الفهرس 
INTRODUCTION
Food additivesOnly 14 pages are availabe for public view
 |  | from | 150 |  |  |
| | | from | 150 | | |
Abstract
Many food products are perishable by nature and require protection from spoilage during their preparation, storage and distribution to give them the desired shelf-life. Several food preservation systems such as heating, refrigeration and addition of antimicrobial compounds can be used to reduce the risk of outbreaks of food poisoning. However, these techniques frequently have associated adverse changes in organoleptic characteristics and loss of nutrients. Therefore, there is still a need for new methods for reducing or eliminating food borne pathogens, possibly in combination with existing methods. Furthermore, the World Health Organization has already called for a worldwide reduction in the consumption of salt in order to reduce the incidence of cardio-vascular disease.
We aimed to evaluate the use of origanum majorana as an organic food preservative in preservation of different food products. This was carried out by evaluating the addition of origanum hydrosol, oil and ground plant on the microbiological profile of different food products after their storage for different periods, and assessing their effects on the pH and organoleptic properties. Also we tried to evaluate its antimicrobial activity.
The following design was adopted:
After getting sufficient amount of food products (10 kgs of each ras,white cheeses); (4 kgs of Kareesh cheese);(10 kgs of each minced meat, beef burger and deboned chicken meat) and( 2kgs of each wheat and corn ); we divided each food product into 10 parts; the first three parts were mixed with 3 levels of oil, the second three parts were mixed with 3 levels of hydrosol and the third three parts were mixed with 3 levels of ground leaves and the remaining tenth part was used as control. Each one kilogram was subdivided into 7 equal portions, one portion of them was taken at zero time for evaluation and the other six portions were stored.
Kareesh cheese was divided into 4 parts (one kilogram each). Each of three parts was mixed with the high concentration of the origanum forms while the fourth part was used as control. Each 4 kilograms of wheat and corn were divided into 4 parts (1kilogram each), that was mixed with only the 3 levels of origanum leaves. All samples of meat products were stored frozen at (-18°C); dairy products were stored below 5°C; while cereals were stored at room temperature till the end of the study period.
Regarding the effects on organoleptic properties:
The present study showed that color mean score and acceptance percentages of milk products treated with oil or hydrosol were more or less similar to the control samples after different storage periods. Moreover, the lowest percentages were in leaves treated samples especially medium and high concentrations (1-2%). This undesirable color could be attributed to the large quantities of leaves added in these concentrations because of their light weight.
Other organoleptic properties-taste, texture and odor- of milk products treated with different origanum forms and concentrations showed significantly lower mean score and acceptance percentages compared to the control especially in high concentrations. It is worth mentioning that with increasing the oil concentration, the odor and taste of milk products were the most affected with significant variation compared to the control at the high concentration.
from our work, we found that there were inverse relationships between increasing the concentrations of different forms of origanum and the mean score and acceptance percentages in most of the studied organoleptic properties of meat products and chicken meat. Moreover, there were significant variations from the control samples (p<0.05) in the odor and taste of samples treated with the high concentrations of all origanum forms; in the texture of samples treated with the high hydrosol concentration; and in the color of samples treated with high concentration of leaves.
The present results revealed that mixing origanum leaves (regardless the concentration) with milk products resulted in significant lower color mean score percentage compared to the control ; but this finding was not evident in meat products treated with low and medium concentrations, which can be explained by the masking effect of the meat color.
Effect of origanum on pH of food products:
In our study, the pH values of the control; oil and hydrosol treated white cheese samples were ranging between 4.3 (at 3rd and 4th months in case of samples treated with low and medium concentrations respectively) and 6 (in case of samples treated with medium concentration of oil at the 3rd month) that was significantly higher when compared to other samples. It is worth mentioning, by the end of the study period, pH values of all treated samples had increased progressively till it reached approximately the zero time values.
Similarly, ras cheese samples treated with all concentrations of all forms of origanum showed significant reduction in pH at the 3rd month of storage. This could be explained by the generation of lactic acid due to microbial fermentation of lactose in cheese. During storage of ras cheese, pH values of the control samples and all treated samples were increasing. However, oil treated samples showed the lowest increase. This could be explained by the growth inhibitory effect of oils on fungi that can grow in the acidic pH. The pH of all ras cheese samples- except those treated with oil- increased to its highest values from the 4th month and thereafter which could be explained by the difference of origanum forms on the microbial decay regarding peptides and amino acids.
Regarding beef burger, there was initial increase in pH values of all treated samples followed by a reduction reaching its maximum at 2nd month especially those treated with origanum oil and hydrosol. This acidic change might be attributed to many reactions-including the enzymatic reactions- that produce peptides and free amino acids during refrigerated storage of meat products. from the 3rd month of storage, there was a rise in the pH values of beef burger samples treated with different forms and concentrations of origanum. These pH values were lower than that of the control samples indicating the antimicrobial effects of origanum-especially oil and hydrosol- against microorganisms capable of releasing ammonia and hydrogen sulfide during their metabolism.
Regarding pH values of minced meat treated with different concentrations of different forms of origanum, we found significant higher values than that of the control samples from the 1st till the 3rd month of storage. The lower pH values recorded in the control samples could be explain by combined effects of enzymatic reaction within the meat and biogenic amines produced by microbial action on the free amino-acids.
Significant reductions in pH values were observed in all chicken samples especially at the 2nd month of storage; however, from the 4th month, pH increased again in samples treated with oil or hydrosol with lower values compared to the control samples and those treated with leaves. This might indicate that both origanum oils and hydrosols are more effective in their antimicrobial action than leaves.
The pH values of -all origanum treated and non-treated- wheat and corn samples were nearly similar throughout the study period and ranging between 6 and 7.2 with the lowest values at zero time and the 6th month of storage.
Microbiological assessment of origanum majorana on food products:
Microbiological evaluation of most different food products samples showed more or less similar aerobic mesophilic counts especially during early months (p>0.05); however meat products treated with 1-2% leaves showed significantly higher counts compared to dairy products at 1st, 3rd and 1st, 6th months respectively. Similarly, the hydrosol (in 2.5 and 5%) was more effective in reducing mesophilic counts in samples of dairy products than meat products. This observation could be explained by the relatively high fat content of meat which markedly reduces the action of essential oils especially from leaves.
Moreover, we noticed that origanum oil was significantly more effective than other forms in reducing the total mesophilic count in dairy products (P<0.05). This could be explained by the difference in compounds found in different forms of origanum.
With the advance of storage period, mesophilic count continued to decrease significantly in all treated food products compared to the zero time values and to the control (p<0.05).We found that origanum oil and hydrosol-even in low concentrations- were more effective in meat products compared to dairy products, with earlier suppression of mesophiles below the detection limits. An observation which might be explained by the relatively lower water content which might hamper the progress of antibacterial agents to the target site in the bacterial cell in addition to the difference in compounds found in different forms of origanum.
We observed significant variations in the mean mesophilic counts in different samples of milk products (white, ras and kareesh cheeses) treated with different origanum majorana forms and concentrations after different storage periods except at zero time in all samples and at the last storage periods in most of treated samples. High concentration of origanum forms was successful in suppressing mesophilies below the limit of detection -especially at the last storage periods- in all cheese samples except kareesh. It is worth mentioning that after different storage periods, all treated cheese samples showed significant reductions in the aerobic mesophilic counts that were fortunately lower than the basal values and to that recorded in the control samples.
The persistance of low bacterial count in our study could be explained by the possible effect of low temperature of storage used for milk products. Failure of high concentration of origanum forms in the suppression of mesophilis in kareesh cheese might be due to its low salt content.
Both medium and high concentrations of all origanum forms were successful in suppressing aerobic mesophiles in beef burger and chicken samples -but not in minced meet- especially at the last storage period when the count reached below the limit of detection. However, mesophilic counts in all treated samples were significantly lower than that at zero time values and that recorded in parallel control samples (p<0.05).
Regarding wheat and corn samples, we found that medium and high concentrations of leaves were the most effective in reducing mesophiles significantly compared to that detected in the control after the 1st month of storage until it could not be detected at the 5th month of corn storage and 6th month of wheat storage (p<0.05).
from our results , it was clear that the higher the concentration of origanum used the earlier the disappearance of mold and yeast from white and ras cheeses; and the lower the count compared to that detected at zero time and control samples (p<0.05). Moreover, in spite of significant variations observed in early storage months of milk products , mold and yeast counts were below the limit of detection especially during late storage periods except in kareesh cheese (p<0.05).
Regarding meat products, we observed significant continuous reduction in yeast and mold counts in minced meat compared to zero time values; and after one month of storage compared to the control(p<0.05) till it reached below the limit of detection in oil and hydrosol treated samples at the 6th month especially with high oil concentration.
Mold and yeast count showed transient significant increase at the 1st and 2nd months of storage in all treated chicken samples. But after the 3rd month there was significant decrease in the counts compared to that detected at zero time and to the control (p<0.05). Moreover, we could not detect any mold or yeast at 6th month of storage in all treated chicken samples; and the higher the concentration of the additive the earlier the disappearance of mold and yeast. Parallel observations were detected in beef burger samples.
Cereals-wheat and corn- treated with origanum leaves showed significantly lower yeast and mold counts compared to the control samples especially after the 2nd month of storage with high concentration of leaves (p<0.05).
Both Coliform and fecal coliform could be detected only at zero time in kareesh cheese samples treated with high concentrations of different origanum forms; in wheat samples treated with different concentrations of leaves; and in meat products treated with different concentrations of different origanum forms–without significant difference compared to control- however it became negative thereafter.
Finally, using disc diffusion method we observed that both origanum oil and leaves showed antibacterial activity against Staphylococcus aureus but the hydrosol did not show any activity.