Preservative Potential of Turmeric Powder on the Quality and Storage Stability of Bronze Featherback (Notopterus notopterus) Fishcake

Introduction: The seafood industry seeks natural, consumer-acceptable alternatives to synthetic preservatives to extend product shelf life while maintaining quality and safety. Plant-derived compounds — essential oils, phenolics and polyphenols — have shown potential to inhibit spoilage organisms and oxidative reactions in fish and seafood products. Turmeric (Curcuma longa L.) is a widely used spice and traditional preservative; its principal bioactive, curcumin, along with other curcuminoids and volatile oils, exhibits antioxidant and antimicrobial properties that can retard microbial growth and lipid oxidation in foods. Several studies report turmeric or curcumin-containing formulations (extracts, microcapsules, films) that improve oxidative stability and reduce microbial spoilage in various foods, including fish and meat products. Given turmeric’s long history of use, low cost, and regulatory acceptance as a food colorant/ingredient (E100), investigating its practical application in ready-to-eat fish products is timely.

This study aimed to evaluate the preservative efficacy of turmeric powder, at different inclusion levels, on the quality and refrigerated storage stability of bronze featherback fishcake. Specific objectives were to: (1) quantify changes in microbiological and biochemical spoilage indices over storage; (2) assess physical and sensory quality retention; and (3) identify the turmeric concentration that best preserves quality while retaining consumer acceptability.

2. Materials and Methods

2.1 Materials

Fresh bronze featherback (Notopterus notopterus) were procured from a local market on the day of processing and transported on ice to the laboratory. Fresh turmeric rhizomes (Curcuma longa) were obtained from a local supplier, washed, dried, and milled to fine powder (mesh 60). All reagents were analytical grade.

2.2 Fishcake Preparation and Treatments

Fish were descaled, eviscerated, filleted and minced. Four treatments were prepared:

• Control (C): fish mince + standard seasonings (salt 1.5% w/w, pepper 0.2%, binder: wheat flour 5%)
• T1: Control + 1% turmeric powder (w/w)
• T2: Control + 2% turmeric powder (w/w)
• T3: Control + 4% turmeric powder (w/w)

The mince and ingredients were mixed uniformly, formed into 50 g patties, and cooked on a hot plate (180 °C) for 4 min each side to an internal temperature of ~72 °C. Samples were cooled to ambient, packaged in polyethylene trays with low-permeability film, and stored at 4 ± 1 °C. At each sampling day (0, 3, 6, 9, 12, 15), triplicate samples from each treatment were analyzed.

2.3 Microbiological Analyses

Total viable counts (TVC) and psychrotrophic counts were enumerated using Plate Count Agar incubated at 37 °C for 48 h (TVC) and at 7 °C for 10 days (psychrotrophs). Results expressed as log CFU/g.

2.4 Chemical and Biochemical Indices

• pH: Measured using a calibrated pH meter on homogenates (10 g sample + 90 mL distilled water).
• Total volatile basic nitrogen (TVB-N): Determined by micro diffusion method and expressed as mg N/100 g sample.
• Thiobarbituric acid reactive substances (TBARS): Measured as mg malonaldehyde/kg sample to estimate lipid oxidation.

2.5 Physical and Sensory Analyses

• Color: L*, a*, b* measured using a colorimeter on cut surfaces.
• Texture Profile Analysis (TPA): Hardness, cohesiveness, springiness measured using a texture analyzer.
• Sensory evaluation: A trained panel (n = 10) evaluated samples for appearance, odor, taste, texture and overall acceptability using a 9-point hedonic scale.

2.6 Statistical Analysis

Data are presented as mean ± standard deviation. One-way ANOVA followed by Tukey’s HSD test determined significant differences (p < 0.05) among treatments and storage days. Statistical analyses were performed using standard software.

3. Results

3.1 Microbiological Changes

TVC for control samples increased rapidly during storage, reaching spoilage levels (>7 log CFU/g) by day 9. Turmeric-treated samples exhibited delayed microbial growth in a dose-dependent manner. Representative TVC (log CFU/g) means:

Day	Control	T1 (1%)	T2 (2%)	T3 (4%)
0	3.4 ±0.2	3.2 ±0.1	3.3 ±0.2	3.1 ±0.1
3	4.8 ±0.3	4.2 ±0.2	4.0 ±0.2	3.8 ±0.2
6	6.1 ±0.4	5.0 ±0.3	4.6 ±0.3	4.2 ±0.3
9	7.5 ±0.5	6.0 ±0.4	5.3 ±0.4	4.7 ±0.4
12	8.0 ±0.4	7.1 ±0.5	6.2 ±0.4	5.5 ±0.4
15	8.5 ±0.5	8.0 ±0.5	7.1 ±0.5	6.0 ±0.5

Psychrotrophic counts followed a similar trend but were overall lower than TVC. The 2% and 4% turmeric treatments maintained microbial counts below spoilage thresholds for an additional 3–6 days compared to control.

3.2 Chemical Indices (TVB-N, pH, TBARS)

TVB-N increased in all samples during storage; however, turmeric treatments showed significantly lower TVB-N levels at each time point than control. Representative TVB-N (mg N/100 g): Control reached 35 mg/100 g by day 9, while T2 remained at ~22 mg/100 g.

TBARS values (mg MDA/kg) indicated pronounced lipid oxidation in control samples (increasing from 0.4 to 1.8 mg/kg by day 9). Turmeric treatments exhibited markedly lower TBARS, reflecting antioxidant action of turmeric compounds. The 2% and 4% groups maintained TBARS below 1.0 mg/kg up to day 12.

pH values remained relatively stable in the initial days but rose with spoilage; turmeric treatments delayed the pH increase compared to control.

3.3 Physical and Sensory Properties

Addition of turmeric imparted a yellow hue (higher b* values and lower L*). Texture parameters (hardness, cohesiveness) were slightly affected at 4% inclusion but remained within acceptable ranges for 1% and 2% treatments.

Sensory scores: Control samples dropped below acceptability (score <5) by day 9. T2 (2%) maintained acceptable sensory attributes (appearance, odor and overall acceptability) until day 12. The 4% group showed increased color intensity and slight bitterness perceived by some panelists; thus 4% had lower acceptability despite better microbial control.

4. Discussion

The antimicrobial and antioxidant properties of turmeric observed in this study align with previous reports showing that turmeric extracts and curcumin retard microbial growth and lipid oxidation in food matrices. The dose-dependent inhibition of TVC and psychrotrophic counts suggests that turmeric constituents — curcuminoids and volatile oils — act synergistically to impair spoilage organisms. Lower TBARS and TVB-N in turmeric-treated fishcake indicate reduced oxidative deterioration and proteolytic spoilage, consistent with studies where turmeric/curcumin reduced lipid oxidation and delayed formation of spoilage indicators in seafood and meat products.

Although the 4% turmeric treatment offered the most pronounced preservative effect, sensory drawbacks (strong color and mild bitterness) reduced its practical acceptability. The 2% inclusion provided a favorable compromise: significant preservation with acceptable sensory properties. These findings echo other food studies where moderate turmeric levels or curcumin formulations were most effective without adversely affecting consumer acceptability.

Mechanistically, curcumin and related polyphenols scavenge free radicals and chelate pro-oxidant metal ions, reducing lipid peroxidation. Antimicrobial effects may result from disruption of microbial cell membranes, interference with quorum sensing and inhibition of key cellular enzymes. Formulation approaches (microencapsulation, incorporation in edible films/coatings, or use with chitosan/alginate matrices) can enhance curcumin stability and controlled release, improving preservative performance in complex food systems.

Limitations of the present (draft) study include the use of turmeric powder rather than standardized extract, and the absence of identification of spoilage microbiota by molecular methods. Future work should compare turmeric powder to purified curcuminoid formulations, explore synergistic combinations with other natural preservatives (e.g., chitosan, plant essential oils), and validate commercial-scale trials including challenge tests for pathogens.

5. Conclusion

Turmeric powder, at 2% (w/w) inclusion, effectively improved the refrigerated storage stability and quality of bronze featherback fishcake by reducing microbial growth, limiting lipid oxidation and maintaining acceptable sensory properties. Turmeric represents a promising, low-cost natural preservative for ready-to-eat fish products; however, optimization to balance efficacy and sensory attributes is necessary before industrial application.

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