Long-term stability of nutrients in a frozen mixed food control material

A mixed food homogenate was prepared as a quality control material for two multi-center clinical feeding trials. Approximately 100 kg of homogenized human diet material was prepared under controlled conditions to maintain the stability of lipid components. More than 4,800 20-25 g aliquots were prepared and stored at -60 degrees C in glass jars with Teflon-lined lids. The homogeneity of the composite was validated by analysis of moisture and total fat in aliquots taken throughout the dispensing sequence. A portion of the material was reserved at the National Institute of Standards and Technology and further characterized as SRM 1544-Fatty Acids in Diet Composite. Moisture, protein, ash, total lipid, fatty acids, cholesterol, sodium, potassium, calcium, and magnesium were assayed as part of routine quality-control analyses. Components were analyzed over a total time period ranging from 29 months (minerals) to 60 months (moisture), and up to 319 values per nutrient were generated. Results for all components assayed were stable over the time period studied. For example, moisture (n = 319; 60 months) ranged from 70.66 to 72.58 g/100 g with a mean, standard deviation (SD), and relative standard deviation (RSD) of 71.90, 0.27, and 0.4%, respectively. The range, mean, SD, and RSD for cholesterol (mg/100 g; n = 98; 49 months) were 13.54-17.96, 15.14, 0.64, and 4%.