Rheological and textural properties of goat milk set type yoghurt as affected by heat treatment, transglutaminase addition and storage

BACKGROUND Production of goat milk set style yoghurt encounters challenges in achieving the texture characteristic for this type of product, primarily due to protein composition of this milk. This study evaluated the effects of using microbial transglutaminase (mTGase) concomitantly with starter culture in the production of goat milk yoghurt, a method which wasn't employed so far with this milk type, indicating the potential of the enzyme to change yoghurt's textural properties. Goat milk set yoghurts were produced from milk heated at 72 °C/30 s and 90 °C/5 min, without (G72 and G90) and with mTGase (G72TG and G90TG) and starter culture addition. Protein profiles of goat milks and yoghurts were also examined by SDS PAGE electrophoresis. Yoghurts were evaluated for rheological properties, texture, microbiological and sensory profile during two weeks to study the influence of mTGase, pasteurization and storage. RESULTS The enzyme caused significant increases of storage moduli at the end of fermentation: 8.32±0.27 (G90TG) and 2.89±0.18 Pa (G72TG) vs. 6.13±0.07 (G90) and 1.27±0.18 Pa (G72) without enzyme. Lower loss tangent values indicated the enhanced elastic character of the gels with enzyme. Enzyme increased yoghurt's firmness from 49.69±2.61 (G90) to 60.81±5.29 g (G90TG) after one day and from 58.21±0.53 (G90) to 80.45±0.59 g (G90TG) after 15 days' storage. Enzyme improved starter bacteria survivability during storage of G72TG yoghurt. CONCLUSION mTGase can be used simultaneously with the starter culture to improve rheological properties and texture of the goat milk yoghurt, without deteriorating effect on its flavour. This article is protected by copyright. All rights reserved.