**3.2. Effect of temperature on the dynamics of fermentation**

According to the information provided by the producer of the lactic culture, respectively to the data found in literature, two different incubation temperatures were tested: 370C and 410C respectively.

The dynamics of both pH and lactic acid (Figure 3) emphasizes the influence of the higher temperature on the rate of acidification. After 24h no significant differences between the pH values were determined, while the lactic acid content of the samples fermented at 410C was 1.24-fold higher comparatively with those fermented at 370C. This situation may be due to the higher amino acids content in the samples fermented at 410C, that act as buffer. Thus, expressed as glycin, the total amount was by 0.165g/100ml at the end of the analyzed interval, which represented an increase by 10% comparatively with the batch fermented at lower temperature.

fermentation (tpH 4.2, hours).

LA-5

410C respectively.

lower temperature.

Inoculum, g/l vmax·10-3

The maximum rate of acidification vmax was calculated as the time variation of pH (dpH/dt) and expressed as pH units/min (Table 1). Other kinetic parameters were also calculated: time to reach vmax (tmax, hours), time to reach pH 5.0 (tpH 5.0, hours), time to complete the

0.2 7.08 4 2.95 8.4 0.3 9.83 2 2.88 8.2 0.4 10.41 2 2.67 8.05 **Table 1.** 1. Acidification kinetic parameters of fermentation of carrot juices by *Lactobacillus acidophilus*

A double amount of inoculum had an insignificant influence on the time to reach pH 5.0, important parameter from the shelf life of the fermented juices. Thus, tpH 5.0 (h) was 1.1-fold higher in the case of the batch with 0.2g/l lyophilized pure culture initial added to juice than that one with 0.4g/l. A different situation was registered concerning the maximum rate of acidification (vmax) and the time to reach this rate (tmax). Thus, a polynomial equation of the form *y = -108.5x2 + 81.75x – 4.93* correlated the size of inoculum with the corresponding values of vmax at R squared = 1. Although at the initial moment of fermentation seems to be advantageous to use a higher amount of pure culture, this aspect lessen in time, from the economic point of view being important to obtain a balance between the quantity of inoculum and the targeted parameters which ensure the preservation of the final product.

The values of the biomass content became close after about 6h of fermentation. No parallel relationship between lactic acid concentration and biomass was observed, result that agrees

However, taking into account the lactic acid accumulation and the dynamics of the number of viable cells, it was obvious that the utilization of higher amount of inoculum is not justified.

According to the information provided by the producer of the lactic culture, respectively to the data found in literature, two different incubation temperatures were tested: 370C and

The dynamics of both pH and lactic acid (Figure 3) emphasizes the influence of the higher temperature on the rate of acidification. After 24h no significant differences between the pH values were determined, while the lactic acid content of the samples fermented at 410C was 1.24-fold higher comparatively with those fermented at 370C. This situation may be due to the higher amino acids content in the samples fermented at 410C, that act as buffer. Thus, expressed as glycin, the total amount was by 0.165g/100ml at the end of the analyzed interval, which represented an increase by 10% comparatively with the batch fermented at

to those obtained by Amrane [12] and Kotzamanidis [13].

**3.2. Effect of temperature on the dynamics of fermentation** 

(units/min.) tmax (h) tpH 5.0 (h) tpH 4.2 (h)

**Figure 3.** pH and lactic acid dynamics during the lactic acid fermentation of carrot juice at different temperatures: 370C ( and ▲) and 410C ( and ●); columns - pH values, lines - lactic acid content

The rate of acidification has been correlated with the glucose consumption: 38.9% in the case of the juice fermented at 370C, respectively 53.89% in the case of the juice fermented at 410C. The different tendency of this parameter became obviously after 4h of fermentation (Figure 4), being the consequence of the different rate of growth of *Lactobacillus acidophilus*, expressed as optical density at 610nm.

**Figure 4.** Glucose consumption and microbial evolution during the lactic acid fermentation of the carrot juices at different temperatures: 370C ( and ▲) and 410C ( and ●); columns - glucose, lines optical density at wavelength by 610nm

Although close, the yields of glucose conversion to lactic acid have inclined the balance in favour of the juices fermented at 370C, the corresponded value being by 0.5, unlike 0.45 in the case of the juices incubated at 410C.

The faster consumption of the carbon source, correlated with the growth of the useful microbiota at higher temperature, respectively with the increase of the lactic acid content until the value by 9.1g/l, was followed at 24h by the decline of the viability of *Lactobacillus acidophilus*. Taking into account the dynamics of all the above mentioned parameters, the incubation temperature applied in the further studies was by 37±0.10C.

Fermentation of Vegetable Juices by *Lactobacillus Acidophilus* LA-5 181

**Figure 5.** pH dynamics in vegetable juices obtained from different raw materials, during fermentation

0 2 4 6 824 **Time (h)**

Referring to the red cabbage juice, although after 24 hours of fermentation the pH values were similar, the lactic acid content was lesser with about 1.5g/l compared with the white

**Figure 6.** Lactic acid accumulation in vegetable juices obtained from different raw materials, during

the fermented juices were observed, especially at elevated onion/cucumber ratio.

[16] studied the fermentation of cucumber juices with a 0.5%, 1% and 2% additions of the onion juices by *Lb. plantarum* CCM 7039. It was found that in the initial stages of fermentation, the presence of onion in the juices positively influenced lactic and acetic acid production. However, in further course of fermentation, slight inhibition effects of onion in

0 4 8 12 16 20 24 **Time (h)**

cabbage juice. This can be due to the amphoteric nature of the anthocyanins.

Cb RCb Rb Cc CcO

with *Lactobacillus acidophilus* LA-5

0

1

2

3

**pH**

4

Cb RCb Rb Cc CcO

5

6

7

fermentation with *Lactobacillus acidophilus* LA-5

**lactic acid (g/l)**
