In the present study, whey powder was added to hyacinth bean extract to provide more substrate (lactose) for lactic fermentation. pH and titratable acidity were significantly influenced by yogurt culture and storage time (P < 0.001). The interaction between yogurt culture and storage time was also significant for pH (P < 0.01) and titratable acidity (P < 0.001). The pH and titratable acidity value were significantly different between the cultures. The pH value for Y-XPL and the titratable acidity value for Y-450 were the highest (Table 1).
Table 1
pH and titratable acidity of yogurt-like products
| pH | Titratable acidity (millimoles NaOH/100 g) |
1 d | 7 d | 14 d | 21 d | 1 d | 7 d | 14 d | 21 d |
Lyofast Y 258 A | 4.47 ± 0.01 | 4.45 ± 0.01 | 4.37 ± 0.01 | 4.34 ± 0.02 | 7.64 ± 0.08 | 7.75 ± 0.00 | 8.36 ± 0.06 | 8.36 ± 0.01 |
XPL-20 | 4.47 ± 0.01 | 4.46 ± 0.01 | 4.40 ± 0.01 | 4.39 ± 0.01 | 7.42 ± 0.17 | 7.58 ± 0.11 | 7.66 ± 0.06 | 8.14 ± 0.06 |
Lyofast Y 450 B | 4.44 ± 0.01 | 4.42 ± 0.01 | 4.35 ± 0.01 | 4.32 ± 0.01 | 7.91 ± 0.08 | 8.05 ± 0.02 | 8.47 ± 0.05 | 9.07 ± 0.10 |
ANOVA |
YC | *** | *** |
ST | *** | *** |
YC ⊆ ST | ** | *** |
Note: Data are expressed as mean value ± standard deviation (n = 3). |
YC: Yoghurt Culture
ST: Storage time
*, ** and ***: Significantly different at P < 0.05, P < 0.01 and P < 0.001, respectively
Yogurt culture and storage time strongly affected the level of GABA and phytic acid level in the yogurt-like samples (P < 0.001) (Table 2). The level of GABA in yogurt-like products was much lower than that in unfermented hyacinth bean extracts. These findings suggest that the GABA-producing/degrading ability of lactic acid bacteria (LAB) during fermentation and storage possibly depend on the species. Therefore, the degradation of GABA might be due to the conversion of GABA to succinic acid by GABA transaminase (GABA-T) released by yogurt cultures. Although the level of GABA rapidly decreased after 1 day of storage, the level of GABA in the yogurt-like products made from germinated hyacinth bean is much higher than that previously reported in soymilk yogurt [2, 9] and cow’s milk yogurt [10].
Table 2
The level of GABA and phytic acid in yogurt-like products
| The level of GABA (mg/g DM) | The level of phytic acid (mg/g DM) |
UFE | 1 d | 7 d | 14 d | 21 d | UFE | 1 d | 7 d | 14 d | 21 d |
Lyofast Y 258 A | 3.18 ± 0.15 | 1.90 ± 0.00 | 1.88 ± 0.03 | 1.71 ± 0.00 | 1.59 ± 0.04 | 21.43 ± 0.09 | 11.73 ± 0.06 | 11.71 ± 0.09 | 11.45 ± 0.06 | 11.40 ± 0.08 |
XPL-20 | 3.18 ± 0.15 | 2.20 ± 0.01 | 2.15 ± 0.01 | 2.12 ± 0.02 | 1.64 ± 0.09 | 21.42 ± 0.19 | 11.82 ± 0.12 | 11.81 ± 0.09 | 11.58 ± 0.10 | 11.47 ± 0.19 |
Lyofast Y 450 B | 3.17 ± 0.14 | 1.68 ± 0.01 | 1.65 ± 0.05 | 1.47 ± 0.06 | 1.39 ± 0.02 | 21.42 ± 0.17 | 11.67 ± 1.10 | 11.61 ± 0.24 | 11.39 ± 0.04 | 11.36 ± 0.08 |
ANOVA |
YC | *** | * |
ST | *** | *** |
YC ⊆ ST | *** | n.s |
Note: Data are expressed as mean value ± standard deviation (n = 3). |
YC: Yoghurt Culture, ST: Storage time, DM: Dry matter, UFE: Unfermented hyacinth bean extract
*, ** and ***: Significantly different at P < 0.05, P < 0.01 and P < 0.001, respectively
n.s: Not significant
According to Oh [2], L. delbrueckii ssp. bulgaricus and S. thermophilus did not significantly influence the level of GABA, meanwhile other LAB such as L. brevis, Lc. lactis and L. rhamnosus could enhance the level of GABA. As shown in Table 2, the level of GABA is significantly different between the yogurt-like products made from different cultures at all periods of storage. Its level in Y-XPL was higher than that in Y-258 and Y-450. Therefore, the degradation of GABA might depend on the strains used for the fermentation.
The level of phytic acid in yogurt-like products was much lower than that in unfermented hyacinth bean extract, probably because of it degradation by the enzyme phytase released from yogurt cultures [11]. During cold storage, the level of phytic acid significantly decreased. This finding is similar to that in soymilk yogurt reported by Nguyen and Do [9].
Table 2 also shows the level of phytic acid varied significantly between the cultures. Y-XPL contained the highest phytic acid. Several studies have suggested that L. delbrueckii ssp. bulgaricus and S. thermophilus and strains of L. acidophilus, L. casei and L. plantarum could degrade phytic acid during fermentation of soymilk [9, 11]. Our findings indicate that fermentation of hyacinth bean with yogurt cultures might potentially improve mineral bioavailability.