The Clarifying Reagent, or how to make the analysis of milk and dairy products easier
Difficulties with the analysis of opaque milk and dairy products can be resolved by rendering the sample transparent. This allows direct photometric measurements of the reaction mixtures, and all sample pre-treatment steps become unnecessary. For this, several reagents have been reported in literature. Among them, the ‘Clarifying Reagent’ is mainly described here: its composition is given because it is now released from patenting restrictions. Its main property is a low absorbance between 340 and 800 nm. So it can be used in many chemical and enzymatic colorimetric measurements for estimating the quality of milk and dairy products.
Lipase activity in Swedish raw milk
Bovine milk contains several enzymes which can affect the quality of milk. One of these enzymes are lipases which hydrolyse the triacylglycerides in milk. In this process off-flavours, odour and product defects are generated. By controlling the enzymes activity, milk quality can be increased and therefore milk and dairy products can be stored for a longer time. This is desirable since the world demand for long shelf-life milk and milk products is increasing. To monitor the quality of raw milk and control the enzyme activity, a well-functioning method to detect lipase activity is desired. Thus, the aim of this thesis was to investigate and improve an existing method to determine lipolytic activity which is based on a fluorescent approach. With this method, a sensitive fluorescent measurement of the lipase activity directly in the natural milk environment is possible. Once the method was evolved, raw milk samples from different regions in Sweden and from different origins, i.e. farm and dairy, were investigated and evaluated for possible differences in lipase activity. No significant difference was found between samples from farm and dairy origins. Between the different regions a significant difference was discovered. The lowest lipase activity in milk was found in milk from the south (Skanemejerier) followed by milk from the mid region of Sweden (Arla) and the highest lipase activity was seen in milk from the north (Norrmejerier). The lipase activity was also correlated to other previously measured properties of the milk. A significant negative correlation to some long chain fatty acids could be seen. This indicates that long chain fatty acids inhibit lipase activity in the milk which has previously been observed in the adipose tissue of rats and in goats milk. The long chain fatty acid content in milk can be influenced by the feed. Thus, the results of this thesis indicate that the raw milk quality could be improved by increasing the amount of long chain fatty acids in the milk through the feed and thereby reduce lipase activity. (Less)
Development of new analytical methods for the determination of caffeine content in aqueous solution of green coffee beans
BackgroundThis study was conducted to develop fast and cost effective methods for the determination of caffeine in green coffee beans. In the present work direct determination of caffeine in aqueous solution of green coffee bean was performed using FT-IR-ATR and fluorescence spectrophotometry. Caffeine was also directly determined in dimethylformamide solution using NIR spectroscopy with univariate calibration technique.ResultsThe percentage of caffeine for the same sample of green coffee beans was determined using the three newly developed methods. The caffeine content of the green coffee beans was found to be 1.52 ± 0.09 (% w/w) using FT-IR-ATR, 1.50 ± 0.14 (% w/w) using NIR and 1.50 ± 0.05 (% w/w) using fluorescence spectroscopy. The means of the three methods were compared by applying one way analysis of variance and at p = 0.05 significance level the means were not significantly different. The percentage of caffeine in the same sample of green coffee bean was also determined by using the literature reported UV/Vis spectrophotometric method for comparison and found to be 1.40 ± 0.02 (% w/w).ConclusionNew simple, rapid and inexpensive methods were developed for direct determination of caffeine content in aqueous solution of green coffee beans using FT-IR-ATR and fluorescence spectrophotometries. NIR spectrophotometry can also be used as alternative choice of caffeine determination using reduced amount of organic solvent (dimethylformamide) and univariate calibration technique. These analytical methods may therefore, be recommended for the rapid, simple, safe and cost effective determination of caffeine in green coffee beans.