Example 6: Pistachio nuts in West Asia

Introduction

Pistachio nuts in this Region are grown commercially in Afghanistan, Iran, Iraq and Turkey. In the first three countries the nuts are usually dehulled very soon after harvest and the nuts in shell are then stored and processed (fast lane). In Turkey, however, the nuts are stored in-hull, sometimes for many months, or even for years (slow lane). Early de-hulling has the advantage of avoiding staining of the shell, but has the disadvantage of exposing the split nuts at an early stage to Aspergillus flavus and A. parasiticus spores which have the potential to produce aflatoxin.

The pistachio nut is the fruit stone of Pistacia vera. Each fruit has a single stone which consists of a kernel covered by a testa and enclosed in a shell. The shell itself is enclosed in a protective hull. One month or more before maturity the shell usually partially splits within the hull. The hull should remain intact, but sometimes it also splits naturally prior to harvest and these 'early splits' and 'growth-splits' are particularly susceptible to aflatoxin contamination. Early splitting allows invasion by insects, particularly the navel orangeworm [Amyelios transitella (Walker)] and insect-damaged nuts are associated with a high risk of aflatoxin contamination.

Different varieties of pistachio trees are grown in the Region. In Iran, Iraq and Afghanistan varieties are grown which tend to have large nuts with hulls which are relatively prone to early splitting, although climatic factors also have a bearing on this. In Turkey the pistachio varieties tend to yield smaller nuts with greener kernels and these have hulls which are not very susceptible to early splitting.

De-hulling can either be carried out using a wet-process or a dry process. The former is used by large-scale factories and some medium-scale factories, whereas the latter process is carried out mostly in cottage industries.

Collecting a representative sample of pistachio nuts for aflatoxin testing is particularly difficult because it has been established that the incidence of significantly contaminated nuts is usually very low, in the order of 1 nut in 10,000 to 1 nut in 30,000 (or more). This means that even a 30 kg sample, as recommended by the European Union, may only contain a single contaminated nut. However, pistachio nuts can contain very high levels of aflatoxin, up to 1,000,000 ng, so a single contaminated nut could give a level of 33 µg/kg (ppb) in a 30 kg sample.

The nuts are exported in a number of forms including: whole raw nuts for further processing; roasted and salted nuts with or without red staining; and kernels for the food manufacturing industry.

This example is based on a blend of two studies that covered the pistachio commodity system across the whole Region. The wet process of de-hulling followed by segregation by flotation is illustrated here. Although this 're-wetting' introduces a potential risk of further aflatoxin contamination, this can be eliminated by the correct use of efficient mechanical driers. If such driers are NOT available, then a dry process should be used.

Pre-requisite programmes that must be in place include: GAP, GSP, GMP, and the more specific 'Codex Recommended International Code of Hygienic Practice for Tree Nuts (CAC/RCP 6-1972) (FAO/WHO,1994b)'. The latter covers basic hygienic requirements for orchard, farm processing, and commercial processing.

Task 1 - The HACCP team

An appropriate HACCP team will include: HACCP specialist, factory manager, factory quality assurance manager, mycotoxicologist, mycologist, edible nut specialist, procurement agency manager, laboratory manager, socio-economist, and representatives of the Department of Agriculture and of the private sector farming, domestic trading and export sectors.

Tasks 2 and 3 - Product description and intended use.

The product description and intended use is given in Table 13.

Target level is < or = 2 µg/kg aflatoxin B₁ for export to the EU and < or = 20 µg/kg total aflatoxin for export to the US.

Tasks 4 and 5: The Commodity Flow Diagram (CFD), Verified

The CFD was established and verified, as in Figure 13.

Task 6: Mycotoxin hazard analysis and identification of possible control measures.

Hazard Analysis

a) Identification of mycotoxin hazard

Aflatoxin is the only mycotoxin hazard for which the EU and US have regulatory limits for edible nuts; consequently, it is the only mycotoxin considered.

b) Identification of steps in the Commodity Flow Diagram (CFD) where mycotoxin contamination is most likely to occur.

Steps 1: On farm, pre-harvest.

This is the step when most aflatoxin contamination will usually occur, and is associated with damage to the hull (Doster, M. A., 1995). This damage is either caused by early-splitting when the hull cannot accommodate the splitting of the shell within, or by growing-split. Subsequent invasion of split-nuts by insects, particularly the navel orangeworm, compounds the problem.

Step 2: On-farm harvesting.

Aflatoxin contamination may occur at this step if pistachio nuts are allowed to fall naturally and remain on the floor, ungathered, for an extended period.

Pistachio nuts can be pre-disposed to subsequent mould and aflatoxin contamination when harvesting is achieved by shaking the tree. This can cause tearing of the hull which can let in mould spores.

Table 13. Product description and intended use of pistachio nuts

Fig. 13. HACCP Process Flow-diagram: Pistaccio Nuts, roasted - West Asia

Note: A factory will usually either be procuring and processing nuts from the "slow-lane" or the "fast-lane", not both at the same time.

Steps 3 to 8 are the 'slow-lane' process flow.

Step 3: Farm drying of nuts in hull.

This is a step designed to reduce aflatoxin contamination by drying to a 'safe' moisture level before storage.

Step 4: Farm, storage of nuts in hull

Aflatoxin contamination is possible if nuts are put into store at an 'unsafe' moisture content, particularly if nuts with damaged hulls are stored.

Step 5: Primary and Secondary Trader

Aflatoxin contamination is possible, particularly if purchased directly from a farmer at harvest.

Step 6: Factory Procurement and storage of nuts in hull (slow lane)

The risk of aflatoxin contamination is low at this step because the nuts have usually dried to a 'safe' moisture content by this time.

Step 7: Factory de-hulling

1. Slow lane

De-hulled nuts are usually further processed without delay, and there is no risk of aflatoxin contamination at this step.

2. Fast lane (Nuts direct from farms)

The wet-process of de-hulling can pre-dispose nuts to subsequent aflatoxin contamination (see step 10).

Step 8: Factory floatation

Levels of aflatoxin will be significantly reduced at this step.

Step 9: Factory drying (and storage in the fast lane)

No aflatoxin contamination is likely at this step, provided that drying to a safe moisture content can be completed within 24 hours. Inadequate drying will leave nuts in the fast lane process susceptible to aflatoxin contamination during subsequent storage.

Step 10: Factory sorting

Levels of aflatoxin will be significantly reduced at this step.

Step 11: Roasting and salting

No aflatoxin contamination is possible at this step. Roasting would be expected to reduce levels of aflatoxin.

Step 12: Factory, aflatoxin testing and grading

No risk of aflatoxin contamination at this step

Step 13: Factory packing

No risk of aflatoxin contamination, but inappropriate packing may make the nuts susceptible to future contamination if re-wetting occurs.

Step 14: Factory storage of finished product

Such storage is usually only short-term and there is negligible risk of aflatoxin contamination.

Step 15: Factory export

No aflatoxin contamination is likely at this stage, or during subsequent transportation. It is very important to select packages, for each consignment, which meet the customer's aflatoxin specification.

c) Possible Mycotoxin Control Measures

The most effective preventative control is to dry pistachio nuts to a water activity of 0.82 for short-term or 0.70 for long-term storage to prevent mould growth and aflatoxin contamination. At 25°C, these critical water activities translate to moisture contents of approximately 10% and 5 to 7 % respectively (Olsen, M., 1999).

Removal of aflatoxin contaminated nuts by means of physical segregation is the most effective control measure for reducing levels of aflatoxin in a batch to an acceptable level. Examples of segregation techniques are: hand-pick sorting, floatation, sorting by size, and the rejection of excessively contaminated batches.

Tasks 7 to 10: Development of a HACCP Plan

A worksheet summarising the HACCP Plan for pistachio nuts is given in Table 14, and development of the plan at each step is discussed below.

Step 1: Farm, preharvest - IPSM/GAP

Pre-harvest aflatoxin contamination can be reduced by applying Integrated Phytosanitary Management (IPSM) (Boutrif, E., 1998) which seeks to minimise the mould spore count in the orchard and minimise the chances of insect attack. Removal or burial of tree litter has been suggested as a measure that would significantly reduce spore count.

Step 2: on-farm harvesting - CCP1

This step is classified as a CCP, with segregation and removal of nuts with damaged hulls as the control measure. This CCP will reduce the mould hazard to acceptable levels, and remove a very high proportion of aflatoxin that has been produced pre-harvest.

The critical limit will be set at <=1% damaged nuts remaining after inspection and the CCP will be monitored by visual observation.

Post-harvest aflatoxin contamination can occur as a result of harvesting by shaking the tree. This can cause tearing of the hull which can let in spores and allow aflatoxin to be produced. Nuts which are allowed to fall to the ground naturally may also become mouldy if they are left on the ground for an extended period. It is considered GAP to place a plastic sheet or tarpaulin under a tree due for harvesting. Pistachios are then either harvested by hand or natural fallers are collected daily.

Steps 3 to 8 are the 'slow-lane' process flow.

Step 3: Farm, drying of nuts in hull - CCP2

This step is identified as a CCP with drying to a safe moisture content as the control measure. Research is required to determine the moisture content of a nut in hull that corresponds with a water activity of 0.7 at 25°C. The critical limits will then be set in terms of number of days sun-drying required to achieve the safe moisture content.

Step 4: Farm, storage of nuts in hull - GSP

Sound nuts at a safe moisture content will store well provided that GSP is in place.

Step 5: Primary and Secondary Trader - GSP

Good storage practice is necessary to prevent re-wetting of the pistachios and to control insect damage.

Step 6: Factory, procurement and storage of nuts in hull (slow lane) - GMP/GSP

It is considered GMP to procure high-quality nuts, with a low percentage of damaged hulls. A premium price for such nuts will encourage traders and farmers to produce this quality, and rejection or a low price will discourage production of poor quality nuts.

Good storage practice will enable long-term storage of nuts in hull, if required. Regular fumigation will be required to control insects.

Step 7: Factory de-hulling - GMP

The wet process should only be used if the factory has a reliable, efficient mechanical drier for use at Step 10. Failing this, the dry process should be used.

Step 8: Factory floatation - CCP3

This step has been identified as a CCP with the removal of nuts that float as the control measure. Studies indicate (Schatzki, T., 1996) that in the order of 40% of aflatoxin will be removed. This CCP, in conjunction with subsequent CCPs will reduce levels of aflatoxin to an acceptable level in a high proportion of batches. Monitoring will be by visual inspection, using trained staff, to check that <1% 0f floating material remains.

Step 9: Factory drying - CCP4

This is a CCP for the fast-lane process, when de-hulled nuts are stored (or exported) prior to further processing. Slow-lane nuts are moved on to step 11 without delay and this is not a CCP for this process.

The control measure is to dry the nuts to a moisture content of 10% within 24 hours, for short-term storage, and to 6% within 48 hours for long-term storage. Critical limits will be set for the operating temperature of the drier, and the dwell time in the drier. The critical limits for temperature will be monitored by regular, or continuous, temperature reading obtained using a calibrated thermometer.

Step 10: Factory sorting - CCP5

The control measure at this CCP is to remove small nuts (scalp) and hand-pick sort (HPS) to remove damaged nuts. Studies in the USA (Schatzki, T. F., 1996) indicate that small nuts (>30 nuts per ounce) contain between 20 to 40% of aflatoxin originally present in a batch. After removal of small nuts, subsequent hand-pick sorting to remove damaged nuts (particularly insect damaged) and nuts having pieces of hull still adhering to the shell, will further substantially reduce levels of aflatoxin. When applied to fast-lane nuts, the hand-pick sorting is extended to include the removal of nuts with stained shells, and this will make the control measure even more effective in reducing levels of aflatoxin.

Monitoring of this CCP is achieved by visual observation by staff trained to detect an unacceptable level (e.g. 5%) of damaged or discoloured nuts remaining after HPS sorting.

Step 11: Roasting and salting - GMP

No aflatoxin contamination is possible at this step. Roasting will reduce levels of aflatoxin, perhaps by of the order of 20%.

Step 12: Factory, aflatoxin testing and grading - CCP6

This step will be a CCP initially, but as aflatoxin control improves the HACCP team may well use aflatoxin testing at this step for verification purposes only.

The control measure is to carry out aflatoxin testing on every batch and to grade the batches accordingly. Unfortunately, a large sample size of 30 kg is required, as explained in the Introduction. The critical limits will be set at the customer specification, e.g. 2 µg/kg aflatoxin B₁ for the EU and 20 µg/kg aflatoxin B₁ for the US. The critical limit is monitored by performing rapid, semi-quantitative aflatoxin testing on representative samples. Alternatively, samples could be sent to an accredited laboratory for certification purposes.

Step 13: Factory packing - GMP

Appropriate packaging is required to prevent re-wetting and to retain other quality factors. Air-tight packaging, either under vacuum or over nitrogen is preferred.

Step 14: Factory storage of finished product -GMP

Storage at ambient temperatures is adequate for short-term storage, but longer term storage requires a reduced temperature of less than or equal to 10°C.

Step 15: Factory export - GMP

Batches of pistachios are selected for export to meet the customers' aflatoxin specification, using information gained at step 12.

Task 11: Establish verification procedures

The HACCP Plan will be audited quarterly, and amended as necessary.

Task 12: Establish documentation and record keeping

The HACCP Plan will be fully documented, and appropriate records will be kept at each CCP.

Table 14. HACCP Plan Worksheet, Pistachio nuts, roasted, produced in West Asia.