330 NASCIMENTO ET AL.: JOURNAL OF AOAC INTERNATIONAL VOL. 100, NO. 2, 2017 Time-Domain Nuclear Magnetic Resonance (TD-NMR) and Chemometrics for Determination of Fat Content in Commercial Products of Milk Powder PALOMA A NDRADE MARTINS NASCIMENTO and PAULO LOPES BARSANELLI Universidade Estadual Paulista “Júlio de Mesquita Filho,” Instituto de Química, Departamento de Química Analítica, Rua Professor Francisco Degni, 55, Araraquara, SP 14800-060, Brazil ANA PAULA REBELLATO and JULIANA AZEVEDO LIMA PALLONE Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos, Departamento de Ciência de Alimentos, Campinas, SP 13083-962, Brazil LUIZ ALBERTO COLNAGO Embrapa Instrumentação, Rua Quinze de Novembro 1452, São Carlos, SP 13561-206, Brazil FABÍOLA MANHAS VERBI PEREIRA 1 Universidade Estadual Paulista “Júlio de Mesquita Filho,” Instituto de Química, Departamento de Química Analítica, Rua Professor Francisco Degni, 55, Araraquara, SP 14800-060, Brazil This study shows the use of time-domain (TD)-NMR transverse relaxation (T 2 ) data and chemometrics in the nondestructive determination of fat content for powdered food samples such as commercial dried milk products. Most proposed NMR spectroscopy methods for measuring fat content correlate free induction decay or echo intensities with the sample’s mass. The need for the sample’s mass limits the analytical frequency of NMR determination, because weighing the samples is an additional step in this procedure. Therefore, the method proposed here is based on a multivariate model of T 2 decay, measured with Carr-Purcell-Meiboom-Gill pulse sequence and reference values of fat content. The TD-NMR spectroscopy method shows high correlation (r = 0.95) with the lipid content, determined by the standard extraction method of Bligh and Dyer. For comparison, fat content determination was also performed using a multivariate model with near-IR (NIR) spectroscopy, which is also a nondestructive method. The advantages of the proposed TD-NMR method are that it (1) minimizes toxic residue generation, (2) performs measurements with high analytical frequency (a few seconds per analysis), and (3) does not require sample preparation (such as pelleting, needed for NIR spectroscopy analyses) or weighing the samples. P owdered milk is obtained by dehydrating whole, skimmed, or semiskimmed cow’s milk using appropriate technological processes and is fit for human consumption. The chemical constituents of dried milk products are lactose, proteins, minerals, and fat, as well as vitamins A, B, and D. However, several factors, such as breeding programs, animal health, and feed or weather conditions may influence dried milk composition (1, 2). Among the components of milk, lipids are a class of molecules with different functions (3) that are insoluble in water but soluble in organic solvents. Lipids are essential for the synthesis of cell membranes and plasma and participate in the formation of structural components of all tissues, as well as being the largest energy reserves in the body (4). Thus, lipids are an important source of energy for the newborn (5) and participate in the protection of vital organs and the transport of fat-soluble vitamins (vitamins A, D, E, and K; 6, 7). Furthermore, lipids play essential roles in neuronal growth, signal transduction, the excitability of neural membranes, and retinal development, as well as in the expression of genes that regulate cellular differentiation and growth (8). Milk lipids consist of fatty acids belonging to two groups: saturated (single bonds) and unsaturated fatty acids (with one or more double bonds). Saturated and monounsaturated fatty acids can be synthesized in the body, unlike polyunsaturated fatty acids, which are considered essential fatty acids (9). Linoleic and α-linolenic acids are prominent polyunsaturated fatty acids due to their importance for the synthesis of lipids in tissues, in the regulation of various metabolic processes of transport and excretion (10), and because they are essential for the healthy growth of infants and children (11). The lipid content provides between 45 and 55% of the total energy in human milk, and a similar content can be found in industrialized infant formula (4). Although the fatty acids in human milk meet these requirements for the infant, in certain circumstances, it is necessary to use powdered milk formulas as a replacement or as a complement to human milk (11). According to Klein (12), the lipid content in infant formula for preterm infants should be between 4.4 and 5.7 g/100 kcal, providing approximately 52% of the total energy. For premature babies, the recommended values should be between 4.4 and 6.4 g/100 kcal, providing approximately 40 to 60% of the total energy. SPECIAL GUEST EDITOR SECTION Guest edited as a special report on “Application of Multivariate Statistical Techniques in Chromatographic and Spectroscopic Fingerprinting of Complex Food and Environmental Samples” by Paweł K. Zarzycki. 1 Corresponding author’s e-mail address: fabiola@iq.unesp.br This research was supported by the Fundunesp (Process 0268/001/14), National Council for Scientific and Technological Development (Process 445729/2014-7), São Paulo Research Foundation (Process 2012/20264-0 and 2016/00779-6), and Finep. DOI: 10.5740/jaoacint.16-0408 Downloaded from https://academic.oup.com/jaoac/article/100/2/330/5654162 by guest on 12 June 2022