Effects of yogurt starter cultures on the survival of Lactobacillus acidophilus

Abstract

Recognized to confer health benefits to consumers, probiotics such as Lactobacillus acidophilus are commonly incorporated into fermented dairy products worldwide; among which yogurt is a popular delivery vehicle. To materialize most of the putative health benefits associated with probiotics, an adequate amount of viable cells must be delivered at the time of consumption. However, the loss in their viabilities during refrigerated storage has been demonstrated previously. This study focused on the effects of yogurt starter cultures on the survival of five strains of L. acidophilus, with emphases on low pH and acid production. Differential survival behavior between L. acidophilus strains was further analyzed. To this end, viable cell counts of L. acidophilus were determined weekly during 4°C storage in various types of yogurts made with Streptococcus thermophilus alone, L. delbrueckii ssp. bulgaricus alone, both species of the starter cultures, or glucono-delta-lactone (GDL). All yogurt types, except for pasteurized yogurts, were co-fermented with L. acidophilus. Yogurt filtrate was analyzed for the presence of any inhibitory substance and for the amount of hydrogen peroxide. Multiplication of L. acidophilus was not affected by the starter cultures as all strains reached high level on day 0 of the storage period. Throughout the 28-day storage period, cell counts of L. acidophilus PIM703 and SBT2062 remained steady (~6 × 10(7)CFU/g) in yogurts made with both starter cultures, whereas those of ATCC 700396 and NCFM were reduced by a maximum of 3 and 4.6 logs, respectively. When starter cultures were replaced by GDL, all strains survived well, suggesting that a low pH was not a critical factor dictating their survival. In addition, the filtrate collected from yogurts made with starter cultures appeared to have higher inhibitory activities against L. acidophilus than that made with GDL. The presence of viable starter cultures was necessary to adversely affect the survival of some strains, as pasteurized yogurts had no effect on their survival. In particular, the inhibitory effect exerted by L. delbrueckii ssp. bulgaricus on L. acidophilus NCFM was highly pronounced than by S. thermophilus, nevertheless, the same effect was not observed on SBT2062. The inhibition against stationary-phase NCFM cells might be caused by the elevated level of hydrogen peroxide produced by L. delbrueckii ssp. bulgaricus. Delineating factors driving the differences in survival trait among probiotic strains will lead to a more efficacious delivery of health benefits in fermented dairy products through targeted technological interventions.

Effect of Colored Barley Flours on Quality Characteristics of Fermented Yogurt by Lactobacillus spp.

“…Gee et al (2007) reported that addition of highly concentrated barley beta-glucan had no significant effect on the ability of the starter cultures to ferment. Low pH (4.6) and glucono delta lacton accumulation had no effect on the survival of L. acidophilus strains (Ng, 2011). As a similar result, Farnworth et al (2007) reported that the falls of the pH values were faster in the soybeverage than in milk.…”

“…Donkor et al (2006) concluded that the decrease in L. acidophilus cell numbers in yogurts was the result of lactic acid and acetic acids accumulation. Moreover, Ng et al (2011) reported that the level of organic acids was found to have a more pronounced effect on the strain's variability than the pH value. Sahan et al (2008) reported that use of β-glucan hydrocollidal composite in the manufacture of non-fat yogurt did not significantly influence pH, titratable acidity, acetaldehyde, volatile fatty acid and tyrosine contents at any storage time.…”

“…Probiotic dairy products are considered to have functional properties because the probiotic bacteria added to the regular fermentation cultures provide therapeutic benefits such as modification of the immune system, reduction in cholesterol, alleviation from lactose intolerance, faster relief from diarrhea, and restoration of a healthy vaginal microbiota (Reid, 2001;Reid et al, 2003). Probiotics are commonly incorporated into fermented dairy products worldwide among which yogurt is a popular delivery vehicle (Ng et al, 2011). Yogurt is a well known fermented dairy food, which is usually manufactured form cow's milk with or without the addition of some natural derivatives of milk, and processes a gel structure that is the result of coagulation of the milk proteins by lactic acid produced by Streptococcus thermophilus and Lactobacillus bulgaricus (Robinson, 2003).…”

Transformation Kinetics During Fermented Milk Production Using Lactobacillus Johnsonii (La1) and Streptococcus Thermophillus: A Comparison With Yogurt Inoculum

“…bulgaricus (Lb); samples prepared with these starter bacteria are labeled Lb-St [1]. In the early stage of the incubation process, Lb stimulates the growth of St releasing amino acids from casein (where the most important is valine) and producing a moderate reduction in pH due essentially to St [2,3]; furthermore, from the start of the process, new chemical structures (exopolysaccharides (EPS) and organic phosphate) are produced.…”

Effect of spraying Lantana Fermented Extract on Growth and Yield of Green Gram (Vigna radiata L.) in Pots

“…It has been shown that during the course of Lactobacillus mediated fermentations, organic acids were released, proteins hydrolyzed and anti-oxidant ferulic acid from plant cell wall materials solubilized (Cheigh et al, 1994). It has been reported that fermentation of Anoectochilus formosanus using Lactobacillus acidophilus boosted its anti-oxidant activity by increasing the total phenol content (Ng et al, 2011). In another study, fermentation was used to enhance the antimicrobial potential of the crude herbal extract of Phyllanthus niruri.…”