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Volume 13, Issue 2, 2024

Online ISSN: 2182-1054

Volume 13 , Issue 2, (2024)

Published: 18.10.2024.

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18.04.2020.

Original scientific paper

Bacterial diversity, biogenic amines and lipids oxidation in traditional dried anchovy (Encrasicholina punctifer) during ambient storage

This study aimed to elucidate the effect of ambient storage (23±2°C, 68% RH) on the bacterial load and diversity, biogenic amines and lipids oxidation in traditional dried anchovy (E. punctifer) in order to evaluate its safety, quality and stability during 12 weeks of storage. Total aerobic bacteria (TAB), Staphylococcus aureus, Enterobacteriaceae (ENT), histidine decarboxylating bacteria (HDB), lysine decarboxylating bacteria (LDB) and ornithine decarboxylating bacteria (ODB) were enumerated and identified by conventional, VITEK 2 compact and sequencing of 16S rRNA gene methods. Histamine, cadaverine and putrescine contents were determined by high performance liquid chromatography. Lipid oxidation was evaluated by peroxide value (PV). Total aerobic bacteria, S. aureus, ENT, HDB, LDB and ODB initial counts of log10 4.9 ± 0.85, 3.7 ± 0.57, 4.2 ± 0.05, 3.7 ± 0.72, 3.9 ± 0.40 and 4.1 ± 0.24 CFU/g respectively did not significantly change (p > 0.05) during 12 weeks of storage. A high bacterial diversity of 27 species belonging to 20 genera was found, with the dominance of S. aureus, Acinetobacter lwoffii and S. warneri and the first incidence of Psychrobacter celer, Desemzia incerta, Granulicatella elegans and Bhargavaea indica in dried fish.  Initial histamine, cadaverine and putrescine contents and PV of 5.2 ± 4.3, 8.5 ± 1.9 and 5.8 ± 0.6 mg/100g and 0.19 ± 0.02 meq/kg respectively did not significantly change (p > 0.05) during 12 weeks of storage. This study found that ambient storage at 23±2°C, 68% RH for 12 weeks did not affect the bacterial load,  biogenic amines and lipids, and that the dried anchovy remained microbiologically safe and of good quality.

Ismail Al Bulushi, Nejib Guizani, Mutamed Ayyash, Mohammed Al Za'abi, Aisha Abushelaibi, Hilton C. Deeth, Zahra Al Kharousi, Fathiya Al Hamadani, Salha Al Maskari, Jamila Alkalbani

01.12.2018.

Professional paper

Moisture sorption isotherm and thermal characteristics of freeze-dried tuna

Water activity is considered an important factor in assessing the stability of food. Understanding the relationship between water activity and equilibrium moisture content (moisture sorption isotherm) benefits food processing in terms of modeling of drying and estimation of shelf life. In addition, glass transition helps to quantify molecular mobility which helps in determining the stability of food. The aim of this study was to determine the moisture sorption isotherm and thermal characteristics of freeze-dried tuna. These characteristics will help in determining the monolayer moisture and glassy state of the product, at which food is considered most stable. Moisture sorption isotherm at 20°C and thermal characteristics (over a wide temperature range i.e. from -90 to 250 °C) of freeze-dried tuna flesh were measured. Isotherm data were modeled by BET (Brunauer-Emmett-Teller) and GAB (Guggenheim-Anderson–De Boer) models. The GAB and BET monolayer water values were determined as 0.052 and 0.089 g g-1 dry-solids (dry-basis), respectively. In the case of samples at moisture contents above 0.10 g g-1 (wet basis), DSC (Differential Scanning Calorimetry) thermograms showed two-step state changes (i.e. two glass transitions), one exothermic peak (i.e. molecular ordering) and another endothermic peak (i.e. solids-melting). However, the sample at moisture content of 0.046 g g-1 showed three-step state changes (i.e. three glass transitions). The multiple glass transition could be explained by the natural heterogeneity of tuna flesh and inhomogeneity due to molecular incompatibility of the different compositions. The moisture content did not affect the first glass transition temperature nor the exothermic peak (p>0.05), whereas the third glass transition temperature decreased (i.e. plasticized) with increasing moisture content (p<0.05). The solids-melting peak temperature decreased, and enthalpy increased with decreasing moisture content (p<0.05).

Mohammad Shafiur Rahman, Mohammed Khalfan Al-Khusaibi, Kutaila Abbas AL-Farsi, Ismail Mohamed Al-Bulushi, Aisha Abushelaibi, Nasser Al-Habsi

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