The present paper describes how the formation of artefactual nitrosodimethylamine (NDMA) may jeopardize attempts at determining volatile nitrosamines in cheese by the mineral oil technique (MOT) or the glycerol isolation technique (GIT). When such isolation techniques were performed at an initial pH of about 11 and a final temperature of 100 degrees C (compared to 70 degrees C), up to about 10 micrograms NDMA per kg was formed. In a meat product, which was examined for comparison, even more extensive artefact formation (up to 70 micrograms NDMA per kg) was found. The addition of 10 mg/kg morpholine, as a readily nitrosatable substrate, to this meat product resulted (under the most unfavourable conditions) in formation of 250 micrograms/kg artefactual nitrosomorpholine. Alkalization of samples before nitrosamine analysis is a widely practised method to prevent artefact formation and has been emphatically recommended by an international working group, convened by the International Agency for Research on Cancer (Lyon). The mechanism of this peculiar artefact formation, which is strongly temperature- and pH-dependent, is not as yet known. It may however involve transnitrosation by C-, S- or O-nitroso compounds, e.g. nitrosophenols, nitrosothiols, alkyl nitrites, sugar nitrite esters, or lipid-nitrite reaction products. Several parameters of initial pH, final temperature and use of inhibitors under which the phenomenon will or will not occur are discussed. The artefact formation described here occurs mostly at pH values which are common to laboratory situations, but which are rare as for as the preparation of food in the household is concerned. Therefore, the effect does not appear to imply a risk to the consumer's health.
Three genotypes of maize plants were provided by Wageningen Plant Research (Ambrosini, 10LG and 5LG), varying in composition hemicellulose/cellulose/lignin. The samples were tested for their suitability as resource to produce sugars for fermentation or for the production of a cellulose pulp. After harvesting and cutting of the maize plants, a heterogeneous mixture of stems and leaves was obtained with various particle sizes/thicknesses. Compared to other lignocellulosic biomasses the samples contained a high amount of water-soluble extractives, most likely due to soluble sugars that are present in the stems. The Ambrosini genotype contained the highest amount of lignin, 5LG sample the lowest. Fermentable sugars All three genotypes were subjected to an acid pretreatment at 130 or 160 °C, followed by enzymatic hydrolysis with a mixture of cellulases and hemicellulases. The treatment at 160 °C resulted in higher glucose and xylose yield compared to 130 °C, and especially for xylose the differences were large. Overall, genotype 5LG resulted in the lowest sugar yield, while genotype 10LG gave the highest yield. Acid treatment of 10LG at 160°C followed by enzymatic hydrolysis gave the highest yield, 24.g glucose and 16.4 g xylose per 100 g dry maize. At mild pre-treatment severity, the higher lignin content made Ambrosini the least digestible genotype. 10LG and 5LG were better digestible. From this part of the study it was concluded that maize plants are an interesting source of sugars, especially when the free sugars (found in the extractives) are included. It was recommended to extract the water-soluble sugars first to prevent sugar degradation of these free sugars in the pretreatment step. A subsequent acid pretreatment followed by enzymatic hydrolysis resulted in overall high yields of sugars (80-90 wt%), leading to a theoretical sugar yield of approximately 50 wt% of the original maize biomass. Cellulose pulp Another part of the study was the conversion of the maize plants to cellulose pulp by four different methods: prehydrolysis followed by organosolv, acid super heated steam (SHS), alkaline super heated steam, and alkaline pulping at 120 °C. Genotype 5LG was selected because of its low lignin and high cellulose content. Retention of cellulose in the samples was the highest for the acid SHS treatment (91%), but also the alkaline treatments resulted in a high retention of cellulose (81%). For removal of hemicellulose, the acid SHS treatment was by far the most efficient one. Under these conditions, only 4% of the hemicellulose remained in the sample and more than 90% was removed by the treatment. Cellulose content of the samples was 65 wt% for the acid-SHS treatment, and 58 wt% for the alkaline treatments, still far from >90 wt% cellulose content required for a dissolving cellulose pulp. Hand sheets The fibre properties of the cellulose pulps, the mechanical and physical properties of hand sheets were determined to get insight in the morphology of the cellulose pulps after chemical treatment, and on the performan...
Eight genotypes of Miscanthus sinensis were provided by WPR with differences in composition and digestibility. The eight genotypes showed significant differences in chemical composition. A correlation between glucose and lignin content and digestibility could be present. Fermentable sugars The 8 genotypes were subjected to a two-stage process to produce fermentable sugars. The first stage consisted of an acid treatment at elevated pressure and temperature, the second stage of an enzymatic hydrolysis. Clear differences in the amount of fermentable sugars obtained were found. The genotype with the highest digestibility (074, lowest amount of cellulose and lignin) also resulted in the highest amount of fermentable sugars. Correlation between the digestibility and fermentable sugar yield of the other genotypes was less clear. Two genotypes (017 and 074) were also subjected to three other pulping processes as first stage (acid super heated steam (SHS), alkaline SHS and alkaline pulping at 120 °C), followed by a second stage of enzymatic hydrolysis. Similar results were obtained: the genotype with the highest digestibility (074, lowest amount of cellulose and lignin) also resulted in the highest amount of glucose. Release of xylose was similar. Overall, glucose release was limited, xylose release was moderate for the alkaline treated pulps. Cellulose pulp Another part of the study was the conversion of two genotypes (017 and 074) to cellulose pulp by four different methods: prehydrolysis followed by organosolv, acid super heated steam (SHS, alkaline SHS and alkaline pulping at 120 °C. The cellulose pulps were used to make hand sheets. The glucose content (cellulose) after treatment was increased from 38% to 60% for Miscanthus 017 and from 30% to 59% for Miscanthus 074. After acid and SHS treatment still a high percentage of lignin (AIL) was present in the product. After alkaline treatment a high amount of xylose (hemicellulose) was still present. For the production of a cellulose pulp, the alkaline 50L treatment of both Miscanthus genotypes was most promising as this treatment resulted in samples with the highest cellulose content, around 60 wt%. However, more purification steps are required to obtain a pure cellulose product. Based on the composition of the starting material Miscanthus 017 is more interesting due to a higher initial cellulose content. Hand sheets The fibre properties of cellulose pulps and the mechanical-and physical properties of hand sheets were analysed. The cellulose-enriched samples were disintegrated, mechanically beaten and handsheets were prepared. The properties of these handsheets were determined to provide insight in the morphology of the pulps after chemical treatment, and on the performance for application in paper products. Results showed that the acid-SHS treatment was less effective in breaking down the fibre bundles of the Miscanthus biomass into fibres compared to the alkaline treatments. The acid treated cellulose pulp was not fully disintegrated into fibres, resulting in a high bul...
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