Determination of phosphine in plant materials: method optimization and validation in interlaboratory comparison tests.

The optimization and validation of a method for the determination of phosphine in plant materials are described. The method is based on headspace sampling over the sample heated in 5% sulfuric acid. Critical factors such as sample amount, equilibration conditions, method of quantitation, and matrix effects are discussed, and validation data are presented. Grinding of coarse samples does not lead to lower results and is a prerequisite for standard addition experiments, which present the most reliable approach for quantitation because of notable matrix effects. Two interlaboratory comparisons showed that results varied considerably and that an uncertainty of measurement of about 50% has to be assessed. Flame photometric and mass spectrometric detection gave similar results. The proposed method is well reproducible within one laboratory, and results from the authors' laboratories using different injection and detection techniques are very close to each other. The considerable variation in the interlaboratory comparison shows that this analysis is still challenging in practice and further proficiency testing is needed.

Occurrence of acrylamide in selected foods and mitigation options.

Acrylamide reduction in certain food products is an important issue for both the food industry and academic research institutions. The present paper summarises past and current research on the occurrence and reduction of acrylamide in potatoes, bakery products, almonds, olives and dried fruit. In potatoes, the control of reducing sugars, process temperature and moisture is imperative to limit acrylamide formation. In bakery products, free asparagine and the type of baking agent largely determine acrylamide formation and present the starting points for reduction. The application of asparaginase is promising in this respect because it acts only on the key precursor, asparagine, whereby the product character remains unchanged. The baking agent NH4HCO3 promotes acrylamide formation in sweet bakery but its replacement by NaHCO3 effectively decreases acrylamide concentrations. Temperature and free asparagine are the key factors for acrylamide formation in roasted almonds. Olives and dried fruit may contain acrylamide and large amounts of acrylamide can be formed upon heating these products, a phenomenon which needs further investigation.

Influence of thermal processing conditions on acrylamide generation and browning in a potato model system.

Fried potato products such as French fries and chips may contain substantial amounts of acrylamide. Numerous efforts are undertaken to minimize the acrylamide content of these products while sensory properties such as color and flavor have to be respected as well. An optimization of the frying process can be achieved if the basic kinetic data of the browning and acrylamide formation are known. Therefore, heating experiments with potato powder were performed under controlled conditions (moisture, temperature, and time). Browning and acrylamide content both increased with heating time at all temperatures and moisture contents tested. The moisture content had a strong influence on the activation energy of browning and acrylamide formation. The activation energy strongly increased at moisture contents below 20%. At higher moisture contents, it was very similar for both parameters. At low moisture contents, the activation energy of acrylamide formation was larger as compared to the one for browning. This explains why the end of the frying process is very critical. Therefore, a lower temperature toward the end of frying reduces the acrylamide content of the product while color development is still good.

Potential of acrylamide formation, sugars, and free asparagine in potatoes: a comparison of cultivars and farming systems.

Glucose, fructose, sucrose, free asparagine, and free glutamine were analyzed in 74 potato samples from 17 potato cultivars grown in 2002 at various locations in Switzerland and different farming systems. The potential of these potatoes for acrylamide formation was measured with a standardized heat treatment. These potentials correlated well with the product of the concentrations of reducing sugars and asparagine. Glucose and fructose were found to determine acrylamide formation. The cultivars showed large differences in their potential of acrylamide formation which was primarily related to their sugar contents. Agricultural practice neither influenced sugars and free asparagine nor the potential of acrylamide formation. It is concluded that acrylamide contents in potato products can be substantially reduced primarily by selecting cultivars with low concentrations of reducing sugars.