Streptococcus thermophilus APC151 Strain Is Suitable for the Manufacture of Naturally GABA-Enriched Bioactive Yogurt

Abstract

Consumer interest in health-promoting food products is a major driving force for the increasing global demand of functional (probiotic) dairy foods. Yogurt is considered the ideal medium for delivery of beneficial functional ingredients. Gamma-amino-butyric acid has potential as a bioactive ingredient in functional foods due to its health-promoting properties as an anti-stress, anti-hypertensive, and anti-diabetic agent. Here, we report the use of a novel Streptococcus thermophilus strain, isolated from the digestive tract of fish, for production of yogurt naturally enriched with 2 mg/ml of gamma-amino-butyric acid (200 mg in a standard yogurt volume of 100 ml), a dose in the same range as that provided by some commercially available gamma-amino-butyric acid supplements. The biotechnological suitability of this strain for industrial production of yogurt was demonstrated by comparison with the reference yogurt inoculated with the commercial CH1 starter (Chr. Hansen) widely used in the dairy industry. Both yogurts showed comparable pH curves [ΔpH/Δt = 0.31-0.33 h^-1], viscosity [0.49 Pa-s], water holding capacity [72-73%], and chemical composition [moisture (87-88%), protein (5.05-5.65%), fat (0.12-0.15%), sugar (4.8-5.8%), and ash (0.74-1.2%)]. Gamma-amino-butyric acid was not detected in the control yogurt. In conclusion, the S. thermophilus APC151 strain reported here provides a natural means for fortification of yogurt with gamma-amino-butyric acid.

Keywords: GABA; Streptococcus thermophilus; bioactive yogurt; biofunctional food; starter.

FIGURE 1

Evolution of bacterial growth, pH and GABA accumulation in yogurt. (A) Growth of S. thermophilus (circles) and Lb. bulgaricus (squares) cell count (cfu/ml) during fermentation and storage of the control (empty symbols) and GABA-enriched (filled symbols) yogurts. In the Y-axis the 0 value means <10 cfu/ml (the detection limit). (B) Acidification curve of S. thermophilus APC151 (circles) and CH1 (squares) during milk fermentation in pure monoculture (empty symbols) or co-cultures with Lb. bulgaricus CH1 (filled symbols). (C) Evolution of GABA accumulation in the GABA-enriched (white bars) and control (black bars) yogurts over fermentation and storage time. Transition between fermentation and storage is indicated by the arrow [h, hours; d, days; w, weeks]. The representation of time on X-axis is not to scale.

FIGURE 2

(A) Change in viscosity (solid line) and pH curve (dotted line) over milk fermentation during 24 h [Empty circles: control yogurt; Filled circles: GABA-enriched yogurt]. (B) Evolution of viscosity over storage time for 1, 2, and 3 weeks [GABA-enriched (filled bars) and control (empty bars)]. ^∗p-value < 0.001.

FIGURE 3

Measurement of water holding capacity of GABA-enriched (filled bars) and control (empty bars) yogurts after storage for 1, 2, and 3 weeks. ^∗p-value < 0.001.