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    Effect of freezing and packaging methods on the organic acid contents of goat cheeses during storage [Utjecaj zamrzavanja i metoda ambalaziranja na udjel organskih kiselina kozjeg sira tijekom skladištenja]
    (2011) Kemal Seçkin A.; Esmer O.K.; Balkir P.; Ergönül P.G.
    Effects of freezing and packaging methods on organic acid content of goat cheese during 12 weeks of storage were determined. Goat cheese milk curds were divided into two parts and stored at 4°C refrigerated control sample and at -18°C for six months frozen experimental samples. After that, cheeses were packed in three different packaging methods: aerobic, vacuum or modified atmosphere. Citric, malic, fumaric, acetic, lactic, pyruvic and propionic acids were analyzed using HPLC method after 1 st, 3 rd, 6 th, 9 th and 12 th week of storage period. Lactic acid was the main organic acids while pyruvic acid had the lowest content in all cheese samples. Citric and fumaric acid levels of frozen samples increased during storage whereas malic, acetic, pyruvic and propionic acid amounts were decreased compared to the beginning of storage. Packaging methods and freezing process also effected lactic acid levels statistically (p<0.05). Fumaric, acetic and lactic acid concentration of refrigerated samples were increased but citric, malic and propionic acids decreased during storage. Pyruvic acid level did not change significantly. It was determined that organic acid concentrations were effected by freezing process, storage time and packaging methods significantly (p<0.05).
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    Moisture sorption isotherms and storage stability of spray-dried yogurt powder
    (2010) Koç B.; Yilmazer M.S.; Balkir P.; Ertekin F.K.
    Moisture adsorption isotherms of spray-dried yogurt powder were determined at 10, 25, and 40°C using the standard, static-gravimetric method. Experimental data were fitted to five mathematical models (Guggenheim-Anderson-de Boer [GAB], Brunauer-Emmett-Teller [BET], Halsey, modified Oswin, and modified Henderson). A nonlinear regression analysis method was used to evaluate the constants of the sorption equations. The shelf-life of yogurt powder was predicted based on the relationship between permeability coefficient of the packaging material and moisture adsorbed by the powder determined by the GAB equation. Furthermore, the storage stability of spray-dried yogurt powder in terms of quality parameters including moisture content, water activity, color change, and thiobarbituric acid (TBA) value was studied in aluminum laminated polyethylene (ALPE) pouches under storage conditions of 25°C and 50% relative humidity (RH). © 2010 Taylor & Francis Group, LLC.
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    Rheological behavior of reconstituted yoghurt powder-An optimization study
    (Elsevier, 2014) Sakin-Yilmazer M.; Koç B.; Balkir P.; Kaymak-Ertekin F.
    The rheological behavior of reconstituted yoghurt powder was investigated using a numerical optimization approach. The maximum values of the rheological properties, apparent viscosity (mPa. s) and consistency in the mouth were targeted as responses together with acceptable moisture content and the maximum survival ratio of the lactic acid bacteria from a previous study [1] to prevent any conflict. It was determined that the air inlet, outlet, and feed temperatures of 170, 61, and 17. °C, were the optimum processing conditions, with a predicted apparent viscosity of 1160.5. mPa. s. The yoghurt powder produced at the optimum condition (±. 1. °C) was reconstituted to different dry matter contents (14, 20, 25, and 30% DM) and subjected to measurements of apparent viscosity and sensorial analysis (consistency in the mouth). The consistency value of the fresh stirred yoghurt corresponded to that of the reconstituted yoghurt between 25 and 30% DM. Also, the thixotropic behavior was observed for the reconstituted yoghurt. © 2014 Elsevier B.V.
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    Spray drying of yogurt: Optimization of process conditions for improving viability and other quality attributes
    (2010) Koc B.; Yilmazer M.S.; Balkir P.; Ertekin F.K.
    Plain yogurt was subjected to spray drying to determine the optimum processing conditions that yield maximum survival ratio of lactic acid bacteria, maximum overall sensory attributes, minimum color change, and acceptable moisture content. The inlet (150-180° C) and outlet air temperatures (60-90° C) and the feed temperature (4-30° C) were the independent factors. A pilot-scale spray dryer was used to conduct a set of drying experiments where the process conditions were selected according to central composite rotatable design (CCRD). The resulting yogurt powder at each condition was also subjected to the measurement of some physical properties (water activity, titratable acidity [lactic acid, %] and pH) to determine the effects of spray-drying conditions. The morphological structure of the powder was inspected by scanning electron microscopy (SEM) analysis. Optimization by the application of the desirability function method resulted in air inlet temperature of 171° C, air outlet temperature of 60.5° C, and feed temperature of 15° C as the optimum processing condition. The mathematical optimum condition was experimentally verified. © 2010 Taylor & Francis Group.