Hasan Yildiz’s research while affiliated with Manisa Celal Bayar University and other places

BACKGROUND Vacuum evaporation (VE) process is widely utilized in fruit juice evaporation to preserve quality attributes of final product. However, it has some disadvantages such as possible degradation of aroma components or volatile fatty acids due to long process time, and low energy efficiency of process. Pomegranate juice having 17.5% total soluble solid (TSS) content was evaporated to 40% TSS by ohmic heating assisted vacuum evaporation (OVE; 7.5, 10 and 12.5 V cm⁻¹) and VE in the present study. The effects of the evaporation methods on pH, titratable acidity and colour values, antioxidant activity (AA), total monomeric anthocyanin (TMA), total phenolic content (TPC), hydroxymethylfurfural (HMF) and invert sugar content of pomegranate juice concentrates were compared. RESULTS The colour properties, TMA, TPC and AA values of pomegranate juice concentrates evaporated by OVE were more influenced than those evaporated by VE. The degradation of sugars was minimized for OVE processes at high voltage gradients (10 and 12.5 V cm⁻¹), and HMF content of pomegranate juice concentrated by OVE was lower than VE. CONCLUSION It is thought that electrochemical reactions occurred because of the use of titanium electrodes during the OVE process caused these quality changes in pomegranate juice concentrates having high acidity. Hence, it was concluded that the utilization of relatively more electrochemically inert electrodes should be investigated in further studies to better evaluate the of influence of OVE method on quality attributes of different fruit juices. © 2018 Society of Chemical Industry

Pomegranate juice having 17.5% total soluble solids (TSS) content was evaporated to 40%TSS by ohmic heating assisted vacuum evaporation (OVE; 7.5 V/cm, 10 V/cm and 12.5 V/cm) and vacuum evaporation (VE) methods. Thermodynamics’ first law and second law analyses were conducted for different TSS contents (20-40%) by taking into account of two different control boundaries; in terms of process boundary (PB) and system boundary (SB). Energy efficiency, specific water removal rate (SWRR) and exergy efficiency reached maximum values for 30% TSS content, then it decreased. It was determined that energetic and exergetic efficiencies of SB were lower than those of PB. For the same TSS content, exergy efficiency value increased and improvement potential (IP) value decreased as the voltage gradient increased. Since highest energy consumption (5844.20 ±29.89 J) was determined at 40% TSS content for 7.5 V/cm (p<0.05) this process condition need the improvement most. It can be concluded that OVE method used the energy more efficiently than VE method for the purpose of the concentration of pomegranate juice.

A novel electrical heating method, named as ohmic heating, was successfully integrated to vacuum evaporation system, and pomegranate juice was concentrated until its total soluble dry matter content reached to 40% by applying three different voltage gradients (7.5, 10, and 12.5 V/cm) at 180 mm Hg absolute pressure in this system. Total evaporation times were determined as 152, 78, and 53 min at the voltage gradients of 7.5, 10, and 12.5 V/cm, respectively. The concentration time of pomegranate juice was shortened about 56% by ohmic heating relative to conventional evaporation. The electrical conductivity values were increased up to reach 25% TSDM for 7.5 V/cm and at 35% TSDM for 10 V/cm, then showed a decreasing pattern. However, it was constant (0.55 ± 0.01 S/m) during evaporation process at 12.5 V/cm. It is recommended that the ohmic heating method could be successfully integrated to vacuum evaporation process to shorten the processing time significantly. Industrial relevance Ohmic heating has been utilized as alternative method for the purpose of heating, pasteurization, cooking etc., and relatively better products can be obtained by ohmic heating. Nowadays, energy efficient systems are needed in concentrated juice production. The integration of ohmic heating to the conventional vacuum systems could serve the production high quality juice concentrates with efficient use of energy. In present study, ohmic heating assisted vacuum evaporation of pomegranate juice was conducted, successfully. This method decreased the total process time for juice concentration, which is critically important for industrial scale productions. This novel method can be implemented to the fruit juice production lines by taking into account of design characteristics of ohmic systems such as electrical conductivity changes depending on both temperature and total soluble solids concentration. The effects of main process parameter, named as voltage gradient, on electrical conductivity changes during electrical heating assisted evaporation process has been also reported in the present study.

Electrical pretreatments at 9 different conditions consisting of the combination of 3 different voltage gradients (20, 27, and 32 V/cm) and 3 different application times (10, 20, and 30 s) were applied on apple slices. Apple slices were osmotically dehydrated in 50% sucrose solution at 40 °C until their total dry matter content (TDM) reached to 40%. The effect of pretreatment conditions on the change of water loss and solid gain during osmotic dehydration was investigated, and effective diffusion coefficients were determined. The time needed to reach up to 40% TDM content was predicted by using the numeric solution of unsteady state mass transfer equations and diffusion coefficients via MATLAB code written. The electrical pretreatments reduced the osmotic dehydration time by in the range of 26–64%. The final water and solid distributions of apple slices were simulated in ANSYS. Modeling and simulation results were in good agreement with experimental data (p < 0.05). Industrial relevance Since the electrical pretreatment both shortens the osmotic dehydration time and increases the water removed per unit energy used, its application prior to osmotic dehydration processes in the commercial productions will be economical. The proposed modeling and simulation approach for assessment of the effects of electrical pretreatments on osmotic dehydration characteristics may provide valuable information on the scaling up of these conditions in the industrial scale systems.

Moderate electric treatment (MET) is based on the growth of pores in cell membranes as a result of electric field applications. In this study, effects of MET applications on yield and quality of pomegranate juice production were investigated. MET was applied to whole pomegranate fruits between 10 and 60 V/cm voltage gradients for 15 s in a pilot scale continues drum-type MET system. Pomegranate juice yields were increased by 2.11–6.99% with electrical treatment. The highest total phenolics were determined at 60 V/cm applications and the highest anthocyanin, antioxidant capacity, ascorbic acid, a value and total color differences were determined at 10 V/cm applications. The electrical treatment significantly decreased the viscosity of juice. It was concluded that MET application could be applied as a pretreatment in pomegranate juice production. Juice extraction is a slow and highly energy-consuming step in the production of fruit juices; thus, various methods have been tried to improve efficiency. And there is an additional effect on juice yield caused by the electric current. Moderate electric treatment (MET) is effective in destroying cellular membranes and different types of electroporation units could be used for the structure of fruits or vegetables and also according to the production method. Through this study, a high potential of MET for the yield and functional improvement of pomegranate juices was found. The drum-type MET system which was used in the study can be used for whole materials without significant temperature increases. In addition, MET treatments can be used to increase the press yield as a nonthermal application and it will eliminate heat exposures, and also drum-type MET system can be adapted to the industrial production lines.

In this study, osmotic dehydration of quince slices was investigated by applying electrical (60 V/cm, 15 s) and ultrasonic (195 W, 15 s) pre-treatments. It was also performed as untreated (control group) for the purpose of comparing the effects of pre-treatments. 50% (w/w) sucrose solution was used as the osmotic drying agent. Changes on total dry matter (TDM) content, solid gain, water loss, weight reduction, dimensions, the electrical conductivity and temperature during the osmotic dehydration were investigated. It was determined that electrically pretreated quince slices reached to 40% TDM content in 240 min although ultrasonic pretreated samples and control group reached in 300 min. Comparing the color values of osmotically dried samples having 40% TDM, L*, a*, Hue angle, and ∆E colour values of either ultrasonic pretreated or control group samples were different than those of electrically pretreated samples (p<0.05). It is found that maximum b/a value was found in electrically pretreated samples whereas minimum was for ultrasonic pretreated samples (p<0.05). It is determined that hardness, gumminess, chewiness and springiness values of osmotically dried products were lower than those of raw material (p<0.05). It was concluded that ultrasonic pre-treatment has minimal effects on quality characteristics rather than electrical pre-treatment.

The chemical composition and nutritional value of a wild edible ectomycorrhizal mushroom from southwestern Anatolia, Tricholoma anatolicum, were analyzed. Moisture, crude oil, protein, ash, total carbohydrate content, and mineral composition of the mushrooms studied, including Fe, Na, K, Zn, Cu, Ca, Cd, and Pb, were determined. The energy values of the samples were also calculated. The analyses were conducted during the 3 different growing stages of the mushrooms: mycelium, young fruiting bodies, and mature fruiting bodies. The highest values for moisture and crude oil contents were found to be in the mycelium, ash, and carbohydrate content of young fruiting bodies. In addition, Na content was found to be the highest in mycelium. The highest values for Fe were found in the young fruiting bodies, and K, Zn, Cu, and Ca were at their highest values in mature bodies. None of the samples contained heavy metals Cd or Pb.

Four different species of wild edible mushrooms (Armillaria mellea, Infundibulicybe geotropa, Meripilus giganteus and Sparassis crispa) representing four different families (Physalacriaceae, Tricholomataceae, Meripilaceae and Sparassidaceae) growing in southwest regions of Anatolia were analyzed for their Fe, Na, K, Zn, Cu, Cd and Pb contents and ash, dry matter, protein, and fat levels. All mineral concentrations were determined on a dry weight basis (d.w.). The mineral content of mushroom samples ranged from 54.00 to 112.33 µg/ g d.w. for Fe, 66.50 to 117.33 µg/ g d.w. for Na, 32.33 to 117.00 µg/ g d.w. for K, 47.40 to 87.40 µg/ g d.w. for Zn, 54.30 to 74.67 µg/ g d.w. for Cu and not detected for Cd and Pb. Na content was higher than other minerals in all mushroom species. This research proves that wild edible fungi can be used in well-balanced diets due to their nutritive values. Also, their heavy metal contents (Pb, Cd) shows that collection areas are not polluted, therefore all collected mushroom species can be unreservedly consumed without any health risk.

The heating method affects the temperature distribution inside a food, and directly modifies the time–temperature relationship for enzyme deactivation. Fresh grape juice was ohmically heated at different voltage gradients (20, 30, and 40 V/cm) from 20 °C to temperatures of 60, 70, 80 or 90 °C and the change in the activity of polyphenoloxidase enzyme (PPO) was measured. The critical deactivation temperatures were found to be 60 °C or lower for 40 V/cm, and 70 °C for 20 and 30 V/cm. Various kinetic models for the deactivation of PPO by ohmic heating at 30 V/cm were fitted to the experimental data. The simplest kinetic model involving one step first-order deactivation was better than more complex models. The activation energy of the PPO deactivation for the temperature range of 70–90 °C was found to be 83.5 kJ/mol.

In this study, cultivation of oyster mushroom, Pleurotus ostreatus, on wheat straw substrate containing tap water and olive mill effluent (OME) mixture containing varying volume of OME was studied in order to investigate the feasibility of using OME as an alternative wetting agent and OME's impact on some fundamental food quality characteristics of mushrooms. Time period for mycelial colonization, primordium initiation and first harvest were comparatively evaluated with the control group. It was shown that the use of OME and tap water mixture consisting of OME up to 25% volumetrically was possible for the purpose of commercial mushroom production. Experimental results obtained from substrate containing 25% OME mixture showed no statistically significant difference compared to control group. The negative effects of increasing volume of OME in the mixture were also indicated by bioefficiency, which was found to be 13.8% for substrates wetted with 100% OME, whereas bioefficiency was 53.6% for control group. Increasing volume of OME in the mixture resulted in deformation of fruit body shape, whereas no significant difference in food quality was observed due to the higher amount of OME. This work suggested that the use of OME up to 25% as moisturizer could be considered, especially for the locations having significant number of olive mills and mushroom producers, both as an environmentally friendly solution for the safe and ecological disposal of OME and a practical way for recovering OME's economic value thereby.