Pustaka Ilmiah Universitas Padjadjaran

Abstrak

The Influence Of Fat Content, Fat Globule Size, Whey Protein Denaturation And Pectin Addition On The Textural And Rheological Properties Of Acidified Dairy Systems

Texture of acidified milk products is largely influenced by milk composition (i.e. protein, fat and stabilizer such as pectin) and the processing conditions (i.e. heat treatment and homogenization). The presence of protein and fat in dairy products has a considerable impact on their physical properties, rheological and textural characteristics. Hydrocolloid/stabilizers such as pectin are used to retain the texture properties of a product when the fat is removed. In the manufacture of dairy products, homogenization is usually performed to change the fat globule size. Heat treatment causes the whey proteins to denaturate and thus also affects the texture of acidified dairy products. A study to develop a texture model for acidified dairy products by means of changing the heat treatment conditions, the fat content, the milk fat globule size and pectin as a stabilizer in acidified dairy systems was performed.

GDL acidified dairy systems were made from cream and reconstituted casein and whey protein powder (protein ratio 8 : 2) high heated at 3 levels. High heating level 0 (HE0) corresponds to the pasteurized protein solution. High heating levels 1 (HE1), 2 (HE2) and 3 (HE3) correspond to already pasteurized protein solution additionally heated in a 97 0C waterbath to expose the protein solution to temperature-time combinations of 76 0C/0 s, 85 0C/0 s and 85 0C/20 min, respectively. Fat content of systems as varied in 3 levels at 0, 2 and 4 %. Cream used to adjust fat content of systems varied in two fat globule size, D32_1 corresponding to 1,2 ìm and D32_2 corresponding to 0,6 ìm. Pectin content was varied at 3 levels, 0, 0.05 and 0.10 %. The acidified dairy systems were tested for texture properties using instrumental texture profile analysis (TPA) and oscillative rheology. Two experimental designs were created and run to investigate the interaction effects between the named factors on the textural parameters (Hardness, Fracturability, Adhesiveness and Cohesiveness).

Increasing the degree of whey protein denaturation (WPD) up to 91,9 % (HE2) by high heating positively correlated with fracturability, hardness, cohesiveness and adhesiveness of systems, while a further increase of WPD to 98,6 % (HE3) slightly decreased those texture parameters at all fat contents. Increasing fat content in HE0 and HE1 tended to reduce fracturability, hardness and cohesiveness, while adhesiveness was increased at increasing fat content. Furthermore, in HE3 systems, fracturability, hardness and cohesiveness increased at increasing fat content.. For systems containing pectin, fracturability, hardness, adhesiveness and cohesiveness were increased as the addition of pectin to the systems. High heating has the highest effect on those texture parameters in systems containing either fat and/or pectin.

In the systems without fat as well as in the systems with fat, the loss angle ä at a frequency of 1 Hz is increased ats increased degree of WPD. The 55 % difference in the degree of WPD between HE0 and HE1 thus caused a marked loss angle difference. Increasing fat content reduces the loss angle at all high heating levels. The presence of fat in the system thus leads to a more elastic behaviour. Increased WPD by high heating results in an increase in G’ and G”, whereas, increasing fat content from 0,0 % to 2,0 % does not change the G’ and G” in HE0 and HE1 systems. Only if fat content is increased from 2,0 % to 4,0 % this results in a marked difference in G’ as well as G”. Reducing the fat globule diameter from 1,2 ìm to 0,6 ìm had no effect on all investigated texture and rheological parameters.