My Thesis- Tolerance of Probiotics in Acidity Simulating to Stomach Condition

Chapter 1

Introduction

 

The application of probiotics which begun since early 1900s has gained a widespread popularity in recent years. The rationale of probiotics usage is that it may restore the balance of intestinal microbes that are caused by the antibiotic treatment or other diseases (Fooks et al., 1999). Concurrently, substantial numbers of studies that are based on double-blind placebo-controlled human intervention trials have confirmed that the daily consumption of probiotics may confer prophylactic and therapeutic effects on human (Saxelin et al., 2005).

 

Food Agricultural Organization and World Health Organization have defined probiotics as the live microorganisms which when administered in adequate amounts confer health benefits to the host. This definition emphasized that the microorganisms should exist in sufficient numbers (>10⁶ colony forming unit per gram, CFU/g) as live or viable cells (Brown et al., 2004). Microorganisms that are commonly considered as probiotics are lactobacilli and bifidobacteria but certain type of yeast such as Saccharomyces boulardii is also included. Most of the probiotics are human origin and safe for human consumption.

 

 

 

Furthermore, the health benefits of probiotics include the treatment of acute infectious diarrhea particularly rotavirus induced diarrhea and antibiotic associated diarrhea. It may alleviate lactose intolerance and constipation. Besides, probiotics exert its effects by influencing the immune system, strengthening the mucosal barrier, competitive exclusion, and suppressing the intestinal inflammation (Brown et al., 2004; Saxelin et al., 2005).

 

The probiotic products that available in our market include yogurt, cultured milk drink and pharmaceutical products. Initially, probiotics were largely formulated into fermented milk-based products, but during recent years, the popularity and demand for non-milk based probiotic formulations has increased. Among these products, pharmaceutical products are being introduced. They are available as single or mixed strain, in the form of capsule, powder or tablet and they are prepared as freeze-dried formulations (McFarland et al., 1997). However, they exhibit different degree of effectiveness (Lin et al., 2006). Hence, stringent selection criteria for the pharmaceutical probiotics are required in order to access the quality of that particular product.

 

The criteria of the probiotics are the ability to survive during manufacture and remain viable in the gastrointestinal tract after consumption (Taumola et al., 2001; Dunne et al., 2001). In this case, probiotics should survive through the complex condition in the stomach in order to be viable and remain active in the target site (Taumola et al., 2001). As such, the initial criterion is that the probiotic strains must tolerate to low pH in the stomach since the low pH is the first host barrier (Taumola et al., 2001).

 

 

In addition, the various types of probiotic products in the market are manufactured in different formulation. Among these products, Bifidobacterium spp. and Lactobacillus particularly L. acidophilus and L. casei were often used in cultured milk drink, yogurt and pharmaceutical preparations. Similarly, substantial studies have been conducted to investigate L. acidophilus, L. casei and Bifidobacterium spp. (Roy, 2001; Tharmaraj et al., 2003) and showed that the activities exhibited by them are strain specific (Matsumoto et al., 2004; Dunne et al., 2001). Hence, it is necessary to investigate L. acidophilus, L. casei and Bifidobacterium spp. in order to access the efficacy of a particular product.

 

The ability of probiotics to survive in low pH is known as acid tolerance. The principle of acid tolerance is based on the maintenance of constant gradient between extracellular and cytoplasmic pH. The F0F1 ATPase is reported to be the mechanism of acid tolerance for Gram positive bacteria whereby the pH homeostasis is maintained by discharging hydrogen ion from the cell at a low extracellular pH. Nevertheless, when the cytoplasmic pH reaches its threshold value, the cellular functions are inhibited. Acid tolerance of probiotics is reported to be strain specific (Charteris et al., 1998; Huang et al., 2001).

 

 

In this study, the pharmaceutical probiotics will be assayed for their viability upon reaching consumer and the degree of acid tolerance exhibited by the pharmaceutical probiotics simulating to the pH of human stomach. The pH of the stomach generally ranges from pH 2.5 to pH 3.5 (Holzapfel et al., 1998). However, a range of pH values, from pH 2 to pH 5, has been used to screen in vitro acid tolerance of Lactobacillus and Bifidobacterium spp. since food intake may increase the pH of the stomach (Berrada et al., 1991; Charteris et al., 1998; Chou et al., 1999; Chung et al., 1999; Liong et al., 2005; Huang et al., 2001; Lin et al., 2006).