AN-R-035
2025-04
用 PEG 法检测香料和调味品的氧化稳定性
Fast and reliable determination without sample preparation due to polyethylene glycol as carrier material
Summary
Herbs, spices, spice blends, flavor enhancers, and other seasonings are integral to modern cuisine. A wide variety of plant parts can be used (e.g., leaves, flowers, bark, seeds, roots, fruits, or sap) which contain flavoring and aromatic compounds as well as essential oils. Thanks to their antioxidant content, spices are also used to preserve foods, beverages, and spice mixtures. This is also known as spices’ antioxidant activity.
The presence of antioxidants may be natural or added artificially. Rosemary, for example, contains high levels of carnosolic acid and has potent antioxidant, antimicrobial, and anti-inflammatory properties. Furthermore, the oxygen radical absorbance capacity of rosemary helps to scavenge free radicals, lending health benefits and possible protection against heart disease. Rosemary powder or extract is therefore used as a natural favorite antioxidant and is of economic importance in the food industry.
However, processing spices (especially drying and storage) reduces the total antioxidant content over time and can lead to a loss in quality. It is therefore important to monitor and analyze the antioxidant compounds in spices as a quality parameter.
The 892 Professional Rancimat is an analytical system to easily and safely determine the oxidation stability of fresh and dried herbs as well as spices and seasonings with the PEG method according to AOCS Cd 12b-92 and ISO 6886.
Introduction
When measuring stability with the Rancimat, the PEG (polyethylene glycol) method has proven to be the most effective analytical technique aside from direct measurement. It is particularly suitable for products with a complex matrix, samples with low fat or high water content, or if time-consuming sample preparation should be avoided.
Because the PEG method requires no sample preparation, the entire sample (including the matrix) is analyzed. As many spices and seasonings naturally contain high antioxidant levels or have added stabilizers (depending on the use in the final product), the PEG method can be used to determine the sample’s antioxidant content and antioxidant capacity.
Sample and sample preparation
This application is demonstrated on ground black and white pepper, sliced rosemary, ground caraway, granulated garlic, curry powder, as well as a common seasoning (powdered) with salt and glutamate, as displayed in Table 1.
No sample preparation is required.
Experimental
The determinations are carried out using an 892 Professional Rancimat (Figure 1).
An appropriate amount of sample and PEG are weighed into the reaction vessel, and then the analysis is started.
With the Rancimat method, the sample is exposed to an airflow at a constant temperature of
100–180 °C. Highly volatile secondary oxidation products are transferred into the measuring vessel along with the airflow where they are absorbed in the measuring solution.
The conductivity of the measuring solution is continuously registered. The formation of secondary oxidation products leads to an increase in the conductivity. The time until occurrence of this marked conductivity increase is referred to as the «induction time», which is a good indicator for the oxidation stability (Figure 2 and Figure 3).
Results
Table 1. Summary of results for the oxidation stability of various spices and seasonings with the 892 Professional Rancimat as measured at 120 °C.
| Sample (n = 4) | Mean value in h | SD(abs) in h | SD(rel) in % |
| Black pepper (ground) | 2.92 | 0.18 | 6.0 |
| White pepper (ground) | 1.45 | 0.03 | 2.1 |
| Rosemary (sliced) | 8.70 | 0.75 | 8.6 |
| Caraway (ground) | 1.87 | 0.13 | 7.1 |
| Garlic (granulated) | 0.47 | 0.01 | 2.0 |
| Curry (powdered) | 1.97 | 0.03 | 1.4 |
| Seasoning (powdered) | 0.66 | 0.02 | 3.2 |
Conclusion
Thanks to the PEG method, a reproducible and accurate determination of the oxidation stability of spices and seasonings is possible. Since no sample preparation is required, the direct influence of the complete matrix of the sample is seen—not just the individual components. Using the Rancimat with PEG is therefore a well-suited antioxidant measurement method.
The results show clear differences between different spices according to their amounts of antioxidants. The induction time for black pepper is nearly twice that of white pepper, while rosemary has the highest induction time of the samples tested in this study.
With the Rancimat, this quality parameter can easily and simultaneously be determined for eight different samples at a time, increasing quality control laboratory throughput. This is possible due to the eight measuring positions in two heating blocks. The built-in display shows the status of the instrument and each individual measuring position. Start buttons for every measuring position enable the measurement start on the instrument.
The use of practical disposable reaction vessels and dishwasher-safe accessories reduces cleaning to a minimum. This saves time and money and significantly improves accuracy and reproducibility.
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