A collaborative study was conducted to test a new rapid procedure for determination of water-insoluble cell wall (WICW) content in feeds. In the method, starch is solubilized near boiling temperature with Termamyl, a heat-stable alpha-amylase, and proteins are solubilized at 40 °C with sodium dodecylsulfate and Pronase. Then, the organic matter of the residue is determined by incineration. Three hours were required to treat 12 different samples, including solubilization treatments, filtrations, and rinses. Eleven unknown products including 9 common feedstuffs of various origin and 2 mixed diets for poultry were analyzed by 7 analysts in France. Coefficients of variation ranged from 2.3 to 6.1%. The results were compared to those for water-insoluble dietary fiber (WIDF), total dietary fiber, and neutral detergent fiber. Agreement was best with the water-insoluble dietary fiber procedure. For most samples, the ratios of WIDF/WICW ranged from 0.981 to 0.842. The differences between WICW and WIDF values correspond to cell wall protein which is accounted for in WICW, but not in WIDF.
A collaborative study was undertaken in which five international laboratories participated to determine amino acid fingerprints in 39 authentic nonfat dry milk (NFDM)/skim milk powder (SMP) samples. A rapid method of amino acid analysis involving microwave-assisted hydrolysis followed by ultra-high performance liquid chromatography-ultraviolet detection (UHPLC-UV) was used for quantitation of amino acids and to calculate their distribution. The performance of this rapid method of analysis was evaluated and was used to determine the amino acid fingerprint of authentic milk powders. The distribution of different amino acids and their predictable upper and lower tolerance limits in authentic NFDM/SMP samples were established as a reference. Amino acid fingerprints of NFDM/SMP were compared with selected proteins and nitrogen rich compounds (proteins from pea, soy, rice, wheat, whey, and fish gelatin) which can be potential economically motivated adulterants (EMA). The amino acid fingerprints of NFDM/SMP were found to be affected by spiking with pea, soy, rice, whey, fish gelatin and arginine among the investigated adulterants but not by wheat protein and melamine. The study results establish an amino acid fingerprint of authentic NFDM/SMP and demonstrate the utility of this method as a tool in verifying the authenticity of milk powders and detecting their adulteration.
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