In storage
The rate of degradation of aldicarb residues in stored potatoes was determined by analysing 100 individual tubers after 0, 1 and 6 months of storage under simulated commercial storage conditions. No residues of parent aldicarb were detected (<0.02 mg/kg) in any of the samples. The residues were mainly the sulfoxide metabolite with smaller amounts of the sulfone. The mean total residues calculated as sulfone after 0, 1 and 6 months storage were 0.45, 0.44 and 0.30 mg/kg respectively (Hunt, 1991).
In processing
Potatoes were treated at 10 times the normal rate to obtain high residues for a study of the effects of processing. Three replicate potato samples (90 kg each) were processed to chips, flakes and French fries by the following procedures which closely resembled commercial practice.
Chips: washing in tub for 5-10 min; sorting; peeling with Hobart Abrasive Peeler; removing damaged potatoes; cutting to about 1.5 mm slices, frying at 163-177°C for 90 seconds; draining and salting.
Flakes: washing in tub for 5-10 min; sorting; steam peeling for 45 seconds at about 0.55-1 MPa; scrubbing to remove peel; cutting into about 12.5 mm slabs; rinsing with tap water to remove starch; precooking 71-74°C for 20 min.; cooling to 32°C for 20 min; steam cooking at 95-100°C for 45 min.; mashing and mixing with pre-weighed additives; drying into thin sheet; milling to obtain finished potato flakes.
Frozen French fries: washing in tub for 5-10 min; sorting; steam peeling for 45 seconds at about 0.55-1 MPa; scrubbing to remove peel; cutting into about 6 x 6 mm shoestrings with French Fry cutter; blanching at 71-74°C for 10 min.; further blanching at 88-92°C for 3 min.; dipping into 1% dextrose solution for 30 sec.; air drying at 71°C for 18 min.; frying dried strips at 175-190°C for 60 sec.; draining and freezing at about -18°C.
A portion of the fries were further fried at about 175°C for 1.5 min in the laboratory under conditions similar to those used in fast-food restaurants. Potato flakes, chips, fries and wet and dry peel samples were analyzed for aldicarb residues in triplicate. The results are summarized in Table 7.
Additional potatoes were harvested and shipped directly to the laboratory where they were used to determine the effects of baking and microwaving on aldicarb residues. The tubers were cut in half and half of each tuber was frozen. The other half of each potato was then either baked or microwaved and frozen after cooking. All raw tuber halves were individually analyzed. Altogether 200 raw halves, and the 30 pieces from the baked and cooked groups corresponding to the raw halves with the highest residues (60 processed halves altogether) were analyzed.
The mean residues, expressed as aldicarb sulfone, before and after cooking were 0.98 and 0.63 mg/kg for baking, and 1.05 and 0.88 mg/kg for microwaving (Tew 1993c).
Table 7. Effect of processing potatoes on the residue levels of aldicarb.
|
Sample |
Aldicarb residues expressed as aldicarb sulfone, mg/kg |
Average change, % |
||
|
1st. proc. |
2nd proc. |
3rd proc. |
||
|
Fresh potato |
0.57 |
0.67 |
0.75 |
|
|
Flakes |
0.77 |
0.76 |
0.73 |
+15 |
|
Chips |
0.40 |
0.48 |
0.55 |
- 27 |
|
Wet peel |
0.42 |
0.33 |
0.40 |
- 41 |
|
Dry peel |
1.36 |
0.51 |
1.36 |
+ 65.3 |
|
Frozen fries |
0.25 |
0.29 |
0.34 |
- 55.5 |
|
Cooked fries |
0.34 |
0.40 |
0.42 |
- 41.7 |
