Rheological properties of poppy seed paste/grape pekmez blends

Abstract

Rheological properties of poppy seed paste (PSP)/grape pekmez blends containing 10%, 15%, 20%, 25%, 30%, 35%, and 40% PSP were determined at different temperatures (10–40 °C). The PSP/grape pekmez blends behaved as a pseudoplastic fluid. The flow behavior index of the blends containing 10% PSP varied between 0.92 and 1.0, however, as the concentration of PSP increased to 40% the flow behavior index decreased to the range of 0.23–0.67. As the temperature increased the viscosity and the consistency coefficient (K) decreased. The activation energies (Ea) of the blends were found in the range of 23,054.8–66,059.1 kJ/kmol. The consistency coefficient increased from the range of 0.25–3.56 Pa sn to 35.63–203.01 Pa sn as the PSP concentration increased from 10% to 40%. The combined effect of the concentration, temperature and shear rate on the viscosity of the PSP/grape pekmez blends were described successfully by a simple equation. The blends showed a rheopectic time‐dependent behavior. Practical applications Rheological properties of fluid foods are necessary for designing and evaluation of food processing lines, quality control and consumer acceptability. In this study, flow behavior and the effect of temperature and PSP concentration on the rheological properties of the PSP/grape pekmez blends were determined. The effect of concentration, temperature, and shear rate on viscosity was represented by a simple equation which can be used in engineering calculations. Time‐dependent flow behavior of the PSP/grape pekmez blends was also determined that it is important for the estimation of changes in the flow behavior during processing.

Rheological behavior of different phases of grape molasses after storage: Effect of concentration and temperature

“…In addition, activation energy is necessary for moving of a molecule, and as the temperature increases, the liquid flows more easily due to higher an activation energy in high temperature (Akbult & Özcan, ). This observation resulted in a decrease in the K and was in agreement with other researchers (Kaya & Belibaǧlı, ; Özkal & Süren, ; Quek et al, ; Sengül, Ertugay, & Sengül, ; Swami‐Hulle, Patruni, & Rao, ). Moreover, the n values of the samples decreased with increasing temperature for all concentrations which means more pseudoplasticity (Table ).…”

“…Quek et al () also addressed that the power law model was the best one to describe the rheological data of soursop juice concentrates. Similar results were observed in other studies regarding sugarcane molasses (Cristina dos Santos Bofo et al, ), poppy seed paste/grape pekmez blends (Özkal & Süren, ), and aloe vera juice concentrates (Swami‐Hulle, Patruni, & Rao, ). Moreover, the rheological behavior of sorghum pekmez was described by the power low model (Akbult & Özcan, ).…”

“…This means that the rheological behavior of the samples (both red and brown phases) was similar to a non‐Newtonian fluid. Similar findings were reported by Alpaslan and Hayta () for tahin/pekmez blends in the temperature range of 30–75°C and pekmez concentrations of 2–6% (w/w), Arslan et al () for pekmez (grape molasses)/tahin (sesame paste) blends in the temperature range of 35–60°C, tahin concentrations of 20–32% (w/w), Cristina dos Santos Bofo et al () for sugarcane molasses in the temperature range of 21–98°C, and concentrations of 50–70°Brix, Quek et al () for soursop juice concentrates in the temperature range of 10–70°C, concentrations of 10–50°Brix, Karaman and Kayacier () for apricot and date molasses in the temperature range of 10–40°C, Özkal and Süren () for poppy seed paste/grape pekmez blends, Sengül, Ertugay, & Sengül () for mulberry pekmez in the temperature range of 30–70°C, and Swami‐Hulle, Patruni, & Rao () for aloe vera juice concentrates in the temperature range of 15–55°C and concentrations of 1.5–5.5°Brix.…”

“…Moreover, the n values of the samples decreased with increasing temperature for all concentrations which means more pseudoplasticity (Table ). The reduction in pseudoplasticity of grape molasses samples (higher values of n ) was observed at lower concentrations, as reported by Chin, Chan, Yusof, Chuah, and Talib () for pummelo juice, Özkal and Süren () for poppy seed paste/grape pekmez blends, Quek et al () for soursop juice concentrates, and Swami‐Hulle, Patruni, & Rao () for aloe vera juice concentrates.…”

“…As can be seen in Table , an increase in temperature caused a considerable decrease in the K values of grape molasses samples. Increasing the temperature from 25 to 65°C increased the thermal energy of molecules and intermolecular distances due to thermal expansion (Özkal & Süren, ). In addition, activation energy is necessary for moving of a molecule, and as the temperature increases, the liquid flows more easily due to higher an activation energy in high temperature (Akbult & Özcan, ).…”