Non-enzymic browning of sulphited dehydrated carrot is measured by extracting brown materials with 2% acetic acid containing 1 % formaldehyde, followed by precipitation of interfering pigments absorbing at 420 nm with 10% lead acetate and ethyl alcohol. The presence of sulphur dioxide is shown to reduce the absorption at 420 nm of a glucose-glycine browning solution and an extract of dehydrated carrot, the effect depending on time of incubation and exposure to light. The use of formaldehyde in the extraction solvent overcomes the effect of sulphur dioxide at concentrations up to 19 200 parts/million. The presence of carotenoids is shown to increase the absorption of browning extracts at 420 nm leading to high results. The interference from pigment materials is overcome by precipitation with lead acetate and ethyl alcohol. The use of both formaldehyde and lead acetate has no additional effect on browning determinations.Comparative tests of the proposed lead-alcohol precipitation method with an alcohol precipitation method, using both a glucose-glycine browning mixture and an extract of dehydrated carrot, shows only the lead-alcohol precipitation method to overcome errors due to carotenoid pigments either originally present in the extract or added as 8-carotene, while the additional use of formaldehyde during extraction is necessary to overcome errors due to sulphur dioxide.Browning of dehydrated sulphited carrot stored for up to 20 days at 50 "C decreased with time of storage when measured by the alcohol precipitation method and in dehydrated non-sulphited carrot, browning showed only a slight increase with storage time. When measured by the lead-alcohol precipitation method, browning showed only a slight increase in stored dehydrated sulphited carrot, but a marked increase in stored dehydrated non-sulphited carrot, in agreement with visual observations.

The influence of blanching and sulphiting of carrot on the stability of carotenoids of dehydrated carrot was evaluated. The carotenoid content of untreated and treated carrots was measured after dehydration and during storage of dehydrated carrot at 37°C. Sulphiting was found to have a marked effect on the stability of carotenoids of both unblanched and blanched carrots during dehydration and storage at 37°C. The effectiveness of sulphur dioxide was reduced by increasing blanching time to over 1 min, the period in which the carrot becomes just adequately blanched. Even 9621 pg g-I SO, in over-blanched carrot was not as effective as less than one-quarter of this concentration in carrot that had been just adequately blanched. The combination of sulphiting, and blanching to a level sufficient to inactivate peroxidase activity, is considered to be the most effective method for enhancing the storage life of the product, and optimisation of the blanching process is highly desirable in order to gain the maximum benefit from the SO, treatment.

The effect of tomato slices being dipped in 1% (w/v) calcium chloride (CaCl 2 ), 2% potassium metabisulphite or 2% sodium chloride (NaCl) solutions before oven-drying on the carotenoid loss and browning development in the dry powder stored in air at 40ЊC for up to 90 d were tested. CaCl 2 greatly increased carotenoid loss after 30 d until it was almost complete at 90 d, whereas metabisulphite decreased losses over most of the storage, only approaching the untreated values at the end. NaCl had no effect on carotenoid loss.Conversely, CaCl 2 almost completely suppressed browning, whereas metabisulphite and NaCl had little or no effect on the rate of browning, but did reduce initial browning during drying. The untreated powder exceeded the shelf-life criteria by the end of drying to about 12% moisture content.

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