Quality of Peanut Products

1998

OBJECTIVE

To monitor the level of aflatoxin contamination in peanuts, peanut butter and other peanut products.

To check the compliance of peanut butter available in the Canberra market relative to Standard requirements.

Background

Peanuts and peas were legumes used to replenish soil fertility after decades of cotton growing in the southern states of America. In the 1870s an agricultural chemist first produced peanut butter. The development of peanut butter saw a rapid expansion of the market for this crop and today it is found in many kitchens for use as a sandwich spread or in many cooking recipes.

Peanut butter comes in two textured forms namely crunchy and smooth. In manufacturing, the peanuts are first roasted and then ground. The degree of grinding determines the final texture. Other ingredients used in the manufacture of peanut butter include sugar, salt, oil, hydrolysed oil and emulsifiers. These help to enhance the flavour, while the emulsifiers stabilise the oil component and reduce the appearance of an oily film on top of the peanut butter.

Peanuts are a nutritious food. They are a good source of protein, oil, B group vitamins (including folic acid), potassium, magnesium and fibre. Most of these ingredients are retained during peanut butter production.

Apart from the large manufacturers and distributors, peanut butter is also commonly sold through specialty health food stores and delicatessens. These products tend to be locally produced and sold in small quantities, often marketed as 100 % peanuts with no additives.

Aflatoxin contamination of peanuts has received a lot of attention in the past, particularly in the 1970s and early 1980s when much research was being conducted to investigate the nature of the problem. Aflatoxin contamination is caused by growth of the moulds Aspergillus flavus and Aspergillus parasiticus, which are commonly found in soils. They are usually benign, but under favourable growing conditions (appropriate temperature and humidity) the moulds infect peanuts which may result in high levels of aflatoxins. Contamination can occur both pre-harvest and post-harvest. For effective monitoring, the peanut crop is regularly tested throughout the manufacturing process. Aflatoxins are potent toxins and are known carcinogens, especially affecting the liver (Ref_4). Continual surveillance from the farm gate to the table, by industry and government authorities is intended to ensure that the risk of contaminated peanuts reaching the consumer in Australia is minimised (Ref_3).

This survey addressed aflatoxin contamination of peanut products and checked compliance of peanut butter available in the Canberra market to other standard requirements in the Code (Ref_1).

FOOD STANDARDS

The standard requirement for peanut butter is indicated in Standard M2 of the Code (Ref_1).

Peanut butter or peanut paste is defined asthe product prepared by comminuting roasted peanut kernels.

The Standard requires peanut butter or peanut paste to be manufactured so that it:-

  • must contain at least 200 grams per kilo protein;
  • may contain sugars, honey;
  • may contain not more than 20 grams per kilo of salt;
  • may contain not more than 30 grams per kilo of approved emulsifier;
  • may contain not more than 25 grams per kilo of hydrogenated vegetable oil;
  • may contain not more than 150 grams per kilo of added vegetable oil;
  • shall not contain more than 550 grams per kilo of fat and oil;
  • shall not contain more than 30 grams per kilo of water

Standard A12-Metals and Contaminants in Food provides standard requirements concerning aflatoxin contamination. As indicated in the standard, peanut butter or peanut paste, nuts and the nut portion of products containing nuts, the proportion of aflatoxins must not exceed 15 ug/kg. For all other foods, the maximum level must not exceed 5 ug/kg.

SURVEY

42 samples of peanut butter, 13 samples of peanuts and 6 samples of other peanut products were collected during the period July to August 1998. This included major supermarket stores and specialty health food stores. The following table shows the sample types collected:

Food

Examples

Number of Samples

Crunchy Peanut Butter

Crunchy, medium crunchy, super crunchy

24

Smooth Peanut Butter

Smooth

18

Peanuts

Granular, crushed, whole peanuts

13

Other peanut products

Chocolate-coated, peanut crackers, satay sauce, sugared peanuts

6

Upon receipt at the laboratory, each sample was homogenised and tested for aflatoxin contamination. For peanut butter samples, further testing was conducted for protein, fat, moisture, and sodium.

RESULTS

Protein

All the peanut butter samples passed the required 200 g/kg of protein. The average result was 243 g/kg, ranging between 211 - 281 g/kg.

Fat

The average fat content for peanut butters was 518 g/kg, ranging between 476 - 563 g/kg. Only two samples exceeded the 550 g/kg standard requirement, both only slightly above at 563 g/kg.

Moisture

The average moisture content for peanut butters was 10.3 g/kg, ranging between

5.4 - 15.2 g/kg. No samples exceeded the standard of 30 g/kg.

Salt

The standard indicates that peanut butter may contain not more than 20 g/kg salt (which is approximately equal to a sodium concentration of 786mg/100gm). Salt is determined on the basis of sodium concentration, which is then converted to salt content. With products containing a Nutritional Information Panel (NIP), the salt content is shown as sodium, usually in milligrams per 100 grams of food. For these products, it is interesting to compare the labelled sodium content to the tested amount (Table_1). Most results fell within 20% of the labelled content. For some, however, the variation is much higher, both above and below the amount stated on the label.

Labelled Sodium Content (mg/100g)

Sodium Content Determined (mg/100g)

Deviation %

629

569

11

275

368

-25

490

518

-5

455

547

-17

490

538

-9

580

523

11

460

477

-4

490

566

-13

455

596

-24

275

313

-12

327

431

-24

698

464

51

685

494

39

117

496

-76

415

409

1

415

331

26

630

110

471

630

131

379

470

491

-4

430

403

7

470

479

-2

No pattern was evident in the peanut butter samples analysed. The levels of sodium, when converted to salt content, fall below the limit of 20 g/kg for all samples tested.

Aflatoxins

Screening of samples for aflatoxins was conducted using the Afla-Cup immunoassay. The cut-off level for the test was 5 ug/kg, which is 3 times lower than Standard requirement.

All samples were screened using this method, and only 5 samples indicated a positive result. These included four peanut butter samples (two imported from overseas) and one chocolate coated peanut sample. No plain peanut samples were found to contain aflatoxins and this may indicate peanuts that are to undergo processing are stored in conditions suitable for mould growth.

The positive screening results only show that these samples contained levels of aflatoxins above 5 ug/kg, however, the test does not indicate the amount above this level. In the normal course of testing, these samples would be re-extracted and levels of aflatoxins determined using more sophisticated techniques. However, due to difficulties in obtaining standard material at the time of testing, more extensive examination could not be conducted.

DISCUSSION and conclusion

In general the peanut products were found to conform to the standards in relation to labelling and compositional requirements, despite some disagreement with sodium content. This is believed to arise because the code allows manufacturers different methods of determining salt content (ranging from chemical analysis of product to averaging of input components).

The screening method used to detect the presence of aflatoxins is not suitable for determining if levels were above 15 ug/kg. The presence of aflatoxins in 12% of samples tested at concentrations above 5 ug/kg indicates further testing of peanut products should be conducted with sufficient preparation to enable levels to be better quantified. This involves purchase of standards from overseas and a survey should only be commenced when these standards become available.

BIBLIOGRAPHY

Australia and New Zealand Food Authority, Food Standards Code (the Code), incorporating amendments up to and including Amendment 38, April 1998.

Food Act 1992 (ACT), reprinted as at 31 January 1996.

Aflatoxins article (paper endorsed by CSIRO Division of Food Processing), Food Australia, February 1989.

John de Vries (editor), Food Safety and Toxicity, CRC Press, 1997.

ACKNOWLEDGEMENTS

Sampling Officers: Helen Kivela and Chris Wixon

Sample analysis: Helen Kivela and Fiona Wojtas

Report: Simon Christen and Wayne Riley

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Quality of Peanut Products