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Examination of the effect of domestic cooking on acrylamide levels in food
Project Code: C03037
Leatherhead Food International
This document is the final report on a project considering acrylamide formation in domestically cooked food. Investigations covered potatoes cooked in a variety of ways, and looked at factors which might affect the levels of acrylamide formed. There were also a limited number of investigations carried out on onions.
The first set of experiments measured acrylamide formation in potatoes that had been baked, boiled, roasted and saut´ed. Potatoes were either cooked from fresh (all cooking methods), or were frozen before cooking (boiled, saut´ed and roasted). No acrylamide was detected in the raw potatoes, or in boiled potatoes. There was also no acrylamide formation in potatoes that had been microwaved in their skins. Acrylamide was found in potatoes that had been saut´ed, roasted or oven-baked in their skins. Acrylamide was increased in potatoes that had been cooked from frozen, except in the case of boiled potatoes, where there was still no acrylamide formed.
Acrylamide formation in onions that had been boiled, fried or baked was also determined. No acrylamide was detected in raw onions, or in onions that had been boiled or baked from fresh. Acrylamide was found in fried onions, with lower levels in onions fried after freezing than in onions fried from fresh. Acrylamide was also found in onions baked after freezing, although at much lower levels than in the fried onions.
The next investigation was of acrylamide levels in commercially-produced chips sold frozen for cooking at home. Chips were cooked according to the packet instructions. In all cases the chips *as sold* were found to contain acrylamide, suggesting that the chips were partially cooked already. Results of the investigation showed a range of acrylamide levels, varying with sample and cooking method. Given that the chips were cooked according to instructions on the packet, it is clear that such cooking instructions are a key factor in controlling the levels of acrylamide formed when the products are cooked at home.
Repeated use of oil for frying chips was also investigated. Corn, sunflower, rapeseed and vegetable oils were used, as well as lard, and each was used to cook five separate batches of chips. Results showed that for most of the oils there was no effect on acrylamide levels when the oils were re-used. For the rapeseed oil there was a slight indication that the acrylamide levels increased with repeated use of the oil, and this may warrant further investigation.
Acrylamide formation in different potato varieties was assessed in retail samples purchased from supermarkets locally, and baked, roast or chipped as recommended either on the packet or according to the British Potato Council website. Differences were seen between varieties cooked by the same method. In particular, Desiree potatoes which were recommended as *general purpose* showed higher levels of acrylamide when cooked (roast or chips) than other potatoes tested. Further investigation of varieties was carried out in combination with storage and pretreatment variables, reported below.
Studies reported in the literature have suggested that lighter-coloured chips are lower in acrylamide, so this was investigated in this project by cooking chips to either yellow or brown and comparing acrylamide levels. Results showed that whilst cooking to the lighter colour did result in lower levels of acrylamide, not all chips were considered edible when cooked to the lighter colour. The level of cooking required, and hence colour of the chips was found to vary with the potatoes used.
In order to reduce the levels of acrylamide formed in foods cooked in the home, one of the aims of the project was to investigate the effect of simple pre-treatments on levels of acrylamide in roast potatoes and chips. For chips, the pre-treatments were washing or soaking in water for 30 minutes or 2 hours, and these were compared with a control which had had no pre-treatment. All of the pre-treatments led to lower acrylamide levels than the control, with chips pre-soaked in water for 2 hours having the lowest levels of acrylamide. The same pre-treatments were investigated for roast potatoes, with the addition of par-boiling as a pre-treatment. Replicate results were more variable for the roast potatoes than for the chips, and so the effects of pretreatments were not so easily seen. Par-boiling or soaking for two hours did reduce the levels of acrylamide compared with controls. However, par-boiled roast potatoes had higher levels of fat than potatoes treated using the other methods, which is a factor that needs to be considered when recommending cooking methods to the consumer.
The effect of pre-treatments was also examined on three varieties of potatoes (Cabaret, Maris Piper and Desiree) stored under controlled conditions. Two of the varieties selected were varieties commonly sold in retail outlets in the UK (Maris Piper and Desiree), and the third (Cabaret) was a variety believed to be low in reducing sugars. Sampling was at three time points, representing short term (6 weeks), mid term (16 weeks) and long term (34 weeks) storage. At each time point, potatoes were chipped, pre-treated and then fried until cooked. Acrylamide levels were compared with control chips (no pre-treatment). Asparagine and sugar levels were measured in samples of the raw potatoes. It was seen that acrylamide levels were higher in those samples with higher reducing sugar content, and that this varied between varieties as well as increasing on storage. Stored samples were therefore higher in acrylamide. For comparison, a number of retail potato samples were purchased to coincide with the second and third time points. One pre-treatment was used (30 minute water soak) and in all cases (all varieties, both time points) this was found to lead to lower acrylamide levels than in control samples with no pretreatment.
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