Effect of dietary fibre and thermal condition on rice bran wax oleogels for biscuits preparation

In this work sunflower oil (SFO) oleogels were obtained using rice bran wax (RBW) at 4.5 and 5.5% wt/wt. Bamboo fibre 40 µm (BF40) at 0.5% was investigated as structuring agent. The effect of fibre addition and cooling temperature (0, 4 and 25°C) on gel properties was evaluated compared to control samples prepared without fibre and at same cooling conditions. Rheological (both in rotational and oscillatory mode), texture and differential scanning calorimetry tests were carried out to assess thermal and structural parameters of gels. Oleogelatinization modified the rheological behaviour of samples, shifting from a typical Newtonian oil trend to a pseudo plastic non-Newtonian behaviour in gels. The gels resulted sensitive to temperature changes since a lower cooling temperature led to a structure weakening. Nevertheless, the fibre addition determined an increase of gel strength especially at 4°C demonstrating the structuring action of bamboo. This latter result was particularly evident on macroscopic scale by texture analysis. In fact, samples prepared at 25°C and without fibre addition showed the highest hardness, gel strength and work of penetration values. All parameters reduced by decreasing in cooling temperature down to 0°C, from which point it was not possible to carry out any more measure. Fibre inclusion determined soaring texture values, where samples prepared at 4°C are comparable to control at 25°C. Gels obtained through cooling at 4°C were used in biscuits preparation, with control recipes with only SFO or with butter. Texture profile analysis on dough revealed that the inclusion of fibre reduces dough firmness affecting positively texture parameters, better resembling the butter control. Biscuits prepared with only SFO showed higher spread values than butter cookies. The use of gelled material reduced the spread ratio even not as much as in butter cookies. Biscuits prepared with fibre-added gels possess a texture closer to butter control, even if all the gel cookies behaved as brittle material with lower fracturability indexes compared to butter ones.