Effects of enzyme resistant starch supplementation on physical and chemical properties of extrudates produced from bread crumbs

In the first part of this study, extrudates were produced from both bread wheat flour and bread crumbs obtained from the breads produced by using the same wheat flour. Three different feed moisture contents (13, 15 or 17%) and three different exit die temperatures (120, 135 or 150°C) were used at the constant extrusion parameters of feed rate (4.0 kg/h), screw speed (200 rpm) and die hole diameter (2.0 mm). The wheat flour extrudates (WFE) and bread crumbs extrudates (BCE) were compared based on their expansion index (EI), bulk density (BD), textural characteristics (hardness and crispness), water solubility, water holding capacity, dietary fiber (DF) and resistant starch (RS) contents. In general, BCEs determined to have better physical properties than WFEs. The best results were obtained for BCEs produced at lower feed moisture contents (13%). On the other hand, the exit die temperatures studied were found to have only a limited effect on product properties. In the present study, it was determined that the effect of feed moisture content on the physical properties of the extrudates was significant (p<0.05). The effect of the die exit temperature on the physical properties of the extrudates was more pronounced at 15 and17% feed moisture contents. DF contents of BCEs (5.75-7.28%) were significantly higher (p<0.05) than those of WFEs (4,58-5.50%). Their RS contents also demonstrated a similar trend. The results proved that bread crumbs is a promising raw material in extrusion cooking and a new value added product group can be developed from bread crumbs by means of extrusion. The aim of the second part of this study was to obtain a functional snack food by supplementing BCEs with RS and thus to meet the requirements of the Turkish Food Codex, Nutrition and Health Statement Regulations for the "increased fiber" declaration for foods. Therefore, BCEs were produced by supplementing bread crumbs with two different commercial RSs (a RS2 and a RS4) at three different ratios (0, 15 and 30%). The BCEs were compared in terms of EI, BD, textural properties (hardness and crispness), water solubility, water binding capacity, DF content and RS content. RS addition decreased EI and crispness and increased BD and hardness values. The DF content of BCEs increased directly proportional to the amount of RS added. In general, the DF contents of BCEs increased with increasing feed moisture contents, while the die exit temperature had no significant effect. RS supplementation had an adverse effect on the properties (e.g. EI and BD values) of BCEs which was generally higher for RS4. In general, RS2 supplemented BCEs had better crispness values. Furthermore, the water solubility values of RS2 supplemented BCEs were higher than RS4 supplemented ones; whereas for the water binding capacity values this tendency was reversed. It can be concluded that, breads with manufacturing defects can be utilized in industrial bakeries for developing innovative functional food products and extrusion-cooking might be a good alternative for the processing of bread crumbs supplemented with RS.