The effects of chitosan nanoemulsion coating containing Hyssopus officinalis essential oil on melanosis phenomenon in chill stored shrimp samples

Shrimp are highly perishable due to the biochemical, microbiological or physical changes during Post-mortem storage, which results in limited shelf life of the product (Farajzadeh et al., 2016). Melanosis is considered a limiting factor for crustacean preservation. This alteration originates by the action of polyphenol oxidase and in some species, as deep-water rose shrimp, also by the action of activated hemocyanin (Martínez-Alvarez et al., 2020). Traditional methods for shrimp preservation such as cold storage, freezing and chilling can’t suppress effectively spoilage (Farajzadeh et al., 2016). Hyssopus officinalis, as valuable medicinal herb, is widely used in traditional medicine. Due to the increased resistance of pathogenic microorganisms to antibiotics and increasing of treatment costs, attentions has been focused to compounds of natural origin (Pirnia et al., 1399). Nano-applications are named as one of the novel methods, which provide high immobilization efficiency for essential oils (keykhosravy e al., 2020). The nanoemulsion is a stable delivery system with unique physicochemical and practical characteristics including high physical stability, optical transparency and high bioavailability (khanzadi et al., 2020). In this study, the effects of chitosan nanoemulsion coating containing Hyssopus officinalis essential oil were investigated on melanosis phenomenon and color evaluation of shrimp samples during 12 days at 4 °C.

First, Hyssopus officinalis essential oil was prepared; Hyssop oil was extracted separately by water distillation. The essential oils components were identified by GC/MS (Pirnia et al., 1399). This study includes two phases of edible coating preparation and food modeling. After preparation of chitosan nanoemulsion containing essential oil, particle size and PDI were determined (keykhosravy e al., 2020). A dynamic light scattering (DLS) device (Malvern Instruments Ltd., United Kingdom) was utilized to measure the particle size of the nanoemulsion droplets. The distribution of droplet size was considered in the terms of the mean droplet size (z-diameter) and polydispersity index (PDI) (Moghimi et al., 2016). Then, Shrimp samples were provided and they were immediately placed in insulated polystyrene ice flasks and transported to the laboratory of food hygiene, Ferdowsi university of Mashhad, Mashhad, Iran. The fillets were washed completely for removing external particles (Mohajer et al., 2021). Shrimp samples were randomly divided into ten groups:CON: without any coating solutionCH: Chitosan coatingSCH: Sonicated Chitosan coatingSMS: Sodium Metabisulfite coatingHEO 0.5%: Hyssopus officinalis essential oil (HEO) 0.5% (W/V)HEO 1%: Hyssopus officinalis essential oil (HEO) 1% (W/V)CE+HEO 0.5%: Chitosan coarse emulsion coating containing 0.5% (W/V) HEOCE+HEO 1%: Chitosan coarse emulsion coating containing 1% (W/V) HEONE+HEO 0.5%: Chitosan nanoemulsion coating containing 0.5% (W/V) HEONE+HEO 1%: Chitosan nanoemulsion coating containing 1% (W/V) HEO The prepared samples were covered with different solutions for 2 min and were allowed to drain for 1 h. All the samples were placed into zip packs. Lastly, the samples were kept at 4 ± 1 °C for 12 days and analyzed for color evaluation and melanosis during 2/4-day intervals (days 0, 2, 4, 8 and 12). Lightness (+L), yellowness (+b), and redness (+a) of samples were measured with a Hunterlab colorimeter (Hunter Associates Laboratory, Inc., Reston, Virginia, USA), using a CIELab scale (Salehi et al., 2018). Whiteness (W) was also calculated, as described by Park, 1994 (Park et., 1994). Melanosis or black spot of shrimp was performed based on ocular evaluations (Sani et al., 2017). First, the basic sensory evaluation techniques and characteristics of shrimp meat (taste, smell, color, and texture) were introduced to the members of the group. 21 evaluators (20-38 years) were selected from among the staff and students of the Food Hygiene Laboratory of the Faculty of Veterinary Medicine, Ferdowsi University of Mashhad. The evaluators evaluated the samples in individual panels with sufficient light and randomly. For each evaluator, drinking water was placed for the intervals between testing the samples (keykhosravy et al., 2021). Sensory evaluation was performed using a 4-point scoring technique. In this method, a score of four indicates the absence of black spots on the shrimp and a score of one indicates the presence of black spots across the surface of the shrimp.

33 compounds were identified in Hyssop. Most of its compounds include isopinocamphen (35.45%), pinocamphen (11.81%) and beta-pinene (10.12%). The results are in agreement with Najafpour et al. (2001) and Fraternale et al. (2004). The z-diameter and PDI values of CE+HEO 0.5% were determined to be 570.3 ± 15.83 nm and 0.63±0.07, while for CE+HEO 1% were 402.2 ± 2.50 nm and 0.50±0.05, respectively. Z-diameter of the NE+HEO 1% and NE+HEO 0.5% were measured as 385.7 ± 3.09 nm and 538.9 ± 4.40 nm, and their PDI values were 0.55±0.03 and 0.76±0.01, respectively. Color is the most important visual feature for consumers in seafood. A value is infinite and positive values are equivalent to red and negative values are equivalent to green. B values are infinite and positive values are equivalent to yellow and negative values are equivalent to blue, and L index is equal to the brightness of the image which is between 0 zero equivalent to black and 100 Equivalent to full reflection of light (Salehi et al., 2018). On day 12, the lowest amount of redness and yellowness was observed in the groups of chitosan nanoemulsion containing Hyssopus officinalis essential oil (1% and 0.5%) compared to the control group. The brightness of the samples decreased with increasing storage time in all treatments; one of the reasons for this decrease is due to the appearance of black spots. Chitosan nanoemulsion treatment containing Hyssopus officinalis 1% had the highest score and control, chitosan and sonicated chitosan treatments had the lowest score in terms of melanosis by the end of the period compared to the control.

According to the results of this study, chitosan nanoemulsion coating containing Hyssopus officinalis essential oil can maintain the color index in shrimp meat compared to the control group and improve its color and replace synthetic compounds such as sodium metabisulfite as an anti-melanosis compound.