Volume 4, Issue 1, March 2015, Pages 33–40
Open Access
Abstract
The
present study was preformed to evaluate the effect of dip treatments by
thyme (Thymus vulgaris) extract (0.5%) and rosemary (Rosmarinus
officinalis) extract (1.5%) on the quality and shelf life of Nile
tilapia (Orechromis niloticus) fillets during refrigerated storage at
2 ± 1 °C. The control (untreated) and treated groups were examined
periodically at day zero and every 3 days (0, 3, 6, 9, 12, 15, 18, ....)
during refrigeration until apparent decomposition of each group, with
sensory, physicochemical and microbiological methods. The obtained
results showed that thyme extract has strong antimicrobial and
antioxidant activity and can maintain the quality parameters and extend
the shelf life of refrigerated Nile tilapia fillets for 9 days longer
than control one, while rosemary extract had efficient antioxidant
activity with weak antimicrobial action.
Keywords
- Thyme;
- Rosemary;
- Nile tilapia;
- Microbiological;
- TBA;
- TVB-N
1. Introduction
About one-third of the world's food production is lost annually as a result of microbial spoilage (Lund et al., 2000).
The high levels of moisture, free amino acids and polyunsaturated fatty
acids, and nutrient content, in addition to high amount of naturally
present autolytic enzymes and high pH render fish an easily perishable
product, often going bad within a short period under refrigerated
conditions (Cakli et al., 2007).
Spoilage of fish results from changes brought about by biological
reactions such as oxidation of lipids, the activities of the fish
muscular enzymes, and the metabolic activities of microorganisms.
Enzymatic and chemical reactions are usually responsible for the initial
loss of freshness whereas microbial activity is responsible for the
obvious spoilage and thereby establishes product shelf life (Arashisara et al., 2004).
Increasing
demand for high quality ready-to-cook fish products with extended
shelf-life has initiated the development of several innovative
techniques to keep quality attributes as long as possible and yield safe
products (Maftoonazad and Badii, 2009).
Due to modern trends consumers adopt towards the consumption of
minimally processed foodstuffs containing no chemical preservatives,
lightly preserved food products with natural additives have become
popular. Thyme and rosemary extracts come to fulfill part of the
increasing demand for products with a ‘‘green image’’, being obtained
exclusively from plant materials, that possess antibacterial,
antioxidant, antiviral and antimycotic properties (Holley and Patel, 2005).
The use of rosemary and thyme as natural preservatives in food industry has been reported previously by several studies (Cadun et al., 2008, Harpaz et al., 2003, Kostaki et al., 2009, Mahmoud et al., 2004, Marino et al., 1999, Offord et al., 1997 and Szczepanik and Stodonik, 2003).
Rosemary
plant (Rosmarinus officinalis) contains certain compounds such as
carnosol and carnosic acid, with high antioxidant activity, and others
with minor activity (Offord et al., 1997).
Carvacrol and thymol (extracted from thyme) are hydrophobic compounds
that dissolve in the hydrophobic domain of cytoplasmic membrane. They
cause increasing in the permeability to ATP that results in lethal
damage to the bacterial cell (Burt, 2004).
In
the present study the antibacterial and antioxidant activities of thyme
and rosemary extracts as natural food preservatives were evaluated by
dipping for quality improvement and shelf-life extension of aerobically
packaged Nile tilapia fillets during refrigerated storage by examining
the sensory, physicochemical and microbiological attributes.
