Transglutaminase-crosslink whey protein/pectin coating act as aneffective water vapour barrier in fryed and baked food

Behavior of pectin and thermally denatured whey proteins at different protein/polysaccharide ratios and pH values was preliminarily investigated to determine the best experimental conditions for obtaining composite films. Experiments were carried out in the absence or presence of transglutaminase, an enzyme able to crosslink proteins by forming (-glutamyl)lysine isopeptide bonds (Porta R., CritRevFoodSciNutr. 51, 223, 2011). Our findings indicated the formation at pH 5.1 (pHc) of transglutaminase-catalyzed crosslinks among soluble ionic whey protein/pectin complexes and the obtained hydrocolloid films showed good mechanical as well as water vapor and oxygen barrier properties. Application of the films by dip-coating technique allowed to create a layer on the surface of bakery foods, such as dry biscuits and donuts, and the effects of the performed coating in controlling food moisture transfer and oil uptake were evaluated. We observed a significant reduction of water absorption by dry biscuits which prevented the loss of their crispness, keeping normal the hardness parameters and improving the springiness and chewiness ones. It is well known that fried foods contain high amounts of fat, considered one of the major risk factors of developing heart diseases. We demonstrated that the coating of donuts by the pectin/whey protein films obtained in the presence of transglutaminase was able to reduce the water loss during the frying process by preventing water migration from the core to the crust of the donuts and, as a consequence, by filling the void that normally allows the fat to enter inside the food. Besides, coated donuts exhibited decreased fat uptake, reduced fat content and improved oil barrier index. In conclusion, the introduction of transglutaminase-catalyzed crosslinks among pectin/whey protein complexes obtained at pHc was shown to clearly confer to the hydrocolloid films good performance in acting as both water and oil absorption barrier for bakery foods