Utilization of Some Essential Oils to Extend The Shelf -Life of Coated Semi Fried NilePerch Fish Fillets during Cold Storage

摘要

This research was performed to evaluate the antioxidant and antimicrobial effects of marjoram (Marjorana hortensis), mint (Mentha piprita) and thyme (Thymus capitatus) essential oils as natural preservatives to extend the shelf - life of coated semi fried Nile perch ( Lates niloticus) fish fillets. Skinless Nile perch fish fillets were treated with two ratios; 0.5 (T1) and 1.0 (T2) ml of marjoram essential oil per 100g fish fillets,1.5 (T3) and 2.0 (T4) ml of mint essential oil per 100g fish fillets and with 0.5 (T5) and 1.0 (T6) ml of thyme essential oil per 100g fish fillets. The treated fish fillets with tested essential oils and untreated one (control sample) were coated with dough mixture (wheat flour, cold water, whole egg, sodium chloride, cumin powder and xanthan gum) and fried at 170±5oC for 1 mint .The coated semi fried fillets were packed in polyethylene bags and after that stored at 4±1oC for 16 days. The physico-chemical quality criteria; total volatile basic-nitrogen (TVB-N) content, trimethylamine-nitrogen (TMA-N) content, thiobarbituric acid (TBA) value, acid value and the pH value, microbiological quality indices; the total viable bacteria (TVB), psychrotrophic bacteria, pseudomonas spp. bacteria and yeasts and molds counts, and sensory analysis were used to evaluate the preservative effect of tested essential oils during storage at 4±1oC for 16 days. The present results showed that there was a significant (P≤0.05) increase in TVB-N, TMA-N, TBA and acid values in different ratios depending on the ratio and the kind of tested essential oil itself. The lowest significant incremental rate was recorded in samples (T2). All treatments, except (T3), gave significantly (P≤0.05) reduction in the TVB-N values and psychrotrophic, and pseudomonas spp. bacteria counts immediately after treatment as compared with control treatment. The marjoram, mint and thyme essential oils in both ratios were able significantly to reduce the yeast and mold counts immediately at zero time .The increase in all tested microbiological quality criteria continued during the cold storage in all treatments which was lower than control sample. The obtained results also showed that there was a significant (P≤0.05) enhancement in sensory quality attributes of fish fillets’ samples treated with marjoram, mint and thyme essential oils at both tested ratios. In general, the tested essential oils’ treatments caused a significant (P≤0.05) extending of the shelf-life, as well as enhancement the physico-chemical, microbiological and sensory quality attributes for coated semi fried Nile perch fish fillets during cold storage. In addition, fish samples treated with 1.0 ml marjoram essential oil (T2) followed by samples treated with 1.0 ml thyme essential oil (T6) per 100 g fish fillets attained the highest scores for sensory quality attributes and exhibited the better acceptability than the control and the other treated fish samples. Therefore, the present findings recommended that the essential oils of marjoram, mint and thyme should be utilized for extending the shelf-life and enhancing quality attributes of coated semi fried fish fillets during cold storage.