Determination of whey protein content in bovine milk-based infant formula finished products using amino acids calculation method: AOAC First Action 2012.08.

A method for the calculation of the whey protein fraction was developed for milk-based infant formula products based upon amino acid ratio calculated from asparaginelaspartic acid, alanine, proline, and phenylalanine amino acid data. Historical and literature amino acid data were combined to establish the reference amino acid values used in the validation study. This method has been evaluated for accuracy versus label claim for 12 products, with results from 90 to 107.5% of label claim and an overall average of 98.7%. Repeatability and intermediate precision were determined over 4 different days. Repeatability results were 4.75, 2.06, 4.18, and 2.44% RSD, respectively, with an overall intermediate precision of 3.68% RSD. Since the amino acid profile of infant formula finished products depends on the amino acid profile of ingredients used, the applicability of the method needs to be confirmed for specific types of infant formula, for which data will be gathered. Additional reference material data are being gathered for better estimation of milk and whey reference values, which are based on being normalized to total amino acid content, during the two year AOAC INTERNATIONAL Official Methods of Analysis method approval process.

Vitamin C in infant formula and adult/pediatric nutritional formula by HPLC with UV detection: First Action 2012.21.

This method for the determination of vitamin C by HPLC allows for the separation and quantitation of L-ascorbic acid in infant, pediatric, and adult nutritional products. Liquids, semisolids, and powders ranging from 2 to 1000 mg/kg in their consumable forms were analyzed during the method validation. The method met the standard method performance requirements and was approved by an AOAC Expert Review Panel on Infant Formula and Adult Nutritionals on October 2, 2012. During validation, the overall intermediate precision was 2.1% RSD (triplicate determinations on 7-10 days); the within-day precision, or repeatability, was 1.54% RSD (triplicate determinations). Accuracy, as spike recovery, ranged from 97.0 to 100.9%. The method detection and quantitation limits were determined experimentally to be 0.02 and 0.06 mg/L, respectively, in prepared samples.

Simultaneous determination of vitamins D2 and D3 by electrospray ionization LC/MS/MS in infant formula and adult nutritionals: First Action 2012.11.

A method was developed for the analysis of vitamins D2 and D3 in a variety of nutritional products. To extract vitamins D2 and D3 from products containing substantial amounts of fat, a saponification with alcoholic potassium hydroxide is required to release the vitamin D. Trideuterium-labeled vitamin D is added to the sample prior to saponification, and quantitation is achieved using linear regression of the ratio of peak response for 2H3-D and vitamin D. Acceptable linearity was achieved between 0.6 and 27 microg/100 g with a correlation requirement of >0.999. The method detection limit of 0.02 microg/100 g was verified by spiking placebo products carried through the saponification and extraction steps of the method. At the quantitation limit (0.12 microg/100 g), the signal was easily distinguished from the background. Vitamin D3 spike recoveries ranged from 107 to 119% at the low level and 104 to 116% at the high-level spike. Vitamin D2 recoveries were 105 to 116% and 91 to 110% for the low- and high-level spikes, respectively. SRM 1849a has a certified concentration of 11.1 +/- 1.7 microg/100 g; using this standard reference material, the range of 9.4 to 12.8 microg/100 g was met on each of the 6 days. Method repeatability, determined in 12 vitamin D3 product matrixes over 6 days, ranged from 3.9 to 48%. The adult nutrition-milk protein sample was the most notable; it failed within-day, as well as day-to-day, precision requirements. There was no attempt to optimize the sample preparation to accommodate any problem matrix.

Determination of vitamins A and E in infant formula and adult/pediatric nutritional formula by HPLC with UV and fluorescence detection: First Action 2012.09.

The method presented is for quantification of alpha-tocopherol (vitamin E), vitamin E acetate, vitamin A acetate, and vitamin A palmitate in infant formula and adult/pediatric nutritionals. The entire lipid fraction, including vitamins A and E, is extracted from product with iso-octane after products are mixed with methanol, which precipitates proteins and disrupts micelles freeing lipids for extraction. Vitamin A palmitate, vitamin A acetate, and vitamin E acetate are separated from alpha-tocopherol on a 3 cm silica column with a 1% methylene chloride, 0.06% isopropanol in iso-octane mobile phase; eluted onto a 20 cm silica column; and, after a column switch, further separated on the 20 cm column before UV detection at 325 nm (vitamin A palmitate and vitamin A acetate) and 285 nm (vitamin E acetate). Alpha-Tocopherol is further separated from other extraneous compounds on the 3 cm silica column and detected by fluorescence at excitation and emission wavelengths of 295 and 330 nm, respectively. Quantification limits in ready-to-feed products were estimated to be 80 IU/L for vitamin A palmitate, 207 International Units (IU)/L for vitamin A acetate, 2.4 mg/L for vitamin E acetate, and < 0.15 mg/L for alpha-tocopherol. Over-spike recoveries and intermediate precision averaged 100.4 and 2.09% RSD for vitamin A palmitate, 100.4 and 1.52% RSD for vitamin E acetate, and 99.6 and 3.02% RSD for alpha-tocopherol. Vitamin A acetate spike recovery data averaged 96.6%, and the intermediate precision for the only product fortified with vitamin A acetate was 2.75% RSD.

Determination of myo-inositol (free and bound as phosphatidylinositol) in infant formula and adult nutritionals by liquid chromatography/pulsed amperometry with column switching: first action 2011.18.

Myo-inositol is a 6-carbon cyclic polyalcohol also known as meso-inositol, meat sugar, inosite, and i-inositol. It occurs in nature in both free (myo-inositol) and bound (inositol phosphates and phosphatidylinositol) forms. For the determination of free myo-inositol, samples are mixed with dilute hydrochloric acid to extract myo-inositol and precipitate proteins, diluted with water, and filtered. For the determination of myo-inositol bound as phosphatidylinositol, samples are extracted with chloroform, isolated from other fats with silica SPE cartridges, and hydrolyzed with concentrated acid to free myo-inositol. Prepared samples are first injected onto a Dionex CarboPac PA1 column, which separates myo-inositol from other late-eluting carbohydrates. After column switching, myo-inositol is further separated on a CarboPac MA1 column using a 0.12% sodium hydroxide mobile phase; strongly retained carbohydrates are eluted from the PA1 column with a 3% sodium hydroxide mobile phase. Eluant from the CarboPac MA1 analytical column passes through an electrochemical detector cell where myo-inositol is detected by pulsed amperometry using a gold electrode. The method showed appropriate performance characteristics versus selected established standard method performance requirement parameters for the determination of myo-inositol: linear response; repeatability (RSDr) of 2%; and intermediate precision (RSDir) of 2.5%. Instrument LOD and LOQ were 0.0004 and 0.0013 mg/100 mL, respectively, and correspond to a free myo-inositol quantitation limit of 0.026 mg/100 g and a phosphatidylinositol quantitation limit of 0.016 mg/100 g. Correlation with the reference microbiological assay was good. The proposed method has been accepted by the Expert Review Panel as an AOAC First Action Method, suitable for the routine determination of myo-inositol in infant formula and adult nutritionals.

Application of a microplate-based ORAC-pyrogallol red assay for the estimation ofantioxidant capacity: First Action 2012.03.

A method was developed for microplate-based oxygen radicals absorbance capacity (ORAC) using pyrogallol red (PGR) as probe (ORAC-PGR). The method was evaluated for linearity, precision, and accuracy. In addition, the antioxidant capacity of commercial beverages, such as wines, fruit juices, and iced teas, was measured. Linearity of the area under the curve (AUC) versus Trolox concentration plots was [AUC = (845 +/- 110) + (23 +/- 2) [Trolox, microM]; R = 0.9961, n = 19]. Analyses showed better precision and accuracy at the highest Trolox concentration (40 microM) with RSD and recovery (REC) values of 1.7 and 101.0%, respectively. The method also showed good linearity for red wine [AUC = (787 +/- 77) + (690 +/- 60) [red wine, microL/mL]; R = 0.9926, n = 17], precision and accuracy with RSD values from 1.4 to 8.3%, and REC values that ranged from 89.7 to 103.8%. Red wines showed higher ORAC-PGR values than white wines, while the ORAC-PGR index of fruit juices and iced teas presented a wide range of results, from 0.6 to 21.6 mM of Trolox equivalents. Product-to-product variability was also observed for juices of the same fruit, showing the differences between brands on the ORAC-PGR index.

Determination of antioxidant activity in foods and beverages by reaction with 2,2'-diphenyl-1-picrylhydrazyl (DPPH): collaborative study First Action 2012.04.

A colorimetric method for the determination of total antioxidant activity in a variety of foods and beverages was validated in both a single-laboratory validation and a collaborative laboratory validation study. The procedure involved extraction of the antioxidants directly into a methanol-water solution containing a known amount of 2,2'-diphenyl-1-picrylhydrazyl (DPPH), thus promoting the rapid reaction of extracted materials with DPPH. The reaction was monitored by spectrophotometric measurement of the absorbance loss at 517 nm. Antioxidant activity was quantified relative to a dilution series of vitamin E analog standards (Trolox), which were analyzed in parallel simultaneously with the food and beverage samples. The antioxidant activities of the samples ranged from 131 to 131 000 micromole Trolox equivalents/100 g. Statistical analysis of the results showed that nine of the 11 matrixes gave acceptable HorRat values, indicating that the method performed well in these cases. The acceptable matrixes include pomegranate juice, blueberry juice, carrot juice, green tea, wine, rosemary spice, ready-to-eat cereal, and yogurt. Two samples failed the HorRat test: the first was an almond milk that had an antioxidant level below the practical LOQ for the method; the second was a sample of canola oil with added omega-3 fatty acid that was immiscible in the reaction medium.