The Effect of Processing on Residues in Foods - ACS Symposium

Chapter 19

The Effect of Processing on Residues in Foods

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The Food Processing Industry's Residue Database Henry B. Chin National Food Processors Association, 6363 Clark Avenue, Dublin, CA 94568 While the casual observer may feel that the testing of foods for pesticide residues by industry has been limited to recent efforts by retailers of fresh fruits and vegetables, the actual record shows that the manufacturers of processed foods have been actively testing and evaluating pesticide residues in foods since the early 1920's. Attention was focused at that time on the effect of sulfur spray residues on the shelf-life of canned fruits. Research was conducted to determine effective methods for the removal of spray residues in those situations where simple peeling was not an alternative (1). During the 1960's National Food Processors Association, NFPA, (then known as National Canners Association) conducted several studies on the effects of food processing operations on residues of DDT, Parathion, Carbaryl, Diazinon, and Malathion in foods (2). In the early 60's NFPA formed a group known as the Committee of Canning Industry Analytical Chemists to work on analytical methods, including methods for pesticide residues. There have been other industry driven efforts to study the effect of pesticides on the development of taints (off-flavors) in canned foods. Thus, the food processing industry has a long and diverse history in evaluating and controlling pesticide residues in processed foods. The data which the industry has accumulated, individually within companies and that cooperatively developed with NFPA, have shown that residues are very infrequently encountered in processed foods and when found are present at levels lower than in the raw agricultural product. Concerns which have been expressed about residues in processed foods frequently reflect a lack of knowledge of food processing operations and their effect on residue levels. In this discussion, the parameters of many processing operations will be discussed, the effect of these individual operations will be reviewed, and the efforts of NFPA to develop a comprehensive database will be presented.

0097-6156/91/0446-0175$06.00A) © 1991 American Chemical Society

Tweedy et al.; Pesticide Residues and Food Safety ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

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Food Processing Operations Unit operations in processing typically include washing the raw product with fairly large amounts of water,frequentlyusing high pressure sprays and often incorporating surfactants or other washing aids; peeling the product mechanically with knives, abrasive discs or water; blanching with hot water or steam; and in the case of canned foods, the cooking of the product at temperatures at or above that of boiling water. Thus, the chemicals which may be present are subject to not only physical removal by washing or peeling, but also acid or base hydrolysis and thermal degradation. Some specific examples of foods and their processing illustrate the processing operations. California produces 80% of the tomatoes which are canned in the United States. In 1982, 8.7 million tons were produced. Tomatoes are mechanically harvested, trucked to the processing plant, conveyed into the plant in water flumes, and are washed with high pressure sprays of water. Most processors now peel tomatoes with lye or steam rather than mechanically or by hand. In the lye peeling process the tomatoes are either immersed or sprayed with a solution of boiling 10-20% lye. The excess lye and adhering peel are removed by water sprays. The tomatoes, like many fruits, are not blanched but go directly into cans along with juice and sometimes citric acid to adjust the level of acidity. The cans are then processed at 100 ° C for about half an hour. Tomatoes, like some other fruits, are also processed into comminuted products like tomato juice and tomato paste. In this process, the fruit is usually not peeled first, but rather chopped and pulped before the peels and seeds are screened out. Many processors heat the chopped tomatoes to 100 °C to inactive enzymes before pulping. The product gets additional heat treatment during concentration and canning. Spinach represents a category of products which are given a more severe heat process. Spinach is usually immersed in water with a surfactant and sprayed with high pressure water in order to remove extraneous materials and residues. The raw product may then be blanched in hot water or steam. Because spinach is a product which is subject to significant food borne illness if underprocessed, the thermal process is more severe than that given tomatoes. It is usually processed at temperatures of 115-122 C for 40 to 120 minutes depending on the size of the container. e

Effect of Processing on Residues The purpose of the previous discussion was to provide an understanding, for those who do not work in the food processing industry, of the magnitude of washing and heat treatments used on raw agricultural products. The net effect of these operations is to reduce residues which may be on the raw product.



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Washing of the produce has been shown to reduce the levels of residues which can be dissolved or physically dislodged from the raw product. For example, when lead arsenate sprays were widely used, some authorities recommended that wash waters be acidified to facilitate the removal of these residues. The extent to which residues can be dislodged depends upon many factors, including the plant matrix and weathering of the residues on the crop. Rainfall after the application of a pesticide can also reduce the levels of the residue on the product. When the effect of washing on residues is examined, percentage decreases may be significantly affected by whether the easily dislodgable residues have already been removed by handling or rainfall in the fields. Thus, the magnitude of removal observed in field studies is sometimes difficult to correlate with decreases observed in actual commercial practice (5). Data developed by NFPA researchers in the late 1960's (2) showed that certain residues, such as Carbaryl and Diazinon on tomatoes could be reduced 97% by washing. In contrast, Parathion residues on spinach appeared not to be removed by a water wash. The incorporation of a detergent in the wash water increased removal of Parathion in spinach by nearly three-fold over than removed by water alone. Food processing often provides opportunities for the hydrolysis of residues under both acid and alkaline conditions. Macerated fruit pulps and juices will generally have pH's in the range of 3.5-4.2 where some acid hydrolysis can occur. The conditions of peeling with boiling lye can certainly promote alkaline hydrolysis. Thus, it would be reasonable to expect that the operations which may promote hydrolysis, especially when combined with heat, will cause significant degradation of some of the residues which may be present. Controlled field treatment studies have also shown a pattern of effective removal of residues during processing. In some instances residues can approach complete removal. For example, over 90% of the Benomyl residues on apples is removed by the time the apple is processed into canned apple slices and 86% of the residue on tomatoes is removed by the time it is processed into canned tomato juice (4). Unfortunately while degradation and hydrolysis is desirable for most pesticides, in terms of their presence in the processed product, there some chemicals which will produce undesirable degradation products. Some of the ethylene-bisdithiocarbamate (EBDC) fungicides which survive washing, peeling, and the other operations which may precede canning can be degraded to residues of ethylenethiourea (ETU), which is classified as a B2 carcinogen by EPA. Washing procedures have been suggested to promote the removal of EBDCs. It has been shown, however, that when residues of EBDC were less than 0.3 ppm on unwashed tomatoes no ETU was detected in the canned juice (5). This emphasizes the point that if residues are not present in significant amounts on the raw produce, the production of toxic metabolites should not be of concern.


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Focal Point of Control Is at Point of Application

This then brings us to the next point, which is that many processors have required for many years that their suppliers adhere to strict pesticide application reporting requirements and that applications are made in accordance with registration standards. The proper focal point for the prevention of illegal and unnecessary pesticide residues is the field where the crops are grown. Since 1960, the food processing industry has had in place a program known as the NFPA Protective Screen Program. This is a set of detailed recommendations that emphasis the importance of a detailed knowledge of sources of raw produce and pesticide chemicals which are permitted for crop production. Many processors have also restricted the pesticides which their suppliers can use. Some processors have records available in many instances which demonstrate that fears about excessive and unnecessary usage of pesticides are unwarranted. This is illustrated by two pesticide application reports of chemicals applied to tomatoes in California during 1989. The first application report consisted only of four chemicals (Vapam, Treflan, Monitor, and Dusting Sulfur), two of which were pre-plant herbicides. This was a crop which matured early in the season and avoided much of the troubles associated with an unseasonal rain. The second application report shows more usage of pesticides (Roundup, Gamoxone, Asana, Guthion, Sulfur, Dithane, and Methyl Parathion), but again two of the applications were of pre-plant herbicides. This crop apparently was affected by the unseasonal rains and required more insecticidal and fungicidal treatments. Nevertheless the numbers of chemicals used were rather limited. Obviously when crops are purchased in the open market for processing, it is much more difficult for processors to acquire these types of records. Study of Commercially Grown Crops

Much of the data which is available and which has been used to examine the fate of pesticides during processing have been from controlled studies, like those used by EPA and the chemical companies in the registration process. For regulatory and scientific purposes, these controlled studies are obviously desirable. The amounts, application and harvest times are controlled to ensure that significant residues are present at the time of harvest so that the residues can be followed during processing. The drawback is that these studies don't necessarily reflect the real world, usually by overestimating residues present. During the summer of 1989 we had the occasion to follow commercially grown tomatoes from arrival at the processing plant through to the finished product. We also had access to the pesticide application reports. The tomatoes were analyzed unwashed, after washing, after the hot break operation, during tomato juice production, after concentration, and



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after canning. The tomato pomace was also analysed. Tomatoes from four fields were followed in this manner. When the samples were analyzed by both multi-residue and single residue methods only Methyl Parathion and EBDC were detected. In two of the four fields which were sampled, Methyl Parathion was applied. Traces were present on the unwashed tomatoes and these traces were not removed by washing (Table I). However, in both cases the chemical was either significantly reduced during the food processing operations or removed completely. The residues stayed with the pomace. Fourfieldswere treated with EBDC fungicide at three pounds per acre, 10-20 days before harvest, but it was detected in only tomatoes from two of the fields when they arrived at the canning plant. Washing of the samples produced variable results in terms of percentage removal but the residue level in the washed tomatoes was determined to be 0.055 and 0.040 ppm (Table II). The literature suggests that EBDC residues of less than 0.30 ppm pre-processing would not produce detectable ETU levels in the finished product. The analysis of the canned tomato paste, after three-fold concentration of the solids, showed no detectable ETU. Data on Residues in Processed Foods The foregoing was intended to provide a basis for the reader to evaluate actual residue data which has been accumulated by NFPA. It seems that almost all compilations of pesticide residue data in foods are individually subject to specific criticisms. Individual databases may be criticized for having too few samples, covering too few pesticides, or having inadequate quality assurance documentation. However, when taken as a whole, all of the databases consistently demonstrate that pesticide residues are infrequently encountered in processed foods. Table III summarizes the results of data from both industry sources, the California Department of Food and Agriculture, and the Florida Department of Agriculture and Consumer Services. In spite of the disparate nature of the sources of the data, the data when combined does show the effectiveness of pre-processing controls and processing on residues in processed foods. This is illustrated by the significant increase in the numbers of non-detectable samples found for processed foods as compared to non-processed raw products. Members of NFPA regularly analyze raw and finished products to obtain residue data that is collected and compiled by NFPA. In 1988, NFPA assembled pesticide residue data for processed and raw products as part of a contract performed for EPA. Of some 85,000 samples of raw and finished products, 81.2% had no detectable residues. Of the 20,310 samples of processed products which were included in this compilation, 93% had no detectable residues. NFPA is continuing to collect data from the industry in order to develop a sound database on pesticide residues in processed foods. A significant part of this effort will be to collect the quality assurance documenta-


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Table

I.

Methyl

P a r a t h i o n on C o m m e r c i a l l y Tomatoes

Grown

Concentration, 1 0.035 0.033 0.030 0.014 0.148

Samples Unwashed Washed Juice Paste Pomace

ppm 2 0.032 0.031 nd nd 0.235

T a b l e I I . EBDC and ETU R e s i d u e s on C o m m e r c i a l l y Tomatoes

Concentration, 1 0.081 0.055 nd nd

Samples Unwashed Washed Juice* Paste*

Grown

ppm 2 0.145 0.040 nd —

* = a n a l y z e d f o r ETU

Table

III.

Summary o f P e s t i c i d e

Residues

i n Foods

RAW

PROCESSED

Product

Tests

NUMBER N. D.

Det.

Tests

NUMBER N.D.

Apples Citrus Corn Peaches Potatoes Tomatoes

2159 2933 710 542 468 4419

2144 2766 710 534 460 4255

15 167 0 8 8 164

776 361 56 40 2168 7288

754 361 56 40 2168 7239

Det. 22 0 0 0 0 49


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tion which will accompany the data. In addition to the data from member companies, the NFPA laboratories will be conducting limited market basket surveys for selected pesticides in processed foods.


Literature Cited 1. Culpepper, C. W.; Moon H. H. Canning Age 1928, 8, 461-462. 2. Farrow, R. P.; Elkins, E. R.; Rose, W. W.; Lamb, F. C.; Ralls, J. W.; Mercer, W. A. Residue Reviews 1969, 29, 73-87. 3. Albach, R. F.; Lime, B. J. J. Agric. Food Chem. 1976, 24, 1217-1220. 4. Elkins, E. R. J. Assoc. Off.Anal.Chem.1989, 72, 533-535. 5. Marshall, W. D.; Jarvis, W. R. J. Agric. Food Chem. 1979, 27, 766-769. RECEIVED September 5, 1990


The Effect of Processing on Residues in Foods - ACS Symposium

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