With the continuous growth of the global dairy market, yogurt specifically has turned out to be one of the fastest advancing sectors. This is particularly the case with the growing popularity of Greek yogurt and the recent emergence of non-dairy yogurt substitutes, such as soy, coconut, and almond. According to a 2015 study, yogurt consumption on a day-to-day basis increased from 4.7% in 1999 to 9.3% in 2013 from a survey population of 33,932 US adults.i A considerable proportion of yogurt’s growth can be attributed to its health benefits, such as being a good source of probiotics, protein, fruits, and other nutrients.
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The measurement of protein is crucial for yogurt manufacturers as it has a direct impact on definition and thickness of the end product (i.e. the amount of protein in Greek yogurt is approximately twice as in conventional yogurt). The production of yogurt involves the addition of live bacterial cultures to milk after exposure to elevated temperature(s) and subsequent cooling. The lactose in the previously heat-treated milk is fermented by the bacterial cultures, thereby producing lactic acid. The decrease in pH, along with the earlier heat treatment, makes milk proteins (whey and casein) to be denatured from higher order structures and form clusters. Thickening of the yogurt occurs when the proteins unwind and bind together. Generally, the thickness of the yogurt is directly proportional to the protein content.
The Sprint® protein analyzer is a perfect solution for yogurt manufacturers to test in-process as well as finished yogurt products. The technology is based on a rapid green chemistry process that enables direct detection of protein within 5 minutes. A proprietary iTag® solution is combined with the sample and directly binds to the backbone of the proteins, particularly the basic amino acids (Lysine, Histidine, and Arginine). Nitrogen-containing adulterants do not have an impact on this direct and rapid protein detection technique. The technique also avoids the use of any hazardous reagents associated with wet chemical techniques, for example, Kjeldahl. Moreover, Sprint’s efficacy is not affected by the unwinding, or denaturation, of proteins at the time of the yogurt production process; in contrast, the denaturation exposes more of the backbone for binding with the iTag solution.
Key System Benefits
- Rapid, within 5 minutes
- Higher repeatability when compared to Kjeldahl and combustion techniques
- Direct protein detection, not total nitrogen
- Not vulnerable to adulteration
- Automates AOAC Methods 930.33 (ice cream and frozen desserts) and 967.12 (milk)
- Green chemistry—harsh, high-temperature chemicals are not used
Samples
Data for 9 in-process samples and 15 finished yogurt samples with different protein levels were gathered for demonstrating the precision and accuracy of the Sprint. The values obtained from Sprint were compared with the Kjeldahl values acquired by performing the AOAC 991.20 (crude protein) and AOAC 991.21 (true protein) methods. The in-process samples included milk permeates, milk retentates, and yogurts. The finished product samples included different types of conventional and Greek yogurts, with and without fruit.
Sample Preparation and Analysis
The Sprint protein analyzer was used for analyzing different yogurt, milk retentate, and milk permeate samples. A disposable pipette or spatula was used for stirring each sample to ensure proper mixing before the analysis.
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Figure 1. Sprint protein analyzer
Note: For optimum results, it is advisable to homogenize yogurt samples that contain fruit with the help of a food processor.ii It would be judicious to avoid any large fruit particles during sampling because their presence in the subsample might make it challenging to obtain a representative aliquot. In case there are visible solids in liquid samples, tempering may be necessary as advised in AOAC 925.21.
Results
Tables 1–6 illustrate the precision and accuracy of the Sprint protein analyzer. An important point to be noted here is the fact that the Sprint can be adjusted to correlate to crude or true protein. Tables 1–4 summarize the data related to crude protein, and Tables 5 and 6 summarize those related to true protein.
From Tables 1 and 2, it can be observed that the differences between Sprint and Kjeldahl were in the range of 0%–0.12% for crude protein with a standard deviation range of 0%–0.08% for in-process yogurts, retentates, and permeates.
Table 1. Accuracy of Sprint for crude protein in in-process yogurts, permeates, and retentates
| Sample |
% Protein |
Difference |
| Sprint |
Kjeldahl |
| Yogurt 1, In-Process |
1.77 |
1.79 |
0.02 |
| Yogurt 2, In-Process |
2.49 |
2.47 |
0.02 |
| Yogurt 3, In-Process |
3.80 |
3.77 |
0.03 |
| Yogurt 4, In-Process |
4.21 |
4.33 |
0.09 |
| Retentate 1 |
6.03 |
6.02 |
0.01 |
| Retentate 2 |
9.54 |
9.64 |
0.10 |
| Retentate 3 |
13.40 |
13.28 |
0.12 |
| Permeate 1 |
0.18 |
0.20 |
0.02 |
| Permeate 2 |
0.52 |
0.52 |
0.00 |
| |
|
Average |
0.04 |
Table 2. Precision of Sprint for crude protein in in-process yogurts, permeates, and retentates
| Sample |
Replicates (% Protein) |
Average |
Range |
StDev |
| 1 |
2 |
3 |
| Yogurt 1, In-Process |
1.77 |
1.77 |
1.76 |
1.77 |
0.01 |
0.01 |
| Yogurt 2, In-Process |
2.49 |
2.49 |
2.48 |
2.49 |
0.01 |
0.01 |
| Yogurt 3, In-Process |
3.80 |
3.81 |
3.80 |
3.80 |
0.01 |
0.01 |
| Yogurt 4, In-Process |
4.21 |
4.21 |
4.21 |
4.21 |
0.00 |
0.00 |
| Retentate 1 |
6.03 |
6.03 |
6.03 |
6.03 |
0.00 |
0.00 |
| Retentate 2 |
9.59 |
9.45 |
9.57 |
9.54 |
0.14 |
0.08 |
| Retentate 3 |
13.35 |
13.46 |
13.39 |
13.40 |
0.11 |
0.06 |
| Permeate 1 |
0.17 |
0.18 |
0.19 |
0.18 |
0.02 |
0.01 |
| Permeate 2 |
0.52 |
0.52 |
0.51 |
0.52 |
0.01 |
0.01 |
Tables 3 and 4 illustrate an average difference between Sprint and Kjeldahl in the range of 0%–0.07% for crude protein with a standard deviation range of 0%–0.08% for finished product yogurts. There were considerable variations in the yogurts shown in these two tables in terms of flavor, protein content, and inclusions (i.e. fruit).
Table 3. Accuracy of Sprint for crude protein in finished yogurts
| Sample |
% Protein |
Difference |
| Sprint |
Kjeldahl |
| Yogurt 1, Plain |
3.56 |
3.50 |
0.06 |
| Yogurt 2, Plain |
4.07 |
4.07 |
0.00 |
| Yogurt 3, Plain |
4.29 |
4.33 |
0.04 |
| Yogurt 1, Fruit |
3.18 |
3.11 |
0.07 |
| Yogurt 2, Fruit |
3.57 |
3.60 |
0.03 |
| Yogurt 3, Fruit |
3.76 |
3.71 |
0.05 |
| Yogurt, Greek, Plain |
10.15 |
10.20 |
0.05 |
| Yogurt, Greek, Honey |
8.32 |
8.28 |
0.04 |
| Yogurt, Greek, Blueberry |
8.50 |
8.54 |
0.04 |
| Yogurt, Greek, Peach |
7.18 |
7.15 |
0.03 |
| Yogurt, Greek, Pineapple |
7.17 |
7.13 |
0.04 |
| Yogurt, Greek, Strawberry |
8.11 |
8.18 |
0.07 |
| |
|
Average |
0.04 |
Table 4. Precision of Sprint for crude protein in finished yogurts
| Sample |
Replicates (% Protein) |
Average |
Range |
StDev |
| 1 |
2 |
3 |
| Yogurt 1, Plain |
3.57 |
3.54 |
3.56 |
3.56 |
0.03 |
0.02 |
| Yogurt 2, Plain |
4.07 |
4.10 |
4.05 |
4.07 |
0.05 |
0.03 |
| Yogurt 3, Plain |
4.28 |
4.29 |
4.30 |
4.29 |
0.02 |
0.01 |
| Yogurt 1, Fruit |
3.19 |
3.17 |
3.17 |
3.18 |
0.02 |
0.01 |
| Yogurt 2, Fuit |
3.57 |
3.58 |
3.57 |
3.57 |
0.01 |
0.01 |
| Yogurt 3, Fruit |
3.76 |
3.75 |
3.76 |
3.76 |
0.01 |
0.01 |
| Yogurt, Greek, Plain |
10.19 |
10.20 |
10.07 |
10.15 |
0.13 |
0.07 |
| Yogurt, Greek, Honey |
8.32 |
8.32 |
8.32 |
8.32 |
0.00 |
0.00 |
| Yogurt, Greek, Blueberry |
8.50 |
8.49 |
8.50 |
8.50 |
0.01 |
0.01 |
| Yogurt, Greek, Peach |
7.16 |
7.20 |
7.20 |
7.18 |
0.04 |
0.02 |
| Yogurt, Greek, Pineapple |
7.23 |
7.08 |
7.18 |
7.17 |
0.25 |
0.08 |
| Yogurt, Greek, Strawberry |
8.11 |
8.11 |
8.10 |
8.11 |
0.01 |
0.01 |
In Tables 5 and 6, an average difference between Sprint and Kjeldahl in the range of 0%–0.07% true protein and standard deviation range of 0.01%–0.03% for three varieties of Greek yogurt are illustrated.
Table 5. Accuracy of Sprint for true protein in finished yogurts
| Sample |
% Protein |
Difference |
| Sprint |
Kjeldahl |
| Greek, Plain |
10.35 |
10.28 |
0.07 |
| Greek, Vanilla |
7.99 |
8.02 |
0.03 |
| Greek, Coconut Vanilla |
7.53 |
7.53 |
0.00 |
| |
|
Average |
0.03 |
Table 6. Precision of Sprint for true protein in finished yogurts
| Sample |
Replicates (% Protein) |
Average |
Range |
StDev |
| 1 |
2 |
3 |
| Greek, Plain |
10.35 |
10.37 |
10.32 |
10.35 |
0.05 |
0.03 |
| Greek, Vanilla |
8.00 |
7.98 |
7.98 |
7.99 |
0.02 |
0.01 |
| Greek, Coconut Vanilla |
7.55 |
7.53 |
7.52 |
7.53 |
0.03 |
0.02 |
These results demonstrate the ability of the Sprint to reliably match prevalent reference chemistry results for the analysis of protein in yogurt, retentate, and permeate samples through the entire manufacturing and membrane separation processes. The data also indicates the potential of the Sprint to realize higher repeatability for a broad range (ca. 0.20%–13.50 % protein) of in-process and finished yogurt samples.
References
i. Nielsen SJ et al., Trends in Yogurt Consumption—US Adults—1999-2012, The FASEB Journal, April 2015, vol 29(1).
ii. CEM recommends homogenizing samples with commercial grade food processors, such as the Robot Coupe.
This information has been sourced, reviewed and adapted from materials provided by CEM Corporation.
For more information on this source, please visit CEM Corporation.