Farnaz Sadeghi; Leila Nateghi
Abstract
Introduction: There have been great efforts to find safe and potent natural antioxidants from various plant sources. Due to the side effects of chemical preservatives and as a support of the idea for consumption of green natural food, demand for studies on the antimicrobial properties of natural preservatives ...
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Introduction: There have been great efforts to find safe and potent natural antioxidants from various plant sources. Due to the side effects of chemical preservatives and as a support of the idea for consumption of green natural food, demand for studies on the antimicrobial properties of natural preservatives and essential oils on the important food borne pathogens in vitro and in food products has been increased. Medicinal plants are complex natural mixtures which contain compounds at quite different concentrations, and their antioxidant activities are due to many substances including some vitamins, flavonoids, terpenoids, carotenoids, phytoestrogens, minerals, etc. Essential oils existed in some herbs or their antioxidant components as preservative agents in food makes them to be proposed as potential substitutes of synthetic antioxidants in food stuff. Antioxidants are also widely used as additives in fats and oils and in food processing to prevent or delay spoilage of foods regarding to the harmful effects of synthetic preservatives on consumers’ health, there is an increasing attention, both in food industry and authorities, to medicinal and aromatic plants as natural preservatives in food products. White brined cheese is a kind of hard cheese which is produced from raw milk of cow, lamb and the main characteristics of the taste are pickling and salinity. White cheese, salt water, including products that may be at the time of manufacture or during storage by microorganisms such as Listeria. The objective of the present study was to investigate physicochemical properties, anti-microbial and sensory properties of frankincense essential oil and shallot oil in white brined cheese. Material and methods: The whole treatments in this research were included: T0 (control), T1 (0.5% (w/w%) Frankincense and 0% shallots essential oil), T2 (0.6% (w/w%) Frankincense and 0% shallots essential oil), T3 (0.7% (w/w%) Frankincense and 0% shallots essential oil), T4 (0% Frankincense and 0.05% (w/w%) shallots essential oil), T5 (0% Frankincense and 0.1% (w/w%) shallots essential oil), T6 (0% Frankincense and 0.2% (w/w%) shallots essential oil), T7 (0.6% Frankincense and 0.1% (w/w%) shallots essential oil). In order to produce a white brine cheese, in the first step, the raw milk was pasteurized at 72 ºC for 15 seconds and cooled at 35ºC, then 5 liters of milk were poured into each of the sterile specialty dishes. Then, Listeria monocytogenes (103 cfu / ml) were then inoculated into milk samples. In the next step frankincense essential oil concentrations (0.5%, 0.1%, 0.6%) and shallot oil concentrations (0.05%, 0.1%, 0.2%) and mixture (0.1%+ 0.6%) were added. Then 0.02% (w/v) calcium chloride was added and after 0.5 % (w/w) of starter culture containing lycoplastic bacteria Lactobacillus bulgaricus and Streptococcus thermophiles were added into the milk samples and mixed. Finally, after the milk pH reached about 6.5, 0.001% (w/v) of microbial rennet was also added (Sanjiu Mito Japan Co.) After dissolving it, sterile water was added into the milk at 35 °C and 8 minutes for milk coagulation resting time was given. After coagulation (60 min), the cheese samples were cut into 1-2 cm slices and wrapped in a cloth to be kept in room temperature for 6 hours under 12 kg weight plates for dewatering. Coagulants were impregnated in 20% (w/v) salt water for 6-8 hours after cheese samples were cut while transferring to 8% salt water at 12-14 ° C for 15 days. Therefore, samples after the initial arrival time to arrive at the final arrival were kept at 4 ° C for 60 days (ISIRI NO. 5772, 2001). The essential oils chemical composition were determined by gas chromatography equipped with mass spectroscopy (GC/MS). GC-MS analysis of the essential oil was performed using Agilent-Technologies 6890N. Physicochemical, microbial and sensory properties of samples immediately on days 1, 30, 60 were measured but protein and fat on day 1after produced were measured. Total protein was determined by macro kjeldahl method with national standard No. 1811 (Anonymous, 1383). Fat was determined by Gerber's method with national standard No. 8587. pH was determined by a MA-Mettler pH-meter and titratable acidity (percentage of lactic acid) was determined by 0.1 normal and phenolphthalein as identifiers using national standard No. 2852 (Anonymous, 1385). Level of moisture was determined by national standard No. 1753 (Anonymous, 1381). Salt percentage was determined by Moher method with national standard No. 1809 (Anonymous, 1356). To measure the number of Listeria monocytogenes, the microorganisms were measured in Palcam Agar Surface cultivation method at 30ºC for 72 hours (Khosravi and Malekan, 2004). Sensory analysis was performed by 10 trained panelists using a five point hedonic method with scales of one (very good), two (good), three (average), four (bad), and five (very bad) for taste, smell, texture, and overall acceptability with national standard No. 3442 (Anonymous, 1387). In order to design the treatments, a completely randomized design with factorial arrangement was used. For data comparison, Duncan's test was used at 95% confidence level. Minitab 16 software was used to analyze the statistical data. Results and discussion: The results showed that the antimicrobial essential oils of the highest possible antimicrobial against Listeria monocytogenes was shallots average number of bacterial treatments 0.2% essential oil shallots (T5) and 0.7% Frankincense essential oil (T3) at the end of the maintenance period cheese was 0.147 ×102 cfu/ml and 0.000 cfu/ml, respectively, when compared with other treatments maximum reduction showed (p≤0.05). Sensory evaluation results showed that the control cheeses had the highest sensory acceptability. Given that treatment with 0.2 shallot oil had the highest germicidal effect and organoleptic properties statistically significant difference between treatment and control samples were not mentioned. Therefore, the use of essential oils 0.2% in the formulation of white cheese shallot salt water in order to prevent the growth of Listeria monocytogenes is recommended and the treatment was selected as the best treatment.
