6. AOACSPIFANMethods-2018Awards

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F eng et al .: J ournal of AOAC I nternational V ol . 100, N o . 2, 2017  517

Table 3. Spike-recovery data obtained in duplicate for different levels on 1 day

Table 5. Repeatability and intermediate precision for three infant formulas

Formula/Replicate

Integrated area

Measured Theoretical

Day

1/1

1/2

2/1

2/2

3/1

3/2

Spike level

Whey, % spiked

Whey, % spiked

Recovery, %

Total whey Casein Whey, % 90447 431555 21.3 95042 450546 21.4

1 2 3 4 5 6

61.0 59.7 60.5 60.0 59.5 59.3

60.8 59.8 59.3 59.9 58.8 59.7

55.9 56.5 56.2 56.1 56.4 57.1

57.2 56.1 56.1 56.6 56.5 57.8

64.4 64.4 64.4 64.2 64.8 64.9

64.2 64.7 65.1 64.2 65.2 64.8

0

1

467929 454430 59.0 37.7 489937 464188 59.6 38.3 686816 457990 67.7 46.4 699775 481562 67.0 45.7 823437 448464 72.0 50.7 847557 455946 72.2 50.9 1181386 467897 77.9 56.6 1179619 504671 76.6 55.3

39.0 39.0 46.2 46.2 50.8 50.8 56.5 56.5

96.6 98.1

2

100.5

 Avg.  RSD r  RSD R

59.9

56.4

64.7

99.0 99.7

, %

0.5

0.8 0.8

0.3 0.7

3

, % 1.0

100.2 100.2

4

Table 6. Repeatability and intermediate precision for SMP and demineralized sweet whey ingredient Day SMP a SMP a DW b DW b 1 21.7 21.2 95.5 98.6 2 20.1 19.8 98.3 97.9 3 21.8 21.4 97.4 97.6 4 21.6 21.9 97.0 98.3 5 22.2 22.4 98.5 99.2 6 22.1 22.4 98.8 97.9  Avg. 21.7 97.9  RSD r , % 1.5 0.9  RSD R , % 3.8 1.0 a  Because SMP is not processed like infant formula, a CF of 1.29 was used. b  Because whey protein contains almost no caseins, no CF was used. Table 7. Repeatability and intermediate precision for two infant formulas Rep. 1 Rep. 2 Rep. 3 Rep. 4 Rep. 5 Rep. 6 Avg. SD RSD Day Formula 4 1 71.2 70.5 70.7 71.1 71.1 70.8 70.9 0.3 0.4 2 71.0 70.7 71.2 70.7 70.7 70.8 70.9 0.2 0.3 3 70.6 70.4 70.1 70.3 70.5 70.3 70.3 0.2 0.2 Total 70.7 0.3 0.5 Formula 5 1 40.7 41.8 41.6 41.3 41.1 41.7 41.4 0.4 1.0 2 41.7 42.4 42.5 41.2 42.2 42.2 42.0 0.5 1.2 3 41.8 42.0 42.0 42.1 41.9 41.6 41.9 0.2 0.4 Total 41.8 0.5 1.1 whey (demineralized) sample (shown in Table 6). Two other infant formula samples were tested by preparing and analyzing six replicates each day on 3 different days using this method (shown in Table 7). The percentage of whey protein was reported to one decimal place for individual and averaged replicates. The SD and percentage RSDs were calculated and also reported to one decimal place. Data are presented in Tables 5–7. The typical e-grams for each infant formula sample are presented in Figures 10–14. The molar attenuation (or molar extinction) coefficient, reflected as the mass-to-area ratio at 220 nm, is an intrinsic

97.8

Accuracy (Spike Recovery)

Accuracy was evaluated in samples where four levels of sweet whey ingredient were spiked into the same level of SMP by comparing the theoretically calculated percentage whey values with the measured values obtained using equations 1 and 2 (for skim milk, where no whey proteins were added, the CF was set to 1.29). The results are listed in Tables 3 and 4. The SMPs and whey protein ingredients used in Tables 3 and 4 are from different lot numbers.

Precision

Two independent sample preparations were tested on each day for 6 separate days for the following: three infant formula samples (shown in Table 5), one SMP sample, and one sweet

Table 4. Spike-recovery data obtained in singlet for different levels on 3 different days

Area

Measured

Theoretical

Total whey Casein

Whey, %

Whey, % spiked

Whey, % spiked

Recovery, %

Level Day

0

1 112590 581315 20.0 2 134644 668598 20.6 3 125910 626821 20.6

1

1 544500 636291 54.5 34.5 32.1 107.6 2 528392 647887 53.3 32.7 31.3 104.4 3 544475 625202 54.9 34.4 33.0 104.2 1 632182 609700 59.2 39.2 37.3 105.0 2 654331 605001 60.2 39.6 36.6 108.1 3 698583 633572 60.7 40.1 38.3 104.8 1 805608 630879 64.1 44.1 41.4 106.6 2 789708 615699 64.2 43.6 40.8 106.9 3 836902 621176 65.4 44.8 42.3 105.8 1 939097 642338 67.2 47.2 44.7 105.6 2 930074 631568 67.3 46.7 44.1 105.8 3 906509 594583 68.1 47.5 45.6 104.3

2

3

4