Author: Zack Ng
Senior Scientist, zack.ng@abvista.com
AB Vista
Post-Pellet Liquid Application (PPLA) is a widely adopted practice in feed mills for applying liquid enzymes after the pelleting process, helping to prevent thermal inactivation and preserve enzymatic activity. Once enzymes are applied, the first and most critical quality control step is to verify the applied dose by measuring enzyme recovery in the finished feed before making any process adjustments or equipment recalibrations. This article outlines key considerations for accurate enzyme quantification, including enzyme storage stability, statistically sound sampling protocols, and intra-laboratory consistency checks – all essential for ensuring data integrity and method robustness.
Figure 1. A typical Post-Pellet Liquid Application system
Follow Your Enzyme Supplier’s Recommended Storage conditions
Proper storage of liquid enzymes is essential to preserve their catalytic activity and ensure consistent in-feed performance. Enzymes such as phytase and xylanase should be stored within the recommended temperature range – typically between 4°C and 23°C – according to product specifications and protected from light exposure and microbial contamination. For enzymes held in intermediate storage tanks, pH stability must be maintained to prevent hydrolytic or oxidative degradation. Routine monitoring of storage parameters, including temperature and pH, is recommended to safeguard enzyme stability prior to application.
Get Sampling Right to Get Recovery Right
After applying the enzyme, the main quality control step is to evaluate how much of the enzyme is retained in the final feed product. To capture within-batch variability, it is recommended to collect approximately 10 feed samples per production run (around 200 g each), strategically sampled across the batch – such as from bags 1 to 2 during the first shift, bags 3 to 5 during the second shift etc. Since one production batch can yield at least 10 bags, the sampling can be spread across different production shifts to better represent the entire batch. Additionally, submitting a retained sample of the liquid enzyme used during the feed application allows for verification of enzyme integrity and stability throughout the process.Top of FormBottom of Form
Accurate Enzyme Recovery Starts with the Right Test
At AB Vista, enzyme verification is conducted using proprietary in-house ELISA (Enzyme-Linked Immunosorbent Assay) methods specifically developed for our phytase (Quantum Blue) and xylanase (Econase XT) products. These assays are optimized for high specificity, minimizing cross-reactivity and reducing the risk of false positives. Compared to conventional wet chemistry methods, ELISA offers advantages in speed, cost-efficiency, and operational simplicity – making it well-suited for routine quality control. For each feed sample, two independent extractions are performed, and each extract is analysed in duplicate, yielding four data points per sample (Figure 2). The data are subjected to statistical evaluation, including coefficient of variation (CV%) checks, to ensure intra-sample consistency before final reporting.
For feed mills equipped with on-site laboratories, ELISA methods can be readily implemented with minimal instrumentation and training. For facilities without in-house testing capabilities, AB Vista offers both regional and global laboratory services, along with support for ELISA method setup, validation, and operator training. Additionally, AB Vista supplies QuickStix™ kits – easy-to-use test strips designed for the rapid detection of phytase or xylanase activity in feed (Figure 3). These qualitative test strips provide quick user-friendly screening results within 15 minutes, serving as a practical first-step tool prior to more detailed quantitative analysis.
Table 1: Example enzyme recovery results from 10 feed samples collected during the same PPLA production run. Note: The numbers provided are examples only and are not drawn from actual measurements.
| Sample description | Expected Activity | Laboratory Results |
| Liquid Enzyme product Lot XXXXXX | Min. 5,000 FTU/g | 6500 FTU/g |
| Sample 1 | 1000 FTU/kg | 1050 FTU/kg |
| Sample 2 | 890 FTU/kg | |
| Sample 3 | 950 FTU/kg | |
| Sample 4 | 980 FTU/kg | |
| Sample 5 | 1100 FTU/kg | |
| Sample 6 | 1090 FTU/kg | |
| Sample 7 | 1200 FTU/kg | |
| Sample 8 | 1120 FTU/kg | |
| Sample 9 | 990 FTU/kg | |
| Sample 10 | 920 FTU/kg |
Interpretation of enzyme recovery results may vary between customers, depending on internal quality assurance protocols and acceptable tolerance thresholds. At AB Vista laboratories, each feed sample is treated as an independent analytical replicate, with reporting based exclusively on the experimentally measured values. This approach ensures objectivity, eliminates bias from assumptions or adjustments, and supports transparency and confidence in the reported enzyme activity data.
Conclusion
Post-Pellet Liquid Application (PPLA) remains one of the most effective methods for preserving enzyme activity during feed production. However, achieving accurate dosing goes beyond application – it requires proper enzyme storage, well-designed sampling protocols, and reliable testing methods. Tools such as ELISA and QuickStix™ provide feed mills with reliable and easy-to-use methods for checking enzyme recovery. At AB Vista, we are committed to supporting the industry with the products, tools, and expertise needed to ensure enzymes are applied consistently and correctly – batch after batch.