Application of Lyophilization for Preparing Reference Materials of Food Composition

This article describes the application of a lyophilization system for preparing reference materials (RMs) of food composition. The aim of the study was to develop a freeze-drying method for preparing an RM of poultry meat composition with certified values of mass fraction of moisture, nitrogen (protein), and fat. Poultry meat was used as the initial material: white (chicken breast, Sample 1) and red (chicken thigh, Sample 2). The procedure for preparing the RM included grinding, boiling, freezing, and lyophilization (syn. freeze-drying). Material homogeneity was studied using a standard air-heat drying technique from the State Primary Standard GET 173-2017. The mass fraction of nitrogen (protein) was measured using the State Secondary Standard GVET 176-1-2010. The mass fraction of fat was measured in accordance with the State Primary Reference Measurement Procedure. The total lyophilization time for Samples 1 and 2 was 19 and 28 h, respectively. The total weight loss was about 63% and 65% for Sample 1 and Sample 2, respectively. The difference in the values of moisture mass fraction for samples dried on different shelves of a freeze dryer was statistically significant, implying the heterogeneity of the material. A homogeneous material was obtained by additional homogenization procedures: grinding in a laboratory mill, sieving through a sieve, thorough mixing, and conditioning. The certified values of moisture, nitrogen, protein, and fat mass fraction for Sample 1 were 4.5%, 14.74%, 92.1%, and 7.9%, respectively. For Sample 2, the respective values were 6.3%, 12.21%, 76.3%, and 23.8%. A lyophilization procedure was developed for producing an RM of the composition of boiled and freeze-dried poultry meat. This lyophilization system ensured the RM expiration period of 6 months at an ambient temperature of (7±3) °C and a relative humidity of no more than 60%. Following the results of this study, the developed RM of the composition of boiled and freeze-dried poultry meat was added to the Register of Certified RMs under the number GSO 11276-2019.