6. AOACSPIFANMethods-2018Awards

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

Figure 8. Typical e-gram of SMP.

still migrate as two groups either before or after the caseins. Caseins were eluted as a single group between light and heavy chains of immunoglobulins, where almost no major whey proteins were found (Figure 8).

protein content was designed to range from 20% (no added whey) to about 80% in the mixtures of whey and skim milk. The typical spiking scheme is presented in Table 1. Analyses were performed in duplicate on a single day, as well as in single analyses on 3 separate days. The relationship between the amount of added whey protein and the whey protein-to-casein ratio proved to be linear, and the coefficients of determination (R 2 ) were all higher than 0.9900 (Table 2). The relationship between the amount of added whey protein and the percentage of added whey in the total protein proved to be logarithmic; the R 2 were also all higher than 0.9900 (Table 2). Typical linearity relationships are shown in Figure 9.

Linearity

Linearity data were obtained by spiking seven different levels of whey protein ingredients into a fixed level of SMP. Whey Table 1. Testing scheme for linearity and accuracy (whey protein ranging from 20 to 80%)

Protein

Weight, mg

DI water, mL b

Ingredients a

% mg/mL

Lot No.

Table 2. Summary of R 2 and the equations for seven levels of whey protein in total proteins for the whey-to-casein ratio and added whey protein as the percentage of total protein

SMP

84.6 162

2.00 1.00

38.5 35.2

16.3

DY19

WPC35

57.0 C22JUL15J1

DI water, μL Total, μL

Whey content, %

Experiment c SMP, μL WPC35, μL

Day 1: Avg. for two replicates

Day 2: Single

Day 3: Single

Day 4: Single

WPCL0

60 60 60 60 60 60 60

0 5

60.0 55.0 50.0 40.0 30.0 20.0

120.0 120.0 120.0 120.0 120.0 120.0 120.0

21.2 37.6 48.0 60.4 67.5 72.2 77.8

WPC35L1 WPC35L2 WPC35L3 WPC35L4 WPC35L5 WPC35L6

Whey/casein

10 20 30 40 60

R 2

0.9931

0.9990

0.9980

0.9984

Equation

y = 0.0378 x + 0.2573

y = 0.0421 x + 0.2119

y = 0.0429 x + 0.2013

y = 0.044 x + 0.2232

Percentage whey added

0.0

R 2

0.9961

0.9942

0.9957

0.9928

a  WPC = Whey protein concentrate. b  DI = Deionized. c  L0–6 = Levels 0–6.

y = 16.564 ln( x ) – 9.7994

y = 17.576 ln( x ) – 13.359

y = 16.339 ln( x ) – 8.6141

Equation

y = 16.909 ln( x ) – 12.42

Figure 9. Typical linearity relationships between the area ratio of whey to casein and measured whey percentage versus whey protein amount added.