 24 h. In the case of a positive result on the BGA, a confirmation on the XLD agar was made (Xylose Lysine Deoxycholate agar; LabM, Heywood, UK). Agar was poured onto a sterile plate and the surface was set after solidification. Subsequently, 1 mL of the inoculated nutrient broth was applied to the surface of the medium and spread over the substrate. The plates were incubated at 37 °C for 24 h. The results are presented as the presence (+) or absence (−) of Salmonella spp.

Samples of the salads (25 g) were mixed with half-Fraser broth (Oxoid, Waltham, MA, USA) and incubated at 37 °C for 24 h. Then, 1 mL was removed and transferred to the Fraser broth (Oxoid, Waltham, MA, USA) and incubated for 24–48 h. In sequence, 15–20 mL of ALOA (Agar Listeria according to Ottaviani and Agosti; LabM, UK) was poured onto sterile plates and the surface was set after setting. Using an automated pipette, a 1 mL test sample was applied to the surface of the substrate and spread evenly over the substrate using a sterile paddle. The cultures were incubated at 37 °C for 24 h. In the case of a positive result on the ALOA, a confirmation on the PALCAM agar was made (LabM, Heywood, UK). Agar was poured onto a sterile plate and the surface was set after solidification. Subsequently, 1 mL of the inoculated Fraser broth was applied to the surface of the medium and spread evenly over the substrate. The plates were incubated at 37 °C for 24 h. The results are presented as the presence (+) or absence (−) of Listeria monocytogenes .

2.2.3. Statistical Analysis

Microbiological tests were performed in three replications (three repetitions with three different products from the same batch). All of the data were analyzed using the Statistica 13 (TIBCO Software Inc., Palo Alto, CA, USA). Correlation coefficients were calculated and a principal components analysis (PCA) using a correlation matrix and a cluster analysis was performed

3. Results and Discussion

The tested salads were characterized by different microbiological quality. Table 3 below shows the results of the number of selected microorganisms and the results of the presence of Salmonella spp. and L. monocytogenes .

Microbiological quality of the tested RTE salads.

Explanatory: AC—aerobic mesophilic total flora, STA— S. aureus , EB— Enterobacteriaceae family, EC— E. coli , LAB—lactic acid bacteria, YM—yeasts and molds; SAL— Salmonella spp., LM— L. monocytogenes ; <1.00—below the detection level. The results are shown as log CFU g −1 ; means ± standard deviation; (+) presence of bacteria in 25 g of the product, (−) absence of bacteria in 25 g of the product; n = 3.

There are not many studies on microbiological tests on salads with dressings/sauces. Typically, the studies apply only to raw vegetables or salad blends [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ], only dressings/sauces and pesto [ 29 ], or RTE products in general [ 30 ]. These mixtures are the least processed and form a large part of the product, but they are not the only factors that determine the quality of the final product. When ingredients are mixed together with green leaves, cross-contamination may occur at any point in the production chain to consumption. Cross-contamination can occur during processing when the equipment in contact with potentially contaminated products is not regularly sanitized and cleaned [ 31 ].

Although there are no established microbiological criteria for ready-to-eat foods in the European Union, the only applicable regulation is Commission Regulation 1441/2007 (formerly Commission Regulation 2073/2005) [ 6 , 7 ]. However, it does not include this category of food, but only their individual components. For fruit and vegetables, the limit is established for bacteria E. coli (1000 CFU g −1 of product) and precut ready-to-eat fruit and vegetables are limited in Salmonella (absence in 25 g of product). Ready-to-eat meat products are limited in L. monocytogenes (100 CFU g −1 of a product or absence in 25 g of a product) [ 7 , 32 ].

Although the total viable count is not a legislation criterion for RTE salads, it is an important hygienic and sensory quality indicator, which may inform about the total microbiological status of the food. In the present study the total number of aerobic mesophilic microorganisms found in the tested salads were on a different level and, on average, about 6 log CFU g −1 (ranged from 2.36 log CFU g −1 to 9.30 log CFU g −1 ) ( Table 3 ). The lowest total viable count of microorganisms was evaluated in salad S4. Salads S8, S9, S10, S11, S16, S19, and S23 were characterized by a high number of total viable counts. The high numbers of organisms in S16 and S23 salads were due to the high number of yeast and molds (7.00 log CFU g −1 and 6.60 log CFU g −1 , respectively) or Enterobacteriaceae family bacteria (6.84 log CFU g −1 ). In salads S16, S19, and S23, high numbers of lactic acid bacteria were found. The count of total microbiota in the salads in this study was similar to those observed in Polish studies by Berthold-Pluta et al. [ 33 ] who reported that the count of aerobic mesophilic total microbiota in leafy vegetables and their mixes ranged from 5.6 log CFU g −1 to 7.6 log CFU g −1 . Similarly, Jeddi et al. [ 34 ] reported that the total mesophilic microbiota observed in vegetables from Iran ranged from 5.3 log CFU g −1 to 8.5 log CFU g −1 . Importantly, the count of aerobic mesophilic microbiota is an indicator of only the overall microbiological quality of a food product and that there are no binding standards for the quality of products of this type [ 33 ]. In general, aerophilic microbiota is capable of growing, even at low temperatures; hence, its high number even when products are stored in a refrigerator. The high number of packed ready-to-eat salads of all types of vegetables in Portugal was classified as unsatisfactory due to the presence of more than 6 log CFU g −1 aerobic mesophilic microorganisms, even if Salmonella and L. monocytogenes were not detected in any ready-to-eat salad samples [ 35 ]. Adopting only this criterion in our research, we should classify 18 out of 30 of the tested salads as being unsatisfactory.

In three of tested salads (S7, S17, and S18) the S. aureus bacteria (2.00 log CFU g −1 , 3.54 log CFU g −1 , and 2.9 log CFU g −1 , respectively) ( Table 3 ) was revealed. In seven samples of salads (S7, S9, S10, S13, S14, S15, and S23), bacteria of the Enterobacteriaceae family in a number higher than 6 log CFU g −1 were found, which indicates a high degree of microbiological contamination. Leff and Fierer [ 36 ] reported that vegetables, e.g., spinach and lettuce, were mainly affected by the Enterobacteriaceae family and half of the salads were contaminated with E. coli . Salads S6, S8, S14, and S23 showed high contamination levels with E. coli (more than 1000 CFU g −1 limited according to the Commission Regulation 1441/2007). In the study of Faour-Klingbeil et al. [ 37 ], in vegetable salads, a high number of bacteria Staphylococcus spp. (1.83–7.76 log CFU g −1 ) and bacteria from the E. coli group (0.33–7.15 log CFU g −1 ) were found, which indicates the possibility of the large contamination of vegetable salads with these bacteria. De Oliveira et al. [ 38 ] reported high contamination vegetable salads with E. coli (53.1% of tested samples). As the authors emphasize, the determination of E. coli is a good indicator for fecal infections, referring to fresh, cut leafy vegetables. Other authors have reported that almost all of the salad samples in Ghana were contaminated with E. coli and Bacillus cereus bacteria (96.7% and 93.3%, respectively) [ 39 ].

Lactic acid bacteria (LAB) were also found in the tested salads, which can be explained mainly by the presence of dairy additives as a salad ingredient, e.g., yogurt, cheese, blue cheese, and mozzarella (salads S1, S3, S5, S6, S7, S8, S9, S14, S19, S23, and S25), or pickled products like pickled cucumber (salads S16 and S18) ( Table 3 ). LAB are a natural vegetable microbiota [ 40 ], but may also contaminate a product [ 41 , 42 ]. Some LAB were found in fresh-cut vegetables (like iceberg, lettuce, or endive). A high number of LAB also affects the total number of bacteria, greatly overstating them. In the majority of the samples tested, a significant of yeast and mold was found (1.00–7.00 log CFU g −1 ). Significant yeast and mold contamination of food products of this type was also determined by Abadias et al. [ 43 ]. The observed numbers of yeasts and molds were lower than bacteria. Furthermore, the ranges in fresh-cut vegetables were from 2.0 log CFU g −1 to 7.8 log CFU g −1 .

Fresh plant-origin products may be a vehicle for the transmission of bacterial pathogens, e.g., E. coli , S. aureus, L. monocytogenes , and Salmonella spp. Food contaminated by fecal microorganisms may be a source of antibiotic resistant organisms that can cause infections in people. Raw vegetables that are particularly vulnerable to contamination with bacteria are: lettuce, spinach, cabbage, cauliflower, celery, broccoli, and all salads packaged in a modified atmosphere [ 44 ]. Among animal products, poultry, meat, and eggs are the main infection sources of Salmonella [ 45 , 46 ].

The microbiological criterion for Salmonella spp. and L. monocytogenes in freshly-cut vegetables is an absence in 25 g of food [ 7 ]. In the salad samples S2, S5, S11, S14, S18, S19, S20, S21, S23, S25, S26, S27, S29, and S30, no pathogenic Salmonella and L. monocytogenes were found (46.7% of samples). Salmonella spp. were found in eight of the tested salads (salads S1, S3, S4, S6, S8, S16, S17, and S24). The L. monocytogenes species were detected in salads S7, S9, S10, S12, S13, S15, S16, S17, S22, and S28 ( Table 3 ). The presence of these indicates high microbiological contamination and may be the cause of being affected by one of the diseases, such as salmonellosis or listeriosis. In the study of Abadias et al. [ 43 ] Salmonella strains were detected in corn salad, lettuce, spinach, and mixed salads (1.7% of samples were contaminated). In other studies, the occurrence of Salmonella in RTE vegetables varies, but usually does not exceed more than a few percent [ 38 ].

Bacteria in the Listeria genus are found in a variety of products, and they are clearly evident in minimal processed food. Listeria is a bacterium with a broad spectrum of development, capable of growing in harsh environmental conditions, and has the ability to create biofilms which may be the cause of cross-contamination [ 47 , 48 , 49 ]. According to the meta-analysis provided by Churchill et al. [ 50 ], the summary estimate of the prevalence of L. monocytogenes was 2.0% in packaged salads. In the study of Söderqvist et al. [ 26 ], L. monocytogenes was isolated from 1.4% of all RTE tested salads. This is a much lower percentage of contamination compared to our own research, as well as the EFSA and ECDC results (13.8%) [ 9 ]. According to the Scientific Report of EFSA [ 51 ], in 2010–2011, ready-to-eat samples were contaminated with L. monocytogenes (1.7%, 0.43%, and 0.06% for fish, meat, and cheese samples, respectively). Gurler et al. [ 52 ] found L. monocytogenes and Salmonella spp. Contamination in RTE foods commercialized in Turkey (6% and 8%, respectively). RTE meat products can be contaminated during or after processing by L. monocytogenes and Salmonella spp. [ 32 ]. Moreover, all of the Salmonella spp. And L. monocytogenes isolates exhibited resistance to one or more of the antimicrobial agents used. The results indicate the need to improve hygiene standards and implement regulations in the RTE food chain in order to ensure microbiological safety. On the other hand, Koseki et al. [ 53 ] presented data about iceberg lettuce in Japan. No pathogenic bacteria, i.e., Salmonella , E. coli O157:H7 and L. monocytogenes , were found. The results of the study could be used to develop risk management policies. In similar results, no pathogenic Salmonella in 233 vegetables, freshly-cut fruits and sprout samples, were detected by Althaus et al. [ 54 ]. Xylia et al. [ 19 ] reported that RTE salads from the Cypriot market are free from S. enterica and L. monocytogenes .

The principal components analysis (PCA) was used to analyze data obtained in the present study and revealed 20 factors that determine the quality of salads, where the first two explain 37.37% of variable variances. A dispersion of the first two factors (PC1 and PC2) on the surface is shown below in Figure 1 and Figure 2 .

Dispersion of quality factors on a surface for the first two principal components (PC). Explanatory: AC—aerobic mesophilic total flora, STA— S. aureus , EB— Enterobacteriaceae family, EC— E. coli , LAB—lactic acid bacteria, and YM—yeasts and molds.

Projection of samples on a surface for the first two principal components (PC).

It was found that the modified atmosphere of package (samples S1, S2, S3, S4, S5, and S6) and preservatives (samples S2, S4, S5, and S14) used in the tested salads were negatively correlated with total aerobic microbiota (−0.46 and −0.42, respectively), as well as with L. monocytogenes presence (−0.35 and −0.28 respectively). Milk ingredients used in salads were correlated with lactic acid bacteria occurrence (0.53), whereas meat (S17) and eggs (S18) were correlated with S. aureus presence (0.31 and 0.37, respectively). On the other hand, salt added to salads was important to prevent Salmonella and yeast and molds developing (−0.45 and −0.33, respectively).

The number of bacterial cells may indicate the contamination of a product, its degree of deterioration, but also may be part of the natural microbiota of the food product. According to FAO/WHO [ 55 ], leafy vegetables (spinach, cabbage, lettuce, and watercress) and fresh herbs (cilantro, basil, chicory, and parsley) are a group with a very high microbiological risk. The threat is mainly E. coli , S. enterica , Campylobacter , Shigella spp., Hepatitis A virus, Noroviruses, Cyclospora cayetanensis , Cryptosporidium , Yersinia pseudotuberculosis , and L. monocytogenes . Leafy vegetables, as a rule, cannot be subjected to thermal treatment, which prevents the deactivation of microorganisms. The cleaning of leaves is a crucial stage in the production process. Moreover, other factors can extend the shelf-life of a product, especially used as hurdle technology.

Increased hygiene at every stage of the production process, application of GHP, GMP, and HACCP principles in the production plant, as well as maintenance of the refrigeration sequence in product storage, can increase the microbiological safety of RTE products [ 3 , 56 , 57 ]. Furthermore, packaging is a key element in the production of ready-to-eat salads, which was found in our study. Samples in which a modified atmosphere was used had lower total aerobic bacteria, as well as the L. monocytogenes count; however the presence of Salmonella spp. was higher. These results being somehow inconsistent, may be a basis for further in-depth research, including more research samples. Packing in a modified atmosphere, which involves the use of a composition of non-atmospheric gases inside the package and the use of appropriate packaging made from permeable materials, was found as an effective method [ 24 , 58 , 59 , 60 ]. The shelf-life of pre-packed salads is determined by microbial and chemical changes. According to Mir et al. [ 61 ] commonly used techniques for the shelf-life prolongation of RTE foods are sanitizers, modified atmosphere packaging, refrigeration, irradiation, high pressure processing, and essential oils.

In ensuring the microbiological safety of products, it is also essential to maintain an appropriate storage temperature [ 28 ]. A low temperature, usually kept at 0–4 °C, inhibits the biochemical and chemical processes of microorganisms, which inhibits their growth in the food product [ 61 ]. Söderqvist et al. [ 26 ] recommended a temperature lower than 4 °C, while the salads tested in this study had the recommended temperature by the manufacturer even up to 10 °C. A low temperature is necessary to prevent the growth of psychrotrophs (like L. monocytogenes ) [ 62 ]. Ziegler et al. [ 63 ] recommended a temperature lower than 5 °C, which could help minimize the risk of L. monocytogenes in RTE salads. Xylia et al. [ 19 ] suggest that shelf-life testing is essential to understanding and developing novel techniques to monitor the safety and quality of ready-to-eat products.

4. Conclusions

Based on the conducted tests, it was found that the microbiological quality of the evaluated ready-to-eat salads was not satisfactory from the safety point of view. Due to the increased interest of consumers in vegetable salad mixes with meat, fish, or cheese, carbohydrate additives (e.g., pasta and toast), and the dressings/sauces available on the market as ready-to-eat products, it is very important to study their microbiological quality. These products are minimally processed; the risk of contamination with microorganisms, including pathogenic ones, is high.

The results presented in this study indicate that there is a significant problem of the presence of pathogenic microorganisms, mainly L. monocytogenes and Salmonella sp. in ready-to-eat salads. Although no negative visual changes of the products were observed, there were a high number of bacteria, yeast, and molds in the products. It is noteworthy that although the products appear edible according to visual inspection, they often contain microorganisms that cause product spoilage, because the first signs of product spoilage may not be visible. Taking into account the limitation of the study, which was the number of samples, future investigation should include more research samples, differentiated in terms of the packaging method and season. Such data would provide valuable information and are in the great interest both of legislators and producers of food products.

It can be summarized that RTE food manufacturers should strive to reduce the possibility of microbial contamination, through the use of widely understood hygiene production guidelines, using hurdle technology, which includes the modified atmosphere and storage of products, especially with a temperature below 5 °C. Where possible, the heat treatment of raw ingredients should be carried out, and raw products, i.e., leafy vegetables, should be thoroughly subjected to washing and drying processes.

Author Contributions

Conceptualization, A.Ł.; methodology, A.Ł. and D.Z.; formal analysis, A.Ł. and P.S.; investigation, A.Ł. and I.B.; resources, A.Ł.; writing—original draft preparation, A.Ł. and D.Z.; writing—review and editing, P.S. and D.K.-K.; visualization, A.Ł. and D.Z.; supervision, D.K.-K. All authors have read and agreed to the published version of the manuscript.

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Conflicts of interest.

The authors declare no conflict of interest.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.