جستجوی مقالات مرتبط با کلیدواژه « تیمول » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Melon (Cucumis melo L.) is one of the most important fruits that is consumed all over the world. The fresh cut fruit and vegetable industry is one of the relatively new and growing sectors of the fresh food products industry. Fresh-cut fruits, in addition to ease of consumption, bring benefits such as higher added value, reduction of waste and losses, increased product variety, improved security and quality, and less work in stores. Quality retention and shelf-life extension of fresh-cut fruits are crucial for industry because of their economic impact. Fresh-cut fruits and vegetables with high pH and water activity are considered to be highly perishable when they are not subjected to preservative processes and delay undesirable biological and biochemical changes. A recent approach to prolong the shelf life of fresh-cut fruit and vegetables is the use of edible coatings either alone or combined with modified atmosphere packaging. Numerous studies on improving the shelf life of fresh-cut fruits are extensive with the application of modified atmosphere packaging, and edible coatings and films. Chitosan, a polysaccharides-based edible coating, has been used individually or in combination with nanocomposite and other biological materials such as extracts or essential oils of various plants. On the other hand, edible films and coatings, due to their high ability to carry active compounds including antimicrobial compounds, can increase product shelf life and reduce the risk of pathogen growth on fresh-cut surfaces. Thymol (2-isopropyl-5-methylphenol) is a monoterpenoid phenol with the molecular formula C4H10O and isomer of carvacrol, which is slightly soluble in water with neutral pH, but is very soluble in alcohols and other organic solvents. MA packaging technology has been representatively used to maintain quality of fresh-cut products during preservation by carbon dioxide elevation and reduction in oxygen levels.

Melon fruit was harvested with full maturity at the right time. The outer surface of the fruit was disinfected with sodium hypochlorite solution (200 ppm) and cube slices with dimensions of 4x4x4 cm3 and an approximate weight of 9 g were prepared from it. To prepare the coating solution, 1 or 2 g of chitosan with 0.5 g of tween 80 was dissolved in 100 g of 1% acetic acid solution and thymol was added to the solution at 3 concentrations (zero, 0.25 and 0.5%). The final pH of the product was adjusted to 5.6 using NaOH 0.1 M. Then the solution was homogenized with a magnetic stirrer (1500 rpm) for 2 min. Fruit slices were immersed in each of the solutions separately for 2 min. After coating and removing excess solutions, the fruit slices were dried at room temperature for 8 min. Then, 30±2 g of treated and the control samples (uncoated) were weighed inside a polyethylene container and covered with a double-layer film (with a total thickness of 85 µm with an outer layer of polyethylene and an inner layer of polyamide) were packed in a modified or natural atmosphere. Atmosphere change was done using a MAP device equipped with a gas injection system. The levels of CO2, O2 and N2 inside the package immediately after sealing were 10, 5 and 85%, respectively. Freshcut packages were kept at 4±2°C for 8 days. All physicochemical (O2 and CO2 levels, weight loss, TSS. TA, ascorbic acid, color and firrmness) charactrestics were performed during storage time (immediately after harvesting, after 4 and 8 days). At the end of the storage time, microbial contamination (total count, mold and yeast count) and sensory characteristics were evaluted.

The results of analysis of variance showed a significant effect of the type of packaging atmosphere on the level of O2 and CO2 gases inside the packages (p<0.05). The results showed the CO2 and O2 levels, repectively increased and decreased inside the different fresh –cut melon packages during storage at 4ºC under natural and modified atmospheres. However, in the samples coated with chitosan and thymol, the intensity of O2 reduction and CO2 increase was less than the uncoated samples (control). This phenomenon is probably due to the gas blocking properties of the chitosan coating and the antimicrobial properties of thymol, which reduce oxygen consumption and carbon dioxide production by reducing the respration rate. At the end of 8 days of storage, the weight loss in the samples coated with chitosan and thymol and stored under modified atmosphere was much less than the control sample (0.34% compared to 13.60%). Chitosan coating and packaging under modified atmosphere provide relative semi-permeable barriers against oxygen, carbon dioxide and moisture, and as a result, weight loss is reduced by decreasing respration rate and moisture loss. Increasing the concentration of chitosan and packaging under modified atmosphere caused an increase in the amount of soluble solids, titratable acid, ascorbic acid, and firmness of the melon slices, but increasing the concentration of thymol had no significant effect on these quality characteristics. The color indices of green-redness (a*), blueyellowness (b*), brightness (L*) and browning index (BI) were also affected by the type of packaging and chitosan concentration. Evaluting the interaction effect of storage time with chitosan concentration showed that the amount of a* and b* indexes in the samples coated with 1% chitosan after 4 days of storage was not significantly different from the first sample. However, after 8 days of storage, these indexes decreased significantly. The interaction effect of chitosan and thymol concentration showed that melon slices treated with 1% chitosan with 0.25% or 0.5% thymol had the lowest microbial load. Coating with chitosan and thymol and the same type of packaging had a significant effect on all sensory attributes of melon slices (color, texture, smell, taste and overall acceptance) (P<0.05). Generally, the panelists preferred 1% chitosan over 2% in overall acceptanc.

The results showed that the physicochemical, sensory and microbial characteristics of fresh melon slices decrease during the storage period. Coating fresh-cut melons with chitosan and thymol due to its gas barrier and antimicrobial properties helped to preserve the quality and also prevent some undesirable changes. The integration of coating and packaging under modified atmosphere caused more maintaining the quality of fresh- cut melons. So that coating with chitosan 1% chitosan with thymol 0.5% and packed under modified atmosphere reduces microbial spoilage and preserves more qualitative features, color components and sensory attributes in fresh -cut melons.

In recent decades, hybrid optimizations methods based on natural phenomenon have placed special position according to their capabilities in finding optimal solutions without expensive computational loads and disassociation on choosing initial points. Artificial Neural Network is used as one of the powerful tools of Artificial Intelligence for process simulation. The employment of the neural network in the modeling of m-Cresol alkylation process of with isopropanol as well as meta-heuristic methods in obtaining the optimal conditions for the catalyst and the reaction can prepare an effective step towards a high efficiency process.

 In the present study, the artificial neural network is applied to model alkylation of m‐Cresol with isopropanol process. In addition, the bee colony is employed in order to optimize the process yield. To verify its performance, the proposed method is used in prediction of the m‐Cresol conversion and Thymol selectivity of the alkylation process with isopropanol 120 data. In this process, the input variables are Weight Hourly Space Velocity (WHSV), pressure and temperature; m-cresol conversion and thymol selectivity are considered as the output variables of the neural network. Five hidden neurons are considered for the proposed neural network. 120 data is used to train the neural network. The meta-heuristic approach based on bee colony (BC) is applied to maximize the yield of the process.

The results confirm that the proposed method develops the accurate model with an R2 value of greater than 97.5%. The maximum yield is obtained 28.9% by bee colony algorithm with adjustable variables that are WHSV of 0.062 hr-1, the pressure of 1.5 bar and the temperature of 300oC. In addition, in order to achieve the better performance of the optimization algorithm, the appropriate values of acceleration coefficient and population size are chosen 100 and 10 during the trial-and-error phase.