مقایسه تطبیقی عملکرد بسترهای فلزی و غیرفلزی در پخت صنعتی نان از نظر کاربردپذیری و خواص کیفی محصول نهایی

Introduction: In most countries, especially developing and underdeveloped, bread has high nutritional importance. Bread provides 40 to 45% of bioavailable carbohydrates, is an essential source of proteins, and plays a vital role in the digestive system (Aminpour and Shariatzadeh, 2013). Traditional Iranian bread is usually thin, flat and compact, and non-porous, and their bake has become commonplace in the past in Iran. The average per capita global consumption of bread is 60 to 70 kg. Large quantities of bread are wasted every year because different factors affect the number of waste products, including flour quality, bread production technology, and the storage condition of the bread. Among the factors affecting the quality of the flatbread, technological factors, including the source and method of heating the dough and the type of baking bed, are very critical. Those factors affect the quality and staleness of the bread and the amount of energy consumed per ton of the produced flatbread. Cast iron baking bed is used in industrial flatbread production in Iran. The heat transfer coefficient of cast iron is high and accelerates the baking process, which leads to drying the bread instead of baking. Therefore, lack of deep baking will result in staling of bread. Baking bread on this bed increases its staling rate and leads to the transfer of the heavy metal from the bed to the dough and bread. The objective of this study was to introduce the new baking bed, improve existing systems and increase product quality and storability.
Materials and methods: In this research, it has been attempted to replace the two new baking beds with a cast iron one. These new baking beds were circular earthenware and ceramic (Cordierite-Mullite). The circular earthenware has made from 50% of SiO2, 10% of Al2O3, and 40% of MgO, Fe2O3, and CaO. The formulation of Cordierite-Mullite was 5SiO2.2Al2O3.2MgO-3Al2O3.2SiO2. Thermal shock resistance, surface hardness, and bending strength of the circular earthenware and Cordierite-Mullite were evaluated. A rotary bread-baking machine with a size of 210× 210 cm and a height of 150 cm is selected to install the new beds and cast iron ones. After installing the baking bed, they were evaluated by baking the flatbread. Baking the flatbread was conducted with wheat flour (18% bran). For this purpose, the dough was prepared according to the common practices in the industry and baked by a skillful operator. The flatbread was also baked simultaneously in the baking machine on all the all using the same dough and was stored in double-layer plastic bags in the same conditions in the refrigerator. To examine the changes in the physical and sensory attributes over time in the same product and the differences between the flatbreads baked using different beds, the bread underwent mechanical tests (using instrumental measurements) and sensory evaluations (by an experienced panel) three times: on the 24, 48 and 72hr after baking. Thus, the quality measurements of the flatbreads (both mechanical and sensory) were conducted during the storage of the products so that the variations in the quality of the flatbreads over time were determined. A puncture test was performed to evaluate the mechanical properties of the flatbread. In performing the sensory evaluations, 15 semi-trained judges (from daily users of flatbread) were asked to assign scores from one (very bad) to 5 (very good) to each identified sensory attribute. Attributes were selected based on the quality criteria of the product according to the AACC standard 01/30-74 (American Association of Cereal Chemists, 2000). The sensory panel evaluated the product 24, 48, and 72hr after baking. In addition, based on the scores assigned to each listed attribute in the quality and customer acceptance evaluations of the flatbreads, weight coefficients were developed for each attribute. The overall acceptability of each type of flatbread was calculated separately for the data from each evaluation date. It is noteworthy that the criteria and environmental conditions for conducting the sensory evaluations were the same during all sensory evaluations. Finally, the total score for each type of flatbread, baked on each baking bed at each time point, was compared with each other, and the trends of changes in the quality of the bread were determined.
Results and discussion: Bending strength of Cordierite-Mullite and circular earthenware plate in the three-point bending test were 23.5, and 9.3 kN, respectively, and their Fracture load was 5.3 and 2.8 kN, respectively. The bending strength of cast iron was higher, but the Cordierite-Mullite plate has enough strength for the baking process. Thermal shock resistance of the Cordierite-Mullite and cast iron beds during the baking operations was too high, and no strain was observed during the heating process at 300 to 35 ◦C for 12 to 14 h. Therefore, the thermal shock resistance, surface hardness, and bending strength of new beds during the baking operations were acceptable. The results showed that these beds were suitable for installation on the baking machine and had enough strength for a long baking operation. The quality index of bread baked on the circular earthenware, and Cordierite-Mullite beds were 4.5, 4.3, and 2.9 at 24, 48, and 72 hours after baking, respectively. It was 4.2, 4, and 2.7 for bread that were baked on the cost iron bed at the exact times, respectively. These results indicated the durability and satisfactory quality of bread baked on the circular earthenware and Cordierite-Mullite beds. The compression force of baked bread on the circular earthenware, and Cordierite-Mullite beds at 24, 48, and 72 hours after baking were 10.4, 12.6, and 16.9 N, 9.3, 13.2, and 18.8 N, respectively. Compared with the bread baked on a cast-iron bed, the compression or stiffness values on the two new beds were relatively lower, implying a good marketable, and shelf life of bread. These results showed that the baked bread on these new beds not only had higher quality but also had a longer shelf life.
Conclusion: In general, the results of the current study indicated that the circular earthenware and Cordierite-Mullite beds have acceptable thermal shock resistance, surface hardness, and bending strength. In addition, bread baked on these beds had higher quality and longer shelf life.