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Brine concentration influences physicochemical composition stability indicators and microbiological quality of Nile tilapia Oreochromis niloticus in Beni Democratic Republic of the Congo

This study demonstrates that brining Nile tilapia with 15% NaCl significantly enhances product stability and microbial safety in eastern Democratic Republic of the Congo by reducing moisture and water activity while eliminating pathogens, thereby supporting the development of standardized artisanal preservation protocols.

Original authors: Patrick Mafikiri Bakwanamaha, Dominique Aganze Mulume, Miyisa Muhiwa Benedictus, Irenge Mitima Honoré, Ortence Kazige Kanyere, Ukweli Ndozondula Martin, Arthur Gladys Ntabala, Lyse Mukuyano Mahinanda

Published 2026-07-14

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Patrick Mafikiri Bakwanamaha, Dominique Aganze Mulume, Miyisa Muhiwa Benedictus, Irenge Mitima Honoré, Ortence Kazige Kanyere, Ukweli Ndozondula Martin, Arthur Gladys Ntabala, Lyse Mukuyano Mahinanda, Djeny Aissi Bisindo, Masika Yalala Dina, Pascaline Ciza Azine

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you have a fresh, juicy Nile tilapia fish. It's like a water balloon filled with delicious protein, but it's also a ticking time bomb for bacteria. In places like Beni, Democratic Republic of the Congo, where refrigerators are rare and the fish spoils fast, people need a way to keep it safe to eat. The researchers in this study decided to test a classic trick: the salt bath, or "brining."

They treated the fish like a science experiment, dunking them into three different "swimming pools" of salty water:

The Fresh Pool (0% salt): Just plain water.
The Mild Pool (7.5% salt): A light sprinkle of salt.
The Heavy-Duty Pool (15% salt): A super-salty ocean.

They left the fish in these pools for 24 hours and then checked what happened. Here is the scoop on what they found.

The Great Water Heist

The most dramatic change was a water heist. Salt is a master thief when it comes to water. When the fish hit the salty pools, the salt pulled the water out of the fish's muscles like a sponge squeezing out a wet towel.

In the Fresh Pool, the fish stayed super wet at 75.42% water.
In the Mild Pool, it dropped to 62.28%.
In the Heavy-Duty Pool, the fish lost a ton of water, ending up at just 56.37% water.

Because the water left, the salt rushed in to take its place. The salt content in the fish jumped from a tiny 0.52% in the fresh pool to a massive 10.89% in the heavy-duty pool. That's nearly twenty times more salt!

The "Dryness" Factor (Water Activity)

The researchers didn't just look at how much water was there; they looked at how available that water was for bacteria to drink. They call this "water activity" ( $a_w$ ). Think of it like a water park: if the water is locked up in a cage (bound to salt), the bacteria can't swim in it.

The fresh fish had a water activity of 0.984 (a huge, open pool for bacteria).
The heavy-duty salt fish dropped to 0.881.

This drop is a big deal. It means the environment became much less friendly for the tiny monsters that cause food to rot. The researchers measured this carefully and found that the 15% salt treatment made the fish much more stable and less likely to spoil quickly.

The Nutritional Shift: Concentration vs. Magic

You might think the fish got "richer" in protein because the numbers went up, but that's a trick of the math. Since the water left, everything else got squished together.

Protein looked like it jumped from 18.72% to 24.13%.
Fat (Lipids) seemed to rise from 2.85% to 4.18%.
Minerals (Ash) skyrocketed from 1.24% to 8.47%.

The paper explains that this isn't magic; it's just concentration. The fish didn't gain new protein; it just lost water, making the protein count look higher. However, one thing actually disappeared: Vitamin C. It dropped from 0.35 mg/100 g to 0.17 mg/100 g. The salt bath washed this sensitive vitamin away, and the fish lost about half of it.

The Microbial Battle: Who Won?

This is where the salt really showed its power. The researchers counted the bacteria like they were counting bugs in a jar.

The Bad Guys (Total Bacteria & Coliforms): In the fresh fish, there were 6.84 log CFU/g of bacteria. In the heavy-duty salt fish, that number crashed to 3.15 log CFU/g. That is a reduction of more than 99%! The salt basically kicked most of the bacteria out of the party.
The Dangerous Invaders: The scary bacteria Salmonella and Shigella were found in the fresh fish but were completely absent in the salted fish. The salt bath wiped them out.
The Tough Survivors: But the salt wasn't a magic wand for everything. Some tough bacteria that love salt (halotolerant) actually grew a bit more in the salty fish. Staphylococcus aureus and yeasts/molds increased slightly. Also, E. coli actually went up a little bit in the salted fish, which suggests that maybe the fish got dirty after the bath or from the water used.

The Verdict

The study used fancy math (like Principal Component Analysis) to show that the amount of salt was the main boss controlling all these changes. The 15% salt bath was the clear winner for making the fish safer and more stable.

However, the paper is careful to say this isn't a "fix-all" solution. While the salt killed the dangerous Salmonella, it didn't stop the tough Staph or the yeasts. The researchers suggest that if you want to use this method, you need to be super clean when handling the fish after the salt bath. You can't just rely on salt alone; you need good hygiene practices too.

So, in the end, a 15% salt bath is a powerful tool to save fish from rotting in hot climates, but it turns the fish into a salty, dry snack that needs to be handled with care to stay safe.

Technical Summary: Influence of Brine Concentration on the Physicochemical and Microbiological Quality of Nile Tilapia in Beni, DRC

Problem Statement
Nile tilapia (Oreochromis niloticus) is a critical source of protein and income in eastern Democratic Republic of the Congo (DRC), particularly in the Beni region. However, the species is highly perishable, and the local lack of cold-chain infrastructure leads to significant post-harvest losses. While traditional brining is widely used by artisanal processors to extend shelf life, the practice often lacks standardized control regarding brine concentration, immersion time, and hygiene. Consequently, there is limited scientific data on how specific brine concentrations affect the physicochemical stability, nutritional profile, and microbiological safety of Nile tilapia under local conditions. This study addresses the need to optimize brining protocols to balance preservation efficiency with product safety and nutritional quality.

Methodology
The study employed a quantitative experimental approach using a Completely Randomized Design (CRD) with three treatments:

T0: Control (0% NaCl, fresh water).
T1: 7.5% NaCl brine solution.
T2: 15% NaCl brine solution.

Healthy Nile tilapia (200–300 g) were sourced from university fish ponds in Beni, DRC. Fish were processed (eviscerated, decapitated) and immersed in the respective brine solutions at a 1:2 (w/v) ratio for 24 hours at 4 ± 1°C. Physicochemical analyses (moisture, pH, NaCl, ash, protein, lipids, water activity, Water Phase Salt) were conducted using AOAC methods. Microbiological quality was assessed using ISO standards for total aerobic mesophilic flora, coliforms, Escherichia coli, Staphylococcus aureus, yeasts/molds, and the presence of Salmonella and Shigella spp. Data were analyzed using ANOVA, Tukey's HSD, correlation analysis, hierarchical clustering, and Principal Component Analysis (PCA).

Key Results
The study found that brine concentration significantly influenced all measured parameters (p < 0.05):

Physicochemical Changes: Increasing salt concentration led to a progressive decrease in moisture (from 75.42% in T0 to 56.37% in T2) and pH (from 6.82 to 6.41). Conversely, NaCl content rose from 0.52% to 10.89%, and Water Phase Salt (WPS) increased from 0.69% to 16.19%. Water activity ( $a_w$ ) decreased significantly from 0.984 to 0.881 in the 15% treatment, indicating enhanced stability.
Nutritional Composition: Apparent increases in protein (18.72% to 24.13%), lipids (2.85% to 4.18%), and ash (1.24% to 8.47%) were observed in the 15% treatment. The authors attribute these changes to concentration effects resulting from osmotic dehydration rather than actual nutrient enrichment. Vitamin C content decreased by approximately 51.4%, likely due to its water-soluble nature and oxidation.
Microbiological Quality: The 15% NaCl treatment (T2) resulted in the most substantial reduction in total aerobic mesophilic counts (from 6.84 to 3.15 log CFU/g) and total coliforms (from 4.80 to 1.85 log CFU/g). Crucially, Salmonella spp. and Shigella spp., present in the control, were eliminated in both brined treatments. However, the study noted a moderate increase in halotolerant organisms, including Staphylococcus aureus and yeasts/molds, and a slight increase in E. coli in the highest salt treatment, suggesting potential secondary contamination during processing.
Multivariate Analysis: Correlation and PCA confirmed that salt concentration was the primary factor driving variability. The analysis clearly separated variables associated with natural fish composition (moisture, pH, endogenous minerals) from those associated with brining (NaCl, ash, WPS).

Significance and Claims
The paper claims that brining is an effective preservation method for Nile tilapia in the Beni region, with the 15% NaCl concentration providing the greatest improvement in product stability and microbial safety. The study demonstrates that this concentration effectively reduces water activity to levels that restrict the growth of many spoilage and pathogenic bacteria, specifically eliminating Salmonella and Shigella.

However, the authors maintain a modest stance regarding total safety. They emphasize that while brining reduces the load of non-halotolerant pathogens, it does not guarantee the elimination of all microorganisms, particularly halotolerant species like S. aureus and fungi. Therefore, the paper concludes that brining must be integrated with strict Good Hygiene Practices (GHP) and Good Manufacturing Practices (GMP) to prevent secondary contamination. The findings support the development of standardized brining protocols for artisanal processors in eastern DRC to reduce post-harvest losses and enhance food security, provided that sodium content and hygiene are carefully managed.

The Great Water Heist

The "Dryness" Factor (Water Activity)

The Nutritional Shift: Concentration vs. Magic

The Microbial Battle: Who Won?

The Verdict

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