Abstract
Omega-3 fatty acids play a role in achieving optimal health and protection against various diseases. However, the instability and oxidation of its essential fatty acids have limited its use in food products. Among the strategies used to avoid these challenges, the encapsulation method has been the most successful. Therefore, the present study was performed to improve the stability of fish oil with the encapsulation method and produce a useful product. In this research, the encapsulation of fish oil with a ratio of 3:1 (oil: coating) with malt dextrin, sodium casein, protein whey concentrates, and modified starch (HICAP) by freeze-drying. Yogurt enriched with encapsulated fish oil powder was produced and the physicochemical and sensory properties of the product were evaluated. The results showed that the particle size, particle dispersion index, and encapsulation efficiency of the capsules were 0.85μm, 0.29 and 90%, respectively. Also, the results showed that the syneresis of yogurt enriched with microcapsules was lower and the water holding capacity was higher than the control and sample enriched with non-encapsulated fish oil. The increase of peroxide values in yogurt enriched with encapsulated fish oil had a slower trend than in yogurt enriched with non-encapsulated oil. In all treatments, pH decreased and acidity increased. The sensory evaluation of the treatments revealed that the quality parameters of the yogurt treatments decreased during storage, and the yogurt treatments were enriched with microencapsulated oil, and the control treatment did not show any significant difference in terms of overall acceptance.
 

INTRODUCTION

Oils with high concentrations of polyunsaturated fatty acids (PUFAs) have been increasingly used in food production. Among these, fish oil is an important source of polyunsaturated fatty acids with multiple double bonds, particularly omega-3 fatty acids, mainly EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) (Shegelman et al., 2019). Encapsulation is a technique used to trap bioactive compounds within a wall structure
made of a carrier material (Mahdavi et al., 2022). Given the high potential of our country in harvesting Kilka fish, the oil from this fish can be optimally utilized for fortifying food products, leading to the development of high-quality products with extended shelf life. Therefore, this study aims to prepare and evaluate fish oil-loaded microcapsules with a polysaccharide-protein complex coating for yogurt fortification and to assess its physicochemical and sensory properties.
 

MATERIALS AND METHODS

Kilka fish (Clupeonella cultriventris caspia) were purchased in spring from Khazar Production Company, located in Bandar Anzali. The oil extraction from Kilka fish was performed using the (Bligh and Dyer,1959). To prepare the emulsion, various wall materials were dissolved in distilled water, including maltodextrin (15 g), sodium caseinate (20 g), whey protein concentrate (20 g), and modified starch (20 g). The total solid concentration was set at 20% (w/w). Fish oil was then added to the solution at a ratio of 3:1 (Gallardo et al., 2013). The prepared emulsions were dried in a freeze-dryer under reduced pressure. Polydispersity index (PDI) was measured (Gallardo et al., 2013). Encapsulation efficiency was calculated using the (Ojagh and Hasani, 2018). To prepare functional yogurt, raw milk with 1.5% fat content was used to produce three samples: control yogurt, yogurt containing 2% (w/w) free fish oil, and yogurt containing 2% (w/w) microencapsulated fish oil. Comparative analyses were performed after production and weekly for 21 days (Tamjidi et al., 2013). Acidity was determined using the (Iranian National Standard No.2752, 1994). Syneresis (Ghorbanzade et al., 2022) and water-holding capacity of the yogurt were measured using (Tamjidi et al., 2013). Viscosity was assessed using a Brookfield rotational viscometer and expressed in centipoise (cP). Yogurt fat extraction was conducted and the peroxide value (PV) of the yogurt fat was also determined (Ghorbanzade et al., 2017). Sensory evaluation of the final product was carried out by a 20-member panel. This study was designed as a split-plot test in time within a completely randomized design.
 

RESULTS

The polydispersity index (PDI) of the fish oil-loaded capsules was reported as 0.29 ± 0.05. The encapsulation efficiency of the produced oil capsules was determined to be 89.3 ± 0.2%. Changes in acidity (g/100 g lactic acid) in the produced yogurts during 21 days of storage indicated that acidity increased in all treatments over time. However, this increase was not significant (p <0.05) from day 14 to the end of the storage period. The syneresis rate in all treatments decreased until day 14 of storage, and the syneresis level in the control yogurt was higher than in yogurts enriched with microencapsulated fish oil and free fish oil. Evaluation of syneresis changes during storage revealed that the highest syneresis occurred in the control and enriched samples during the final week of storage. According to the results, the viscosity values of the control and free fish oil-enriched yogurt treatments increased over time. However, in the yogurt treatment enriched with microencapsulated fish oil, the viscosity increased until day 14 of storage and then decreased. The water-holding capacity of all treatments improved over time. Additionally, the peroxide value in yogurts enriched with microencapsulated and free fish oil increased with storage time, with a slower increase observed in the microencapsulated fish oil-enriched yogurt. It was also found that there was no significant difference in overall acceptability between the control yogurt and the yogurt enriched with microencapsulated fish oil.
 

DISCUSSION AND CONCLUSION

Encapsulation efficiency is one of the key factors in determining the stability of encapsulated compounds, as it reflects the presence of surface oil on powder particles and the ability of wall materials to prevent the leakage of encapsulated oil (Ghorbanzade et al., 2017). In the study by Jafari et al. (2008), a relationship was demonstrated between the rapid formation of a shell and a reduced surface oil content. They attributed this to the fact that a quickly formed shell reduces the likelihood of core materials (such as fish oil) reaching the particle surface. Based on the results of the acidity test, it can be concluded that incorporating fish oil into yogurt slows down the pH reduction and acidity increase. These findings are consistent with those of Nejat Pirsaraii et al. (2021), who reported higher acidity levels in cheese enriched with encapsulated fish oil. Syneresis can be considered a primary defect in yogurt, where serum appears on the gel's surface (Ghorbanzade et al., 2022). The highest syneresis levels in the samples occurred during the final week of storage, attributed to increased acidity and the hydrolysis and digestion of soluble proteins by microorganisms over time. This process causes proteins responsible for the desired texture to lose their properties, breaking their bonds with water (Nouri et al., 2013). In yogurt enriched with microencapsulated fish oil, viscosity increased up to day 14 of storage and then declined, which can be attributed to the hydrolysis of soluble proteins by microorganisms as storage time progressed (Hamed et al., 2019). Tamjidi et al. (2013) demonstrated that the peroxide value in yogurt enriched with free fish oil increased more rapidly than in yogurt enriched with microencapsulated fish oil, consistent with the findings of this study. The objective of this research was to develop fish oil-containing microcapsules using different coatings to fortify yogurt. Based on the results, microcapsules containing fish oil can be used for yogurt enrichment without introducing undesirable odors or flavors.
 

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