Fermented milk products: effects of lactose hydrolysis and fermentation conditions on the rheological properties

Dairy Sci. & Technol. (2016) 96:199–211 DOI 10.1007/s13594-015-0259-9 O R I G I N A L PA P E R Fermented milk products: effects of lactose hydrolysis and fermentation conditions on the rheological properties C. Schmidt 1 & S. Mende 1 & D. Jaros 1 & H. Rohm 1 Received: 2 July 2015 / Accepted: 3 September 2015 / Published online: 2 October 2015 # INRA and Springer-Verlag France 2015 Abstract Lactose-free dairy products become increasingly important for lactoseintolerant consumers, but there are only few studies concerning the rheological properties of fermented dairy products from lactose-hydrolysed milk. Hydrolysation was performed with commercial β-galactosidase either before or during fermentation (cohydrolysis). In each trial, fermentation of the base milk was carried out simultaneously using the same starter cultures for (a) untreated milk (reference) (b) hydrolysed milk as substrate and (c) by performing lactose hydrolysis and fermentation simultaneously (co-hydrolysis). In total, five thermophilic starter cultures and two products (yoghurt and Greek-style yoghurt) were investigated. Results show that the influence of hydrolysis of lactose on the properties of the fermented dairy products strongly depends on starter culture and substrate. For starters C and D, apparent viscosity (extracted from flow curves at a shear rate of 75 s−1) of fermented milks was only marginally affected by lactose hydrolysis, ranging between approx. 0.34–0.31 and 0.37–0.31 Pa.s, respectively. Hydrolysed products from starters A and E exhibited significant lower apparent viscosity (0.16 and 0.24 Pa.s) compared with their respective references (0.29 and 0.35 Pa.s). Fermentation of both substrates (regular yoghurt, Greek-style yoghurt) with starter B resulted in a decrease of yield stress and apparent viscosity because of lactose hydrolysis only for Greek-style yoghurt. Furthermore, a trend towards higher EPS synthesis was found when using hydrolysed milk. The results clearly show that products made from lactose-hydrolysed milk with similar rheological properties as the reference product can be obtained but that there is a lack of information concerning the complex interactions between starter culture and milk substrate. Keywords Yoghurt . Lactose hydrolysis . Rheological properties * D. Jaros 1 Chair of Food Engineering, Technische Universität Dresden, 01062 Dresden, Germany 200 C. Schmidt et al. 1 Introduction Lactose intolerance comes from the insufficient resorption of lactose in the small intestine, caused by a reduced activity or the absence of β-galactosidase. Consequently, undigested lactose reaches the colon where it is fermented by the colon microbiota into e.g. methane, hydrogen and lactate which cause symptoms such as flatulence, abdominal pain and diarrhoea (Mlichová and Rosenberg 2006; Schaafsma 2008). Because of these negative effects, lactose-intolerant consumers avoid the intake of milk and lactose-containing foods. Sales opportunities of lactose-free products are high all over the world, especially in countries with a high percentage of lactoseintolerant people (Harju et al. 2012; Jelen and Tossavainen 2003). More than 70% of the world population suffers from lactose intolerance (Vasiljevic and Jelen 2003), but its occurrence largely depends on the population group: only approx. 10% of Northern Europeans but more than 90% of South-East Asians suffer from this intolerance (Jelen and Tossavainen 2003). β-D-Galactopyranosyl-(1→4)-D-glucose (= lactose) is the main carbohydrate in milk (Schaafsma 2008). Hydrolysis by β-galactosidase, which can be isolated from, e.g. plants, animals, yeasts, fungi and bacteria (Harju et al. 2012; Husain 2010; Mlichová and Rosenberg 2006), is one of the most important biotechnological processes in the food industry. β-Galactosidases from Kluyveromyces lactis, Kluyveromyces fragilis, Aspergillus niger and Aspergillus oryzae are most commonly applied because they are available in high amounts and low-priced compared to lactase of animal or herbal origin (Husain 2010; Mlichová and Rosenberg 2006). Not only lactose hydrolysis serves for producing milk products that are tolerated by lactose-intolerant people, but also hydrolysed products taste sweeter because of the higher sweetness of the individual monosaccharides (Adhikari et al. 2010; Harju et al. 2012; Novalin et al. 2005). Consequently, in yoghurt from hydrolysed milk, the amount of added sugar can be reduced, resulting in a product with lower energy (Mlichová and Rosenberg 2006). For the manufacture of lactose-free base milk, mainly free enzymes are used. Some lactases, however, exhibit proteolytic activities that may cause a bitter after taste (Harju et al. 2012; Nagaraj et al. 2009). Only a few studies refer to the influence of lactose hydrolysis on the characteristics of fermented milk. Some studies reported on a reduction of fermentation time in case of hydrolysed base milk (Matijević et al. 2011; Nagaraj et al. 2009), whereas others (Ibarra et al. 2012; Toba et al. 1986) observed an increase of fermentation time or rather no effects. Consequently, a strong influence of the starter culture must be assumed. Hydrolysis of lactose can also be performed simultaneously with fermentation. This so called co-hydrolysis is usually preferred, because it saves extra processing time for hydrolysis and omits additional energy costs (Günther 1983). Concerning fermented products, Vènica et al. (2013) did not detect differences in syneresis and sensory properties between drinkable yoghurt from not hydrolysed and co-hydrolysed milk, whereas in sensory tests of Toba et al. (1986), co-hydrolysed yoghurt was rated as unacceptable because of its strong sweetness and the occurrence of an off-flavour. Ibarra et al. (2012) found that the sensory quality of yoghurt declined with increasing lactose hydrolysis degree, and Nagaraj et al. (2009) detected increased syneresis of yoghurt from hydrolysed milk. Yoghurt from milk with 50 and 70% of lactose hydrolysed before Fermented milk products: effects of lactose hydrolysis 201 fermentation exhibited a creamier texture and a better flavour than yoghurt from nothydrolysed milk, whereas 90% lactose hydrolysis resulted in products with lower viscosity and a too sweet flavour. Martins et al. (2012) hydrolysed more than 97% of lactose during fermentation with 0.5 and 1.0 g.L−1 lactase. The products that contained less enzyme exhibited higher viscosity and lower syneresis despite a similar degree of hydrolysis. The authors speculated that this can be explained by a lower amount of exopolysaccharides (EPS) synthesised in case of higher enzyme concentration; however, EPS concentration was not determined. The aim of our study was to investigate the influence of different strategies of lactose hydrolysis and the contribution of the starter cultures on viscosity and texture of regular yoghurt and Greek-style yoghurt. For a systematic approach, fermentations of not hyd (...truncated)