Microbiological and Organoleptic Quality Assessment of Milkfish (Chanos chanos) from Kupang Aquaculture Ponds, Sidoarjo, Indonesia

Introduction

Indonesia, an archipelagic nation with more than two-thirds of its territory consisting of aquatic environments, possesses extensive fisheries and aquaculture resources that play an important role in food security and economic development (1, 2). Among cultivated fish species, milkfish (Chanos chanos) is one of the dominant aquaculture commodities in Indonesia due to its adaptability to brackish water environments, ease of cultivation, and high consumer demand (3). In East Java, milkfish consumption exceeds 182, 000 tons annually, highlighting its significant contribution to regional food supply and the local economy (4, 5).

However, aquaculture production in several regions faces increasing environmental challenges, particularly in pollution-prone areas such as Sidoarjo Regency (6). The Porong River and adjacent coastal inlets, which serve as water sources for many brackish aquaculture ponds including those in Kupang Village, Jabon Subdistrict, are known to receive industrial discharge, domestic waste, and residual pollutants originating from the Lapindo mudflow area (7). These environmental pressures raise concerns regarding the safety and quality of aquaculture products, especially fish intended for direct human consumption.

Previous studies in Sidoarjo have reported the presence of environmental contaminants, including toxic metals and pathogenic microorganisms, in aquatic environments and aquaculture products (8). Such contaminants may enter the food chain and potentially pose risks to human health. Nevertheless, not all forms of environmental contamination directly affect the external appearance or immediate sensory characteristics of fish, making targeted quality assessment essential.

Several studies conducted in Sidoarjo have examined heavy metal accumulation and bacterial contamination in aquaculture products; however, most of these investigations focused on individual parameters rather than integrated quality assessment (9, 10). As a result, information combining microbiological safety and sensory-based quality indicators remains limited, particularly for milkfish produced in environmentally vulnerable aquaculture areas. Microbiological contamination and organoleptic quality are widely recognized as primary indicators of fish safety and freshness. Pathogenic bacteria such as Salmonella spp. and Escherichia coli are commonly used as indicators of hygiene and food safety, with Salmonella subject to a zero-tolerance standard in fresh fish products (8). In parallel, organoleptic assessment evaluates sensory attributes including appearance, odor, flesh firmness, and texture, providing a practical measure of freshness, marketability, and consumer acceptability.

Although chemical contaminants such as toxic metals have been reported in previous studies in the Sidoarjo area, this study does not address chemical contamination as a primary focus. Instead, the present research concentrates on microbiological safety and organoleptic quality as practical and directly observable indicators of milkfish safety and freshness.

Therefore, this study aims to evaluate the microbiological quality and organoleptic characteristics of milkfish (Chanos chanos) harvested from aquaculture ponds in Kupang Village, Jabon Subdistrict, Sidoarjo Regency. By focusing on the detection of Salmonella spp. and Escherichia coli alongside standardized organoleptic assessment, this research seeks to provide an integrated evaluation of milkfish quality in an economically important yet environmentally challenged aquaculture region.

Experimental Section

Study Design and Rationale

This study employed a descriptive cross-sectional design to evaluate the microbiological safety and organoleptic quality of fresh milkfish (Chanos chanos) harvested from aquaculture ponds in Kupang Village, Jabon Subdistrict, Sidoarjo Regency. The study area was selected because aquaculture ponds in this region utilize water from the Porong River, which has been reported to be influenced by various anthropogenic activities.

Sampling Strategy and Sample Size

Milkfish samples were collected from aquaculture ponds in Kupang Village using purposive sampling. A total of 20 fresh milkfish samples were collected and analyzed in this study. All samples were subjected to organoleptic assessment and microbiological examination to ensure consistency between methods and results.

Microbiological Procedures

Microbiological analysis was conducted to detect Salmonella spp. and Escherichia coli in fresh milkfish (Chanos chanos) in accordance with SNI 2729: 2021 concerning microbiological criteria for fresh fish. A 25 g portion of fish flesh was aseptically homogenized in 225 mL Buffered Peptone Water (BPW) and incubated at 37 ± 1°C for 24 h for pre-enrichment. Enriched samples were streaked onto selective media for bacterial isolation. Salmonella spp. was isolated using Bismuth Sulfite Agar (BSA), while Escherichia coli was detected using MacConkey Agar.

Presumptive colonies were confirmed through Gram staining and standard biochemical tests. Confirmation of E. coli included inoculation into Brilliant Green Bile Broth (BGBB), with gas production interpreted as a positive result. All procedures were performed under aseptic conditions in accordance with good laboratory practices.

Organoleptic Assessment

Organoleptic assessment was conducted to evaluate the sensory quality of fresh milkfish (Chanos chanos) using standardized methods in accordance with SNI 01-2346-2006 concerning sensory evaluation of fresh fish. The assessment was carried out by a trained panel consisting of five individuals with prior experience in fish quality evaluation.

Each sample was evaluated based on key sensory attributes, including eye clarity and condition, gill color and mucus, flesh firmness and elasticity, and the presence of off-odors. All evaluations were performed under controlled laboratory conditions to minimize external influences on panelist perception. A nine-point hedonic scale was applied, with higher scores indicating superior freshness and quality. Samples were classified into predefined quality categories ranging from “very fresh” to “spoiled” based on their average scores. The organoleptic assessment complemented microbiological findings by providing a qualitative indicator of freshness, marketability, and suitability for human consumption.

Data Analysis

Microbiological results were interpreted descriptively and compared with microbiological criteria for fresh fish quality as specified in SNI 2729: 2021. Organoleptic scores were summarized using descriptive statistics and interpreted according to standard quality categories: fresh (≥ 7), medium (5-6), and spoiled (< 5). Cross-tabulation was used to explore the relationship between microbiological results and sensory quality.

Results and Discussion

Organoleptic and Microbiological Quality of Fresh Milkfish

Microbiological analysis was conducted on 20 fresh milkfish (Chanos chanos) samples to detect the presence of Salmonella spp. and Escherichia coli in accordance with SNI 2729: 2021, which stipulates microbiological safety criteria for fresh fish. The results showed that 3 out of 20 samples (15%) tested positive for Salmonella spp., while the remaining 17 samples (85%) were negative. Presumptive Salmonella colonies observed on selective media were subsequently confirmed through Gram staining and biochemical tests. In contrast, Escherichia coli was not detected in any of the analyzed samples.

Although Salmonella spp. contamination was detected in a relatively small proportion of samples, its presence is of particular concern because SNI 2729: 2021 applies a zero-tolerance standard for pathogenic bacteria in fresh fish. This means that even a single positive detection renders the product unsafe for consumption. These findings indicate that good visual quality does not necessarily reflect microbiological safety.

Organoleptic Quality of Milkfish from Kupang Village Aquaculture

Kupang Village, located in Jabon Subdistrict, Sidoarjo Regency, is the largest milkfish aquaculture area in the region and a major supplier to local and regional markets, including the Sidoarjo Fish Market (BPS, 2018) (11). However, several inland ponds rely exclusively on water from the Porong River, which has been reported as environmentally contaminated and potentially harmful to aquaculture products and public health (12).

To assess sensory quality, an organoleptic evaluation was conducted on 20 milkfish samples using a nine-point hedonic scale following the Indonesian National Standard for fresh fish (SNI 01-2346-2006) (13). The evaluation revealed organoleptic scores ranging from 7 to 9, indicating good to excellent freshness and confirming that the fish were sensorially acceptable for consumption (Table 1).

Organoleptic evaluation was conducted on 20 fresh milkfish samples using a nine-point hedonic scale in accordance with SNI 01-2346-2006. The assessed sensory attributes included appearance, odor, flesh firmness, and texture. Scores ranged from 1 (very poor/spoiled) to 9 (very fresh/excellent quality). The overall mean organoleptic score calculated from all 20 samples was 8.05 ± 0.82 (mean ± standard deviation), indicating generally high sensory quality.

Microbiological Safety Assessment of Milkfish

Microbiological testing followed a multi-stage protocol comprising pre-enrichment, selective enrichment, bacterial isolation, and biochemical confirmation to ensure reliable detection of Salmonella spp. contamination. Of the 20 samples tested, only three were confirmed positive after biochemical profiling, indicating citrate-positive, methyl red-positive, Voges Proskauer-negative, and indole-negative reactions consistent with the positive control strain.

The detection of Salmonella spp. in milkfish samples is likely associated with several contributing factors, including the use of aquaculture water sourced from the Porong River, suboptimal sanitation of harvesting and storage equipment, and inadequate temperature control during transportation and market handling. Warm environmental conditions and poor hygiene practices can accelerate bacterial proliferation and compromise microbiological quality (16).

Although only 3 of 20 samples tested positive, the 15% prevalence of Salmonella spp. remains critical because SNI 2729: 2021 enforces a zero-tolerance standard for pathogenic bacteria in fresh fish. This prevalence falls within the range reported in comparable tropical aquaculture systems (approximately 5–20%), particularly in ponds utilizing untreated surface water sources.

The contrast between the high organoleptic scores (8.05 ± 0.82) and the presence of Salmonella spp. highlights that sensory freshness does not guarantee microbiological safety. Organoleptic parameters primarily reflect physical freshness and spoilage-related changes, whereas pathogenic bacteria may be present without causing noticeable alterations in odor, texture, or appearance.

The 15% prevalence observed in this study is comparable to findings reported in other tropical aquaculture regions, where Salmonella contamination ranges from 8–18% in surface-water-based pond systems. However, the absence of Escherichia coli in all samples suggests that fecal contamination may be intermittent rather than continuous. Importantly, pathogenic bacteria such as Salmonella do not necessarily produce early spoilage metabolites detectable through sensory evaluation, which explains why samples with high organoleptic scores (≥ 8) may still harbor microbiological hazards. Organoleptic parameters primarily reflect biochemical spoilage processes (e. g. , proteolysis and lipid oxidation), whereas pathogenic contamination can occur without visible or olfactory alterations.

Similar findings have been reported in previous studies, which emphasize that acceptable organoleptic quality does not guarantee microbiological safety (14, 15). Therefore, routine microbiological monitoring and stricter implementation of cold-chain systems are essential to minimize foodborne risks.

Improving awareness among aquaculture practitioners regarding proper sanitation, water quality management, and post-harvest handling is strongly recommended. Support from local authorities particularly in providing technical training, cold-storage infrastructure, and regular monitoring of pond water quality will be crucial to ensuring sustainable and safe milkfish production in Kupang Village (17–20).

Conclusion

This study found that milkfish (Chanos chanos) from Kupang Village ponds generally exhibited good physical freshness, although Salmonella sp. contamination was detected in 3 of 20 samples, posing potential food safety risks. The research was limited to testing Salmonella sp. and E. coli, without assessing other pathogens, using molecular diagnostics, or considering seasonal variations. Strengthening cold-chain management, improving pond water quality, and expanding microbial monitoring are recommended to enhance product safety and sustainability.