LACOTS/PHLS Co-ordinated Food Liaison Group Studies:

The Microbiological Examination of Ready-to Eat Organic Vegetables from Retail Establishments

SK Sagoo, CL Little and RT Mitchell.

PHLS Environmental Surveillance Unit, 61 Colindale Avenue, London NW9 5EQ.

On behalf of the Local Authorities Co-ordinated Body on Food and Trading Standards and the Public Health Laboratory Service.

Summary

There has been a significant expansion of the UK organic market since 1998/99. Of the various commodity sectors making up the organic market, fruit and vegetables is the largest sector and this has been reflected in an increased interest in their microbiological safety. During May and June 2000 a microbiological study of uncooked ready-to-eat organic vegetables was undertaken to determine the microbiological quality of these organic vegetables on retail sale, and is the first study to provide such information. Examination of organic vegetables from supermarkets, health food shops, farmers' shops or markets, greengrocers, market stalls, and box schemes revealed that the vast majority (3185 of 3200; 99.5%) were of satisfactory/acceptable quality whilst only 15 (0.5%) were of unsatisfactory quality. Unsatisfactory results were due to Escherichia coli and Listeria spp. (not L. monocytogenes) levels in excess of 10² cfu/g. L. monocytogenes, Salmonella spp., Campylobacter spp. and Escherichia coli O157 were not detected in any of the samples examined, indicating that overall agricultural, hygiene, harvesting and production practices were good.

Introduction

Organic food is grown using those principles and techniques that predated the introduction of modern agrochemical and intensive farming techniques⁷. On-going food concerns, specifically about Bovine Spongiform Encephalopathy (BSE) and Genetically Modified (GM) foods are without doubt generating a significantly increased interest in organic food^{5, 6.} The word 'organic' may only be applied to crop products that have been grown, processed and packaged in accordance with the requirements of the European Community (EC) Regulation 2092/91² (implemented in the UK as the Organic Products Regulations 1992, as amended)^21. All food sold as organic must come from growers, processors or importers who are registered and subject to regular inspection. In the UK, the United Kingdom Register of Organic Food Standards (UKROFS) ensures that the various UK certification bodies, such as the Soil Association, properly apply the Regulation. EC legislation for organic produce also require labels to indicate, by a unique code number the organic certification body (e.g. in the UK, 1 to 7) with which the producer or packer is registered⁹.

Organic food is a small but growing part of the food industry in the European Union, and its existence provides an element of consumer choice, for which there is growing demand¹⁸. From 1993 to 1998/99 the sale of organic food in the UK has risen markedly from £100 million to £390 million¹⁹. The largest sector is fruit and vegetables, and in 1998/99 this commodity area accounted for £175m (45% of the total), of which 82% was imported. Overall, 70% of organic food was sold in supermarkets during 1998/99¹⁹. With an annual market growth of 50%, it is estimated that by 2005 organic food in the UK will account for 20% of the total food market with a potential value of over £1billion by early 2001^5,17.

Manure and other animal wastes are widely used in agriculture, both organic and conventional. The use of manure as fertiliser, whether in organic or conventional agriculture, gives rise to concern about the possible contamination of produce with microbial pathogens, especially Escherichia coli O157⁷. However, the Soil Association recommendations for manure storage and treatment on organic farms may lead to enhanced reductions to the levels of pathogens in stored manures that are to be spread to land¹⁹. The UK Food Standards Agency (FSA) view is that there is currently no firm evidence to support the assertion that organic produce is more or less microbiologically safe than conventionally farmed produce⁴. A recent review by the Ministry of Agriculture, Fisheries and Food also concludes that at present there is insufficient information to state categorically whether the risk of pathogen transfer to produce on organic farms differs significantly from the risk associated with conventional farming practice⁸.

As a consequence of the lack of information concerning the microbiological quality of organic vegetables, despite their increased consumption, the Local Authorities Co-ordinating Body on Food and Trading Standards (LACOTS) / and the Public Health Laboratory Service (PHLS) Co-ordinated Food Liaison Group programme undertook a study on the microbiological quality of uncooked ready-to-eat organic vegetables on retail sale in the UK. The study was specifically not a comparative study of organic and conventionally produced vegetables.

Materials and Methods

Sample Collection

Ready-to-eat organic vegetables collected from retail outlets and doorstep delivery schemes were examined in PHLS and non-PHLS laboratories in the UK between 1st May and 30th June 2000 according to a standardised protocol and reporting system. Vegetables included in the study were those that could be consumed without any cooking or further preparation by the consumer other than portioning as necessary and light washing and/or scraping. Vegetables sampled (~150g) were those that were grown in close proximity or in contact with soil (e.g. broccoli, cabbage, carrot, cauliflower, celeriac, celery, cress, lettuce, mushrooms, radish, spring onions, watercress), and other salad vegetables, such as cucumber, pepper, and tomato. Samples were collected from supermarkets, health food stores, greengrocers, farmshops/markets, market stalls, doorstep box-scheme deliveries, and warehouse/storage area box-schemes by staff from local Environmental Health Departments and were transported to the laboratory in accordance with the Food Safety Act 1990, Code of Practice No 7¹⁰.

Information on the organic vegetable samples and outlets was obtained by observation and enquiry and recorded on a standard proforma. This included the country of origin, organic certification body number, packaging, and details concerning the retail display of the product.

Sample Examination

Four representative (~25g) samples from the organic vegetables were required for microbiological examination (Table 1). Samples were collected and examined within their ‘best before date’ or ‘display date’. Gram-negative pathogenic organisms if detected would be sent to the Laboratory of Enteric Pathogens (LEP), Central Public Health Laboratory (CPHL). Listeria monocytogenes at levels at 10³ cfu/g or more and other species of Listeria at levels of 10⁴ or more were sent to the Food Safety Microbiology Laboratory (FSML), CPHL for further characterisation.

Table 1. Methods for the microbiological examination of ready-to-eat organic vegetables

Microorganism		Microbiological Method
Escherichia coli	Enumeration	PHLS Standard Methods for Food Products F20^13
Listeria spp.	Enumeration	Based on BS EN ISO 11290-2: Part 2 1998^2, using Oxford Listeria Agar incubated at 30°C in place of PALCAM agar incubated at 37°C
Listeria monocytogenes	Enumeration	Based on BS EN ISO 11290-2: Part 2 1998^2, using Oxford Listeria Agar incubated at 30°C in place of PALCAM agar incubated at 37°C
Campylobacter spp.	Detection	PHLS Standard Methods for Food Products F21^14
Salmonella spp.	Detection	PHLS Standard Methods for Food Products F13^15
Escherichia coli O157	Detection	PHLS Standard Methods for Food Products F17^16

Results

A total of 3200 uncooked ready-to-eat organic vegetable samples were examined by 43 laboratories (30 Public Health Laboratories (PHLS) from all 8 PHLS Groups; 13 non-PHLS) in England, Wales, Scotland and Northern Ireland. Fifty-two Local Authority Food Liaison Groups participated in this study (Annex 1) and samples were submitted by 350 Local Authorities. A further 352 samples did not fit the criteria described in the study protocol and were not included in the analysis as they were either not ready-to-eat vegetables or were fruit.

Microbiological Results

E. coli was detected in 1.5% (48/3200) of ready-to-eat organic vegetable samples, and was present at 10² cfu/g or more in 0.3% (11) samples (Table 2). Listeria spp. (not including L. monocytogenes) were detected in 0.2% (6/3200) samples, and were present at 10² cfu/g or more in 0.1% (4) samples. Further characterisation of the two Listeria spp. found in excess of 10³ cfu/g revealed the organisms to be L. innocua (from a sample of watercress) and L. seeligeri (from a sample of radish). L. monocytogenes, Salmonella spp., Campylobacter spp. and E. coli O157 were not detected in any of the samples examined.

Table 2. Microbiological results of 3200 uncooked ready-to-eat organic vegetables

	ND* in 25g	D^§ in 25g	<20^†	20-<10^2	10^2 - <10^3	10^3 - <10^4	10^4 - <10^5	10^5 - <10^6	10^6 - <10^7	³10^7	NE^¶
Escherichia coli			3150^a	37	9	2					2
Listeria spp.			3192^a	2	2	2					2
L. monocytogenes			3198^a								2
Campylobacter spp.	2883										317**
Salmonella spp.	3196										4
Escherichia coli O157	3193										7

*ND; Not detected; §D, Detected; ¶NE, Not examined (full set of microbiological parameters not performed on sample due to insufficient sample collected)

†, cfu/g

** These were not examined due to unavailability of the selective supplement cycloheximide during May - June 2000

a, lower limit of detection 20 cfu/g

Microbiological Quality of Uncooked Ready-to-eat Organic Vegetables

Based on the PHLS Microbiological Guidelines for some ready-to-eat foods sampled at the point of sale¹², 3146 (98.5%) of 3200 ready-to-eat organic vegetables were satisfactory, 39 (1%) acceptable, and 15 (0.5%) were of unsatisfactory microbiological quality. E. coli and Listeria spp. (not L. monocytogenes) were the microbiological parameters associated with unsatisfactory results. None of the samples examined were of unacceptable microbiological quality (Figure 1 and Table 3).

Table 3. Key to classification¹²

Criterion	Microbiological quality (cfu per gram unless stated) Satisfactory Acceptable Unsatisfactory Unacceptable/ potentially hazardous
Escherichia coli	<20	20 - <10^2	³10^2	N/A*
Listeria spp.	<20	20 - <10^2	³10^2	N/A
Listeria monocytogenes	<20	20 - <10^2	N/A	³10^2
Campylobacter spp.	Not detected in 25g			Detected in 25g
Salmonella spp.	Not detected in 25g			Detected in 25g
Escherichia coli O157	Not detected in 25g			Detected in 25g

*, N/A, Not applicable

A major feature of the data is that of the microorganisms tested (Table 2), none were found in 3146 of the 3200 (98.5%) samples examined. As this forms the vast majority of the data, information collected on the organic vegetable samples and outlets (presented below) had no significant effect on the microbiological quality of the vegetables with regard to samples of unsatisfactory quality (data not shown), i.e. no correlation was found between samples of unsatisfactory quality and product information.

Product Information

Types of Ready-to-eat Organic Vegetables

A total of 21 different vegetable types were examined (Table 4). The majority of the vegetables examined were grown in close proximity or in contact with the soil (74%; 2349/2300) with the remainder being non-soil contact vegetables (26%; 851).

Table 4. Types of ready-to-eat organic vegetables (n=3200)

Organic vegetable type	Number of samples (%)
Those grown in close proximity or in contact with soil (n=2349): Broccoli Cabbage Carrot Cauliflower Celeriac Celery Cress Lettuce Mushrooms Radish Spring onions Water cress Other (spinach, leeks, shallots, chard)	209 159 478 70 11 193 12 415 425 17 87 65 208	(7) (5) (15) (2) (<1) (6) (<1) (13) (13) (<1) (3) (2) (7)
Non soil contact vegetables (n=851): Cucumber Pepper Tomato Other (babycorn, cherry tomato)	221 184 428 18	(7) (6) (13) (<1)
Total	3200	(100)

Type of Outlet

Over three-quarters (79%; 2528/3200) of samples were collected from supermarkets, 214 (7%) from health food shops, 175 (5%) from farm shops/markets, 70 (2%) from greengrocers, 54 (2%) from doorstep box-scheme deliveries, 37 (1%) from market stalls, and 24 (1%) from warehouse/storage areas. Other outlets (butchers, garden centre, nursery shop, and organic product specialist) accounted for 76 (2%). For 36 (1%) of outlets visited this information was not recorded (Fig. 2).

Packaging & Display

Of the ready-to-eat organic vegetables sampled (3200), 2586 (81%) were pre-packed vegetables and 567 (18%) were unwrapped or loose on sale. For the remaining 47 (1%) of samples this information was not recorded. The vast majority of samples obtained from supermarkets (96%; 2434/2528) were pre-packed. Most of the samples (96%; 3067/3200) collected were displayed and stored in a clean environment as judged by the Sampling Officer, while 59 (2%) were not. For 74 (2%) of samples this information was not recorded. A quarter of samples (24%; 770) collected had visible soil contamination, however most did not (73%; 2339). For the remaining 91 (3%) of samples this information was not recorded. Of the samples that did have visible soil contamination most were unwrapped or loose on sale (78%; 590/770).

Country of Origin

Of the 3200 organic vegetables sampled, the majority were imported (70%; 2240) with most originating from Spain (31%) and the Netherlands (15%) (Table 5). Of the 30% (943) of samples produced in the UK, nearly a quarter (24%; 226/943) originated in England, however most (67%; 634/943) samples specified UK only.

Table 5. Country of origin of ready-to-eat organic vegetables collected (n=3200)

Country of Origin	Number of samples		(%)
United Kingdom (n=943): - England - Northern Ireland - Scotland - Wales - UK	943	226 12 8 63 634	(30)	(24.0) (1.0) (1.0) (7.0) (67.0)
Other EC Countries (n=1774): Austria Belgium France Germany Greece Ireland Italy Netherlands Portugal Spain	6 47 90 1 2 2 176 464 7 979		(<1) (2) (3) (<1) (<1) (<1) (5) (15) (<1) (31)
Third Countries (n=316): Argentina Canary Islands Channel Islands Egypt Israel Mexico Morocco New Zealand Tunisia USA Zambia Zimbabwe	8 38 1 23 162 51 1 10 3 17 1 1		(<1) (1) (<1) (1) (5) (2) (<1) (<1) (<1) (<1) (<1) (<1)
Produce of two or more countries (not UK)	19		(<1)
Not recorded	148		(5)
Total	3200		(100)

Identification as organic (Certification Body Number)

The majority (81%; 2585/3200) of organic ready-to-eat vegetable samples were identified as organic by labelling containing a UK certification body number (Fig. 3), and of these almost three-quarters (74%; 1919) were by the Soil Association. The remainder (11%; 364) was identified as organic by other EC Member State certification bodies. However, for 252 (8%) of samples this information was not known.

Discussion

This study has shown that the vast majority (99.5%) of the uncooked ready-to-eat organic vegetables sampled at retail in the UK were of satisfactory/acceptable microbiological quality. Only 0.5% were classed as unsatisfactory according to published guidelines¹². Unsatisfactory results were due to E. coli and Listeria spp. (not L. monocytogenes) counts at 10² cfu/g or more. E. coli is a faecal organism and both E. coli and Listeria spp. are environmental microorganisms that are found in soil and water. Therefore, vegetables may easily become contaminated with these bacteria. However, the absence of pathogens (L.monocytogenes, Salmonella, Campylobacter, and E. coli O157) and the low incidence (1.5%) of E. coli and Listeria spp. associated with these organic vegetables indicates that overall agricultural, hygiene, harvesting, and production practices were good.

The greatest growth in organic sales has been through the main multiple retailers (supermarkets). More consumers will have access to these outlets on a national basis than can be reached by other distribution methods, such as farmers' markets and box schemes⁵. In this study over three-quarters (79%) of vegetables were collected from supermarkets and this may reflect the continued phenomenal growth of the organic market that has occurred since 1998/99 (annual market growth of 100% during the last two years) ^{5, 17.} Overall, 80% of fresh fruit and vegetables sold in the UK are imported³. A lower proportion (70%) of imported vegetables was examined in this study. However, vegetables were collected during the months of May and June and this may reflect market supply due to the issue of seasonality. Presentation of organic vegetables sold by supermarkets is generally in a pre-packed format. This is partly to do with the need to retain the integrity of the organic vegetables as well as to provide information to consumers via labelling³. This is reflected by the findings in this study where most (81%) of the organic vegetables sampled were pre-packed.

Between 1992 and 1999 foodborne outbreaks made up over a third (35%; 1408/4083) of general outbreaks reported from England and Wales, and of these foodborne outbreaks, ready-to-eat fruit and vegetables accounted for a very small proportion (4.3%; 60 affecting 2170 people)¹¹. This is the first such study to provide information on the microbiological quality on uncooked ready-to-eat organic vegetables. This study was not a comparative study and therefore did not aim to produce conclusive