Nutritional and Rheological Features of Lentil Protein Isolate for Yoghurt-Like Application

Abstract

The substitution of animal protein with proteins of plant origin is a viable way to decrease the negative impact caused by animal husbandry on the environment. Pulse consumption has been widely promoted as a nutritious contribution to protein supplementation. In this study, an emulsion of lentil (Lens culinaris) protein isolate is fermented with lactic acid bacteria (LAB) to manufacture a yoghurt alternative and the techno-functional properties compared to a dairy- and a soy-based product with similar protein contents. The yoghurt-like products are subjected to large and small deformation analysis, quantification of fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP), water holding capacity tests, protein profile analysis and the gel structure is visualised by confocal laser scanning microscopy (CLSM). The lentil yoghurt alternative shows good water holding capacity, high firmness and consistency values in large deformation analysis, with cohesiveness and viscosity not significantly different from that of dairy yoghurt. The high gel strength and rigidity of the lentil yoghurt gels measured by small deformation analysis is well-reflected in the dense protein matrix in the CLSM graphs. FODMAP content of the lentil yoghurt is very low, making it suitable for consumption by irritable bowel syndrome (IBS) patients. Our results show that lentil protein isolate is an excellent base material for producing a plant-based yoghurt alternative.

Keywords: fermentation; lactic acid bacteria; plant-based; pulses.

Figure 1

Acidification during fermentation as measured by pH (solid lines) and total titratable acidity (TTA) in ml NaOH 0.1 M per g of yoghurt (dashed lines). The fermentation was ended if a pH of 4.5 was reached, or the pH did not drop significantly in 2 consecutive measurements 1 h apart. Fermentation of dairy controls was ended after 4 h, so no data points for 5 h and 6 h are given for dairy controls.

Figure 2

Liquid expulsion as measured with the centrifugation method (light grey) and drainage method (dark grey). Values with different superscript letters within columns for the centrifugation (capital letters) or drainage method (lowercase letters) are significantly different (p ≤ 0.05).

Figure 3

Textural properties of the fermented samples: Means of firmness (light grey) and consistency (dark grey) (a) and cohesiveness (light grey) and viscosity (dark grey) (b). Values with different superscript letters within columns for firmness and cohesiveness (capital letters) or consistency and viscosity index (lowercase letters) are significantly different (p ≤ 0.05).

Figure 4

Results of the three interval thixotropy test. The gap in values between 120–240 s is due to test characteristics. Error bars have been omitted for clarity.

Figure 5

Results of frequency sweep: Dependence of storage modulus G′, loss modulus G″ and complex viscosity |η*| on frequency. Error bars have been omitted for clarity.

Figure 6

Development of a gel structure during fermentation in the rheometer, measured by G′ and G″ and tan(δ). Error bars have been omitted for clarity.

Figure 7

CLSM images of protein of non-fermented (left side) and fermented (right side) samples. (a,b) Lentil, (c,d) dairy, (e,f) soy.

Figure 7

CLSM images of protein of non-fermented (left side) and fermented (right side) samples. (a,b) Lentil, (c,d) dairy, (e,f) soy.

Figure 8

Photographs of the fermented samples, (a) lentil, (b) dairy, (c) soy and non-fermented milks, (d) lentil, (e) dairy, (f) soy.

Figure 9

Protein profiles under reducing conditions as measured with the Agilent Bioanalyzer. (a) Lentil, (b) dairy and (c) soy samples. M—marker, NF—non-fermented samples, F—fermented samples, FS—fermented samples, soluble proteins. Green and purple bands are marker bands, and the bands at 3.5 kDa are system peaks that do not derive from the samples.

Figure 9

Protein profiles under reducing conditions as measured with the Agilent Bioanalyzer. (a) Lentil, (b) dairy and (c) soy samples. M—marker, NF—non-fermented samples, F—fermented samples, FS—fermented samples, soluble proteins. Green and purple bands are marker bands, and the bands at 3.5 kDa are system peaks that do not derive from the samples.