Media and process parameters affecting the growth, strain ratios and specific acidifying activities of a mixed lactic starter containing aroma-producing and probiotic strains

Abstract

Aims: The effects of medium‐composition and fermentation parameters on the properties of mixed mesophilic starters were studied. The starter was composed of Lactococcus lactis ssp. lactis (L. lactis), Lactococcus lactis ssp. cremoris (L. cremoris), Lactobacillus rhamnosus (Lact. rhamnosus) and Leuconostoc mesenteroides ssp. cremoris (Leuc. cremoris). Methods and Results: The media used were reconstituted skim milk (RSM), and whey‐based media with either citrate or phosphate buffers. The fermentation parameters were incubation temperature (22°C or 32°C), no pH control, and pH control in pH zones of either pH 6·0–5·8 or pH 6·0–5·2. The starter properties were strain ratio, specific acidifying activity (SAA), total population, residual carbohydrates and organic acids produced. The growth of L. lactis was favoured under pH control in whey‐based media. High concentrations of Lact. rhamnosus were favoured in whey‐based media prepared at 32°C. The highest contents of Leuc. cremoris were obtained in starters prepared in RSM at 22°C without pH control. Starters prepared under pH control gave the highest populations and made it possible for significantly lower inoculation rates (IR) to be used to carry out subsequent milk fermentations. However, the SAA of starters prepared under pH control were lower than the SAA of starters grown without any pH control. Conclusions: None of the conditions enabled the strain ratio at inoculation to be maintained. The data show that it is possible to prepare a mesophilic starter that has a significant probiotic Lact. rhamnosus content; this starter could be used in the preparation of probiotic‐containing cheeses or in Leuc. cremoris for aroma production in fermented milks. Significance and Impact of the Study: This study provides data on what should be expected with respect to strain ratios and IR if cheesemakers decide to shift their aroma‐producing starter production method from the traditional ‘milk‐based without pH control’ method to whey‐based media used with pH‐zone control strategies.

Fermentation pH Influences the Physiological-State Dynamics of Lactobacillus bulgaricus CFL1 during pH-Controlled Culture

“…The effect of pH on cellular physiology is confirmed by other studies which show that it influences acidification activity of lactic acid bacteria (23)(24)(25). Whereas Wang et al (25) indicated that Lactobacillus acidophilus cells grown at optimal pH display a higher residual acidification activity than cells grown at lower pH control values, Schepers et al (24) and Savoie et al (23) demonstrated that this activity is higher when starters are produced without pH control or at low pH control values.…”

“…Compared to acidic fermentations, pH-controlled cultures led to higher growth yields and productivity (9,23) as a result of the lower level of nondissociated lactic acid in the culture medium (2,12,15). The acidification of the cytoplasm induced by the nondissociated form of the weak organic acid leads to the collapse of the proton motive force (13).…”

“…Lactic acid starters are currently produced using pH-controlled pure cultures (6), during which pH is generally regulated at an optimal value by continuously adding sodium hydroxide or ammonia in the bioreactor (23). Various growth characteristics such as maximal biomass concentration, specific growth rate, fermentation time, sugar consumption or growth, and product yields are significantly influenced by the pH control value (1,4).…”

Optimization of Low-Cost Culture Media for the Production of Biomass and Bacteriocin by a Urogenital Lactobacillus salivarius Strain

“…However, other inexpensive nutrients can be used as ingredients of the fermentation medium, which could further reduce the cost of production. Several studies have replaced the expensive MRS medium for lactobacilli with supplemented whey permeate [11,32] or several carbon and nitrogen sources of vegetal origin, such as potato extracts [13], molasses, soy milk [34] and corn syrup [12]. Continuous control of pH has also been used to improve the growth and metabolite production of LAB [11,32].…”

Probiotic Lactococcus lactis: A Review

“…Gemelas et al (2013) has reported KCA the most selective medium for specific enumeration of lactococci. Savoie et al (2007) studied the effects of medium composition and fermentation parameters on the properties of L. lactis ssp. lactis and L. lactis ssp.…”