Rheological and physical characteristics of non-fat set yogurt prepared with EPS-producing Streptococcus thermophilus and an H⁺-ATPase-defective mutant Lactobacillus delbrueckii subsp. bulgaricus

Figures & data

Table 1. The pH, WHC, and textural properties of low-fat yogurt batches fermented by ropy EPS-producing S. thermophilus S3.3 and L. bulgaricus LTM or the L. bulgaricus H⁺-ATPase-defective mutant L6 at 30, 37, or 42°C and stored for 21 days at 4°C.

Culture	Fermentation temperature (°C)	Storage period (day)	pH	WHC (%)	Textural properties
					Firmness (g)	Consistency (g·sec)	Cohesiveness (g)
LTM+S3.3	30	1	4.55 ± 0.01^aA	51.2 ± 1.4^aA	49 ± 7^aA	440 ± 33^aA	15 ± 3^aA
		7	4.21 ± 0.02^bA	50.4 ± 1.2^bA	94 ± 7^bA	671 ± 36^bA	27 ± 3^bA
		21	4.00 ± 0.02^cA	50.0 ± 0.8^bA	109 ± 6^cA	846 ± 40^cA	31 ± 3^bA
	37	1	4.51 ± 0.02^aA	44.9 ± 1.1^aA	70 ± 8^aA	620 ± 38^aA	21 ± 3^aA
		7	4.19 ± 0.04^bA	40.7 ± 1.6^bA	106 ± 10^bA	851 ± 43^bA	33 ± 2^bA
		21	3.91 ± 0.03^cA	36.2 ± 1.0^cA	96 ± 7^cA	829 ± 40^bA	33 ± 2^bA
	42	1	4.59 ± 0.02^aA	41.4 ± 0.9^aA	72 ± 10^aA	623 ± 28^aA	20 ± 4^aA
		7	4.10 ± 0.03^bA	38.1 ± 0.7^bA	112 ± 9^bA	954 ± 36^bA	37 ± 4^bA
		21	3.88 ± 0.04^cA	36.7 ± 1.1^bA	111 ± 8^bA	971 ± 35^bA	41 ± 3^bA
L6+S3.3	30	1	4.56 ± 0.03^aA	64.7 ± 1.6^aB	43 ± 6^aB	351 ± 46^aB	14 ± 2^aB
		7	4.30 ± 0.02^bB	56.9 ± 1.1^bB	90 ± 6^bB	803 ± 33^bB	32 ± 3^bB
		21	4.25 ± 0.03^bB	54.4 ± 0.7^cB	92 ± 5^bB	847 ± 35^bA	38 ± 2^cB
	37	1	4.55 ± 0.02^aA	46.8 ± 1.1^aB	68 ± 11^aA	612 ± 26^aA	26 ± 3^aB
		7	4.28 ± 0.01^bB	45.7 ± 1.1^bB	116 ± 9^bB	937 ± 29^bB	37 ± 4^bB
		21	4.21 ± 0.03^bB	45.8 ± 0.8^bB	119 ± 9^bB	959 ± 28^bB	38 ± 3^bB
	42	1	4.53 ± 0.02^aA	45.8 ± 1.2^aB	61 ± 7^aB	549 ± 45^aB	19 ± 1^aB
		7	4.33 ± 0.02^bB	41.2 ± 1.5^bB	120 ± 4^bB	956 ± 27^bA	41 ± 3^bB
		21	4.26 ± 0.01^bB	42.9 ± 0.9^bB	122 ± 5^bB	961 ± 35^bA	43 ± 3^bB

Lower case superscripted letters in a column denote significant differences between samples prepared at the same temperature with different days of storage for culture (three samples).

Capital superscripted letters in a column indicate significant differences between the formulations prepared at the same temperature on the same storage day.

Figure 1. Storage modulus (G′) of non-fat set yogurt batches as a function of the oscillatory frequency. Yogurt samples were produced using S. thermophilus S3.3 with L. bulgaricus LTM or mutant L6 at 30, 37, or 42°C (▽, ○, and △ for LTM and ☆, ◁, and ╂ for L6) and stored for 21 days at 4°C. Samples were taken on A: day 1, B: day 7, and C: day 21 of storage.

Figure 2. The thixotropy loops of non-fat set yogurt batches prepared using S. thermophilus S3.3 with L. bulgaricus LTM or mutant L6 at 30, 37, or 42 °C (▼,

, and

for LTM, ☆, ◁, and ╂ for L6,) and stored for 1 or 21 days at 4°C. Samples were taken on A: day 1 and B: day 21 of storage.

Figure 3. Confocal laser scanning micrographs of non-fat set yogurts prepared using S. thermophilus S3.3 with L. bulgaricus LTM (A, B, and C) or mutant L6 (D, E, and F) at 30, 37, or 42°C, respectively, and then stored for 21 days at 4°C.