M.A. Lluch

Effect of addition of gelatin on microstructure of acidic milk gels and yoghurt and on their rheological properties

Abstract A study was made of the effect of the addition of gelatin on the microstructure of acid-heat-induced milk gels (90°C, pH=5.3) and yoghurt with and without the addition of 5% of milk solids, and a comparison was made with the microstructure of acidic milk gelatin gels obtained without heating (pH=5.3). It was seen that in the acid-heat-induced gels and in yoghurt the gelatin interacted with the network of milk proteins as a connection between the clusters formed, whereas it was the gelatin alone that was the basis of the formation of the gel when the milk did not reach the casein coagulation point (pH=5.3, unheated). The results of firmness tests indicated that the addition of 1.5% of gelatin developed fairly firm, deformable systems in all the cases studied, with a definite break point and almost total absence of syneresis. Dynamic rheology showed that the yoghurts with added gelatin exhibited more solid-like behaviour than the ones prepared without it.

Microstructure Changes During the Xixona Turrón Manufacture Analyzed by Light Microscopy

Xixona turrón [Xixona nougat] is a typical Spanish confectionery product made still according to the traditional craft method. This work analyzed the microstructural changes during Xixona turrón manufacture by light microscopy. Different sample preparation methods provided useful complementary information for the understanding of the Xixona turrón structure. A progressively closer contact between a ‘‘sugar phase’’ and a ‘‘fat phase’’ is observed during processing. Inside these phases were immersed many protein bodies and a lot of cellular debris from almond tissue. At the initial stages of mixing the toasted almond paste with the sugar and honey mass, the lipid and sugar phases were relatively discrete. However, as the process developed, the relatively large aerated sugar particles, and to some extent the almond cell debris and protein bodies, were trapped within the lipid phase. In the step when the paste is heated at 65°C, gently stirred, the sugar and plant cell wall material tended to become more finely dispersed. The finished product seemed to consist of twin continuous phases in which the sugar, plant cell wall and protein bodies have formed a ‘‘sugar phase’’ that is infiltrated by the lipid fraction or ‘‘fat phase’’. This structure could contribute to the relatively ‘‘crispy’’ texture of Xixona turrón although the ‘‘oily’’ feel of the product clearly stated that the lipid phase was not extensively encapsulated in the product.