Location: Food Processing and Sensory Quality Research
2024 Annual Report
Objectives
The objective of this research project is to stimulate consumer demand for U.S. farm raised catfish products and increase the profitability of the Catfish Industry through improved product quality.
Approach
By improving methodology for detecting the presence of off-flavor compounds in farm raised catfish, fewer off-flavor fish should reach the consumer, resulting in an increased demand and market share for U.S. farm raised catfish. To improve quality, this project will assess and provide feedback to individual catfish processing plants on the proportion of fish with off-flavors, passing through their plant and will work directly with these plants to control off-flavor issues at the plant. Additionally, current methods for mitigating off-flavors are primarily pre-harvest approaches, and can be costly, time consuming and increase fish stress. Post-harvest research is proposed to treat mildly off-flavored fillets with weak acids and marinades to mitigate the off-flavor compounds and expand the catfish line of products. Furthermore, methods for improving shelf life of fresh and frozen fillets will be examined using UV-C light, and vacuum packaging. Research proposed here will enable the existing U.S. Catfish Industry to better control quality, provide new co-products and improve shelf life.
Progress Report
The research unit has successfully filled the vacant Research Chemist position, which is critical for ongoing projects. This ensures the research unit can continue research into catfish off-flavor issues, enhancing the quality and efficiency of research.
In support of Objective 1, ARS scientists at New Orleans, Louisiana conducted research on consumer lexicons (postponed 12-month milestone) and sensitivity to geosmin off-flavor in water. In this multiregional U.S. study, ARS scientists collected data from 188 consumers in the Southern region (at Louisiana State University), 115 consumers in the Northeastern region (at Rutgers University), and 186 consumers in the Midwestern region (at Bowling Green State University). Overall, consumers used “earthy” most often to describe geosmin aroma and flavor. However, consumers’ location and native language significantly influenced descriptors selected. Assessors in New Jersey were more likely to use the terms “beets” and “musty” than their counterparts in Louisiana, while those in Ohio were less likely to select “muddy.” Non-native English speakers were more likely to use the term “moldy” and less likely to use “dirt.” The research also revealed that 39% of consumers detected no aroma at the lowest geosmin concentration tested (20 ng/L), and 9% of consumers still reported no aroma at the highest concentration (1,000 ng/L). Consumers experienced higher intensities based on flavor than aroma. These results allow for improved evaluation of geosmin in sensory studies of consumers, who vary in their sensitivity and terminology used for off-flavors.
In support of Objective 2, ARS researchers collaborated with Kodiak Island WildSource, a Sun’aq Tribe-owned seafood business, to produce smoked catfish fillets and bellies as a value-added product during FY23. After preliminary sensory testing of these prototypes, ARS researchers optimized smoking parameters, allowing for the products to be produced at SRRC at research-level volumes. ARS scientists have designed consumer and expert sensory tests to be conducted in the Pacific Northwest and Alaska, respectively. Along with evaluating key sensory attributes and overall acceptability, the questionnaire focusses on the willingness-to-pay response. The resultant data will inform viability of hot smoking as a value-added processing method for catfish bellies and fillets.
ARS scientists in New Orleans, Louisiana have completed development of a new method for off-flavor quantitation using stable isotope dilution to increase accuracy and precision in detecting geosmin and other off-flavor compounds in fish flesh. This method improves upon the traditional analytical methods, which previously suffered from inconsistent analyte recoveries. The new approach accounts for this large variability (20-85%) while increasing sample throughput.
The potential use of weak acids to remove off-flavors in post-harvest catfish was investigated by ARS researchers in New Orleans, LA. The reactivity of two off-flavor compounds, geosmin and 2-methylisoborneol, was evaluated in acidic aqueous solutions at various pH levels. Highly acidic conditions (pH < 3), which are impractical for treatment of catfish fillets, were necessary to induce degradation of either compound. Additionally, the observed reactivity was reversible upon pH neutralization. These results suggest that flavor improvements in citrus-treated catfish may be due to a different mechanism, such as flavor-masking, rather than degradation.
Researchers from the ARS in New Orleans, LA evaluated low doses of germicidal UV-C light for reducing surface bacteria on fresh catfish fillets. Reductions in surface bacteria were observed in UV-C treated fillets during 3 days of storage when compared to untreated fillets. However, subsequent experiments with greater sample sizes showed inconsistent results. They hypothesized that the variability in efficacy stems from the samples' inherently variable optical properties. They observed no negative changes in quality, such as color or rancidity following the UV-C light treatment. These findings suggest that UV-C light can complement other shelf-life extending techniques like modified atmosphere packaging without negatively affecting quality. However, due to the variable nature of catfish fillets, further research is needed to optimize the treatment's efficacy. To address this, ARS scientists have started collaborations with Louisiana State University to investigate various packaging technologies and their effects on fish fillet shelf-life when combined with UV-C treatments.
Accomplishments
1. Enhanced method for accurate, precise, and efficient detection of off-flavor compounds in catfish. Researchers estimated the total economic loss from off-flavor catfish to be $74 million in a $366,843,000 industry in 2022. Accurate and precise detection of off-flavors is critical to studying and resolving this issue. ARS researchers in New Orleans, Louisiana, focused on enhancing the detection of geosmin, 2-methylisoborneol (MIB), and other off-flavors in fish flesh. Traditional methods for detecting these compounds proved inconsistent, with variability ranging from 20-85%. This inconsistency challenged accurate quantification and analysis of off-flavors. To address this issue, ARS scientists developed a method using stable isotope dilution, significantly improving both the accuracy and precision of detecting off-flavor compounds in fish flesh. Additionally, the approach enhances sample throughput, unlike the traditional microwave distillation method, which processes single samples and is labor-intensive. The new method can analyze up to 20 samples simultaneously, resulting in an approximately 160-fold increase in sample throughput. Furthermore, it reduces labor and equipment needs by cutting down the reliance on glassware and significantly minimizing time spent on preparation and cleanup, thus streamlining the entire process. This new method enables scientists and industry professionals to conduct more precise and accurate analyses of off-flavors in fish flesh. With this new method, scientists and industry professionals are now able to assess the effectiveness of off-flavor mitigation strategies both pre- and post-harvest.
