Investigation of the Synergistic Effect of Satureja Hortensis Essential Oil and Inulin on the Increase of the Shelf life and Quality of Taftoon Bread

Introduction: bread waste is a major problem in country that use high amount of bread because it causes economic damage and health problems. Mold spoilage and stalling are two important factors that can increase bread waste. Bread staling is one of the complicated physicochemical process which change flavor, taste and texture of bread. Stale bread is dry and hard which indicates decreasing consumer acceptance (Gomes 2018). Hydrocolloids such as inulin can decrease bread staling. Inulin is a type of fermentable oligosaccharide called a fructan can’t digest in body but it’s essential to good health as promote digestive health, control blood sugar, decrease cancer risk.... inulin have prebiotic action for increase probiotic bacterial growth and activity. In addition, inulin has different roles in food as stabilizer, delay staling bread, antimicrobial effect, …( Leo et al., 2018, Alhozen 2013, lakzadeh et al., 2019). Natural antimicrobial materials are used for decreasing mold spoilage according to many researches. Some molds in spoilage bread can produce mycotoxin as aflatoxin. This toxin has negative effects in human and animals as allergy, cancer, … (luz et al., 2018).
Savory essential oil can create good taste in bread and increase its shelf life by antioxidant materials (Mohamad Hosseini and Biravandn). Aim of this study was survey on the effect of inulin and savory essential oil alone and together for producing of the bread with good quality, shelf life and functional effect on body.
Material and methods: for this purpose, Satureja hortensis essential oil was extracted by Clevenger set and essential oil (0.03%, 0.05%, 0.07%), inulin (0.5%, 1%, 1.5%) and the combination of 0.5% inulin and 0.05% Satureja hortensis essential oil was used in Taftoon bread formulation. In this research, the combination of 0.5% inulin and 0.05% Satureja hortensis essential oil was used for preparation compound treatment because inulin in high percentage could change taste of bread and essential oil increase bread stiffness and produce rapid odor. Microbial, physicochemical, rheological and sensory tests were done on these treatments. YGC medium was used for mold count and moisture, pH were measurement according to the Iran national standard (Standard 108999, 2705). Puncher test for texture analysis was done by Brookfield system (Ghanbari and Farmandi 2013). 15 Panelists assess sensory evaluation by Hedonic test (Taghdir et al., 2017). Statistical analysis was performed using SPSS-21 software. Factorial experiment was conducted in a randomized complete block design. One-way analysis of variance (ANOVA) was used to investigate the significant differences between the treatments and Duncan's test at the significant level of 5% was used to compare the means.
Results and discussion: The results of bread tests during 12 days of storage in refrigerator showed that the microbial shelf life of bread increased with increase of the concentration of essential oil. As the treatments, containing 0.07% essential oil with the lowest pH changes could preserve the microbial shelf life of bread up to 9 day with 70 cfu/g mold and yeast. Iranian National Standard permits 100 cfu/g of mold and yeast in bread (Iranian national standard, No, 19888). Lotfinia et al., (2014) used different percentages of cinnamon essential oil (maximum 1500 ppm in starch foam) for microbial shelf life in bread. In their study, the maximum microbial shelf life was 6 days in compartment to the savory essential oil. Although this difference may be due to the initial microbial load, the type and amount of essential oil, the method of production, storage, packaging and type of bread (Lotfinia et al., 2014).
The pH of the bread samples decreased during storage due to the activity of the microorganism and the conversion of sugar to acid and reached to the lowest value on 12th day. After 12 days, the control sample had the lowest pH (4.01) and the essential oil treatments had the highest pH (5.0). Essential oil inhibited the growth of fungi and pH change in bread. As, the pH reduction in the control sample was about 2.11 and it was 0.51 in the samples containing savory essential oil after 12 days. According to National Iranian Standard, the pH of Taftoon bread should be in the range of 5-6. In this study, the pH of all samples except the control treatment was in this range. This indicates the high quality of raw materials was used in bread cooking and the production and maintenance of bread were done in good conditions (Iranian national standard, No, 2628).
Bread stiffness and staling were delayed with increase of the inulin concentration due to the moisture retention. The treatment containing 1.5% inulin had the highest moisture (25.32 ± 0.68 %) and the lowest stiffness (3.99 ± 0.5) on the 12th day. Bread moisture is one of the important factors in determining the freshness, shelf life and staling of bread. Bread moisture content decreases during storage due to migration of free water into the environment. Analysis of variance showed significant difference between the moisture content of the inulin treatments and the essential oil and the control treatments (p < 0.05). Generally, inulin-containing samples had the highest moisture content. According to the results, the stiffness of the control treatments were more than other treatments on 0, 3 and 6 days but the stiffness of the essential oil increased like control in the following days. These data showed the relation between moisture and stiffness in bread.
In addition, inulin-containing treatments had significantly lower number of molds and yeast than the control in all days. So that, there was a significant difference in all days except the zero day. This result was similar to research on use inulin in pomegranate juice at 28 days. They explained that inulin had a good antifungal effect compared to the control sample (Lakzadeh et al., 2019). The cause of this antimicrobial effect has been described to the inulin effects on the degradation of the cytoplasmic membrane, the change of the cell's ionic charge, intracellular coagulation and the inhibition of enzyme production in the microbial cell (Lotfinia et al., 2014).
The compound treatment with inulin and essential oil was selected simultaneously as the best treatment for microbial properties and delaying the staling, in addition to the gain the highest sensory acceptance
Conclusion: inulin can retard Taftoon bread staling and savory essential oil decrease mold spoilage. Therefore, the use of natural additives in the appropriate ratio can decrease bread waste meanwhile they produce new taste and functional useful product for consumers' health.