Theses supervised by Prof. Dr. Fahrettin Göğüş
11 theses · Gaziantep University
The effect of air assisted radiofrequency drying on chemical and physical properties of onion
In this study, drying of onions using air-assisted radiofrequency drying technique and changes in their quality values were investigated and it was aimed to evaluate the drying behavior of onion during drying in a hot air assisted radiofrequency system and also to evaluate the final powder quality obtained from onion. The effect of sample thickness, radiofrequency electrode gap on drying behavior was determined. The most efficient drying took place at 70 mm electrode gap and 2 cm sample thickness. This drying technique was also compared with other drying techniques, namely hot air, radiofrequency and freeze drying, in terms of quality values. Physical quality parameters such as moisture content, ash content and particle size and chemical quality parameters such as protein, total phenolic content and total antioxidant activity were used. In these comprehensive findings, it is clear that the hot air-assisted radiofrequency drying method holds great promise for the dehydration of onions, not only providing effective moisture removal but also preserving the quality, color and nutritional properties of the final product.
Organik üzümsü meyvelerden mikrodalga destekli fenolik ekstraksiyonunun optimizasyonu
Berries are considered to be the rich sources of polyphenols. In the present work, the influence of microwave-assisted extraction (MAE) on the recovery of phenolic compounds from berries was investigated. Response surface methodology was applied to optimize the extraction conditions. Microwave power, extraction time and solvent to berry sample ratio were selected as extraction parameters. Ranges of independent variables were 100-300 W of microwave power, 2-16 min of extraction time and 5:1-25:1 mL/g for strawberry and 5:1-50:1 mL/g for blueberry of solvent to sample ratio. Responses of model were extraction yield and total phenolic content (TPC) for extraction of strawberry and extraction yield, TPC and total anthocyanin content (TAC) for extraction of blueberry. Optimum conditions of MAE based on maximum levels of responses were 265 W of microwave power, 2 min of extraction time, 24:1 mL/g of solvent to sample ratio for strawberry and 287 W of microwave power, 13 min of extraction time, 40:1 mL/g of solvent to sample ratio for blueberry. Maximum levels of responses under optimum conditions obtained as extraction yield of 77.03 %, TPC of 19.65 mg GAE/g dry strawberry for strawberry and extraction yield of 78.35 %, TPC of 30.75 mg GAE/g dry blueberry powder and TAC of 8.92 mg Cyn-3-glu/ g dry blueberry powder for blueberry. According to results, 86.9% of phenolics of blueberry and 88.7% of phenolics of strawberry could be extracted by MAE in a short time.
Extraction of pectin from grapefruit peel by using microwave technique
Grapefruit peel is an agricultural waste of grapefruit juice production and exists abundantly in the worldwide. One of the most important utilization way of grapefruit peels is production of pectin from the peels. The aim of this study was to investigate the effects of different extraction parameters on microwave assisted extraction (MAE) of pectin from grapefruit peel and to optimize the extraction conditions to obtain maximum yield and quality of pectin. Response surface methodology (RSM) was applied to model and optimize extraction conditions: time (7-25 min), temperature (85-125 °C) and water:peel ratio (7:1-13:1, wt:wt). The best fitting quadratic model was determined by regression and backward elimination. The optimum extraction conditions were found to be extraction time 20 min, temperature 98˚C and water:peel ratio 10:1 (wt:wt). The predicted highest pectin yield was found as 21.31 % at these conditions. Properties of MAE pectins, obtained at the optimum conditions, was also compared with conventional extracted pectin. As a result; higher pectin yield (21.09%), lighter color, higher viscosity (10 cP), lower ash content (2.8%), lower moisture content (2.01%), higher degree of esterification (85.76%) and galacturonic acid content (78.37%) were obtained in MAE than that of conventional extraction. The overall results showed that MAE technique is more efficient than conventional extraction.
Optimization of microwave-assisted extraction of pomegranate (Punica granatum L.) seed oil and evaluation of its physicochemical and bioactive properties
Pomegranate seed oil was extracted in a closed-vessel high-pressure microwave system. The characteristics of the obtained oil such as fatty acid composition, free fatty acidity, total phenolic content, antioxidant activity and color, were compared to those of the oil obtained by cold solvent extraction. Response surface methodology was applied to optimize extraction conditions: power (176-300 W), time (5-20 min), particle size (d= 0.125-0.800 mm), solvent/sample ratio (2:1, 6:1 and 10:1, by mass). The predicted highest extraction yield (35.19 %) was obtained using microwave power of 220 W, particle size in the range of 0.125-0.450 mm and solvent/sample ratio of 10:1 (by mass) in 5 min extraction time. Microwave-assisted solvent extraction (MASE) resulted in higher extraction yield than that of Soxhlet (34.70 % in 8 h) or cold extraction (17.50 % in 8 h). The dominant fatty acid of pomegranate seed oil was punicic acid (86 %) irrespective of the extraction method. Oil obtained by MASE had better physicochemical properties, total phenolic content and antioxidant activity than the cold solvent extracted oil. Key words: pomegranate seed oil, microwave-assisted solvent extraction, extraction optimization, bioactive properties
Effect of pectin-wax coating on the quality of fresh-cut apples
Efficacy of different coating materials including citric acid (CA) as a control, pectin-wax (PW) mixture and pectin-wax mixture containing pistachio hull extract (PWE) were investigated using fresh-cut apples by considering quality attributes at time 0 and at the termination of gauged storage time. The specimens were kept under two separate temperatures at 5 °C for 8 days and at 20 °C for 32h. Changes in weight, color, total phenolic content, were examined at different time points along storage time. Results indicated that the apple pieces coated with PWE showed the lowest increase in browning index followed by specimens coated with PW. The applications of coatings were effective on delaying the degradation of specimens' colors. The effect of coating fresh-cut apples with PWE was less pronounced on a* values than on L* and b* values. The effect of coating by PW and PWE was significant compared to Sample control, furthermore coating with PW was affected L* values significantly. It is worthy to mention that temperature also was a factor affecting the specimens color. It was observed that specimens kept at lower temperature have maintained the color coordinates. Weight loss was observed significantly in uncoated specimens comparing to those prepared with coating, over time of storage at both temperatures. The coatings were effective in maintaining phenolic components where losing in phenolics was higher in non-coated specimens.
Production of a healthy snack bar
In this study, a new healthy and nutritious snack bar was produced. Firstly, the candidate ingredients (Pistachio, chia seed, flax seed, quinoa and mulberry molasses / apple concentrate) were selected. During the selection of these components, being nutritional, preservative-free and having minimum amount of sugar were the main criteria. Mucilage (gel-like substance) extracted from the water suspension of chia and flaxseed was used to minimize the level of sugar, which is commonly in use as binding agent and sugar sweetener in the snack bar industry. Molasses and apple juice concentrate were used to obtain a sweet taste and oil seeds were preferred because of their high PUFA, protein and pulp content. Thus, three different possible product formulations were developed. The product, which contains pistachio, chia, flax seed, apple juice concentrate and quinoa formulation, received a higher score (6.93 compared to 7-point hedonic scale) at the sensory analysis. Following the selection of the components, drying methods (atmospheric oven, vacuum oven and vacuum oven combined with microwave oven) and time were studied. Texture profile analysis (hardness, fracturability), color analysis and 7-point hedonic sensory analysis (in terms of fracturability, hardness, chewiness and overall acceptability) performed to determine the appropriate drying method and time to be used in the highest scored product. Finally, energy (594.8 kcal), sugar (15.05g), protein (16.89g), fat (33.17g), ash (2.38g) and total phenolic (2436mg GA) contents were determined for 100g of the final product.
Effect of combined radio-frequency and solar assisted air drying on properties of dried apricot
Dried apricot, one of the most important agricultural export commodities of Turkey, is still produced by using traditional drying (sun drying) method with the expense of high product losses and low grade products with lower economical value. In this study, the experimental design was generated using response surface methodology for radio-frequency drying experiments following solar assisted air pre-drying. For this purpose, the effect of independent variables on the response values was investigated with Box Behnken experimental design for drying of unsulfured apricots. Independent variables were pre-drying temperature (50-70°C), pre-drying time (300-1140 min), radio-frequency electrode gap (77-85 mm) and radio-frequency drying time (270-690 min). Moisture content (%), quantity of browning products (A420/gdryweight), total color change (ΔE) and hardness value (N) were selected as the responses. The drying conditions were optimized for minimum process time, browning, color change and optimum hardness and moisture content. Under optimum conditions of 63.5 °C pre-drying temperature, 895 min pre-drying time, 77 mm distance between radio-frequency electrodes and 385 min radio-frequency drying time; the moisture content (%), quantity of browning products (A420/gdryweight), total color change (ΔE) and hardness (N) were 22.31±2.82, 0.69±0.03, 37.65±2.23 and 1293.46±61.96, respectively. Radio-frequency drying following solar assisted air drying system provided high quality whole apricots while reducing the processing time.
Antioxidative effect of essential oils of Thymbra spicata on palm and corn oils
In this study, Rancimat Method, which is one of the Accelerated Shelf-Life Test(ASLT) method, was used to determine the effect of Thymbra spicata extract on theoxidative stability of corn oil and palm oil. For the comparison of the effect ofThymbra spicata extract butylated hydroxyltoluene (BHT) was used as a standardantioxidant. During the ASLT, the conductivity was followed at three temperatures,90, 100 and 120oC, with the addition of Thymbra spicata essential oils and BHT tocorn and palm oils. The concentrations of Thymbra spicata essential oils and BHTused were in the range of 1.39-5.49 mg ml-1 and 0.014-2.4 mg ml-1 respectively.The same concentrations of both antioxidants used were also added into corn andpalm oils to observe the chenge in peroxide value under storage temperatures of 15,25 and 35oC.2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging test was used for thedetermination of scavenging effect of Thymbra spicata extract. BHT was used as thestandard antioxidant. The scavenging effect of Thymbra spicata extract was found tobe 75.7 % while scavenging effect of BHT was found to be 73.7 %. Scavengingeffect of Thymbra spicata was found to be significant compared to BHT.It was observed that the corn oil was less stable to oxidation than palm oil. Theaddition of Thymbra spicata and BHT increased the induction times of corn oil andpalm oil at each studied temperature. As the temperature decreased the inductiontime increased. Thymbra spicata extract was more effective than BHT.
The use of durum clear flour in combination with hazelnut cake and different pomaces in the production of extruded food
The durum clear flour (8-20%), partially defatted hazelnut flour (PDHF) (5-15%), fruit waste blend (3-7%) and rice grit were blended in various ratios and then extruded using single screw extruder. Response surface methodology was used to simulate effects of process variables such as the feed moisture content (12-18%), barrel temperature (150-175oC), and screw speed (200-280 rpm) and feed composition on physical and functional properties of the produced extrudates. The product properties of extrudates were mostly affected by changes in PDHF content. Increasing PDHF content caused increase in bulk density, water solubility index (WSI), L value, total phenolic content and antioxidant activity but decrease in radial expansion ratio, porosity, hardness, water absorption index (WAI), percent starch gelatinization and starch digestibility values of the extruded products. Changing fruit waste content generally affected the texture, color and functional properties of produced extrudates. Physical and functional properties of extruded products were influenced from extrusion process conditions. Increasing moisture content and decreasing temperature increased expansion ratio and porosity whereas it decreased bulk density for most product formulations. WSI decreased at high temperature and moisture content, whereas WAI increased. Screw speed influenced values of WSI, WAI and hardness. Moisture content and temperature influenced significantly the total phenolic content, antioxidant activity, percent starch gelatinization and starch digestibility values. In extruded samples, positive correlations were determined between antioxidant activity and total phenolic matter and percent starch gelatinization and the starch digestibility values, respectively. It was observed that well expanded extruded products with acceptable sensory attributes were obtained at low PDHF content at the end of sensory evaluation of extruded samples.
Production of low caloric and spreadable lipid by enzymatic interesterification of terebinth fruit (Pistacia terebinthus L.) oil
The overall objective of the study is to produce a low-calorie and spreadable structured lipid (SL) from terebinth fruit oil. For this purpose, the sn-1,3 specific immobilized lipase (from Rhizomucor miehei) catalyzed acidolysis reaction of terebinth fruit oil with caprylic and palmitic acids was performed in a batch stirred tank reactor and recirculating packed bed reactor (PBR) systems. The effect of reaction conditions and relationship among them were analyzed and optimized by the response surface methodology with a four-factor five-level central composite rotatable experimental design. The major factors chosen were enzyme load, reaction time, temperature, substrate mole ratio and flow rate. The substrate mole ratio, enzyme load, reaction time and temperature were found as key factors for modulating the distribution of reaction products. The PBR system was found more effective to produce target SL. In this system, optimum reaction conditions at 45 oC for reaction time, enzyme load, flow rate and substrate mole ratio were 5.9 h, 10 %, 4 mL/min and 1:3.10:2.07, respectively. The caloric value of the produced SL was found as 38.96 kJ/g. The produced SLs were compared to fat phases of some commercial margarine in terms of solid fat content, melting profile and microstructure. The results of the study showed that the produced SL had similar melting characteristics and microstructure with those of commercial margarine fat extracts. So, it could be used in spreadable fats.
Standardization of roasting and grinding conditions of powdered pistacia terebinthus fruit coffee
In this study, the effects of roasting methods, grinding and reduction in oil content on the characteristics of powdered Pistacia terebinthus fruit coffee were investigated. Pistacia terebinthus fruit was roasted by microwave, pan and combined (microwave and convection) methods. The degree of roasting was determined by L*, a*, b* color values. L*, a*, b* values for various roasting methods were found in the ranges of 18.12-18.37, 1.14-1.20 and 1.63-1.84, respectively. The roasting times were 1500, 1900 and 1620 seconds for microwave, pan and combined roasting methods, respectively. Cold press was used to reduce the oil content both prior to roasting and after the roasting. The critical oil content was determined to be 26 % to obtain a product in powder form. However, the oil content was reduced to around 21.5 % in all roasting methods to approach to that of coffee beans. Powdered Pistacia terebinthus fruit coffee brews produced with variety of roasting methods was compared with each other and Turkish coffee in terms of aroma, flavor, acidity aftertaste, and overall acceptability. Sensorial analysis results showed that coffee brews prepared by pressing after the roasting process were better than those pressing prior to roasting. As a result, roasting methods were not found significant on sensory properties of powdered Pistacia terebinthus coffee and powdered Pistacia terebinthus coffee was not found to be different compared with Turkish coffee statistically in terms of sensory properties.