Fresh ready-to-cook fish fillets are susceptible to loss of freshness and accumulation of off-odour due to accelerated microbial spoilage. Suboptimal storage temperature and packaging conditions accelerate this process, limiting the economic potential. This study investigated the effects of modified atmosphere packaging (MAP) and storage temperature (0 °C and 4 °C) on the volatile compounds (VOCs) of Cape hake (Merluccius capensis) fish fillets as a predictor of shelf life and quality. Fresh Cape hake fillets were packaged under active modified atmosphere (40% CO2 + 30% O2 + 30% N2) and passive modified atmosphere (0.039% CO2 + 20.95% O2 + 78% N2) with or without an absorbent pad and stored at 0 °C and 4 °C for 12 d. The results obtained demonstrated that changes in VOCs and concentration were significantly (p < 0.05) influenced by MAP conditions, storage temperature and duration. A total of 16 volatiles were identified in the packaged Cape hake fillets: 4 primary VOCs and 12 secondary VOCs. The spoilage VOCs identified include tri-methylamine (TMA) (ammonia-like), esters (sickeningly sweet) and sulphur group (putrid). The concentration of secondary VOCs increased continuously during storage. Active-MA-packaged fillets performed better and had lower TMA values of 0.31% at 0 °C on day 12 in comparison to 7.22% at 0 °C under passive on day 6. Ethyl acetate was detected in passive-MA-packaged fillets stored at 0 °C on day 3, and the levels increased to 3.26% on day 6, while active-MA-packaged fillets maintained freshness. This study showed that in conjunction with TMA, VOCs such as esters and sulphur-related compounds could be used as spoilage markers for Cape hake fish fillets.

Mucus, a waste product produced when African catfish undergoes stress, has lubricating effects and could be a potential emulsifier. Emulsions are thermodynamically unstable; researchers have documented synthetic bio-polymers as emulsifiers, but its sustainability is in question. This research aims to establish some physicochemical properties of African catfish mucus (ACM) and its effect in soya milk emulsions. A Zetasizer and Turbiscan were used to measure stability, morphology was determined with Transmission electron microscopy (TEM), while functional groups in ACM and ACM-stabilized soya milk emulsions were determined using Attenuated Total Reflection Fourier Transform Infra-red spectroscopy. ACM is a stable hydrogel with negatively charged (−36.2 mV) loosely bound electrons with polar and non-polar portions. ACM concentrations of 1, 3, and 5 g w/w stabilized soya milk emulsions after 180 min of storage. The spectra of stabilized emulsion revealed interactions with soya milk droplets. ACM encapsulated the stabilized emulsion and conferred a kind of cohesive interaction and stability. Turbiscan revealed that the mucin formed strong cohesive connections with stabilized emulsions and the mucin exhibited adhesive properties. ACM is an excellent natural emulsifier with mucoadhesive properties as it encapsulates soya milk to enhance stability.

Nanoemulsions are alternative means of incorporating functional components into systems. This research aims to model the effect of African catfish mucilage (ACM) concentrations on the particle size (PS) of stable oil-in-water (O/W) nanoemulsions formulated by ultrasonication. A D-optimal mixture design was used to study the influence of three mixture components (MCs) ACM, oil, and water on PS. Morphology and PS were determined with Cryo-TEM and Zetasizer. Findings show that the higher the ACM–emulsifier oil ratio, the higher the nanoemulsion stability as depicted by lower PS. ACM concentration was the factor that had the most dominant effect on the dependent variable (DV) PS. Morphology studies revealed that structural stability was a result of ACM which encapsulated the nanoemulsion by mucoadhesion. The model’s lack of fit (F [0.17, 0.11] = 0.3104; p = 1.49) was not significant, and the predicted R-squared value was 0.9977 and adequate precision was 104.158 indicating a model with adequate goodness-of-fit. The model was adequate to determine the effects of the three MCs on the precise stability parameter for the investigated dependent variable particle size. Therefore, ACM could be used as a natural stabilizer in oil-in-water nanoemulsions that are applicable in biomedical and personal care industries.

This study investigated the effects of modified atmosphere packaging (MAP), storage temperature, and the use of absorbent pads (PAD) on the quality attributes of Cape hake (Merluccius capensis) fish fillets. Fresh Cape hake fillets were packaged under active-MA (40% CO2 + 30% O2 + 30% N2) or passive-MA (0.039% CO2 + 20.95% O2 + 78% N2), with and without PAD, and stored at 0 °C, 4 °C, and 8 °C (to mimic abuse temperature). The control fresh fillets were stored under passive-MAP without PAD at 0 °C, 4 °C, and 8 °C. Headspace O2 gas composition continuously decreased below critical limits under passive-MAP, with an increase in storage temperature. Similarly, O2 levels decreased under active-MAP but did not reach critical levels, with the lowest being 9.5% at 0 °C. The interaction of storage temperature and modified atmosphere had a significant effect on quality attributes of Cape hake fillets. Drip loss was higher in active-MAP packaged fillets without PAD (0.64%) than passive-MAP packaged fillets without PAD (0.27%). Drip loss was significantly reduced when using absorbent pads (p < 0.05). Firmness, color, and pH were better maintained under active-MAP at the lowest temperature of 0 °C. Firmness (work of shear) of active-MA packaged fillets on day 12 at 0 °C and 4 °C was 527 N/s and 506 N/s, respectively. Fillets packaged under active-MAP at 0 °C had longer shelf-life than control passive-MAP fillets.