EFFECTS OF DIFFERENT PEKMEZ (FRUIT MOLASSES) TYPES ON CHEMICAL, NUTRITIONAL CONTENT AND STORAGE STABILITY OF CAKE

Preparation of Cake

Control and pekmez added cake doughs were prepared by using the following ingredients on a 100 g flour basis.

Brix values of pekmez samples were adjusted to 70% with the addition of distilled water. To prepare cake dough, egg and sugar were whipped to a cream in a Hobart mixer (Hobart N50, Canada Inc., North York, Canada) at maximum speed for 5 min. Then, other ingredients were added into the mixer, and it was mixed for 1 min. One hundred thirty grams of cake batter was poured in baking pans with a 7.5 cm × 6.6 cm × 12 cm dimensions, and baked in an oven (Arçelik ARMD-580, Arçelik Inc., Gebze, Turkey) at 180C. Cake samples were kept at room temperature (22C) by packaging to determine the 0, 7 and 21 days storage stability.

Chemical and Physical Analysis

Total dry matter, crude protein and ash were determined according to standard AACC (1990) methods; pH, total and soluble dry matter were determined according to Cemeroğlu (1992). pH was measured with a pH meter (WTW-315 model, GmbH, Weilheim, Germany); soluble dry matter was determined with an ATAGO model refractometer.

Total sugar, invert sugar and sucrose were quantitated by the Lane-Eynon method (Cemeroğlu 1992). Hydroxymethylfurfural (HMF) was determined quantitatively following the procedure described by the IFJJP (1964), based on the colorimetric reaction between barbituric acid, p-toluidin and HMF, forming a red-colored complex. The intensity red color was measured at 550 nm by using Shimadzu UV-Visible 160 A model spectrophotometer (Shimadzu Corporation, Tokyo, Japan).

For color analysis, the instrument was calibrated with a white reference tile (No: 14533046) before measurements. Colors of samples were analyzed by measuring Hunter L* (brightness; 100: white, 0: black), a* (+: red; −: green) and b* (+: yellow; −: blue) parameters with a colorimeter (Minolta Model CR 400, Osaka, Japan). Hue angle (h), which describes the hue or color of pekmezes, was calculated (arctan [b*/a*]), as was the saturation index (SI) ([a*² + b*²]^1/2), which describes the brightness or vividness of color (Akbulut and Çoklar 2008). Three measurements were taken of each sample. The hardness of cake samples were measured after baking and the 7th and 21st day of storage by a biologic material-test device using the procedure of Aydın and Öğüt (1991). Biologic material-test device developed by Aydın and Öğüt (1992), has three main components which are a stable forced and moving platform, a driving unit (AC electric motor and electronic variator) and a data acquisition (dynamometer, amplifier and XY recorder) system.

Water activity (A_w) values of cake samples were measured with an A_w meter (Novasina-ms1, Pfaeffikon, Switzerland).

Elemental Composition

For analyzing the mineral contents of the cakes, about 0.5 g of dried and ground cakes samples were put into a burning cup and 15-mL pure HNO₃ was added. The sample was incinerated in a microwave oven (MARS-5 Cem Corp., Matthews, NC) at 200C and dissolved ash was diluted to a certain volume with water. Concentrations were determined with an inductively coupled plasma-atomic emission spectrometer (ICP-AES) (Vista Series, Varian International AG, Zug, Switzerland) (Bubert and Hagenah 1987).

Statistical Analysis

The data were compared using analysis of variance with respect to different kinds of pekmez addition. The values were average of triplicate determinations on two replicate cake preparations. The means, which were statistically different from each other, were compared using Duncan's multiple comparison tests at 5% confidence interval. TARIST (version 4.0, İzmir, Turkey) software was used to perform the statistical analyses.

Physical and Chemical Characteristics of Pekmez

Physical and chemical characteristics of pekmez samples are given in Table 1. Soluble dry matter values of pekmez samples changed between 70.0 and 79.0%. Generally, pekmez is produced from sugar-rich fruits by concentration of juices up to 70–80% soluble dry matter content (Alpaslan and Hayta 2002). Different researchers found soluble dry matter values between 52 and 81% in 76 pekmez samples (Aktan 1940; Yazıcıoğlu and Gökçen 1976; Kayahan 1982; Batu 1991a,b). All pekmezes contained high amounts of total sugar, which is composed of 78.16–99.22% invert sugar. Mulberry pekmez had higher soluble dry matter, total and reducing sugar than other pekmezes. Apricot pekmez had 12.69 g/100 g saccharose, which is approximately 12 times higher than the saccharose content of grape or mulberry pekmez. Ash and protein content changed between 1.71 and 2.43% and 0.21 and 0.35%, respectively. HMF content of grape pekmez (34.1 mg/L) was the highest value of all types of pekmez, but it was under the legal limits (TS 1989). HMF is an indicator of quality deterioration, which occurs as a result of excessive heating in food (Cemeroğlu 1992). Pekmez color values (L*, a* and b*) showed a small difference due to the natural color of its fruit. a* values of elecampane pekmez were a bit higher than others. A high redness value a* occurs as the result of excessive caramelization of sugar and high a* values are not desired. Hue angle and SI values of grape pekmez were lower than other pekmez samples.

Chemical Characteristics of Cakes

Chemical properties of cakes are given in Table 2. A_w values of cakes changed between 0.485 and 0.558 and the lowest A_w values were obtained with apricot and grape pekmez addition. Generally, pekmez addition reduced A_w value except elecampane. Reduced A_w values are important in terms of lower microbiological activity during the storage of cakes.

Pekmezes increased the ash amount of cakes with its high ash content. Compared with the control, apricot and elecampane pekmez addition gave 1.99 and 1.93 times higher ash content, respectively. Protein content of cakes did not change with pekmez addition due to its too low protein content (0.21–0.35%) (Tables 1 and 2). Total sugar contents of mulberry, apricot, elecampane, grape and watermelon pekmez-added cake were 29.07, 26.27, 17.65, 27.38 and 28.32%, and the ratio of reducing sugar to total sugar was 98.04, 78.19, 92.18, 97.3 and 86.12 respectively. This ratio was only 1.13% in control cake sample. Saccharose content of control cake was high because of the usage of crystal sugar (Table 2).

HMF content of cake samples ranged from 2.03 (control) to 15.78 mg/kg. Maximum HMF content was obtained with grape pekmez addition, which has 34.1 mg/kg HMF (Tables 1 and 2). In Turkish Pekmez Standard (TS 1989), maximum HMF in pekmez is declared as 50 mg/kg.

Crust and Crumb Color of Cakes

Color values of cakes were summarized in Table 3. Crust and crumb lightness (L*) value of cakes reduced with addition of pekmez. The natural dark colors of pekmez affected cake color directly and the darkest crust color (17.09) was observed with mulberry pekmez addition. Crumb redness (a*) increased with pekmez addition and the highest value (12.05) was obtained with elecampane pekmez. In contrast to the a* value, yellowness (b*) decreased with addition of pekmez and the lowest value (8.55) obtained with elecampane pekmez also. Crust and crumb hue angle and SI values of control samples were higher than pekmez-added cake samples. Crust and crumb SI were the lowest in mulberry pekmez-added cake.

Mineral Content of Cakes

Mineral composition of cake samples is given in Table 4. With the addition of pekmez to cake samples, Ca, Cu, Fe, K, Mg, Mn, P and Zn content of the samples increased when compared with the control samples. This increase was 1.25–2.4 times in Ca, 1.65–12.77 times in Cu, 2.27–12.61 times in Fe, 3.68–5.89 times in K, 2.23–2.62 times in Mg, 1.24–2.25 times in Mn, 1.25–2.04 times in P and 1.27–2.13 times in Zn. Ca is a very important mineral in human nutrition and apricot and elecampane pekmezes increased Ca values up to 177.82 and 143.58 mg/100 g, respectively. In the control sample, the amount of Ca was only 73.89 mg/100 g (Table 4). Kavas (1990) reported that the Ca concentration of grape pekmez was 400–500 mg/100 g. A significant increase was observed in Fe content of cake with the addition of elecampane (22.70 mg/100 g) and grape (21.71 mg/100 g) pekmez. Control samples without pekmez had 1.80 mg/100 g Fe element (Table 4). Pekmez is an excellent source of iron, which is very important for the human body and which has many roles in some biochemical reactions. Karakaya and Artık (1990) reported that Fe content of Zile pekmez was 0.3 mg/kg. K amount of samples increased with pekmez addition and the highest values were obtained with apricot (7,208.45 mg/100 g) and elecampane (7,160.01 mg/100 g) addition. Batu et al. (1992), Karakaya and Artık (1990) and Kavas (1990) found K values of pekmez as 1,359–2,874 mg/kg and 1,160 mg/kg and 1,470 mg/100 g, respectively. Apricot, mulberry and elecampane pekmezes increased P value up to 375.72 mg/100 g, 403.78 mg/100 g and 416.41 mg/100 g, respectively. P content of grape pekmez was given between 28.7 and 652.2 mg/kg by Batu (1991b). Grape and watermelon pekmezes addition increased the Zn content of cakes more than two times.

The Recommended Dietary Allowances (RDAs) for adult males are 800 mg of calcium, 10 mg of iron, 1.6–2.0 g of potassium, 350 mg of magnesium, 800 mg of phosphorus and 15 mg of zinc. When 100-g (dry matter) pekmez-added cakes were consumed, 11.6–22.2% of RDA for Ca, 40.9–227% of RDA for Fe, 250–400% of RDA for K, 22.3–26.2% RDA for Mg, 31.9–52.1 of RDA for P and 19.4–32.4% of RDA for Zn were taken by the human body. These RDA ratios were 9.2% of Ca, 18% of Fe, 68% of K, 10% Mg, 25.5% of P and 15.2% of Zn in the control cake sample. Especially high Fe contents of cakes are important to overcome the anemia problem which occurs due to iron deficiency.

Change of pH, Color and Hardness during Storage

Effects of 21-day storage on pH, color and hardness values were given in Table 5. pH values of cakes decreased descriptively during 21 days but did not change statistically except mulberry pekmez-added cakes. In this cake, pH did not change during the first 7 days, but a statistically significant decrease (P < 0.05) was observed at the end of 21 days. In all cake samples, the highest pH values were observed in control samples (Table 5).

Lightness value of cakes did not change during the 21-day storage statistically (P < 0.05). Control and mulberry-added cakes protected the highest and the lowest lightness value, respectively, during the 21-day storage. Redness value (a*) of control and mulberry pekmez-added cakes decreased after 7 days of storage. In contrast, apricot pekmez addition increased a* value before 7 days of storage (Table 5). Storage period did not affect the yellowness values of the cakes statistically. During the 21-day storage period of apricot-added cakes, hue angle decreased, but SI value increased.

Hardness values increased at all samples after the 21-day storage statistically (P < 0.05). After 7 and 21 days of storage, the hardest cakes were mulberry and elecampane pekmez-added cakes like 0 day (Table 5). At the end of 7 and 21 days of storage, apricot and watermelon pekmezes gave softer texture to cakes than other pekmez and control. These two pekmezes gave increased shelf life to the cakes by delaying the staling process.